Laser diode frequency stabilization bases on Iodine saturated absorption and sinusoidal phase modulation with suppression of residual amplitude modulation

Abstract

Recently in precision engineering, the laser diodes (LD) are widely used as light sources for displacement measuring interferometers and the others optical applications. The advantages of LDs compared traditional gas lasers are higher power, longer lifetime, and smaller size to be easily commercialized. However, typically low frequency stability of the LDs is a big drawback that limits their application. A conventional solution for this problem is locking the LDs frequency to some atomics-molecular transitions, such as Iodine molecular saturated absorption line for the wavelength near 633 nm. In this research, we use a sinusoidal phase modulation by an electro-optic modulator and a frequency modulation spectroscopy technique for LDs frequency stabilization. The LD frequency is stabilized to an Iodine absorption 1st harmonic using a null method. From calculations and simulations, the effects of residual amplitude modulation (RAM) and modulation index (m) to the Iodine frequency stabilized LD are investigated and discussed. Next, some experiments are performed to confirm the stability of the LD with different modulation indexes. Finally, we combine a RAM compensation technique to improve the frequency stability of the LD. Comparing with a commercial Iodine stabilized He-Ne laser, a frequency stability of the LD ~3.2×10-11 for 1000s was achieved.