Electro-absorption modulated laser for analog and digital satellite payload applications

Abstract

Optical technologies play an increasing role in telecom satellite payloads for analog or digital applications. When large SWaP (size, weight, and power) is prohibitive or for applications where low cost is a major design goal, an electro-absorption modulated laser (EML) can provide a good balance between integration and performance optimization through separated control of emission and modulation. 1550 nm EML for ground applications were evaluated for optical local oscillator (LO) distribution, photonic RF frequency conversion, digital and analog free-space optical (FSO) communications. An EML-based LO distribution was assessed in terms of RF output power, spectral purity and phase noise. Using optical amplification, large-scale distribution of a 13 GHz LO was achieved with similar or greater RF power and a limited noise floor penalty compared to what is possible with a CW laser and Mach-Zehnder modulator (MZM). Photonic RF frequencyconversion was assessed as well and EML was found to perform better than direct modulation laser. For optical inter-satellite links in constellations, SWAP and cost really matter and EML is therefore an interesting candidate. An EML-based transmitter was evaluated for digital modulation at 10 and 20 Gbps as well as for RF analog modulation in transmit Ka band (20 GHz). For digital modulation, an EML module exhibited a similar dynamic extinction ratio as a MZM, and a limited penalty in detection sensitivity. For RF modulation, the carrier-to-noise ratio was measured as a function of the received optical power for various EML operating conditions: equivalent RF performance were achieved as well.