Tunable narrow-linewidth photonic microwave generation using semiconductor laser dynamics

Generation of a broadly tunable narrow-linewidth microwave subcarrier on an optical wave by exploiting the nonlinear dynamics of a semiconductor laser through a proper combination of optical injection and optoelectronic feedback is experimentally demonstrated. The microwave frequency is generated by the period-one oscillation of an optically injected semiconductor laser. It is tuned in the range from 10 to 23 GHz by varying the optical injection strength, and its linewidth can be narrowed by optoelectronic feedback alone. The linewidth is reduced from the range of 40-120 MHz without stabilization by three orders of magnitude to the range of 10-160 kHz with stabilization through optoelectronic feedback alone. The effect of a small microwave modulation is also investigated. It reduces the linewidth to below the 1-kHz resolution limit of our instrument.     

Optomechanical Monte Carlo Tolerancing Study of a Packaged Free-Space Intra-MCM Optical Interconnect System

We report on the performance of an intra-multichip-module free-space optical interconnect that integrates microlenses and a deflection prism above a dense optoelectronic chip, under various fabrication and assembly errors. This paper describes the results of a combination of mechanical Monte Carlo analysis and optical simulations. Both the technological requirements to ensure a high process yield, and the specifications of the technology we use at our laboratories to fabricate the microoptical and micromechanical components, deep lithography with protons (DLP), are discussed. Therefore, we first conduct a sensitivity analysis that is subsequently used to set the variances of the random perturbations of the Monte Carlo simulation. By scaling these variances, we are able to investigate the effect of a technology accuracy enhancement on the fabrication and assembly yield. We estimate that 40% of the systems fabricated with DLP will show an optical transmission efficiency above$-4.32$dB, which is$-3.02$dB below the theoretical obtainable value. In this paper, we also discuss our efforts to implement an optomechanical Monte Carlo simulator. It allows us to deal with specific issues not directly related with the microoptical or DLP components, such as the influence of gluing layers and structures that allow for self-alignment, by combining mechanical tolerancing algorithms with optical simulation software. In particular, we determine that DLP provides ample accuracy to meet the requirements of a high manufacturing yield (around 91% meet an optical transmission that is$-0.75$dB below the theoretical maximum). The adhesive bonding of optoelectronic devices in their package, however, is subject to further improvement to enhance the tilt accuracy of the devices with respect to the optical interconnect modules.     

Recent Advances in Optical Processing Techniques Using Highly Nonlinear Bismuth Oxide Fiber

We report our recent studies on nonlinear processing of optical signals using a 35-cm highly nonlinear bismuth oxide fiber (Bi-NLF). Our findings are based on self-phase modulation, cross-phase modulation, and four-wave mixing in the Bi-NLF. We demonstrate applications of the nonlinear techniques in optical signal regeneration, tunable optical delay, stabilization of multiwavelength laser source, tunable optical pulse generation, microwave photonic carrier frequency multiplication, and all-optical wavelength conversion.     

Optical receivers for optoelectronic VLSI

We describe our work on the design and testing of optical receivers for use in optoelectronic VLSI. The local nature of the optoelectronic VLSI system permits novel receiver designs, incorporating multiple optical beams and/or synchronous operation, while the requirement of realizing large numbers of receivers on a single chip severely constrains area and power consumption. We describe four different receiver designs, and their different operating modes. Results include 1-Gb/s high-impedance, two-beam diode-clamped FET-SEED receivers, single and dual-beam transimpedance receivers realized with a hybrid attachment of multiple-quantum well devices to 0.8-μm linewidth CMOS operating to 1 Gb/s, and synchronous sense-amplifier-based optical receivers with low (~1 mW) power consumption. Finally, we introduce a measure of receiver performance that includes area and power consumption     

Three-Dimensional Finite-Difference Time-Domain Simulation of Facet Reflection Through Parallel Computing

Precise evaluation of facet reflection is highly desirable in the design and simulation of optoelectronic devices such as super-luminescent light emitting diodes (SLEDs) and semiconductor optical amplifiers (SOAs). In this study, the Three-Dimensional (3D) Finite-Difference Time-Domain (FDTD) method was implemented on a parallel computing algorithm for the calculation of facet reflection in optical waveguides. The FDTD provides the versatility necessary for simulating devices with a complex structure. The parallelization of the algorithm eliminates the limit on the size of the structure, which is usually associated with the FDTD method. 3D FDTD has been used to show that even a subtle difference in the waveguide ridge shape has significant impact on modal reflectivity.     

A coupled pendula system as an analogy to coupled transmissionlines

The aim of this paper is to present a practical and easy to analyze coupled pendula system in order to demonstrate, by analogy, the behavior of coupled transmission lines and related devices. The importance of the coupled mode theory is first explained and its derivation is worked out through the use of the spring-coupled pendula, followed by a statement of the theory and its restrictions. The theory is then used for coupled transmission lines in general and a comparison is made between the coupled pendula and coupled transmission lines in order to extract analogous quantities and to recognize the limitations of such an analogy. The coupled pendula are then used to demonstrate the behavior of a forward coupler, tunable filter, optical switch, and parametric amplifier     

Novel linear and nonlinear optical properties of electromagnetically induced transparency systems

We describe some interesting linear and nonlinear optical properties of three-level electromagnetically induced transparency (EIT) systems, such as absorption reduction, sharp dispersion change, and enhanced Kerr nonlinearity. These novel optical properties are very useful in enhancing efficient nonlinear optical processes, which can find applications in optoelectronic devices. We present some experiments done in our group in the past few years with three-level atomic systems, especially more recent experiments with EIT medium inside an optical cavity.     

Novel approach to RF photonic signal processing using an ultrafast laser comb modulated by traveling-wave tunable filters

The analogy between optical frequencies and RFs leads to a novel technique for RF photonic signal processing using a femtosecond laser comb modulated by a traveling-wave tunable filter, such as an acoustooptic tunable filter (AOTF) or a novel electrooptic tunable filter (EOTF). In this new scheme, the recent history of an applied RF waveform to-be-processed slides into the tunable filter and a femtosecond pulse train diffracts off the moving acoustooptically or electrooptically induced dielectric grating, producing a shaped optical pulse train with each shaped pulse as a compressed replica of the RF waveform contained within the device aperture that is sped up by the ratio between the center optical and RF frequency. For a CW RF tone input, only a narrowband group of the frequency comb lines in the incoming laser comb is spectrally filtered and modulated due to the phase-matching condition in the filter and is simultaneously Doppler shifted by that RF due to the traveling-wave grating obeying the conservation of energy. This allows us to use the traveling-wave tunable filter as a spectrally mapped Doppler-shifted modulator that encodes different RF components onto the corresponding optical frequency comb lines. RF signal processing can then be performed by using optical techniques to manipulate the spectrally modulated laser comb. To reconstruct the processed RF signal, the Doppler-shifted and optically processed pulse train is heterodyne detected by beating with a reference femtosecond pulse train from the same laser source. A high repetition rate femtosecond laser comb is modulated by an AOTF to experimentally demonstrate this novel RF photonic signal processing technique. We demonstrate an RF tunable bandpass/notch filter, an RF down-converter, and an RF jammer er as novel applications of ultrafast lasers.     

Spatially resolved chromatic dispersion measurement by abidirectional OTDR technique

A technique for spatially resolved chromatic dispersion measurement of installed optical fiber links is presented. The method is based on the analysis of bidirectional optical time-division reflectometer (OTDR) traces at different wavelengths obtained by a specifically designed tunable external source. Measurement accuracy is improved through a particular algorithm that corrects the OTDR nonlinearity error. Experimental data on spatially resolved chromatic dispersion of installed dispersion-shifted and nonzero-dispersion fibers are reported     

Optical Signal Processing by Phase Modulation and Subsequent Spectral Filtering Aiming at Applications to Ultrafast Optical Communication Systems

This paper describes optical signal processing based on optical phase modulation and subsequent optical filtering, which is applicable to 160-Gb/s optical time-division multiplexed (OTDM) subsystems. Ultrafast phase modulation of an optical signal is done by self-phase modulation (SPM) and cross-phase modulation (XPM) when an optical pulse passes through a nonlinear optical fiber. Such phase modulation induces the spectral shift of the optical signal. Various types of optical signal processing are realized simply by filtering out the spectral-shifted component. Using SPM-based pulse reshaping in a 500-m-long silica-based highly nonlinear fiber (HNLF), we demonstrate highly stable generation of a 10-GHz 2-ps optical pulse train tunable over the entire C band. A phase-locked loop (PLL) can suppress the slow phase drift of the output pulse train induced by fluctuations of the nonlinear fiber length, enabling the application of the pulse generator to a 160-Gb/s OTDM transmitter. Based on XPM in a 2-m-long photonic crystal fiber, optical time-division demultiplexing of 160-Gb/s optical signals is demonstrated. The long-term stability is drastically improved as compared with the device composed of a conventional silica-based HNLF, because the short fiber length reduces the phase fluctuation between the signal and control pulses. Instead of nonlinear fibers, an electrooptic modulator such as a (LN) modulator also performs the phase modulation in a more practical manner. We propose and demonstrate an optoelectronic time-division demultiplexing scheme for a 160-Gb/s OTDM signal, which consists of an LN phase modulator driven by a 40-GHz electrical clock and an optical bandpass filter (BPF). We also demonstrate base-clock recovery from a 160-Gb/s optical signal with an optoelectronic PLL. The phase comparator is simply composed of an LN phase modulator and an optical BPF, ensuring the stable and reliable operation in the 160-Gb/s receiver.     

The integration of III-V optoelectronics with silicon circuitry

The integration of III-V optoelectronics with silicon circuitry provides the potential for fabricating dense parallel optical interconnects with data links capable of Terabit aggregate data rates. This paper reviews many of the current approaches used for the fabrication of integrated optoelectronic devices and then highlights the performance results. Finally, the applied method is reviewed in greater detail with recent results on VCSEL, MESFET, and photodiode integration presented     

Interferometric near-field imaging technique for phase andrefractive index profiling in large-area planar-waveguide optoelectronicdevices

A versatile, interferometric optical technique is described for nondestructively imaging the near-field output phase uniformity and refractive index profile in broad-area optoelectronic waveguide devices or heterostructure materials. In active traveling-wave optical power amplifier devices, measurements are presented for thermal lensing, solder bond inhomogeneities, heatsink impedance, and carrier-lensing effects due to nonuniform gain saturation by the amplifier input beam, transverse amplified spontaneous emission, or intensity filaments. The thermal performance of diamond and copper heatsinks for high-power optical amplifiers is compared. In passive devices, the technique is used to observe heteroepitaxial material compositional uniformity, defects, photoelastic stress, and intentional structural waveguide index modifications. The technique has a phase and spatial resolution as low as λ/100 and 1 μm. The corresponding refractive index and temperature resolutions (dependent on device length) are as low as Δn=10^-5 and ΔT=0.025°C for 1000-μm-long devices     

Photonic Crystal-Based MOEMS Devices

In this paper, a new class of microoptoelectromechanical system (MOEMS) devices combining photonic crystals (PCs) formed in in-plane waveguiding membranes (in-plane 1-D or 2-D large contrast modulation of the optical index) and a multilayer stack (1-D "vertical" modulation of the optical index) according to the so-called 2.5-D micronanophotonics approach is reported. The operation of the devices is based on the resonant coupling between radiated optical modes and slow Bloch modes waveguided in the particular membranes of the stack, which are laterally patterned to form a PC. Use of high-index contrast PC gratings result in enhanced lateral compactness of the devices. The MOEMS functionality is achieved via micromechanical subwavelength vertical displacement of some of the suspended membranes. Recent demonstrations of devices (including tunable filters and surface-emitting microsources) operating along these principles are presented     

Performance analysis of a time-division-multiplexed fiber Bragggrating sensor array by use of a tunable laser source

The results of an investigation of the performance of a time-division-multiplexed (TDM) fiber Bragg grating (FBG) sensor array using a tunable laser source are reported. The system performance is found limited by the extinction ratio of the optical pulse modulator used for pulse amplitude modulation. Formulas that relate the crosstalk to the extinction ratio of the optical pulse modulator, the modulation parameters of the tunable laser, and the optical path differences among sensing channels are derived. Computer simulation shows that an array of 20 FBG sensors with 3 με resolution can be realized with a commercially available single Mach-Zehnder type optical pulse modulator of -35-dB extinction ratio     

Optoelectronic parallel computing using optically interconnectedpipelined processing arrays

We describe our research on optoelectronic parallel computing systems. Our architecture is based on a multilayer pipeline of two-dimensional optoelectronic device arrays in which each pixel is composed of an optical input channel, a general purpose programmable processor, local memory, and a surface-emitting laser diode as an optical output channel. Free-space optics provides parallel, global communication between layers in the pipeline via optical paths which are dynamically reconfigurable. Demonstration systems and some applications are described     

Ferroelectric Materials for Microwave Tunable Applications

A review of the properties of ferroelectric materials that are relevant to microwave tunable devices is presented: we discuss the theory of dielectric response of tunable bulk materials and thin films; the experimental results from the literature and from own work are reviewed; the correspondence between the theoretical results and the measured properties of tunable materials is critically analyzed; nominally pure, real (defected), and composite bulk materials and thin films are addressed. In addition, techniques for characterization of tunable ferroelectrics and applications of these materials are briefly presented.     

Morphological and Optical Characterization of Sol-Gel Synthesized Ni-Doped ZnO Nanoparticles

Abstract

In this work, Ni-doped ZnO nanoparticles (NPs) were successfully synthesized by sol-gel method. The as-synthesized nanoparticles were characterized to investigate their morphology, structure, purity and optical properties. XRD analysis confirmed the formation of nanoparticles with average particle size of approx. 30?nm. SEM observations show the agglomeration of nanoparticles. The purity of the as-prepared NPs was confirmed by EDX analysis. The defect states were revealed from the photoluminescence (PL) spectra. The overall results obtained indicate that Ni-doped ZnO nanoparticles are promising candidate to fabricate nanoscale optoelectronic devices due to their wide band gap and excellent UV emission properties.     

The AMOEBA switch: an optoelectronic switch for multiprocessornetworking using dense-WDM

We present a single-chip asynchronous multiprocessor optoelectronic bit-sliced arrayed (AMOEBA) crossbar switch. The AMOEBA switch addresses the challenge to produce a large-scale, nonblocking packet switch through dense integration of photonic devices directly onto silicon VLSI circuits. Optoelectronic-VLSI technology is used to integrate the switch fabric, routing controller, packet buffers, line interface circuits, and optoelectronic conversion devices on a single chip. We show how free-space optical interconnects and wavelength-and-space-division-multiplex networking on single-mode fibers can provide switched interconnection between multiple nodes in a distributed computing environment. An optomechanical transceiver package accomplishes the free-space-to-fiber interfacing. We report the implementation and testing of the key components of a 16-channel AMOEBA prototype switch with a potential capacity of 12.8 Gb/s (or 800 Mb/s/channel), and capable of switching 16 million packets per second     

Modelling surface effects in nano wire optoelectronic devices

Recent research on optoelectronic devices focuses on nano structuring which is expected to improve the performance and reduce the production costs of light emitting diodes for lighting purposes and solar cells, for instance. Structuring on the sub-micrometer scale increases the surface with respect to the active volume so that surface effects become crucial for the device performance. In this work we demonstrate the computational modelling of nano structured optoelectronic devices to complement the experiment. The implementation of the simulation model considers surface effects in these devices using a true area box method discretization. The derived surface models are applied on the self-consistent simulation of nano wire quantum disk light emitting diodes. By the computational study we demonstrate that the surface physical effects are critical for the performance of nano-structured optoelectronic devices and that surface recombination can lead to a low efficiency.