Self-stabilization quantum key distribution (QKD) systems are often based on the Faraday magneto-optic effect such as “plug and play” QKD systems and Faraday–Michelson QKD systems. In this article, we propose a new anti-quantum-channel disturbance decoder for QKD without magneto-optic devices, which can be a benefit for the photonic integration and applications in magnetic environments. The decoder is based on a quarter-wave plate reflector–Michelson (Q–M) interferometer, with which the QKD system can be free of polarization disturbance caused by quantum channel and optical devices in the system. The theoretical analysis indicates that the Q–M interferometer is immune to polarization-induced signal fading, where the operator of the Q–M interferometer corresponding to Pauli Matrix σ2 makes it satisfy the anti-disturbance condition naturally. A Q–M interferometer based time-bin phase encoding QKD setup is demonstrated, and the experimental results show that the QKD setup works stably with a low quantum bit error rate about 1.3% for 10 h over 60.6 km standard telecommunication optical fiber.

In this paper, a kind of coupled opto-electronic oscillators (COEOs), constructed with a traditional opto-electronic(OEO) ring and a mode-lock laser ring, was presented. The COEO could output optical pulses as well as spectrally pure microwave signals simultaneously. The repetition of the optical pulse train and the frequency of output RF signal could be controlled and locked by a microwave filter and a phase-locked loop (PLL). As a result, we obtained optical pulses as short as ps and a microwave signal as high as 20GHz. By cooperated with a 100MHz high-stable crystal oscillator, the COEO was applied in a 2-bit frequency agile microwave generating system. The output frequency could be controlled by TTL signals rapidly or configured by software commands as well. The frequency switching time was measured to be 23ns by using a bit error rate tester(BERT). These experiments demonstrates that COEOs are promising sources for frequency agile radar systems.

采用ANSYS建立电磁炉有限元模型，对电磁炉工作时的磁场和涡流分布进行了仿真。结果显示，磁芯对线圈产生的磁场具有明显的束缚作用，随着磁芯相对磁导率的减小，其对磁场的束缚作用明显减小，而且相同区域的磁通量密度也逐渐减小；电磁炉的涡流分布呈圆环形，且分布在锅的底部，仿真结果与实际情况吻合。

Vanadium dioxide (VO₂) film will be phase-transitioned from insulator into metal, accompanied with dramatic change on conductivity, which is named as photo-induced insulator-metal phase transition. Such phase transition of VO₂ film has important application potentials in modulators or other functional devices for terahertz waves. In this paper, the transmission spectrum variations before and after the photo-induced insulator-metal phase transition of vanadium dioxide film are investigated, and the phase transition properties in terahertz(THz) region are analyzed. In the experiment, the phase transition of the VO₂ film was induced by a continuous wave (CW) laser source and a femtosecond (fs) laser source, respectively. Obvious changes on the THz waveforms were observed for the both mentioned means of excitation, and the amplitude attenuation, as well as the signal distortion, was intensified with the increase of the impinging optical power. The fast Fourier transform (FFT) spectra of the transmitted THz time-domain signals were analyzed and it was found that the amplitude of the transmitted spectrum decreased synchronously with the increase of the optical power, accompanied with deformation of the spectrum line shape at the same time. The reason was that the macroscopic dielectric properties of the VO₂ film approached gradually to that of a metal as laser power was increased. A parameter, transmission modulation function, was defined in the paper as the amplitude difference between the transmission spectra of the VO₂ film before and after the laser excitation, to describe the dispersivity of the photo-induced phase transition more clearly. From the curve of the transmission modulation function, strong frequency-dependent properties at THz frequencies were found to vary regularly with the incident light power. After furthermore comparison, it was found that, though the insulator-metal phase transition could be trigged by both CW laser source and fs laser source, the corresponding impinging optical power values were obviously alternative for the equivalent transmission modulation function. At the end of the paper, the difference of the phase transition efficiency between the two excitation methods was analyzed and discussed.

为实现超宽带的微波/毫米波测试,基于飞秒激光技术设计并搭建了一套光学谐波混频系统.该系统采用飞秒激光脉冲序列作为光载波,利用飞秒脉冲包络信号的高次谐波与被测信号进行混频,将被测信号下变频至直流进行进一步测量.由于飞秒脉冲序列特有的宽带谐波成分,该系统能够实现100 GHz以上测试带宽.利用该系统分别测试了6.56 GHz与100 GHz的天线口面场的电场幅度分布,并与微波仿真结构进行了比较,实验与仿真结果吻合,验证了该设计的正确性.设计中采用的谐波混频器为基于泡克耳斯效应的铌酸锂电光晶体.

The aperture-field mapping is very important to diagnosing the amplitude and phase distribution of the antenna under test(AUT). Since such measurements need to be done without influence to the actual field distribution near the aperture, traditional metallic near-field probes, such as horn antennas, waveguide slots, et al, are irrespective. Miniature electrooptic E-field sensors offer good possibility for such near-field or very near-field measurements, because of its small size and little perturbation to the AUT. Moreover these devices have high resolution and reduced dimensions. In this paper, we have present a simple photonic microwave probe to measure the electric field vector distribution at a distance shorter than one wavelength from the aperture plane of a antenna. The photonic E-field probe is a type of pigtailed electro-optic sensor and consists of an electro-optic crystal supported by a quartz sleeve. The probe is all-dielectric, without any metallic materials. Those physical and electrical features make the photonic sensor attractive when used as a probe for near-field antenna measurements. A patch antenna with a resonant frequency at 6.5GHz was designed and fabricated. Both amplitude and phase distribution of the two tangential E-field components are mapped by using the present photonic probe. Simulation was carried out as well, and compared with the experimental measurements. The result shows great correspondence for amplitude distribution between simulations and experiments, as well as for the phase distribution except for some random tiny fluctuations. The methods to improve the stability of measurement system are briefly discussed.

We investigate the optical response of silicon-based VxOy film for terahertz (THz) transmission. We find that absorption of the THz wave by the film can be controlled by laser excitation. Using THz time-domain spectroscopy (THz-TDS), we observe that the amplitude of the THz pulse is modulated by the external optical beam. The linearity of the optical modulation is also analyzed. Weak modulation nonlinearity is found to be within tolerable range.

We present a review of the development of a compact and high-power broadband terahertz (THz) source optically excited by a femtosecond photonic crystal fiber (PCF) amplifier.The large mode area of the PCF and the stretcher-free configuration make the pump source compact and very efficient.Broadband THz pulses of 150 μW extending from 0.1 to 3.5 THz are generated from a 3-mm-thick GaP crystal through optical rectification of 12-W pump pulses with duration of 66 fs and a repetition rate of 52 MHz.A strong saturation effect is observed,which is attributed to pump pulse absorption;a Z-scan measurement shows that three-photon absorption dominates the nonlinear absorption when the crystal is pumped by femtosecond pulses at 1 040 nm.A further scale-up of the THz source power is expected to find important applications in THz nonlinear optics and nonlinear THz spectroscopy.

A modified Z-scan experimental setup based on a Yb-doped photonic crystal fiber amplifier was used to achieve polarization-resolved measurement of the nonlinear properties of bulk intrinsic GaP. The experiment results reveal that three-photon absorption dominated the nonlinear absorption processe at room temperature. The anisotropy and crystal Orientation dependence of the nonlinear absorption and nonlinear refractive index was experimentally studied and the nonlinearities showed saturation at high pump intensities.

Along with the booming development of multi-component blending fabrics, the accurate detection of component of fabrics has become a major goal in textile testing. Terahertz sensing technology provides a new way for detecting the materials. THz time-domain spectroscopy (THz-TDS) is a novel spectroscopic technique which measures the electric field of the radiation through a sample and provides the phase and amplitude changes of the radiation, which can provide information unavailable through conventional methods such as microwave and X-ray techniques. In this investigation, THz-TDS technology was introduced into the textile differentiation. Three kinds of cellulose textile fibers, cotton fiber, bamboo fiber and viscose fiber, were prepared as the sample and detected by THz-TDS at room temperature in the absence of vapor. The temporal and frequency signals of the fibers were obtained. In the THz absorption spectrum, the characteristic absorption peaks of textile fibers in THz wave band were found, which can be used to recognize the fibers. This approach provides a novel non-contact examine method for fiber identification in complicated textiles.

Nonlinear processes associated with terahertz radiation generated via optical rectification from undoped GaP crystal, including second harmonic generation (SHG) and multiphoton absorption processes, are examined. Experimental results of polarization-resolved SHG are obtained.

We present the generation of a terahertz pulse train from a rectangular GaP waveguide emitter pumped by a compact photonic crystal fiber femtosecond amplifier. The effects of the pump pulse width and chirp characteristics on the terahertz conversion efficiency and the generated THz spectrum were studied. The peak spectrum could be easily tuned by altering the separation of the compression grating pair.

We report the coupling between surface plasmons and dipole-localized surface plasmons in a composite hole-patch structure at terahertz frequencies. The coupling is found to be changed by increasing the inner patch size, which causes prominent resonance frequency shift in the enhanced transmission. The experimental results show good agreement with numerical simulation. The study clarifies well the nature of coupling between surface plasmons and dipole-localized surface plasmons and is thus of help to identify the role of surface plasmons in the enhanced transmission observed in subwavelength metallic structures.

The photo-induced insulator-metal transition for silicon-based VO2 nanofilm is studied by THz time-domain spectroscopy (THz-TDS). Obvious variations of THz ray transmittance are observed before and after the CW laser beam exciting, and the conductivity of metallic-phased VO2 film in the THz region is calculated in the thin film approximation. According to the measured results, the metallic-phased VO2 film is characterized equivalently with Drude’s model, and complex conductivity, dielectric function and refractive index are acquired by the model. As an examination on the equivalent Drude model, numerical simulation based on the finite integral method in time domain is carried out. The results show that they are in good agreement with the experimental results. This work provides a reference for the study on phase transition of VO2 nanofilm and its application in the THz region.

A modified Z-scan method was used to achieve polarization-resolved measurement of nonlinear properties of undoped bulk GaP excited by a femtosecond laser at 1040 nm. The optical Kerr nonlinearities of ⟨100⟩-, ⟨110⟩- and ⟨111⟩-cut GaP slabs were characterized experimentally at room temperature. The open aperture Z-scan curves demonstrate that three-photon absorption in GaP dominates the nonlinear absorption processes under the experimental conditions. In addition, experimental results show that both three-photon absorption and Kerr nonlinearity of undoped GaP possess the same anisotropy and crystal orientation dependence.

We demonstrate a scalable, compact, high-power, and broadband terahertz (THz) source based on a cutting-edge large-mode-area photonic-crystal-fiber amplifier system. A 3-mm < 110 >-cut bulk GaP crystal was used as the THz emitter based on an optical rectification technique. Systematic optimization of the operation parameters allowed a THz output up to 150 mu W to be achieved with an input laser power of 12 W in the GaP crystal.

Using terahertz time-domain spectroscopy (THz-TDS), we have investigated the THz spectra of astaxanthin and riboflavin and the spectra of two kinds of cell, haenatcoccus plusivalis and bacillus subtilis, which could produce astaxanthin and riboflavin, respectively, during their metabolite process. Riboflavin was found to be much more absorptive to THz radiation and have richer spectral characteristics than astaxanthin. As an intracellular metabolite, riboflavin could be distinguished from the cells by using THz-TDS. The technique has potential applications in high-throughput screening of industrial strains.