Single-crystal modifications of the Mach-Zehnder electro-optic modulator

Two single-crystal modifications of the Mach-Zehnder electro-optic modulator are described. Preliminary theoretical estimates show that these variants are capable of ensuring the amplitude modulation of laser beams with elevated power (no less than several watts) at frequencies up to 4 GHz. The obtained modulation characteristics show that the modulation depth in the proposed devices reaches 50–80% and a half-wave voltage of these devices amounts to 100–160 V.     

On-line simultaneous monitoring of polarization mode dispersion and chromatic dispersion

We have developed new expressions for power fading and average power fading owing to polarization mode dispersion (PMD) and chromatic dispersion in terms of the angle of precession of the output state of polarization about the PMD vector. Based on these expressions, a simple and novel pilot-tone-based technique for simultaneous monitoring of chromatic dispersion and PMD is proposed. Experimental results demonstrate the effectiveness of the proposed technique; these results agree well with the theoretical analysis.     

Calibration of laser frequency scan with an electro-optic modulator

An electro-optically modulated laser beam was used to excite the Yb1S0 (6s ) 2?3P1 (6 s 6 p ) transition. Fluorescence was recorded as the laser frequency was scanned across the transition. Each isotope generated multiple peaks in the spectrum separated by the modulation frequency that permitted the frequency scan to be calibrated. The resulting isotope shifts agree well with existing data obtained with an interferometer to monitor the change in laser frequency. Electro-optic modulators have the advantages of being relatively inexpensive and simpler to operate than interferometers whose length must typically be stabilized with a laser whose wavelength is locked to an atomic transition.     

Scheme for feed-forward polarization mode dispersion compensation

We propose a feed-forward polarization mode dispersion (PMD) compensator with three segments that is capable of compensating for the first- and second-order PMD in a transmission fiber. All control parameters are analytically obtained by the PMD concatenated rules. The influence of all possible perturbations on the compensation is investigated with Monte Carlo simulations. The main advantage of our PMD compensation module over the models reported so far is that it shows excellent robustness to all possible perturbations.     

A new experimental approach to second-order polarization mode dispersion analysis for optical communications systems

This article analyzes the polarization mode dispersion (PMD) in optical fibers and presents a new approach for its measurement. This approach permits the combined analysis of the first-order PMD and the second-order polarization mode dispersion (SOPMD) in optical systems for different values of temperature. The relation between SOPMD and the differential group delay (DGD) in a single-mode fiber is discussed. The analysis is based on time/wavelength and temperature variations changing/impacting PMD and DGD measured values. We present long-term statistical characteristics of SOPMD acquired by a PMD emulator constructed with some pieces of high birefringence fiber, and the correlation between the SOPMD, depolarization (Depol) and polarization-dependent chromatic dispersion (PCD) was investigated. A new interpretation of SOPMD is presented to analyze the problem of the temperature spectral stability. The actual techniques for SOPMD determination, consequently Depol and PCD, use the variation with time and/or wavelength. In some studies, the results obtained for SOPMD are correlated to first-order PMD. We demonstrate experimentally that the temperature is an important factor for the correlation between SOPMD and PMD and cannot be neglected in the optimization of high-speed optical communications links.     

Spectral density matrix description of polarization mode dispersion

We introduce a power spectral density matrix formalism that incorporates both the pulse shape and the field polarization and can therefore easily describe averages over random fluctuations of the local birefringence vector. We demonstrate that quantities such as the differential time delay, power diffusion, and decoherence effects can be obtained directly from the equations of motion for the power density matrix. This approach can be applied to pulses with arbitrary frequency-dependent polarization and intensity distributions and in particular makes possible the minimization of the eye-opening penalty through the proper choice of the initial pulse profile.     

Operator expansions for polarization mode dispersion analysis and compensation

We present analytic third- and fourth-order expansions of the Jones matrix as products of exponentials of individual matrices. In our first formalism, these are polarization mode dispersion (PMD) matrices of definite orders. We then discuss an alternative procedure that instead employs exponentials of general skew-Hermitian matrices with a low-order dependence on the deviation of the optical frequency from a central reference frequency. Our expressions correspond to PMD compensators formed from a succession of relatively simple optical components each of which has the frequency response of a single operator in the product.     

Polarization mode dispersion measurement based on continuous polarization modulation

A novel technique is proposed for measurement of the group delay (GD) and the differential group delay (DGD) of optical material, components, and fiber. This new method is based on continuous polarization modulation of the stimulus optical field as opposed to sequential polarization state switching used in the traditional phase shift method. A new complete derivation of the phase shift method, based on the modified Jones calculus of elementary matrices, is presented. The derivation reveals that the phase shift measurement actually depends on all eight elementary parameters that represent DGD and optical frequency derivatives of polarization-dependent loss (PDL). Thus, the new expression for the phase shift includes the combined effect of PDL and DGD. The proposed method is evaluated by measuring a section of polarization-maintaining fiber and a 50 km length of single-mode fiber over a wavelength range from 1530 to 1610 nm. Measurements of DGD in a long single-mode fiber are shown to be highly insensitive to environmentally induced GD drift.     

Design of an ultracompact low-power all-optical modulator by means of dispersion engineered slow light regime in a photonic crystal Mach-Zehnder interferometer

We present the design procedure for an ultracompact low-power all-optical modulator based on a dispersion-engineered slow-light regime in a photonic crystal Mach-Zehnder interferometer (PhC MZI), selectively infiltrated by nonlinear optical fluids. The dispersionless slow-light regime enhancing the nonlinearities enabled a 22 μm long PhC MZI to operate as a modulator with an input power as low as 3 mW/μm. Simulations reveal that the switching threshold can be controlled by varying the optofluidic infiltration.     

Velocity matching of a GaAs electro-optic modulator

New designs for the velocity matching of a deep-etched semiconductor electro-optic modulator are presented. A tantalum pentoxide (Ta2O5) coating is considered here for achieving velocity matching between the microwave and the optical signals. The effects of the velocity mismatch, the conductor loss, the dielectric loss, and the impedance mismatch are studied in relation to the optical bandwidth of a high-speed semiconductor modulator. It is shown that both the dielectric loss and the impedance matching play key roles for velocity-matched high-speed modulators with low conductor loss. The effects of Ta2O5 thickness on the overall bandwidth and on the half-wave voltage-length product VpiL are also reported.     

First- and second-order polarization mode dispersion generated by a two-stage emulator

A two-stage polarization mode dispersion (PMD) emulator design consisting of two variable delay lines separated by a rotatable half-wave linear retarder is analyzed and shown to generate an adjustable amount of first- and second-order PMD without any higher orders. This two-stage PMD emulator configuration provides a simple easy-to-breadboard solution for second-order PMD emulators. When compared with PMD emulators based on birefringent crystals, this two-stage emulator is simpler to calibrate.     

基于表面等离激元的偏振不灵敏型电光调制器的理论研究

由于受到表面等离激元(SPP)固有偏振性的影响,基于表面等离激元的波导型调制器只支持横磁模式(TM)传播。本文提出了一种在垂直方向和水平方向上均构建混合(hybrid)波导结构的表面等离激元电光调制器,以实现调制器的低偏振灵敏性。在组合的混合波导中,垂直和水平偏振方向上的表面等离激元被限制在相应的混合波导中。通过调控介质和ITO界面处形成载流子积累层中载流子浓度可实现光吸收调制。在经优化的结构中两个偏振态的消光比差为0.005dB/μm。通过3D-FDTD模拟调制器的光场调控,清楚地显示了传统硅波导与偏振不灵敏调制器间的耦合传输特性。两种偏振态下,偏振不灵敏调制器与硅波导之间的耦合效率均达到了74%以上。此项研究将为表面等离激元电光调制器在偏振不灵敏光集成回路中的应用提供解决方案,为其与具有偏振随机态光纤回路的集成奠定了基础。     

Chebyshev and Taylor approximations of polarization mode dispersion for improved compensation bandwidth

We examine a series of experimentally realizable procedures for wide-bandwidth polarization mode dispersion compensation based on Taylor and Chebyshev approximations to the transfer matrix for light polarization in optical fibers. Our results demonstrate that a symmetric ordering of compensator elements in the Taylor procedure improves performance and that methods based on the Chebyshev approximation can significantly widen the compensation bandwidth.     

Coherent quantum measurement for the direct determination of the degree of polarization and polarization mode dispersion compensation

Abstract

An example of a coherent measurement for the direct evaluation of the degree of polarization of a single-mode optical beam is presented. It is applied to the case of great practical importance where depolarization is caused by polarization mode dispersion. It is demonstrated that coherent measurement has the potential of significantly increasing the information gain, compared to standard incoherent measurements.     

利用DOP数值搜索的偏振模色散补偿算法

根据光域动态反馈的PMD补偿方案中在线测量的偏振度波动特点,提出了一种基于搜索最优DOP数值的PMD补偿控制算法。此算法在以变步长精确搜索全局最值的基础上,采用近似定步长的搜索策略,避免陷入局部极值区域,得到全局最优DOP数值,从而较好地补偿高速光纤链路中的PMD。将此算法用于人工神经网络训练的仿真中,能够使训练后的网络达到最小网络误差,提高网络的泛化能力。仿真结果验证了该算法的正确性和良好的搜索性能。     

New approach to determine the effects of polarization mode dispersion and chromatic dispersion on pulse and RF signals

We present a novel analytical expression relating the output state of polarization (SOP) and the polarization mode dispersion (PMD) vector, including polarization-dependent chromatic dispersion (PCD), in terms of the angle of precession of the output SOP around the PMD vector. We derive a number of new expressions incorporating for the first time this angle of precession. First, a general relation to study the effect of differential group delay, PCD, and chromatic dispersion on pulses of arbitrary shapes is given. From this general relation, we derive expressions for pulse broadening and power penalty for Gaussian pulses. Moreover, a new expression for PMD-induced power fading for single-sideband modulated radio frequency signals is also derived. Measured experimental results are presented to support the derived expressions.     

Measurement of the complex polarization mode dispersion vector using Jones matrix analysis

The polarization mode dispersion (PMD) of a nondepolarizing optical system is analyzed. A new method is proposed to calculate the complex PMD vector by measuring two Jones matrices at two different wavelengths.     

Theoretical simulation of a polarization modulator based on mechanical rotation of a polarizing element

The properties of three alternative designs for a polarization modulator of potential use for the measurement of vibrational circular dichroism (VCD) are evaluated and compared by use of Mueller calculus. The analysis shows that the combination of a fixed polarizer plus either a photoelastic modulator or a rotating quarter-wave plate possesses nearly the same capability for generation of time-varying, circularly polarized light. However, a modulator composed of a rotating polarizer plus a fixed birefringent plate entails considerable theoretical and experimental difficulties for use in the measurement of VCD spectra. While VCD spectra obtained with the rotating devices can be calibrated in the same manner as spectra obtained with a photoelastic modulator, Mueller analysis shows that the form of the resultant calibration signal will have a different shape. The relevant expressions for VCD and linear dichroism as well as the calibration signals are presented, and consequences for practical realization of these experiments are discussed.     

Theoretical waveguide optimization in a Ti:LiNb0(3) Mach-Zehnder modulator by Mg diffusion

Magnesium diffusion can be used to optimize the characteristics and performance of a Ti:LiNbO(3) Mach-Zehnder modulator. Suitable use of titanium/magnesium double diffusion reduces fiber-waveguide coupling loss, minimizes the modulator size by increasing the bend radius of curvature without increasing bend losses, and decreases separation of the modulator arms. The proposed method also makes it possible to reduce the modulating voltage by improvement of guided-wave lateral confinement. Secondary ion mass spectrometry and 771-line techniques are used to characterize Ti/Mg:LiNbO(3) waveguides. A numerical optimization procedure based on the full vectorial beam-propagation method is presented.