A new technique for 100-fold increase in the FSR of optical recirculating delay line filters using a time compression...

A new technique that increases the free spectral range (FSR) of a recirculating delay line filter, is presented. The concept is based on a time-compression unit, which is used in conjunction with a frequency-shifting recirculating loop that generates multi-spectral characteristics, and the idea exploits the optical wavelength domain by wavelength-to-time mapping of the taps using an oppositely time-oriented dispersive element so that the taps travel different lengths, to time compress the tap separation. This technique solves, for the first time, the long-standing problem of the small FSR limitation in recirculating microwave photonic delay line filters, opening the way to realize the main functionalities required in microwave photonic filters. Experimental results are presented which demonstrate a large 100-fold increase in the FSR of the bandpass filter response.