Lightwave Components Research Articles

Simple method for frequency response measurement of photodetectors based on wavelength-to-time mapping.

A simple method is proposed for measuring frequency responses of photodetectors (PDs) based on wavelength-to-time mapping in this paper. The proposed method is an all-optical scheme, which is simple, fast, accurate and free from any extra calibration. Optical pulses emitted from a mode-locked laser are firstly pre-chirped by a spool of dispersive compensation fiber. In this way, the frequency spectrum of the pulses is mapped into time domain. Then, the pre-chirped pulses beat with a reference continuous wave laser with a fixed wavelength in the PD under test and generate a linearly chirped microwave signal. The frequency response information of the PD can be decoded by analyzing the generated linearly chirped microwave signal. Experimental results show that the frequency response of the PD with 3-dB bandwidth of ∼15GHz has been accurately measured with a resolution of ∼390MHz. The measurement result agrees well with the one measured by the commercial lightwave component analyzer.

Engineered Stresses for a Functional Si Light Emitter at Bandgap: An Overview

Interfacing various materials results in stresses and strains that typically alter the properties of either or both interfaced surfaces. In this work, we focus on enhanced light emission properties at the bandgap for silicon interfaced with silica or layers of silica and silicon nitride. This discovery is corroborated by several evidences of engineered stresses and strains at the bulk or interface such as implantation and/or diffusion of dopants in silicon and rough silicon surfaces formed by wafer cutting or etching and patterning. Silicon light emitters are being eagerly sought, and upon achieving reasonable efficiencies, they may be at hand soon. The significant investment in Si-photonics by dominant semiconductor players implies that such devices will be welcomed particularly in applications such as optical emitters for next-generation integrated optical circuits and interconnects; all-Si transceivers and cross connects for integrated circuit chips; light-wave components and high-power discrete and array emitters. Engineered stresses and strains modulate the indirect Si bandgap, resulting in enhanced radiative electron–hole recombination, which competes more effectively with non-radiative recombination.

High-responsivity 40 Gbit/s InGaAs/InP PIN photodetectors integrated on silicon-on-insulator waveguide circuits**Project supported by the High-Tech Research and Development Program of China (Nos. 2015AA016904, 2015AA012302), the National Basic Research Program of China (Nos. 2012CB933503, 2013CB932904), and the National Natural Foundation of China (Nos. 61274069, 61176053, 61021003, 61435002).

This paper presents a high-responsivity and high-speed InGaAs/InP PIN photodetector integrated onto the silicon waveguide substrate utilizing the divinyltetramethyldisiloxane-benzocyclobutene (DVS-BCB) adhesive bonding method. A grating coupler is adopted to couple light from the fiber to the silicon waveguide. Light in the silicon photonic waveguide is evanescently coupled into the photodetector. The integrated photodetector structure is first simulated using the FDTD (finite difference time domain) solutions software and the simulation results show a detection efficiency of 95%. According to the simulation result, the integrated photodetector is fabricated. The measured responsivity of the fabricated integrated photodetector with a detection length of 30 μm is 0.89 A/W excluding the coupling loss between the fiber and the grating coupler and the silicon propagation loss at the wavelength of 1550 nm with a reverse bias voltage of 3 V. Measured 3-dB bandwidth is 27 GHz using the Lightwave Component Analyzer (LCA). The eye diagram signal test results indicate that the photodetector can operate at a high speed of 40 Gbit/s. The integrated photodetector is of great significance in the silicon-based optoelectronic integrated chip which can be applied to the optical communication and the super node data transmission chip of the high-performance computer.

Extracting S-parameters of bilateral electro-optic network for lightwave component analyzer calibration

A new method for extracting E/O and O/E S-parameters of a bilateral electro-optic network (BEON) is theoretically proposed. It is based on measuring reflection coefficients from three optical loads: an absorber and two mirrors. This technique includes two series of reflections measurements: first when loads are connected to optical port of BEON directly and second when loads are connected in series with optical waveguide of fixed length. Using two BEONs and this calibration technique allows to make calibrated lightwave measurements with a standard microwave network analyzer without using additional electro-optical equipment such as lightwave component analyzer or optical heterodyne techniques.

Controlling the spectrum of photons generated on a silicon nanophotonic chip.

Directly modulated semiconductor lasers are widely used, compact light sources in optical communications. Semiconductors can also be used to generate nonclassical light; in fact, CMOS-compatible silicon chips can be used to generate pairs of single photons at room temperature. Unlike the classical laser, the photon-pair source requires control over a two-dimensional joint spectral intensity (JSI) and it is not possible to process the photons separately, as this could destroy the entanglement. Here we design a photon-pair source, consisting of planar lightwave components fabricated using CMOS-compatible lithography in silicon, which has the capability to vary the JSI. By controlling either the optical pump wavelength, or the temperature of the chip, we demonstrate the ability to select different JSIs, with a large variation in the Schmidt number. Such control can benefit high-dimensional communications where detector-timing constraints can be relaxed by realizing a large Schmidt number in a small frequency range.

Coherent synthesis of optical multilevel signals by electrooptic digital-to-analog conversion using multiparallel modulator

This paper presents an electrooptic vector digital-to-analog converter (EO-DAC) for coherent synthesis of optical multilevel signals, such as quadrature-amplitude modulation (QAM) signals. For generation of an optical multilevel/QAM signal, the inphase (I) and quadrature (Q) components of a carrier lightwave should be orthogonally modulated in multi-levels. Conventionally, inphase-quadrature (IQ) orthogonal modulators have been utilized for this purpose. In the scheme, however, the symbol rate available for multilevel/QAM signals is limited, and it is difficult to obtain a clear constellation because of the difficulty involved in handling with electrical multilevel signals. The EO-DAC employing multiparallel modulator, described in this paper, can be used to synthesize multilevel signals through the combination of binary data streams. Using this proposed technology, multilevel signals can be coherently synthesized at a high bit rate, and clearer constellations can be obtained. Further, because of its flexibility, and versatility, the EO-DAC can be used for the several types of multilevel modulation formats. In this paper, we describe the EO synthesis of optical multilevel signals especially focusing on the method based on the EO-DAC, along with comparisons with other conventional methods.

Measurement of microwave behavior in optical links

The aim of this article is to give an overview of how S-parameter techniques can be used and misused to measure the behavior of microwave photonic components and links-a field known as lightwave component analysis. Along the way, we clarify what is meant by the term behavior when it is applied to what in effect are nonmicrowave components. We find that while it is desirable to extend the S-parameter approach to the lightwave domain, it is not as easy as we would hope.

Light emission from silicon: Some perspectives and applications

Research on efficient light emission from silicon devices is moving toward leading-edge advances in components for nano-optoelectronics and related areas. A silicon laser is being eagerly sought and may be at hand soon. A key advantage is in the use of silicon-based materials and processing, thereby using high yield and low-cost fabrication techniques. Anticipated applications include an optical emitter for integrated optical circuits, logic, memory, and interconnects; electro-optic isolators; massively parallel optical interconnects and cross connects for integrated circuit chips; lightwave components; high-power discrete and array emitters; and optoelectronic nanocell arrays for detecting biological and chemical agents. The new technical approaches resolve a basic issue with native interband electro-optical emission from bulk Si, which competes with nonradiative phonon- and defect-mediated pathways for electron-hole recombination. Some of the new ways to enhance optical emission efficiency in Si diode devices rely on carrier confinement, including defect and strain engineering in the bulk material. Others use Si nanocrystallites, nanowires, and alloying with Ge and crystal strain methods to achieve the carrier confinement required to boost radiative recombination efficiency. Another approach draws on the considerable progress that has been made in high-efficiency, solar-cell design and uses the reciprocity between photo- and light-emitting diodes. Important advances are also being made with silicon-oxide materials containing optically active rare-earth impurities.

A Comparison of three Novel Optical Wavelength Filters with Cascaded Directional Couplers

We compare three novel structures of optical wavelength filters. They are composed of cascaded directional couplers. The improved filtering devices have narrower lateral widths and occupy smaller areas than our original design. And their optical characteristics and performances are analyzed by the finite difference beam propagation method employing the Runge-Kutta method (RKBPM). The simulation results shows that these new types of filters have better suppression of lightwave components at short wavelengths.

Integrated electroabsorption attenuator-photodetector for optical power control in WDM transmission systems

A new InP-based waveguide device capable of functioning simultaneously as an optical power monitor and variable optical attenuator is reported. It allows easy integration with passive InP-based lightwave components by using a new technique referred to as single-mode vertical integration. The device exhibits high on-chip responsivity of /spl sim/0.93 A/W and attenuation values exceeding 25 dB. It is shown to effectively stabilize a time-varying input power signal by monitoring the input light level while simultaneously adjusting its internal attenuation. Integrated with planar (de)multiplexers, it enables very compact, monolithically integrated components for power controlling in WDM transmission systems to be realized.

A bilateral lightwave network analyzer-architecture and calibration

The first bilateral lightwave network analyzer (BLNA) architecture that is capable of two-port S-parameter measurements is reported in this paper. A combined two-tier calibration is proposed and implemented for electrooptic and optoelectronic measurements. Calibrated measurement results showing the good performance of the BLNA for all types of lightwave components are also presented.

RF small-signal equivalent circuitof MQW InGaAs/InAlAselectroabsorption modulator

An RF small-signal equivalent circuit of an MQW InGaAs/InAlAs electroabsorption modulator has been developed and compared with measurements of the responsivity and impedance in the photodetector mode. Calibrated optical/electrical and electrical measurements were performed with a 20 GHz lightwave component analyser by contacting the modulator directly with a coplanar on-wafer probe.

Simulation and implementation of lightwave component characterization using a bilateral electro-optic network

The simulation and implementation of a bilateral electro-optic network has been demonstrated. The advantage of the proposed network is that it can be used as a black box to convert a microwave network analyzer into a two-port lightwave network analyzer. Simulations have been carried out to determine the sensitivity of the bilateral network to optical reflections. Measurement results on one-port optical structures are more accurate than those obtained with commercial lightwave analyzers and indicate the viability of this approach for full two-port lightwave measurements.

A transfer standard for measuring photoreceiver frequency response

We have developed a photoreceiver frequency response transfer standard which can be used to measure the optical modulation transfer function of a modulated optical source. It combines a photodiode with an RF power sensor or an amplified receiver with an RF power sensor. It is calibrated with an expanded uncertainty of 0.06 dB (coverage factor=2) using a heterodyne technique at 1.319 /spl mu/m. We present a theory which allows use of the transfer standard with arbitrary source modulation depth. The calibration is transferred to a SDH/SONET test equipment manufacturer giving a final uncertainty well below the 0.3 dB uncertainty specified by ITU-TS (formerly CCITT) recommendation G.957. The transfer standard may have other applications including calibration of CATV test equipment, light-wave component analyzers, and light-wave spectrum analyzers.

Current status of lightguide component and device technologies in Korea

We review the current state of lightwave component and device technology in South Korea, particularly focusing on the recent progress in research, development and implementation in conjunction with a government programme. The plan for the communications infrastructure is being conducted in three stages. The first stage consists of installation of optical fibre cables interconnecting all the cities in South Korea as well as digitalization of the telecommunications networks by 1997. The second stage (1997 to 2001) will make available optical fibre network for CATV to apartment complexes and densely populated areas to provide the subscribers with multimedia services of the future. The third stage of the plan will start in 2002, and will offer broader applications of B-ISDN for user networks supporting broadband local loop. Along with these major projects, our current activities in the three major areas of optical fibre components and devices, microoptics and integrated optics, and optical fibre sensors are discussed.

Standards to support lightwave communications

Lightwaves are becoming the dominant communication medium, advanced by the successful development of fiber-optic technology. A crucial element in maintaining and extending the practical and economic success of fiber optics has been effective measurement supported by reliable measurement standards. Standards are now available for the important physical and transmission properties of optical fiber, however, the development of more complex, higher capacity systems is creating new measurement challenges. Lower uncertainties in existing standards are needed as system designers demand even tighter system margins, while the performance of active and passive lightwave components is becoming a significant strategic issue, calling for new standards. In addition, optical frequency standards are being developed to support frequency and wavelength division multiplexing techniques, which will allow the enormous bandwidth of fibers to be exploited.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Measurement of dispersion and nonlinearity in murtiamplifier systems

A lightwave component analyser is used to measure the frequency response of a 6300km optically amplified testbed. The position of the nulls is shown to be very sensitive to the fibre parameters and the optical power level and agrees well with numerical predictions. Such measurements could be used to detect any changes occurring between factory tests and the installation of a long-haul optically amplified system.

Simple dispersion measurement technique with high resolution

A new highly accurate dispersion measurement technique is presented, which uses a standard lightwave component analyser. By employing a tunable external laser source the dispersion is measured over a wavelength range of 70 nm with an accuracy of 0.02 ps/km/nm, which enables us to observe dispersion fluctuations and substructures on the dispersion curve.

Novel electrical noise source based on lightwave components

A novel electrical noise source is proposed, based on lightwave components and internal shot-noise calibration, which offers an attractive alternative to conventional 50-Ω noise sources. This report describes the principle, and the experimental verification of various quality aspects like linearity, absolute accuracy, and impedance robustness. © 1992 John Wiley & Sons, Inc.

Link analysis of a deformable mirror device based optical crossbar switch

An optical crossbar switch is proposed that uses a semiconductor-addressed, deformable-mirror spatial light modulator to direct gigabit-per-second optical transmissions to several receivers. The switch performance is described in terms of size, number, and deflection range of micromechanical mirror elements, as well as emitter, detector, and lens dimensions. These parameters are incorporated in a link energy budget and estimates of system dimensions. Maximum-sized 128- to 1000-channel crossbars appear feasible based on current and projected performance limits of various lightwave components.