Dichroic atomic vapour laser locking module using MEMS Rb atomic vapour cell

Laser frequency stabilization is a basic requirement of several types of laser instrumentation, optical communication, optical metrology, high precision spectroscopy and quantum sensing systems. Many of these systems are being developed in miniature forms for field deployable operations. Low power, narrow line width solid state lasers such as Vertical Cavity Surface Emitting Laser (VCSEL) and Distributed Bragg Reflector (DBR) are often used in such applications. The laser frequency has to be actively stabilized to an atomic transition to prevent thermal drift. In this paper, we present the development of a compact magneto optical (MO) package that uses the principle of Dichroic Atomic Vapour Laser Locking (DAVLL) technique to stabilize the frequency of a VCSEL laser to an \(^{85}\) $_{}^{85}$ Rb absorption resonance. The Rb vapour is held in a MEMS atomic vapour cell fabricated in the authors’ laboratory. The magneto optical package (50 mm x 30 mm x 20 mm) comprises of MEMS vapour cell, magnets, quarter wave plate, polarizing beam splitter and Si photodetector. Detector processing and servo feedback electronics are developed in house. Low cost fabrication techniques have been used to demonstrate the prototype housing. A DAVLL sensitivity of 0.36 mV/MHz has been demonstrated. The frequency of a VCSEL laser has been stabilized to⁸⁵Rb absorption resonance (F \(=2\rightarrow\) $=2\to$ \(\hbox {F}^{\prime }\) ${\text{F}}^{\prime }$ ) at 795 nm. Using the DAVLL scheme with the compact MO package and feedback electronics, the frequency drift of VCSEL was reduced from 500 MHz/hr to < 10 MHz/hr. Allan deviation study established that fractional frequency stability of the VCSEL was 10⁻⁹, corresponding drift of the center frequency of 350 kHz at 1 s averaging time.