Development of multi-mode, high-power, large-aperture two-dimensional VCSEL arrays, operating at a nominal wavelength of 940nm, with highly stable beam profile will be presented. They are designed and fabricated using Trilumina’s proprietary flip-chip-bondable back-side-emitting VCSEL array chip technology. We have demonstrated that a 150-element VCSEL chip array with the improved design shows divergence angle (FWHM) of less than 15°. Additionally, we have integrated this design into drive circuitry that allows us to achieve peak optical powers in excess of 400W.
Substrate-emitting GaAs based oxide-confined 980-nm vertical-cavity surface-emitting lasers (VCSELs) with top-surface high-frequency ground-source-ground contact pads are designed, fabricated, and characterized. The devices are composed of standard top and bottom epitaxially-grown AlGaAs distributed Bragg reflectors (DBRs). The top (p)DBR is capped with p-contact Ti then Au thin-film metals for uniform current injection and laser emission is through the GaAs substrate. The devices are realized on a single epitaxial wafer with n-ohmic-contacts placed on a thick (n+)GaAs buffer layer beneath the bottom (n)DBR and alternatively with the n-ohmic-contacts placed on an (n)GaAs intra-cavity layer lying within the same bottom (n)DBR. Static device parameters including threshold current and rollover current, differential resistance, peak optical output power, and wall-plug efficiency are extracted for VCSELs with oxide-aperture diameters ranging from about 3 to 9-µm and at different temperatures. At room temperature threshold currents are achieved from the sub-mA range up to about 3.5-mA with maximum output powers exceeding 15-mW. Increasing the temperature up to 85 °C slightly increases the threshold current while the peak output power is about halved. The differential resistance at the thermal rollover current is comparable for standard and intra-cavity n-metal-contacts. Small-signal analysis is performed for different bias currents, temperatures, oxide-aperture diameters, and the two n-contact options. Under optimal bias conditions the 3-dB bandwidth exceeds 15 GHz. Direct current modulation-based on-off keying signal generation is investigated from 10 to 40-Gb/s. The influence of an anti-reflection-coated substrate, a thinned substrate, and the combination of both is investigated and discussed.
James Rosprim, Li Wang, David Podva, Eric J. Martin, Preethi Dacha, Christopher Helms, Thomas Wilcox, Nein-Yi Li, Richard Carson, Mial Warren, James Lott
scalable optical power outputs and the capability to separately address sub-array regions while maintaining fast turn-on and turn-off response times. Performance of these devices is critically dependent both on the design of the VCSEL devices and the design of the sub-mount, which provides both the electrical and thermal contacts for the array. Recent results for modelling and optimization of the VCSELs and their corresponding sub-mounts are discussed.
Flip-chip bonding enables a unique architecture for two-dimensional arrays of VCSELs. Such arrays feature scalable power outputs and the capability to separately address sub-array regions while maintaining fast turn-on and turn-off response times. These substrate-emitting VCSEL arrays can also make use of integrated micro-lenses for beam shaping and directional control. Advances in the performance of these laser arrays will be reviewed and emerging applications are discussed.
A unique architecture for two-dimensional arrays of VCSELs that allow for simultaneous high-power output and highbandwidth modulation has been developed for a variety of applications. The arrays use integrated micro-lenses for beam shaping and control, and to enable incoherent beam combining to make compact, high-brightness sources with low coherence noise. The fabrication and performance of the laser arrays are reviewed and sample applications are discussed.
Compact, radiation-hardened free-space optical data links are enabled by two-dimensional VCSEL arrays that can be modulated at high data rates while being scaled to produce high power levels. The combination of high modulation speed and scalability of power is enabled by the use of arrays which are flip-chip mounted onto sub-mounts that contain electrical strip line waveguides to provide an impedance match for the VCSELs. For laser wavelengths in the 910 nm to 1020 nm range, the lasers can be back-emitting through the GaAs substrate, which enables the use of etched microlenses to manipulate the beams from the individual elements. This approach of using VCSELs in arrays is inherently reliable and radiation-hard. The resulting free space optical data links are particularly advantageous for space-borne applications where size, weight, and power are important factors. Performance characterization of links constructed with these lasers demonstrates their suitability for short distance to medium distance data transfer at up to 10 Gb/s.
Emcore's 850 nm UltralaseTM VCSELs, operating at a data rate from 1 Gb/s to 25 Gb/s, is presented. They were based
on our low-cost and hermetic-by-design chip platform which contains the same element for either singlets or arrays with
a 250 μm pitch. First, we discuss high-speed VCSEL evolutions, device designs, manufacturing processes, and device
characteristics. Secondly, we present performance of Emcore's TOSAs, 40 Gb/s parallel optic modules (S12), 120 Gb/s
CXP modules, active connect cables (40 Gb/s QDR and 56 Gb/s FDR), as well as comprehensive reliability
qualifications of UltralaseTM VCSELs. Lastly, we briefly go over the recent progress of 20 Gb/s and 25 Gb/s VCSEL
developments. We have successfully achieved a 3dB bandwidth of 15 GHz at 85°C and 8 mA for a 7.5 μm aperture
UltralaseTM VCSEL.
In this paper, we summarize the recent VCSEL development effort at Emcore. The focus of this effort is on
performance, reliability and manufacturability. We will report the performance of Emcore's 14Gbps VCSEL for the
new fibre channel application. We will also present the work on manufacturing both singlet and various VCSEL arrays,
with performance up to 10Gbps, using a universal mask set to deliver both high performance and high manufacturability.
The reliability data and the work on wafer level burn-in will be updated as well.
Extensive VCSEL reliability enhancements have been carried out at Emcore in the past year with significant results.
In this talk, we will present the failure mechanisms, the method and effectiveness of wafer and die screening, and
the approaches to eliminate these failure mechanisms. Results of improved reliability will also be discussed.
Vertical-cavity surface-emitting lasers (VCSELs) are uniquely suited to miniaturized free-space optical systems in which surface-mounting and hybrid assembly techniques can be used to combine different technologies together. Two examples are described of such microsystems that are being developed for sensing applications. The first example is an optical position sensing system for rotating parts. Progress on fabricating similar system by flip-chip bonding techniques is then discussed. The second examples is a chemical sensing/analysis system which uses a miniature fluorescence detection model that is based on surface- mounted VCSELs and diffractive optical elements. The detection modules is integrated with a capillary electrochromatography separation system and uses substrate- mode light propagation to focus the VCSEL beam on the capillary channel.
We discuss tow examples of integration of micro- electromechanical system (MEMs) and a photonic device. In the first instance, a MEMs locking device pin is driven by a voltage generated by photovoltaic cells connected in series, which are driven by a laser. In the second case, a VCSEL emitting at 1.06 micrometers is packaged together with a metallized MEMs shutter. By appropriate alignment to the opening in the shutter, the VCSEL is turned on and off by the movement of the Si chopper wheel.
High quality optical fiber to OEIC pigtailing, using non-conventional technology, is required to create a real integrated optical
system for optical communications, computing, signal processing, control, and sensing. In this paper, Physical Optics
Corporation (POC) presents a novel singlemode fiber to singlemode GaAs channel waveguide pigtailing approach. This
pigtailing approach involves two key technologies. First, a fiber end-face lensing technology was used to improve modeprofile
matching between singlemode fiber and singlemode channel waveguide, so fiber to waveguide coupling efficiency
could be improved. Second, resistance layer assisted dual-carrier-soldering (RLADCS) technology was introduced to facilitate
fiber and waveguide chip alignment and fixing, so accurate, convenient, and reliable fiber to optoelectronic integrated cicuit
(OEIC) pigtailing could be achieved. By using radiation hardened fiber and special OEIC, this pigtailing and packaging
technology has potential applications in a space environment. This publication addresses all aspects of this pigtailing
approach, including theoretical analysis, design, fabrication, testing, and measurement results.
Present and future space-based applications such as sensors, low-weight and low-power data links for satellites, communication between electromagnetically-shielded modules, and short-distance cross-links within satellite constellations may benefit from the inclusion of small, low-power, and high-efficiency lasers such as the recently-developed Vertical Cavity Surface-Emitting Laser (VCSEL). Many factors influence the application of these devices to space. Temperature response, operational lifetime and reliability, and power consumption are all important considerations for space applications. In addition, the space radiation environments must be considered. In this work, the effects of ionizing radiation on VCSELs are studied with an emphasis on proton damage, and with comparisons to related neutron and gamma-induced phenomena. The influence of proton irradiation is studied in-depth for selected VCSEL structures by the use of an ion microbeam. The experiments indicate that VCSELs exhibit much less threshold current shift for a given radiation dose, compared to the more traditional edge-emitting semiconductor lasers, but that self-heating is a more important consideration for VCSELs. The high current densities associated with VCSELs also lead to a strong influence from forward-bias annealing. These effects are common to various VCSEL types (780 nm and 850 nm) and their magnitude at a given dose is strongly dependent on device size. This indicates that, while VCSELs appear to be very insensitive to ionizing radiation when compared with alternative technologies, there are a number of factors that must be taken into account when optimizing for the space environment.
Advanced device technologies such as vertical cavity surface emitting lasers (VCSELs) and diffractive micro lenses can be combined with novel packaging techniques to allow low-power interconnection of parallel optical signals. These interconnections can be realized directly on circuit boards, in a multi-chip module format, or in packages that emulate electrical connectors. For applications such as stacking of multi-chip module (MCM) layers, the links may be realized in bi-directional form using integrated diffractive microlenses. In the stacked MCM design, consumed electrical power is minimized by use of a relatively high laser output from high efficiency VCSELs, and a receiver design that is optimized for low power, at the expense of dynamic range. WIthin certain constraints, the design may be extended to other forms such as board-level interconnects.
The integration of optical components with polysilicon surface micromechanical actuation mechanisms shows significant promise for signal switching, fiber alignment, and optical sensing applications. Monolithically integrating the manufacturing process for waveguide structures with the processing of polysilicon actuators allows actuated waveguides to take advantage of the economy of silicon manufacturing. The optical and stress properties of the oxides and nitrides considered for the waveguide design along with design, fabrication, and testing details for the polysilicon actuators are presented.
Future advances in the application of photonic interconnects will involve the insertion of parallel-channel links into Multi-Chip Modules (MCMs) and board-level parallel connections. Such applications will drive photonic link components into more compact forms that consume far less power than traditional telecommunication data links. These will make use of new device-level technologies such as vertical cavity surfaceemitting lasers and special low-power parallel photoreceiver circuits. Depending on the application, these device technologies will often be monolithically integrated to reduce the amount of board or module real estate required by the photonics. Highly parallel MCM and board-level applications will also require simplified drive circuitry, lower cost, and higher reliability than has been demonstrated in photonic and optoelectronic technologies. An example is found in two-dimensional point-to-point array interconnects for MCM stacking. These interconnects are based on high-efficiency Vertical Cavity Surface Emitting Lasers (VCSELs), Heterojunction Bipolar Transistor (HBT) photoreceivers, integrated micro-optics, and MCM-compatible packaging techniques. Individual channels have been demonstrated at 100 Mb/s, operating with a direct 3.3V CMOS electronic interface while using 45 mW of electrical power. These results demonstrate how optoelectronic device technologies can be optimized for low-power parallel link applications.
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.
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.
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.
Photonics activities at Sandia National Laboratories are founded on an extensive materials research program. In 1988, the Compound Semiconductor Research Laboratory was established at Sandia to bring together device and materials research and development, in support of Sandia's role in weapons technologies. Recently, industrial competitiveness has been added as a major mission for the national laboratories. As a result, present photonics programs are not only directed towards internal applications-driven projects, but are increasingly tied to the Department of Energy's Technology Transfer Initiatives, Cooperative Research and Development Agreements, and participation in partnerships and consortia. This evolution yields a full range of photonics programs, ranging from materials synthesis and device fabrication to packaging, test, and subsystem development. This paper presents an overview of Sandia's photonics-program directions, using three applications as examples.
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.
Dielectric optical waveguides exhibit properties that are well suited to sensor applications. They have low refractive index and are transparent to a wide range of wavelengths. They can react with the surrounding environment in a variety of controllable ways. In certain sensor applications, it is advantageous to integrate the dielectric waveguide on a semiconductor substrate with active devices. In this work, we demonstrate a tamper sensor based on dielectric waveguides that connect epitaxial GaAs-GaAlAs sources and detectors. The tamper sensing function is realized by attaching particles of absorbing material with high refractive index to the surface of the waveguides. These absorbers are then attached to a lid or cover, as in an integrated circuit package or multi-chip module. The absorbers attenuate the light in the waveguides as a function of absorber interaction. The absorbers are placed randomly on the waveguides, to form a unique attenuation pattern that is registered by the relative signal levels on the photodetectors. When the lid is moved, the pattern of absorbers changes, altering the photodetector signals. This dielectric waveguide arrangement is applicable to a variety of sensor functions, and can make use of resonant coupling properties between low refractive index dielectric waveguides and high-index absorbing materials.
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.
Opticallytriggered thyristor switches often operate in adverse environments such as high temperature and high dose-rate transient radiation which can result in lowered operating voltage and premature triggering. These effects can be reduced by connecting or monolithically integrating a reverse-biased compensating photodiode or phototransistor into the gate of the optically-triggered thyristor. We have demonstrated the effectiveness of this hardening concept in silicon thyristors packaged with photodiodes and in gallium arsenide optically-triggered thyristors monolithically integrated with compensating phototransistors.
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