Dispersion suppression scheme for Mach-Zehnder interferometer based interleaver using phase shifter

To suppress the dispersion effect, an improved scheme was proposed for Mach-Zehnder intefferometer （MZI） based interleaver. The device consists of an MZI, a fiber loop （FL）, and a phase shifter inserted in FL. The introduction of π phase shifter into FI, dramatically suppresses the dispersion effiect. Then the transmission response remains square-like shape, with low frequency deviation and high extinction ratio. Moreover, the lower frequency deviation is achieved by reducing the dispersion coefficient. For 100GHz-spacing interleaver, the 0.08nm deviation is reduced to 0.02nm by replacing G.652 with G.655.

Electro-Optical Effect Measurement of Thin-Film Material Using PM Fiber Mach-Zehnder Interferometer

A polarization-maintaining （PM） fiber Mach-Zehnder （MZ） interferometer has been established to measure the EO effect of very thin film materials with optical anisotropy. Unlike a common MZ interferometer, all the components are connected via polarization-maintaining fibers. At the same time, a polarized DFB laser with a maximum power output of 10mW is adopted as the light source to induce a large extinction ratio. Here,we take it to determine the electro-optical coefficients of a very thin superlattice structure with GaAs, KTP, and GaN as comparative samples. The measured EO coefficients show good comparability with the others.

Time-Modulated Hamiltonian for Interpreting Delayed-Choice Experiments via Mach-Zehnder Interferometers

Many delayed-choice experiments based on Mach-Zehnder interferometers （MZI） have been considered and made to address the fundamental problem of wave-particle duality. Conventional wisdom long holds that by inserting or removing the second beam splitter （BS2） in a controllable way, microscopic particles （photons, electrons, etc.） transporting within the MZI can lie in the quantum superposition of the wave and particle state as ψ= aw ψ wave ＋ ap ψ particle. Here we present an alternative interpretation to these delayed-choice experiments. We notice that as the BS2 is purely classical, the inserting and removing operation of the BS2 imposes a time- modulated Hamiltonian H mod （t） = a（t）Hin ＋ b（t）Hout, instead of a quantum superposition of H in and Hour as H = awHin ＋ apHout, to act upon the incident wave function. Solution of this quantum scattering problem, rather than the long held quantum eigen-problem yields a synchronically time-modulated output wave function as ψ mod （t） = a（t） ψ wave ＋b（t） ψ particle, instead of the stationary quantum superposition state ψ = aw ψ wave ＋ ap ψ particle. As a result, the probability of particle output from the MZI behaves as if they are in the superposition of the wave and particle state when many events over time accumulation are counted and averaged. We expect that these elementary but insightful analyses will shed a new light on exploring basic physics beyond the long-held wisdom of wave-particle duality and the principle of complementarity.

Simulation of distributed optical fiber disturbance detection system based on Sagnac/Mach-Zehnder interferometer and cross-correlation location

A distributed optical fiber disturbance detection system consisted of a Sagnac interferometer and a Mach-Zehnder interferometer is demonstrated. Two interferometers outputs are connected to an electric band-pass filter via a detector respectively. The central frequencies of the two filters are selected adaptively according to the disturbance frequency. The disturbance frequency is obtained by either frequency spectrum of the two interferometers outputs. An alarm is given out only when the Sagnac interferometer output is changed. A disturbance position is determined by calculating a time difference with a cross-correlation method between the filter output connected to the Sagnac interferometer and derivative of the filter output connected to the Mach-Zehnder interferometer. The frequency spectrum, derivative and cross-correlation are obtained by a signal processing system. Theory analysis and simulation results are presented. They show that the system structure and location method are effective, accurate, and immune to environmental variations.

In-Fiber Mach-Zehnder Interferometer Based on Waist-Enlarged Taper and Core-Mismatching for Strain Sensing

An in-fiber Mach-Zehnder interferometer for strain measurement is proposed and experimentally demonstrated. The sensor consists of a taper followed by a short section of a multi-mode fiber （MMF） and a dispersion com- pensating fiber （DCF）, which is sandwiched between two single mode fibers （SMFs）. The taper is used as a fiber coupler to excite cladding modes in the SMF, and these cladding modes transmit within the MMF and the DCF. The core mode and the cladding modes interfere in the DCF SMF fusion point to form intermodal interference. A well-defined interference spectrum is obtained in the experiment. Selected interference dips are used to measure the strain changes. The experimental results show that this device is sensitive to strain with the wavelength-referenced sensitivity of 2.6 pm/με and the power-referenced sensitivity of 0. 0027 dB/με, respectively.

Quantitative Visualization of the Thermal Boundary Layer of Forced Convection on a Heated or Cooled Flat Plate with a 30°Leading Edge Using a Mach-Zehnder Interferometer

This study focuses on the experimental measurements of the heat transfer coefficient over a flat plate with a 30° leading edge. Under forced convection by a hot/cold air and flow over a cooled/heated flat plate, the thermal boundary layer and its thickness are quantitatively visualized and measured using a Mach-Zehnder interferometer. In addition, the variation in the local heat transfer coefficient is evaluated experimentally with respect to the air flow velocity and temperature. Differences within the heat transfer performance between the plates are confirmed and discussed. As a result, the average heat transfer performance is about the same for the heated plate and the cooled plate under all air velocity conditions. This contrasts with the theoretical prediction in the case of low air velocity, the reason considered was that the buoyancy at the 30° leading edge blocked air from flowing across the surface of the plate.

Temperature-induced effect on refractive index of graphene based on coated in-fiber Mach-Zehnder interferometer

The temperature-induced complex refractive index（CRI） effect of graphene is demonstrated theoretically and experimentally based on a graphene coated in-fiber MZI（Mach-Zehnder interferometer）. The relationships between real and imaginary parts of the graphene CRI and temperature are obtained through investigating the dip wavelength and intensity of the MZI interference spectrum changing with temperature, respectively. The temperature effect of CRI of the graphene is also analyzed theoretically. Both experimental and theoretical studies show that the real part and imaginary part of the CRI nonlinearly decrease and increase with temperature increasing, respectively. This graphene-coated in-fiber MZI structure also possesses the advantages of easy fabrication, miniaturization, low cost and robustness. It has potential applications in nanomaterial-based optic devices for communication and sensing.

Compact temperature-insensitive modulator based on a silicon microring assistant Mach-Zehnder interferometer

On the silicon-on-insulator platform, an ultra compact temperature-insensitive modulator based on a cascaded microring assistant Mach-Zehnder interferometer is proposed and demonstrated with numerical simulation. According to the calculated results, the tolerated variation of ambient temperature can be as high as 134 ℃ while the footprint of such a silicon modulator is only 340 μm2.

An Improved Experiment to Determine the‘Past of a Particle’in the Nested Mach-Zehnder Interferometer

We argue that the modification proposed by Li et al. [Chin. Phys. Lett. 32 （2015）050303] to the experiment of Danan et al. [Phys. Rev. Lett. 111 （2013） 240402] does not test the past of the photon as characterized by local weak traces. Instead of answering the questions： （i） were the photons in A？ （ii） were the photons in B？ and （iii） were the photons in C？ the proposed experiment measures a degenerate operator answering the questions： （i） were the photons in A？ and （ii） were the photons in B and C together？ A negative answer to the last question does not tell us if photons were present in B or C. On the other hand, a simple variation of the proposal by Li et al. does provide conceptually better evidence for the past of the pre- and post-selected photon, but this evidence will be in agreement with the results of Danan et al.

Theoretical Analysis and Experiment of Temperature Stability for Fiber-optic Mach-Zehnder Interferometer Filter

Fiber optic Mach Zehnder interferometer(MZI) can be used as wavelength multiplexers and demultiplexers. The △ L and △ directly influence the properties of MZI. To lengthen the △ L can demultiplex much more wavelengths, but when the △ L is longer, the temperature will influence MZI more seriously. A method to solve this problem is proposed, which enables MZI to work stably. The wavelength distance is 0.8 nm, and the extinction ratio is high.

Two-Photon Interference Constructed by Two Hong–Ou–Mandel Effects in One Mach-Zehnder Interferometer

We present a two-photon interference experiment in a modified Mach-Zehnder （MZ） interferometer in which two Hong-Ou-Mandel effects occur in tandem and construct superposed two-photon states. The signal photons pass both the arms of the MZ interferometer while the idler photons pass one arm only. Interestingly, the probability of the idler photons emerging from any output port still shows a sine oscillation with the two-photon phase difference and it can be characterized only by the indistinguishability of the two-photon amplitudes. We also observe a two-photon interference pattern with a period being equal to the wavelength of the parametric photons instead of the two-photon photonie de Broglie wavelength due to the presence of two-photon phase difference, in particular, with complementary probabilities of finding the two-photon pairs in two output ports. The abundant observations can facilitate a more comprehensive understanding of the two-photon interference.

An Ideal Experiment to Determine the ’Past of a Particle’ in the Nested Mach-Zehnder Interferometer

An ideal experiment is designed to determine the past of a particle in the nested Mach-Zehnder interferometer （MZI） by using standard quantum mechanics with quantum non-demolition measurements. We find that when the photon reaches the detector, it only follows one arm of the outer interferometer and leaves no trace in the inner MZI. When it goes through the inner MZI, it cannot reach the detector. Our result obtained from the standard quantum mechanics contradicts the statement based on two-state vector formulism, ＇the photon did not enter the （inner） interferometer, the photon never left the interferometer, but it was there＇. Therefore, the statement and also the overlapping claim are incorrect.

基于光纤锥级联的Mach-Zehnder干涉湿度传感器

提出了一种基于光纤锥级联纤芯失配的Mach-Zehnder干涉湿度传感器。将两段色散补偿光纤对芯熔接光纤锥,并依次级联,再接入一段6 mm的多模渐变光纤,构成了Mach-Zehnder干涉仪,其中多模渐变光纤和芯径失配处的两个节点起到了光纤耦合器的作用。环境湿度变化,引起传感器透射谱能量发生改变。实验结果表明:透射谱波峰能量和湿度有较好的线性关系。当湿度在35%～95%RH范围内变化,传感器灵敏度为-0. 074 9 d B/%RH,线性度R2为0. 995。设计的传感器结构紧凑、灵敏度高,可以广泛应用于不同领域的湿度测量。

臂长差啁啾型级联Mach-Zehnder干涉仪滤波性能

为增大自由频谱区(FSR),优化级联Mach-Zehnder干涉仪(MZIs)的带通滤波性能,利用其与阶梯形滤波器原理的相似性,用啁啾型臂长差替代恒定臂长差.用传输矩阵法建立了臂长差啁啾型级联MZI的数学模型,分析3 dB带宽及FSR的变化规律,验证了理论模型及分析方法的正确性.仿真结果表明,通过合理选取啁啾系数,臂长差啁啾型级联MZI同时获得了较大的FSR和较小的3 dB带宽,且最佳啁啾系数随衍射级数增大而增大.

一种全光纤Mach-Zehnder干涉式温度传感器设计

本文提出了一种基于全光纤马赫-曾德尔(Mach-Zehnder)干涉式光纤温度传感器结构,是在单模光纤(SMF)上熔接一段30mm长的细芯径光纤,利用光纤的纤芯模和包层模对温度灵敏度的差异,来测量在不同波长处的波长温度关系,实现对温度的测量。实验中我们分别对波长1531.2375nm和1544.39nm处的干涉波谷进行测量,得到两个波谷的温度灵敏度分别为89pm/℃和94.7pm/℃,该温度灵敏度系数远远大于光纤布拉格光栅,且测试曲线呈现很好的线性度。该类传感器具有结构简单、温度灵敏度高、造价低等优点。

熔融七芯光纤球对称的Mach-Zehnder干涉传感特性

提出了一种基于七芯光纤和单模光纤熔球对称型Mach-Zehnder干涉传感器。单模光纤端面熔接制作直径180μm光纤球,将2个光纤球中间熔接一段七芯光纤,位于Mach-Zehnder干涉结构中间的七芯光纤长度为9 mm。传感器外界环境温度、曲率的改变都会使传感器的纤芯基模和包层模的光程差发生改变,从而引起传感器干涉谱发生变化,通过监测干涉谱可以实现对外界物理量的测量。通过建立的有限差分光束传播法仿真分析结果可知:光纤球结构增加了七芯光纤的光耦合效率,七芯光纤结构的干涉效应得到了有效改善。实验结果表明:当温度在20~95℃范围内变化时,传感器的温度灵敏度为58. 97 pm/℃,线性度为0. 996 22;曲率在0~1 m-1变化范围内,传感器的曲率灵敏度为2. 55 nm/m-1,线性度为0. 996 73。设计的传感器结构紧凑、制作工艺简单、可靠性高。

Characterize and optimize the four-wave mixing in dual-interferometer coupled silicon microrings

By designing and fabricating a series of dual-interferometer coupled silicon microrings, the coupling condition of the pump, signal, and idler beams can be engineered independently and then we carried out both the continuous-wave and pulse pumped four-wave mixing experiments to verify the dependence of conversion efficiency on the coupling conditions of the four interacting beams, respectively. Under the continuous-wave pump, the four-wave mixing efficiency gets maximized when both the pump and signal/idler beams are closely operated at the critical coupling point, while for the pulse pump case, the efficiency can be enhanced greatly when the pump and converted idler beams are all overcoupled. These experiment results agree well with our theoretical calculations. Our design provides a platform for explicitly characterizing the four-wave mixing under different pumping conditions, and offers a method to optimize the four-wave mixing, which will facilitate the development of on-chip all-optical signal processing with a higher efficiency or reduced pump power.

一种融合Φ-OTDR和MZI的PCCP断丝监测系统

设计了一种融合相位敏感型光时域反射计(Φ-OTDR)和马赫-曾德尔干涉仪(MZI)的预应力钢筋混凝土管(PCCP)断丝监测系统。通过引入优化的IQ解调算法,减少了40%以上的数据运算量。实验结果证明该系统的单端测量距离不低于20 km,频率响应不低于20 kHz,空间定位误差在±2 m以内,具备长距离定位断丝故障和分辨振动事件特征频率的能力,为PCCP的全生命周期在线结构健康监测提供了一种可靠的技术手段。

Complementarity via Minimum Error Measurement in a Two-Path Interferometer

We study the fringe visibility and the which-path information(WPI) of a general Mach-Zehnder interferometer with an asymmetric beam splitter(BS). A minimum error measurement in the detector is used to extract the WPI. Both the fringe visibility V and the WPI I_(path) are affected by the initial state of the photon and the second asymmetric BS. The condition in which the WPI takes the maximum is obtained. The complementarity relationship V^2 + I_(path)~2 ≤ 1 is found, and the conditions for equality are also presented.

Fringe visibility and correlation in Mach–Zehnder interferometer with an asymmetric beam splitter

We study the wave–particle duality in a general Mach–Zehnder interferometer with an asymmetric beam splitter from the viewpoint of quantum information theory.The correlations(including the classical correlation and the quantum correlation)between the particle and the which-path detector are derived when they are in pure state or mixed state at the output of Mach–Zehnder interferometer.It is found that the fringe visibility and the correlations are effected by the asymmetric beam splitter and the input state of the particle.The complementary relations between the fringe visibility and the correlations are also presented.