Metrological characterization of custom-designed 894.6 nm VCSELs for miniature atomic clocks

We report on the characterization and validation of custom-designed 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 x 10(-11) Hz(-1) at 10 Hz Fourier frequency, for a laser power of 700 mu W. 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 approximate to 1 x 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 x 10(-11) at tau = 1 s and few 10(-12) at tau = 10(4) s integration time. (c) 2013 Optical Society of America