A Photonic QPSK Modulator Aimed at Space Applications
Résumé
This paper addresses the subject of the satellite payload signal transmission and the digital-microwave link. Usually, the carrier modulation data transmitter (DT) employs in-phase (I) and quadrature-phase (Q) processing to achieve phase shift keying (M-PSK). Typically, this I/Q processing is obtained by multiplying a low-frequency reference signal. Such systems usually have many stages of multipliers, amplifiers and filters. As a result, the microwave transmitter is complicated, bulky and costly. The results presented are based on a photonic circuit that achieves QPSK modulation directly at the microwave frequency carrier. The QPSK modulation was performed using a carrier frequency of 2 GHz and 2 Mbps I/Q signal from a pattern generator using a photonic circuit with a pair of Mach-Zehnder optical modulators arranged in a parallel configuration. The source of the photonic circuit is a DFB diode laser with a wavelength equal to 1550 nm. The modulated optical signal direct detection comes from an InGaAs photodetector. The optical modulator circuit output can be directly connected to the high power amplifier (HPA) and the transmission antenna. The resulting system enables one to achieve a microwave data transmitter with a reduced mass and volume, further lowering power consumption. These achievements are very important for spacecraft engineering teams during the conception of the satellite payloads when starting a new satellite project. Gamma radiation and thermal effects of the space environment are also discussed.
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