The main laser parameters are:
- Amplitude Noise (RIN). Dominates in direct detection scheme particularly in analog systems Frequency or Phase Noise;
- Frequency Stability;
- Output Power;
- Tuning Range (Frequency).
In frequency modulation (FM) formats phase or frequency, fluctuations compete with the signal. Reducing these fluctuations increases a signal to noise ratio. A laser signal may be used to interrogate path length changes in sensors such as a fiber Bragg grating (FBG) or Mach-Zehnder interferometer (MZI). If the frequency or phase of the laser changes it appears as a change of the path length thus degrading the signal to noise ratio.
There are different types of low phase noise lasers:
- Solid state ring laser. Usually a Nd: YAG DPSS laser, a very long ring cavity is created within the Nd: YAG stabilizing the phase.
- Fiber laser. The laser is created using pairs of FBG’s at the ends of a long fiber. The large optical path length is enabled by the fiber.
- External-cavity semiconductor laser. An FBG or VBG close to the laser chip provides optical feedback stabilizing the phase of the laser mode
- DFB with electronic feedback. A small amount of power is tapped from the output and passed through an FBG which acts as an FM to AM converter. The error signal is then used to change laser drive current to reduce FM fluctuations.
Laser phase noise is an intrinsic impairment which is linked with the presence of the spectral band of the emitted light. The measurement of the laser phase noise can reveal the spectral linewidth of the laser source and laser linewidth information is essential in many situations. If the estimated laser phase noise is multiplied with one of the channels which have equal but opposite phase noise, it can cancel laser phase noise.
Optromix Company provides world-class laser systems and it is our highest priority to deliver the best quality products. Our main specialization is manufacturing single frequency fiber lasers. If you would like to know more information about lasers, please contact us: email@example.com or +1 617 558 98 58.