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.
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.
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.