PC5271 wiki - User contributions [en]

Photodetector with wavelength @ 780nm and 1560nm

2025-04-27T07:18:57Z

Sunke: /* Project Outline */

=== Photodetector with wavelength @ 780nm and 1560nm ===

Team members: Sunke Lan

To design photodetector as power monitor with power within 10mW.

== Project Outline ==

=== 1. Objective ===
* Design and evaluate photodetectors for 780 nm and 1560 nm applications.

=== 2. Components ===
* Photodiodes (S5971, G12180-010A)
* BNC and PCB test boards
* Operational amplifier (OP27G) for transimpedance amplification

---

=== 3. 780 nm Photodetector Design ===

==== 3.1 Circuit and Components Overview ====

[[File:testcircuit.png|center|thumb|400px|Test Circuit for 780 nm Photodetector]]

The 780 nm photodetector circuit is based on a standard transimpedance amplifier (TIA) configuration, designed to convert the photocurrent generated by a silicon PIN photodiode (S5971) into a measurable voltage signal.

In this design:
* The photodiode is operated under a reverse bias of 1 V, applied externally to widen the depletion region, reduce junction capacitance, and improve both linearity and response speed. Compared to higher bias voltages (e.g., 15 V), a 1 V bias offers a balance between depletion width and minimized dark current, suitable for steady-state detection at 780 nm.
* The photocurrent generated by incident photons is injected into the inverting input of the OP27G operational amplifier. The amplifier maintains a virtual ground condition at the inverting input, ensuring linear current-to-voltage conversion without significant voltage swing at the photodiode terminal.
* A feedback resistor <math>R_f = 10\,\mathrm{k}\Omega</math> connects the output to the inverting input, governing the output voltage according to:
<math>V_{\text{out}} = -I_{\text{photo}} \times R_f</math>
where <math>I_{\text{photo}}</math> is the photocurrent proportional to the incident optical power.

The OP27G is selected for its excellent low input offset voltage (typically 25 µV), low noise (3 nV/√Hz at 1 kHz), and moderate gain-bandwidth product (8 MHz), making it ideal for precise low-frequency optical measurements.

To ensure stable operation:
* Proper bypass capacitors (0.1 µF ceramic + 10 µF electrolytic) are placed close to the amplifier’s supply pins to suppress high-frequency noise.
* Decoupling capacitors are connected across the photodiode bias supply to stabilize the reverse bias voltage.

{| style="width:100%;"
| [[File:back.jpg|400px|thumb|center|Back side with photodiode mounted]]
| [[File:front.jpg|400px|thumb|center|Front side with lumped circuit elements]]
|}

This current-to-voltage architecture enables reliable detection of 780 nm light with sufficient sensitivity, stability, and low noise performance for laboratory testing.

----

==== 3.2 Theory and Circuit Design Concept ====

The underlying detection principle is the direct conversion of the photogenerated current into a voltage signal using a transimpedance amplifier. By operating the photodiode under reverse bias and maintaining a virtual ground at the amplifier’s inverting input, the circuit ensures linear and efficient current-to-voltage conversion without distorting the photocurrent signal.

The output voltage follows:

<math>V_{\text{out}} = -I_{\text{photo}} \times R_f</math>

where <math>I_{\text{photo}}</math> is the photocurrent and <math>R_f</math> is the feedback resistance.

Careful selection of bias conditions, feedback network, and amplifier characteristics optimizes the signal-to-noise ratio and ensures stability within the low-frequency operating range appropriate for 780 nm light detection.

----

==== 3.3 Feedback Resistor Selection ====

The feedback resistor <math>R_f</math> determines the transimpedance gain of the photodetector, i.e., the voltage generated per unit photocurrent. A value of <math>R_f = 10\,\mathrm{k}\Omega</math> was chosen to balance signal amplitude and system stability.

Key considerations include:
* **Signal strength:** Typical photocurrents under 780 nm illumination are in the nanoampere to microampere range. With a 10 kΩ feedback resistor, output voltages reach measurable levels without requiring excessive amplification.
* **Noise performance:** Although increasing <math>R_f</math> amplifies both signal and noise, a 10 kΩ resistor provides a favorable trade-off, maintaining a reasonable signal-to-noise ratio (SNR).
* **Frequency stability:** Larger <math>R_f</math> values, combined with the photodiode’s junction capacitance, can reduce bandwidth and induce phase shifts. A 10 kΩ resistor ensures sufficient stability across the targeted low-frequency range.

Thus, the 10 kΩ feedback resistor enables clean, stable, and easily detectable voltage outputs under typical laboratory conditions.

----

==== 3.4 Testing and Results ====

The 780 nm photodetector circuit was tested under indoor lighting conditions to assess its performance. A Tektronix TDS 2024C digital oscilloscope was used to monitor the output under various amplifier supply voltages, capturing the 50 Hz AC mains modulation.

Test results are summarized as follows:

{| style="width:100%;"
| [[File:Test1.jpeg|400px|thumb|center|Output without OP-AMP amplification]]
|}

Without amplification, the photodiode output is too weak to be detected by the oscilloscope.

{| style="width:100%;"
| [[File:Test2.jpeg|400px|thumb|center|Output with OP-AMP supply of ±1 V]]
|}

With a ±1 V supply, a small output fluctuation appears, indicating initial amplification.

{| style="width:100%;"
| [[File:Test3.jpeg|400px|thumb|center|Output with OP-AMP supply of ±3 V]]
|}

With a ±3 V supply, a clear quasi-sinusoidal waveform corresponding to 50 Hz ambient lighting is observed, indicating effective amplification.

{| style="width:100%;"
| [[File:Test4.jpeg|400px|thumb|center|Output with OP-AMP supply of ±5 V]]
|}

At ±5 V, significant distortion and oscillations occur due to instability caused by the combination of weak input signals, high open-loop gain, and parasitic effects from the breadboard assembly.

----

In summary:
* Without amplification, the photodiode signal remains undetectable.
* A ±3 V supply allows for stable and effective signal amplification.
* Excessive supply voltages (> ±5 V) without proper PCB layout introduce instability.
* The detector demonstrates clear sensitivity to low-frequency ambient light variations.

----

==== 3.5 Discussion ====

While the breadboard-based photodetector successfully detects low-frequency optical signals, several limitations exist. Parasitic capacitances and imperfect grounding inherent to the breadboard setup contribute to instability at higher supply voltages. Furthermore, the lack of a fully optimized feedback compensation network restricts bandwidth and dynamic range.

Future improvements include:
* Transitioning to a PCB design to minimize parasitic effects.
* Implementing better shielding against environmental noise.
* Optimizing feedback networks to achieve broader bandwidth and enhanced stability.

These enhancements would enable more precise and higher-speed optical measurements beyond the low-frequency regime demonstrated here.

---

=== 4. G12180 Photodetector Design ===

==== 4.1 Circuit and Components Overview ====

[[File:front1.jpg|center|thumb|400px|Front view of G12180 PD PCB board]]
[[File:back1.jpg|center|thumb|400px|Back view of G12180 PD PCB board]]

To improve stability and reduce parasitic effects, a dedicated PCB was fabricated for the G12180-010A photodiode. The layout was designed to minimize parasitic capacitance and inductance by shortening trace lengths and optimizing grounding.

The circuit adopts a TIA configuration featuring:
* A 10 kΩ feedback resistor for gain control.
* Bypass capacitors (0.1 µF and 10 µF) near the amplifier supply pins for noise suppression.
* Decoupling capacitors across the photodiode bias supply for voltage stabilization.

The Hamamatsu G12180-010A photodiode is optimized for near-infrared and visible light detection, offering high speed and low noise characteristics.

Mechanical mounting uses a four-screw configuration for optical alignment and stability, with a BNC connector for easy signal extraction.

This setup offers significantly improved stability and sensitivity compared to the breadboard-based design.

----

==== 4.2 Theory and Circuit Design Concept ====

The detection principle remains the direct conversion of photocurrent into voltage via a transimpedance amplifier. The PCB design significantly reduces parasitic effects, improves system bandwidth, and enhances immunity to electromagnetic interference (EMI).

The output voltage relation is:

<math>V_{\text{out}} = -I_{\text{photo}} \times R_f</math>

where <math>I_{\text{photo}}</math> is the photocurrent and <math>R_f = 10\,\mathrm{k}\Omega</math> is the feedback resistor.

The PCB-based structure enables cleaner and more accurate optical signal measurements over a broader frequency range.

----

==== 4.3 Testing and Results ====

The PCB-based G12180 photodetector was tested under indoor lighting conditions, with output monitored using a Tektronix TDS 2024C oscilloscope.

{| style="width:100%;"
| [[File:1560test.jpg|400px|thumb|center|Output waveform of PCB-based G12180 photodetector under ambient light]]
|}

As shown, the output signal is highly stable with minimal low-frequency noise. No significant oscillations or distortions were observed, marking a substantial improvement over the breadboard setup.

The enhanced performance is attributed to:
* Reduced parasitic capacitance and inductance.
* Effective bypassing and decoupling.
* Improved grounding and signal integrity through the PCB design.

Overall, the PCB implementation enables clean, low-noise photodetection suitable for both DC and low-frequency optical measurements.

Photodetector with wavelength @ 780nm and 1560nm

2025-04-27T07:16:57Z

Sunke: /* 4. G12180 Photodetector Design */

=== Photodetector with wavelength @ 780nm and 1560nm ===

Team members: Sunke Lan

To design photodetector as power monitor with power within 10mW.

== Project Outline ==

=== 1. Objective ===
* Try to design photodetector for 780nm and 1560nm
*

=== 2. Components ===
* Photodiodes (S5917, G12180-010A), BNC test boards, PCB test boards, op-amp (OP27G) (for target 1)

=== 3. 780 nm Photodetector Design ===

==== 3.1 Circuit and Components Overview ====

[[File:testcircuit.png|center|thumb|400px|Test Circuit for 780 nm Photodetector]]

The photodetector circuit is based on a standard transimpedance amplifier (TIA) configuration, designed to convert the photocurrent generated by a silicon PIN photodiode (S5971) into a measurable voltage output.

In this design:
* The photodiode is operated under a reverse bias of 1 V, supplied externally, to expand the depletion region, reduce junction capacitance, and enhance linearity and response speed. Compared to higher bias voltages (e.g., 15 V), a 1 V bias provides a trade-off between sufficient depletion width and minimized dark current, which is suitable for steady-state light detection around 780 nm.
* The photocurrent generated by incident photons is injected into the inverting input of the operational amplifier (OP27G). The amplifier maintains a virtual ground condition at the inverting input, ensuring linear current-to-voltage conversion without significant voltage swing at the photodiode terminals.
* A feedback resistor <math>R_f = 10\,\mathrm{k}\Omega</math> is connected between the output and the inverting input. The output voltage is governed by:
<math>V_{\text{out}} = -I_{\text{photo}} \times R_f</math>
where <math>I_{\text{photo}}</math> is the photocurrent proportional to the incident optical power.

The OP27G was selected for its excellent low input offset voltage (typically 25 µV), low input bias current, and low noise characteristics (3 nV/√Hz at 1 kHz), making it ideal for precise low-frequency optical measurements. Its moderate gain-bandwidth product (8 MHz) provides sufficient speed while maintaining high stability under typical experimental conditions.

To ensure stable operation:
* Proper bypass capacitors (0.1 µF ceramic + 10 µF electrolytic) are placed close to the amplifier’s power supply pins to suppress high-frequency noise and prevent self-oscillation.
* Decoupling capacitors are connected across the 1 V photodiode bias supply to maintain a clean and stable reverse bias, minimizing potential noise coupling.

{| style="width:100%;"
| [[File:back.jpg|400px|thumb|center|Back side with photodiode mounted]]
| [[File:front.jpg|400px|thumb|center|Front side with lumped circuit elements]]
|}

This current-to-voltage conversion circuit architecture enables reliable detection of light intensities at 780 nm, providing sufficient sensitivity, stability, and low noise performance for laboratory testing and calibration purposes.

----

==== 3.2 Theory and Circuit Design Concept ====

The underlying principle of this photodetector is based on the direct conversion of the photogenerated current into a voltage signal using a transimpedance amplifier structure. By operating the photodiode under reverse bias and maintaining a virtual ground at the amplifier’s inverting input, the circuit ensures linear and efficient current-to-voltage conversion without distorting the photocurrent signal.

The output voltage relationship is given by:

<math>V_{\text{out}} = -I_{\text{photo}} \times R_f</math>

where <math>I_{\text{photo}}</math> is the photocurrent proportional to the incident optical power, and <math>R_f</math> is the feedback resistor.

Through careful selection of bias voltage, feedback network, and amplifier characteristics, the circuit optimizes signal-to-noise ratio while maintaining stability across the low-frequency operating range suited for 780 nm light detection.

----

==== 3.3 Feedback Resistor Selection ====

The feedback resistor <math>R_f</math> determines the transimpedance gain of the photodetector, i.e., how much voltage is generated per unit of photocurrent. The choice of <math>R_f = 10\,\mathrm{k}\Omega</math> in this design is a compromise between achieving a sufficient output signal amplitude and maintaining stability against high-frequency oscillations.

Key considerations include:
* **Signal strength:** A typical photocurrent generated under moderate illumination at 780 nm falls in the range of nanoamperes to microamperes. With a 10 kΩ feedback resistor, the corresponding output voltage becomes easily measurable in the millivolt to volt range without requiring excessive amplification stages.
* **Noise performance:** Increasing <math>R_f</math> enhances the signal amplitude but also amplifies thermal (Johnson) noise. A 10 kΩ resistor keeps the noise contribution low while providing an adequate signal-to-noise ratio (SNR) for steady-state measurements.
* **Frequency stability:** Larger <math>R_f</math> values combined with the photodiode’s junction capacitance can reduce the system bandwidth and introduce phase shifts leading to potential oscillations. A 10 kΩ feedback resistor maintains a higher stability margin while covering the low-frequency range of interest in this application.

Overall, a 10 kΩ feedback resistor ensures that the photodetector system delivers clean, stable, and easily detectable voltage outputs under typical laboratory light levels at 780 nm.

----

==== 3.4 Testing and Results ====

The photodetector circuit was tested under indoor illumination (standard room lighting driven by AC mains) to evaluate its sensitivity and stability. A Tektronix TDS 2024C digital oscilloscope was used to monitor the output signal under different amplifier supply voltages. The observed signals primarily reflect the 50 Hz modulation from the AC power source.

Test results under different conditions are as follows:

{| style="width:100%;"
| [[File:Test1.jpeg|400px|thumb|center|Output without OP-AMP amplification]]
|}

In the first test, the photodiode was connected directly to the oscilloscope without using the operational amplifier. As shown in the figure, no significant signal was detected. This indicates that the photocurrent generated under normal room lighting is too small (typically in the nanoampere range) to be directly observed by the oscilloscope without amplification.

{| style="width:100%;"
| [[File:Test2.jpeg|400px|thumb|center|Output with OP-AMP supply of ±1 V]]
|}

In the second test, the OP-AMP (OP27G) was powered with a ±1 V supply. A small but noticeable output fluctuation appeared. This result suggests that even with low supply voltage, the amplifier begins to operate and provides a weak but observable amplification of the photocurrent signal.

{| style="width:100%;"
| [[File:Test3.jpeg|400px|thumb|center|Output with OP-AMP supply of ±3 V]]
|}

When the OP-AMP supply voltage was increased to ±3 V, a clear quasi-sinusoidal output waveform emerged. The output signal corresponds to the 50 Hz ambient lighting modulation from the AC mains. This indicates that the photodetector circuit is capable of effectively capturing low-frequency optical signals when properly biased and powered.

{| style="width:100%;"
| [[File:Test4.jpeg|400px|thumb|center|Output with OP-AMP supply of ±5 V]]
|}

At a higher OP-AMP supply voltage of ±5 V, significant output distortion and oscillations were observed. Although the OP27G is designed to operate up to ±15 V, the combination of extremely low input signal (small photocurrent) and high supply voltage led to internal instability, likely due to excessive open-loop gain and insufficient input signal amplitude. Additionally, the use of a solderless breadboard for circuit assembly introduced parasitic capacitances and poor grounding, further exacerbating the instability and promoting self-oscillation at higher supply voltages.

----

In summary:
* Without OP-AMP amplification, the photodiode signal is too weak to be detected.
* Properly powering the OP-AMP at ±3 V provides clear and stable signal amplification.
* Excessively high supply voltages (beyond ±5 V) without appropriate compensation or PCB layout lead to instability and self-oscillation.
* The photodetector demonstrates good sensitivity to low-frequency ambient light variations when operated under appropriate conditions.

==== 3.5 Discussion ====

While the current photodetector setup demonstrates effective detection of low-frequency optical signals under ambient lighting, several limitations remain. The use of a solderless breadboard introduces significant parasitic capacitances and imperfect grounding, which contribute to instability at higher amplifier supply voltages. Moreover, the absence of a fully optimized feedback compensation network limits the bandwidth and dynamic range of the detection system.

Future improvements could include designing a printed circuit board (PCB) for the photodetector circuit to minimize parasitic effects, implementing better shielding against environmental noise, and optimizing the feedback network to achieve higher stability and broader bandwidth. These refinements would enable more precise, high-speed optical measurements beyond the low-frequency regime demonstrated here.

=== 4. G12180 Photodetector Design ===

==== 4.1 Circuit and Components Overview ====

[[File:front1.jpg|center|thumb|400px|Front view of G12180 PD PCB board]]
[[File:back1.jpg|center|thumb|400px|Back view of G12180 PD PCB board]]

In order to improve the stability and reduce parasitic effects observed in breadboard-based circuits, a dedicated printed circuit board (PCB) was fabricated for the G12180-010A photodiode module. The PCB layout was designed to minimize parasitic capacitance and inductance by shortening the connection traces and implementing proper grounding strategies.

The circuit follows a basic transimpedance amplifier (TIA) configuration, using:
* A 10 kΩ feedback resistor to set the transimpedance gain.
* Bypass capacitors of 0.1 µF and 10 µF close to the operational amplifier supply pins to suppress high-frequency noise.
* Additional decoupling capacitors across the photodiode bias supply to ensure a stable operating voltage.

The photodiode used is the Hamamatsu G12180-010A, which is optimized for near-infrared and visible light detection, and is particularly suitable for high-speed and low-noise applications.

Mechanical mounting was achieved using a four-screw configuration for robust optical alignment and mechanical stability. A BNC connector was used for convenient signal extraction to the oscilloscope or subsequent signal processing stages.

This setup provides a more reliable platform for sensitive optical measurements compared to the previous breadboard implementation.

----

==== 4.2 Theory and Circuit Design Concept ====

The core detection principle remains the direct conversion of photocurrent into voltage through the use of a transimpedance amplifier. By adopting a PCB design:
* The parasitic capacitances and inductances were significantly reduced.
* The stability and bandwidth of the photodetector system were improved.
* The influence of environmental electromagnetic interference (EMI) was minimized due to better grounding and shielding options.

The output voltage of the photodetector follows the relation:

<math>V_{\text{out}} = -I_{\text{photo}} \times R_f</math>

where <math>I_{\text{photo}}</math> is the photogenerated current and <math>R_f = 10\,\mathrm{k}\Omega</math> is the feedback resistance.

This structure enables a cleaner and more accurate measurement of incident optical signals across a wider frequency range compared to the breadboard setup.

==== 4.3 Testing and Results ====

The PCB-based G12180 photodetector module was tested under similar indoor lighting conditions to evaluate its performance improvements compared to the breadboard prototype. The output was monitored using a Tektronix TDS 2024C digital oscilloscope.

{| style="width:100%;"
| [[File:1560test.jpg|400px|thumb|center|Output waveform of PCB-based G12180 photodetector under ambient light]]
|}

As shown in the figure, the output signal exhibits a highly stable DC level with minimal low-frequency noise. No significant oscillations or distortions were observed throughout the measurement window. This contrasts sharply with the breadboard setup, where high supply voltages led to visible instability and oscillations.

The improved stability can be attributed to:
* Reduced parasitic capacitance and inductance due to the compact and controlled PCB layout.
* Proper bypassing and decoupling of the power supply lines near the operational amplifier.
* Enhanced grounding and signal integrity through a carefully designed ground plane and connector arrangement.

Overall, the PCB implementation successfully suppresses unwanted noise and oscillations, enabling clean, low-noise photodetection suitable for both DC and low-frequency optical measurements.

File:1560test.jpg

2025-04-27T07:16:07Z

Sunke:

Photodetector with wavelength @ 780nm and 1560nm

2025-04-27T07:15:17Z

Sunke: /* 4. Testing and Results */

=== Photodetector with wavelength @ 780nm and 1560nm ===

Team members: Sunke Lan

To design photodetector as power monitor with power within 10mW.

== Project Outline ==

=== 1. Objective ===
* Try to design photodetector for 780nm and 1560nm
*

=== 2. Components ===
* Photodiodes (S5917, G12180-010A), BNC test boards, PCB test boards, op-amp (OP27G) (for target 1)

=== 3. 780 nm Photodetector Design ===

==== 3.1 Circuit and Components Overview ====

[[File:testcircuit.png|center|thumb|400px|Test Circuit for 780 nm Photodetector]]

The photodetector circuit is based on a standard transimpedance amplifier (TIA) configuration, designed to convert the photocurrent generated by a silicon PIN photodiode (S5971) into a measurable voltage output.

In this design:
* The photodiode is operated under a reverse bias of 1 V, supplied externally, to expand the depletion region, reduce junction capacitance, and enhance linearity and response speed. Compared to higher bias voltages (e.g., 15 V), a 1 V bias provides a trade-off between sufficient depletion width and minimized dark current, which is suitable for steady-state light detection around 780 nm.
* The photocurrent generated by incident photons is injected into the inverting input of the operational amplifier (OP27G). The amplifier maintains a virtual ground condition at the inverting input, ensuring linear current-to-voltage conversion without significant voltage swing at the photodiode terminals.
* A feedback resistor <math>R_f = 10\,\mathrm{k}\Omega</math> is connected between the output and the inverting input. The output voltage is governed by:
<math>V_{\text{out}} = -I_{\text{photo}} \times R_f</math>
where <math>I_{\text{photo}}</math> is the photocurrent proportional to the incident optical power.

The OP27G was selected for its excellent low input offset voltage (typically 25 µV), low input bias current, and low noise characteristics (3 nV/√Hz at 1 kHz), making it ideal for precise low-frequency optical measurements. Its moderate gain-bandwidth product (8 MHz) provides sufficient speed while maintaining high stability under typical experimental conditions.

To ensure stable operation:
* Proper bypass capacitors (0.1 µF ceramic + 10 µF electrolytic) are placed close to the amplifier’s power supply pins to suppress high-frequency noise and prevent self-oscillation.
* Decoupling capacitors are connected across the 1 V photodiode bias supply to maintain a clean and stable reverse bias, minimizing potential noise coupling.

{| style="width:100%;"
| [[File:back.jpg|400px|thumb|center|Back side with photodiode mounted]]
| [[File:front.jpg|400px|thumb|center|Front side with lumped circuit elements]]
|}

This current-to-voltage conversion circuit architecture enables reliable detection of light intensities at 780 nm, providing sufficient sensitivity, stability, and low noise performance for laboratory testing and calibration purposes.

----

==== 3.2 Theory and Circuit Design Concept ====

The underlying principle of this photodetector is based on the direct conversion of the photogenerated current into a voltage signal using a transimpedance amplifier structure. By operating the photodiode under reverse bias and maintaining a virtual ground at the amplifier’s inverting input, the circuit ensures linear and efficient current-to-voltage conversion without distorting the photocurrent signal.

The output voltage relationship is given by:

<math>V_{\text{out}} = -I_{\text{photo}} \times R_f</math>

where <math>I_{\text{photo}}</math> is the photocurrent proportional to the incident optical power, and <math>R_f</math> is the feedback resistor.

Through careful selection of bias voltage, feedback network, and amplifier characteristics, the circuit optimizes signal-to-noise ratio while maintaining stability across the low-frequency operating range suited for 780 nm light detection.

----

==== 3.3 Feedback Resistor Selection ====

The feedback resistor <math>R_f</math> determines the transimpedance gain of the photodetector, i.e., how much voltage is generated per unit of photocurrent. The choice of <math>R_f = 10\,\mathrm{k}\Omega</math> in this design is a compromise between achieving a sufficient output signal amplitude and maintaining stability against high-frequency oscillations.

Key considerations include:
* **Signal strength:** A typical photocurrent generated under moderate illumination at 780 nm falls in the range of nanoamperes to microamperes. With a 10 kΩ feedback resistor, the corresponding output voltage becomes easily measurable in the millivolt to volt range without requiring excessive amplification stages.
* **Noise performance:** Increasing <math>R_f</math> enhances the signal amplitude but also amplifies thermal (Johnson) noise. A 10 kΩ resistor keeps the noise contribution low while providing an adequate signal-to-noise ratio (SNR) for steady-state measurements.
* **Frequency stability:** Larger <math>R_f</math> values combined with the photodiode’s junction capacitance can reduce the system bandwidth and introduce phase shifts leading to potential oscillations. A 10 kΩ feedback resistor maintains a higher stability margin while covering the low-frequency range of interest in this application.

Overall, a 10 kΩ feedback resistor ensures that the photodetector system delivers clean, stable, and easily detectable voltage outputs under typical laboratory light levels at 780 nm.

----

==== 3.4 Testing and Results ====

The photodetector circuit was tested under indoor illumination (standard room lighting driven by AC mains) to evaluate its sensitivity and stability. A Tektronix TDS 2024C digital oscilloscope was used to monitor the output signal under different amplifier supply voltages. The observed signals primarily reflect the 50 Hz modulation from the AC power source.

Test results under different conditions are as follows:

{| style="width:100%;"
| [[File:Test1.jpeg|400px|thumb|center|Output without OP-AMP amplification]]
|}

In the first test, the photodiode was connected directly to the oscilloscope without using the operational amplifier. As shown in the figure, no significant signal was detected. This indicates that the photocurrent generated under normal room lighting is too small (typically in the nanoampere range) to be directly observed by the oscilloscope without amplification.

{| style="width:100%;"
| [[File:Test2.jpeg|400px|thumb|center|Output with OP-AMP supply of ±1 V]]
|}

In the second test, the OP-AMP (OP27G) was powered with a ±1 V supply. A small but noticeable output fluctuation appeared. This result suggests that even with low supply voltage, the amplifier begins to operate and provides a weak but observable amplification of the photocurrent signal.

{| style="width:100%;"
| [[File:Test3.jpeg|400px|thumb|center|Output with OP-AMP supply of ±3 V]]
|}

When the OP-AMP supply voltage was increased to ±3 V, a clear quasi-sinusoidal output waveform emerged. The output signal corresponds to the 50 Hz ambient lighting modulation from the AC mains. This indicates that the photodetector circuit is capable of effectively capturing low-frequency optical signals when properly biased and powered.

{| style="width:100%;"
| [[File:Test4.jpeg|400px|thumb|center|Output with OP-AMP supply of ±5 V]]
|}

At a higher OP-AMP supply voltage of ±5 V, significant output distortion and oscillations were observed. Although the OP27G is designed to operate up to ±15 V, the combination of extremely low input signal (small photocurrent) and high supply voltage led to internal instability, likely due to excessive open-loop gain and insufficient input signal amplitude. Additionally, the use of a solderless breadboard for circuit assembly introduced parasitic capacitances and poor grounding, further exacerbating the instability and promoting self-oscillation at higher supply voltages.

----

In summary:
* Without OP-AMP amplification, the photodiode signal is too weak to be detected.
* Properly powering the OP-AMP at ±3 V provides clear and stable signal amplification.
* Excessively high supply voltages (beyond ±5 V) without appropriate compensation or PCB layout lead to instability and self-oscillation.
* The photodetector demonstrates good sensitivity to low-frequency ambient light variations when operated under appropriate conditions.

==== 3.5 Discussion ====

While the current photodetector setup demonstrates effective detection of low-frequency optical signals under ambient lighting, several limitations remain. The use of a solderless breadboard introduces significant parasitic capacitances and imperfect grounding, which contribute to instability at higher amplifier supply voltages. Moreover, the absence of a fully optimized feedback compensation network limits the bandwidth and dynamic range of the detection system.

Future improvements could include designing a printed circuit board (PCB) for the photodetector circuit to minimize parasitic effects, implementing better shielding against environmental noise, and optimizing the feedback network to achieve higher stability and broader bandwidth. These refinements would enable more precise, high-speed optical measurements beyond the low-frequency regime demonstrated here.

=== 4. G12180 Photodetector Design ===

==== 4.1 Circuit and Components Overview ====

[[File:front1.jpg|center|thumb|400px|Front view of G12180 PD PCB board]]
[[File:back1.jpg|center|thumb|400px|Back view of G12180 PD PCB board]]

In order to improve the stability and reduce parasitic effects observed in breadboard-based circuits, a dedicated printed circuit board (PCB) was fabricated for the G12180-010A photodiode module. The PCB layout was designed to minimize parasitic capacitance and inductance by shortening the connection traces and implementing proper grounding strategies.

The circuit follows a basic transimpedance amplifier (TIA) configuration, using:
* A 10 kΩ feedback resistor to set the transimpedance gain.
* Bypass capacitors of 0.1 µF and 10 µF close to the operational amplifier supply pins to suppress high-frequency noise.
* Additional decoupling capacitors across the photodiode bias supply to ensure a stable operating voltage.

The photodiode used is the Hamamatsu G12180-010A, which is optimized for near-infrared and visible light detection, and is particularly suitable for high-speed and low-noise applications.

Mechanical mounting was achieved using a four-screw configuration for robust optical alignment and mechanical stability. A BNC connector was used for convenient signal extraction to the oscilloscope or subsequent signal processing stages.

This setup provides a more reliable platform for sensitive optical measurements compared to the previous breadboard implementation.

----

==== 4.2 Theory and Circuit Design Concept ====

The core detection principle remains the direct conversion of photocurrent into voltage through the use of a transimpedance amplifier. By adopting a PCB design:
* The parasitic capacitances and inductances were significantly reduced.
* The stability and bandwidth of the photodetector system were improved.
* The influence of environmental electromagnetic interference (EMI) was minimized due to better grounding and shielding options.

The output voltage of the photodetector follows the relation:

<math>V_{\text{out}} = -I_{\text{photo}} \times R_f</math>

where <math>I_{\text{photo}}</math> is the photogenerated current and <math>R_f = 10\,\mathrm{k}\Omega</math> is the feedback resistance.

This structure enables a cleaner and more accurate measurement of incident optical signals across a wider frequency range compared to the breadboard setup.

Photodetector with wavelength @ 780nm and 1560nm

2025-04-27T06:55:13Z

Sunke: /* 3. 780 nm Photodetector Design */

=== Photodetector with wavelength @ 780nm and 1560nm ===

Team members: Sunke Lan

To design photodetector as power monitor with power within 10mW.

== Project Outline ==

=== 1. Objective ===
* Try to design photodetector for 780nm and 1560nm
*

=== 2. Components ===
* Photodiodes (S5917, G12180-010A), BNC test boards, PCB test boards, op-amp (OP27G) (for target 1)

=== 3. 780 nm Photodetector Design ===

==== 3.1 Circuit and Components Overview ====

[[File:testcircuit.png|center|thumb|400px|Test Circuit for 780 nm Photodetector]]

The photodetector circuit is based on a standard transimpedance amplifier (TIA) configuration, designed to convert the photocurrent generated by a silicon PIN photodiode (S5971) into a measurable voltage output.

In this design:
* The photodiode is operated under a reverse bias of 1 V, supplied externally, to expand the depletion region, reduce junction capacitance, and enhance linearity and response speed. Compared to higher bias voltages (e.g., 15 V), a 1 V bias provides a trade-off between sufficient depletion width and minimized dark current, which is suitable for steady-state light detection around 780 nm.
* The photocurrent generated by incident photons is injected into the inverting input of the operational amplifier (OP27G). The amplifier maintains a virtual ground condition at the inverting input, ensuring linear current-to-voltage conversion without significant voltage swing at the photodiode terminals.
* A feedback resistor <math>R_f = 10\,\mathrm{k}\Omega</math> is connected between the output and the inverting input. The output voltage is governed by:
<math>V_{\text{out}} = -I_{\text{photo}} \times R_f</math>
where <math>I_{\text{photo}}</math> is the photocurrent proportional to the incident optical power.

The OP27G was selected for its excellent low input offset voltage (typically 25 µV), low input bias current, and low noise characteristics (3 nV/√Hz at 1 kHz), making it ideal for precise low-frequency optical measurements. Its moderate gain-bandwidth product (8 MHz) provides sufficient speed while maintaining high stability under typical experimental conditions.

To ensure stable operation:
* Proper bypass capacitors (0.1 µF ceramic + 10 µF electrolytic) are placed close to the amplifier’s power supply pins to suppress high-frequency noise and prevent self-oscillation.
* Decoupling capacitors are connected across the 1 V photodiode bias supply to maintain a clean and stable reverse bias, minimizing potential noise coupling.

{| style="width:100%;"
| [[File:back.jpg|400px|thumb|center|Back side with photodiode mounted]]
| [[File:front.jpg|400px|thumb|center|Front side with lumped circuit elements]]
|}

This current-to-voltage conversion circuit architecture enables reliable detection of light intensities at 780 nm, providing sufficient sensitivity, stability, and low noise performance for laboratory testing and calibration purposes.

----

==== 3.2 Theory and Circuit Design Concept ====

The underlying principle of this photodetector is based on the direct conversion of the photogenerated current into a voltage signal using a transimpedance amplifier structure. By operating the photodiode under reverse bias and maintaining a virtual ground at the amplifier’s inverting input, the circuit ensures linear and efficient current-to-voltage conversion without distorting the photocurrent signal.

The output voltage relationship is given by:

<math>V_{\text{out}} = -I_{\text{photo}} \times R_f</math>

where <math>I_{\text{photo}}</math> is the photocurrent proportional to the incident optical power, and <math>R_f</math> is the feedback resistor.

Through careful selection of bias voltage, feedback network, and amplifier characteristics, the circuit optimizes signal-to-noise ratio while maintaining stability across the low-frequency operating range suited for 780 nm light detection.

----

==== 3.3 Feedback Resistor Selection ====

The feedback resistor <math>R_f</math> determines the transimpedance gain of the photodetector, i.e., how much voltage is generated per unit of photocurrent. The choice of <math>R_f = 10\,\mathrm{k}\Omega</math> in this design is a compromise between achieving a sufficient output signal amplitude and maintaining stability against high-frequency oscillations.

Key considerations include:
* **Signal strength:** A typical photocurrent generated under moderate illumination at 780 nm falls in the range of nanoamperes to microamperes. With a 10 kΩ feedback resistor, the corresponding output voltage becomes easily measurable in the millivolt to volt range without requiring excessive amplification stages.
* **Noise performance:** Increasing <math>R_f</math> enhances the signal amplitude but also amplifies thermal (Johnson) noise. A 10 kΩ resistor keeps the noise contribution low while providing an adequate signal-to-noise ratio (SNR) for steady-state measurements.
* **Frequency stability:** Larger <math>R_f</math> values combined with the photodiode’s junction capacitance can reduce the system bandwidth and introduce phase shifts leading to potential oscillations. A 10 kΩ feedback resistor maintains a higher stability margin while covering the low-frequency range of interest in this application.

Overall, a 10 kΩ feedback resistor ensures that the photodetector system delivers clean, stable, and easily detectable voltage outputs under typical laboratory light levels at 780 nm.

----

==== 3.4 Testing and Results ====

The photodetector circuit was tested under indoor illumination (standard room lighting driven by AC mains) to evaluate its sensitivity and stability. A Tektronix TDS 2024C digital oscilloscope was used to monitor the output signal under different amplifier supply voltages. The observed signals primarily reflect the 50 Hz modulation from the AC power source.

Test results under different conditions are as follows:

{| style="width:100%;"
| [[File:Test1.jpeg|400px|thumb|center|Output without OP-AMP amplification]]
|}

In the first test, the photodiode was connected directly to the oscilloscope without using the operational amplifier. As shown in the figure, no significant signal was detected. This indicates that the photocurrent generated under normal room lighting is too small (typically in the nanoampere range) to be directly observed by the oscilloscope without amplification.

{| style="width:100%;"
| [[File:Test2.jpeg|400px|thumb|center|Output with OP-AMP supply of ±1 V]]
|}

In the second test, the OP-AMP (OP27G) was powered with a ±1 V supply. A small but noticeable output fluctuation appeared. This result suggests that even with low supply voltage, the amplifier begins to operate and provides a weak but observable amplification of the photocurrent signal.

{| style="width:100%;"
| [[File:Test3.jpeg|400px|thumb|center|Output with OP-AMP supply of ±3 V]]
|}

When the OP-AMP supply voltage was increased to ±3 V, a clear quasi-sinusoidal output waveform emerged. The output signal corresponds to the 50 Hz ambient lighting modulation from the AC mains. This indicates that the photodetector circuit is capable of effectively capturing low-frequency optical signals when properly biased and powered.

{| style="width:100%;"
| [[File:Test4.jpeg|400px|thumb|center|Output with OP-AMP supply of ±5 V]]
|}

At a higher OP-AMP supply voltage of ±5 V, significant output distortion and oscillations were observed. Although the OP27G is designed to operate up to ±15 V, the combination of extremely low input signal (small photocurrent) and high supply voltage led to internal instability, likely due to excessive open-loop gain and insufficient input signal amplitude. Additionally, the use of a solderless breadboard for circuit assembly introduced parasitic capacitances and poor grounding, further exacerbating the instability and promoting self-oscillation at higher supply voltages.

----

In summary:
* Without OP-AMP amplification, the photodiode signal is too weak to be detected.
* Properly powering the OP-AMP at ±3 V provides clear and stable signal amplification.
* Excessively high supply voltages (beyond ±5 V) without appropriate compensation or PCB layout lead to instability and self-oscillation.
* The photodetector demonstrates good sensitivity to low-frequency ambient light variations when operated under appropriate conditions.

==== 3.5 Discussion ====

While the current photodetector setup demonstrates effective detection of low-frequency optical signals under ambient lighting, several limitations remain. The use of a solderless breadboard introduces significant parasitic capacitances and imperfect grounding, which contribute to instability at higher amplifier supply voltages. Moreover, the absence of a fully optimized feedback compensation network limits the bandwidth and dynamic range of the detection system.

Future improvements could include designing a printed circuit board (PCB) for the photodetector circuit to minimize parasitic effects, implementing better shielding against environmental noise, and optimizing the feedback network to achieve higher stability and broader bandwidth. These refinements would enable more precise, high-speed optical measurements beyond the low-frequency regime demonstrated here.

=== 4. Testing and Results ===
==== 4.1 Test Circuit ====

==== 4.2 Data and Analysis ====

Photodetector with wavelength @ 780nm and 1560nm

2025-04-27T06:49:30Z

Sunke: /* 3.4 Testing and Results */

File:Test4.jpeg

2025-04-27T06:47:18Z

Sunke:

File:Test3.jpeg

2025-04-27T06:46:41Z

Sunke:

File:Test2.jpeg

2025-04-27T06:41:37Z

Sunke:

File:Test1.jpeg

2025-04-27T06:38:43Z

Sunke:

Photodetector with wavelength @ 780nm and 1560nm

2025-04-27T06:05:46Z

Sunke: /* 3. 780 nm Photodetector Design */

Photodetector with wavelength @ 780nm and 1560nm

2025-04-27T06:02:03Z

Sunke: /* 3. 780 nm Photodetector Design */

Photodetector with wavelength @ 780nm and 1560nm

2025-04-27T06:00:18Z

Sunke: /* 3. 780nm PD */

Photodetector with wavelength @ 780nm and 1560nm

2025-04-27T05:56:44Z

Sunke: /* 3. Test circuits */

Photodetector with wavelength @ 780nm and 1560nm

2025-04-27T05:48:24Z

Sunke: /* 3.1.2 Theory and Circuit Design Concept */

Photodetector with wavelength @ 780nm and 1560nm

2025-04-27T05:47:35Z

Sunke: /* 3. Test circuits */

Photodetector with wavelength @ 780nm and 1560nm

2025-04-27T05:35:19Z

Sunke: /* Project Outline */

Photodetector with wavelength @ 780nm and 1560nm

2025-04-06T14:37:26Z

Sunke: /* 3. Design Considerations */

=== Photodetector with wavelength @ 780nm and 1560nm ===

Team members: Sunke Lan

To design photodetector as power monitor with power within 10mW.

== Project Outline ==

=== 1. Objective ===
* 1.1 Try to design photodetector for 780nm and 1560nm
* 1.2 Measure optical power up to 10mW( depends on which light we will measure finally) to stabilize the intensity of laser

=== 2. Components ===
* 2.1 Photodiodes (S5917, G12180-010A), BNC test boards, PCB test boards, op-amp (OP27G) (for target 1)
* 2.2 Oscilloscope, Rotation Mount with Resonant Piezoelectric Motors(ELL 14K), SHG optical system (for target 2)

=== 3. Test circuits ===
* 3.1.1 Basic current-voltage transferring circuit for S5971
[[File:testcircuit.png|center|thumb|400px|Test Circuit for 780nm Photodetector]]
Based on the reference circuit, we changed the biase voltage of photodiode to 1V, and used op-amp OP27E to do the current-voltage transferring.

{| style="width:100%;"
| [[File:back.jpg|400px|thumb|center|the side with PD]]
| [[File:front.jpg|400px|thumb|center|the side with basic lump elements]]
|}

=== 4. Testing and Results ===
==== 4.1 Test Circuit ====

==== 4.2 Data and Analysis ====

Photodetector with wavelength @ 780nm and 1560nm

2025-04-06T14:34:29Z

Sunke: /* 3. Design Considerations */

=== Photodetector with wavelength @ 780nm and 1560nm ===

Team members: Sunke Lan

To design photodetector as power monitor with power within 10mW.

== Project Outline ==

=== 1. Objective ===
* 1.1 Try to design photodetector for 780nm and 1560nm
* 1.2 Measure optical power up to 10mW( depends on which light we will measure finally) to stabilize the intensity of laser

=== 2. Components ===
* 2.1 Photodiodes (S5917, G12180-010A), BNC test boards, PCB test boards, op-amp (OP27G) (for target 1)
* 2.2 Oscilloscope, Rotation Mount with Resonant Piezoelectric Motors(ELL 14K), SHG optical system (for target 2)

=== 3. Design Considerations ===
* 3.1.1 Basic current-voltage transferring circuit for S5971
[[File:testcircuit.png|center|thumb|400px|Test Circuit for 780nm Photodetector]]
Based on the reference circuit, we changed the biase voltage of photodiode to 1V, and used op-amp OP27E to do the current-voltage transferring.

{| style="width:100%;"
| [[File:back.jpg|400px|thumb|center|the side with PD]]
| [[File:front.jpg|400px|thumb|center|the side with basic lump elements]]
|}

=== 4. Testing and Results ===
==== 4.1 Test Circuit ====

==== 4.2 Data and Analysis ====

Photodetector with wavelength @ 780nm and 1560nm

2025-04-06T14:32:01Z

Sunke: /* 3. Design Considerations */

=== Photodetector with wavelength @ 780nm and 1560nm ===

Team members: Sunke Lan

To design photodetector as power monitor with power within 10mW.

== Project Outline ==

=== 1. Objective ===
* 1.1 Try to design photodetector for 780nm and 1560nm
* 1.2 Measure optical power up to 10mW( depends on which light we will measure finally) to stabilize the intensity of laser

=== 2. Components ===
* 2.1 Photodiodes (S5917, G12180-010A), BNC test boards, PCB test boards, op-amp (OP27G) (for target 1)
* 2.2 Oscilloscope, Rotation Mount with Resonant Piezoelectric Motors(ELL 14K), SHG optical system (for target 2)

=== 3. Design Considerations ===
* 3.1.1 Basic current-voltage transferring circuit for S5971
[[File:testcircuit.png|center|thumb|400px|Test Circuit for 780nm Photodetector]]
Based on the reference circuit, we changed the biase voltage of photodiode to 1V, and used op-amp OP27E to do the current-voltage transferring.

{| style="width:100%;"
| [[File:back.jpg|400px|thumb|center|Circuit for 780nm Photodetector]]
| [[File:front.jpg|400px|thumb|center|Circuit for 1560nm Photodetector]]
|}

=== 4. Testing and Results ===
==== 4.1 Test Circuit ====

==== 4.2 Data and Analysis ====

Photodetector with wavelength @ 780nm and 1560nm

2025-04-06T14:30:15Z

Sunke: /* 3. Design Considerations */

=== Photodetector with wavelength @ 780nm and 1560nm ===

Team members: Sunke Lan

To design photodetector as power monitor with power within 10mW.

== Project Outline ==

=== 1. Objective ===
* 1.1 Try to design photodetector for 780nm and 1560nm
* 1.2 Measure optical power up to 10mW( depends on which light we will measure finally) to stabilize the intensity of laser

=== 2. Components ===
* 2.1 Photodiodes (S5917, G12180-010A), BNC test boards, PCB test boards, op-amp (OP27G) (for target 1)
* 2.2 Oscilloscope, Rotation Mount with Resonant Piezoelectric Motors(ELL 14K), SHG optical system (for target 2)

=== 3. Design Considerations ===
* 3.1.1 Basic current-voltage transferring circuit for S5971
[[File:testcircuit.png|center|thumb|400px|Test Circuit for 780nm Photodetector]]
Based on the reference circuit, we changed the biase voltage of photodiode to 1V, and used op-amp OP27E to do the current-voltage transferring.
[[File:back.jpg|center|thumb|400px|Test Circuit for 780nm Photodetector]]

=== 4. Testing and Results ===
==== 4.1 Test Circuit ====

==== 4.2 Data and Analysis ====

File:Front1.jpg

2025-04-06T14:29:53Z

Sunke:

File:Back1.jpg

2025-04-06T14:29:35Z

Sunke:

File:Back.jpg

2025-04-06T14:24:24Z

Sunke:

File:Front.jpg

2025-04-06T14:23:44Z

Sunke:

Photodetector with wavelength @ 780nm and 1560nm

2025-04-06T14:19:20Z

Sunke: /* 3. Design Considerations */

=== Photodetector with wavelength @ 780nm and 1560nm ===

Team members: Sunke Lan

To design photodetector as power monitor with power within 10mW.

== Project Outline ==

=== 1. Objective ===
* 1.1 Try to design photodetector for 780nm and 1560nm
* 1.2 Measure optical power up to 10mW( depends on which light we will measure finally) to stabilize the intensity of laser

=== 2. Components ===
* 2.1 Photodiodes (S5917, G12180-010A), BNC test boards, PCB test boards, op-amp (OP27G) (for target 1)
* 2.2 Oscilloscope, Rotation Mount with Resonant Piezoelectric Motors(ELL 14K), SHG optical system (for target 2)

=== 3. Design Considerations ===
* 3.1.1 Basic current-voltage transferring circuit for S5971
[[File:testcircuit.png|center|thumb|400px|Test Circuit for 780nm Photodetector]]
Based on the reference circuit, we changed the biase voltage of photodiode to 1V, and used op-amp OP27E to do the current-voltage transferring.

=== 4. Testing and Results ===
==== 4.1 Test Circuit ====

==== 4.2 Data and Analysis ====

Photodetector with wavelength @ 780nm and 1560nm

2025-04-06T14:19:06Z

Sunke: /* 3. Design Considerations */

=== Photodetector with wavelength @ 780nm and 1560nm ===

Team members: Sunke Lan

To design photodetector as power monitor with power within 10mW.

== Project Outline ==

=== 1. Objective ===
* 1.1 Try to design photodetector for 780nm and 1560nm
* 1.2 Measure optical power up to 10mW( depends on which light we will measure finally) to stabilize the intensity of laser

=== 2. Components ===
* 2.1 Photodiodes (S5917, G12180-010A), BNC test boards, PCB test boards, op-amp (OP27G) (for target 1)
* 2.2 Oscilloscope, Rotation Mount with Resonant Piezoelectric Motors(ELL 14K), SHG optical system (for target 2)

=== 3. Design Considerations ===
* 3.1.1 Basic current-voltage transferring circuit for S5971
[[File:testcircuit.png|center|thumb|400px|Circuit for 780nm Photodetector]]
Based on the reference circuit, we changed the biase voltage of photodiode to 1V, and used op-amp OP27E to do the current-voltage transferring.

=== 4. Testing and Results ===
==== 4.1 Test Circuit ====

==== 4.2 Data and Analysis ====

Photodetector with wavelength @ 780nm and 1560nm

2025-04-06T14:18:39Z

Sunke: /* 3. Design Considerations */

=== Photodetector with wavelength @ 780nm and 1560nm ===

Team members: Sunke Lan

To design photodetector as power monitor with power within 10mW.

== Project Outline ==

=== 1. Objective ===
* 1.1 Try to design photodetector for 780nm and 1560nm
* 1.2 Measure optical power up to 10mW( depends on which light we will measure finally) to stabilize the intensity of laser

=== 2. Components ===
* 2.1 Photodiodes (S5917, G12180-010A), BNC test boards, PCB test boards, op-amp (OP27G) (for target 1)
* 2.2 Oscilloscope, Rotation Mount with Resonant Piezoelectric Motors(ELL 14K), SHG optical system (for target 2)

=== 3. Design Considerations ===
* 3.1.1 Basic current-voltage transferring circuit for S5971
[[File:reference circuit.png|center|thumb|400px|Circuit for 780nm Photodetector]]
Based on the reference circuit, we changed the biase voltage of photodiode to 1V, and used op-amp OP27E to do the current-voltage transferring.

=== 4. Testing and Results ===
==== 4.1 Test Circuit ====

==== 4.2 Data and Analysis ====

Photodetector with wavelength @ 780nm and 1560nm

2025-04-06T14:13:34Z

Sunke: /* Project Outline */

=== Photodetector with wavelength @ 780nm and 1560nm ===

Team members: Sunke Lan

To design photodetector as power monitor with power within 10mW.

== Project Outline ==

=== 1. Objective ===
* 1.1 Try to design photodetector for 780nm and 1560nm
* 1.2 Measure optical power up to 10mW( depends on which light we will measure finally) to stabilize the intensity of laser

=== 2. Components ===
* 2.1 Photodiodes (S5917, G12180-010A), BNC test boards, PCB test boards, op-amp (OP27G) (for target 1)
* 2.2 Oscilloscope, Rotation Mount with Resonant Piezoelectric Motors(ELL 14K), SHG optical system (for target 2)

=== 3. Design Considerations ===
* 3.1.1 Basic current-voltage transferring circuit
[[File:testcircuit.png|center|thumb|400px|Circuit for 780nm Photodetector]]

=== 4. Testing and Results ===
==== 4.1 Test Circuit ====

==== 4.2 Data and Analysis ====

Photodetector with wavelength @ 780nm and 1560nm

2025-04-06T14:04:14Z

Sunke: /* Project Outline */

Photodetector with wavelength @ 780nm and 1560nm

2025-04-06T14:02:56Z

Sunke: /* Photodetector with wavelength @ 780nm and 1560nm */

=== Photodetector with wavelength @ 780nm and 1560nm ===

Team members: Sunke Lan

To design photodetector as power monitor with power within 10mW.

==== Project Outline ====

# Objective
## Design photodetector for 780nm and 1560nm
## Measure optical power up to 10mW

# Components
## Photodiodes (S5917, G12180-010A), BNC test boards, PCB test boards, and basic lump elements
## Transimpedance amplifier, op-amp (OP27G)

# Design Considerations
## Wavelength sensitivity
## Linearity within 10mW

# Testing and Results

## Test Circuit

[[File:testcircuit.png|center|thumb|400px|Circuit for 780nm Photodetector]]

## Data and Analysis

Photodetector with wavelength @ 780nm and 1560nm

2025-04-06T14:01:29Z

Sunke: /* Project Outline */

=== Photodetector with wavelength @ 780nm and 1560nm ===

Team members: Sunke Lan

To design photodetector as power monitor with power within 10mW.

==== Project Outline ====
# Objective
## Design photodetector for 780nm and 1560nm
## Measure optical power up to 10mW

# Components
## Photodiodes(S5917, G12180-010A), BNC test boards, PCB test boards, and basic lump elements.
## Transimpedance amplifier, op-amp(OP27G)

# Design Considerations
## Wavelength sensitivity
## Linearity within 10mW

# Testing and Results
## Test Circuirt
[[File:testcircuit.png|thumb|400px|Circuit for 780nm Photodetector]]
## Data and analysis

File:Testcircuit.png

2025-04-06T13:58:52Z

Sunke:

Photodetector with wavelength @ 780nm and 1560nm

2025-04-06T13:44:55Z

Sunke: /* Project Outline */

=== Photodetector with wavelength @ 780nm and 1560nm ===

Team members: Sunke Lan

To design photodetector as power monitor with power within 10mW.

==== Project Outline ====
# Objective
## Design photodetector for 780nm and 1560nm
## Measure optical power up to 10mW

# Components
## Photodiodes(S5917, G12180-010A), BNC test boards, PCB test boards, and basic lump elements.
## Transimpedance amplifier, op-amp(OP27G)

[[File:testcircuit.png|thumb|400px|这是图片的说明文字]]

# Design Considerations
## Wavelength sensitivity
## Linearity within 10mW

# Testing and Results
## Calibration method
## Data and analysis

Photodetector with wavelength @ 780nm and 1560nm

2025-04-06T13:40:01Z

Sunke: /* Project Outline */

=== Photodetector with wavelength @ 780nm and 1560nm ===

Team members: Sunke Lan

To design photodetector as power monitor with power within 10mW.

==== Project Outline ====
# Objective
## Design photodetector for 780nm and 1560nm
## Measure optical power up to 10mW

# Components
## Photodiodes(S5917, G12180-010A), BNC test boards, PCB test boards, and basic lump elements.
## Transimpedance amplifier, op-amp(OP27G)

# Design Considerations
## Wavelength sensitivity
## Linearity within 10mW

# Testing and Results
## Calibration method
## Data and analysis

Photodetector with wavelength @ 780nm and 1560nm

2025-04-06T13:33:10Z

Sunke: /* Photodetector with wavelength @ 780nm and 1560nm */

=== Photodetector with wavelength @ 780nm and 1560nm ===

Team members: Sunke Lan

To design photodetector as power monitor with power within 10mW.

==== Project Outline ====
# Objective
## Design photodetector for 780nm and 1560nm
## Measure optical power up to 10mW

# Components
## Photodiode
## Transimpedance amplifier

# Design Considerations
## Wavelength sensitivity
## Linearity within 10mW

# Testing and Results
## Calibration method
## Data and analysis

Photodetector with wavelength @ 780nm and 1560nm

2025-02-17T16:01:40Z

Sunke: Created page with "===Photodetector with wavelength @ 780nm and 1560nm=== Team members: Sunke Lan To design photodetector as power monitor with power within 10mW."

===[[Photodetector with wavelength @ 780nm and 1560nm]]===
Team members: Sunke Lan

To design photodetector as power monitor with power within 10mW.

Main Page

2025-02-17T15:59:40Z

Sunke: /* Projects */

'''Welcome to the wiki page for the course PC5271: Physics of Sensors!'''

This is the repository where projects are documented. Creation of new accounts have now been blocked,and editing/creating pages is enabled. If you need an account, please contact Christian.

==Projects==
===[[Project 1 (Example)]]===
Keep a very brief description of a project or even a suggestion here, and perhaps the names of the team members, or who to contact if there is interest to join. Once the project has stabilized, keep stuff in the project page linked by the headline.

===[[Laser Gyroscope]]===
Team members: Darren Koh, Chiew Wen Xin

Build a laser interferometer to detect rotation.

===[[Laser Distance Measurer]]===
Team members: Arya Chowdhury, Liu Sijin, Jonathan Wong

Description: To build a device that uses lasers to measure distances.

===[[Alcohol Concentration Measurement]]===

Team members: Lim Gin Joe,Sun Weijia, Yan Chengrui, Zhu Junyi

This project aims to build a sensor to measure the concentration of alcohol by optical method

(CK: you can check Optics Letters <b>47</b>, 5076-5079 (2022) https://doi.org/10.1364/OL.472890 for some info)

===[[Ultrasonic Acoustic Remote Sensing]]===
Team member(s): Chua Rui Ming

How well can we use sound waves to survey the environment?

===[[Blood Oxygen Sensor]]===
Team members: He Lingzi, Zhao Lubo, Zhang Ruoxi, Xu Yintong

This project aims to build a sensor to detect the oxygen concentration in the blood.

===[[Terahertz Electromagnetic Wave Detection]]===
Team members: Shizhuo Luo

This project aims to detect Terahertz waves, especially terahertz pulses (This is because they are intense and controllable). We may try different ways like electro-optical sampling and VO2 detectors.

===[[Air contaminant measurement with interferometry]]===
Team member(s): Ta Na, Cao Yuan

This project aims to make use of the change in refractive index, hence different path length, due to different contaminants present in the air.

===[[Photodetector with wavelength @ 780nm and 1560nm]]===
Team members: Sunke Lan

To design photodetector as power monitor with power within 10mW.

==Resources==
===Books and links===
* A good textbook on the Physics of Sensors is Jacob Fraden: Handbook of Mondern Sensors, Springer, ISBN 978-3-319-19302-1 or [https://link.springer.com/book/10.1007/978-3-319-19303-8 doi:10.1007/978-3-319-19303-8]. There shoud be an e-book available through the NUS library at https://linc.nus.edu.sg/record=b3554643

===Software===
* Various Python extensions. [https://www.python.org Python] is a very powerful free programming language that runs on just about any computer platform. It is open source and completely free.
* [https://www.gnuplot.info Gnuplot]: A free and very mature data display tool that works on just about any platform used that produces excellent publication-grade eps and pdf figures. Can be also used in scripts. Open source and completely free.
* Matlab: Very common, good toolset also for formal mathematics, good graphics. Expensive. We may have a site license, but I am not sure how painful it is for us to get a license for this course. Ask if interested.
* Mathematica: More common among theroetical physicists, very good in formal maths, now with better numerics. Graphs are ok but can be a pain to make looking good. As with Matlab, we do have a campus license. Ask if interested.

===Apps===
Common mobile phones these days are equipped with an amazing toolchest of sensors. There are a few apps that allow you to access them directly, and turn your phone into a powerful sensor. Here some suggestions:

* Physics Toolbox sensor suite on [https://play.google.com/store/apps/details?id=com.chrystianvieyra.physicstoolboxsuite&hl=en_SG Google play store] or [https://apps.apple.com/us/app/physics-toolbox-sensor-suite/id1128914250 Apple App store].

===Data sheets===
A number of components might be useful for several groups. Some common data sheets are here:
* Generic Silicon pin Photodiode type [[Media:Bpw34.pdf|BPW34]]
* Thermistor type [[Media:Thermistor B57861S.pdf|B57861S]] (R0=10kΩ, B=3988Kelvin). Search for [https://en.wikipedia.org/wiki/Steinhart-Hart_equation Steinhart-Hart equation]. See [[Thermistor]] page here as well.
* Resistor color codes are explained [https://en.wikipedia.org/wiki/Electronic_color_code here]

==Some wiki reference materials==
* [https://www.mediawiki.org/wiki/Special:MyLanguage/Manual:FAQ MediaWiki FAQ]
* [[Writing mathematical expressions]]
* [[Uploading images and files]]

== Old Wiki ==
You can find entries to the wiki from [https://pc5271.org/PC5271_AY2324S2 AY2023/24 Sem 2]