Experimental demonstration of microring quadrature phase-shift keying modulators

Advanced optical modulation formats are a key technology to increase the capacity of optical communication networks. Mach-Zehnder modulators are typically used to generate various modulation formats. Here, we report the first experimental demonstration of quadrature phase-shift keying (QPSK) modulation using compact microring modulators. Generation of 20 Gb/s QPSK signals is demonstrated with 30 μm radius silicon ring modulators with drive voltages of ~6 V. These compact QPSK modulators may be used in miniature optical transponders for high-capacity optical data links.     

Design of an electromagnetic system for wide-band optical modulators

The parameters of a slot-type electromagnetic system that can be used in ultrahigh-frequency wide-band optical modulators are studied. Analytical expressions for the bandwidth of the device are obtained, and this parameter in prototypes is estimated. Experiments on optical radiation modulation by microwave signals show that these electromagnetic systems are promising for volume optical modulators.     

偏置M-Z调制器构建2-bits电光模数转换相位编码方法的分析与模拟

为了降低电光相位编码器功率消耗和解决内部M Z调制器一致性要求高的问题,利用2个偏置M Z调制器构成了用于电光模数转换的2 bits电光相位编码器。理论分析了偏置M Z调制器实现2 bits电光相位编码的方法、特点和性能。仿真结果验证了采用偏置M Z调制器构成的2 bits相位编码方法可行性,并实现了对1 GHz模拟电信号的采样速率12 GSa/s模数转换。分析和仿真结果表明,采用该方法对调制器一致性要求低,对输入信号功率要求低于0.32 W。分析结果表明,调制器直流漂移不影响最低位量化结果,引起最高位量化结果的判决模糊低于3.8%。     

Broadband 10 Gb/s operation of graphene electro‐absorption modulator on silicon

High performance integrated optical modulators are highly desired for future optical interconnects. The ultra‐high bandwidth and broadband operation potentially offered by graphene based electro‐absorption modulators has attracted a lot of attention in the photonics community recently. In this work, we theoretically evaluate the true potential of such modulators and illustrate this with experimental results for a silicon integrated graphene optical electro‐absorption modulator capable of broadband 10 Gb/s modulation speed. The measured results agree very well with theoretical predictions. A low insertion loss of 3.8 dB at 1580 nm and a low drive voltage of 2.5 V combined with broadband and athermal operation were obtained for a 50 μm‐length hybrid graphene‐Si device. The peak modulation efficiency of the device is 1.5 dB/V. This robust device is challenging best‐in‐class Si (Ge) modulators for future chip‐level optical interconnects.     

Effect of energy losses on the amplitude-frequency characteristic of the electrodynamic system of optical modulators

The results of calculations of main parameters of a slot-type electrodynamic system taking into account losses in a single-mode nonresonance regime of excitation and in the regime of responance excitation in the vicinity of the cutoff frequency are presented. Analytic expressions obtained for the transmission coefficient, resonance frequency, and transmission band can be used in designing wide-band optical modulators. Experimental verification of laboratory prototypes of electrodynamic systems and their application in available modulators confirms the possibility of employment of such analysis for choosing optimal designs of ultrahigh-frequency modulators of optical radiation.     

Carrier suppression in quadruple frequency modulation by cascaded optical external modulators for millimeter-wave generation

The optical carrier suppression in optical quadruple frequency modulation by cascaded external modulators is investigated theoretically and experimentally. Theoretical analysis demonstrates that the optical carrier suppression ratio is related with not only the initial phase difference of electrical signals applied on the two modulators, but also the optical phase shift between the two modulators. The maximum suppression ratio can be achieved when the total phase difference is equal to nπ＋π/2 （n = 1, 2,…）, which is verified by experiments. By properly controlling the total phase shift, 40-GHz millimeter-wave is generated by using a 10-GHz radio frequency （RF） source and the modulators.     

Real-time electro-optical heterodyne signal processors

A cross-correlation function of two time-varying signals and two spatial signals is considered analytically for real-time signal processing. An electro-optical heterodyne signal processor with a set of two successive ultrasonic light modulators and two optical masks is simply used because this optical system is not so sensitive in its alignment as conventional Mach-Zehnder-like interferometers for photomixing. As two special cases, a convolution function of two rectangular pulses fed to both the modulators and a correlation function of a rectangular pulse, fed only to one of the modulators, with a rectangular aperture made in one mask are produced experimentally for verification.     

应用于ROF系统中的单边带调制微波毫米波生成技术研究

介绍了单边带调制微波毫米波生成技术研究的背景及意义,综述了几种主要的单边带调制微波毫米波生成技术方案,包括移相法、滤波法、非线性效应法,以及在此基础上的改进方法,如应用于ROF系统中基于谐波抑制的新型单边带调制方案、应用超窄双传输峰光纤光栅实现光学单边带调制等。还介绍了两种新型单边带调制生成微波毫米波技术,包括基于极性反转电光调制器的单边带调制技术以及新型光学注入锁定单边带调制实验系统     

Silicon microring-based signal modulation for chip-scale optical interconnection

Electro-optic modulation plays a critical role in implementing space-, power- and spectrally efficient optical interconnection for high-capacity computing systems. Microring resonators exhibit a great potential to achieve compact, low power-consumption and high-speed modulators. In this paper, we briefly review our efforts on designing and analyzing the microring modulators. Three types of single-ring modulators are discussed, from device behavior to possible system impact. We then present two novel double-ring modulators in which a passive ring resonator is added, enabling higher operation speed and lower power consumption. We also describe an opportunity of introducing phase modulation data formats into the on-chip communication environment. In this paper, our emphasis is placed on linking the devices’ physics to their system performance and providing potential technical solutions to physical-layer challenges of optical interconnection.     

液晶空间光调制器在光信息综合实验中的应用

提出了一种把液晶空间光调制器应用于光电信息综合实验的光学实验系统。系统中的空间光调制器采用光寻址液晶光阀和电寻址液晶光阀。给出了利用这一系统开设的四个光学信息处理实验。实践表明,该系统具有较好的教学效果。     

Electrooptic sensor module fabrication for near-field intrabody communication

In this paper, we describe how to obtain a low cost electrooptic (EO) sensor module for the mass production of near-field intrabody communication devices. In our previous study, we used a bulk cleavage technique to fabricate EO modulators without the need for any optical polishing or washing processes. In this study, we fabricated EO modulators as a miniaturized chip sensor without a base portion, and clarified the feasibility of assembling optical components by only a passive alignment technique with a compact housing.     

Nonlinear effects in blue-shift waveguide EAM's

To exploit the vast bandwidth of optical communication systems for high bit-rate long-haul transmission, external modulators show a better system performance than directly modulated lasers. One of the main advantages of electroabsorption modulators (EAM's) compared with Mach–Zehnder modulators is the possibility to integrate the modulator with a laser having the same active layer. This reduces processing complexity and system costs. Usually the quantum confined Stark effect results in a red shift of the absorption, which leads to a small gain due to a detuned operation of the integrated laser. In contrast, blue shift structures have been proposed for these integrated devices as they show both good laser and modulator properties. These structures suffer from the drawback that saturation effects may occur for higher optical power as these devices absorb the optical power at low applied bias. The aim of this paper is to investigate the influence of nonlinear saturation effects like carrier accumulation, Burnstein–Moss-effect and carrier screening.     

Electro-absorption and refraction in Fabry-Perot quantum well modulators: a general discussion

Fabry-Perot resonators have long been advocated to improve the limited contrast ratio of multiple quantum well optical modulators used in photonic switches based on self electrooptic effect devices (SEEDs) and in other array based optical interconnection schemes. Using data on field dependent GaAs/AlGaAs quantum well absorption and refraction, we have modelled the reflectivity, modulation depth and contrast ratio of resonant modulators. Our results are generally valid for any quantum well modulator and demonstrate 23the important role played by electro-refraction even in regions of strong absorption. Resonators give large contrast ratios but there are trade-offs in the maximum reflectivity change achievable with Fabry-Perot resonators compared to simple modulators. The model gives the optimum number of quantum wells and reflectivity values required to make a resonator at any wavelength for a given quantum well structure. Understanding the limits of Fabry-Perot quantum well modulator performance is important for their application in symmetric self electrooptic effectiveness for photonic switching where modulation and detection properties are both used and for optical interconnection systems.     

ZnS Nanospheres for Optical Modulator in an Erbium-Doped Fiber Laser

Zinc sulfide (ZnS), which belongs to transition metal monochalcogenides, is a semiconductor material with wide direct band gap. It can potentially show some special applications (such as luminescence, phosphor, sensors, infrared window materials, photocatalysis) by changing the morphology, size, and crystal structure of semiconductor materials. However, ZnS nanospheres have not been studied as optical modulators until now. Herein, ZnS nanospheres are synthesized by the hydrothermal method and are used to realize optical modulators in an Er-doped fiber laser. The evanescent field effect is utilized to incorporate the ZnS nanospheres on a tapered fiber. Furthermore, with the increase in pump power, the modulation interval gradually decreases to a minimum of 34.36 ns corresponding to the modulation frequency of 29.1 MHz, which is the highest modulation frequency to our knowledge in a ring cavity all-fiber laser. These results demonstrate ZnS nanospheres together with the interaction of dispersion and nonlinearity in optical fibers can modulate the proposed lasers. This not only provides a new method for controlling the power and frequency of all optical modulators, but also marks an important step for ZnS materials in optics research and device applications.     

Semiconductor waveguide optical switches and modulators

Semiconductor waveguide optical switches and modulators are reviewed from the view point of material and structure. As material for switches and modulators, effects of both variations of refractive index and absorption are considered. As for the structure of switches and modulators, basic characteristics of devices, including length, speed, and consumption power, are investigated, and recent experimental performances are shown. For further improvement of switches and modulators, the importance of low-dimensional quantum-well structures and strained quantum-well structures are pointed out.     

微环辅助Mach-Zehnder光调制器的线性特性

分析了有损耗的多环辅助Mach-Zehnder(MZ)光调制器,获得了在偏置点处令二阶和三阶高次项同时为零的方程,并在此基础上解得单环和双环辅助下的设计参量的解析表达式.利用解析式可方便地得到在偏置点处二阶和三阶高次项同时为零的高线性MZ光调制器的设计方案.同时对微环辅助MZ光调制器的特性进行了分析.     

Optical Single-Sideband Modulators and Their Applications

We review our recent work in the implementation of optical single-sideband (OSSB) modulation and in the application of this modulation format to microwave photonics and optical testing systems. We have developed an enhanced OSSB modulator for wide-band operation, the so-called bidirectional OSSB modulator, and a simplification of this scheme for narrow-band applications. These OSSB modulators are based on the use of a standard single-electrode Mach-Zehnder electro-optic modulator (MZ-EOM) and passive fiber-optic components. In both designs, the OSSB operation is shown to be independent of the MZ-EOM bias. Therefore, the optical modulation depth at the output of the device can be enhanced using minimum transmission biasing to provide suppression of the optical carrier. Finally, we demonstrate the application of OSSB modulators to the improvement of microwave/millimeter-wave subcarrier multiplexing fiber-optic links and to narrow-band fiber radio systems. In addition, we analyzed the feasibility and the limitations of an optical vector network analysis technique based on OSSB modulation that can provide sub-picometer wavelength resolution.     

Optical Single-Sideband Modulators and Their Applications

We review our recent work in the implementation of optical single-sideband (OSSB) modulation and in the application of this modulation format to microwave photonics and optical testing systems. We have developed an enhanced OSSB modulator for wide-band operation, the so-called bidirectional OSSB modulator, and a simplification of this scheme for narrow-band applications. These OSSB modulators are based on the use of a standard single-electrode Mach-Zehnder electro-optic modulator (MZ-EOM) and passive fiber-optic components. In both designs, the OSSB operation is shown to be independent of the MZ-EOM bias. Therefore, the optical modulation depth at the output of the device can be enhanced using minimum transmission biasing to provide suppression of the optical carrier. Finally, we demonstrate the application of OSSB modulators to the improvement of microwave/millimeter-wave subcarrier multiplexing fiber-optic links and to narrow-band fiber radio systems. In addition, we analyzed the feasibility and the limitations of an optical vector network analysis technique based on OSSB modulation that can provide sub-picometer wavelength resolution.     

Concurrent generation of an optical code label and payload data by use of phase and intensity modulators for all-optical packet switching

We propose and experimentally demonstrate the concurrent generation of an optical code label and payload data by use of off-the-shelf optical intensity and phase modulators in a tandem structure. This technique is capable of reconfigurable generation of an arbitrarily long optical code label of phase-shift keying concurrently with the generation of payload data, without the need for a special class of optical encoder. This technique will be powerful for all-optical packet switching networks, based on scalability and compactness, for optical code labels.     

Analyses for various doping structures of SOI-based optical phase modulator using free carrier dispersion effect

This paper highlights the study on various structure of silicon-on-insulator (SOI) optical phase modulators based on free carrier dispersion effect. The proposed modulators employ the forward biased P-I-N diode structure integrated in the waveguide and will be working at 1.55 μm optical telecommunications wavelength. Three kinds of structure are compared systematically where the p+ and n+ doping positions are varied. The modeling and characterization of the SOI phase modulators was carried out by 3D numerical simulation package. Our results show that the position of doping regions have a great influences to the device performance. It was discovered that the best structure in this work demonstrated modulation efficiency of 0.015 V cm with a length of 155 μm.