Photonic assisted simultaneous microwave ASK and FSK signal generation based on gain switching in VCSEL

Abstract A novel photonic scheme for the simultaneous generation of microwave amplitude shift keying (ASK) and frequency shift keying (FSK) signal based on gain switching in Vertical Cavity Surface Emitting Laser (VCSEL) is proposed, for the first time. In this approach, gain switched VCSEL is utilized to produce optical frequency comb (OFC) and the linearly polarised OFC signal is splitted into two orthogonal polarizations using polarisation controller and polarisation beam splitter. Two electro absorption modulators (EAM) are employed to modulate each polarization by 1Gbps data. Microwave FSK signals at 2/4 GHz and 6/8 GHz with 1 Gbps data are detected at the photodetector. Moreover, microwave ASK signals are also generated from each polarization branch at 2 GHz and 4 GHz. Simulations are performed to substantiate the proposed system. The influence of VCSEL modulating signal power and EAM reverse bias on FSK output power is also discussed. Results predict a maximum sideband suppression ratio of 33 dB, for a modulating signal current and EAM reverse bias voltage of 15 mA and 1.5 V respectively. The receiver sensitivity of the FSK signal at 2/4 GHz for a 20 km fibre transmission is found to be −16.3 dBm with a Q factor of 6, at a BER of 10 −9 . This scheme offers a simple, cost-effective approach and requires a low modulating current and its applications include radar, wireless and optical communications.