Visva-Bharati (Central University), Santiniketan, West Bengal, India

Biography: Taraprasad Chattopadhyay is a full professor of Physics in Visva-Bharati (Central University), Santiniketan, West Bengal, India, for more than 13 years . He received Japanese Government Scholarship and Fellowship of AIEJ, Japan, for carrying out research work in the field of optical engineering in Kyoto University, Japan. He was an invited Researcher of ERATO, JRDC, Japan, and worked on the design of high frequency light modulators in the Semiconductor Research Institute, Sendai, Japan. He was a visiting Professor of Research Institute of Electrical Communication (RIEC), Tohoku University, Japan. He was a Ministry of Human Resource Development (MHRD) seconded faculty (Professor) in Asian Institute of Technology, Bangkok, Thailand. He received networking award from Royal Society , London. He has authored more than 120 papers in National and International Journals and Conferences. He has guided and has been guiding Ph.D. students as a sole supervisor. He has conducted a number of major research projects from various funding agencies in India. He has been a reviewer of many international journals of IEEE (USA), IEE (UK), Elsevier Journals, Indian Journals and some Conferences. He is a senior member of IEEE (USA) and a Fellow of IETE (India).

Speech Title: QUANTUM CASCADE LASERS AND INJECTION LOCKING
Abstract: Quantum cascade laser (QCL) is a new type of laser, first demonstrated in Bell Labs. in 1994, where a photon is emitted due to intraband transition of electrons. In QCL, a single electron slides down a stair case-like potential in the conduction band leading to the generation of a cascade of identical photons. These lasers (QCL) can lase in the Mid-infra red (IR) region and also in the terahertz (THz) region.
The phenomenon of injection locking, where a master QCL controls the phase and frequency of a slave QCL, finds potential applications in Mid IR communication systems such as amplification of angle-modulated IR signals, frequency modulation (FM) to intensity modulation (IM) conversion, demodulation of angle-modulated IR signals, suppression of relative intensity noise (RIN) of the master QCL, etc.
The author has developed a unique theory of injection locking of QCLs which is based on transmission line model. A key factor which can influence the injection locking process in QCL is the line width enhancement factor (LEF). The LEF can have profound effect on the frequency response characteristics of the injection locked QCL. Angle-modulated Mid IR signals can be amplified through injection locking of QCL, and the LEF can have considerable effect on the QCL amplifier performance. Amplification of two-tone angle-modulated IR signals and the same of subcarrier multiplexed (SCM) angle-modulated IR signals have been investigated keeping the intermodulation distortion (IMD) level under control.
Demodulators for Mid IR PM signals are difficult to design. Injection locked QCLs can convert the input Mid IR PM signal into corresponding IM signal and the latter can be detected by a photodetector. The dependence of PM-IM conversion on physical parameters such as modulation frequency, injection power level, value of LEF have also been investigated.