Optical characterization of a vertical cavity surface emitting laser for a coherent population trapping frequency reference

Abstract

Characterization of a vertical cavity surface emitting laser source for a frequency reference that uses coherent population trapping with atomic rubidium is reported. The frequency reference requires a low-noise laser that operates in a single transverse mode at 794.7 nm. We show that biasing the laser at low output power and modulating it at higher frequency than its low relaxation oscillation frequency are necessary to obtain symmetric modulation sidebands and improve the long-term performance of the frequency reference.

Experimental and Theoretical Investigations on the Modulation Capabilities of Vertical Cavity Surface Emitting Laser Diodes for Atomic Vapour Applications

“…The IM response is proportional to the modulation transfer function H(ω m ), which relates the output of a system to its input. This allows to write [7] P…”

“…(b) Phases θ IM and θ F M of the response functions and their difference. For the calculation, the values γ = 6.8 × 10 9 s −1 , γ P P = 3.4 × 10 9 s −1 and ω R /2π = 2.81 × 10 10 Hz were taken from [7].…”

“…The IM response to a sinusoidal modulation with modulation frequency ω m is described by the modulation transfer function [7]…”

“…6.834 GHz. This frequency modulation is achieved with a modulation of the laser bias current [6] which also produces a residual intensity modulation (IM) of the emitted laser light [7]. This IM influences the first order side band amplitudes and therefore the excitation of the CPT resonances used for CDSM's measurement principle.…”

Intensity nonlinearity of the error-signal frequency shift in the modulation spectroscopy of dark resonances and approaches to its reduction

“…Partial decay rates to the ground states levels are assumed to be the same and equal to γu/2 and γ d /2, respectively. der k. However, a typical VCSEL spectrum under injection current modulation differs from the spectrum of the phase-modulated field: while the frequency spacing between spectrum components k+1 and k is equal to Ω, the amplitudes of its spectral components can not be considered as given by the Bessel functions [43][44][45]. Moreover, the VCSEL spectra are asymmetric, i.e., powers of components |k| and −|k| are unequal in the vast majority of cases.…”