Raktim Haldar

Theory and Design of Off-Axis Microring Resonators for High-Density On-Chip Photonic Applications

In this paper, we have developed a theory of an off-axis microring resonator (MRR) with single and multiple off-axis rings. The off-axis inner ring introduces tunable extra notches with many striking features in the transmission spectrum which facilitates its use as efficient modulators and sensors. A few such notches when closely packed have been used to design a compact band rejection filter with improved bandwidth (>10 nm). Moreover, these closely packed extra notches achieved by serially coupled MRRs with off-axis inner rings are tunable to reject arbitrarily chosen WDM channels. Through numerical simulations, based on both transfer matrix method and finite difference time domain method, it has been examined that off-axis MRRs cater superior performances in comparison to the serially coupled conventional MRR with respect to the device size, faster response, and low dispersion. The proposed off-axis MRRs may be used for cluster to cluster interconnects and can have other potential on-chip photonic applications in network layer. Necessary design parameters are computed from the coupled mode theory.

Triple-core collinear and noncollinear plasmonic photonic crystal fiber couplers

Numerical analysis of single and multiple gold nanowires embedded in triple cores arranged in collinear and noncollinear configurations in photonic crystal fibers (PCFs) is reported. A full-vectorial finite element method is used to achieve coupling characteristics of plasmonic PCF couplers for both x and y polarizations. It is demonstrated numerically that the PCF plasmonic couplers exhibit polarization-independent tunable broadband filter characteristics that can be tuned according to the diameter of the embedded gold rod(s).

On-chip broadband ultra-compact optical couplers and polarization splitters based on off-centered and non-symmetric slotted Si-wire waveguides

In this work, we propose novel schemes to design on-chip ultra-compact optical directional couplers (DC) and broadband polarization beam splitters (PBS) based on off-centered and asymmetric dielectric slot waveguides, respectively. Slot dimensions and positions are optimized to achieve maximum coupling coefficients between two symmetric and non-symmetric slotted Si wire waveguides through overlap integral method. We observe >88% of enhancement in the coupling coefficients when the size-optimized slots are placed in optimal positions, with respect to the same waveguides with no slot. When the waveguides are parallel, in that case, a coupling length as short as 1.73 μm is accomplished for TM mode with the off-centered and optimized slots. This scheme enables us to design optical DC with very small footprint, L c ~ 0.9 μm in the presence of S-bends. We also report a compact (L c ~ 1.1 μm) on-chip broadband PBS with hybrid slots. Extinction ratios of 13 dB and 22.3 dB are realized with very low insertion loss (0.055 dB and 0.008 dB) for TM and TE modes at 1.55 μm, respectively. The designed PBS exhibits a bandwidth of 78 nm for the TM mode (C-and partial L-bands) and >100 nm for the TE mode (S + C + L wavelength bands). Such on-chip devices can be used to design compact photonic interconnects and quantum information processing units efficiently. We have also investigated the fabrication tolerances of the proposed devices and described the fabrication steps to realize such hybrid devices. Our results are in good agreement with 3D FDTD simulations.

Compact Athermal Electro-optic Modulator Design Based on SOI Off-axis Microring Resonator

In this work, we propose efficient electro-optic modulation using compact SOI off-axis microring resonator. We show that adding an extra off-axis inner-ring in conventional microring structure provides control to compensate thermal effects on electro-optic modulator.

Design of CMOS compatible and compact, thermally-compensated electro-optic modulator based on off-axis microring resonator for dense wavelength division multiplexing applications

In this work, we propose and demonstrate the performance of silicon-on-insulator (SOI) off-axis microring resonator (MRR) as electro-optic modulator (EOM). Adding an extra off-axis inner-ring in conventional microring structure provides control to compensate thermal effects on EOM. It is shown that dynamically controlled bias-voltage applied to the outer ring has the potency to quell the thermal effects over a wide range of temperature. Thus, besides the appositely biased conventional microring, off-axis inner microring with pre-emphasized electrical input message signal enables our proposed structure suitable for high data-rate dense wavelength division multiplexing scheme of optical communication within a very compact device size.

Sub-Wavelength Dual Capillaries-Assisted Chalcogenide Optical Fibers: Unusual Modal Properties in Mid-IR (2–5 μ m) Spectral Range

In this study, we apply the concept of sub-wavelength light confinement to achieve flat effective mode area (Aeff) characteristics over a wide wavelength range of 1400 nm in nano-sized dual capillary assisted chalcogenide core optical fibers. An unusual spectral behavior of Aeff is observed where the effective mode area increases, remains constant for a wide bandwidth, decreases and again increases with the increase in wavelength. The spectral region, in which this behavior is observed, can be tuned by varying the structural parameters of the fiber. Additionally, we noticed that the fiber exhibits four zero dispersion wavelengths for a particular polarization which suggests that sub-wavelength light localization can be an alternative solution for the dispersion engineering in order to attain multiple zero dispersion wavelengths. The fabrication tolerance of the dispersion profile has been found to fall within the current fabrication accuracies achievable. We believe that our findings might be useful in different applications such as light-matter interaction and spatial soliton propagation.

Breakdown of optical lattice formation in dual-pumped supercavity soliton states

Variable-free spectral range frequency comb (FC) and composite FC can be generated through dual-pumped microresonator (MR) which are very useful candidates for WDM communications. In such configurations, temporal cavity soliton (CS) rests on an oscillatory background and can exhibit enriched nonlinear dynamics. In this work, we investigate the super cavity soliton (SCS) states in MR under bi-chromatic pumping scheme. The SCS states are known to exist under the application of high pump power when the Kerr induced phase shift exceeds 2π. This leads to the observation of multi-stability and supports several exciting nonlinear states which we observe in dual-pump configurationakin to single-pump driven MR system under similar scenarios. We have performed numerical simulations of such systems based on the Ikeda formalism. We explore the possibility of optical lattice formation in dualpump MR configuration for the SCS states. We find that the optical lattice formation takes place conditionally for the case of SCSs. The analytical relation to describe the steady state of the optical lattice in the context of dual-pump driven MR is derived. We observe that the CS resting on a CW background allows the formation of an optical lattice. Even if the CS originates from chaotic MI region randomly, it gets slowly attracted to the nearest equilibrium position. However, we observe a breakdown of this optical lattice formation in case of CS existing on MI induced temporal background. Apart from indicating the caveats in the process of lattice formation with regards to the SCS states, our work will help to gain an insight into the process of the formation of cavity solitons from MI and the resulting phase of the generated solitons in the context of bi-chromatic pumping.

Stability analysis and bandwidth estimation of free-carrier driven Kerr frequency-comb

Free-carrier dispersion-led nonlinear cavity detuning is observed through the reverse Kerr-tilt of the resonant-peaks of steady-state solutions of Lugiato-Lefever equation. Effects of nonlinear losses on the gain-spectrum and the gain-bandwidth of modulation-instability are also studied.

Fabrication and Performance Analysis of Mach-Zehnder Interferometer Coupled Polymer Microring Resonator with Microfluidic Channel for Refractive-Index Sensing

Mach-Zehnder interferometer coupled polymer microring resonator possessing microfluidic channel is proposed, numerically studied and fabricated for refractive-index sensing applications. Numerical results suggest an improved sensitivity of 202nm/RIU.

Pulse-Splitting and Pulse-Locking Dynamics in Multi-Mode Optical Fibers

We study the multimode propagation dynamics in a fiber, observe the pulse-splitting and pulse-locking marked by a significant portion of the LP01-mode pulse moving together with the LP02-mode pulse despite of significant walk-off between them.