Yuxiao Xu

Influence of film thickness and nanograting period on color-filter behaviors of plasmonic metal Ag films

The effects of film thickness and nanograting period on color filter behaviors of the device, fabricated by sub-micrometers patterning on plasmonic silver thin films, have been studied. It is found that color filter properties strongly correlate with film thickness and nanograting period. Based on obtained results, the relationship of the wavelength of transmission minima with film thickness and nanograting period was derived. This equation can predict the transmission minima for a given thickness and period in one-dimensional Ag metallic film nanograting on glass substrate, which could guide to design color filter device with desirable wavelength.

Time-Frequency Uncertainty in the Photonic A/D Converters Based on Spectral Encoding

In recent years, some approaches to realize photonic analog-to-digital conversion based on spectral encoding have been proposed. In these approaches, the amplitude information of input analog signals is first converted into the frequency information of the optical carrier via a nonlinear process, which is equivalent to optical frequency modulation; then, the spectral information of the optical carrier is quantized and encoded with the help of an optical filter group. In this letter, we propose, for the first time to our knowledge, that the time-frequency uncertainty principle puts a fundamental limit on this type of photonic analog-to-digital converters (ADCs). The condition for achieving acceptable performance in terms of effective number of bits is discussed. The presented theoretical results are verified by numerical simulations and a proof-of-concept experiment in electrical domain. We believe that the presented result is important to the design of spectral-encoding-based photonic ADCs.

Photonic Generation of Dual-Chirp Waveforms With Improved Time-Bandwidth Product

We present a photonic method for the generation of dual-chirp signals. In this approach, a single-tone RF signal is first modulated using a modulator in order to generate two optical carriers, which are further modulated by a linearly chirped signal by another modulator. Square-law detection in a photodiode then generates a dual-chirp signal whose center frequency and time-bandwidth product (TBWP) are fourfold increased. The dual-chirping and the improved TBWP can improve the range resolution of the radar system and help avoid the range measurement error caused by the range-Doppler coupling effect. The generation of bandwidth-quadrupled S-band dual-chirp waveforms is demonstrated experimentally. The processing of the dual-chirp signal is also discussed, in order to show its advantages over single-chirp signals. We believe that the proposed approach is a potential solution for the generation of dual-chirp signals with high center frequency and large bandwidth in modern radar systems.

Spurious-Free Dynamic Range of the Photonic Time-Stretch System

Analog-to-digital conversion based on photonic time-stretch (PTS) has been widely studied. The performance of PTS systems is limited by the inherent nonlinearity of external modulators. In this letter, for the first time, to the best of our knowledge, we analytically characterize the spurious-free dynamic range (SFDR) by obtaining the exact expressions for the power distribution of the third-order intermodulation products in the PTS system with either a single-arm Mach–Zehnder modulator (MZM) or a push–pull MZM. The relation between the SFDR and the time-stretch factor and several effective ways to improve the SFDR of the PTS system are also investigated. Both simulation and experimental results are given to verify the theoretical model. The presented results can largely simplify the design of PTS systems with desired performance.

Nonlinearity analysis of photonic time stretch system

In this paper, we analyze the nonlinearity in the photonic time stretch (PTS) system and present exact expressions for the intermodulation products and harmonics at the system output. Based on the nonlinearity analysis of the PTS system, the spurious-free dynamic range of the PTS system is also investigated.

System of Thermal Micro/Nano Printing and its Application in Metallic Glass

A micro/nano thermal printing system was developed in this paper. The system has the characteristics of high resolution, large imprinting areas, convenient operation and low cost. Some experiments on metallic glass (La-Co-Al) were carried out by the system. The results indicated that this system has the elegant performance and the metallic glass is one of the best materials to fabricate the microstructures.

Time-bandwidth product of photonically generated wideband microwave signals based on frequency-to-time mapping

In this paper, we focus on the maximum achievable time-bandwidth product of the photonically generated wideband microwave signals, which include the chirped and phase-coded signals and are generated based on spectrum shaping and frequency-to-time mapping.