Under CSIR network (R-Nano) programme, various photonic crystal (PhC) structures and waveguides including line-defect, coupled cavity and ring-type PhC structures on silicon-on-insulator (SOI) substrates were designed using finite difference time domain (FDTD) method. These structures could be used as a refractive index based sensor platform for chemical and bio-chemical sensing applications. Fig. 1 shows one of such designs based on ringtype PhC waveguide structure (design parameters are listed in the table), where the sensitivity was estimated ~ 513 nm/RIU. Recently, some of the PhC structures were fabricated on selected region of SOI wafer using photolithography, dry etching (for realising the waveguides and outline of PhC region) and focused ion beam (FIB) facility at CSIR-NPL, New Delhi (for the realisation of PhC structures), as shown in Fig. 2. Further development is in progress.

Fig. 1: Ring-type photonic crystal structures on SOI wafer for sensing applications

Table 1

Parameters Value
Lattice constant (A1=A2) 500 nm
Outer hole diameter (D) 420 nm
Inner hole diameter (d) 220 nm
Defect diameter 270 nm
Ring thickness (D-d)/2) 100 nm
Band gap 0.308-0.345 a/λ
Si guiding layer thickness 220 nm
Si (guiding layer) refractive index 3.45
Buried oxide layer (lower cladding) refractive index 1.45
Air (upper cladding) refractive index 1

Fig. 2: Various types of photonic crystal (PhC) structures fabricated on SOI wafer using FIB