We demonstrate an ultrastable miniaturized transportable laser system at 1550 nm by locking it to an optical fiber delay line (FDL). To achieve optimized long-term frequency stability, the FDL was placed into a vacuum chamber with a five-layer thermal shield, and a delicate two-stage active temperature stabilization, an optical power stabilization, and an RF power stabilization were applied in the system. A fractional frequency stability of better than 3.2×10-15 at 1 s averaging time and 1.1×10-14 at 1000 s averaging time was achieved, which is the best long-term frequency stability of an all-fiber-based ultrastable laser observed to date.

We demonstrate an all-fiber-based photonic microwave generation with 10-15 frequency instability. The system consists of an ultra-stable laser by optical fiber delay line, an all-fiber-based “figure-of-nine” optical frequency comb, a high signal-to-noise ratio photonic detection unit, and a microwave frequency synthesizer. The whole optical links are made from optical fiber and optical fiber components, which renders the whole system compactness, reliability, and robustness with respect to environmental influences. Frequency instabilities of 3.5×10-15 at 100 s for 6.834 GHz signal and 4.3×10-15 at 100 s for 9.192 GHz signal were achieved.

A high-performance transportable fountain clock is attractive for use in laboratories with high-precision time-frequency measurement requirements. This Letter reports the improvement of the stability of a transportable rubidium-87 fountain clock because of an optimization of temperature characteristics. This clock integrates its physical packaging, optical benches, microwave frequency synthesizers, and electronic controls onto an easily movable wheeled plate. Two optical benches with a high-vibration resistance are realized in this work. No additional adjustment is required after moving them several times. The Allan deviation of the fountain clock frequency was measured by comparing it with that of the hydrogen maser. The fountain clock got a short-term stability of 2.3×10 13 at 1 s and long-term stability on the order of 10 ¹⁶ at 100,000 s.

Excess frequency noise induced by mechanical vibration is the dominant noise source at low Fourier frequencies in fiber-delay-line stabilized lasers. To resolve this problem, a double-winding fiber spool is designed and implemented that has ultralow acceleration sensitivity in all spatial directions. By carefully choosing the optimal geometry parameters of the fiber spool, we achieve acceleration sensitivity of 8 × 10 ¹¹/g and 3 × 10 ¹¹/g (g denotes the gravitational acceleration) in axial and radial directions, respectively.

We demonstrate the frequency stabilization of a 1.55 μm erbium-doped fiber laser by locking it to a 5-km-long optical fiber delay line (FDL). The stabilized laser is characterized via comparison with a second identical laser system. We obtain a fractional frequency stability of better than 3 × 10 ¹⁵ over time scales of 1–10 s and a laser linewidth of 0.2 Hz, which is the narrowest linewidth of an FDL-stabilized laser observed to date.

In this Letter, we describe an optical assembly that is designed for the engineering application of the atomic laser cooling techniques. Using a folded optical path scheme, we have built a miniaturized, compact magneto-optical trap (CMOT) for an Rb87 atomic fountain clock. Compared with the conventional magneto-optical traps used in other clocks, our system is more robust, more compact, more stable, and saves about 60% laser power. This optical setup has operated for about a year in our fountain system, passed the thermal cycle tests and the mechanical vibration and shock tests, and maintained a high performance without a need for realignment.