Ultra-rapid dual-comb ranging with an extended non-ambiguity range.

In this Letter, we report a scheme that combines time-of-flight (ToF) ranging detection of multi-repetition-rate pulses with asymmetric dual-comb ranging (DCR) measurement. Notably, this combination extends the non-ambiguity range (NAR) of the DCR method without sacrificing its refresh rate and distance precision. With this scheme, we demonstrate absolute distance measurement of moving targets with an NAR of 1.5 km, which is 5× larger than that allowed solely by the DCR method for a given refresh rate at 500 kHz. The ranging precision in a single measurement of 2 µs reaches 10 µm at an effective distance of 571 m (down to 60 nm in 0.1 s). This combined scheme benefits remote sensing of high-speed objects.

[A New Method for Measurement of Laser-Induced Damage Threshold].

With the development of the laser towards high-power and high energy, laser-induced damage threshold of optics becomes one of the important parameters to evaluate the laser damage resistance of optics. Therefore, accurately measuring of the laser-induced damage threshold optics become the focal point studied. And the key to accurately measuring of the laser-induced damage threshold is whether the laser-induced damage can be accurately identified when it occurs. In order to solve low accuracy, long testing time, narrow scope of applications and complex operation of the common damage identification methods, a new testing method to diagnose the laser-induced damage of optics, called plasma diagnosis, is proposed in this paper. Based on this new method, the testing platform was set up, and the spectrum obtained by fiber spectrometer was analyzed under laser radiation by different laser energies. Take whether the spectral lines of the feature element contained in the measured optics occur as standard. The laser-induced damage threshold of K9 glass has been tested, and the test result was compared to that measured by the plasma flash method and the microscope method. The results show that, the plasma diagnosis method proposed in this paper has high-accurate judgment, high- testing speed, simple testing equipment, and easy to realization, which can greatly improve the testing efficiency of the laser-induced damage threshold of optics.

Tilted Nano-Grating Based Ultra-Compact Broadband Polarizing Beam Splitter for Silicon Photonics.

An ultra-compact broadband silicon polarizing beam splitter is proposed based on a tilted nano-grating structure. A light cross coupling can be realized for transverse-magnetic mode, while the transverse-electric light can almost completely output from the through port. The length of the coupling region is only 6.8 µm, while an extinction ratio of 23.76 dB can be realized at a wavelength of 1550 nm. As a proof of concept, the device was fabricated by a commercial silicon photonic foundry. It can realize a 19.84 dB extinction ratio and an 80 nm working bandwidth with an extinction ratio of larger than 10 dB. The presented device also shows a good fabrication tolerance to the structure deviations, which is favorable for its practical applications in silicon photonics.