A temperature-stable optical link for the transmission of fast analogue signals

A Vertical Cavity Surface Emitting Laser (VCSEL)-based optical link has been developed for the transmission of nanosecond rise time signals. Uniquely the optical transmitter compensates for variations in the transmitted pulse area due to changes in the temperature of the VCSEL by automatically adjusting the bias current supplied to it. Our new design incorporates a higher performance VCSEL than was previously available, the ZL60052. The optical link exhibits good linearity (to within 12%) over a large dynamic range of 61 dB with an acceptable amount of pulse-shape and harmonic distortion across the entire bandwidth of ∼250MHz, which is itself limited by the response of the receiver. The transmitter alone exhibits a significantly larger bandwidth of ∼470MHz. Future work is required to increase the bandwidth and dynamic range for use with the next generation of photo detectors and digitisation electronics.