arXiv subjects

Nadir Ali

Publications and source records attributed to Nadir Ali.

3 recordsLinked to original sources

arXiv2020

Electrically reconfigurable silicon photonic filter enabled by embedded phase change material in microring resonator

We report a tunable optical filter based on phase change material $Ge_{2}Sb_{2}Te_{5}$ embedded in a silicon microring resonator. The high thermo-optic coefficient of $Ge_{2}Sb_{2}Te_{5}$ in amorphous phase enables tuning of resonance wavelength in broad range with a very small active volume. The low-loss indium-tin-oxide electrodes are employed to induce Joule heating in $Ge_{2}Sb_{2}Te_{5}$-Si active waveguide region. The electrically induced heating in the active region alters the effective refractive index of hybrid microring resulting in a wavelength tuning of 1.04 nm for an applied voltage of only 3V. The device exhibits high extinction ratios in the range of 20-41 dB and a compact active footprint 0.96 $μm^{2}$ only and is suitable for the large scale reconfigurable integrated photonic circuits.

physics.app-ph↗

arXiv2019

Mid-IR non-volatile silicon photonic switches using nanoscale Ge\textsubscript{2}Sb\textsubscript{2}Te\textsubscript{5} embedded in SOI waveguide

We propose and numerically analyze the hybrid Si-Ge\textsubscript{2}Sb\textsubscript{2}Te\textsubscript{5} strip waveguide switches for Mid-IR wavelength of 2.1 $μ$m. The switches investigated are one input-one output (on-off) type and one input-two outputs (directional coupler) type. The reversible transition between the switch states is achieved by inducing the phase transition from crystalline to amorphous and vice-versa by application of voltage pulses. The approach of embedding the nanoscale active material Ge\textsubscript{2}Sb\textsubscript{2}Te\textsubscript{5} within the Si waveguide is taken to enhance the interaction of light with the active region of the switches. The dimensions of the active regions of the switches are optimized to achieve low insertion loss, low switching energy, and high extinction ratio. In case of one input-one output switch, an extinction ratio of 33.79 dB along with an extremely low insertion loss of 0.52 dB is achieved using optimum Ge\textsubscript{2}Sb\textsubscript{2}Te\textsubscript{5} length of only 0.92 $μ$m. For one input-two outputs switch, an extinction ratio of 10.33 dB and 5.23 dB is obtained in cross and bar state respectively using an active length of 52 $μ$m. These values of extinction ratio, which are otherwise 18.59 dB and 8.33 dB respectively, are due to the necessity of doping the Si beneath the Ge\textsubscript{2}Sb\textsubscript{2}Te\textsubscript{5} to facilitate the electrical conduction needed for Joule heating. A suitable gap of 100 nm is kept between the active and passive arm of the directional coupler switch. The electro-thermal co-simulations confirm that phase change occurs in whole of the Ge\textsubscript{2}Sb\textsubscript{2}Te\textsubscript{5} region in both types of switches.

physics.app-ph↗

arXiv2018

Design of nano-scale high static performance phase-change on-off silicon photonic switch

We report design of a high static performance on-off optical switch using nanoscale phase change material Ge2Sb2Te5 embedded into silicon-on-insulator waveguide. This active material can be switched between amorphous and crystalline states using electrical/optical pulses. The fundamental mode propagating through Silicon waveguide drastically alters its properties due to high index change at Si-Ge2Sb2Te5 interfaces and absorption in Ge2Sb2Te5. The optical switch made of Silicon waveguide with Ge2Sb2Te5 of volume 400 nm x 180 nm x 450 nm (length x height x width) embedded in to it, provides high extinction ratio of 43 dB with low insertion loss of 2.76 dB in ON state at communication wavelength of 1550 nm. There is trade-off between insertion loss and extinction ratio. For 10 dB extinction ratio, The insertion loss can be as low as 1.2 dB and corresponding active volume is also pretty low (100 nm x 150 nm x 450 nm (length x height x width)). Further, spectral response investigations reveal that this switch maintains extinction ratio more than 30 dB in wavelength span 1500-1600 nm. The high static performance of optical switch reported here is a direct result of proper dimensional engineering of active volume as well as its incorporation into the silicon-on-insulator waveguide. We also propose figure-of merit for non volatile optical switches that takes into account relevant parameters of static performance.

physics.app-ph↗