Metrological characterization of custom-designed 8946 nm VCSELs for miniature atomic clocks

Abstract

Abstract:We report on the characterization and validation of customdesigned 894.6 nm vertical-cavity surface-emitting lasers (VCSELs), for use in miniature Cs atomic clocks based on coherent population trapping (CPT). The laser relative intensity noise (RIN) is measured to be 1 × 10 −11 Hz −1 at 10 Hz Fourier frequency, for a laser power of 700 μW. The VCSEL frequency noise is 10 13 · f −1 Hz 2 /Hz in the 10 Hz < f < 10 5 Hz range, which is in good agreement with the VCSEL's measured fractional frequency instability (Allan deviation) of ≈ 1 × 10 −8 at 1 s, and also is consistent with the VCSEL's typical optical linewidth of 20-25 MHz. The VCSEL bias current can be directly modulated at 4.596 GHz with a microwave power of −6 to +6 dBm to generate optical sidebands for CPT excitation. With such a VCSEL, a 1.04 kHz linewidth CPT clock resonance signal is detected in a microfabricated Cs cell filled with Ne buffer gas. These results are compatible with state-of-the-art CPT-based miniature atomic clocks exhibiting a short-term frequency instability of 2-3×10 −11 at τ = 1 s and few 10 −12 at τ = 10 4 s integration time.

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

“…• For the determination of the m F a linear relation between the applied microwave power P mw and m F was assumed. This idea is based on the results presented in [20] which show a linear relation between m F and P mw . With this, a frequency modulation index can be associated for each measured modulation power.…”

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.…”

A high-overtone bulk acoustic wave resonator-oscillator-based 4.596 GHz frequency source: Application to a coherent population trapping Cs vapor cell atomic clock

“…Figure 8 presents the Cs CPT clock experimental setup. The laser source is a 25 MHz-linewidth customdesigned VCSEL tuned at 894.6 nm on the Cs D 1 line 28,29 . The laser injection current is directly modulated at 4.596 GHz by a local oscillator to generate two phase-coherent first-order optical sidebands frequency-split by 9.192 GHz for CPT interaction.…”