Compact and inexpensive frequency stabilization technique for 850-nm vertical cavity surface emitting lasers based on Fabry-Perot resonator

We have demonstrated a compact and inexpensive frequency stabilization technique for commercially available 1mW, 850nm vertical cavity surface emitting laser (VCSEL) using a Fabry-Perrot cavity as frequency standard. Recently VCSEL has been widely prevailed for uses of low cost and small sized sensors, since it may afford low power operations and manufacturing costs in comparison with edge emitting type Fabry-Perrot laser diodes. Therefore, a highly versatile and inexpensive frequency stabilized coherent light source which can be mass producible will be available if the frequency stabilization for this type of VCSEL's is carried out. Generally, it has been commonly accepted that a satisfactory degree of coherence may be easily obtained from VCSEL's without any additional frequency stabilization technique since highly reflective coatings are to be put on their laser cavity edges. Nevertheless, some VCSEL devices, especially inexpensive type commercial products show multi-mode behaviors along with polarization instabilities. In the present work, as a simple and inexpensive approach to commercially available VCSEL devices, we have demonstrated a frequency stabilization scheme using a Fabry-Perrot cavity. The error signal was derived by phase sensitive detection for the transmitted light from the Fabry-Perrot resonator. Thus, the lasing frequency of the VCSEL was locked to the zero-crossing of the error signal by negative feedback for injection current via a PID controller. As a result, we have successfully suppressed the amount of frequency fluctuations in the free-running VCSEL of as much as 2GHz to be within 500MHz at measuring time of 30sec, that is, the attained Allan variance is 4.1×10E-8.