High gain optical amplifiers with low noise are desirable to pre-amplify free-space optical communications signals to usable levels prior to detection without causing significant distortion of the data stream. We report design characteristics and performance of an Optical Low Noise Amplifier (OLNA) for space applications which meet the growing needs of government and industry. Our OLNA technology features high gain ⪆ 60 dB for input powers as low as ⪅ -60 dBm, can operate without optical damage at input powers ⪆ -10 dBm, and has demonstrated noise figures ≤ 4.3 dB (3.8 dB without input isolator) in a non-PM architecture across the 1540-1560 nm band. The system architecture is specifically designed for long-term operation in space environments. Results will be presented verifying the performance of the OLNA through spectral noise figure measurements as well as testing using a variety of communications formats and data rates.
KEYWORDS: Laser communications, Receivers, Telecommunications, Acquisition tracking and pointing, Single mode fibers, Signal to noise ratio, Optical amplifiers, Mirrors, Free space optics, Free space
This work highlights 10G uncoded OOK communications signals in a lab-based over-the-air demonstration through one of Fibertek’s terminals designed for 1G LEO direct to earth links. Our demonstration not only proves that the 1G terminals are capable of higher data rates without penalty but also validate the pointing stability of the system. The bit error rate tests resulted in a less than 3-dB power penalty compared to back-to-back measurements at 1e-9 which is in line with the theoretical half-angle divergence-to-jitter ratio (w0/σ) of around 7. This ratio meets the design goals for the terminal. We show that the jitter performance of the terminal meets the design goals of providing optimal performance for error free requirements of 1e-9 and demonstrate that through both direct measurement of the jitter on a PSD and the performance impact on a communications signal.
Distributed satellite mesh networks utilizing low-cost small satellites require communications components that have low impact on the cost, size, weight and power (SWaP-c) while long range, high bandwidth communications can reduce the number of required satellites in the mesh network. Free space laser communications provide a potential for low-SWaP, long-range communications links by leveraging high aperture gains due to short wavelengths yielding narrow divergence. Additionally, wide band optical booster amplifiers frequently operate with an average power limit rather than a peak power limit enabling low-duty cycle formats to take advantage of high peak powers. Full realization of these benefits depends on the format being utilized. New-space laser communications terminals leverage much of the existing fiber optical telecommunication infrastructure to repurpose products for long range free space applications that currently only have a launch amplifier and, potentially, a preamplified receiver. While long haul fiber applications favor binary phase shift keying formats, low cost applications of optical fiber telecommunications links that require low-SWaP on the transmitter and receiver ends of the link frequently drive designs towards intensity modulated direct drive (IM-DD) links. We investigate extending the range of a free space optical link through use of three different variable data rate methods including, reducing receiver bandwidth, utilizing burst waveforms, and pulse position modulation formats (PPM). Our results indicate that although a higher SNR is required for PPM formats, orders higher than 64 can acquire links at comparable average power and data rate as differential phase shift keying formats under similar receiver conditions.
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
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.
In recent years, various terrestrial free-space optical (FSO) communications systems have been demonstrated to achieve high-bandwidth communications between mobile platforms. The terminal architectures fall into three general categories: (1) single aperture systems with tip/tilt control, (2) multi-aperture system with tip/tilt control, and (3) single aperture systems with tip/tilt control and higher order adaptive optics correction. Terrestrial modem approaches generally use direct detection receivers because they provide high bandwidth capability (0.1-10 Gbps) without the complexity of coherent detection. Modems are often augmented with a mix of forward error correction (FEC), interleaving, and/or retransmission for improved data transport. This paper will present a terminal and modem architecture for a low-SWAP FSO communications system that enables robust, high-bandwidth communications under highly scintillated links as found in terrestrial applications such as air-to-air, air-to-surface, and surface-to-surface links.
Optical time and frequency transfer offers extremely high precision wireless synchronization across multiple platforms for untethered distributed systems. While large apertures provide antenna gain for wireless systems which leads to robust link budgets and operation over increased distance, turbulence disrupts the beam and limits the full realization of the antenna gain. Adaptive optics can correct for phase distortions due to turbulence which potentially increases the total gain of the aperture to that for diffraction-limited operation. Here, we explore the use of adaptive optics terminals for free-space time and frequency transfer. We find that the requirement of reciprocity in a two-way time and frequency transfer link is maintained during the phase compensation of adaptive optics, and that the enhanced link budget due to aperture gain allows for potential system operation over ranges of at least tens of kilometers.
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.