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.
This paper describes Fibertek’s progress toward developing high performance, compact, space laser communications terminals and lasers for commercial and government customers. Previous developments have addressed a variety of applications including deep space CubeSats, LEO, GEO and SmallSats. We are currently working on lunar and beyond optical com terminals. Fibertek has also developed high TRL space laser for space optical communications ranging from small CubeSat 0.5 to 3W up to 50 W WDM amplifiers supporting deep space PPM CCSDS modulations and WDM Tbps WDM space networks.
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.
Global wind measurements are critically needed to improve and extend NOAA weather forecasting that impacts U.S.
economic activity such as agriculture crop production, as well as hurricane forecasting, flooding, and FEMA disaster
planning.1 NASA and the 2007 National Research Council (NRC) Earth Science Decadal Study have also identified
global wind measurements as critical for global change research. NASA has conducted aircraft-based wind lidar
measurements using 2 um Ho:YLF lasers, which has shown that robust wind measurements can be made. Fibertek
designed and demonstrated a high-efficiency, 100 W average power continuous wave (CW) 1940 nm thulium (Tm)-
doped fiber laser bread-board system meeting all requirements for a NASA Earth Science spaceflight 2 μm Ho:YLF
pump laser. Our preliminary design shows that it is possible to package the laser for high-reliability spaceflight operation
in an ultra-compact ~ 2″x8″x14″ size and weight <8.5 lbs. A spaceflight 100 W polarization maintaining (PM) Tm laser
provides a path to space for a pulsed, Q-switched 2 μm Ho:YLF laser with ~ 30-80 mJ/pulse range at 100-200 Hz
repletion rates.
A cladding-pumped, LMA ErYb fiber-based, amplifier is presented for use in a LIDAR transmitter for remote sensing of atmospheric CO2 from space. The amplifier is optimized for high peak power, high efficiency, and narrow linewidth operation at 1572.3nm. Using highly reliable COTS components, the amplifier achieves 0.5kW peak power (440uJ pulse energy), 3.3W average power with transform limited (TL) linewidth and M2<1.3. The power amplifier supports a 30% increase in pulse energy when linewidth is increased to 100MHz. A preliminary conductively cooled laser optical module (LOM) concept has size 9x10x1.25 in (113 in3) and estimated weight of 7.2lb (3.2 kg). Energy scaling with pulse width up to 645uJ, 1.5usec is demonstrated. A novel doubleclad ErYb LMA fiber (30/250um) with high pump absorption (6 dB/m at 915nm) was designed, fabricated, and characterized for power scaling. The upgraded power amplifier achieves 0.8kW peak power (720uJ pulse energy) 5.4W average power with TL linewidth and M2<1.5.
NASA’s Goddard Space Flight Center (GSFC) is working on maturing the technology readiness of a laser transmitter designed for use in atmospheric CO2 remote-sensing. GSFC has been developing an airplane-based CO2 lidar instrument over several years to demonstrate the efficacy of the instrumentation and measurement technique and to link the science models to the instrument performance. The ultimate goal is to make space-based satellite measurements with global coverage. In order to accomplish this, we must demonstrate the technology readiness and performance of the components as well as demonstrate the required power-scaling to make the link with the required signal-to-noise-ratio (SNR). To date, all the instrument components have been shown to have the required performance with the exception of the laser transmitter. In this program we are working on a fiber-based master oscillator power amplifier (MOPA) laser transmitter architecture where we will develop a ruggedized package and perform the relevant environmental tests to demonstrate TRL-6. In this paper we will review our transmitter architecture and progress on the performance and packaging of the laser transmitter.
A 1um fiber laser outputting high energy (<1mJ) pulse-bursts with high peak powers (<15kW) and narrow linewidth (<300MHz) is an attractive pump source for tunable periodically poled crystal (PPx) based OPA’s which are used in gas sensing, imaging and communication applications. Here a turn-key 1064nm PM Yb-doped fiber amplifier capable of generating high pulse burst energies with transform limited linewidth is presented. The ~20W average power capable laser is optimized for high energy (0.5-2mJ) and high peak power (<10kW) operation at low duty cycles (<0.1%). The laser is capable of operating at <10x the saturation energy level of the final stage gain fiber and achieves a high level of pulse-to-pulse peak power uniformity within pulse-burst. Stimulated Brillion Scattering (SBS) limited micro pulse energy up to 40uJ is achieved and SBS dependence on micro pulse width and separation are characterized. High wall plug efficiency (<20%) for the FPGA controlled system is maintained by temporal and spectral ASE suppression and by spreading the necessary pulse pre-shaping losses (~12dB) to three different amplitude modulation points in the amplifier chain.
A Yb LMA fiber amplifier based laser transmitter capable of operating with high average power and high
energy (~500W, 1mJ) is presented. The prototype, all-fiber, high TRL level laser transmitter is designed to meet all
the single aperture requirements of an eight aperture deep space laser beacon system. The high speed FPGA
controlled transmitter supports a directly modulated DFB laser and two acousto-optic modulators which are used to
implement an open loop pattern dependent -pulse pre-shaping algorithm. Ultra-fast high power diode drivers are
used for generating outer nested PPM modulation with Binary PPM (67usec, 33mJ pulses) and for implementing
<1usec loss of signal (LOS) protection. Optical performance to be presented will include diffraction limited
(M2~1.2) nested PPM optical outputs with >300W average and 9kW peak power with >70% o-o efficiency for the
final power stage.
We utilize a novel hybrid wavelength division multiplexed, optical time division multiplexed (WDM-OTDM) model locked semiconductor laser for applications in ultrahigh data rate communication links, computer interconnects, and optical sampling applications. The key philosophy behind using a hybrid approach is that state-of-the-art system performance can be achieved without the necessity of operating at the limits of either a pure WDM or OTDM technology platform.
Parallel transmission and processing of high-speed data may be accomplished by using multiple wavelength channels. To process this type of wavelength division multiplexed information, it is necessary to be able to switch the multiple wavelengths, simultaneously. In this paper we demonstrate multiwavelength switching with a single switch, utilizing a nonlinear optical loop mirror with a semiconductor optical amplifier. Switching is shown for 14 wavelength channels across a 14-nm bandwidth for data rates up to 2.5 GHz. Switching contrasts of 10 dB are shown with control energy as low as 1.6 pJ.
We utilize a novel hybrid wavelength division multiplexed, optical time division multiplexed (WDM-OTDM) modelocked semiconductor laser for applications in ultrahigh data rate communication links, computer interconnects, and optical sampling applications. The key philosophy behind using a hybrid approach is that state-of-the-art system performance can be achieve without the necessity of operating at the limits of either a pure WDM or OTDM technology platform.
Semiconductor laser diodes may play an important role in synchronous optical networks as sources of optical modelocked pulse trains with robust timing stability. In this paper, it is demonstrated how injection modelocked semiconductor lasers can be used in all-optical clock recovery systems. Experimental measurement of clock recovery dynamics shows that these devices offer robust clock recovery with low injected data power (less than 6 uW), large repetition rate locking bandwidth (2.9 X 10-3 fractional bandwidth), and small timing jitter (less than 93 fs). Clocking from an injected data stream at 1/50th the clocking repetition rate is demonstrated.
Semiconductor laser diodes play an important role in synchronous optical networks as sources of optical modelocked pulse trains with robust timing stability. In this paper, it is demonstrated how these diodes may be used in such applications as optical clock distribution, photonic network synchronization, and all-optic clock recovery. Emphasis is placed on all-optical clock recovery with preliminary results presented.
KEYWORDS: Optical amplifiers, Semiconductor lasers, Semiconductors, Systems modeling, Optical semiconductors, Mode locking, Laser systems engineering, High power lasers, Prisms, Dispersion
Semiconductor diode lasers are playing important roles in high speed information processing, telecommunications, and high speed measurement and diagnostic systems. This paper presents recent developments in the generation, amplification, and utilization of high power modelocked optical pulses from traveling wave semiconductor optical amplifier devices.
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