Variable delay of Gbit/s data using coded Brillouin dynamic gratings

Abstract

Dynamic Brillouin gratings (DBGs), inscribed by co-modulating two writing pump waves with a bi-phase code, are analyzed theoretically, simulated numerically, demonstrated and characterized experimentally. A comparison is made between modulation by pseudo-random bit sequences (PRBS) and perfect Golomb codes. Numerical analysis shows that Golomb codes provide lower off-peak reflectivity, due to the unique properties of their cyclic auto-correlation function. Golomb coded DBGs can therefor allow for the long variable delay of one-time probe waveforms with higher signal-tonoise ratios, and without averaging. A figure of merit is proposed, in terms of the optical signal-to-noise ratio of reflected waveforms and the delay-bandwidth product of the setup. As an example, the variable delay of return-to-zero, on-off keyed data at 1 Gbit/s rate, by as much as 10 ns, is successfully demonstrated. The eye diagram of the reflected waveform remains open, whereas PRBS modulation of the pump waves results in a closed eye.

Brillouin-based light storage and delay techniques

“…To overcome this limitation, BDG-based delay schemes that implement advanced modulation schemes of the pump waves were implemented [66][67][68][69][70]. The modulation of the BDG pumps creates a localized correlation peak within the fiber.…”

Phase-Coded and Noise-Based Brillouin Optical Correlation-Domain Analysis

“…For example, Prof. Solomon Golomb of the University of Southern California (USC) developed a class of phase codes with cyclic auto-correlation values of exactly zero for all off-peak delays [38]. The employment of such perfect Golomb codes does not entirely eliminate off-peak SBS interactions, since the exponential windowing involved in Brillouin stimulation does not perfectly replicate the cyclic correlation operation [21,39]. Nevertheless, both analysis and experiments show that the OSNR in Brillouin gain measurements may be improved by a factor of 3-4 when Golomb codes are used instead of a PRBS, depending on the sequence period NT [21,39,40].…”

“…The employment of such perfect Golomb codes does not entirely eliminate off-peak SBS interactions, since the exponential windowing involved in Brillouin stimulation does not perfectly replicate the cyclic correlation operation [21,39]. Nevertheless, both analysis and experiments show that the OSNR in Brillouin gain measurements may be improved by a factor of 3-4 when Golomb codes are used instead of a PRBS, depending on the sequence period NT [21,39,40]. Figure 3 shows an example of calculated |Q(z, t)| maps for a Golomb code and a PRBS of equal rates and periods [21].…”