This paper presents experimental demonstration of optical components applicable in free space laser communication systems for bi-directional transmission of Gigabit Ethernet (GBE) telemetry data and control messages using a dual atmospheric effect mitigation approach. The objective is to address the challenges for optical transmission of telemetry data. (1) Turbulence effects which cause optical beam scintillation, wander and breakup, all of which cause signal degradation at the receiver. (2) An optical signal in free space has a fading effect which is caused by communications terminal equipment‘s in-ability to maintain perfect pointing along a line of sight due to vibrations/motions of the mobile platform.
Normally, reliable, reproducible, high-yield packaging technologies are essential for meeting the cost,
performance, and service objectives for the harsh environment of space applications. This paper describes
a new improved micro packaging method of hermetic seal mini-DIL (dual in line) laser diode module.
The problem of using a softer solder resulted in failure mechanisms observed in the mini-DIL laser diode
module based laser firing unit (LFU) for ordinance ignition of a missile system. These failures included:
(1) failure in light output pulse power, (2) fiber pigtail damage inside the package snout which caused low
LFU production yield. Our distinctive challenge for this project is the micro packaging of mini-DIL. For
this package a new technique for the hermetic sealing using a micro-soldering process was developed.
The process is able to confine the solder seal to a small region inside the snout near the fiber feed-through
hole on the wall of the mini-DIL package. After completing the development, which included temperature
and thermal cycling, X-rays analysis showed the new method had no fiber damage after the microsoldering
seal. The new process resulted in 100% success in the packaging design and was granted a
patent for the innovative development.
Recently there has been strong interest in wireless optical (WO) communication link applications in airplanes and
avionics platforms for size, weight, power, cost, and electromagnetic interference (EMI) reduction. Wireless optical
link has additional advantage of providing network security because the optical signal from wireless optical link is well
confined within an airplane or avionics vehicle. In this paper we discuss some potential wireless optical link
applications in commercial airplanes and the challenges in the implementation of wireless optical links for these
applications. We will present our experimental results on using white LED (WLED), visible laser source and free-space
small-form-factor (SFF) optical transceivers to demonstrate the viability of applying wireless optical links in avionics
platforms.
One of the major challenges to free space laser communications and ladar is the impact of turbulence on beam
propagation, one example of which is signal fading. These impacts can be exacerbated on airborne platforms by
turbulence in the vicinity of the laser system aperture and the platform wake. There are a number of strategies to
mitigate this, including adaptive optics, active flow control, and various dimensions of diversity: wavelength,
polarization, temporal, and spatial diversity. In this paper we will discuss spatial diversity implemented in the focal
region of optical telescopes. We will briefly compare this with other methods, describe results of requirements analysis
of array features and optical configurations for various atmospheric turbulence states, and suggest several attractive
configurations. We will also report on the design and test of one configuration, implemented in a prototype, and tested
for noise performance, optical transmission, modulation bandwidth, and BER performance with our dynamic turbulence
simulator. Early evidence shows significant BER improvements of several orders of magnitude at high turbulence
fluctuation frequencies using this technique.
In the past, Boeing had successfully developed and produced the hermetic ARINC 636 fiber optic transmitter and receiver modules for the PLANET System in the Boeing 777 commercial airplanes. These hermetic fiber optic modules had demonstrated over 4 millions aggregate flight hours with zero failure; the hermetic fiber seal technology is a key contributor to this outstanding reliability record. Recently, we have investigated failure mechanisms in commercial-off-the-shelf (COTS) hermetic mini-dil (dual-in-line) laser diode modules; and developed new hermetic fiber seal process for low cost mini-dil form factor packages. In addition, we are also developing cost effective hermetic multi-channel fiber optic array modules technology for aerospace applications.
Recently there has been strong interest in wireless white LED (WLED) communication link applications in airplanes and
avionics platforms for size, weight, cost, and electromagnetic interference (EMI) reduction. Wireless WLED link has
additional advantage of providing network security because the optical signal from WLED link is well confined within
an airplane or avionics vehicle. In this paper we discuss and analyze commercial-off-he-shelf WLED design and color
measurement results. An experimental implementation of a low cost WLED transceiver which shows error free freespace
operation at 10Mb/s is successfully demonstrated. The feasibly of implementing free space optical link which
meets both lighting and communication requirements using WLED array is analyzed by mathematical modeling using
MATLAB simulation technique.
Many applications, both in commercial and defense industries, require uniform diffusion at either a broad
wavelength range, or at multiple discrete wavelengths. Currently employed technologies have trade-off's
between their ability to control the angular distribution and uniformity of the output beams intensity profile,
and the ability to suppress 0th order for the devices in a way that can be volume manufactured to tolerate
environmental extremes. At Tessera, we have developed a binary lithography technique which nearly
eliminates the 0th order over a much broadened wavelength range, while maintaining much greater control
over the angular distribution of the beam. In this paper we describe technology and how it has been applied to
the design and manufacture of a top-hat diffuser profile for the wavelengths of 3.95μm and 4.6μm. The
procedures used for testing, as well as the test results, are provided courtesy of Aculight Corporation.
Aculight has demonstrated spectral beam combining of four diode laser bars in a single optical cavity; each 1 cm wide diode bar included 200 individual single mode laser emitters. The beam combining was accomplished in the plane of the diode bar -- slow direction. In earlier work, Aculight has reported near diffraction limited performance from single diode laser bars where we have spectrally beam combined 200 laser emitters while maintaining a beam quality near the diffraction limit. Without spectral beam combination these diode laser bars will have a beam quality, in the plane of the bar, corresponding to an M2 of 1000. In current work, Aculight is extending this technology to demonstrate a spectrally beam combined, diode laser system of 50 Watts, with near diffraction limited beam quality. To accommodate multiple diode laser bars, optical modeling was used to design and complete sensitivity analysis of a unique optical cavity based on the Schmidt telescope principal to remove off-axis aberrations. Error trees have been developed for beam quality and efficiency that illustrates just how the efficiency and beam quality have been maintained within this system.
The use of diode laser bars has traditionally been limited in many applications because of their poor beam quality in the plane of the junction (slow direction). Spectral Beam Combination (SBC) corrects this defect with minimal impact on efficiency. Aculight has demonstrated efficient SBC of nearly 400 single transverse mode semiconductor lasers. The semiconductor lasers were packaged in two adjacent 1-cm wide, 200 emitter bars. The M2 of a single 1-cm wide diode bar is typically greater than 1000. Using SBC we have measured an output M2 of less than 1.5. The output bandwidth of the device is ~10 nm; and it is this spectral width that allows combination with the result that each of the 200 lasers deliver power through the same output aperture. The efficiency of this process was measured at >70% when high quality optical components were employed. Efficiency is defined as the SBC output power normalized to the power provided by the diode bars without SBC. With single emitters we have achieved SBC efficiencies of >80%.
KEYWORDS: Semiconductor lasers, Commercial off the shelf technology, Avalanche photodetectors, Free space optical communications, High power lasers, Diodes, Receivers, Telecommunications, Quantum wells, Transmitters
In our Photonics West 98 paper, we presented our study results on using commercially available 860 nm high power laser diodes and high-speed laser driver for free-space laser communication terminal application. We demonstrated the feasibility of a free space laser communication link using a junction-up 860 nm high power laser diode driven by a high current laser driver from Hytek Microsystems up to 622 Mb/s. Recent development in high speed InGaAs/GaAs strained layer quantum well (SLQW) laser at 980 nm has provided an additional design option for a laser communication terminal. The advantages of using the 980 nm laser are: (1) WDM market in the telecom industry has created a volume demand for the 980 nm pump lasers. The future cost of 980 nm lasers is expected to be lower due to the economy of scale. (2) In our previous publications, we have demonstrated CW operation of strained layer QW laser at temperature higher than 200 degree(s)C. There is a potential for this type of laser diode to operate in a much harsher and higher temperature environment, and (3) 980 nm pump laser has output power comparable to high power 860 nm laser diodes. In this paper, we will present the high data rate characteristics of a high-speed 980 nm (SLQW) pump laser. Using commercial-off-the-shelf laser drivers we will demonstrate the laser transmitter system characteristics from 622 Mb/s to 3 Gb/s. Detail experimental results on bit- error-rate measurement for a 980 nm device will be presented.
KEYWORDS: Semiconductor lasers, Diodes, Commercial off the shelf technology, High power lasers, Transmitters, Free space optical communications, Avalanche photodetectors, Capacitance, Modulation, Laser applications
Recently, there has been strong interest in the application of commercial-off-the-shelf (COTS) electronic and optoelectronic (O/E) components for free space laser communication application. Besides the space qualified packaging issues, the main problems of using COTS O/E transmitter are: (1) Telecom grade laser transmitters do not have sufficient power to meet the free space laser communication requirements; (2) COTS laser diode transmitter driver circuits have limited peak drive current, usually below 100 mA, which is too low for driving high power laser diodes; and (3) COTS high power laser diodes are usually not used for high data rate applications since the high speed performance of the laser/driver combination is usually inadequate. In this paper we will present our latest study results on the SDL 5430 and SDL 580 high power laser diodes driven by high current laser drivers at data rates from 600 Mb/s to over 1 Gb/s. Several models from the HY6000 family of high current and high speed laser diode drivers from Hytek Microsystems Inc., designed for free space laser communication applications, have been tested with the SDL high power laser diodes. Using direct drive technique with NRZ modulation, average output power over 100 mW at 622 Mb/s were obtained with these low cost Hytek drivers. For data rates over 1 Gb/s, the parasitic associated with the laser diode becomes an important limitation factor. We have measured the capacitance of the SDL 5430 and the new junction up SDL 580 laser diodes, an equivalent circuit model is developed to examine the effect of these parasitics on the speed of the laser diode. The results are consistent with our experimental observations.
The dual-rate 1773 (DR1773) fiber optic data bus (FODB) experiment is one of twenty four space fight experiments on the Naval Research Laboratory's (NRL) microelectronics and photonics test bed (MPTB). MPTB is an NRL satellite payload that will be composed of modern technology microelectronics and photonic experiments. The Goddard Space Flight Center (GSFC) experiment on MPTB will evaluate the in-flight performance characteristics of the Society of Automotive Engineers (SAE) Aerospace Standard (AS) 1773 FODB in the space radiation environment. AS1773 is a passive star coupled FODB that operates at data rates of Mbps and 20 Mbps. This protocol is commonly referred to as 'dual-rate 1773 (DR1773).' Two different DR1773 fiber optic transceiver designs are tested on the experiment. These devices are the Boeing DR1773 and the SCI DR1773 transceiver. The transceiver devices on the experiment are implemented in a star coupled system and are tested at the higher 20 Mbps data rate. It is estimated that DR1773 at 20 Mbps will meet approximately 80% of NASA's current data rate requirements. DR1773's predecessor, Mil-Std-1773, is currently being flown on several NASA spacecraft. Mil-Std-1773 operates at a single rate of 1 Mbps. Because DR1773 is based on an existing bus protocol, incorporating DR 1773 into the NASA spacecraft program would be both time and cost effective. Success of the DR1773 experiment will provide valuable data on the DR1773 FODB space radiation performance as well as proof of concept for use of the DR1773 FODB for future NASA spacecraft systems.
Kenneth LaBel, Mark Flanegan, George Jackson, Donald Hawkins, Cheryl Dale, Paul Marshall, Donald Johnson, Christina Seidleck, Rodney Bonebright, Jae Kim, Eric Chan, Thomas Bocek, William Bartholet
NASA Goddard Space Flight Center (GSFC) along with the Naval Research Laboratory (NRL) has been at the forefront of the space community in terms of the use of fiber optic data busses and links in the space radiation environment. Previously, we have described the ground radiation test program of the small explorer data system (SEDS) 1773 1 Mbps fiber optic data bus (FODB), as well as its associated in- flight space radiation-induced performance. Further work has also been presented covering higher speed photonic components utilizing III-V materials. Because of the success of the SEDS 1773 FODB coupled with the radiation testing of III-V devices, a second generation FODB capable of both 1 Mbps and 20 Mbps operation is being developed for spaceflight utilization. We present herein preliminary ground test radiation results of hybrid transceiver devices manufactured by Boeing Space Systems that perform the electro-optic and opto-electric translations in support of this medium rate FODB, the AS1773 bus. These devices, designed to be radiation hard (or rad hard), will be flying on NRL's Microelectronics and Photonics Testbed (MPTB) payload as a NASA experiment. This experiment is described in detail elsewhere in this proceedings.
Boeing has first developed a space-qualifiable, radiation- hardened, dual-rate MIL-STD-1773A fiber-optic transceiver for military command/response time division multiplexed data bus applications. This will provide an enhancement path from a fixed low data rate MIL-STD-1553 bus to a high data rate MIL-STD-1773 bus with minor modification of terminals supporting the existing function. The transceiver operates at dual-rates of both 1 and 20 Mbps over temperature (minus 25 to plus 85 degrees Celsius), and it shows a large dynamic range of greater than 20 dB in support of 32-node star network; a sensitivity of up to minus 38.7 dBm and a saturation of minus 16.1 dBm (limited mainly by test source power) at BER less than or equal to 1 multiplied by 10-10. These transceivers are currently being utilized for space and military applications at DARPA, NASA, and JPL. In this paper we describe the dual-rate transceiver design requirements, ASIC and hybrid design, and performance test results.
Langley Research Center has several atmospheric remote sensing programs which utilize high energy pulsed lasers. These lasers typically have many damaged optics after several million shots. Damage is defined herein as color changes and/or optical flaws seen in microscopic inspection, and does not necessarily relate to measured performance degradation of the optic. Inspections and measurements of some of these optics indicate that energy thresholds for several million shots damage is about an order of magnitude lower than that for single shot damage. Damage initiation is often at micron size areas at the coating interface, which grows and sometimes develops as erosion of the top of the coating. There is a wide range in polish and coating quality of new optics, even on different faces of the same optic. Military Standard 1246C can be used to provide overall particulate, and molecular film, or nonvolatile residue cleanliness scales. Microscopic inspections and photography at 10X to 500X with brightfield (perpendicular) and darkfield (oblique) illumination are useful in assigning cleanliness levels of new and in-service optics. Microextraction (effecting concentration of molecular films to small areas) provides for enhanced optical detection and surface film chemical analysis by electron-microscope energy-dispersive-spectroscopy. Similar measurement techniques can be used to characterize and document optical damage initiation and optical damage growth. Surface contamination interferes with and complicated measurements of polish and coating quality, and of optical damage. Our work indicates ultrasonic cleaning, and packaging of optics in Teflon sleeves or cups is advantageous over conventional cleaning and packaging for characterization of new optics.
With the growing maturation of vertical cavity surface emitting laser (VCSEL) technology as a source of commercial off-the-shelf components, the question of VCSEL suitability for use in avionics-qualifiable fiber-optic systems naturally follows. This paper addresses avionics suitability from two perspectives. First, measured performance and burn-in reliability results, determined from characterization of Honeywell VCSELs, are compared with application-based military and commercial avionics environmental requirements. Second, design guidelines for developing a cost-effective VCSEL optical subassembly (VCSEL/OSA) are outlined.
Packard-Hughes Interconnect has developed a detachable connector for plugging to military and commercial aerospace fiber-optic modules. The connector comprises floating spring loaded fiber-optic termini with 1-mm ceramic ferrules, all contained within a 0.136-in thick, low-profile connector plug body. The connector is mated to the package via a patented retention clip mechanism which secures the plug body to metal posts attached to the package sidewall. Optical alignment between the connector plug terminus and the package is accomplished by an alignment sleeve and mating 1-mm ceramic ferrule mounted in the package nosetube. Connector demating is performed by actuating a release button mechanism integral to the connector plug body. The fiber-optic termini in the connector plug body are easily maintained without replacing the entire connector. This makes the repair/replacement process for a broken fiber pigtail or damaged terminus endface a low cost, fast, and simple operation. The insertion loss for a simplex connector mated to a Boeing FDDI Transmitter receptacle package using 100/140 micrometers graded index optical fiber is less than 0.5 dB at 1.3 micrometers wavelength.
A design, as well as verification measurements, are presented for an end pumped, 20 Watt output power, single frequency, Tm:YAG laser driver for pumping a HBr mid-IR laser. Efficient end pumping of the Tm:YAG is achieved by `close lens coupling' 15 Watt average power, room temperature, 785 nm diode bars to several Tm:YAG rods. The Tm:YAG laser is operated single frequency (injection seeded) in order to couple efficiently its output to the narrow absorption band of HBr. A 2 micron laser operating multi-line, but with a bandwidth less than 1 - 2 GHz, is also under consideration using a HBr laser with increased pump absorption characteristics obtained by increasing the pressure or by placing the HBr laser inside the 2 micron laser using intra-cavity 2 micron pumping.
The survivability for satellite applications of two classes of quantum-well-based fiberoptic light sources was evaluated by MeV-proton space-environment simulation studies. The first was an InGaAs/GaAs strained-layer quantum-well (QW) laser; the second was a broad-band light-emitting diode (LED) based on dual asymmetric quantum wells in the InGaAs/GaAs/AlGaAs system. In contrast to earlier reports comparing bulk active-region heterostructure LEDs with similarly structured laser diodes, these QW LEDs were more tolerant of proton irradiation (-3dB power at ~3xl013 protons/cm2) than the QW lasers (- 3dB power at ~3xl012 protons/cm2). The LEDs were operated far into gain saturation with a high-loss cavity structure, while the lasers were operated in a region where gain was more sensitive to current density. Therefore, atomic displacement-related recombination sites had a greater detrimental effect upon the lasers than the LEDs. The lasers held constant slope efficiency, and current thresholds increased linearly with proton fluence, while both LED power and slope efficiency decreased with proton fluence. The degradation was similar to that predicted from a universal damage relation for GaAs electronic devices, and extends that relation to include these QW photonic devices.
One way of achieving high-power diode-end pumped lasers is to angularly multiplex several diodes on each end of the laser rod. We have successfully multiplexed four 15 W diode arrays on each end of a 6.3 mm diameter X 7.5 mm long Nd:YAG rod to produce an approximately equals 2 mm diameter pump spot. Higher laser power was achieved by adding a second laser rod pumped at both ends. The addition of the second rod facilitates thermally induced birefringence compensation by introducing a quartz polarization rotator between the rods. In addition, it was necessary to add an aspheric lens to compensate the thermal aberration induced at these high, nonuniform pump powers. With this arrangement, > 90 W has been extracted multimode, and > 60 W in a near-diffraction-limited beam.
We report the scaling considerations, design details, and experimental results for an efficient, high-power, diode-pumped laser. This Nd:YAG laser produces a cw output power of 60 W in a near-diffraction-limited beam (i.e., M2 < 1.3). In multimode operation, the laser produces an output power of 92 W. The optical-to-optical efficiency is 26% for TEM00 operation and 44% for multimode operation (based on the diode output power). The near- diffraction-limited average power in Q-switched operation is 40 W at a repetition rate 10 kHz. Polarized output powers of 40 W and extinction ratios of 40:1 have also been obtained for cw TEM00 operation.
A radially polarized laser beam is useful for applications such as laser particle acceleration. The issues of transporting and focusing (with an axicon) a radially polarized beam that was generated in the laboratory are examined. Problems of preserving the polarization while directing the beam are solved by using a compound 90-deg-fold out-of-plane pair of mirrors. When focused by an axicon, the radially polarized beam produces a diffraction-free Bessel beam. The transverse intensity distribution agrees with theory.
The effect of high temperature on the threshold gain and threshold current density of an InGaAs (GaAs based) strained quantum well laser is examined both theoretically and experimentally. It is shown that designing a quantum well laser for low threshold gain through the use of a long laser cavity and/or high reflectivity facet coatings will reduce the temperature induced threshold current increase. This result is related to the nonlinear dependence of quantum well gain and current density on carrier density. The high temperature characteristics of strained InGaAs and GaAs QWs are also compared.
The Lidar In-Space Technology Experiment (LITE) laser transmitter module (LTM) flight laser optical architecture has been space qualified by extensive testing at the system, subsystem, and component level. The projected system output performance has been verified using an optically and electrically similar breadboard version of the laser. Parasitic lasing was closely examined and completely suppressed after design changes were implemented and tested. Oscillator and amplifier-type heads were separately tested to 150 million shots. Critical subassemblies have undergone environmental testing to shuttle qualification levels. A superior three-color anti reflection coating was developed and tested for use on 14 surfaces after the final amplifier.
InGaAs/GaAs strained-layer quantum well (SQW) laser structures have been investigated for avionic applications requiring high-temperature performance. These lasers offer availability of wavelengths in the range of 0.9-1.1 micrometers for important applications in Er-doped fiber amplifiers and optoelectronic integrated circuits. For the first time, InGaAs/GaAs SQW lasers capable of cw operation up to 200 degree(s)C have been successfully demonstrated. The lasers show threshold current density of 200 A/cm2, differential quantum efficiency of 60%, output power of approximately equals 1 W for 50-micrometers oxide-stripe and 120 mW for 3-micrometers ridge- waveguide lasers, and characteristic temperature (TO) of 130-140K. In this paper, the optimization of the stripe width, orientation and cavity length for the laser performance have been studied. The characteristics of these devices are described. Measured I-V, L-I, spectrum, farfield pattern and reliability data are presented.
A standardized interface for fiber-optic sensor systems based on wavelength-division- multiplexing (WDM) has been successfully demonstrated using a novel broad-spectrum quantum-well LED and a high-resolution waveguide spectrograph. This efficient interface allows a 40-decibel system loss in 20 sensor channels. The new broadband LED and slab- waveguide spectrograph represent key enabling components for the WDM interface system. The LED produces a spectral width a factor of 3 times larger than that from conventional edge emitting LEDs in the 750-900 nm range. The compact slab-waveguide spectrograph's channel resolution (4-5 nm) and grating efficiency (>50%) compare favorably with other multimode WDM elements.
High power superluminescent diodes (SLD) with buried crescent heterostructure have been successfully developed. The output power as high as 10 mW at 180 mA and the spectral width as wide as 30 nm are achieved. The fabrication and performance characteristics of these diodes are described. Good far field patterns are obtained in both directions. Measured I-V, L-I and emission spectrum are presented.
In this work, the issues of broadband tuning in the design of a high average power Ti:Sapphire amplifier for a chromatic scanning lidar system are addressed. A novel pump delay and staging scheme is used to maintain high extraction efficiency with flat temporal and spatial pulse profiles while tuning over a 700-900 nm range. The effects of the chromatic scanning scheme on ASE suppression and beam pointing are discussed in relation to the amplifier optical system. The average power scaling for three power amplifier geometries (zigzag slabs, parallel plates, and active mirrors) was investigated to determine the limitations of each. Pump light is provided by diode laser-pumped Nd:GGG slab lasers which make up over 60 percent of the system weight. Predicted electrical to light laser efficiency was 3-4 percent over the wavelength tuning range.
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