Current Research Areas

Hybrid Si/III–V Integration

It is widely recognized that the most important and exciting work in optoelectronics today is to combine optical functions (lasing, modulation, amplification, and detection) with traditional Si electronics. We have proposed a novel scheme by means of which the modal gain inside the hybrid structure can be enhanced several times without loss of other advantages. We are presently working on the experimental demonstration of this scheme.

Optical Phase-Lock Loops

Phase-Lock Loop systems are the main enablers of many key applications in the field of RF (radio-frequency) electronics, such as wireless communications, CDMA, FM demodulation and clock recovery, to name a few. In contrast, almost all of the information applications of lasers to date have been based on a manipulation of their amplitude (Differential Phase-Shift Keying is one exception). The Semiconductor Laser is the prime candidate to play the role of the Voltage Controlled Oscillator in the optical domain. This is due to its very large current-frequency sensitivity, its fast response (>30 GHz), its small volume, and its compatibility with electronic circuits.

The research in our group focuses on the use of semiconductor lasers as current controlled oscillators in optical phase-lock systems to enable a range of diverse applications. The optical phase and frequency of the laser output is controlled by purely electronic means using RF VCOs and phase shifters, thus eliminating the need for bulky optical phase and frequency modulators. Recent and ongoing experiments have focused on the phase-locking of arrays of semiconductor lasers for many diverse applications such as coherent power combination, "coherence cloning" - where the spectral properties of a high quality laser are cloned onto a number of inexpensive semiconductor lasers, optical phase controlled apertures, and the generation of electronically controlled ultra-wideband optical waveforms.

Slow Light in Coupled Resonators and Grating Structures

Slow light by reducing the group velocity in engineered structures may find applications like optical delay lines, optical buffers, interferometers, and nonlinear optics. In our group, we have proposed, analyzed, and experimentally demonstrated Coupled-Resonator Optical Waveguides (CROW), in which light propagates by virtue of the coupling between adjacent resonators.

Presently, we are working on designing all the coupling coefficients in a coupled-ring or cascaded-grating CROW to achieve better transmission spectrum in the presence of loss or gain. We are also working on an analogy of Electromagnetically Induced Transparency (EIT), which uses two co-spatial gratings on a few-mode waveguide to couple three waveguide modes.

Secure Communication using Fiber Systems

The need for secure key distribution has created a large interest in physical-layer based cryptographic protocols, which may provide powerful complementary capabilities to those of the more traditional, information theory based coding systems. The most widely known example is that of quantum key distribution (QKD) protocols, in which the key is generated by measurements of the quantum mechanical properties of single photons. However, practical implantation of the idea is complicated.

In our group, we have proposed, analyzed and provided an experimental proof of concept for a classical key generation system, based on establishing laser oscillation between two parties, which is realized using standard fiber-optic components. In our Ultra-long Fiber Laser (UFL) system, each user places a randomly chosen, spectrally selective mirror at his/her end of a fiber laser, with the two-mirror choice representing a key bit. We demonstrated the ability of each user to extract the mirror choice of the other using a simple analysis of the UFL signal, while an adversary could only reconstruct a small fraction of the key. The simplicity of this system renders it a promising alternative for practical key distribution in the optical domain. Research on this topic is carried out in collaboration with the group of Dr. Jacob Scheuer, at the School of Electrical Engineering, Tel-Aviv University, Israel.