High Power Optical Amplifier (HPOAs) for Free Space

The objective of this proposal is to develop innovative highly reliable High Power Optical Amplifier (HPOA) modules for optical satellite communications (SATCOM) operating over broad ranges of temperatures (i.e. from -40 to +80 0C) and of radiation environment (i.e. total dose of 300krads with a rate of 108rad/s), enabling 20-year full-duty cycle lifetime of Geosynchronous Earth Orbit (GEO) mission. The Phase I effort is focused on investigating the feasibility of manufacturing of such a HPOA by means of modeling and designing the HPOA for the desired optical specs as well as modeling and designing optic/electronic components and packaging for the required reliability specs. In the projected work, we will also manufacture and assembly key components of the HPOA as proof-of-concept studies. Photon-X has an extensive expertise on radiation hardened broadband fiber based optical amplifiers with state-of-the-art designs of optical and electronic layers as well as packaging, Fig. 1 [related patents in Section 4]. Our proposed design is based on two stage rare earth doped fiber amplifier. The first stage is a pre-amplifier with a low noise figure (i.e. 3dB) consisting of a small core area Erbium doped fiber (EDF) as means to increase dynamical range and lower overall noise figure (NF) of the HPOA. The second stage is a high power amplifier based on an Erbium Ytterbium doped fiber (EYDF) with single or/and double clad structures that would provide high output power (i.e. from 500mW to several Watts) in saturation when pumped with multimode pumps at 976nm (e.g. 1 to 6). The key element of the HPOA is the gain medium, where we employ our proprietary (i.e. patent pending) EYDF radiation hardening technique based on pre-exposure and annealing methods. In the proposed designs, besides radiation hardened EYDF, HPOA consists of all commercial-off-the-shelf (COTS) components that have been widely used in telecommunications with proven reliability (i.e. Telecordia standards) in terms of power handling and life time. In addition to Telecordia standards where the minimum operation temperature is 00C, pump lasers’ temperature controller (TEC) circuitry will be modified to accommodate an operation temperature down to -400C. For the pump lasers’ driving current and TEC controllers, we will use our patented ultralow power consumption circuitry designs as means to minimize required operation power and associated thermal management issue [1-2]. For accelerated radiation reliability testing, we utilize low dose (100rad/hr) Cs137 rod source (RWJU Radiation Research center, NJ) for Master Curve analysis to obtain lifetime prediction, and high energy linear accelerator source (St. Mary Radiation Research Center, IN) for high dose (62MeV, LET) radiation burst testing. In the proposed work, our main consultant is Dr. E. Long of Longhill Technologies who will provide expertise on GEO radiation environment modeling and radiation shielding material simulations. In addition, we will utilize thermal modeling tool, COSMOSM, to provide thermal management of DCs and TECs. The projected dimensions and weight of the proposed HPOAs are of 15x12x3cm3 and 1.8lb, respectively. BENEFIT: The intensity of growth in bandwidth demand with the network centric warfare strategies of the future has been challenging RF based SATCOM with the requirement of ever increasing bandwidth capacity. FSO laser communications provide a key advance in SATCOM in terms of increasing capacity and capability (i.e. several orders of magnitude higher), reducing in weight, size and power consumption as well as immunity to EMI, thus increasing reliability. Since HPOAs are an enabling technology for laser based SATCOM, the availability of reliable HPOA’s promotes warfighter’s mission effectiveness with significantly greater battlefield bandwidth to access all of the information required to maximize mission effectiveness. We believe that our HPOAs that will immediately enable reliable communication bandwidth capacity without sacrificing size, weight and power consumption as well as radiation environment failure issues.