Hemant Sankar Dutta

Sensitivity enhancement in photonic crystal waveguide platform for refractive index sensing applications

Abstract. A photonic crystal (PhC) waveguide platform based on ring-shaped holes in a silicon-on-insulator substrate is proposed in order to realize a refractive index sensor with an improved sensitivity. The three-dimensional finite-difference time domain method is used to analyze the proposed design. The sensitivity is estimated by measuring the shift in the upper band-edge of the output transmission spectrum. Sensitivity analysis of a conventionally designed PhC waveguide, followed by modification of the structure, has been carried out for improving the sensitivity by introducing a row of holes that forms the line defect. Further improvement in sensitivity is obtained by replacing the defect row of holes by ring-shaped holes, which shows a significantly high sensitivity along with considerable output signal strength. The optimized design shows a wavelength shift of 210 nm for a change in ambient refractive index from air (RI=1) to xylene (RI=1.5), corresponding to an average sensitivity of 420  nm/RIU.

Fabrication of Photonic Crystal Line Defect Waveguides by Use of Optical Lithography and Focused Ion Beam

A fabrication strategy for realizing photonic crystal structures with long interfacing waveguide has been reported. The technique utilizes a combination of optical lithography and focused ion beam milling to fabricate the device.

Realization of large-scale photonic crystal cavity-based devices

Abstract. This paper demonstrates an approach for fabricating large-scale photonic crystal (PhC)-based devices using a combination of optical and focused ion beam (FIB) lithography techniques. Optical lithography along with reactive ion etching parameters is optimized to realize the layout of device structure and thereafter FIB milling is optimized to realize the designed PhC structure at those identified locations. At first, with the help of a specially designed mask and using optical lithography along with reactive ion etching, a number of rectangular areas of dimension of 10  μm×20  μm along with input and output waveguides of width ∼700  nm and thickness of ∼250  nm have been fabricated. Subsequently, use of FIB milling, a periodic PhC structure of lattice constant of 600 nm, having a hole diameter of ∼480  nm along with a defect hole diameter of ∼250  nm have been realized successfully on the selected areas. This method shows a promising application in fabricating PhC structure with device size >1  cm2 at large scale, eliminating the problems of standard nanolithography techniques.

Design and analysis of photonic crystal micro-cavity based optical sensor platform

In this paper, the design of a two-dimensional photonic crystal micro-cavity based integrated-optic sensor platform is proposed. The behaviour of designed cavity is analyzed using two-dimensional Finite Difference Time Domain (FDTD) method. The structure is designed by deliberately inserting some defects in a photonic crystal waveguide structure. Proposed structure shows a quality factor (Q) of about 1e5 and the average sensitivity of 500nm/RIU in the wavelength range of 1450 – 1580 nm. Sensing technique is based on the detection of shift in upper-edge cut-off wavelength for a reference signal strength of –10 dB in accordance with the change in refractive index of analyte.

Realization of Rod-type Photonic Crystal Structure for Optical Sensing using Dip-Pen Nano-lithography

Following design optimization, a rod-type photonic crystal structure is realized using dip-pen nano-lithography. Dots are written by 16-MHA on metal-coated silicon substrate. After dry-etching, SEM images confirm the rod-diameter of ~250nm and lattice-constant of ~470nm.

Design and Analysis of Silicon Nitride Material Based Photonic Crystal Structure for Refractive Index Sensing in Visible Range

A silicon nitride material based photonic crystal platform is proposed for realizing a refractive index sensor in visible wavelength region. Proposed design is analyzed using 3D FDTD simulations and showed a sensitivity of 130nm/RIU.