Frequency stabilization of an InGaAsP distributed feedback laser to an NH3 absorption line at 15137 Å with an external frequency modulator

Abstract

The oscillation frequency of a 1.5‐μm InGaAsP distributed feedback laser is stabilized to an NH₃ linear absorption line at 15137 Å. A LiNbO₃ external frequency modulator is used instead of direct frequency modulation of the laser to extract error signals. An effective bandwidth of 100 kHz for the feedback loop is obtained through this external modulation scheme. Frequency stability of σ(2,τ)=4×10⁻¹¹ is achieved for an averaging time of 1 s≤τ≤100 s.