Silicon oxynitride integrated waveguide for on-chip optical interconnects applications

This work explores the microfabrication technology for realizing miniature waveguide structure for on-chip optical interconnects applications. Thick oxynitride films were prepared by plasma enhanced chemical vapor deposition (PECVD) with N₂O, NH₃ and SiH₄ precursors. The composition and the bonding structure of the oxynitride films were investigated with Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and secondary ion mass spectroscopy. Results showed that the silicon oxynitride deposited with gas flow rates of NH₃/N₂O/SiH₄ = 10/400/10 (sccm) has favorable properties for integrated waveguide applications. The refractive index of this layer is about 1.5 and the layer has comparative low densities of O–H and N–H bonds. The hydrogen bonds can be further eliminated with high temperature annealing of the as-deposited film in nitrogen ambient and the propagation loss can be reduced significantly with thermal annealing. An integrated miniature waveguide with cross-section of 2 μm × 3 μm was realized with the proposed technology. The waveguide is able to transmit signal in either TE or TM mode with propagation loss <0.6 dB/cm (at 1550 nm) and bending radius of about 6 μm.     

Monolithic wavelength-graded VCSEL and resonance-enhancedphotodetector arrays for parallel optical interconnects

Monolithic arrays of wavelength-graded vertical-cavity surface-emitting lasers (VCSELs) and resonance-enhanced photodetectors (PDs) have been realized with the same epilayer structure using the topography-controlled enhancement and reduction of the metal-organic chemical vapor deposition (MOCVD) growth rate on a patterned substrate. The repeatability of this technique was demonstrated by using different VCSEL and resonance-enhanced photodetector (REPD) arrays from the same wafer     

High-brightness slab-coupled optical waveguide laser arrays

We have constructed high brightness slab-coupled optical waveguide laser arrays. Devices in the array emit in large nearly circular single-spatial modes. We have shown that optical cross-coupling in closely spaced devices is not an issue for maintaining single-mode output, including the effects of slab-coupling. By appropriate heat-sinking, we have shown linear continuous-wave power densities of 98 W/cm along the array emission aperture.     

Spatial optical solitons in waveguide arrays

We overview theoretical and experimental results on spatial optical solitons excited in arrays of nonlinear waveguides. First, we briefly summarize the basic properties of the discrete nonlinear Schrodinger (NLS) equation frequently employed to study spatially localized modes in arrays, the so-called discrete solitons. Then, we introduce an improved analytical model that describes a periodic structure of thin-film nonlinear waveguides embedded into an otherwise linear dielectric medium. Such a model of waveguide arrays goes beyond the discrete NLS equation and allows studying many new features of the nonlinear dynamics in arrays, including the complete bandgap spectrum, modulational instability of extended modes, different types of gap solitons, the mode oscillatory instability, the instability-induced soliton dynamics, etc. Additionally, we summarize the recent experimental results on the generation and steering of spatial solitons and diffraction management in waveguide arrays. We also demonstrate that many effects associated with the dynamics of discrete gap solitons can be observed in a binary waveguide array. Finally, we discuss the important concept of two-dimensional (2-D) networks of nonlinear waveguides, not yet verified experimentally, which provides a roadmap for the future developments of this field. In particular, 2-D networks of nonlinear waveguides may allow a possibility of realizing useful functional operations with discrete solitons such as blocking, routing, and time gating.     

Guided-wave planar optical interconnects using highly multiplexedpolymer waveguide holograms

An intraplanar interconnection scheme using substrate guided modes in conjunction with a highly multiplexed waveguide volume hologram is proposed. Acoustooptically addressed 1-to-50 passive and 1-to-2-to-100 reconfigurable interconnections with a fan-out diffraction efficiency of 55% at 514-nm wavelength are demonstrated. A coordinate transformation converts the 3-D diffraction problem into a 2-D one, which significantly simplifies the theoretical calculation. Intraplane massive fan-out optical interconnection using substrate guided mode provides both collinear and coplanar fan-out capability for data and clock signals. Colinearity of signal distribution allows the 2-D input signal array to be processes. The laminated waveguide device containing a highly multiplexed dichromated gelatin (DCG) hologram has been evaluated     

Flexible optical waveguide film fabrications and optoelectronic devices integration for fully embedded board-level optical interconnects

This paper demonstrates a flexible optical waveguide film with integrated optoelectronic devices (vertical-cavity surface-emitting laser (VCSEL) and p-i-n photodiode arrays) for fully embedded board-level optical interconnects. The optical waveguide circuit with 45/spl deg/ micromirror couplers was fabricated on a thin flexible polymeric substrate by soft molding. The 45/spl deg/ couplers were fabricated by cutting the waveguide with a microtome blade. The waveguide core material was SU-8 photoresist, and the cladding was cycloolefin copolymer. A thin VCSEL and p-i-n photodiode array were directly integrated on the waveguide film. Measured propagation loss of a waveguide was 0.6 dB/cm at 850 nm.     

Design and analysis of novel multimode optical filters indielectric waveguide

A new multimode filter design for wavelength multiplexing/demultiplexing applications is investigated. An asymmetric bend generates a number of higher-order modes with appropriate amplitudes from a single-mode incident wave containing two wavelengths. These modes, after travelling along a straight section of multimode waveguide, are recombined in the output Y-branch in such a way that the optical signals at two wavelengths are split and redirected toward different output branches. The structure is analyzed by a combination of finite-difference/time-domain (FD/TD) procedure and a recently developed physical optics method. Numerical results on a sample structure are presented and issues related to the accuracy of results are addressed     

Comparison of different polymeric multimode star couplers forbackplane optical interconnect

This paper describes a comparison of three types of 8×8 multimode star couplers made in polymeric multimode waveguides. Their geometry was designed with a ray tracing tool, measurements show low loss for all designs, but a symmetrical design, based on a tree of Y-junctions yields the best uniformity     

Propagation model for multimode optical-fibre waveguide

Pulse dispersions of 5 ps/m have been measured in cladded-glass and liquid-core multimode fibres. A theoretical model is proposed which gives excellent agreement with measured propagation delay and pulse dispersion. In the fibres used, there is little light scattering either in the core or at the core-cladding interface.     

High performance selectively oxidized VCSELs and arrays forparallel high-speed optical interconnects

High-bandwidth single-mode selectively oxidized vertical-cavity surface-emitting laser (VCSEL) arrays operate at 980 nm or 850 nm emission wavelength for substrate or epitaxial side emission. Coplanar feeding lines and polyimide passivation are used to reduce electrical parasitics in top-emitting GaAs and bottom-emitting InGaAs VCSELs. To enhance fundamental single-mode emission for larger devices of reduced series resistance a surface relief transverse mode filter is employed. Fabricated VCSELs are applied in various interconnect schemes. InGaAs quantum-well based VCSELs at 935 nm emission wavelength are investigated for use in perfluorinated graded-index plastic-optical fiber (GI-POF) links. We obtain a 7 Gb/s pseudo random bit sequence (PRBS) nonreturn-to-zero (NRZ) data transmission over 80 m long 155 μm diameter GI-POF. We investigate data transmission over standard 1300 nm, 9 μm core diameter single-mode fiber with selectively oxidized single-mode GaAs and InGaAs VCSELs. We achieve biased 3 Gb/s and bias-free 1 Gb/s pseudo-random data transmission over 4.3 km at 830 nm emission wavelength where a simple fiber mode filter is used to suppress intermodal dispersion caused by the second order fiber mode. For the first time, we demonstrate 12.5 Gb/s data rate transmission of PRBS signals over 100 m graded-index multimode fiber or 1 km single-mode fiber using high performance single-mode GaAs VCSELs of 12.3 GHz modulation bandwidth emitting at λ=850 nm     

High-power two-dimensional waveguide CO2 laser arrays

A two-dimensional, 39 element array of waveguide carbon dioxide lasers has produced a total CW laser power output of 750 W, using RF excitation of a compact, close packed assembly. Thermal effects associated with close-packing in the array are evaluated in terms of discharge wall temperature rise and cavity mirror distortion. The array elements are shown to have a 30% power derating relative to a single isolated laser channel, caused mainly by internal temperature rise. Mirror distortion and waveguide constructional errors do not degrade the beam quality of the array emission, which matches the theoretical value. However mirror distortion is shown to be responsible for a large spread in laser frequency between channels in the array. Based on the results, prospects are good for the construction of larger, multikilowatt incoherent arrays     

Calculation of approximate propagation characteristics for any given two-dimensional optical waveguide

An approximation technique of determining propagation characteristics of a given cross-section graded-index optical waveguide is presented. The numerical technique gives very short computational times and is easy to use.     

Real-time 850 nm multimode VCSEL to 1 550 nm single mode VCSEL data routing for optical interconnects

Short-reach optical interconnects among massive serves in data centers have attracted extensive research recently. Increasing capacity, cost and power efficiency as well as wavelength switching between data center network nodes are still key challenges for current optical interconnects. In this work, we experimentally demonstrate the real-time inter-mode optical wavelength switching technique, for high-speed wavelength flexible data center interconnects. A 10 Gbit/s 1 550 nm single mode vertical cavity surface emitting laser (VCSEL) is optically injected and used to control a 10 Gbit/s multimode VCSEL carrier at 850 nm. Results show that a clearly open eye diagram is achieved at back-to-back analysis, implying a successful wavelength switch and error-free operation at 10 Gbit/s. A fully optical wavelength conversion of a multimode VCSEL operation at 850 nm using a single mode VCSEL subject to external optical injection at 1 550 nm is reported. This work opens new perspectives towards the development of a cost effective high-speed real-time inter-band wavelength switching technique between servers and network devices operating at different transmission windows at network nodes, for current and future optical interconnects.     

多模掩埋式平面玻璃波导的制作及测试

利用加电场的离子交换和热处理等方法制作膜厚深的多模玻璃波导,并采用二步法制作了多模掩埋式平面玻璃波导,测试了m线谱,用White法计算了波导的折射率分布。     

A five-order mode converter for multimode waveguide

A numerical model of five-order mode converter that converts the order of modes in an integrated-optic multimode waveguide is proposed. Such a structure is useful in optical guiding wave devices for mode control and mode shuffling. The dimensions and index profile of the device are well within the capabilities of the state of the art of integrated optics technology. We have successfully optimized the structural design of the device for propagation loss of less than 13.1 dB at an operating wavelength of 1.55 /spl mu/m. A cascaded form of the five-order mode converter is also proposed for selective mode conversion without the need of restructuring the connection within the device.     

Measurements of waveguide structure fluctuation in a multimode optical fiber by backscattering technique

Utility of a backscattering technique for measuring waveguide structure fluctuation along a fiber is confirmed quantitatively. The backscattering technique is applied to three graded-index fibers: one fiber has uniform structure and the others have core diameter and refractive-index difference changes along the fiber length. The structural parameter fluctuations measured by the technique are in good agreement with those measured directly by the interference microscopy at several positions along the fibers. The resolvability and accuracy of the measured results by the backscattering technique is also compared with the relative error of the direct measurements.     

Selfrouting optical interconnects

A new type of selfrouting optical interconnect (SROI) is described where an optical signal beam or optical data packet is routed to a destination using an all optical switch where the destination is defined within the optical signal by the autocorrelation function of the optical signal.<>     

基于波导间隔余弦分布的光学相控阵研究

为了提高稀疏光学相控阵的精度和效率，采用输出波导间隔成余弦分布的结构，基于绝缘体上硅平台设计出1×16光学相控阵; 结合有效折射率法和2-D有限差分传播法进行了远场强度分布仿真模拟。结果表明，边瓣抑制比从89.72%减小到41.46%，主瓣半峰全宽从1.20°被压缩到0.81°; 这种设计方法能够显著抑制栅瓣，进一步压缩主瓣。该研究在机器人避障、无人驾驶、目标探测等光束偏转领域将有广泛的应用前景。     

Hybrid integration of a laser diode and high-silica multimode optical channel waveguide on silicon

An InGaAsP laser diode with 1.34 ?m wavelength and a high-silica multimode optical waveguide were integrated on a common Si substrate using an alignment guide, which is formed simultaneously with the waveguide, for laser diode mounting. The laser-waveguide coupling efficiency was 30%.     

Determination of two-dimensional optical waveguide indexdistribution function parameters from effective indexes

The method described is based on the least-squares method and gives the maximum-likelihood estimate of the parameters. Its practicality is demonstrated by application to waveguides with three types of refractive index distribution. First, the convergence of the method is shown by computer simulations of a waveguide with an exponential refractive index distribution. Second, a Ti-diffused LiNbO ₃ waveguide is considered as an example of a Gaussian refractive index distribution. The computed refractive index distribution agrees with computational results obtained by S. Fouchet et al. (1987). Third, a proton-exchanged LiNbO₃ waveguide is considered as an example of a step refractive index distribution. The computed depth of the waveguide agrees with the measured depth