All-photonic clock: Laser-atomic oscillator

Laser-atomic oscillator is a newly developed method for simultaneously generating stable optical and electrical modulations with only a few components. It requires a semiconductor laser, a vapor cell, and maybe a few optical components. No photodetector and electronic feedback are needed. In this new system, the ground-state hyperfine coherence of alkali-metal atoms is spontaneously generated. The modulated laser light with a spectrum of a small optical comb is automatically produced, and the spacing between the comb teeth is photonically locked to the hyperfine frequency. The charge carriers in the semiconductor laser are also modulated at the hyperfine frequency. A well-designed laser-atomic oscillator can be thought as an ldquoall-photonic clock,rdquo a new kind of active atomic clock. The system is like an active maser in photonic version. It does not need a local oscillator and the assistance of microwave circuitry, and it consumes less power for the operation compared to passive, vapor-cell atomic clocks. Besides, laser-atomic oscillator can be very compact due to its simple structure. Recently, small or miniature atomic clocks have been considered to have many applications, and passive atomic clock is the main approach of making miniature atomic clocks. Complexity and the power consumption are still the major challenges. We believe that the technique of laser-atomic oscillator can bring some advantages in manufacturing small atomic clocks.