A unidirectional output optical frequency conversion device with anasymmetric-κ DBR structure

A novel optical frequency conversion device that successfully demonstrates optical frequency conversion and unidirectional transmission of optical signals has been designed and fabricated. The device is composed of a gain region and saturable absorber region with monolithically integrated distributed Bragg reflector (DBR) mirrors with different coupling coefficients. The device structure is optimized to achieve three functions: 1) unidirectional light output, 2) converted-light wavelength tuning, and 3) optically triggered optical frequency conversion. The output power of converted light from the light input-end facet of the device is 30 dB smaller than that from the output-end facet, and the converted light wavelength can be scanned over 4 nm without a bias current to the input-end DBR region, and it is widened to 7.8 nm by injecting current to that region. The device emits converted light only when light input is injected and optical signals are unidirectionally transmitted, and its response frequency is estimated to be 0.8 GHz     

Optical frequency conversion in quasi-phase-matched stacks of nonlinear crystals

We present a quantitative theory of nonlinear frequency conversion in stacks of crystals where the phase mismatch due to dispersion is compensated by changing the sign of the nonlinear coupling coefficient in successive crystals-a method first proposed by Armstrong et al. We include pump depletion in our calculations of the second harmonic generation and sum and difference frequency generation. We start with ideal stacks in which the crystal lengths are tailored to achieve perfect phase compensation. When the conversion in each coherence length is small, all crystal lengths tend to equal the coherence lengthpi/Deltak. Frequency conversion in such stacks is well approximated by that in an equivalent phase-matched crystal with the nonlinear coupling coefficient reduced by a factor of2/pi. The effect of systematic as well as random departures in crystal lengths are studied with special attention to the evolution of the relative phase. We show that with appropriate choice of the signs of the nonlinear coupling coefficient in various crystals, high efficiency frequency conversion should be possible using practically any sufficiently large set of nonlinear crystals. The theory of second harmonic generation in periodic stacks and in rotationally twinned crystals of zinc-blend structure is described in detail.     

High-speed signal wavelength conversion using aunidirectional-output wavelength conversion device withasymmetric-κ DBR structure

The wavelength conversion device whose frequency response is evaluated analytically and experimentally in this work has a saturable absorber region, which acts as an optical gate, within the active region. The 3-dB bandwidth of this device was measured to be 800 MHz and found to be limited by the frequency response of the saturable absorber region. To speed up this device, the electrodes of the saturable absorber and the gain regions were connected electrically so that the device would act as a unidirectional-output distributed Bragg reflector (DBR) laser. When the active region (saturable absorber and the gain regions) of this DBR laser were biased above threshold condition, the 3-dB bandwidth was more than 10 GHz, and clear eye patterns were observed when the input TM-polarized light intensity was modulated by a 10-Gbit/s pseudo-random NRZ signal. These results show that high-speed wavelength conversion can be achieved when the device is operated as a laser diode     

基于STM32的交流异步电机变频控制实验装置设计

文章提出一种基于STM32的交流异步电机控制实验装置的设计方法,通过嵌入式微控制器STM32的PWM输出模式控制输出SVPWM波形,三相SVPWM互补信号给三相逆变IPM模块,三相逆变IPM模块输出交流电控制交流异步电机的运转。实验结果证明,本方案可以实现交流异步电机的启动、停止、调速和电机过流保护。     

Optical frequency electronics

Presents exactly what the carrier-envelope phase of an ultrafast pulse denotes. Following a brief review of how ultrashort optical pulses are generated, we will cover how the carrier-envelope phase can be detected and stabilized in the frequency domain. This will provide a connection to a brief discussion of the resulting advances in optical-frequency metrology. Finally, we will discuss possible methods for measuring the "absolute" carrier-envelope phase and experiments that are enabled by a carrier-envelope phase measurement.     

A novel vertical Δκ directional coupler switch usingliquid crystals

To decrease the switching length of the directional coupler switch and to use the advantages of the electro-optic properties of (LC's), we propose a novel vertical Δκ directional coupler switch using LC's and present the calculated results relevant to the design considerations. Because of the large birefringence of LC's, a very short switching length less than 60 μm is possible. Besides, a N×N switch is also proposed for practical applications     

Optical semiconductor device reliability

Based on the degradation modes and mechanisms clarified in 1980s and 1990s, reliability of laser diodes and photodiodes is discussed for application to current optical fiber networks such as communication systems employing wavelength-division-multiplexing technique (WDM), high-frequency modulation technique, etc.     

复合k-m/Gamma衰落信道下的平均信道容量

A new analytical expression is presented for the instantaneous power Probability Density Function (PDF) of receiver signals over composite κ-μ/gamma fading channels. Moreover, the exact expression of channel capacity is derived in the form of an infinite series, while an accurate approximation expression is obtained in closed form. To reveal the implications of the model parameters on capacity, we provide an expression for the case of a high-SNR environment. The relationship of the presented results with previously reported results on generalised-K and K fading chan-nels is also discussed. Finally, numerical and simulation results are presented to prove the correctness of our derived expressions.     

电容式机电转换装置的研究

采用弹力计算和产生弹力的判定方法,研究了圆平行板、球形和圆柱形电容器产生的弹力,结果表明:球形电容器产生的弹力最大,平行板电容器产生的弹力最小。在此基础上,提出了电容器圆锥台极板结构及机电转换装置的优化设计方案。该装置在电容器的两极板间填充高介电常数液体,并采用冲压及化学腐蚀极板的方法来增大电容值,该装置节能、成本低,可在实用化工作电压和小功率的场合替代电磁式机电转换装置。     

Optical frequency synthesis spectroscopy

In order to measure the super narrow spectral features of cooled atoms and ions, in the optical region, optical frequency synthesis (OFS) techniques rather than wavelength techniques must be used. It is anticipated that many of these resonances will be in the optical region of the spectrum, and this paper will address the state-of-the-art of the measurements of frequencies in that region. Two recent optical frequency measurements of iodine transitions in the visible will be described as well as recent improvements in fabricating the point-contact diode used in these measurements.     

Polarisation independent switch and polarisation splitter employingΔβ and Δκ modulation

The authors report a novel type of polarisation independent directional coupler switch on X-cut, Y-propagating Ti:LiNbO₃, with modest fabrication tolerances. The device can also be used as a polarisation splitter. The principle of operation and experimental results are given     

非对称共面波导弯曲结构模式转换的研究

针对传统共面波导弯曲结构传输损耗较大的问题,研究了非对称共面波导弯曲结构.将时域多分辨率分析算法与从Y参数提取c模、π模特性阻抗的方法相结合,推导了二端口两种模式的散射矩阵计算公式.计算了非对称共面波导弯曲结构的传输系数.在理论分析的基础上,提出了一种测试模式间能量转换的实验装置.理论分析和实验结果证明：相对于传统共面波导弯曲结构,非对称共面波导弯曲结构的模式间能量转换更低,传输损耗更小.     

Optical multistability in the mirrorless electrooptic device with feedback

Optical multistable operations are controllably accomplished in the mirrorless electrooptic device with feedback by arranging the polarizer and/or analyzer at appropriate angles with respect to the crystallographic axes of an electrooptic crystal. Moreover, different operating characteristics in two optical output powers with orthogonal polarizations separated from each other by an analyzer are examined theoretically and experimentally.     

一种中频相同的微波光子信道化接收机

提出一种基于相干光处理的微波信道化接收机,采 用 自由谱范围(FSR)不同的两套光频率梳(OFC,optical frequen cy combs)分别作为 光载波和光本振,使得各个信道的输出具有相同的中频。本文方法将微波信号调制到载波 OFC的每一个 频率分量上,并用法布里-珀罗(F-P)光滤波器对多个信道的调制光边带同时进行带通滤 波,然后与 本振OFC进行相干探测实现频率下转换。若载波OFC比本振OFC的FSR大于1个 信道带宽,并使 F-P滤波器的FSR与本振OFC相等,可得 到等带宽、等中频的微波信道,降低了后续电路的复杂度。对 两个相邻信道进行了实验,将9.74～9.86GHz和9.86～9.98GHz波段的信号分别下转换到两个带宽为120MHz 的中频信道,两个中频信道的中心频率仅相差4MHz分别为900MHz和 896MHz,表明本文方法能够实现等中频的信道输出。     

Optical mode conversion using chirped gratings

A design is presented for a 3 dB TE0-TE1 optical waveguide mode convertor using a chirped grating. Devices were fabricated in Ti in-diffused lithium niobate by ion beam etching the grating pattern into the waveguide surface. TE0-TE1 mode coupling was observed experimentally with an insertion loss of 1.5 dB.     

Turbo codes cascaded with high-rate block codes for (O,κ)-constrained channels

We consider several issues in the analysis and design of turbo coded systems for (O, κ) input-constrained channels. These constraints commonly arise in magnetic recording channels. This system is characterized by a high-rate turbo code driving a high-rate (n-1)/n, small-length (O, κ) block code. We discuss the properties of the (O, κ) code that affect its performance on both an additive white Gaussian noise (AWGN) and a precoded dicode channel. We address soft-in soft-out (SISO) decoding of linear and nonlinear (O, κ) codes and show that good (O, κ) codes exist even when d_min=1. For the (O, κ) constrained AWGN channel, we present several rate (n-1)/n block codes that optimally tradeoff bit-error-rate performance with κ. For the precoded dicode channel, we show that the systematic (O, n-1) modulation codes are superior to most other rate (n-1)/n block codes in terms of error-rate performance, and their attractiveness is increased by the fact that they do not contribute any significant complexity to the overall system