Optical MEMS for Lightwave Communication

The intensive investment in optical microelectromechanical systems (MEMS) in the last decade has led to many successful components that satisfy the requirements of lightwave communication networks. In this paper, we review the current state of the art of MEMS devices and subsystems for lightwave communication applications. Depending on the design, these components can either be broadband (wavelength independent) or wavelength selective. Broadband devices include optical switches, crossconnects, optical attenuators, and data modulators, while wavelength-selective components encompass wavelength add/drop multiplexers, wavelength-selective switches and crossconnects, spectral equalizers, dispersion compensators, spectrometers, and tunable lasers. Integration of MEMS and planar lightwave circuits, microresonators, and photonic crystals could lead to further reduction in size and cost     

光通信中的LiNbO3集成波导电光器件

本文介绍了现在应用的几种LiNbO_3集成波导电光器件,讨论了调制器、开关、偏振器、滤光器等的工作机制和性能,并侧重介绍了当今光通信中应用最多的调制器件。     

High-density integrated planar lightwave circuits using SiO2-GeO2 waveguides with a high refractive indexdifference

GeO₂-doped silica waveguides with a high refractive index difference of 1.5% are successfully fabricated on Si substrates. Their propagation loss, measured in 200-cm-long test circuits with a minimum curvature radius of 2 mm, is 0.073 dB/cm. The waveguides are used as high-density integrated planar lightwave circuits in 1×4 Mach-Zehnder (MZ) type multi/demultiplexers for optical frequency division multiplexing (FDM) transmission systems and in modified MZ type multi/demultiplexers with a ring resonator, which have a compact device size of 15×50 mm² and a frequency spacing of 10 GHz     

Planar lightwave circuit platform with coplanar waveguide foropto-electronic hybrid integration

We propose a planar lightwave circuit (PLC) platform constructed on a silica-on-terraced-silicon (STS) substrate for opto-electronic hybrid integration. This platform consists of an embedded silica PLC region, a terraced silicon region for optical device assembly, and a high-speed electrical circuit region. In the electrical circuit region, the coplanar waveguides (CPW) are prepared on a thick-silica/silicon substrate. This structure reduces the propagation loss of the CPW drastically to 2.7 dB/cm at 10 GHz, because the loss tangent (tan δ) of the dielectric constants of silica is much smaller than that of silicon. In order to study the feasibility of this PLC-platform for multi-gigabit operation, we used it to fabricate an LD module in which an LD chip and LD-driver integrated circuits (IC) are assembled on the PLC-platform. A bit error rate measurement of this LD module in a 2.5 Gb/s NRZ showed that this platform is applicable to multi-gigabit optical signal processing     

Liquid crystal variable optical attenuators integrated on planarlightwave circuits

Variable optical attenuators using polymer-network liquid crystal have been integrated with the pitch of 250 μm on planar lightwave circuits. Trenches are cut in the direction perpendicular to the parallel light waveguides into planar lightwave circuits, a transparent electrode is deposited inside the trenches, and the trenches are filled with polymer-network liquid crystal. The typical attenuation range is 18 dB when the driving voltage is <20 Vrms at 1.55-μm wavelength. The power consumption is estimated to be very low (200 nW/ch)     

A 10 Gb/s hybrid-integrated receiver array module using a planarlightwave circuit (PLC) platform including a novel assembly regionstructure

A planar lightwave circuit (PLC) platform for optoelectronic hybrid integration shows potential for achieving 10 Gb/s operation. It uses AuSn bump-type bonding pads on a silica layer to decrease parasitic capacitance, which limited the CR time constant in the optical chip assembly region, and two-layer electrical wiring to reduce parasitic inductance, which caused resonance in the electrical circuit region. An arrayed receiver module fabricated by integrating a two-channel monolithic opto-electronic integrated circuit (OEIC) chip on the PLC platform demonstrated a 3 dB-bandwidth of 8 GHz in both channels, which is equal to the bandwidth of the OEIC chip. This shows the feasibility of using this PLC platform for multichannel 10 Gb/s operation. Furthermore, this PLC platform can combine the versatile optical circuit functions of a PLC, such as an arrayed-waveguide grating wavelength multiplexer, with the high-speed signal processing function of mature electronic IC circuits. Consequently, this platform is a key device that will lead to high-capacity optical signal processing systems using optical wavelength/frequency routing     

Optical-signal-processing device based on waveguide-type variable delay lines and optical gates

In this paper, an optical-signal-processing device mainly designed for time-slot switching is demonstrated. The device is composed of variable delay-line arrays fabricated by planar lightwave circuit technology and high-speed optical gates. The variable delay-line arrays consist of transversal-form or lattice-form optical circuits. The operating principle is based on serial-to-parallel conversion, adjustment of the delay time between the parallel signals, and the gating of the optical bits or packets in the optical region. The device does not require any interaction between lightwaves through optical nonlinear effects or filter banks for code matching. As an example of its operation, label-processing functions are demonstrated, specifically the label swapping of optical return-to-zero pulses. The merits of the proposed device are described and problems that must be solved are also discussed.     

Novel realization of monotonic Butterworth-type lowpass, highpass,and bandpass optical filters using phase-modulated fiber-opticinterferometers and ring resonators

A novel realization of monotonic Butterworth-type lowpass, highpass, and bandpass optical filters (from their electrical digital filter characteristics) by cascading the all-pole and all-zero resonators is presented. A graphical method for fast derivation of the transfer functions, quick inspection of the resonance effects, and important characteristics of any photonic circuits is described. It is shown that incorporation of the optical amplifiers and optical phase modulators into the delay lines of two basic optical resonators, whose pole and zero can be adjusted independently of each other, provides great design flexibility which would otherwise not possible using conventional passive optical resonators. Possible applications of these optical filters as optical pulse equalizers and receiver shaping filters in long-haul coherent lightwave transmission systems are discussed. Possible application of basic resonators comprising of optical phase modulators as tunable optical filters for spectrum analyzers is also considered     

InGaAsP/InP monolithic integrated circuit with lasers and an optical switch

InGaAs/InP monolithic integrated circuits composed of a compact carrier-injection optical switch and distributed feedback laser diodes are fabricated. These integrated circuits have a variety of functions, such as monolithic modulators, switches and optical amplifiers for optical communication systems.     

Integrated acoustooptic and magnetooptic devices for opticalinformation processing

Acoustooptic (AO) Bragg interactions between guided optical waves and surface acoustic waves (SAW's) and the resulting AO Bragg cell modulators have evolved in integrated AO technology in recent years. A variety of hybrid multichannel integrated AO device modules including power and interferometric RF spectrum analyzers, space switches, tunable filters, frequency shifters and modulators, analog algebraic processors, programmable correlators and other multichannel device modules have been realized in common LiNbO₃ substrate up to 1.0×3.7 cm ² in maximum size. The prospects for realization of their counterparts in monolithic integrated format in a common substrate of InGaAsP material system are also significantly enhanced recently. These AO device modules have shown a high degree of modularity and suggested applications in optical information processing and communications. In the meantime, the magnetooptic (MO) Bragg interactions between guided optical waves and magnetostatic waves (MSWs) in yttrium iron garnet-gadolinium gallium garnet (YIG-GGG) waveguides have resulted in miniaturized MO Bragg cell modulators in analogy with the guided-wave AO Bragg cell modulators. Most recently the performance of such MO Bragg cell modulators has been significantly improved and the modulators have been integrated with ion-milled waveguide lenses to realize hybrid integrated MO device modules, and have been utilized to demonstrate a number of novel applications. In this paper, a review of some of these integrated AO and MO device modules and applications together with some unpublished new results are presented     

SOI光波导高速电光调制器的研究进展

介绍了不同截面大小的SOI(silicon-on-insulator)波导单模条件,详细描述了几种降低传输损耗,消除偏振相关,提高耦合效率的技术手段.分析比较了一种带有MOS(metal-oxide-semiconductor)电容结构和一种具有微环结构的高速电光调制器,其调制频率分别达到10和1.5GHz.     

Guided-wave devices for optical communication

We review the current status of guided-wave optical communication devices. The operation and presently demonstrated performance characteristics of waveguides switches, modulators, filters, and polarization transforming devices are discussed. Emphasis is given to recent developments with very high speed modulators and polarization insensitive devices.     

Coherent optical transversal filter using silica-based waveguidesfor high-speed signal processing

A coherent optical transversal filter with a tapped delay-line structure is described. Utilizing phase information this filter can express arbitrary tap coefficients (including general complex numbers) by coherently combining tapped signals. Experimental filters using silica-based single-mode optical waveguides, monolithically integrated on silicon substrates were developed for stable and high-speed operation. Experimental results demonstrate the operating capabilities of the filters for high-speed signal processing. The operating bandwidth was experimentally estimated. Degradation of the frequency characteristics due to both deviation of fiber fabricating parameters and errors in setting tap-coefficients has been estimated theoretically     

硅基光波导及光波导开关的研究进展

ＳｉＯ２ 光波导、重掺杂光波导、ＳＯＩ光波导、合金光波导及聚合物光波导等低损耗硅基光波导的研究已取得了很大的进展,随着这些波导的硅基光开关不断研制出来,各种光开关结构也不断提出来了。为了解决硅的线性电光系数为零的问题,采用了多种方法,以获得强的线性电光效应,实现高速光开关。文章回顾了近十年来硅基光波导及光开关的研究进展。     

Negative refraction in a Si-polymer photonic Crystal membrane

We have observed negative refraction in a photonic crystal (PC) membrane structure at near-infrared wavelengths. The device is fabricated on a silicon-on-insulator substrate and consists of a silicon rod matrix suspended in a polymer where optical energy is delivered by ridge waveguides with various incident angles. The propagation direction inside the PC shows extraordinary refraction with an angle consistent with our two-dimensional numerical simulations. To our knowledge, this is the first experimental observation of isotropic negative refraction in a Si-based planar PC structure at optical frequencies. The realization of negative refraction in a planar Si-based system enables applications in negative index imaging to be integrated into compact optical circuits.     

Coupling efficiencies in reflective self-organized lightwave network (R-SOLNET) simulated by the beam propagation method

The reflective self-organized lightwave network (R-SOLNET) enables the formation of self-aligned waveguides in the photorefractive (PR) material between misaligned optical devices by introducing a write beam. The incident write beam from one device and the reflected write beam from the second device induce self-focusing in the PR material and construct a coupling waveguide. A wavelength filter on the waveguide edge is used to facilitate the reflected beam. The beam propagation method reveals that R-SOLNET exhibits higher coupling efficiencies and better tolerances than the one-beam-writing SOLNET and the free-space coupling. The apparent usefulness of R-SOLNET is remarkable for gaps wider than 100 /spl mu/m in 8-/spl mu/m-wide waveguide circuits. For 240-/spl mu/m gap, coupling efficiency better than 50% can be achieved even when the lateral misalignment is as large as 4 /spl mu/m. The results indicate that R-SOLNET may be useful for vertical waveguide constructions of optical z-connections in three-dimensional intrachip optical interconnects and switching systems, as well as for self-aligned optical couplings with devices that cannot emit write beams such as vertical-cavity surface-emitting lasers, photodetectors, and electrooptic switches.     

Demultiplexing of 168-Gb/s data pulses with a hybrid-integratedsymmetric Mach-Zehnder all-optical switch

We have developed a hybrid-integrated symmetric Mach-Zehnder all-optical switch and evaluated the demultiplexing of 168-Gb/s data pulses at a repetition rate of 10 GHz with this switch. A compact, stable device was realized by assembling semiconductor optical amplifiers as nonlinear waveguides on a planar lightwave circuit in a self-aligned manner. A 6.0-ps switching window needed for 168-Gb/s demultiplexing was provided by the push-pull operation of the symmetric Mach-Zehnder all-optical switch. Demultiplexed signal light showed a high extinction ratio of better than 18 dB. Error-free demultiplexing with a bit error rate of 10^-11 was achieved     

Theoretical analysis of integrated collimating waveguide lens

An integrated collimating waveguide lens is analyzed for applications which require the focusing of an optical beam onto the waveguide of a planar lightwave circuit. The lens has a refractive index profile which is parabolically graded as a function of height to focus light in the vertical plane, and has a convex front face to focus light in the horizontal plane. Analysis based on the propagation of a Gaussian field is used to design a lens pair which minimizes the optical loss for a given propagation length. The beam propagation method is used to identify fabrication tolerances which may have impact on the performance of the lens pair. The lens pair has application in micro-optoelectromechanical (MOEM) switches based on planar optical waveguide circuits.     

Proposal of a DMUX with a Fabry-Perot all-reflection filter-basedMMIMI configuration

Proposes a novel optical device for (de)multiplexing. The device is based on a Bragg grating assisted multimode interference Michelson interferometer (MMIMI) coupler. The analysis is based on the mode propagation theory. Silica-on-silicon planar lightwave circuits is presently the most promising technology for realizing this kind of device     

TM-pass polymer modulators with poling-induced waveguides and self-aligned electrodes

Transverse magnetic (TM) mode selective polymer Mach-Zehnder modulators with self-aligned electrodes were fabricated for the first time in the electro-optic polymer material APC-CPW1 by employing a poling-induced (PI) writing method. The waveguides support only a TM polarisation, when an arbitrarily polarised optical source is incident. Modulators with a single 3 cm long driving electrode show a V/sub /spl pi// of 3.5 V at 1.55 /spl mu/m.