Experimental demonstration of localized Brillouin gratings with low off-peak reflectivity established by perfect Golomb codes.

Dynamic Brillouin gratings (DBGs), inscribed by comodulating two writing pump waves with a perfect Golomb code, are demonstrated and characterized experimentally. Compared with pseudo-random bit sequence (PRBS) modulation of the pump waves, the Golomb code provides lower off-peak reflectivity due to the unique properties of its cyclic autocorrelation function. Golomb-coded DBGs allow the long variable delay of one-time probe waveforms with higher signal-to-noise ratios, and without averaging. As an example, the variable delay of return-to-zero, on-off keyed data at a 1 Gbit/s rate, by as much as 10 ns, is demonstrated successfully. The eye diagram of the reflected waveform remains open, whereas PRBS modulation of the pump waves results in a closed eye. The variable delay of data at 2.5 Gbit/s is reported as well, with a marginally open eye diagram. The experimental results are in good agreement with simulations.

True time delays using conversion/dispersion with flat magnitude response for wideband analog RF signals.

We demonstrate optical true time delays using wavelength conversion coupled with chromatic dispersion. The transfer function of the delay system is investigated, and it is shown that 3-dB bandwidth of the system can be increased over 40 GHz by using offset pumps. A flat magnitude response (<1 dB peak-peak, 0.2 dB RMS deviation) is achieved in the 1-30 GHz band. Calculated matched filter output to LFM pulses shows good performance, maintaining a > 30 dB peak-to-sidelobe-ratio. The effect of pump depletion during wavelength conversion is also investigated.

Slope-assisted fast distributed sensing in optical fibers with arbitrary Brillouin profile.

We present a novel method, based on stimulated Brillouin scattering (SBS), for the simultaneous distributed measurement of fast strain variations along the entire length of the sensing fiber. A specially synthesized and adaptable probe wave is used to place the Brillouin interaction always on the slope of the local Brillouin gain spectrum, allowing a single pump pulse to sample fast strain variations along the full length of a fiber with an arbitrary distribution of the Brillouin frequency shift. In this early demonstration of the method, strain vibrations of a few hundred Hz are demonstrated, simultaneously measured on two different sections of an 85 m long fiber, having different static Brillouin shifts and with a spatial resolution of 1.5 m.