Research

Time-stretch Photonic Analog-to-Digital Converters

One of the most promising Photonic Aanalog-to-Digital Converter technology which has enormous commercial potential and viability is time-stretched photonic ADCs (TS-PADC). In TS-PADC, architecture, the electrical signal to be digitized, is first imprinted on an optical pulse train, and the optical pulse is time-stretched by passing it through a dispersive medium (DM). The effective bandwidth of the signal to be sampled is reduced as much as the stretch factor, thus enabling sampling and quantization at lower bandwidths using E-ADCs. Single-shot PADC allow the capture of sporadic events with high bandwidth while continuous PADC enables RF signals such as in radar systems - to be captured continuously. 


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Photonic sub-sampled down-converter

Sub-sampling or bandpass-sampling is an attractive strategy to be used, when a very small signal bandwidth around a high carrier frequency is to be sampled. When a narrow bandwidth signal (bandwidth = B) modulated at a high frequency carrier (f) is sampled by sampling pulse train with sampling frequency (fs), where fs << f, the spectral replicas of the signal appear in digital frequency domain intervals which are separated equally by fs/2. A packaged sub-Nyquist sampled photonic analog-to-digital converter (PADC) is demonstrated with a bandwidth of 42.3 MHz for S-band operation. Linear operation over 50 dB is demonstrated with a sensitivity of -70 dBm.


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Modal decomposition of few-mode fiber (FMF) using Stochastic Parallel Gradient Descent (SPGD) Algorithm 

Modal decomposition serves as an excellent tool for determining the transverse modal dynamics of multi-mode fibers (MMFs) or few-mode fibers (FMFs). This technique finds applications in a variety of scenarios in mode-division multiplexed optical communication systems as well as in fiber lasers such as estimation of mode resolved bending loss, determination of angular orbital momentum composition of light, adaptive mode control, measurement of fiber-to-fiber coupling losses, evaluation of specialty fiber designs, wave-front reconstruction, beam quality evaluation, determination of mode resolved gain/loss, laser beam cleanup and for the diagnosis of mode instabilities in high power fiber lasers. Using SPGD based modal decomposition method, the weights and phases of the constituent scalar modes are extracted from the intensity profile of the composite beam. 


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Mode resolved bending loss measurement of few-mode fiber utilizing digital modal decomposition

Mode resolved bending loss measurement of few-mode fiber utilizing digital modal decomposition

Bending loss (BL) is one of the key characteristic parameters of optical fibers, especially when these are used for long distance communication and distributed sensing. Different spatial modes are utilized for data transmission in space division multiplexing (SDM) systems utilizing few-mode fibers (FMFs). Mode resolved bending loss (MRBL) – is one of the key parameters required to be measured for few-mode fibers (FMFs). We have developed a novel technique which is based on digital modal decomposition technique in order to measure MRBL. Proposed technique takes care of mode-coupling phenomena and is simpler as compared to CGH based and (S2) imaging methods.

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Finite Difference Method (FDM) based Mode Solver for graded index two-mode fiber

Bending loss (BL) is one of the key characteristic parameters of optical fibers, especially when these are used for long distance communication and distributed sensing. Different spatial modes are utilized for data transmission in space division multiplexing (SDM) systems utilizing few-mode fibers (FMFs). Mode resolved bending loss (MRBL) – is one of the key parameters required to be measured for few-mode fibers (FMFs). We have developed a novel technique which is based on digital modal decomposition technique in order to measure MRBL. Proposed technique takes care of mode-coupling phenomena and is simpler as compared to CGH based and (S2) imaging methods.

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All-optical logic gates and combinational circuits by exploiting non-linear effects inside Highly non-linear fibers (HNLFs) 

All-optical logic gates and combinational circuits by exploiting non-linear effects inside Highly non-linear fibers (HNLFs) 

All-optical signal processing (AOSP) will be required in modern & next generation large capacity networks to avoid inefficient optical-electronic-optical (O-E-O) conversions by processing data in optical domain itself. In order to execute complex AOSP tasks, high-speed logic all-optical logic gates serve as backbone elements. In particular, all-optical logic gates can be used to realize combinational circuits such as half-adder, half-subtracter, comparator, decoder etc. which can be further utilized to perform complex AOSP tasks, such as packet checksum calculation, encryption/decryption of data, TTL decrementing and loop control etc. A number of simultaneous
implementations of all-optical combinational circuits have been developed with emphasis on usage of minimum number of no-linear elements (NLEs) and optical sources. 


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Optimization of gain recovery time of semiconductor optical amplifier (SOA) for speed enhancement of all-optical half-subtracter based on cross-gain modulation (XGM) phenomenon

SOAs have been heavily employed in the past for the realization of all-optical logic devices due to its excellent features such as compactness and capability to integrate. A number of nonlinear effects such as XGM, XPM and FWM have been harnessed by various researchers in SOAs for the implementation of all-optical computing devices. In this work, an attempt has been made to reduce the gain recovery time of SOAs by optimizing its structural and operational parameters. The influence of improvement in gain recovery dynamics of SOAs achieved by structural optimization has been further illustrated on the performance of realized all-optical half-subtracter based on XGM phenomena in terms of two performance metrics: quality factor (Q-factor) and extinction ratio (ER). 


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