A compact, lightweight, laser transmitter using space-qualified heritage oscillator from the currently on-orbit ICESat-2 transmitter was built and tested. The Nd:YVO4 oscillator’s cavity length was reduced by 30% compared with ICESat-2 transmitter and achieved an intermediate 1064 nm energy of ~180 μJ. Final 532 nm output performance after external cavity frequency doubling and beam shaping showed pulse energies <80 μJ and pulse widths < 1 ns. The system was engineered and packaged for an overall dimension of 5.4” L × 3.1” W × 4.1” H and a total mass <1.5 kg. The laser housing and optics were hermetically sealed for contamination control to reduce laser damage and improve reliability. Environmental testing was done, and this packaging design is intended for future space-qualified operation.
Fibertek has developed a ground based high-power (7 kW) optical communication uplink laser to support NASA’s Jet Propulsion Laboratory’s (JPL) Deep Space Optical Communication (DSOC) program. The uplink laser assembly (ULA) provides a beacon laser and Binary PPM (BPPM) modulation signaling to the DSOC spacecraft terminal. Laser beacons with scalable power (multi-kW) are needed for Earth-to-asteroid, inter-planetary (Mars), and deep-space optical communication uplinks. This paper describes the ULA design, development, and performance verification testing. A single laser system was delivered in 2020 for performance testing and initial integration with the optical uplink telescope system. The full ULA laser was delivered and installed in NASA JPL’s Optical Communications Telescope Laboratory (OCTL) optical ground station facility in 2021. DSOC will fly on the NASA Psyche asteroid mission in 2022 and demonstrate deep space laser communications to earth. The ULA is an automated system with a comprehensive user interface that commands and controls ten (10) individual pulsed Yb fiber lasers. The individual lasers are incoherently combined and propagated to the Psyche satellite. ULA commands and monitors the performance of each individual laser, provides redundancy for high availability, and provides multiple safety interlocks to safeguard equipment and personnel. Each Yb fiber laser is collimated individually with a beam quality of M2 < 1.2 at 1064 nm in a pulsed PPM format with 2.7 kW of peak power. This paper describes the DSOC requirements and provides performance verification data.
Fibertek has developed a space qualifiable 50W 8Ch. WDM Amplifier prototype that is designed to meet all the environmental and optical requirements of a DSOC mission. The deliverd amplifier is optimized for efficiency and athermal performance achieving 22% e-o efficiency. The high TRL 1.5-μm high TL fiber amplifier supports up to 6W/channel, with >128-ary pulse-position-modulation (PPM) format, and with 25-nm gain-flat bandwidth. Output electro-optic characteristics, the System Reliability Analysis, Mechanical Thermal analysis and Mechanical Structural and Vibration analysis of the high TRL delivered laser prototype are presented. A power efficient TDM based FWM mitigation technique that improves PEV performance of Tx, is demonstrated.
51W average power, 7 Channel WDM Fiber Laser Transmitter with 25nm flat gain has been demonstrated for optical space communication applications. Power Amplifier supports >10kW/channel SBS limited peak power and achieves o-o efficiency 44%. Pulse energy variation (PEV) due to gain dynamics and four wave mixing of the PPM tx output is characterized. Significant improvement in PEV with wavelength dependent pre-pulse shaping is demonstrated. A high reliability 50W 8 WDM channel amplifier design is described. The amplifier will be housed in a high TRL small SWAP space laser package with dimensions 10.6x13.8x 5.3” and weighs 28.7 lbs
Fibertek reports on the design and performance of two high power ruggedized Thulium fiber laser systems designed for spaceborne and airborne applications. The spaceflight system is a 100 W average power, linearly polarized, 1940 nm thulium doped fiber laser (TDFL) packaged in a hermetic 11-liter module. The airborne system is an all-fiber, narrowlinewidth, master oscillator power amplifier architecture with staged thulium fiber amplifiers with 80 W peak power and 20 W average power in a quasi-continuous temporal waveform. The airborne laser includes programmable digital phase codes with bit rates up to several GHz. We will discuss the overall system performance and environmental qualification testing of both systems.
We report on the design, fabrication and testing of a 1645 nm injection-seeded and locked Er:YAG laser resonator with single-frequency output operating at a methane line with > 500 μJ/pulse at 4-7 kHz pulse repetition frequencies with a pulse width < 1 μsec. The state-of-the-art technology for lidar methane sensing uses Optical Parametric Oscillator (OPO)/Optical Parametric Amplifier (OPA)–based systems. A key innovation of our system is the use of resonantly 1532 nm pumped Er:YAG gain crystals, which results in improved efficiency and a reduced footprint compared with the current OPO systems. Another feature adapted in our system is the high bandwidth injection locking technique which includes fast piezoelectric mirror and in-house developed FPGA locking algorithm, capable of active locking and wavelength control for each pulse as pulse repetition frequencies up to 10 kHz. The single frequency laser output follows the seed diode wavelength and which scans across the targeted methane absorption line.
We describe Fibertek’s progress toward commercializing space laser communications and new features of our secondgeneration compact laser communication terminal (LCT). The LCT design is modular, flexible and can accommodate a variety of waveforms and data formats. Fibertek has a unit deployed in space for initial testing followed by additional units for more broad-based market applications. Our first-generation optical telescope assembly was originally designed for NASA Deep Space CubeSat laser communications. It was customized as a complete commercial LEO LCT system which is 2U in size, 2 kg in mass, and provides Gbps data rates. The optical transceiver has a shared transmit/receive optical path that uses a laser beacon to ensure high pointing accuracy, active control of the pointing stability, and ensures a strong optical signal-to-noise ratio (SNR) during link operation. The terminal has been manufactured and tested, providing high accuracy pointing and low jitter. Our second generation LCT system features bidirectional operation and support for an eyesafe beacon for uplink applications. Bi-directional operation is attractive for inter-satellite links (ISL), uplinks of data, pointing acquisition and tracking (PAT), position, navigation and timing (PNT), and for telemetry, tracking, and command (TTandC). The eyesafe uplink beacon makes it easier to get FCC authorization for operation. The LCT includes a 64 mm telescope and a 1.5-μm fiber-amplifier with >2 W optical power that enables future updates to allow operation up to GEO orbit with the addition of SCPPM and 10-100 Gbit/sec.
Fibertek has designed and is building a spaceflight (TRL 5-6) high-efficiency, high reliability (97.2% for 5-year mission) 100 W average, 1940 nm thulium doped fiber laser (TDFL) meeting all requirements for a NASA Earth Science spaceflight 2 μm Ho:YLF pump laser. These include polarization extinction ratio <16dB, diffraction limited beam quality, narrow linewidth (0.35nm) and >50% optical to optical efficiency. High reliability laser package, optimized for space environment and SWAP has size 10.6”x13.8”x4.4”and weight 30lbs. A summary of laser package design is presented, including structural and thermal analysis. Preliminary environmental testing results of the space laser are also presented. A spaceflight 100 W PM Tm laser provides a path to space for a pulsed, Q-switched 2 μm Ho:YLF laser with ~80 mJ/pulse at 100-200 Hz.
A long-lived UV laser is an enabling technology for several high-priority, space-based lidar instruments. These include a next generation cloud and aerosol lidar that incorporates a UV channel, a direct detection 3-D wind lidar, and an ozone differential absorption lidar (DIAL) system. To advance the TRL of UV lasers we have designed and built a High Energy UV Demonstrator (HEUVD) that has increased output power and space-qualifiable packaging and that is mechanically robust, thermally-stable, and fully conductively cooled. Contamination control processes and optical coatings have been chosen that are compatible with multi-billion shot lifetimes. The diode pumped laser contains an essentially polymer free internal module that houses the third harmonic generator and beam expansion optics. When operated at 150 Hz the laser has demonstrated 275 mJ per pulse at 1064 nm, second harmonic conversion efficiencies of 70%, and third harmonic conversion efficiencies of 45%, thus meeting the 355 nm 100 mJ/pulse goal with margin. We have successfully completed a full power 532 nm life test, a half power (50 mJ/pulse) UV lifetest, and a full power (100 mJ/pulse @ 150 Hz) lifetest. These tests have validated the importance and success of our approach to contamination control for achieving a long-lived UV laser. They also resurfaced the need for the qualification of the pump laser diodes and more attention to the external optics in a UV lidar system.
We report on the cause and corrective actions of three amplifier crystal fractures in the space-qualified laser systems used in NASA Goddard Space Flight Center’s (GSFC) Ice, Cloud, and Land Elevation Satellite-2 (ICESat-2). The ICESat-2 lasers each contain three end-pumped Nd:YVOO4 amplifier stages. The crystals are clamped between two gold plated copper heat spreaders with an indium foil thermal interface material, and the crystal fractures occurred after multiple years of storage and over a year of operational run-time. The primary contributors are high compressive loading of the NdYVO4 crystals at the beginning of life, a time dependent crystal stress caused by an intermetallic reaction of the gold plating and indium, and slow crack growth resulting in a reduction in crystal strength over time. An updated crystal mounting scheme was designed, analyzed, fabricated and tested. Thee fracture slab failure analysis, finite-element modeling and corrective actions are presented.
Fibertek has developed and demonstrated an ideal high-power; low-risk; low-size, weight, and power (SWaP) 2051 nm laser design meeting the lidar requirements for satellite-based global measurement of carbon dioxide (CO2). The laser design provides a path to space for either a coherent lidar approach being developed by NASA Jet Propulsion Laboratory (JPL)1,2 or an Integrated Path Differential Lidar (IPDA) approach developed by Harris Corp using radio frequency (RF) modulation and being flown as part of a NASA Earth Venture Suborbital Mission—NASA’s Atmospheric Carbon and Transport – America.3,4 The thulium (Tm) fiber laser amplifies a <500 kHz linewidth distributed feedback (DFB) laser up to 25 W average power in a polarization maintaining (PM) fiber. The design manages and suppresses all deleterious non-linear effects that can cause linewidth broadening or amplified spontaneous emission (ASE) and meets all lidar requirements. We believe the core laser components, architecture, and design margins can support a coherent or IPDA lidar 10-year space mission. With follow-on funding Fibertek can adapt an existing space-based Technology Readiness Level 6 (TRL-6), 20 W erbium fiber laser package for this Tm design and enable a near-term space mission with an electrical-to-optical (e-o) efficiency of <20%.
A cladding-pumped PM Tm fiber-based amplifier optimized for high efficiency and high-power operation at 2051 nm is presented. The two-stage amplifier has been demonstrated to achieve 25 W average power and <16 dB polarization extinction ratio (PER) out of a single-mode PM fiber using a <500 kHz linewidth JPL DFB laser5-7 and 43 dB gain. The power amplifier’s optical conversion efficiency is 53%. An internal efficiency of 58% is calculated after correcting for passive losses. The two-stage amplifier sustains its highly efficient operation for a temperature range of 5-40°C. The absence of stimulated Brillouin scattering (SBS) for the narrow linewidth amplification shows promise for further power scaling.
Fibertek has developed an injection locked, resonantly pumped Er:YAG solid-state laser operating at 1.6 μm capable of pulse repetition rates of 1 kHz to 10 kHz for airborne methane and water differential absorption lidars. The laser is resonantly pumped with a fiber-coupled 1532 nm diode laser minimizing the quantum defect and thermal loading generating tunable single-frequency output of 1645-1646 nm with a linewidth of < 100 MHz. The frequency-doubled 1.6 μm Er:YAG laser emits wavelengths in the 822-823 nm spectrum, coincident with water vapor lines. Various cavity designs were studied and optimized for compactness and performance, with the optimal design being an injection seeded and locked five-mirror ring cavity. The laser generated 4 W of average power at pulse repetition frequencies (PRFs) of 1 kHz and 10 kHz, corresponding to 4 mJ and 400 μJ pulse energies, respectively. The 1645 nm was subsequently frequency doubled to 822.5 nm with a 600 pm tuning range covering multiple water absorption lines, with a pulse energy of 1 mJ and a pulse repetition frequency of 1 kHz. The resonator cavity was locked to the seed wavelength via a Pound Drever Hall (PDH) technique and an analog Proportional Integral Derivative (PID) Controller driving a high-bandwidth piezoelectric (PZT)-mounted cavity mirror. Two seed sources lasing on and off the methane absorption line were optically switched to tune the resonator wavelength on and off the methane absorption line between each sequential output pulse. The cavity locking servo maintained the cavity resonance for each pulse.
We report on the development, testing, and initial space qualification of a 1.5-μm, high-power (6 W), high wall-plug efficiency (∼15%), pulse-position-modulated (PPM), polarization-maintaining, fiber laser transmitter subsystem for deep-space laser communication links. Programmable high-order PPM modulation up to PPM-128 formats, with discrete pulse slots ranging from 0.5 to 8 ns, satisfies variety of link requirements for deep-space laser communication to Mars, asteroids, and other deep-space relay links, as per the National Aeronautics and Space Administration’s space laser communication roadmap. We also present initial space qualification results from thermal-vacuum tests, vibration testing, radiation testing, and an overall reliability assessment.
A long-lived UV laser is an enabling technology for a number of high-priority, space-based lidar instruments. These
include next generation cloud and aerosol lidars that incorporates a UV channel, direct detection 3-D wind lidars, and
ozone DIAL (differential absorption lidar) systems. In previous SBIR funded work we developed techniques for
increasing the survivability of components in high power UV lasers and demonstrated improved operational lifetimes. In
this Phase III ESTO funded effort we are designing and building a TRL (Technology Readiness Level) 6 demonstrator
that will have increased output power and a space-qualifiable package that is mechanically robust and thermally-stable.
For full space compatibility, thermal control will be through pure conductive cooling. Contamination control processes
and optical coatings will be chosen that are compatible with lifetimes in excess of 1 billion shots. The 1064nm output
will be frequency tripled to provide greater than 100 mJ pulses of 355 nm light at 150 Hz. The laser module build was
completed in the third quarter of 2015 at which time a series of life tests were initiated. The first phase of the lifetime
testing is a 532 nm only test that is expected to complete in April 2016. The 532 nm lifetest will be followed by a 4
month half power UV life test and then a four month full power UV life test. The lifetime tests will be followed by
thermal/vacuum (TVAC) and vibration testing to demonstrate that the laser optics module design is at TRL 6.
We report on the development, testing and initial space qualification of a 1.5-μm, high-power (6W), high wall-plug efficiency (~15%), pulse-position-modulated (PPM), polarization-maintaining (PM), fiber laser transmitter subsystem for deep-space laser communication links. Programmable high-order PPM modulation up to PPM-128 formats, with discrete pulse slots ranging from 0.5- to 8-nsec, satisfies variety of link requirements for deep space laser communication to Mars, asteroids, and other deep-space relay links, per NASA's space laser communication roadmap. We also present initial space qualification results from thermal-vacuum tests, vibration testing, radiation testing and overall reliability assessment.
A long-lived UV laser is an enabling technology for a number of high-priority, space-based lidar instruments. These include next generation cloud and aerosol lidars that incorporates a UV channel, direct detection 3-D wind lidars, and ozone DIAL (differential absorption lidar) system. In previous SBIR funded work we developed techniques for increasing the survivability of components in high power UV lasers and demonstrated improved operational lifetimes. In this Phase III ESTO funded effort we are designing and building a TRL (Technology Readiness Level) 6 demonstrator that will have increased output power and a space-qualifiable package that is mechanically robust and thermally-stable. For full space compatibility, thermal control will be through pure conductive cooling. Contamination control processes and optical coatings will be chosen that are compatible with lifetimes in excess of 1 billion shots. The 1064nm output will be frequency tripled to provide greater than 100mJ pulses of 355nm light at 150 Hz. After completing the laser module build in the third quarter of 2015 we will initiate lifetime testing, followed by thermal/vacuum (TVAC) and vibration testing to demonstrate that the design is at TRL 6.
We report on the completion of the space qualification testing program for NASA Goddard Space Flight Center’s
(GSFC) Ice, Cloud, and Land Elevation Satellite 2 (ICESat-2) program. This paper describes the final performance
results of the fully integrated (laser and electronics) flight laser system with an emphasis on the system design evolution
from a breadboard demonstration to a fully space-qualified laser system. The 532 nm ICESat-2 laser transmitter
generates diffraction limited pulse energies of 1 mJ, pulsewidths of < 1.5 ns, and 10 kHz pulse repetition frequency and
has minimum lifetime of 1 trillion pulses on-orbit. A combination of engineering design units and correlated structural
thermal optical analysis was used to systematically improve reliability and performance over the operating environment.
The laser system qualification and acceptance test programs included electromagnetic interference (EMI), vibration, and
thermal vacuum (TVAC) testing. This paper presents key laser performance results and lessons learned on the multi-year
laser development to facilitate future space-qualified laser developments, improve reliability, and increase performance.
Fibertek is under contract from NASA Goddard to build four space qualified laser transmitters for the ICESat-2 (Ice, Cloud, and Land Elevation Satellite) program, a second generation orbiting laser altimeter. Pertinent laser parameters driving the design included laser wall plug efficiency, laser reliability, a relatively narrow linewidth with wavelength tunability, high beam quality (M2<1.6), short pulsewidths (<1.5ns), and energy scalable from 250 μJ to 900μJ in predefined steps. The laser design employs fiber coupled 880nm diodes and end-pump Nd:YVO4 slabs as the gain medium in a master oscillator/power amplifier (MOPA) architecture with an LBO second harmonic generator (SHG). Following the SHG is a telescope that sets the final beam size and divergence requirements. The first laser built will be the Integration and Test Laser (ITL) used for qualification of the design. The ITL will set the baseline parameters for the flight laser builds. The ITL will also validate the design for the telescope and will be subjected to the full environmental testing required for a space hardened flight laser. Environmental testing includes vibration, thermal vacuum conditions, and electromagnetic interference (EMI). Our presentation will address the measured laser parameters from ITL as compared to the as designed laser.
Fibertek has developed a space qualifiable, highly efficient, high power (<5W), fiber based 1.5um laser optical module (LOM). The transmitter achieves 6W average and <1kW peak power out of a 2m long single mode delivery fiber with 8nsec pulses and <6Ghz linewidth. Stimulated Brillouin Scattering (SBS) is managed by precise linewidth control and by use of LMA gain fiber in the power stage while maintaining the required diffraction limited, and highly polarized (PER<20dB) output. Size and weight of the built LOM are 8”x10”x2.375” and 3 kg, respectively. With improvements in the modulation scheme and component specification, achieved LOM electrical to optical efficiency is over 17.0%. Highly efficient operation is sustained for a wide range of pulse-position modulation (16 to 128-ary PPM) formats with pulse widths varying from 8nsec to 0.5nsec and operation temperature 10-50C. Pressure stress analysis, random vibration analysis and thermal analysis of the designed LOM predicts compliance with NASA GEVS levels for vibration and thermal cycling in a vacuum environment. System will undergo both thermal vacuum and vibration testing to validate the design.
Space based laser remote-sensing for Earth observation and planetary atmospheres has traditionally relied on the mature diode-pumped solid-state laser and nonlinear frequency conversion technology. We highlight representative examples, including ongoing space mission programs at Fibertek. Key design issues are highlighted, and the lessons learned from a multi-disciplinary design process addressing the space-qualification requirements. Fiber laser/amplifier system provides an agile optical platform for space based laser applications ‒ space lasercom, space-based Earth (or planetary) remote sensing, and space-based imaging. In particular we discuss ongoing efforts at Fibertek on a space-qualifiable, high-performance 1.5-μm Er-doped fiber laser transmitter for inter-planetary lasercom. Design and performance for space qualification is emphasized. As an example of an agile laser platform, use of above fiber laser/amplifier hardware platform for space based sensing of atmospheric CO2 is also highlighted.
Launching a precision optical instrument, such as a laser, into space presents a challenge due to the harsh structural and acoustic coupled loads that result from the launch vehicle engines. Special precautions must be implemented to protect the payload and attenuate the high frequency random vibration environment while still maintaining accurate alignment and beam pointing. Fibertek has designed, analyzed, and tested novel Ti6Al4V flexures for isolating a space laser from a high g-load random vibration launch environment. Detailed finite element analysis was done to verify structural integrity of flight hardware by assessing the applied loads, load paths, and critical failure modes. Experimental data validated the modeling and the overall conclusions.
The design of space-flight hardware is typically required to be at a Technology Readiness Level (TRL) of 6 before the build of the actual flight hardware can begin. At the early design phase the "relevant environment" for TRL-6 is frequently not well defined. For the ICESat-2 laser relevant environment was defined as the qualification levels in GEVS (General Environmental Verification Standard, GSFC-STD-7000). Our approach to dealing with the high-frequency content of the 14.1 grms random vibration levels in GEVS was a flexure mounted canister design that filtered the highfrequency content. In our talk we will discuss the program and system level implications of this design approach.
Fibertek has developed an environmentally hardened Technology Readiness Level-6 laser transmitter system for the NASA Ice, Cloud and land Elevation Satellite-2 (ICESat-2). The laser transmitter generates over 9 W of 532 nm output with a pulse repetition rate of 10kHz and a FWHM pulse width of < 1.5 ns with an expected lifetime of > 1 trillion shots. This paper presents the results of the Structural, Thermal and Optical analysis, details on the NASA General Environmental Verification Specification testing requirements, and the success of the laser transmitter performance through vibration and thermal vacuum testing.
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