The increase in computational requirements for real-time image processing, complex computational fluid dynamics, very large scale data mining in the health industry/Internet, and predictive models for financial markets are driving computer architects to consider new paradigms that rely upon very high speed interconnects within and between computing elements. Further challenges result from reduced power requirements, reduced transmission latency, and greater interconnect density. Optical interconnects may solve many of these problems with the added benefit extended reach. In addition, photonic interconnects provide relative EMI immunity which is becoming an increasing issue with a greater dependence on wireless connectivity. However, to be truly functional, the optical interconnect mesh should be able to support arbitration, addressing, etc. completely in the optical domain with a BER that is more stringent than "traditional" communication requirements. Outlined are challenges in the advanced computing environment, some possible optical architectures and relevant platform technologies, as well roughly sizing these opportunities which are quite large relative to the more "traditional" optical markets.

Silica waveguide technology transitioned from laboratories to commercial use in early 1990. Since then, various applications have been exploited based on this technology. Tens of thousands of array waveguide grating (AWG) devices have been installed worldwide for DWDM Mux and Demux. The recent FTTH push in Japan has renewed the significance of this technology for passive optical network (PON) application. This paper reviews the past development of this technology, compare it with competing technologies, and outline the future role of this technology in the evolving optical communications.

The monolithic integration of CMOS microelectronics with photonics is inevitable and benefits both technologies. Photonic integration to microelectronics provides such solutions as overcoming microprocessor communication roadblocks through the use of optical interconnection. Microelectronic integration can provide benefits to photonic structures by optimizing electronic signals generated by photonic biosensors for example. Photonic integration must complement, build on, and enhance the existing state of CMOS microelectronic technology. Photonic approaches that ignore the realities of CMOS architectures (such as power and thermal limitations), provide little benefit to the CMOS device performance, are incompatible with CMOS silicon manufacturing processes, or are incapable of achieving levels of long term reliability already well demonstrated by microelectronic devices, give little reason for photonic/microelectronic integration. Practical implementation of photonics on chip, monolithically with CMOS type microelectronic devices, remains in the laboratory. This work presents architectures to integrate photonics and microelectronics that address CMOS fabrication realities, increase performance of both the electronic and optical functions, and retain current levels of reliability. Fabricating these structures with the limited CMOS material set and/or typical photonic materials requires materials to be molecularly engineered to provide required properties. Materials have been investigated that enable economic fabrication of photonic structures for monolithic integration. Low loss self assembled silicon nanocomposite VIPIR waveguide structures are combined with long term stable non-linear poled polymers for fabrication of electro-optic active devices. Materials are fabricated using low temperature plasma enhanced chemical vapor deposition (PECVD).

We present deep UV light-emitting diodes and photodetectors based on high Al-composition AlGaN. We have obtained very short wavelength UV LEDs (<255 nm) with milliwatt level optical output powers, based on an AlGaN multiple-quantum well active region. Solar-blind photodetectors have also been fabricated with quantum efficiencies in excess of 70%. Based on these photodetectors, focal plane arrays have been fabricated.

In this paper, techniques of quantum dot interdiffusion such as impurity free vacancy disordering and ion implantation induced disordering as well as the selective area epitaxy by metal-organic chemical vapour deposition have been used to tune the emission wavelength of self-orgainsed quantum dot structures. Under optimized experimental conditions, large differential band gap energies have been achieved by all approaches which is essential for quantum dot-based photonic integrated circuits.

Photonic integrated circuits require the ability to integrate both lasers and waveguides with low absorption and coupling loss. This technology is being developed at LLNL for digital logic gates for optical key generation circuits to facilitate secure communications. Here, we demonstrate an approach of integrating InGaAs DQW edge emitting lasers (EEL) with electron beam evaporated dielectric waveguides. The EELs are defined by electron cyclotron resonance etching (ECR). This approach results in highly anisotropic etched mirrors with smooth etched features (sidewall rms roughness = 28 Å, surface rms roughness = 10 Å). The mirror is etched to form both the laser cavity and define the waveguide mesa, which accommodates a dielectric stack, where the core is aligned with the active region of the laser to achieve maximum vertical mode overlapping. The waveguides are based on SiO₂/Ta₂O₅/SiO₂ which yields a high index contrast of 0.6, resulting in low loss guides (~2-3dB/cm). The design of the interface has taken into account the waveguide transmission loss, air gap spacing and tilt between the laser and waveguide. The critical feature for this deposition technique is its required high directionality or minimal sidewall deposition and corner effects. In the butt coupled EEL/waveguide system we have measured a slope efficiency to be as high as 0.45 W/A. We have in conclusion demonstrated a technology that allows direct coupling of a dielectric optical interconnect to a semiconductor laser monolithically fabricated on the semiconductor substrate.

We studied the impurity-free vacancy diffusion (IFVD) of In_0.2Ga_0.8As/GaAs multi-quantum well (MQW) structures for advanced optoelectronic devices and their integration. To gain deeper insight in IFVD, the influence of the plasma enhanced chemical vapor deposition parameters, such as SiH₄ flow rate, deposition temperature, deposition pressure and rf power, of SiO_x and SiN_x capping layers on the band gap energy shift induced by IFVD was investigated. We observed that the magnitude of the blue shift increases with the decrease of SiH₄ flow rate for SiO_x and SiN_x capping layers. The blue shift of the PL peak energy increases greatly with the increase of deposition pressure and slightly with the decrease of deposition temperature. The influence of rf power was found to be negligible. All these dependences are related to the porosity in the dielectric capping layers in the QW intermixing. We fabricated the wavelength shifted ridge-waveguide InGaAs/GaAs MQW lasers with 967, 946 and 927 nm emission wavelengths that have undergone IFVD using SiO₂ capping layers at different annealing temperatures of 850, 900 and 950 °C, respectively. Also, multi-wavelength InGaAs/GaAs MQW lasers by the area-selective IFVD using different stoichiometric SiO_x capping layers were studied. The lasing wavelength difference of about 31 nm is obtained between the ridge-waveguide laser diodes fabricated with the MQWs that had undergone the same thermal treatments using the SiO_x film provided with SiH4 flow rates of 20 and 300 sccm.

We investigate waveguide resonators, and a coupled system based on two-dimensional silicon-on-insulator photonic crystal (PhC) slabs. First, we show a way of designing PhC waveguides and PhC resonators to overcome the radiation loss that occurs in the thickness direction in a two-dimensional system and how to couple a PhC waveguide to an optical fiber. Next, we effectively couple PhC waveguides to PhC resonators, devise a three-port-resonant-tunneling filter, and develop an ultrasmall multi-port channel-drop filter. Finally, we describe a two-beam optical switch operating with very low power that employs a PhC coupled resonator-waveguide system.

Photonic crystal microcavity devices containing InGaAs active layers grown on GaAs substrates have demonstrated poor performance largely because of rapid, non-radiative recombination at the air-InGaAs interface formed during the fabrication of the photonic crystal slab. We have used selective area epitaxial regrowth of the quantum well active layer to localize it to the defect of the photonic crystal structure. The fabrication process is described and the potential application to resonant photonic crystal devices is discussed.

Photonics on chip could enable a platform for monolithic integration of optics and microelectronics for applications in which high data streams are required in a small footprint. Recent results in Nanophotonics have shown the ability to guide, filter, bend and split light on Silicon chips using nano-size structures. Using highly confined photonic structures we have demonstrated ultra-compact silicon photonic components with very low loss. The highly confined photonic structures enhance the effective light matter interaction in the structures.

We employ ultranarrow silicon-on-insulator (SOI) waveguides to demonstrate significant Raman gain using low CW pump powers from a diode laser. Starting with measurements based on spontaneous Raman scattering in nanowire SOI waveguides, we obtain the parameters necessary to develop a useful numerical modeling tool for our system. This work shows clearly the feasibility of an SOI-based low-loss, low-power, on-chip Raman amplifier in the silicon nanowire system. We have also developed a rigorous coupled wave model to examine temporal effects in our Raman system.

We report, in the form of review, on the results of our study on the fabrication and assembly of polymer-based optical waveguide arrays and micro/nano-photonic devices for optical printed circuit boards (O-PCBs) application. The O-PCBs are designed to perform the functions of transporting, switching, routing and distributing optical signals on flat modular boards, substrates or chips. We have assembled and constructed O-PCBs using optical waveguide arrays and circuits made of polymer materials and have examined their information handling performances. We also designed power beam splitters and waveguide filters using nano-scale photonic band-gap crystals. We discuss scientific and technological issues concerning the processes of miniaturization, interconnection and integration of polymer optical waveguide devices and arrays for the O-PCBs as applicable to board-to-board, chip-to-chip, and intra-chip integration for computers, telecommunications, and transportation systems.

We report on a single-chip 32-channel reconfigurable optical add/drop multiplexer (ROADM) based on a polymer planar lightwave circuit platform. This subsystem on a chip consists of 32x8 switches and arrays of 32 add/drop switches, variable optical attenuators (VOA's), power taps, and photodiodes. The architecture, design and optical performance are presented.

A vertically interconnected structure is a key feature of a photonic integrated circuit application, like an optical printed circuit board. Conventional vertical interconnecting structures have a 45 degree mirror, with or without metal coating to enhance its reflectance. We have designed a curved-shape semi-spherical type vertical interconnecting structure to enhance vertical interconnecting efficiency, and also developed simple fabrication procedure to realize it.

A new process has been developed to create vertically-integrated photonic and optoelectronic circuits in silicon. The approach is the 3-D extension of the SIMOX process where buried SiO2 sections can be selectively created by using oxygen implantation, through a mask, followed by annealing. By controlling the implant energy, dose, mask area and thickness, arbitrary 3-D arrangements of Silicon/SiO2 can be created. The process has been used to create vertically coupled microdisk resonators and add-drop wavelength multiplexers on a silicon wafer.

The Faraday effect of magnetically doped Fe:InP with Fe concentration of 3 x 10¹⁶ cm^-3 doping is characterized. It demonstrates a Verdet coefficient of 23.8 °/cm/T at 1550 nm. For 45°rotation, the insertion loss at this wavelength is 1.66 dB. A zero-birefringence waveguide is designed and fabricated. The loss and birefringence of the waveguide are characterized.

We present experimental results on 40 Gb/s large-signal modulation performance of 1.31μm monolithic integrated laser-modulator in the InGaAlAs/InP material system, exploiting the gain and absorption properties of an identical multiple quantum well (MQW) active layer. In continuous wave operation, at 15°C, the devices achieved threshold currents < 28 mA, fiber coupled optical power levels up to +0.4 dBm. The measured small-signal modulation bandwidth was about 32 GHz. An air-cavity based Fabry-Perot interferometer has been realized to characterize the spectral chirp of the integrated structures in the time domain up to 40 Gb/s.

An InP-based tunable wavelength converter is investigated which monolithically combines a waveguide photodetector with a sampled-grating distributed Bragg reflector laser diode. We employ advanced device simulation to study internal physical mechanisms and performance limitations. Our three-dimensional finite-element model self-consistently combines carrier transport, optical waveguiding, and nanoscale many-body theory to accurately account for optical transitions within the quantum wells. Good agreement with measurements is achieved. The validity of several model simplification options is discussed.

Wavelength converters are seen as important to the scalability, flexibility, and cost of future optical networks. These devices have opportunities for deployment in optical switches, routers and add/drop multiplexers. This talk will outline the latest results of monolithic and hybrid photocurrent-driven wavelength converters (PD-WC) based on either the direct modulation of a bipolar cascade SGDBR laser or by external modulation using an Electro-absorption (EA), or Mach-Zehnder (MZ) modulator using integration building blocks such as a semiconductor optical amplifiers (SOA), SGDBR lasers, PIN detectors and EA and MZ modulators. As the input and output waveguides are separate in this configuration of wavelength converter, an optical filter is not required to reject the input signal at the output which is desirable particularly with wavelength tunable applications where the response time of a filter could limit system performance.

The integration of active optoelectronic devices, passive optical devices, and electronics into planar lightwave integrated circuits (PLICs) at the chip level, and planar lightwave integrated systems (PLIS) at the substrate or package level, have applications in optical interconnection, optical signal distribution and processing, and in integrated optical sensing. Heterogeneous integration of thin film devices is an effective method of creating PLICs and PLIS. Thin film InP-based edge emitters and thin film photodetectors have been integrated with polymer waveguides to create planar lightwave systems.

We report on hybrid organic-inorganic optoelectronic sysbsystems that integrate passive and active optical functions. The integration approaches involve various levels of hybridization, from splicing of pigtailed elements, to chip-to-chip attachment, to hybrid on-chip integration involving grafting and flip-chip mounting, and finally to true heteroepitaxy. The materials integrated include polymer, silica, silicon, silicon oxynitride, lithium niobate, indium phosphide, gallium arsenide, yttrium iron garnet, and neodymium iron boron. The functions enabled by this hybridization approach span the range of functions needed in optical circuitry, while using the highest-performance material system for each element. We demonstrate a number of hybrid subsystems, including fully reconfigurable optical add/drop multiplexers and tunable optical transmitters.

The need for efficient detection of biochemical agents is becoming more compelling. High sensitivity chemical and biological sensors, based on etched core fiber Bragg gratings that detect change in the index of refraction of surrounding solutions, were developed to measure the index of refraction of different solutions. A sensitivity of 1394 nm/riu was achieved for a core diameter of 3.4 μm. Assuming an experimental wavelength resolution of 0.01 nm, we were able to detect an index change of 7.2⋅10-6. These chemical sensors, properly sensitized using common glutaraldehyde chemistry, can be effectively used as biosensors. A 20 base single stranded DNA of concentration of 0.7 μg/ml was successfully detected. Some ideas are also proposed for sensitivity improvement of the sensor, like using the higher order modes. It is shown that the higher order modes can also provide information about the cause of the fundamental shift, whether it is due to refractive index change or due to external effects like temperature and stress.

Dielectric and semiconductor microspheres coupled to optical fibers are used for optical channel dropping in the infrared communication wavelengths of 810 and 1300 nm. Additionally, a dielectric microsphere coupled to an optical fiber and placed in close proximity to a silicon photodiode is used for resonant detection of communication signals at 810 nm. The observed resonances have quality factors of 100.000. The measured quality factors are limited by the sensitivity of the measurement setup. These optical resonances provide the necessary narrow linewidths that are needed for high resolution optical communication applications. The microsphere, optical fiber, and detector system shows promise as a building block for optoelectronic integration.

We show that the self-imaging principle still holds true in multi-mode photonic crystal (PhC) line-defect waveguides just as it does in conventional multi-mode waveguides. To observe the images reproduced by this self-imaging phenomenon, the finite-difference time-domain computation is performed on a multi-mode PhC line-defect waveguide that supports five guided modes. From the computed result, the reproduced images are identified and their positions along the propagation axis are theoretically described by self-imaging conditions which are derived from guided mode propagation analysis. We report a good agreement between the computational simulation and the theoretical description. As a possible application of our work, a photonic crystal 1-to-2 wavelength de-multiplexer is designed and its performance is numerically verified. This approach can be extended to novel designs of PhC devices.

Integrated optical switches based on multimode interference (MMI) structures in a generalized Mach-Zehnder configuration can be used to achieve space-division switching. This paper examines the fundamental limitations of these optical switches and assesses their suitability for use as optical cross-connects.

We report on low-loss light propagation at the communication wavelength of 1.55 µm through straight two-dimensional photonic crystal waveguides patterned into InGaAsP/InP heterostructures. The linear defect waveguides along the ΓK direction of a triangular lattice of air holes were etched deeply into the semiconductor by Cl₂/Ar electron cyclotron resonance reactive ion etching. Efficient waveguiding was observed for both polarization directions, although a photonic band gap exists for only one of the polarization states. Propagation losses, determined by the Fabry-Perot resonance method, are as low as 0.2 dB/mm and 1.5 dB/mm for waveguides based on seven and three missing rows of holes, respectively. Waveguide resonators with 100 GHz channel spacing and quality factors up to 15,000 have been realized by inserting photonic crystal mirrors into the waveguides. The dispersion of the resonators was measured using a phase shift technique. Values for the group velocity dispersion range from -250 ps/nm to +250 ps/nm at wavelengths around 1.55 μm, which is sufficient to compensate for the dispersion of 15 km standard single-mode fiber. Controlling the device temperature allows to tune the dispersive properties of the devices.

We have designed and integrated a high density micro-ring resonator and photonic crystal waveguide array for wavelength division multiplexing (WDM) microsystem applications. First, we designed and optimized micro-ring resonators. Using the non-unitary transfer matrix method (NU-TM), we have been able to analyze the transfer characteristics of the micro-ring and micro-racetrack resonator system. The track-length dependence, which is not obvious in the unitary transfer method (U-TM) analysis, is clearly found in the NU-TM analysis. By optimizing the WDM filter characteristics such as FSR (Free Spectral Range) and cross-talk, we have found the optimal dimensions, such as length, of the racetrack resonator. And then for improving the WDM filter characteristics of microring resonator, we have designed bent photonic crystal waveguide. Integrating microring resonator with bent photonic crystal waveguide can offer additional functions such as band pass filtering function.

High efficiency small-area waveguide bends and splitters for perfluorocyclobutane (PFCB) copolymer materials have been designed with air trench structures (ATSs). An air trench at the intersection of one input and two output waveguides can function as a high efficiency splitter. High efficiency small-area waveguide bends are achieved by placing ATSs at the waveguide bend corners and operate through total internal reflection (TIR). In this paper we discuss bends and splitters that are designed specifically for constructing a ring resonator and a Mach-Zender interferometer. Two dimensional (2-D) finite difference time domain (FDTD) analysis has been used for design. In order to further examine the performance of realistic small-area air trench bend structures, we have also employed three dimensional (3-D) FDTD. From 3-D FDTD simulation results, we find that the 2-D designs are representative of actual devices. By combining small-area air trench bends and splitters, we show how a compact ring resonator can be realized. Simulation results show attractive properties for the proposed ring resonator design. Preliminary ATS etch results of PFCB with CO and O₂ shows the possibility of fabricating the proposed devices.

The continuous penetration of optical data transport into diverse applications is driving an imperative to find lower cost fabrication routes to high performance waveguides and devices. Strip-loaded waveguides (SLWG) offer a unique opportunity to enable ultra-low cost processing and excellent performance in these applications. In this paper we will show that simple waveguides and devices may be fabricated that have compelling performance metrics. Similarly it is shown that the waveguide design is easily accomplished and that the designs may be rendered with limiting precision using standard process tool-sets. The combination of good design and facile manufacturing practice suggests that, unlike conventional waveguide technology, the SLWG is eminently suited to a wide variety of applications. It will also be shown that the simplicity of the processing offers new opportunities to apply this approach to waveguides in a wide variety of materials and on diverse substrates. Forward design and rendition of devices with excellent reconciliation of measured performance with the design parameters provides a feasibility proof for the validity and manufacturability of the SLWG. Perhaps contrary to pre-conception it is proven that very low coupling loss with normal, single mode, fibres is readily achieved with waveguides of this type. This has been shown both by simulation and via the measured performance of devices. Processing of the test artifacts was via conventional silica-on-silicon planar waveguide manufacturing processes. However, other processes are shown to offer a strong proposition for much lower cost and a diversification of the utility and applicability of waveguides on many substrates.

We describe a cost-effective new packaging platform for CWDM passives. The Compact CWDM (CCWDM) devices use free-space beam cascading schemes and offer far better size, performance and reliability measures than traditional counterparts built by cascading 3-port thin-film filters.

In this paper, the measurement system based on optical low-coherence interferometry was constructed to characterize propagation characteristics of Optical-Printed Circuit Board (O-PCB). With this system, the propagation loss of optical waveguides embedded in O-PCB was measured, and the back-reflection from several interfaces within O-PCB was done also. The polymer optical waveguide was prepared with UV embossing technique and its core had the width of 50um, the height of 50um, and the length of 2cm, respectively. The propagation loss of the waveguide was measured to be less than 2dB/cm and the back-reflectance at each interconnection point was about 5.83%. In the near future, the sensitivity will be improved with applying the balanced detection and signal modulation techniques in order to measure propagation characteristics of more complex O-PCB.

We demonstrate the first integration of polymer waveguides and electrically switchable gratings in a single substrate for the application of optical interconnect. The electrically switchable gratings are used to couple optical signals from VCSEL to waveguide or from waveguide to photodetector. This switchable coupling feature provides a promising solution to facilitate dynamically reconfigurable on-chip optical interconnect architecture for intrachip and chip-to-chip data communication.

Optical interconnection is recent issue for high-speed data transmission. The limitation of high-speed electrical data transmission is caused by impedance mismatching, electric field coupling, microwave loss, and different length of the electrical signal lines. To overcome these limitations, the electrical signal in the current electrical system has to be changed by the optical signal. The most suitable optical source in the OPCB (Optical Printed Circuit Board) is VCSEL (Vertical Cavity Surface Emitting Lasers) that is low-priced and has the characteristic of vertical surface emitting. In this paper, we propose an electrical model of the VCSEL as E/O converting devices for the OPCB. The equivalent circuit of the VCSEL based on the rate equations includes carrier dynamics and material properties. The rate equation parameters are obtained by full analysis based on rate equation and experiment results. The electrical model of the VCSEL has the series resistance determined by I-V characteristic curve, and the parallel capacitance by the parasitic response of the VCSEL chip. The bandwidth of the optical interconnection is analyzed considering those parameters. We design and fabricate the optical transmitter for OPCB considering proposed electrical model of VCSEL.

We present a new approach in the design of a photonic crystal bandpass filter by using waveguide bending. The bandpass filter was designed by introducing two bends with the modified geometry into the both ends of a photonic crystal waveguide. We show that such a filter exhibits step-like spectral profile in the range of 1500-1600 nm, with a maximum transmission of 100%. In contrast to the other designs proposed, the present one does not involve either insertion of small defects or control of cavity-lengths.

We have designed and fabricated PIN photodiode based ROSA used for FTTX applications. The critical nonlinearity parameters of Inter-modulation Distortion (IMD) were measured by two RF modulated light sources near 1550nm wavelength channels. A cost effective measuring system with narrow pass band filter was set up and some procedures were utilized for determining the low level signals of IMD. Obtained test results were used in real time to guide packaging process to achieve best receiver performance.

We report an experiment where InAs/GaAs self-organized Quantum Dots (QD) are coupled to the evanescent field of very-high-Q Whispering Gallery Modes (WGM) in a silica microsphere. The high performance of these microcavity and nanoemitters allowed to achieve very low threshold (200 &mu;m) laser operation at room temperature, involving a few thousands of QD. We show that such a low threshold relies heavily on WGM deconfinement and reconstruction in the micromesa etched in GaAs sample. Next, we present some prospects on further experiments involving various semiconductor nanostructures coupled to microspheres or to silica microtoroids integrated on a Si chip (as recently introduced by K.J.~Vahala and coworkers at Caltech).