Optical Communication and Signal Processing

Phase Sensitive Amplfiiers

Optical amplifiers are an integral part of any commercial optical communication system. In addition to adding a specific gain, optical amplifiers add a definite noise to the signal that degrades the optical signal-to-noise ratio of the signal after amplification. When advanced modulation formats such as Polarization multiplexed QPSK and 16QAM are used for optical communication, increase in noise - especially a phase noise due to spontaneous emission in an amplifier like erbium doped fiber amplifier is highly detrimental. In the project, we demonstrate parametric and phase sensitive amplifiers that are suitable specifically for phase modulated data. We use semiconductor optical amplifier as a compact and energy efficient nonlinear medium to achieve this target.

Mode division multiplexing with Few-Mode Fibers

The increasing requirement of bandwidth has resulted in pushing the capacity of a single mode fiber by utilizing advanced modulation formats like QPSK and QAM in optical communication. The complexity of digital signal processing and the limitations in the achievable SNR are the challenges in these designs. The use of few-mode-fibers is considered to be the next big step towards the increase in bandwidth in long haul and access networks. In this scheme, the data to be transported is modulated in the fundamental and few higher order modes in a suitably designed fiber, resulting in mode-division-multiplexing. The project aims at addressing the challenges involving characterization of such fibers for specific parameters such as dispersion and nonlinearities, establishing the enhancement of bandwidth proportional to the number of modes, development of indigenous digital signal processing techniques for data processing, establishing a long-haul (two-span) link using the mode division multiplexed system, establishing the feasibility of mode division multiplexing in short distance links such as access and data center networks.

Optical signal processing

Increase in baud rates result in a corresponding overhead in the digital signal processing domain. An alternate approach is to use nonlinear effects in compact highly nonlinear media to augment the signal processing functionalities in the optical domain. All-optical logic gates, wavelength conversion and optical clock recovery has already been demonstrated in the past, for advanced modulation format. The current work is on phase conjugation, phase quantization and photonic analog to digital conversion


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