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We propose a model to reduce the influence that the light-shift induced frequency drift has on the long-term stability of coherent population trapping (CPT)-based low-power atomic clocks. We experimentally validated the proposed model using the chip-scale atomic clock architecture. The model considers both the drift of the dc-bias current to compensate for the wavelength aging of the vertical-cavity surface-emitting laser (VCSEL) and the variation in the modulation index of the light field generated by the VCSEL. We investigated the dc-bias-current-dependency of the frequency drift in an atomic clock module both theoretically and experimentally, confirming that the frequency drift can change as a function of the VCSEL basic parameters. When the atomic clock module was operated over a period of five months at the dc-bias current affording a zero-crossing of the clock frequency drift, the Allan standard deviation and clock frequency drift for long-term stability were 8.0×10−12 for averaging times of 4×106 s and 2.4×10−13/day, respectively. Our approach is promising to improve the long-term stability of CPT-based low-power atomic clocks.

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We propose an image cross-connector using an organic photorefractive polymer. With this device, it is possible to perform a reconfigurable connection between multiple input-output image ports by setting the incident angle of individual control beams to minute levels. The use of a polymer can reduce the thickness of the index grating to be induced inside the medium, which can also reduce the distortion of the output image and bring about high precise image connection without an additional optical system. We conduct an experiment with a hole-transport polymer PATPD to verify the operations of an image cross-connector, in which different images from a vertical array of input images would be connected separately to two output ports by two control beams that were injected at different angles.

We realized a Cs gas cell for a chip-scale atomic clock fabricated from single-crystal sapphire chips, which have extremely-low gas penetration coefficients. The coherent population trapping (CPT) resonance spectrum was evaluated to validate the developed sapphire Cs gas cell. A CPT resonance with a contrast of 1.5%, a frequency shift (from the Cs hyperfine transition frequency) of 55.9 kHz, and a full width at half maximum of 2.2 kHz was obtained at an incident light intensity of 40 μW cm−2. The frequency shift was mainly caused by the collision between Ne sealed in the gas cell and Cs atoms. From the experimental results, the pressure of Ne was estimated to be 10.7 kPa.