Laser Gyroscope

2025-04-11T03:21:49Z

Darren: /* 2nd setup */

Some Description

==Team members==
Darren e0303300@u.nus.edu

Wen Xin e0309271@u.nus.edu

==Idea==
This project aims to measure some rotation by using the Sagnac effect, by using a loop of fiber as a ring interferometer.

'''Sagnac effect'''

When two beams of light are sent into the two ports of a ring interferometer, they travel clockwise (CW) and counter-clockwise (CCW) paths respectively. For a stationary ring interferometer, since the path length traversed by each beam is the same, this leads to complete constructive interference at the output port.

Now let's say the interferometer is spinning in the CW direction with rotation rate <math> \Omega </math>. Then there will be a difference in path length:

<math> \Delta L = R\Omega t_{CW} </math>

which results in a timing difference of:

<math> t_{CW} = \frac{2\pi nR + R\Omega t_{CW}}{c}, \quad t_{CCW} = \frac{2\pi nR - R\Omega t_{CCW}}{c} </math>

where ''n'' is the refractive index of the medium. Simplifying,

<math> t_{CW} = \frac{L_{0}}{c-R\Omega}, \quad t_{CCW} = \frac{L_{0}}{c+R\Omega}, \quad \Delta t = t_{CW} - t_{CCW} = \frac{L_{0} \cdot 2R\Omega}{c^{2}} \cdot \frac{1}{1+\left(\frac{R\Omega}{c}\right)^{2}} </math>

as <math> R\Omega << c </math>,

<math> \Delta t \approx \frac{2RL_{0}}{c^{2}} \cdot \Omega </math>

For a fiber loop with radius ''R'' and number of loops ''N'',

<math> \Delta t = \frac{4N\pi nR^{2}}{c^{2}} \cdot \Omega </math>

Thus, for light of frequency ''f'', we can calculate the Sagnac phase shift:

<math> \Delta\phi_{S} = 2\pi f \cdot \Delta t = \frac{8\pi nN A}{\lambda c} \cdot \Omega </math>

The change in the phase difference between the two paths changes the degree of constructive or destructive interference that happens, resulting in a change in the intensity detected. This is illustrated by the sketch of the graph below. As such, the change in the voltage across the detector corresponds to <math> \Omega </math>

[[File:intensity_shift.jpeg|400px]]

==Parts==
50m smf28 fiber spools

20km smf28 fiber spools

2x Thorlabs FGA01FC photodiodes

1550nm Fiber circulator

Fiber paddle

Laser driver

1550nm Laser diode

1550nm Fiber isolator

==1st Setup==
11 and 14 March
The main setup will be a fiber based Sagnac interferometer. The setup is as shown below:

[[File:FirstSetup_drawing.jpeg|400px]]
[[File:FirstSetup_picture.jpeg|400px]]

Parts used are:
1x laser driver
1x 1550nm DFB laser diode
1x fiber isolator to prevent backreflections to the laser diode
1x 50:50 fiber beam splitter at 1550nm
1x 50m smf28 fiber coil
1x FGA01FC photodiode
a lot of fiber to fiber connectors
1x 1m smf28 fiber for connecting beam splitter to the photodiode
2x apc to pc smf28 fiber

The fiber loop is placed on top of a rotating chair, and the interferometer output is sent to a photodiode which is connected to an oscilloscope.

During out 1st iteration, rotating the 50m fiber coil causes a change in the voltage output of the photodiode. However, the change in the voltage output remains even after the fiber coil is stationary, which should not happen since the voltage change we think we should observed should only come from movement and should not depend on the final orientation.

To further investigate, we removed the fiber loop and connected only the 2 ends of the fiber beam splitter together. In practice, rotating this setup should show a very small change or no change since the area enclosed by the fiber is much smaller as compared to the fiber coil. However, we still observe the same voltage change as before. Suspected that the voltage change we observe might be due to birefrigence in the fiber instead. Fiddling with the fiber, the voltage change was observed as well. So the voltage change is likely due to the polarization change when the fiber was moving instead. This would cause a change in the intensity of the interfereometer output.

Stray fibers were also taped down to prevent them moving and changing the polarization of the light but it does not seem to work.

Planned to investigate this further using a circulator and a seperate photodiode to conver the sagnac configuration into a mach-zender configuration and look at the output of both ports.

==2nd setup==
18 March

[[File:SecondSetup_drawing.jpeg|400px]]
[[File:SecondSetup_picture.jpeg|400px]]

We moved all the components to another breadboard. All fibers are taped down to the breadboard with only 2 fibers untaped. 1 from the 1550nm laser diode and the other leading to the photodiode. With this new setup, we seem to get the expected behaviour? A voltage change from the photodiode is only observed when the fiber coil is moving and returns to its original value when its stationary.

In order to verify the rotation rate of the fiber coil, we placed a phone with a gyroscope readout enabled (phyphox). We then turn the chair clockwise and counter-clockwise continuously, and plot the results below:

[[File:SecondSetup_CWCCW.jpeg|600px]]

The orange trace represents the output from the phone's gyroscope, while the blue trace and green trace represents the voltage readings from PD1 (connected to the 50:50 beam splitter) and PD2 (connected to the circulator) respectively. Clearly, we do observe correlation between when the chair is rotated, and when fluctuations in the PD voltage outputs are observed. We also see that the fluctuations from PD1 and PD2 are anti-correlated, which verifies the observation of interference.

However, there are clearly several issues from this measurement. First, we observe much greater noise, and much lower sensitivity from PD2's output. We suspect that the circulator might be the cause of this. Given that, we will mainly be looking at the PD1 voltage readings. Second, we expect the voltage signal to change one way when the chair is rotated CW, and to change the other way when the chair is rotated CCW. The plot of PD1 voltage above shows that when the rotation rate <math> \Omega </math> is negative (CW), the voltage change is positive, whereas when <math> \Omega </math> is negative (CCW), the voltage change can be both positive or negative. We suspect that this might be due to the operating point being close to a minima in the interference pattern (the sketch in the idea section), and the CCW rotation is sufficient to push the signal over the minima.

We also observe fluctuations at the peaks of the rotation rate when <math> \Omega < 0 </math>, which does not agree with the relatively smooth rotations as indicated by the phone gyroscope readings.

==Third setup==

[[File:ThirdSetup_drawing.jpeg|400px]]
[[File:ThirdSetup_image.jpeg|400px]]

The results from the previous setup seems to indicate some improvements can still be made. The first improvement is to include a polarization paddle at one side of the fiber coil, which should allow us to tune the polarization of the light interfering at the 50:50 BS to some extent. We also noticed that the fiber from the laser source to the isolator was hanging, and lightly disturbing this fiber led to small but visible fluctuations in the PD readings. So we squeezed the laser source onto the chair (this seemed to be the cause of the fluctuations discussed at the end of the previous section).

[[File:ThirdSetup_CWCCW_Imid.jpeg|400px]]

blahblah

[[File:ThirdSetup_CWCCW_Imin&Imax.jpeg|800px]]

blahblah

[[File:ThirdSetup_CCW_smallrotation.jpeg|400px]]

== Fourth Setup ==

Since we have a 20km fiber loop lying around, we decided to replace the 50m fiber loop with the 20km fiber loop.

[[File:FourthSetup_image.jpeg|400px]]

[[File:FourthSetup_CW&CCWslow.jpeg|800px]]

Laser Gyroscope

2025-04-11T03:14:07Z

Darren: /* Idea */

Some Description

==Team members==
Darren e0303300@u.nus.edu

Wen Xin e0309271@u.nus.edu

==Idea==
This project aims to measure some rotation by using the Sagnac effect, by using a loop of fiber as a ring interferometer.

'''Sagnac effect'''

When two beams of light are sent into the two ports of a ring interferometer, they travel clockwise (CW) and counter-clockwise (CCW) paths respectively. For a stationary ring interferometer, since the path length traversed by each beam is the same, this leads to complete constructive interference at the output port.

Now let's say the interferometer is spinning in the CW direction with rotation rate <math> \Omega </math>. Then there will be a difference in path length:

<math> \Delta L = R\Omega t_{CW} </math>

which results in a timing difference of:

<math> t_{CW} = \frac{2\pi nR + R\Omega t_{CW}}{c}, \quad t_{CCW} = \frac{2\pi nR - R\Omega t_{CCW}}{c} </math>

where ''n'' is the refractive index of the medium. Simplifying,

<math> t_{CW} = \frac{L_{0}}{c-R\Omega}, \quad t_{CCW} = \frac{L_{0}}{c+R\Omega}, \quad \Delta t = t_{CW} - t_{CCW} = \frac{L_{0} \cdot 2R\Omega}{c^{2}} \cdot \frac{1}{1+\left(\frac{R\Omega}{c}\right)^{2}} </math>

as <math> R\Omega << c </math>,

<math> \Delta t \approx \frac{2RL_{0}}{c^{2}} \cdot \Omega </math>

For a fiber loop with radius ''R'' and number of loops ''N'',

<math> \Delta t = \frac{4N\pi nR^{2}}{c^{2}} \cdot \Omega </math>

Thus, for light of frequency ''f'', we can calculate the Sagnac phase shift:

<math> \Delta\phi_{S} = 2\pi f \cdot \Delta t = \frac{8\pi nN A}{\lambda c} \cdot \Omega </math>

The change in the phase difference between the two paths changes the degree of constructive or destructive interference that happens, resulting in a change in the intensity detected. This is illustrated by the sketch of the graph below. As such, the change in the voltage across the detector corresponds to <math> \Omega </math>

[[File:intensity_shift.jpeg|400px]]

==Parts==
50m smf28 fiber spools

20km smf28 fiber spools

2x Thorlabs FGA01FC photodiodes

1550nm Fiber circulator

Fiber paddle

Laser driver

1550nm Laser diode

1550nm Fiber isolator

==1st Setup==
11 and 14 March
The main setup will be a fiber based Sagnac interferometer. The setup is as shown below:

[[File:FirstSetup_drawing.jpeg|400px]]
[[File:FirstSetup_picture.jpeg|400px]]

Parts used are:
1x laser driver
1x 1550nm DFB laser diode
1x fiber isolator to prevent backreflections to the laser diode
1x 50:50 fiber beam splitter at 1550nm
1x 50m smf28 fiber coil
1x FGA01FC photodiode
a lot of fiber to fiber connectors
1x 1m smf28 fiber for connecting beam splitter to the photodiode
2x apc to pc smf28 fiber

The fiber loop is placed on top of a rotating chair, and the interferometer output is sent to a photodiode which is connected to an oscilloscope.

During out 1st iteration, rotating the 50m fiber coil causes a change in the voltage output of the photodiode. However, the change in the voltage output remains even after the fiber coil is stationary, which should not happen since the voltage change we think we should observed should only come from movement and should not depend on the final orientation.

To further investigate, we removed the fiber loop and connected only the 2 ends of the fiber beam splitter together. In practice, rotating this setup should show a very small change or no change since the area enclosed by the fiber is much smaller as compared to the fiber coil. However, we still observe the same voltage change as before. Suspected that the voltage change we observe might be due to birefrigence in the fiber instead. Fiddling with the fiber, the voltage change was observed as well. So the voltage change is likely due to the polarization change when the fiber was moving instead. This would cause a change in the intensity of the interfereometer output.

Stray fibers were also taped down to prevent them moving and changing the polarization of the light but it does not seem to work.

Planned to investigate this further using a circulator and a seperate photodiode to conver the sagnac configuration into a mach-zender configuration and look at the output of both ports.

==2nd setup==
18 March

[[File:SecondSetup_drawing.jpeg|400px]]
[[File:SecondSetup_picture.jpeg|400px]]

We moved all the components to another breadboard. All fibers are taped down to the breadboard with only 2 fibers untaped. 1 from the 1550nm laser diode and the other leading to the photodiode. With this new setup, we seem to get the expected behaviour? A voltage change from the photodiode is only observed when the fiber coil is moving and returns to its original value when its stationary.

In order to verify the rotation rate of the fiber coil, we placed a phone with a gyroscope readout enabled (phyphox). We then turn the chair clockwise and counter-clockwise continuously, and plot the results below:

[[File:SecondSetup_CWCCW.jpeg|600px]]

The orange trace represents the output from the phone's gyroscope, while the blue trace and green trace represents the voltage readings from PD1 (connected to the 50:50 beam splitter) and PD2 (connected to the circulator) respectively. Clearly, we do observe correlation between when the chair is rotated, and when fluctuations in the PD voltage outputs are observed. We also see that the fluctuations from PD1 and PD2 are anti-correlated, which verifies the observation of interference.

However, there are clearly several issues from this measurement. First, we observe much greater noise, and much lower sensitivity from PD2's output. We suspect that the circulator might be the cause of this. Given that, we will mainly be looking at the PD1 voltage readings. Second, we expect the voltage signal to change one way when the chair is rotated CW, and to change the other way when the chair is rotated CCW. The plot of PD1 voltage above shows that when the rotation rate <math> \omega </math> is negative (CW), the voltage change is positive, whereas when <math> \omega </math> is negative (CCW), the voltage change does not have a fixed polarity. We suspect that this might be due to the operating point being close to a minima in the interference pattern, and the CCW rotation is sufficient to push the signal over the minima.

We also observe fluctuations at the peaks of the rotation rate when <math> \omega < 0 </math>, which does not agree with the relatively smooth rotations as indicated by the phone gyroscope readings.

==Third setup==

[[File:ThirdSetup_drawing.jpeg|400px]]
[[File:ThirdSetup_image.jpeg|400px]]

The results from the previous setup seems to indicate some improvements can still be made. The first improvement is to include a polarization paddle at one side of the fiber coil, which should allow us to tune the polarization of the light interfering at the 50:50 BS to some extent. We also noticed that the fiber from the laser source to the isolator was hanging, and lightly disturbing this fiber led to small but visible fluctuations in the PD readings. So we squeezed the laser source onto the chair (this seemed to be the cause of the fluctuations discussed at the end of the previous section).

[[File:ThirdSetup_CWCCW_Imid.jpeg|400px]]

blahblah

[[File:ThirdSetup_CWCCW_Imin&Imax.jpeg|800px]]

blahblah

[[File:ThirdSetup_CCW_smallrotation.jpeg|400px]]

== Fourth Setup ==

Since we have a 20km fiber loop lying around, we decided to replace the 50m fiber loop with the 20km fiber loop.

[[File:FourthSetup_image.jpeg|400px]]

[[File:FourthSetup_CW&CCWslow.jpeg|800px]]

File:Intensity shift.jpeg

2025-04-11T03:08:40Z

Darren:

Laser Gyroscope

2025-04-11T03:08:06Z

Darren: /* Idea */

Some Description

==Team members==
Darren e0303300@u.nus.edu

Wen Xin e0309271@u.nus.edu

==Idea==
This project aims to measure some rotation by using the Sagnac effect, by using a loop of fiber as a ring interferometer.

'''Sagnac effect'''

When two beams of light are sent into the two ports of a ring interferometer, they travel clockwise (CW) and counter-clockwise (CCW) paths respectively. For a stationary ring interferometer, since the path length traversed by each beam is the same, this leads to complete constructive interference at the output port.

Now let's say the interferometer is spinning in the CW direction with rotation rate <math> \Omega </math>. Then there will be a difference in path length:

<math> \Delta L = R\Omega t_{CW} </math>

which results in a timing difference of:

<math> t_{CW} = \frac{2\pi nR + R\Omega t_{CW}}{c}, \quad t_{CCW} = \frac{2\pi nR - R\Omega t_{CCW}}{c} </math>

where ''n'' is the refractive index of the medium. Simplifying,

<math> t_{CW} = \frac{L_{0}}{c-R\Omega}, \quad t_{CCW} = \frac{L_{0}}{c+R\Omega}, \quad \Delta t = t_{CW} - t_{CCW} = \frac{L_{0} \cdot 2R\Omega}{c^{2}} \cdot \frac{1}{1+\left(\frac{R\Omega}{c}\right)^{2}} </math>

as <math> R\Omega << c </math>,

<math> \Delta t \approx \frac{2RL_{0}}{c^{2}} \cdot \Omega </math>

For a fiber loop with radius ''R'' and number of loops ''N'',

<math> \Delta t = \frac{4N\pi nR^{2}}{c^{2}} \cdot \Omega </math>

Thus, for light of frequency ''f'', we can calculate the Sagnac phase shift:

<math> \Delta\phi_{S} = 2\pi f \cdot \Delta t = \frac{8\pi nN A}{\lambda c} \cdot \Omega </math>

[[File:intensity_shift.jpeg|400px]]

==Parts==
50m smf28 fiber spools

20km smf28 fiber spools

2x Thorlabs FGA01FC photodiodes

1550nm Fiber circulator

Fiber paddle

Laser driver

1550nm Laser diode

1550nm Fiber isolator

==1st Setup==
11 and 14 March
The main setup will be a fiber based Sagnac interferometer. The setup is as shown below:

[[File:FirstSetup_drawing.jpeg|400px]]
[[File:FirstSetup_picture.jpeg|400px]]

Parts used are:
1x laser driver
1x 1550nm DFB laser diode
1x fiber isolator to prevent backreflections to the laser diode
1x 50:50 fiber beam splitter at 1550nm
1x 50m smf28 fiber coil
1x FGA01FC photodiode
a lot of fiber to fiber connectors
1x 1m smf28 fiber for connecting beam splitter to the photodiode
2x apc to pc smf28 fiber

The fiber loop is placed on top of a rotating chair, and the interferometer output is sent to a photodiode which is connected to an oscilloscope.

During out 1st iteration, rotating the 50m fiber coil causes a change in the voltage output of the photodiode. However, the change in the voltage output remains even after the fiber coil is stationary, which should not happen since the voltage change we think we should observed should only come from movement and should not depend on the final orientation.

To further investigate, we removed the fiber loop and connected only the 2 ends of the fiber beam splitter together. In practice, rotating this setup should show a very small change or no change since the area enclosed by the fiber is much smaller as compared to the fiber coil. However, we still observe the same voltage change as before. Suspected that the voltage change we observe might be due to birefrigence in the fiber instead. Fiddling with the fiber, the voltage change was observed as well. So the voltage change is likely due to the polarization change when the fiber was moving instead. This would cause a change in the intensity of the interfereometer output.

Stray fibers were also taped down to prevent them moving and changing the polarization of the light but it does not seem to work.

Planned to investigate this further using a circulator and a seperate photodiode to conver the sagnac configuration into a mach-zender configuration and look at the output of both ports.

==2nd setup==
18 March

[[File:SecondSetup_drawing.jpeg|400px]]
[[File:SecondSetup_picture.jpeg|400px]]

We moved all the components to another breadboard. All fibers are taped down to the breadboard with only 2 fibers untaped. 1 from the 1550nm laser diode and the other leading to the photodiode. With this new setup, we seem to get the expected behaviour? A voltage change from the photodiode is only observed when the fiber coil is moving and returns to its original value when its stationary.

In order to verify the rotation rate of the fiber coil, we placed a phone with a gyroscope readout enabled (phyphox). We then turn the chair clockwise and counter-clockwise continuously, and plot the results below:

[[File:SecondSetup_CWCCW.jpeg|600px]]

The orange trace represents the output from the phone's gyroscope, while the blue trace and green trace represents the voltage readings from PD1 (connected to the 50:50 beam splitter) and PD2 (connected to the circulator) respectively. Clearly, we do observe correlation between when the chair is rotated, and when fluctuations in the PD voltage outputs are observed. We also see that the fluctuations from PD1 and PD2 are anti-correlated, which verifies the observation of interference.

However, there are clearly several issues from this measurement. First, we observe much greater noise, and much lower sensitivity from PD2's output. We suspect that the circulator might be the cause of this. Given that, we will mainly be looking at the PD1 voltage readings. Second, we expect the voltage signal to change one way when the chair is rotated CW, and to change the other way when the chair is rotated CCW. The plot of PD1 voltage above shows that when the rotation rate <math> \omega </math> is negative (CW), the voltage change is positive, whereas when <math> \omega </math> is negative (CCW), the voltage change does not have a fixed polarity. We suspect that this might be due to the operating point being close to a minima in the interference pattern, and the CCW rotation is sufficient to push the signal over the minima.

We also observe fluctuations at the peaks of the rotation rate when <math> \omega < 0 </math>, which does not agree with the relatively smooth rotations as indicated by the phone gyroscope readings.

==Third setup==

[[File:ThirdSetup_drawing.jpeg|400px]]
[[File:ThirdSetup_image.jpeg|400px]]

The results from the previous setup seems to indicate some improvements can still be made. The first improvement is to include a polarization paddle at one side of the fiber coil, which should allow us to tune the polarization of the light interfering at the 50:50 BS to some extent. We also noticed that the fiber from the laser source to the isolator was hanging, and lightly disturbing this fiber led to small but visible fluctuations in the PD readings. So we squeezed the laser source onto the chair (this seemed to be the cause of the fluctuations discussed at the end of the previous section).

[[File:ThirdSetup_CWCCW_Imid.jpeg|400px]]

blahblah

[[File:ThirdSetup_CWCCW_Imin&Imax.jpeg|800px]]

blahblah

[[File:ThirdSetup_CCW_smallrotation.jpeg|400px]]

== Fourth Setup ==

Since we have a 20km fiber loop lying around, we decided to replace the 50m fiber loop with the 20km fiber loop.

[[File:FourthSetup_image.jpeg|400px]]

[[File:FourthSetup_CW&CCWslow.jpeg|800px]]

Laser Gyroscope

2025-04-11T02:54:38Z

Darren: /* 2nd setup */

Some Description

==Team members==
Darren e0303300@u.nus.edu

Wen Xin e0309271@u.nus.edu

==Idea==
This project aims to measure some rotation by using the Sagnac effect, by using a loop of fiber as a ring interferometer.

'''Sagnac effect'''

When two beams of light are sent into the two ports of a ring interferometer, they travel clockwise (CW) and counter-clockwise (CCW) paths respectively. For a stationary ring interferometer, since the path length traversed by each beam is the same, this leads to complete constructive interference at the output port.

Now let's say the interferometer is spinning in the CW direction with rotation rate <math> \Omega </math>. Then there will be a difference in path length:

<math> \Delta L = R\Omega t_{CW} </math>

which results in a timing difference of:

<math> t_{CW} = \frac{2\pi nR + R\Omega t_{CW}}{c}, \quad t_{CCW} = \frac{2\pi nR - R\Omega t_{CCW}}{c} </math>

where ''n'' is the refractive index of the medium. Simplifying,

<math> t_{CW} = \frac{L_{0}}{c-R\Omega}, \quad t_{CCW} = \frac{L_{0}}{c+R\Omega}, \quad \Delta t = t_{CW} - t_{CCW} = \frac{L_{0} \cdot 2R\Omega}{c^{2}} \cdot \frac{1}{1+\left(\frac{R\Omega}{c}\right)^{2}} </math>

as <math> R\Omega << c </math>,

<math> \Delta t \approx \frac{2RL_{0}}{c^{2}} \cdot \Omega </math>

For a fiber loop with radius ''R'' and number of loops ''N'',

<math> \Delta t = \frac{4N\pi nR^{2}}{c^{2}} \cdot \Omega </math>

Thus, for light of frequency ''f'', we can calculate the Sagnac phase shift:

<math> \Delta\phi_{S} = 2\pi f \cdot \Delta t = \frac{8\pi nN A}{\lambda c} \cdot \Omega </math>

==Parts==
50m smf28 fiber spools

20km smf28 fiber spools

2x Thorlabs FGA01FC photodiodes

1550nm Fiber circulator

Fiber paddle

Laser driver

1550nm Laser diode

1550nm Fiber isolator

==1st Setup==
11 and 14 March
The main setup will be a fiber based Sagnac interferometer. The setup is as shown below:

[[File:FirstSetup_drawing.jpeg|400px]]
[[File:FirstSetup_picture.jpeg|400px]]

Parts used are:
1x laser driver
1x 1550nm DFB laser diode
1x fiber isolator to prevent backreflections to the laser diode
1x 50:50 fiber beam splitter at 1550nm
1x 50m smf28 fiber coil
1x FGA01FC photodiode
a lot of fiber to fiber connectors
1x 1m smf28 fiber for connecting beam splitter to the photodiode
2x apc to pc smf28 fiber

The fiber loop is placed on top of a rotating chair, and the interferometer output is sent to a photodiode which is connected to an oscilloscope.

During out 1st iteration, rotating the 50m fiber coil causes a change in the voltage output of the photodiode. However, the change in the voltage output remains even after the fiber coil is stationary, which should not happen since the voltage change we think we should observed should only come from movement and should not depend on the final orientation.

To further investigate, we removed the fiber loop and connected only the 2 ends of the fiber beam splitter together. In practice, rotating this setup should show a very small change or no change since the area enclosed by the fiber is much smaller as compared to the fiber coil. However, we still observe the same voltage change as before. Suspected that the voltage change we observe might be due to birefrigence in the fiber instead. Fiddling with the fiber, the voltage change was observed as well. So the voltage change is likely due to the polarization change when the fiber was moving instead. This would cause a change in the intensity of the interfereometer output.

Stray fibers were also taped down to prevent them moving and changing the polarization of the light but it does not seem to work.

Planned to investigate this further using a circulator and a seperate photodiode to conver the sagnac configuration into a mach-zender configuration and look at the output of both ports.

==2nd setup==
18 March

[[File:SecondSetup_drawing.jpeg|400px]]
[[File:SecondSetup_picture.jpeg|400px]]

We moved all the components to another breadboard. All fibers are taped down to the breadboard with only 2 fibers untaped. 1 from the 1550nm laser diode and the other leading to the photodiode. With this new setup, we seem to get the expected behaviour? A voltage change from the photodiode is only observed when the fiber coil is moving and returns to its original value when its stationary.

In order to verify the rotation rate of the fiber coil, we placed a phone with a gyroscope readout enabled (phyphox). We then turn the chair clockwise and counter-clockwise continuously, and plot the results below:

[[File:SecondSetup_CWCCW.jpeg|600px]]

The orange trace represents the output from the phone's gyroscope, while the blue trace and green trace represents the voltage readings from PD1 (connected to the 50:50 beam splitter) and PD2 (connected to the circulator) respectively. Clearly, we do observe correlation between when the chair is rotated, and when fluctuations in the PD voltage outputs are observed. We also see that the fluctuations from PD1 and PD2 are anti-correlated, which verifies the observation of interference.

However, there are clearly several issues from this measurement. First, we observe much greater noise, and much lower sensitivity from PD2's output. We suspect that the circulator might be the cause of this. Given that, we will mainly be looking at the PD1 voltage readings. Second, we expect the voltage signal to change one way when the chair is rotated CW, and to change the other way when the chair is rotated CCW. The plot of PD1 voltage above shows that when the rotation rate <math> \omega </math> is negative (CW), the voltage change is positive, whereas when <math> \omega </math> is negative (CCW), the voltage change does not have a fixed polarity. We suspect that this might be due to the operating point being close to a minima in the interference pattern, and the CCW rotation is sufficient to push the signal over the minima.

We also observe fluctuations at the peaks of the rotation rate when <math> \omega < 0 </math>, which does not agree with the relatively smooth rotations as indicated by the phone gyroscope readings.

==Third setup==

[[File:ThirdSetup_drawing.jpeg|400px]]
[[File:ThirdSetup_image.jpeg|400px]]

The results from the previous setup seems to indicate some improvements can still be made. The first improvement is to include a polarization paddle at one side of the fiber coil, which should allow us to tune the polarization of the light interfering at the 50:50 BS to some extent. We also noticed that the fiber from the laser source to the isolator was hanging, and lightly disturbing this fiber led to small but visible fluctuations in the PD readings. So we squeezed the laser source onto the chair (this seemed to be the cause of the fluctuations discussed at the end of the previous section).

[[File:ThirdSetup_CWCCW_Imid.jpeg|400px]]

blahblah

[[File:ThirdSetup_CWCCW_Imin&Imax.jpeg|800px]]

blahblah

[[File:ThirdSetup_CCW_smallrotation.jpeg|400px]]

== Fourth Setup ==

Since we have a 20km fiber loop lying around, we decided to replace the 50m fiber loop with the 20km fiber loop.

[[File:FourthSetup_image.jpeg|400px]]

[[File:FourthSetup_CW&CCWslow.jpeg|800px]]

File:SecondSetup drawing.jpeg

2025-04-11T02:52:05Z

Darren:

Laser Gyroscope

2025-04-11T02:51:48Z

Darren: /* 2nd setup */

Some Description

==Team members==
Darren e0303300@u.nus.edu

Wen Xin e0309271@u.nus.edu

==Idea==
This project aims to measure some rotation by using the Sagnac effect, by using a loop of fiber as a ring interferometer.

'''Sagnac effect'''

When two beams of light are sent into the two ports of a ring interferometer, they travel clockwise (CW) and counter-clockwise (CCW) paths respectively. For a stationary ring interferometer, since the path length traversed by each beam is the same, this leads to complete constructive interference at the output port.

Now let's say the interferometer is spinning in the CW direction with rotation rate <math> \Omega </math>. Then there will be a difference in path length:

<math> \Delta L = R\Omega t_{CW} </math>

which results in a timing difference of:

<math> t_{CW} = \frac{2\pi nR + R\Omega t_{CW}}{c}, \quad t_{CCW} = \frac{2\pi nR - R\Omega t_{CCW}}{c} </math>

where ''n'' is the refractive index of the medium. Simplifying,

<math> t_{CW} = \frac{L_{0}}{c-R\Omega}, \quad t_{CCW} = \frac{L_{0}}{c+R\Omega}, \quad \Delta t = t_{CW} - t_{CCW} = \frac{L_{0} \cdot 2R\Omega}{c^{2}} \cdot \frac{1}{1+\left(\frac{R\Omega}{c}\right)^{2}} </math>

as <math> R\Omega << c </math>,

<math> \Delta t \approx \frac{2RL_{0}}{c^{2}} \cdot \Omega </math>

For a fiber loop with radius ''R'' and number of loops ''N'',

<math> \Delta t = \frac{4N\pi nR^{2}}{c^{2}} \cdot \Omega </math>

Thus, for light of frequency ''f'', we can calculate the Sagnac phase shift:

<math> \Delta\phi_{S} = 2\pi f \cdot \Delta t = \frac{8\pi nN A}{\lambda c} \cdot \Omega </math>

==Parts==
50m smf28 fiber spools

20km smf28 fiber spools

2x Thorlabs FGA01FC photodiodes

1550nm Fiber circulator

Fiber paddle

Laser driver

1550nm Laser diode

1550nm Fiber isolator

==1st Setup==
11 and 14 March
The main setup will be a fiber based Sagnac interferometer. The setup is as shown below:

[[File:FirstSetup_drawing.jpeg|400px]]
[[File:FirstSetup_picture.jpeg|400px]]

Parts used are:
1x laser driver
1x 1550nm DFB laser diode
1x fiber isolator to prevent backreflections to the laser diode
1x 50:50 fiber beam splitter at 1550nm
1x 50m smf28 fiber coil
1x FGA01FC photodiode
a lot of fiber to fiber connectors
1x 1m smf28 fiber for connecting beam splitter to the photodiode
2x apc to pc smf28 fiber

The fiber loop is placed on top of a rotating chair, and the interferometer output is sent to a photodiode which is connected to an oscilloscope.

During out 1st iteration, rotating the 50m fiber coil causes a change in the voltage output of the photodiode. However, the change in the voltage output remains even after the fiber coil is stationary, which should not happen since the voltage change we think we should observed should only come from movement and should not depend on the final orientation.

To further investigate, we removed the fiber loop and connected only the 2 ends of the fiber beam splitter together. In practice, rotating this setup should show a very small change or no change since the area enclosed by the fiber is much smaller as compared to the fiber coil. However, we still observe the same voltage change as before. Suspected that the voltage change we observe might be due to birefrigence in the fiber instead. Fiddling with the fiber, the voltage change was observed as well. So the voltage change is likely due to the polarization change when the fiber was moving instead. This would cause a change in the intensity of the interfereometer output.

Stray fibers were also taped down to prevent them moving and changing the polarization of the light but it does not seem to work.

Planned to investigate this further using a circulator and a seperate photodiode to conver the sagnac configuration into a mach-zender configuration and look at the output of both ports.

==2nd setup==
18 March

[[File:SecondSetup_drawing.jpeg|400px]]
[[File:SecondSetup_picture.jpeg|400px]]

Instead of further investigation, moved all components onto an optical breadboard. All fibers are taped down to the breadboard with only 2 fibers untaped. 1 from the 1550nm laser diode and the other leading to the photodiode. With this new setup, we seem to get the expected behaviour? A voltage change from the photodiode is only observed when the fiber coil is moving and returns to its original value when its stationary.

In order to verify the rotation rate of the fiber coil, we placed a phone with a gyroscope readout enabled (phyphox). We then turn the chair clockwise and counter-clockwise continuously, and plot the results below:

[[File:SecondSetup_CWCCW.jpeg|600px]]

The orange trace represents the output from the phone's gyroscope, while the blue trace and green trace represents the voltage readings from PD1 and PD2 respectively. Clearly, we do observe correlation between when the chair is rotated, and when fluctuations in the PD voltage outputs are observed. We also see that the fluctuations from PD1 and PD2 are anti-correlated, which verifies the observation of interference.

However, there are clearly several issues from this measurement. First, we observe much greater noise, and much lower sensitivity from PD2's output. We suspect that the circulator might be the cause of this. Given that, we will mainly be looking at the PD1 voltage readings. Second, we expect the voltage signal to change one way when the chair is rotated CW, and to change the other way when the chair is rotated CCW. The plot of PD1 voltage above shows that when the rotation rate <math> \omega </math> is negative (CW), the voltage change is positive, whereas when <math> \omega </math> is negative (CCW), the voltage change does not have a fixed polarity. We suspect that this might be due to the operating point being close to a minima in the interference pattern, and the CCW rotation is sufficient to push the signal over the minima.

We also observe fluctuations at the peaks of the rotation rate when <math> \omega < 0 </math>, which does not agree with the relatively smooth rotations as indicated by the phone gyroscope readings.

==Third setup==

[[File:ThirdSetup_drawing.jpeg|400px]]
[[File:ThirdSetup_image.jpeg|400px]]

The results from the previous setup seems to indicate some improvements can still be made. The first improvement is to include a polarization paddle at one side of the fiber coil, which should allow us to tune the polarization of the light interfering at the 50:50 BS to some extent. We also noticed that the fiber from the laser source to the isolator was hanging, and lightly disturbing this fiber led to small but visible fluctuations in the PD readings. So we squeezed the laser source onto the chair (this seemed to be the cause of the fluctuations discussed at the end of the previous section).

[[File:ThirdSetup_CWCCW_Imid.jpeg|400px]]

blahblah

[[File:ThirdSetup_CWCCW_Imin&Imax.jpeg|800px]]

blahblah

[[File:ThirdSetup_CCW_smallrotation.jpeg|400px]]

== Fourth Setup ==

Since we have a 20km fiber loop lying around, we decided to replace the 50m fiber loop with the 20km fiber loop.

[[File:FourthSetup_image.jpeg|400px]]

[[File:FourthSetup_CW&CCWslow.jpeg|800px]]

2025-03-18T05:51:57Z

Darren: /* 1st Setup */

Laser Gyroscope (Darren and Wen Xin)

2025-01-28T07:41:30Z

Darren: /* Team members */

Some Description

==Team members==
Darren e0303300@u.nus.edu

Wen Xin e0309271@u.nus.edu

==Idea==
This project aims to measure some rotation by using the Sagnac effect.

==Setup==
The main setup will be a fiber based sagnac intereferometer with detection of the output done using photodiodes. We are aiming to build everything in the 1550nm wavelength range.

==Measurements==
....

Laser Gyroscope (Darren and Wen Xin)

2025-01-28T07:41:22Z

Darren: Created page with "Some Description ==Team members== Darren e0303300@u.nus.edu Wen Xin e0309271@u.nus.edu ==Idea== This project aims to measure some rotation by using the Sagnac effect. ==Setup== The main setup will be a fiber based sagnac intereferometer with detection of the output done using photodiodes. We are aiming to build everything in the 1550nm wavelength range. ==Measurements== ...."

Some Description

==Team members==
Darren e0303300@u.nus.edu
Wen Xin e0309271@u.nus.edu

==Idea==
This project aims to measure some rotation by using the Sagnac effect.

==Setup==
The main setup will be a fiber based sagnac intereferometer with detection of the output done using photodiodes. We are aiming to build everything in the 1550nm wavelength range.

==Measurements==
....

Main Page

2025-01-28T07:38:24Z

Darren: /* 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 (Darren and Wen Xin)]]===
Build a laser interferometer to detect rotation.

==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]