Bhatia, Nitin

We propose a method to achieve stable oscillation of an additional mode, along with the highest gain mode, for achieving direct dual mode emission from a homogeneously broadened buried heterostructure laser.

We incorporate the effect of two-dimensional (2D) carrier diffusion in a BH laser source to establish the condition on modal reflectivity for stable dual polarized mode oscillation.

There is an increasing need for high data rate and massive connectivity requirements in the Internet of Things (IoT) based communication applications. Therefore, visible light communications (VLC) have become a popular area of research for both academia and industry. This is due to wide bandwidth, license-free spectrum, energy efficiency, and low implementation cost of VLC. In addition, traditional radio frequency (RF) based communications face issues with spectral congestion. In this paper, we develop an experimental setup of VLC based data transmission and reception. We demonstrate text and audio transmission over a single VLC link of upto 2 m using light emitting diode (LED) and collimating lens as the transmitter and receiving lens with a PIN photodetector as receiver. VLC system's link length improved up to 4m with an amplify-and-forward (AF) relay for data transmission and reception. Further, it is presented that with 4 LEDs, the distance for error-free transmission for text data increased from 50 cm to 180 cm. Useful insights into the VLC systems performance are obtained through the experimental measurements of the received power for various link lengths, receiver angular position with respect to the transmitter, and the number of the transmitting white LEDs used.

We show that the output beam exiting from the end facet of a single-mode–multimode–few-mode device can be designed to be a highly pure LG00 or LG01 mode. Our investigation provides a method to generate LG beams in free space using a low-cost, all-fiber solution that also shows potential for an integrated device.

This paper presents experimental results for a free-space optical-fiber converged (FSO-FC) communication system under varying turbulence and foggy conditions. Based on the experimental measurements, we statistically characterize the FSO channel under different levels of turbulence and fog in terms of their respective probability density functions (PDFs). Our experimental PDFs fit well with the theoretical PDFs proposed in the literature. We experimentally evaluate the average bit error rate (ABER) of the considered FSO-FC communication system under different levels of turbulence and fog. Further, to compensate for the effects of turbulence and fog, we use multimode fiber as the receiver and compare the results with single-mode fiber as the receiver. Finally, we show the improvement in ABER under varying turbulence and fog by adding cyclic redundancy check bits to data bits.

We show that the mode propagation analysis in a 2D confined optical device can be bifurcated into two 1D problems. In our method, a given 2D launch field profile is divided into two 1D profiles and suitably aligned with the 1D waveguide, acting as independent launching conditions. This method shows that the complete propagation problem of a 2D waveguide, which involves the computation of 2D mode field profiles and their propagation constants, can indeed be solved as two 1D problems. Our method is verified with the beam propagation method through a commercial simulator. Based on our analysis, we design MMI-based optical devices using square core multimode optical fiber such as wideband power divider and combiner at 1550 nm. Furthermore, the practical considerations, such as fabrication tolerance and operation bandwidth for these devices, are investigated to ascertain operational advantages.

We investigate the performance of a highly compact (≤ 1 cm) all-fiber multimode interference (MMI) device for splitting optical power from a standard single mode fiber (SMF) input port to four (4) SMF output ports. In C-band, the best and worst case uniformity among the output ports are obtained as 0.14 dB and 1 dB, respectively. This compact device provides a low-cost, high-performing solution for potential usage in optical networks.

We show an all-fiber multimode interference device for splitting the power propagating in a few mode fiber (FMF) into four (4) identical FMF ports. The splitting operation is achieved efficiently for individual modes, as well as a complex field comprising multiple propagating modes, ensuring mode transparent operation. The fabricated device, with length $\leq 1$ cm, shows uniform power splitting in the C-band with less than $0.8$ dB power variation among the output ports. The device could provide a possible solution for power splitting in future FMF networks employing the mode division multiplexing technique.

Stable dual-wavelength emission from a laser is desirable for microwave signal generation using the optical heterodyning method. As both optical wavelengths are generated from the same cavity, the phase noise of the generated microwave signal is minimized. In this work, we exploit the inherent birefringence in the buried heterostructure semiconductor laser to generate dual polarized modes. We carefully analyze the mode competition between various modes in the cavity and propose the desirable gain modification conditions for stable dual mode oscillations when the laser is operating near the threshold. We show that the required asymmetry in the gain for two stable modes can be obtained from the mode confinement factors and facet losses. We also show the applicability of our results to a homogeneously broadened multimode laser.

The traditional PBFT consensus mechanism in a blockchain network tolerating 33% node failure faces various challenges, including incorrect data verification, transaction communication complexity, and higher consensus delay in larger networks. In case of appending a block carrying the Educational Certificates (ECs) the impact of node error due to external attacks could lead to production of fake degrees in the system. To address the challenge of fraudulent degree verification, we propose a novel Grouping nodes-based Practical Byzantine Fault Tolerance (GnPBFT) consensus algorithm. We show that the GnPBFT algorithm gives higher probability to prevent fake certificate verification as compared to the PBFT in same network setting. Furthermore, we also show that our scheme is resilient against Sybil attack, with improved performance metrics such as 33% reduction in transaction overhead and 29% decrease in consensus latency. © 2025 Copyright held by the owner/author(s).