The Single Mode Fiber

Haijiang Gong
SUNY at Stony Brook
Optics Rotation Project in Laser Teaching Center for Fall 2001
Advisor: Dr. John No



Experiment Setup

Alignment Methods

Measurements and Results

Further Study




1. Introduction

The purpose of my project is to study the polarization effect of the single mode fiber.  It is really an interesting topic.

First of all, we should couple as many as possible laser into fiber. It is a really hard job full of skills and tricks.

Studying the frequency fluctuation in Helium-Neon lasers is important for experiments that depend on laser intensity. Through adjusting the polarizer, we can get the most stable polarization laser. Here we should adjust polarizer angle patiently and find the suitable angle at last.

After that, we can measure the polarization effect of  the fiber by adding another polarizer at the end of fiber. Through twisting or bending fiber, we can measure different polarization effect generated by fiber.

2. Experiment Setup

Apparatus List:

3. Alignment Methods

'Focusing a collimated beam into a single-mode fiber is like searching for a golfball on a football field while blindfolded. It can be a difficult and time consuming repetitious process.'

Laser Center at SUNY Stony Brook

1).Adjust four screws on mirrow 1 and 2 to collimate laser in the center of the PAF. Here I use a cross on a paper to make sure laser through PAF paralleled to the horizontal plane and no big dispersion.

2).Plug in multi-mode fiber step by step and adjust screws on every step to get the maximum output until fiber is completedly tightened with PAF.

3).Plug in single-mode fiber. Repeat 2) until get the maximum output.

At last, I can couple 20% of laser light into the fiber. (Laser:15.0mV; Laser after fiber:3.5mV--->23%) Anyway it is not good enought but enough for me to continue next step.

4. Measurements and Results

1). Some interesting phenomena on polarization(something involved in circular dichroism and birefringence)

2). Intensity fluctuation of a polarized Helium-Neon Laser

Relative fluctuation
Here we define I=(Imax-Imin)/(Imax+Imin)
The minimum(left) and maximum(right) intensity fluctuation
The intensity fluctuation during the first 50 minutes of warmup (The polarizer was set at about 70 degrees.)

3). Polarizaion change of a Helium-Neon Laser through a single-mode fiber

The polarized phase shift between tightened loop and loosened loop fiber
The polarized phase shift between straight and loop fiber
Straight Fiber Setup Loop Fiber Setup

5. Further Study

It is hard to keep the fiber fixed under the twist only by hand and tape. So I did not get the twist result in my project in quantity. After that, I hope I can do this using some specific equipments that are introduced by Dr. John Noe. So I can give precise quantity result by changing status of fiber accurately.

6. Conclusion

1). We can obtain a lot of interesting insights into the operation of He-Ne lasers with quite simple apparatus and straight-forward experiments. 

2). By bending the fiber, we measure the different polarized laser through the same single mode fiber. 

7. Acknowledgements

I am very appreciated for Dr. John Noe and for his instruction and generous help, both for the physics and the use of software and hardware. Many thanks to Jing Wang and Doug Broege for helping me set up the experiment system.

8. References

1. Fiber Optics Communication Systems By Govind P. Agrawal

2. Introduction to Fiber Optics  by Ajoy Ghatak and K. Thyagarajan.

3. Polarization Fluctuations in a Helium-Neon Laser by Stephane Lim at Laser Teaching Center