arXiv subjects

Harikumar K. Chandrasekharan

Publications and source records attributed to Harikumar K. Chandrasekharan.

4 recordsLinked to original sources

arXiv2025

Resolving polarization-dependent mode dynamics in multimode fibers with 2D single-photon detector arrays

Monitoring polarization dynamics in multimode fibers is critical for a range of applications, spanning from optical communication to sensing. Although the modal behavior of multimode fibers is well understood through interferometry and advanced detection techniques, most studies focus on a single polarization state of specific modes, leaving the spatial mode dynamics of the other polarization state unexplored. A variety of optical phenomena can arise during the transport of spatial modes in fibers, driven by stress-induced fiber deformations. These phenomena include changes in the effective refractive index of modes, modal dispersion, and polarization-dependent mode coupling. Observing such modal behavior typically requires complex systems, such as multi-axis interferometry. In this paper, we present quasi-real-time observation of spatial mode dynamics in a two-mode fiber using 2D single-photon avalanche diode (SPAD) arrays configured in a dual-axis setup under different fiber deformation conditions. By utilizing the time-resolved capabilities of the SPAD arrays, we capture the modal behavior of two spatial modes in the fiber during stress induced by uncontrolled deformations, enabling direct observation of spatial correlations of the modes. Additionally, we demonstrate dual-polarization mode dynamics under controlled fiber conformation, where the modal behavior remains stable within acceptable error limits. Our work opens new avenues for exploring polarization-dependent phenomena in both fundamental and applied optics, as well as in biological systems.

physics.optics↗

arXiv2024

In-situ multicore fibre-based pH mapping through obstacles in integrated microfluidic devices

Microfluidic systems with integrated sensors are ideal platforms to study and emulate processes such as complex multiphase flow and reactive transport in porous media, numerical modeling of bulk systems in medicine, and in engineering. Existing commercial optical fibre sensing systems used in integrated microfluidic devices are based on single-core fibres, limiting the spatial resolution in parameter measurements in such application scenarios. Here, we propose a multicore fibre-based pH system for in-situ pH mapping with tens of micrometer spatial resolution in microfluidic devices. The demonstration uses custom laser-manufactured glass microfluidic devices (called further micromodels) consisting of two round ports. The micromodels comprise two lintels for the injection of various pH buffers and an outlet. The two-port system facilitates the injection of various pH solutions using independent pressure pumps. The multicore fibre imaging system provides spatial information about the pH environment from the intensity distribution of fluorescence emission from the sensor attached to the fibre end facet, making use of the cores in the fibre as independent measurement channels. As a proof-of-concept, we performed pH measurements in micromodels through obstacles (glass and rock beads), showing that the particle features can be clearly distinguishable from the intensity distribution from the fibre sensor.

physics.app-ph↗

arXiv2018

State-recycling and time-resolved imaging in topological photonic lattices

Photonic lattices - arrays of optical waveguides - are powerful platforms for simulating a range of phenomena, including topological phases. While probing dynamics is possible in these systems, by reinterpreting the propagation direction as "time," accessing long timescales constitutes a severe experimental challenge. Here, we overcome this limitation by placing the photonic lattice in a cavity, which allows the optical state to evolve through the lattice multiple times. The accompanying detection method, which exploits a multi-pixel single-photon detector array, offers quasi-real time-resolved measurements after each round trip. We apply the state-recycling scheme to intriguing photonic lattices emulating Dirac fermions and Floquet topological phases. In this new platform, we also realise a synthetic pulsed electric field, which can be used to drive transport within photonic lattices. This work opens a new route towards the detection of long timescale effects in engineered photonic lattices and the realization of hybrid analogue-digital simulators.

physics.optics↗

arXiv2016

Multiplexed Single-Mode Wavelength-to-Time Mapping of Multimode Light

We demonstrate that photonic lanterns based on tapered multicore fibres provide an efficient way to couple multimode states of light to a two-dimensional array of Single-Photon Avalanche Detectors (SPADs), each of which has its own Time-to-Digital Converter (TDC) for Time-Correlated Single-Photon-Counting (TCSPC). Exploiting this capability, we demonstrate multiplexed single-mode wavelength-to-time conversion of multimode states of light using a multicore-fibre photonic lantern with 121 single-mode cores, coupled in a one-to-one fashion to 121 SPADS on a 32 $\times$ 32 pixel CMOS SPAD array. The application of photonic lanterns for coupling multimode light to SPAD arrays in this manner may find wide-ranging applications in areas such as Raman spectroscopy, coherent LIDAR and quantum optics.

physics.optics↗