Numerical correction of optical vortex using a wrapped phase map analysis algorithm

We demonstrate experimentally a technique for the numerical correction of an optical vortex with a unitary topological charge. A developed algorithm based on the axial behavior of a reconstructed wavefront is used in the detection of the optical vortex. Optimizations of the number of axial phase maps and the window size used in the algorithm yield the precise coordinates of the vortex eye. The obtained coordinates and vortex handedness are used in designing a proper filter, facilitating numerical correction of the vortex phase map. The developed algorithm can be applied to absolute phase and phase difference maps obtained through any reconstruction method.     

Mach-Zehnder interferometer with a uniform wavelength period

We have realized a first optical filter composed of optical delay lines and couplers that has a periodic response with respect to wavelength, whereas a conventional optical filter is known to have a periodic response to relative optical frequency. This new filter can be constructed by using a phase-generating coupler (PGC) that supplies the optical delay lines with a wavelength-dependent nonlinear phase. The PGC, which is also composed of optical delay lines and couplers, can simultaneously provide a desired phase and an arbitrary amplitude coupling ratio. We applied our transformation method to a conventional Mach-Zehnder interferometer (MZI) as an example of an optical frequency filter and converted it to an optical wavelength filter. We fabricated the designed MZI on a silica-based planar lightwave circuit and successfully realized what is believed to be the first MZI with a uniform wavelength period.     

Generalized optical interferometry for modal analysis in arbitrary degrees of freedom

We generalize the traditional concept of temporal optical interferometry to any degree of freedom of a coherent optical field. By identifying the structure of a unitary optical transformation that we designate the generalized phase operator, we enable optical interferometry to be carried out in any modal basis describing a degree of freedom. The structure of the generalized phase operator is that of a fractional optical transform, thus establishing the connection between fractional transforms, optical interferometry, and modal analysis.     

Bragg光纤光栅用作滤波器时的输出光脉冲波形分析

对光纤光栅用作接收端光噪音滤波器进行了详细的理论分析,计算了通信系统中矩形光脉冲信号经“强”、“弱”Bragg光纤光栅滤波器后的输出光脉冲波形,同时也计算了矩形光脉冲信号经匹配光滤波器、现行光通信系统中常用F-P滤波器的输出光脉冲波形,对四种滤波器的输出光脉冲波形进行了分析和比较,并分析了输出信号在抽样判决时的码间干扰情况,从输出波形分析认为,光纤光栅用做接收端噪音滤波器比F-P滤波器具有更大的优越性.     

相位解码的时-空重建算法

基于相位映射的三维传感技术对几何形状和拓扑结构复杂或表面梯度很大的物体进行绝对相位测量及相位重建仍然是一个困难的问题。近年来国际上提出了一种时间维度相位重建算法可以对此提供一种解决方案。然而,该算法对结构光照明系统提出了很高的要求,当系统无法满足算法要求时,重建结果存在严重的噪声。针对这一问题,提出了一种利用分段函数构造的相位解码的时空重建算法。该算法在相位重建过程中同时考虑时间维度和空间维度相位的相对关系,使得空间频率非严格按指数增长的条纹序列可以得到正确的重建,消除了跳变边界的相位模糊问题,从而可以更加有效地解决深度表面不连续和存在相互孤立物表面拓扑结构的景物相位重建问题。实验结果证明了此算法的可行性和有效性。     

WDM compatible and electrically tunable SPE-OCDMA system based on the temporal self-imaging effect

A coding/decoding setup for a spectral phase encoding optical code-division multiple access (SPE-OCDMA) system has been developed. The proposal is based on the temporal self-imaging effect and the use of an easily tunable electro-optic phase modulator to achieve line-by-line coding of the transmitted signal, thus assuring compatibility with WDM techniques. Modulation of the code is performed at the same rate as the data, avoiding the use of high-bandwidth electro-optic modulators. As proof of concept of the technique, experimental results are presented for a back-to-back coder/decoder setup transmitting a 10 GHz unmodulated optical pulse train within an 80 GHz optical window and using 8-chip Hadamard codes.     

Analysis of polarization-independent tunable optical comb filter by cascading MZI and phase modulating Sagnac loop

A novel scheme of tunable optical comb filter constructed by cascading a polarization-swapping MZI and a phase modulating Sagnac loop is proposed. The key features of this comb filter design are its polarization-independence and high speed in wavelength tuning. The wavelength tunability can be readily achieved by incorporating an electro-optic phase modulator into the Sagnac loop. In addition, the filter can be made amplitude adjustable as well. The filter will be desirable for multi-wavelength fiber lasers, multi-channel optical signal processing and optical WDM systems.     

Time-domain interferometry for direct electric-field reconstruction by use of an acousto-optic programmable filter and a two-photon detector

We introduce a new approach to the characterization of femtosecond optical pulses based on a remarkably simple setup combining a two-photon detector and a pulse shaper consisting of a longitudinal acousto-optic programmable filter. The operation of this setup is demonstrated through the use of a new version of spectral phase interferometry for direct electric-field reconstruction based on time-domain instead of on frequency-domain interferometry.     

A novel scheme of optical Meyer wavelet filter based on time lenses in nonlinear multi-span optics fiber communication system

In this work, a novel scheme to realize optical Meyer wavelet filter based on time lenses and Mach–Zehnder modulators in optical domain was proposed and the transfer functions of Meyer wavelet decomposition and reconstruction processed in frequency domain were derived to realize Meyer wavelet de-noising for optical signal. The filter could be used to reduce the nonlinear noise induced by the interaction of EDFA’s ASE noise, fiber’s dispersion and nonlinearity in high bit rate multi-span optical communication systems without photo-electric conversion. The bit error rate curves of the optical bit sequence without and with optical Meyer wavelet filter were plotted to show the effectiveness of the optical Meyer wavelet filter, which can achieve better result and improve the optical communication quality in dispersion compensation links.     

On the interrelations between an optical differentiator and an optical Hilbert transformer

We show analytically and numerically that a practically realizable first-order optical Hilbert transformer (OHT) can simultaneously function as a negative/positive first-order temporal optical differentiator (OD) in the stopband and a broadband ±90° phase shifter in the passbands. An integrated-optic OHT based on a four-tap finite impulse response filter is designed using the Remez iteration algorithm and is numerically verified.     

利用飞秒脉冲光谱全息实现空域信息向时域信息的转换

在Mazurenko提出的时域超短脉冲光谱全息结构的基础上,提出了改进型的飞秒脉冲光谱全息结构,并推导了当输入脉冲光场中包含时、空分布时光谱全息的记录和再现。结果发现当在光谱全息记录和再现时,如果频谱面上添加空间滤波器,可以实现飞秒脉冲包含的空域信息向时域信息的转换。结论可以应用到超短脉冲整形,超高速光通信和光信息处理等领域。     

非对称三区光瞳滤波器实现一维横向超分辨

基于严格的光学成像矢量衍射理论,以4倍缩小倍率的成像系统和x线偏振光照明为例,得到经光瞳滤波器调制的大数值孔径光学系统焦区横向场表达式.通过详细研究非对称三区复振幅型光瞳滤波器的内外环归一化半径、各环相位分布和第一层透过率t对y方向分辨率增益比Gty,斯特尔比Sy和第一旁瓣与主瓣相对强度Iry的影响.设计了一种非对称三区相位型光瞳滤波器,实现Gty=0.8345,Sy=0.4087,Iry=0.4923,使得y方向分辨率比没有加光瞳滤波器时提高了将近20%.     

Programmable multiple true-time-delay elements based on a Fourier-domain optical processor

A new technique to realize an array of multiple true-time-delay elements, which can be independently and continuously tuned, is reported. It is based on a WDM parallel signal processing approach in conjunction with a diffraction-based Fourier-domain optical signal processor. Programmable linear optical phase transfer functions are realized to obtain different electrical true-time delays. The technique can scale to a large number of wideband true-time-delay lines, with continuously tunable programmable delay. Results demonstrate multiple true-time-delay elements with independent tuning control and verify the concept by tuning the free spectral range of a microwave photonic notch filter. To our best knowledge, this is the first demonstration of multiple independently controllable true-time-delay lines for microwave photonic systems.     

空间滤波法检测透明材料的相位缺陷

利用二元滤波器改造透明材料光信号频谱,实现光信号的相位调制到光信号的强度调制,从而检测到透明材料的相位缺陷.给出了利用高通滤波器、低通滤波器、相位滤波器、刀口滤波器检测人工相位缺陷和普通玻璃的自然相位缺陷的试验结果.     

High-speed all-optical differentiator based on a semiconductor optical amplifier and an optical filter

We demonstrate a novel all-optical differentiator that carries out the first-order temporal derivation of optical intensity variation at high speed. It consists of a semiconductor optical amplifier (SOA) and an optical filter (OF) serving as an optical phase modulator and a frequency discriminator, respectively. A polarity-reversed derivative pair with a certain bias can be obtained by locating the probe wavelength at the positive or negative slope of the OF. Differentiations of super-Gaussian and Gaussian signals are obtained at various data rates. Defined as the mean absolute deviation of the measured result from the ideal result, total average errors of less than 0.12 are observed in all cases. Input power dynamics as well as control wavelength dependence are investigated and show that the cross-gain modulation in the SOA is detrimental to the differentiation performance.     

Linear self-referenced complex-field characterization of fast optical signals using photonic differentiation

This paper reviews recent work on a new group of linear and self-referenced techniques for full (amplitude and phase) characterization of fast optical signals based upon the concept of photonic differentiation, generally referred to as ‘phase reconstruction using optical ultrafast differentiation’ (PROUD). These techniques are particularly well adapted for applications in the context of fiber-optics telecommunications. PROUD methods can be implemented using simple and practical optical fiber-based setups and they rely on a direct, non-iterative phase recovery numerical algorithm. They can be used over a very wide range of pulse time durations, from the sub-picosecond to the nanosecond regime, and they can provide measurements in a single shot and in real time with power sensitivities down to the microwatt level. Previously reported PROUD methods are treated here under a unified, single framework, facilitating their analysis and comparison.     

Temporal filtering using time lenses for optical transmission systems

An optical signal processing scheme using time lenses in a 4-f configuration for optical communication systems is proposed. The first time-lens combined with a dispersive element such as an optical fiber produces the Fourier transform of the input signal and the second time lens combined with an optical fiber placed after the temporal filter produces the inverse Fourier transformation. Typically, in an optical signal processing scheme based on space/time-lens, the signal at the output is space/time-reversed because of the direct Fourier transformation after the spatial/temporal filter, which is undesirable for a practical optical communication system. Here, we propose a technique to implement both direct and inverse Fourier transformation using time lenses which has no spatial analogue. As a result, the bit sequence at the output is not time-reversed. Two applications of the proposed scheme, a demultiplexer for wavelength division multiplexing (WDM) systems and a higher-order dispersion compensator, have been discussed and numerically implemented.     

单轴晶体相位型光瞳滤波器

提出了一种基于单轴晶体制作的相位型光瞳滤波器,与普通的相位型光瞳滤波器相比较,单轴晶体相位型光瞳滤波器不仅制作简单,而且相位差有一定的可调节性。与液晶制作的相位型光瞳滤波器相比较,虽然单轴晶体相位型光瞳滤波器的可调节性不如液晶相位型光瞳滤波器,但是单轴晶体相位型光瞳滤波器成本低,而且也不会对光的衰减过大。单轴晶体相位型光瞳滤波器可以实现对焦斑分布的连续调节。通过理论分析和数值计算,论证了单轴晶体相位型光瞳滤波器的可行性,并且具体设计了两区型的单轴晶体相位型光瞳滤波器。     

Effect of binary phase plate on incident radially polarized hollow Gaussian beam

Effect of a pure binary phase filter on the three-dimensional light intensity distributions in focal region is theoretically investigated in this paper. The results show that the proposed binary phase filter may induce flat top profile with large depth of focus and reduced focal spot by properly adjusting the geometrical parameters of the binary phase filter of incident radially polarized hollow Gaussian beam (HGB) beam. On the other hand, the HGB beam benefits the most from the use of an annulus. Such kind of system is potentially useful for lithography, imaging, optical data storage, optical trapping, optical excitation of molecules, or coupling to optical fibers.     

Incoherent digital holographic spectral imaging with high accuracy of image pixel registration

Fresnel incoherent correlation holography(FINCH) is a unique three-dimensional(3 D) imaging technique which has the advantages of scanning-free,high resolution,and easy matching with existing mature optical systems.In this article,an incoherent digital holographic spectral imaging method with high accuracy of spectral reconstruction based on liquid crystal tunable filter(LCTF) and FINCH is proposed.Using the programmable characteristics of spatial light modulator(SLM),a series of phase masks,none of whose focal lengths changes with wavelength,is designed and made.For each wavelength of LCTF output,SLM calls three phase masks with different phase constants at the corresponding wavelength,and CCD records three holograms.The spectral images obtained by this method have a constant magnification,which can achieve pixel-level image registration,restrain image registration errors,and improve spectral reconstruction accuracy.The results show that this method can not only obtain the 3 D spatial information and spectral information of the object simultaneously,but also have high accuracy of spectral reconstruction and excellent color reproducibility.