Hardware and Measurement Techniques

This chapter deals with hardware and measurement techniques. It begins with soliton sources, followed by temporal lens and clock recovery. Soliton transmission requires a reliable source of unchirped pulses, whose intensity envelopes are, to good approximation, either of Gaussian or sech shape, and whose repetition rate can be easily adjusted to the desired bit rate. The temporal lens consists of a phase modulator, appropriately driven in synchronism with the locally recovered clock, and followed by an essentially linear dispersive element. Clock recovery is easier when the signals are in return-to-zero (RZ) format, as they are for soliton transmission. The chapter describes several important techniques for the measurement of dispersion, which is an important parameter in soliton transmission. It also discusses accurate measurement of pulse widths using a detector with finite response time. The detector is first calibrated by measuring the microwave spectrum of the detector's response to reference pulses, whose widths are preferably short on the scale of the detector response. The ratio of that measured response to the expected Fourier transform of the reference pulses is then stored, to be used as a set of normalizing factors. The spectral intensities of a given measurement are divided by those normalizing factors, and the adjusted spectrum is then fit to a spectrum of the suspected pulse shape and width.