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Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE

Investigation of room-temperature slow light in photorefractives for optical buffer applications

Zhijie Deng, Philip Hemmer

Published Jun 17, 2004• 3 citations
Publisher

Abstract

Lately, active research has been conducted in slowing down light pulses to the order of tens of meters per second or below. An interesting application would be an optical buffer for all optical routers, where solid state devices operating under room temperature are desired. In this paper, we investigate the possibility of such a device with a Ce:BaTiO3 crystal. Group velocity as slow as 2 mm/s is obtained in the two-wave coupling experiment. By modulating the angular-multiplexed pump beams in the experiment, we also demonstrate the modulation of the output waveform, which could be used to address the problem of pulse broadening that so far limits the application of room temperature slow light.

DOI
10.1117/12.528124

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Lately, active research has been conducted in slowing down light pulses to the order of tens of meters per second or below. An interesting application would be an optical buffer for all optical routers, where solid state devices operating under room temperature are desired. In this paper, we investigate the possibility of such a device with a Ce:BaTiO3 crystal. Group velocity as slow as 2 mm/s is obtained in the two-wave coupling experiment. By modulating the angular-multiplexed pump beams in the experiment, we also demonstrate the modulation of the output waveform, which could be used to address the problem of pulse broadening that so far limits the application of room temperature slow light.
For many applications of slow or stopped light, the delay-time-bandwidth product is a fundamental issue. So far, however, slow-light demonstrations do not show a large delay-time-bandwidth product, especially in room temperature solids. Here we demonstrate that the use of artificial inhomogeneous broadening has the potential to solve this problem. A proof-of-principle experiment is done using slow light produced by two-beam coupling in a photorefractive crystal Ce:BaTiO3 where Bragg selection is used to provide the artificial inhomogeneity. Examples of how to generalize this concept for use with other room temperature slow-light solids are also given.
Slow and fast light are achieved in two experiments using SPS photorefractive crystal at room temperature. We report that the photorefractive gain achieved by the two wave mixing (TWM) method can control the group velocity of the transmitted light pulses at visible wavelength. It is shown theoretically and experimentally that the time delay and the shape of the output pulse change as a function of the photorefractive gain. The beam fanning has also been used to control the velocity propagation of a single light pulse in the same crystal at λ = 1064 nm. Depending on the orientation of the polar axis, it is possible to accelerate or decelerate a short pulse with duration of order of μs in the crystal.
For many applications of slow or stopped light, the delay-time-bandwidth product is a fundamental issue. However, existing slow light demonstrations do not give a satisfactory delay-time bandwidth product, especially in room temperature solids. Here we demonstrate that the use of artificial inhomogeneous broadening has the potential to solve this problem by simultaneously slow down all the frequency components of the input pulse. The proof of principle experiment was done using three-wave mixing in a photorefractive crystal Ce:BaTiO3 where Bragg selection is used to provide the inhomogeneity.
The ability to delay short light pulses is a promising solution for all-optical telecommunications, but suffers from a large distortion of the delayed pulse as a consequence of the high material dispersion. In this Letter, we demonstrate the possibility to all-optically control the group delay in a photorefractive (PR) crystal by the use of the two-wave mixing (TWM) effect in the pulse regime at room temperature. Most importantly, we show that a proper choice of the pump pulse width in the TWM process enables us to slow down shorter or longer signal pulses without distortion. The technique is demonstrated both at visible (638 nm) and infrared (1064 nm) wavelengths and for slowed-down pulses with durations ranging from 10 ns up to 30 ms, hence confirming its broad applicability.
Slow-down of the light velocity has potential applications in information processing [1] and interferometers. Recently, several works have experimentally [2] demonstrated the deceleration of light in photorefractive crystals using a two wave mixing (TWM). A low velocity value of the order of 0.02 cm/s has been reported in BaTiO3crystal for Gaussian pulse profiles of long duration of 1.3 s [3]. It was also reported that the time delay depends mainly on the coupling photorefractive gain. However, the photorefractive grating build-up time in that crystal does not allow to slow down pulses shorter than ms, which limits its interest for telecoms applications.
In this work, we experimentally demonstrate the capacity of the photorefractive (PR) crystal to control the group velocity of light pulses, specifically at the telecommunication wavelength, by using the so-called beam fanning at room temperature. Significantly, we show for the first time that this method can effectively decelerate a modulated signal propagating through this material at 1310 nm. Furthermore, we illustrate that the performance of this slow light system can be adjusted by changing the intensity, duration, and angle of polarization of the input pulse. The results obtained through this technique can potentially improve the performance of specific components in telecommunication networks.