Yupeng Liu

Numerical simulation on spectral compression of frequency-shifting femtosecond pulses in photonic crystal fiber

We present a numerical investigation of nonlinear propagation of femtosecond pulses in photonic crystal fibers (PCFs) by solving the generalized nonlinear Schrodinger equation. The PCFs have a second-order dispersion of -48 ps2/km, nonlinear coefficient of 115 W-1km-1, and third-order dispersion (TOD) ranging from 0.1 ps3/km to 1 ps3/km at 1550-nm wavelength. The simulation results show that efficient spectral compression of ultrashort pulses can be induced in the regime of soliton self-frequency shift (SSFS) in PCFs when the input pulse parameters satisfy the condition 0.9 ≤N ≤ 1.2 for the soliton order N. It is found that the output spectral width is dependent on the peak power of input pulse and the PCF length. A spectral-compression factor up to 2.2 can be achieved for 50-fs, 1550-nm solitons propagating through 10-m PCF with a TOD of 0.5 ps3/km, where the soliton wavelength shifted from 1550 nm to 1698 nm. The effect of initial pulse chirp on output spectral width can be negligible for large PCF length. Greater spectral-compression factor can be obtained using PCF with larger TOD value. This SSFS-based spectral-compression scheme offers much promise for generation of narrow line-width tunable light sources in photonic applications.

A Novel Microwave Tunable Band-Pass Filter Integrated Power Divider Based on Liquid Crystal

This paper proposes a novel microwave continuous adjustable band-pass filter integrated power divider based on nematic liquid crystals (LCs). The proposed power divider uses liquid crystal (LC) as the dielectric material. It can realize phase shift by changing the dielectric anisotropy, when biasing the high anisotropy nematic liquid crystal. It is mainly used in microwave frequencies. It has a large number of advantages compared to conventional filter integrated power divider, such as low loss, multifunction integration, continuous adjustable, miniaturization, low processing costs, low operating voltage, high phase shift, and convenient manufacture. Therefore, it has shown great potential for application.

Tunable microwave bandpass filter integrated power divider based on the high anisotropy electro-optic nematic liquid crystal

A novel, compact microwave tunable bandpass filter integrated power divider, based on the high anisotropy electro-optic nematic liquid crystal, is proposed in this letter. Liquid crystal, as the electro-optic material, is placed between top inverted microstrip line and the metal plate. The proposed structure can realize continuous tunable bandpass response and miniaturization. The proposed design concept is validated by the good performance of simulation results and experimental results. The electro-optic material has shown great potential for microwave application.

A U-band Wilkinson type UWB power divider in LTCC technology

This paper introduces a 1:2 ultra-wideband (UWB: 41-48 GHz) Wilkinson power divider. This power divider, with microstrip, is realized on low-temperature co-fire ceramic(LTCC) substrate which has the dielectric constant of 5.7. |S₁₁| better than 15 dB were simulated by HFSS. |S₂₁| and |S₃₁| less than 3.6 dB were also simulated |S₂₂| and |S₃₃| are better than 16dB. And |S₃₂| are better than 22 dB by HFSS simulation result. The size of the power divider is 3.705 × 5.77 × 0.203mm³.

Tunable substrate integrated waveguide bandpass filter using liquid crystal material

A microwave tunable substrate integrated waveguide bandpass filter using nematic liquid crystals is researched in this paper combined with the complementary split-ring resonators. The nematic liquid crystal is used to control the corresponding working frequency, with its permittivity changing caused by deflection angle of the liquid crystal molecules. And its deflection angle changing is controlled by the bias voltage. The simulation results show that the permittivity of liquid crystal changes from 2.79 to 3.56 to make the passband frequency achieve 490 MHz frequency offset.

An optimization model of the stripline-to-stripline vertical interconnect in LTCC technology

This paper presents a microwave stripline-to-stripline vertical interconnect in Low Temperature Co-fired Ceramic (LTCC) Technology. Two circular grooves are separately designed in the stripline lower ground plane and the stripline upper ground plane to reduce the insertion loss and improve the return loss. The mentioned structure has been simulated by HFSS. According to the simulation comparison results, the insertion loss can reduce 0.04 dB on average and the return loss can increase 17.5 dB on average over a band from 0.3 Ghz to 30 Ghz.

All-optical high-speed sampling based on nonlinear polarization rotation in a semiconductor optical amplifier

A novel all-optical high speed sampling method using nonlinear polarization rotation (NPR) in a semiconductor optical amplifier (SOA) is proposed in this paper. Using the carrier rate equation in a SOA for the propagation of an optical pulse, a model is proposed to describe the relationship between the polarization rotating angles of probe light and the pump light power. Meantime, affection introduced by the initial polarization of the probe light, as well as the injected current of the SOA is studied. The numerical results indicated that the initial polarization of the probe light affects the transfer curve between the output light power of probe light and the pump light power, and the injected current of SOA could affect the linearly dynamic range and the rise slope of the transfer curve. In order to obtain suitable slope and larger linear dynamic range, the parameters are optimized. The primarily simulated results indicated that the pump light power is not more than 1mW. It is also shown that the all-optical sampling mentioned in this paper has promoting potential to improve the sampling rate at hundreds GS/s and needs considerable lower optical power than others.