MPB has developed a 10W Polarization Maintaining Optical Fiber amplifier (1550 nm) for space applications. The prototype is based on three stages of optical amplification with photodiodes at each stage, monitoring the output power. It includes the control electronics and software with feedback loops to dynamically control and monitor the amplifier. The design had to overcome many challenges to comply with the mechanical, thermal, radiation, and vacuum requirements for the LEO satellite space environment, while at the same time meeting the price targets for LEO constellations by maximizing the use of commercial off the shelf (COTS) components. The following were the main challenges: a) to effectively dissipate the heat generated (75-90 W); b) to select radiationtolerant electronics to drive the needed electrical current; c) to source and effectively implement components, such as the combiners and isolators, in the high power optical path compatible with vacuum at 10W output. The major challenge with regard to heat management was to find an optimal method to dissipate the heat from the third stage (high power) Erbium Ytterbium Doped Fiber. Commonly, this fiber is spooled on an Aluminium spool. The difference in the Constant Temperature Extension (CTE) between the fiber (low) and Aluminium (high) leads to a detachment of the fiber at low temperature with a high risk of breaking the fiber when passing from OFF to ON. At high temperatures, the Aluminium extends much more than the fiber, leading to an over tension on the fiber with a high risk of mechanical breakage. Different designs of the spool, supports inside the box, selection of materials, and process implementations were tried. An innovative, proprietary method was developed to satisfy this requirement. The unit successfully passed performance testing between -20°C and +40°C in vacuum with 10W output, with a wall plug efficiency of 11%. The lower temperature limitation was due to the specification of the high-power laser diodes. The higher temperature was limited by the local heating and risk of mechanical breaking of the third-stage COTS combiner and isolator. Vibration and mechanical shock are not foreseen to be an issue. The simulation demonstrated the prototype is complying with these requirements. Moreover, MPB has built similar instruments at lower power levels that have successfully passed these qualification tests. The components used were available as COTS products, including the radiation-tolerant electronics. All the components were qualified individually for > 30 krad, in vacuum, and for the temperature range -35°C to +65°C except for the highpower laser diodes which were limited to -25°C. MPBC is continuing the qualification, implementing minor design changes, in order to satisfy the complete temperature range (-35°C to +65°C).

MPB is developing space qualified 10 W End Of Life (EOL) optical amplifiers for longer range applications. Their design employs Polarization Maintaining (PM) Erbium and Erbium-Ytterbium Double Clad Fiber (EDF, EYDF) singlemode fibers. Absorption losses of the EDF and EYDF due to radiation in space are the major challenge to overcome. The gamma radiation tests show that the PM fibers have a greater sensitivity than standard fibers. However, in many applications, PM amplifiers show greater performances which is important for the power consumption.Furthermore, MPB's design minimizes Stimulated Brillouin Scattering in the fibers, a major obstacle to be overcome at this power level, even for on ground applications. Moreover, the compatibility with space environment (vacuum, temperature cycling, and radiation) of the high-power optical and electronic components (isolators, laser-diode pumps, current drivers) has to be demonstrated.The proposed optical designs compensate for radiation-induced losses, without resorting to the use of expensive radiation qualified fibers-a unique method of power recuperation through the photo-bleaching of the active fiber.

High capacity throughputs are more and more requested by satellite owners, even before launching the first generation of optical constellations. MPB is developing a commercially-competitive photonics subsystem that increases the data throughput of a "free-space" optical link in a space environment. The objective is to build and demonstrate an optical subsystem suitable for deployment in space with a target capacity of ≥100Gbit/s having a scalable architecture optimized for cost per Gbit, while maintaining acceptable (e.g. 10-4) pre-FEC bit error ratio (BER), high reliability, design flexibility.The two most promising solutions for the 100Gbps links use either a suitably-adapted commercial 100 Gbps x 1ch transceiver (e.g. commercial Dual-Pol 28Gbaud, 4 bits/symbol) or wavelength-agile WDM 10 Gbps x 10ch, or similar system (e.g. 12.5 Gbps x 8ch). The subsystem is based on the selected optimal architecture, convenient for space environment, and potentially comprising one or more of the "throughput-enhancing" possible approaches; such as the Modulation bitrate, Wavelength multiplexing (WDM), and Spectral efficiency. A large number of the performance parameters are also involved in the evaluation of the optimal solution, including: OSNR, Power at Rx, Mass and Volume, Cost, Complexity of the Software and Hardware to develop, Reliability/Redundancy, Power-Consumption and wall-plug Efficiency (W/Gbps), Signal Modulation, BER, and Stimulated Brillouin Scattering.MPB plans to verify that the 100G commercial transceiver, a coherent module optimized for terrestrial use, is compatible with the harsh space environment. Moreover, its design needs to be modified (in collaboration with the manufacturer) in order to employ distinct Tx and Rx wavelengths. Although such an approach enables all data to be sent over a single wavelength, in the event of an e.g. Tx optical-amplifier failure all transmission capability would be lost. The coherent transceivers themselves are very complicated in design, but this development has already been carried out by the manufacturer for terrestrial applications.The WDM option 10 G x 10ch has a larger mass, volume, and power per Gbps, however, the technology is based on MPB-developed boosters for space applications and offers higher redundancy (i.e. if one optical Tx amp fails, the other nine channels can still transmit). This option adds more complexity and cost since it needs to develop more software and hardware items. This development is useful for the other amplifiers with similar requirements from space primes. In addition, we are including a detailed study and prototyping of a space-borne Reconfigurable Optical Add-Drop Multiplexer (ROADM), which would enable greatly enhanced dynamic bandwidth allocation.The two approaches (single-channel high BW vs multi-channel medium BW) have respective advantages and disadvantages.