Optical channelizing filters with narrow linewidth are of interest for optical processing of microwave signals. Fabrication tolerances make it difficult to place exactly the optical resonance frequency within the microwave spectrum as is required for many applications. Therefore, efficient tuning of the filter resonance is essential. In this paper we present a tunable ring resonator filter with an integrated semiconductor optical amplifier (SOA) fabricated on an InP based photonic integrated circuit (PIC) platform. The ring resonance is tuned over 37 GHz with just 0.2 mA of current injection into a passive phase section. The use of current injection is often more efficient than thermal tuning using heaters making them useful for low-power applications. The single active ring resonator has an electrical FWHM of 1.5 GHz and shows greater than 16 dB of extinction between on and off resonance. The effects of SOA internal ring gain and induced passive loss on extinction and linewidth will be shown. Agreement between experimentally demonstrated devices and simulations are shown. The integration of the active and passive regions is done using quantum well intermixing and the resonators utilize buried heterostructure waveguides. The fabrication process of these filters is compatible with the monolithic integration of DBR lasers and high speed modulators enabling single chip highly functional PICs for the channelizing of RF signals.
We demonstrate chemical/biological sensor arrays based on high quality factor evanescent microring waveguide
resonators in a process that is compatible with CMOS fabrication, glass microfluidic integration, and robust surface
chemistry ligand attachment. We cancel out any fluctuations due to liquid temperature variations through a
differential dual sensor design. Using laser locking servo techniques we attain detection sensitivities in the ng/ml
range. This combination of silicon photonic sensors, robust packaging, high sensitivity and arrayed design is capable
of providing a platform for multiplexed chem-bio sensing of molecules suspended in solution.
Subwavelength diffractive features etched into a substrate lead to form birefringence that can produce polarization sensitive elements such as wave plates. Using etched features allows for the development of pixelated devices to be used in conjunction with focal plane arrays in polarimetric imaging systems. Form birefringence exhibits dispersion that can be advantageous to the design of wave plates with an achromatic response. Taking advantage of this dispersion, diffractive wave plates with good achromatic characteristics can be designed for the 2- to 5-µm spectral region. Previous work in this area has produced good results over a subset of this wavelength band, but designing for this extended band is particularly challenging. The fabrication processes for the subwavelength features will be discussed and fabricated devices with a measured average phase retardation of 80.6 deg and rms variation of 9.41 deg will be presented.
Monolithically-integrated optical gain-competition inverters are demonstrated at 1.55 μm in the InGaAsP/InP material system. The optical inverters consist of etched-facet slave lasers that are side-injected with tapered etchedfacet master lasers. Single-input optical inverters show improved quenching contrast for devices with larger taper width with respect to the slave laser length. Inverter performance also shows a dependence on the ridge width and lasing modes of the slave laser. Two-input optical inverters are characterized which demonstrate NAND and NOR logic operation at different slave laser currents.
We report here on an effort to design and fabricate a polarization splitter that utilizes form-birefringence to disperse an input beam as a function of polarization content as well as wavelength spectrum. Our approach is unique in the polarization beam splitting geometry and the potential for tailoring the polarized beams' phase fronts to correct aberrations or add focusing power. A first cut design could be realized with a chirped duty cycle grating at a single etch depth. However, this approach presents a considerable fabrication obstacle since etch depths are a strong function of feature size, or grating period. We fabricated a period of 1.0 micron form-birefringent component, with a nominal depth of 1.7 microns, in GaAs using a CAIBE system with a 2-inch ion beam source diameter. The gas flows, ion energy, and sample temperature were all optimized to yield the desired etch profile.
The large refractive index difference between silicon nitride and silicon dioxide allows silicon nitride/dioxide waveguides to have a small mode size and low radiation bending loss. Low radiation bending loss enables high quality (Q) factor microring resonators. In this paper, we will present a record high quality factor microring resonator using silicon nitride and silicon dioxide on a silicon wafer. The microring resonator was fabricated using a deep UV photolithography and etching process. The microring resonator was critically coupled to a straight waveguide. An intrinsic quality factor of 240,000 has been measured. We will also present our result of using on-chip high-Q microring resonators for liquid phase chemical sensing application.
Optical waveguide propagation loss due to sidewall roughness, material impurity and inhomogeneity has been the focus of many studies in fabricating planar lightwave circuits (PLC's) In this work, experiments were carried out to identify the best fabrication process for reducing propagation loss in single mode waveguides comprised of silicon nitride core and silicon dioxide cladding material. Sidewall roughness measurements were taken during the fabrication of waveguide devices for various processing conditions. Several fabrication techniques were explored to reduce the sidewall roughness and absorption in the waveguides. Improvements in waveguide quality were established by direct measurement of waveguide propagation loss. The lowest linear waveguide loss measured in these buried channel waveguides was 0.1 dB/cm at a wavelength of 1550 nm. This low propagation loss along with the large refractive index contrast between silicon nitride and silicon dioxide enables high density integration of photonic devices and small PLC's for a variety of applications in photonic sensing and communications.
The large refractive index contrast between silicon nitride and silicon dioxide allows silicon nitride/dioxide planar waveguides to have a small mode size and low radiation bending loss compared with doped silicon dioxide waveguides. Small waveguide bend with low radiation loss can help make small integrated planar lightwave circuits (PLCs), and also high-Q waveguide ring resonators. This presentation will talk about the design, fabrication and characterization of low loss silicon nitride/dioxide planar waveguide devices including waveguide bend, waveguide cross, and leaky mode waveguide polarizer. The key contribution of this work is the use of the lateral mode interference (LMI) 3dB splitter to accurately measure the loss of the planar lightwave circuit devices. We will also talk about the waveguide ring resonators with silicon nitride/dioxide materials. The application for photonic biochemical sensors will also be discussed.
Design details and performance data are presented for (Al,Ga)As and polymeric monolithic tapered rib waveguides achieving modal spot-size transformation for mode-matching from a variety of devices to single-mode optical fiber. 2D expanded output modes of waveguide modulators and lasers are achieved using 1D and 2D tapers between non-critical initial and final widths well suited for optical lithography.
RF and mm-wave photonic devices and circuits have been developed at Sandia National Laboratories for applications ranging from RF optical data links to optical generation of mm-wave frequencies. This talk will explore recent high- speed photonics technology developments at Sandia including: (1) A monolithic optical integrated circuit for all-optical generation of mm-waves. Using integrated mode-locked diode lasers, amplifiers, and detectors, frequencies between 30 GHz and 90 GHz are generated by a single monolithic (Al,Ga)As optical circuit less than 2 mm in its largest dimension. (2) Development of polarization-maintaining, low- insertion-loss, low v-pi, Mach-Zehnder interferometer modulators with DC-to-potentially-K-band modulation bandwidth. New low-loss polarization-maintaining waveguide designs using binary alloys have been shown to reduce polarization crosstalk in undoped (Al,Ga)As waveguides, yielding high extinction ratio (> 40 dB) and low on-chip loss (< 6 dB) in Mach-Zehnder interferometers. RF drive voltage is reduced through use of 45 mm-active length devices with modulator sensitivity, v-pi, less than 3 V.
Shawn-Yu Lin, Joel Wendt, G. Allen Vawter, James Fleming, Dale Hetherington, Bradley Smith, W. Zubrzycki, Edmond Chow, Steven Kurtz, B. Hammons, Pierre Villeneuve, John Joannopoulos, Rana Biswas, Kai Ho, Mihail Sigalas
In this paper, I describe realistic applications of photonic band gap (PBG) materials in optoelectronics at the mm-wave, IR and optical wavelength regimes. Examples are highly dispersive PBG-prisms and PBG-lasers. I will also describe our recent breakthrough at Sandia in the successful fabrication of 3D silicon photonic crystal operating at IR wavelengths.
Monolithic, uniformly-wavelength-graded, vertical-cavity surface- emitting laser (VCSEL) and wavelength-selective resonance- enhanced photodetector (REPD) arrays are key enabling technologies for many wavelength-multiplexed optical network and interconnect architectures. These arrays can be produced in a repeatable and uniform manner by controlling the local MOCVD growth rate of the epilayers on a topographically patterned substrate, which resulted in wavelength-differentiated devices with more uniform optical characteristics. Multi-wavelength VCSEL and REPD arrays have been monolithically integrated on the same substrate to improve the wavelength matching between the source and detector elements. The performance characteristics of these arrays are discussed. We also describe a wavelength-division- multiplexing and demultiplexing experiment in which several channels of optical data are multiplexed together using a multi- wavelength VCSEL array and transmitted on a single optical fiber, and are demultiplexed at the other end using a wavelength- selective REPD array with closely-matching wavelengths.
Monolithic, multiple-wavelength VCSEL arrays have been obtained by using the surface-controlled enhancement and reduction of the MOCVD epitaxial growth rate to produce a periodic and repeatable grading of the resonance wavelength over a span of greater than 30 nm. Room temperature, electrically-injected, cw lasing has also been achieved with a wavelength span of greater than 20 nm. We show here both the enhancement and the reduction of the growth rate of the entire VCSEL structure and demonstrate the controlled variation of the VCSEL lasing wavelength over a widened spectral range by exploiting both of these effects. Using the same growth techniques, wavelength-selective, resonance-enhanced photodetector arrays with closely-matched resonance wavelengths can be monolithically integrated on the same epilayer structure. We demonstrate the repeatability of this technique using different arrays from the same growth run.
Recent advances in the design of high-speed optical switches and transceivers for a reconfigurable, spatially-multiplexed optical interconnection network are described. Monolithic switches based on the integration of vertical-cavity surface-emitting lasers with heterojunction bipolar transistors and photodetectors have achieved switching operation at a data rate of close to 1 Gb/s. Optical transmission experiments through fibers have been carried out using these switches at a data rate between 650 Mb/s and 1 Gb/s. For future improvements in performance, the photonic and electronic elements should be separately integrated and independently optimized. To facilitate photonic integration, VCSELs and resonance-enhanced photodetectors have been integrated on the same substrate.
Mode-locked semiconductor lasers have drawn considerable attention as compact, reliable, and relatively inexpensive sources of short optical pulses. Advances in the design of such lasers have resulted in vast improvements in pulsewidth and noise performance, at a very wide range of repetition rates. An attractive application for these lasers would be to serve as alternatives for large benchtop laser systems such as dye lasers and solid-state lasers. However, mode- locked semiconductor lasers have not yet approached the performance of such systems in terms of output power. Different techniques for overcoming the problem of low output power from mode-locked semiconductor lasers are discussed. Flared and arrayed lasers have been used successfully to increase the pulse saturation energy limit by increasing the gain cross section. Further improvements have been achieved by use of the MOPA configuration, which utilizes a flared semiconductor amplifier stage to amplify pulses to energies of 120 pJ and peak powers of nearly 30 W.
We have fabricated sub-wavelength diffractive optical elements with binary phase profiles for operation at 975 nm. Blazed transmission gratings with minimum features 63 nm wide were designed by using rigorous coupled-wave analysis and fabricated by direct-write e-beam lithography and reactive ion beam etching in gallium arsenide. Transmission measurements show 85% diffraction efficiency into the first order. Anti-reflection surfaces, with features 42 nm wide were also designed and fabricated.
An optical interconnection system is being developed to provide vertical, digital data channels for stacked multichip modules. A key component of the system is an array of individually addressable vertical-cavity surface-emitting lasers with diffractive lenses integrated into the substrate to control beam divergence and direction. The lenses were fabricated by direct-write e-beam lithography and reactive ion beam etching into the GaAs substrate. Preliminary device performance data and the design and fabrication issues are discussed.
We review our progress in the development of an optical interconnect technology consisting of optical and optoelectronic switches that integrate vertical-cavity surface-emitting lasers (VCSELs) with other photonic and electronic components, including heterojunction phototransistors (HPTs) and heterojunction bipolar transistors (HBTs). We describe a reconfigurable multi-access optical network architecture that allows many high speed electronic processors to simultaneously communicate with each other and with other shared resources, and for its implementation, an integrated optoelectronic switching technology that combines the functions of an optical transceiver and a spatial routing switch. The network provides parallel and dynamically reconfigurable optical interconnections between nodes, as well as optoelectronic interfaces to each processor. By converting data between the electrical and optical formats, these multi-functional switches can receive or transmit optical data, or to bypass and re-route it to another node. Optical switching has been demonstrated experimentally at a data rate of 200 Mb/s, and electrical-to-optical data conversion has been achieved at a data rate of > 500 Mb/s.
Compact, low-cost photonic integrated circuits (PICs) have long been a desire of systems engineers. Unfortunately, the majority of PICs in use today use regrown buried heterostructure waveguides to achieve low crosstalk at reasonable packing density. These regrown structures are very expensive and limit PIC applications to high performance niches. The alternative low- cost approach is to use etched-rib, or strip-loaded, waveguides. Strip-loaded waveguides are simple to manufacture but may have guided slab-modes carrying unwanted light between devices within the PIC. These slab modes can result in very high crosstalk or low device density. This paper addresses techniques for control of stray light in strip-loaded PICs. Methods include mesa isolation of waveguides and ion implantation outside the waveguide rib. In addition, some devices such as Mach-Zehnder interferometers and waveguide power combiners generate radiation and slab modes as a fundamental means of operation. Improved designs for both of these structures with proper removal of both radiated and slab-mode light and high contrast-ration operation will be covered.
New kinds of semiconductor microcavity lasers are being created by modern semiconductor technologies like molecular beam epitaxy and electron beam lithography. These new microcavities exploit 3D architectures possible with epitaxial layering and surface patterning. The physical properties of these microcavities are intimately related to the geometry imposed on the semiconductor materials. Among these microcavities are surface-emitting structures that have many useful properties for commercial purposes. This paper reviews the basic physics of these microstructured lasers.
Monolithic integration of a rare-earth-ion-based active waveguide on the same wafer as its diode pump laser would permit compact packaging of the technology demonstrated in fiber lasers and amplifiers. This new monolithic technology would offer the potential for developing compact infrared and visible (up- conversion) lasers, amplifiers, and other photonic integrated circuit components. One approach that we are investigating for such monolithic integration uses a high concentration of one or more rare-earth ions incorporated into polysiloxane spin-on glasses that are solvent-cast onto III-V semiconductor wafers. This `fiber on chip' technology substitutes a relatively high- ion-concentration, short-length metal-ion spin-on glass (MISOG) waveguide for the low-ion-concentration, long-length fiber. Progress to date on developing MISOG waveguide materials and technology is discussed.
A high-speed distributed electrode phase modulator has been designed and fabricated. The processing of this device presented many challenges: (1) smooth rib waveguides etched to an accuracy of +/- 200angstroms; (2) polyimide planarization of 5micrometers step heights, with vias patterned as small as 1.6 micrometers ; (3) contact metalization with resistivities as low as 1 X 10-6(Omega) -cm2; (4) coplanar n and p gold contacts 2.5 micrometers thick, with a 0.5 micrometers gap between contacts; (5) ion- implantation to achieve both electrical and optical isolation. A brief description of how each of these processes have been accomplished will be presented. The epitaxial growth structure of this device will be discussed, including SEM cross-sections of the completed device.
High-speed high-performance optical phase modulators are being developed for use in a coherent Photonic Integrated Circuit(PIC) technology. These phase modulators are the critical component of a PIC program at Sandia National Laboratories targeted for microwave/millimeter-wave signal processing and control including phased-array antenna control. The primary design goals for these modulators are amenability for integration into PICs, high figure of merit (FOM) and large bandwidths allowing for operation at MMW frequencies. Depletion-edge-translation optical phase modulators have been selected as the device technology of choice due to their high FOM. These modulators unfortunately suffer from a large terminal capacitance which greatly limits speed. To overcome this problem, a distributed electrode design based on the use of slow-wave coplanar strips has been developed. Device design and measurements are presented in this paper.
Vertical-cavity surface-emitting lasers (VCSELs) are of increasing interest to the photonics community because of their surface-emitting structure, simple fabrication and packaging, wafer-level testability, and potential for low cost manufacture. Scaling VCSELs to higher power outputs requires increasing the device area, which leads to transverse mode control difficulties if devices become larger than about 5 microns. One approach to increasing the device size while maintaining a well controlled transverse mode profile is formation of coupled or phase-locked 2D arrays of VCSELs that are individually single-transverse mode. Such arrays have unique optical properties, not all of which are desirable. This paper covers some of the basic principles of these devices and reviews recent work on device designs, fabrication and operation. A technique for improving the far- field properties of the arrays is demonstrated and performance limitations are discussed.
Vertical-cavity surface-emitting lasers (VCSELs) can be integrated with heterojunction phototransistors (HPTs) and heterojunction bipolar transistors (HBTs) on the same wafer to form high speed optical and optoelectronic switches, respectively, that can be optically or electrically addressed. This permits the direct communication and transmission of data between distributed electronic processors through an optical switching network. The experimental demonstration of an integrated optoelectronic HBT/VCSEL switch combining a GaAs/AlGaAs heterojunction bipolar transistor (HBT) with a VCSEL is described, using the same epilayer structure upon which binary HPT/VCSEL optical switches are also built. The monolithic HBT/VCSEL switch has high current gain, low power dissipation, and a high optical to electrical conversion efficiency. Its modulation response has been measured and modeled.
The properties of vertical-cavity surface-emitting lasers (VCSELs) and VCSEL-based optical switches using MOCVD-grown epitaxial material are discussed and summarized. Also discussed are some of the factors that limit their performance.
Arrangements of discrete photonic waveguide devices are currently being integrated to form circuits. These Photonic Integrated Circuits (PICs) require test methods that are adaptable as circuit size and complexity grows. Here, we describe tests used to characterize a GaAs/GaAlAs waveguide-based PIC being developed for phase-shift control in phased-array antenna applications. The various elements of the PIC include digital and analog waveguide modulators, light-guide splitters and combiners, turning mirrors, and input-output polarization-maintaining single-mode optical fibers. These basic elements are combined to perform higher-order functions such as optical frequency translation (single side-band suppressed carrier modulation), and phase shifting on multiple optical taps. Tests used to characterize the elements include optical loss, guided-wave modal characteristic, antireflection coating effectiveness, electro-optical (phase) modulation efficiency, electrical frequency response, and optical frequency translation. These tests are integrated with the fiber attachment and RF packaging sequence to construct working device prototypes. They are currently being applied to discrete components of the circuit, and will be adapted as the various parts are integrated.
Progress will be presented regarding circuit elements to be eventually incorporated into a Photonic Integrated Circuit (PIC). Data from elements such as phase modulators and couplers will be reviewed. They have been developed employing ridge waveguides in MBE grown GaAs/AlGaAs material structures. A general approach to PICs will be discussed as well as their incorporation into optical frequency translation (OFT) modulation circuits for coherent optical systems. Detailed theoretical discussion of one, two, and four-arm phase-modulator-based OFT circuits is included.
The influence of processing on the design of optical devices and optoelectronic integrated circuits is
discussed. Process compatibility of devices used as the basis of a complete optoelectronic integrated
circuit will be discussed along with some potential optoelectronic integrated circuits employing only
phase modulators and couplers. Specific examples of the application of reactive-ion-beam etching in the
formation of passive optical waveguide phase modulators, optical interconnects, turning mirrors, and
output couplers in GaAs/AlGaAs are given.
An all optical circuit in GaAs/AlGaAs for control of phased-array systems using a single photonic integrated circuit chip has the potential for high performance control of phased-array system from a small, lightweight, package. Such a circuit based exclusively on combinations of reverse-biased optical phase modulators, waveguide interconnects, corner reflectors, and power splitter combiners with optical-fiber output to the antenna elements has been designed at Sandia National Laboratories. This paper presents some basic features of optical phase modulators for photonic circuit applications and provide relevant performance data as achieved to date. Current structures have been shown to operate with a 76.5 degree/V-mm figure of merit at 1.06 micron and losses as low as 2/cm. A digital phase shifter to allow direct digital control of phased arrays is also proposed and demonstrated.
An optical based RF beam steering system is proposed for phased-array antenna systems. The system, COMPASS (Coherent Optical Monolithic Phased Array Steering System), is based on optical heterodyning employed to produce microwave phase shifting. At the heart of the system is a monolithic Photonic Integrated Circuit (PIC) constructed entirely of passive components. Microwave power and control signal distribution to the antenna is accomplished by optical fiber, thus separating the PIC and its control functions from the antenna. This approach promises to reduce size, weight, and complexity of future phased-array antenna systems.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.