Slow and Fast Light In Semiconductor Optical Amplifiers

Velocity of light is a very fundamental quantity in physics and has deep implications in the understanding of our universe. Much of the modern internet based communications use light pulses to transmit information across long distances. As opposed to electrical signals, communication through light is fast and information can be transmitted with very little loss of energy. The ability to control the velocity of information (usually referred to as group velocity) opens up a whole new field of slow and fast light that has exciting applications. Here “slow light” means the velocity of information is lower than the speed of light in the medium and “fast light” means the group velocity is larger than the speed of light!

There are numerous applications for slow and fast light such as optical storage, optical buffering, optical routing, phased array radar, and RF signal processing.  For example, a key component in phased array radar is true time delay because it allows beam steering and signal processing to be applied to multi-frequency or broadband radar signals.  Similarly, optical communication has long suffered from a serious bottleneck that arises because of the need to convert optical signals into electronic signals and back again in order to relay or re-route signals in high-speed fiber optic networks.  Here, the solution is to perform all the required node operations directly on the optical signals without converting to electronic signals.  To resolve contention at the switching node, a variable optical memory is the most critically sought after component. 

Semiconductor-based devices are ideal for achieving slow and fast light because they are extremely compact, operate at room temperature and are easily integrable with existing optical communication systems. Using Four wave mixing in semiconductor optical amplifiers [1], we have demonstrated fractional delays exceeding 50% at 0.5 Gb/sec. To obtain delays at THz bandwidths, we use ultra-fast non-linear processes including spectral hole burning and carrier heating. Recently, we have demonstrated a fractional advance of 250% (fast light) using this scheme [2]. This is a world record performance for semiconductor based materials at room temperature. Currently work is in progress to achieve slow light and to use multiple devices to increase the delay.

References:

Journal publications
1. Bala Pesala, Zhangyuan Chen, Connie Chang-Hasnain, “Experimental demonstration of Slow and Super luminal light in Semiconductor Optical Amplifiers”, Optics Express 14, 12968-12975 (2006).

2. F. G. Sedgwick, B. Pesala, J. -Y. Lin, W. S. Ko, X. Zhao, and C. J. Chang-Hasnain, “THz-bandwidth tunable slow light in semiconductor optical amplifiers,” Optics Express 15, 747-753 (2007)

Conference Publications

3. Bala Pesala, F. G. Sedgwick, Connie Chang-Hasnain, “ Ultra high bandwidth THz tunable delays using cascaded Semiconductor Optical Amplifiers”, CLEO 2007, Baltimore

4. F. G. Sedgwick, Bala Pesala, Jui-Yen Lin, Wai Son Ko, Xiaoxue Zhao, Connie Chang-Hasnain, “ THz tunable slow light in Semiconductor Optical Amplifiers”, OFC 2007, Anaheim, CA

5. Bala Pesala, Zhangyuan Chen, Alexander V. Uskov, Connie Chang-Hasnain, “Slow and Superluminal light based on Four-Wave Mixing in Semiconductor Optical Amplifiers”, CLEO 2006, Long Beach, CA.

6. Bala Pesala, Zhangyuan Chen, Connie Chang-Hasnain, “Tunable pulse delay demonstration using Four-Wave mixing in Semiconductor Optical Amplifiers”, OSA Topical meeting 2006, Washington D.C.

7. Zhangyuan Chen, Bala Pesala, Connie Chang-Hasnain, “Experimental Demonstration of Slow light via Four-Wave Mixing in Semiconductor Optical Amplifiers”, OFC 2006, Los Angeles, CA.