相位光时域反射仪中信号采样率的双频光倍增

在相位光时域反射仪中引入等时分双频光,提高扰动信号采样率,降低相邻相位的绝对差值,从而使得相位解缠绕正确实现,进而精确重构相位信号。然而,引入双频光使得初相位的不一致变得更加复杂,以致相位信号无法精确重构,即扰动信号的采样率难以真正得到提升。为此,在等时分双频光相位光时域反射仪中,基于模值最小值的乘积来快速确定参考位置并补偿脉冲序列方向初相位的不一致,对光纤长度方向初相位的不一致进行二次静态补偿。在实验中,当外界扰动为700 Hz的Burst信号时,使用单频探测脉冲光已无法进行正确解缠绕,而使用双重静态补偿方案的等时分双频光相位光时域反射仪却能够精确求解出Burst信号,且正弦部分的均方根误差仅为0.3872 rad,即在相位光时域反射仪中实现了信号采样率的双频光倍增和相位信号的精确重构。

Optical Rectification Induced by Al-Si Schottky Barrier Potential and Mechanism of Two-Photon Response

By observing two-photon response and anisotropy of the light-induced voltage in Al-Si Schottky barrier potential,it is certified from the experimental and theoretical analysis that the built-in electric field generated by the Schottky barrier potential will induce the phenomena of optical rectification in Si photodiode.Thus,it is deduced that there must be double-frequency absorption caused by phase-mismatch in the mechanism of two-photon response of Si photodiode.If the intensity of the built-in electric field is strong enough,the double-frequency absorption will be the main factor of the two-photon response,which is different from the conventional opinion that the two-photon response is just the two-photon absorption.

Roll-to-roll imprint for high precision grating manufacturing

In this paper,a novel roll-to-roll imprint process is proposed to fabricate gratings in large area. The key challenges in roll-to-roll imprint process,such as the roller mold preparation,imprint system,misalignment of imprint roller and backup roller,and also the imprint pressure,are investigated. Various gratings with different periods and profiles are obtained by the roll-to-roll process. To calibrate the measuring ability of the self-made grating by imprint,a calibration system is built with a dual-frequency laser interferometer. By the calibration,the self-made gratings can achieve ±4μm accuracy in 45mm measuring distance.

Temperature Dependence of Thermal Emission Rate in Cr: GaAs

The new method of measuring the ratio of thermal emission rate to the photoexcitation constant is presented. The temperature dependence of the ratio for Cr:GaAs is calculated by using the previously published data of two-wave mixing. Results show that the calculating data and previous phenomenological theoretic ones coincide with each other very well.

Intensity Dependence of Stationary Energy Transfer in Codirectional Photorefractive Two－wave Mixing

The intensity and phase formulas that are valid for the saturation and intermediate regime (before saturation) are derived, and the analytical expressions with the ratio of saturation intensity to total incident intensity as their explicit variable are obtained. The intensity dependence of stationary energy transfer in photorefractive codirectional two-wave mixing is examined. It is necessary to using these formulas in some problems, such as the temperature or intensity dependence of two-wave mixing. A method of measuring exponential gain coefficient is presented, which is suitable for two-wave mixing in intermediate regime.

Influence of a Single Frequency Electromagnetic Wave on Energy Spectrum of Nonpolariton System in a Kerr Nonlinear Blackbody

In a Kerr nonlinear blackbody, bare photons with opposite wave vectors and helieities are bound into pairs and unpaired photons are transformed into a different kind of quasiparticle, the nonpolariton. The present paper investigates the influence of a single frequency electromagnetic wave on the energy spectrum of the nonpolariton system. We find that the wave can lead to an energy shift of nonpolaritons. Moreover, we calculate the first-order energy shift on certain conditions.

Diode-pumped Q-switched Extra-cavity Frequency-dou bled Nd∶YVO_4/KTP Green Laser

A diode-pumped acousto-op ti cal(A-O) Q-switched extra-cavity frequency-doubled Nd∶YVO_ 4/ KTP (KTiO PO_ 4) green laser formed with a simple plane-plane cavity has been demonst rated. With the incident pump power of 12.7 W, A-O Q-switched average output power at 1 064 nm was 3.81 W with a duration of 25 ns at a repetition rate of 20 kHz, extra-cavity frequency doubling with KTP as the nonlinear crystal y ielded the maximum output power of 1.92 W at 532 nm, the corresponding optical conversion efficiency from 1 064 nm to 532 nm light is 50.4%. The continuous -wave(CW) laser properties of diode-pumped Nd∶YVO_ 4 crystal operating at 1 064 nm have been studied. With the incident pump power of 25 W, the maximu m CW output power of 13.81 W was obtained with the corresponding optical conver sion efficiency of 55.24%.

The Growth of KLN Crystals

The growth temperature curve of the growth system for the potassium lithium niobate (KLN) has been measured and the temperature decrease program has been calculated. KLN crystals with a size up to 30mm 15mm 5 mm have been grown by flux method. The primary factors of the cracking of KLN crystal have been discussed. A blue laser light output has been obtained by optical parametric oscillator pumping.\=

基于双驱动马赫-曾德尔调制器的激光测距研究

提出了一种基于双驱动马赫-曾德尔调制器(DD-MZM)的激光测距技术。通过对DD-MZM的单路进行调制可产生测距用的类双频光源,DD-MZM中两路光的时间延迟差很小,可有效抑制两路光拍频信号的强度噪声。为了进一步抑制由温度变化造成的两路光的相位差噪声,通过实时反馈控制DD-MZM的直流输入端,补偿了两路的相位差。首先基于光场传输函数建立了测距理论模型,分析了相位反馈控制的机理;然后基于理论模型搭建了测距系统,采用降频法采样信号;最后利用相位法反演出距离值。结果显示,在动态控制相位差后,系统相位差的长期漂移抑制比可达11 dB,距离测量的稳定度达到0.4μm。该方案有利于提高激光测距系统的稳定性和集成度。

[C(NH)]PO·2HO: A new metal-free ultraviolet nonlinear optical phosphate with large birefringence and second-harmonic generation response

[PO_(4)]3-possesses small microscopic secondorder susceptibility and polarizability anisotropy,which inherently result in weak second-harmonic generation (SHG)and small birefringence.Herein,a new noncentrosymmetric phosphate,[C(NH_(2))3]3PO_(4)·2H_(2)O,was successfully designed and synthesized by a solution evaporation method.[C(NH_(2))3]3PO_(4)·2H_(2)O without metal ions is composed of planar conjugated guanidine cations and PO_(4)tetrahedrons,which are connected by hydrogen bonds,forming a three-dimensional network.Physical property measurements indicate that the title compound displays an SHG response of 1.5×KH_(2)PO_(4)(KDP) and a larger birefringence (0.055@546.1 nm)compared with most reported ultraviolet nonlinear optical phosphates.Furthermore,first-principles calculations reveal that theπ-conjugated planar[C(NH_(2))3]+cations and[PO_(4)]3-groups are responsible for its excellent linear and NLOproperties.

Design and testing of micro-tribometer with macro applied load

With the development of superlubricity, the requirement for the accuracy of measuring super low friction force becomes more and more high. In this study, a novel micro-tribometer has been designed. The resolution and accuracy of friction force are 0.01 m N by using the dual frequency laser interferometer. Experiments were performed to investigate the ability of measuring friction force from different aspects. The interference signal mixed in the measured friction force curve was analyzed and can be removed by a designed filter. The results of experiment show that the tribometer is capable of measuring a super low friction force in the order of magnitude of 0.01 m N with an applied load up to 1 N.

A compact dual-band bandpass filter based on porous silicon dual-microcavity of one-dimensional photonic crystal

We propose a compact dual-band bandpass filter(BPF)based on one-dimensional porous silicon(PS)photonic crystal by electrochemical etching.By inserting three periods of high and low reflective index layers in the center of porous silicon microcavity(PSM),two sharp resonant peaks appear in the high reflectivity stop band on both sides of the resonance wavelength.Through simulation and experiment,the physical mechanisms of the two resonance peaks and the resonance wavelength are also studied.It is found that the resonance wavelength can be tuned only by adjusting the effective optical thickness(EOT)of each PS layer,in which different resonance wavelengths have different widths between the two sharp resonance peaks.Besides,the analysis indicates that oxidization makes the blue shift become larger for high wavelength than that for low wavelength.Such a fabricated BPF based on PS dual-microcavity is easy to be fabricated and low cost,which benefits the application of integrated optical devices.