Yu Sheng Bai

High-efficiency nonvolatile holographic storage with two-step recording in praseodymium-doped lithium niobate by use of continuous-wave lasers

We have observed efficient two-photon, two-step recording in a praseodymium-doped lithium niobate crystal by use of cw lasers. Single-photon erasure during the readout at near-infrared wavelengths was found to be negligible. Nonvolatile holographic image storage was demonstrated. This progress is an important step in the realization of an economically feasible nonvolatile read-write holographic recording system based on low-cost semiconductor diode lasers.

Coherent time-domain data storage with a spread spectrum generated by random biphase shifting

We report time-domain data storage of as much as 1.6 kbits at a rate of 40 Mbits/s in Eu3+:YOS. Use of a pseudorandom biphase shifting technique to spread the data spectrum proved to be of critical importance in preventing saturation of the transition by the long data pulse train. The experimentally inferred storage capacity, ≳ 5 × 104 bits/spatial spot, plus the competitive single-channel throughput rate, demonstrate the potential of this optical memory.

Reprogrammable optical matched filter for biphase-coded pulse compression

We demonstrate the use of stimulated echoes for high-speed phase-modulated signal processing. The specific example chosen here involves the compression of biphase-coded pulses-a technique widely used in radar systems to achieve high range resolution and high signal-to-noise ratios. Experimental results obtained with the 5- and 13-bit Barker codes are presented, along with the measurements of a systems dynamic range and signal-to-noise enhancement. Advantages of this technique over the existing methods for signal processing are discussed.

Resonant two-photon photorefractive grating in praeseodymium-doped strontium barium niobate with cw lasers

We report experimental observation of resonant two-photon photorefractive gratings in Pr-doped SBN:60. Long-lived 4f intermediate states significantly reduced intensity threshold, thus permitting use of cw lasers for the two-photon transitions. Both two-beam one-color two-photon gratings and three-beam two-color gratings were observed. We expect these results to be extended to other rare-earth dopants.

Time-Domain Optical Memory in Hole-Burning Materials

Abstract We have demonstrated storage of 2 Kbits of data at 40 Mbits/s in the Eu3+ doped Y2SiO5 crystal using the time-domain echo approach. Preventing coherent saturation, caused by the long data pulse train, is critical to the successful implementation of this technique. The experimentally inferred storage capacity of 6 × 104 spatial spot demonstrates the potential of this optical memory.

Two-step photorefractive effect in rare-earth-doped ferroelectric crystals

We have demonstrated non-volatile holographic storage with two-photon, two-step recording in rare-earth doped ferroelectric crystals using cw lasers. Single photon erasure during the read out at near infrared wavelengths was found to be negligible. This progress paves the way to the realization of an economically viable, non-volatile read/write holographic recording system based on low cost semiconductor diode lasers.

Random-access stimulated-echo optical cache memory

We describe a new approach to develop a high-speed, high-density random access cache memory. This new technique is based on a novel approach using, in essence, a hybrid of the time domain stimulated echo (SE) concept and the frequency domain scheme. It has been demonstrated that the rare-earth doped crystals, can at low temperatures store large amounts of information for up to 24 hours using SE. The basic approach we have developed is the partitioning of the absorption frequency domain into smaller bins, so that each frequency bin stores a smaller portion of information independently. The bins are distinguishable by their different absorption frequencies and they are accessed by changing the laser frequency (color). However, information is still stored and retrieved using the time-domain pulse sequency used in SE. Specifically, with the laser frequency set at the particular absorption of a frequency bin, the laser is externally modulated by an acousto-optic modulator to produce amplitude modulated pulses representing the digital data, the write pulse, and the read pulse, during the write and retrieve operation, respectively. The advantages of this approach are that memory can be stored in space, time, and frequency domain, allowing us to tailor a flexible memory architecture to match those of the computational processor.