This paper describes progress toward a space -based 51 W average power amplifier for deep space PPM and Earth GEO links. We demonstrated a broadband WDM amplification at 50W with flat gain across a 25 nm bandwidth. Similarly, for 5 W amplifier we demonstrated a flat gain across a 32 nm bandwidth. These amplifiers demonstrate the feasibility for multi-channel space optical communications links. To increase the bandwidth GEO links to multi-Tbps and deep space links to > Gbps. The laser supports kW/channel SBS limited peak power for PPM and achieves an optical-to-optical efficiency of > 40%. In a separate but related effort for a deep space uplink beacon, we achieved 500 W average power, 2.6 kW peak power PPM (2,2) for a 1 μm uplink transmitter. Reliable SBS free operation is achieved with phase modulation resulting in 26 GHz transmitter linewidth. Uplink transmitter is optimized for 65 usec (pulsewidth) slot size—achieving fastest possible rise/fall times (<10 usec) and pulse uniformity.
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.
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.
Fibertek has demonstrated a dual-wavelength narrow linewidth UV laser transmitter for NASA airborne ozone DIAL remote sensing application. The application requires two narrow linewidth lasers in the UV region between 300 nm and 320 nm with at least 12 nm separation between the two wavelengths. Each UV laser was based on a novel ring structure incorporating an optical parametric oscillator (OPO) and a sum frequency generator (SFG). The fundamental pump source of the UV laser was a single frequency 532 nm laser, which was frequency-doubled from a diode-pumped, injection-seeded single frequency Nd:YAG laser operating at 1064 nm and 50 Hz repetition rate. The ring frequency converters generated UV wavelengths at 304 nm and 316 nm respectively. The demonstrated output energies were 2.6 mJ for 304 nm and 2.3 mJ for 316 nm UV lines, with room to potentially achieve more energy for each laser. Linewidth narrowing was achieved using a volume Bragg grating as the output coupler of the OPO in each ring oscillator. We obtained spectral linewidths (FWHM) of 0.12 nm for the 304 nm line and 0.1 nm for the 316 nm line, and the UV energy conversion efficiencies of 12.2% and 9.1%. Fibertek built an airborne DIAL transmitter based on the reported demonstration, which was a single optical module with dual-wavelength output at the demonstrated wavelengths. NASA plans to field the UV laser transmitter as a key component of the High Spectral Resolution Lidar–II (HSRL–II) high altitude airborne instrument to perform autonomous global ozone DIAL remote sensing field campaigns.
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.
Fibertek has demonstrated a single frequency, wavelength stabilized near infrared laser transmitter for NASA airborne water vapor DIAL application. The application required a single-frequency laser transmitter operating at 935 nm near infrared (NIR) region of the water vapor absorption spectrum, capable of being wavelength seeded and locked to a reference laser source and being tuned at least 100 pm across the water absorption spectrum for DIAL on/off measurements. Fibertek is building a laser transmitter system based on the demonstrated results. The laser system will be deployed in a high altitude aircraft (ER-2 or UAV) to autonomously perform remote, long duration and high altitude water vapor measurements.
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.
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