Measurement of Refractive Index Ranging from 1.42847 to 2.48272 at 1064 nm Using a Quasi-Common-Path Laser Feedback System

Wavelength 1064 nm is one of the most widely used laser wavelengths in industries and science. The high-precision measurement of the refractive index of optical materials at 1064 nm is significant for improving the optical design. We study the direct measurement of refractive index at 1064nm of lasers, including cMcium fluoride （CaF2）, fused silica and zinc selenide （ZnSe）, whose refractive indices cover a large range from 1.42847 to 2.48272. The measurement system is built based on the quasi-common-path Nd：YAG laser feedback interferometry. The thickness can be measured simultaneously with the refractive index. The results demonstrate that the system has absolute uncertainties of ~10-5 and ~10-4 mm in refractive index and thickness measurement, respectively.

Photonic-assisted approach for instantaneous microwave frequency measurement with tunable range by using Mach-Zehnder interferometers

A novel photonic-assisted approach to microwave frequency measurement is proposed and experimentally demonstrated. The proposed scheme is based on the frequency-to-power mapping with different transmis- sion responses. A polarizer is used in one output branch of a phase modulator to simultaneously implement phase modulation and intensity modulation. Owing to the complementary nature of the transmission re- sponses and the Mach-Zehnder interferometers （MZIs）, this scheme theoretically provides high resolution and tunable measurement range. The measurement errors in the experimental results can be kept within 0.2 GHz over a freauencv ranee from 0.1 to 5.3 GHz.

Ultra-high range resolution demonstration of a photonics-based microwave radar using a high-repetition-rate mode-locked fiber laser

We experimentally demonstrate the ultra-high range resolution of a photonics-based microwave radar using a high repetition rate actively mode-locked laser（AMLL）. The transmitted signal and sampling clock in the radar originate from the same AMLL to achieve a large instantaneous bandwidth. A Ka band linearly frequency modulated signal with a bandwidth up to 8 GHz is successfully generated and processed with the electro-optical upconversion and direct photonic sampling. The minor lobe suppression（MLS） algorithm is adopted to enhance the dynamic range at a cost of the range resolution. Two-target discrimination with the MLS algorithm proves the range resolution reaches 2.8 cm. The AMLL-based microwave-photonics radar shows promising applications in high-resolution imaging radars having the features of high-frequency band and large bandwidth.

Performance analysis of source ranging by use of virtual receiver technique under different frequency bands

The traditional matched field processing localization need complicated computation to get the replica field and has high dependence on environment parameters and acoustic field model. To overcome the shortcoming, virtual receiver technique is used for source ranging. A virtual receiver is constructed by correlating the two signals of the guide source and the objective source received by a vertical line array. Then, the slope of the interference striation of the virtual field is estimated using relevant signal processing method. Combining with the waveguide invariant/3, the range of the objective source is determined. Through the numerical simulations and data processing collected from the experiment carried out in the South China Sea in 2004, the virtual receiver technique for broadband source ranging under the slope- bottom shallow water environment is discussed. As the frequency increases, the frequency bands should be broadened to obtain complete interference striation for good ranging results. In data processing, the receiving array spacing is too large to promise the orthogonality of the modes as the frequency increases and ranging results become worse.