Vinod Chacko - Academia.edu (original) (raw)

Papers by Vinod Chacko

Research paper thumbnail of Omnidirectional reflection band in multi-layered graphite film based one dimensional photonic crystal nanostructure

We report the omnidirectional reflection (ODR) in one dimensional photonic crystal (PC) structur... more We report the omnidirectional reflection (ODR) in one dimensional photonic crystal (PC) structure consisting of alternate layers of Graphite as material of low refractive index and Tellurium (Te) as material of high refractive index. The effects of the incidence angles on the spectral reflectance have been investigated using transfer matrix method (TMM). The proposed structure gives 100% reflection within a wide range of wavelengths in the visible-near IR region and can be used effectively in wavelength filters, optical resonators and mirrors for visible-near IR region of electromagnetic spectrum. Due to considerable control of absorption of low frequency radiation in graphite, the damping and skin effect in the PC are also suppressed . The investigation has also been made for the study of role of ambient medium and the effect of number of layers in formation of ODR.

Research paper thumbnail of Effect of dispersion on omnidirectional reflection band in zinc oxide-based one-dimensional photonic crystal heterostructures

Journal of Nanophotonics, 2018

Abstract. We report a numerical study of the effect of material dispersion on the omnidirectional... more Abstract. We report a numerical study of the effect of material dispersion on the omnidirectional reflectors (ODR) properties in the case of one-dimensional photonic crystal structures consisting of alternate layers of zinc oxide as material of high refractive index and SiO2 as material of low refractive index. The interplay of dispersion and structural parameters on the ODR properties of the structure of interest has been analyzed. Taking into account the material dispersion properties, shift in the wavelength range for ODR from (1079 − 1158 nm) to (1133 − 1103 nm) is observed. This shows the narrowing of the bandwidth for ODR from 79 to 30 nm as a result of material dispersion. The wavelength range of interest is close to optical communication wavelengths and is useful in many optical device applications.

Research paper thumbnail of Application of a Fiber Optic Probe for Blood Oxygenation Measurement Using Near Infrared Spectroscopy

Journal of Lasers, Optics & Photonics, 2016

In this paper, the design and development of dual wavelength noninvasive fiber optic probe based ... more In this paper, the design and development of dual wavelength noninvasive fiber optic probe based oxyhemoglobin sensor has been presented. This instrument can be used for real time monitoring contents in the blood. It is well known that in blood, the oxygen is carried by the hemoglobin. It uses the dual wavelength spectroscopy which can be performed on blood to determine the oxyhemoglobin saturation. The two sources used are of wavelength 632.8 nm and 830 nm. Two probes containing a bundle of fibers are designed out of which two are source fiber and one is detector fiber. Two finger holders are also designed to prevent any variation in intensity due to finger movement. The backscattered intensity and transmitted intensity of red light and near infrared light are measured. With the help of the ratio of the backscattered intensities and transmitted intensities of red light and near infrared light, oxyhemoglobin saturation is determined.

Research paper thumbnail of Effect of anisotropy on the spectral characteristics of one-dimensional porous silicon photonic crystal microcavity for optical sensing applications

Journal of Nanophotonics, 2019

Abstract. We present a numerical study of the effect of anisotropy on the spectral characteristic... more Abstract. We present a numerical study of the effect of anisotropy on the spectral characteristics of one-dimensional porous silicon microcavity (1D-PSMC) with single defect layer. These structures have strong potential applications in optical sensing of chemicals and bioanalytes. Bruggeman’s effective medium approximation (BEMA) and (4 × 4) general transfer matrix method are used for theoretical modeling of spectral response of anisotropic 1D-PSMC. The potential of this structure as a sensing material is illustrated by analyzing wavelength shift in the defect mode induced by infiltration of biochemical analytes of different refractive indices inside the pores. Observed wavelength shift is found to be linearly dependent on the refractive index of analytes. We propose two 1D-PSMC-based sensors with a microcavity wavelength around 800 and 1200 nm. An anisotropic sensor with an operating wavelength around 800 nm shows a maximum sensitivity of 190 while an isotropic sensor with the same design parameters displays a maximum sensitivity of 150. In the case of an anisotropic sensor designed around 1200 nm, the maximum sensitivity is 260; for the isotropic sensor with similar structure, maximum sensitivity of 210 is obtained. Increased sensitivity is observed in anisotropic structures as compared to the isotropic ones. Design parameters play an integral role to obtain desired sensitivity in 1D-PSMC structure for sensor applications. These sensors can be used for high precision optical sensing of chemical-analytes, bioanalytes, gases, and environmental pollutants.

Research paper thumbnail of Enhancement of omnidirectional bandgap in graphene based quasi-periodic one dimensional photonic crystal heterostructures

We study the omnidirectional reflection (ODR) in one dimensional photonic crystal (PC) structures... more We study the omnidirectional reflection (ODR) in one dimensional photonic crystal (PC) structures consisting of alternate layers of graphene as material of high refractive index and SiO 2 as material of low refractive index. The effects of the thickness of layers and incidence angles on the spectral reflectance have been investigated using transfer matrix method (TMM). The proposed structure gives high reflection within a wide range of wavelengths in the visible and near infrared region and can be used effectively in wavelength filters, optical resonators and mirrors. We also propose here the considerable enhancement of omnidirectional reflection band in near infrared region by changing the design parameters using a gradual constant. Due to considerable control of absorption and small dissipation of electromagnetic energy in graphene, the damping and skin effect in the PC are also obscured.

Research paper thumbnail of Broad inhibition of transmission frequency in multilayered dielectric one dimensional photonic crystal nanostructure

We report the omnidirectional reflection (ODR) in one dimensional photonic crystal (PC) structure... more We report the omnidirectional reflection (ODR) in one dimensional photonic crystal (PC) structure consisting of alternate layers of Cryolite (Na 3 AlF 6 ) as material of low refractive index and Germanium (Ge) as material of high refractive index. The effects of the thickness of layers and incidence angles on the spectral reflectance have been investigated using transfer matrix method (TMM). The proposed structure gives 100% reflection within a wide range of wavelengths in the visible-near IR region (600 nm- 850 nm) which can be tuned according to the design parameters. We observe that cryolite based photonic crystal structure can be used as a good candidate for wavelength filter or broad reflector in the near infrared spectrum which is very useful in many imaging sensors in the field of optical technology.

Research paper thumbnail of Omnidirectional reflection band in multi-layered graphite film based one dimensional photonic crystal nanostructure

We report the omnidirectional reflection (ODR) in one dimensional photonic crystal (PC) structur... more We report the omnidirectional reflection (ODR) in one dimensional photonic crystal (PC) structure consisting of alternate layers of Graphite as material of low refractive index and Tellurium (Te) as material of high refractive index. The effects of the incidence angles on the spectral reflectance have been investigated using transfer matrix method (TMM). The proposed structure gives 100% reflection within a wide range of wavelengths in the visible-near IR region and can be used effectively in wavelength filters, optical resonators and mirrors for visible-near IR region of electromagnetic spectrum. Due to considerable control of absorption of low frequency radiation in graphite, the damping and skin effect in the PC are also suppressed . The investigation has also been made for the study of role of ambient medium and the effect of number of layers in formation of ODR.

Research paper thumbnail of Effect of dispersion on omnidirectional reflection band in zinc oxide-based one-dimensional photonic crystal heterostructures

Journal of Nanophotonics, 2018

Abstract. We report a numerical study of the effect of material dispersion on the omnidirectional... more Abstract. We report a numerical study of the effect of material dispersion on the omnidirectional reflectors (ODR) properties in the case of one-dimensional photonic crystal structures consisting of alternate layers of zinc oxide as material of high refractive index and SiO2 as material of low refractive index. The interplay of dispersion and structural parameters on the ODR properties of the structure of interest has been analyzed. Taking into account the material dispersion properties, shift in the wavelength range for ODR from (1079 − 1158 nm) to (1133 − 1103 nm) is observed. This shows the narrowing of the bandwidth for ODR from 79 to 30 nm as a result of material dispersion. The wavelength range of interest is close to optical communication wavelengths and is useful in many optical device applications.

Research paper thumbnail of Application of a Fiber Optic Probe for Blood Oxygenation Measurement Using Near Infrared Spectroscopy

Journal of Lasers, Optics & Photonics, 2016

In this paper, the design and development of dual wavelength noninvasive fiber optic probe based ... more In this paper, the design and development of dual wavelength noninvasive fiber optic probe based oxyhemoglobin sensor has been presented. This instrument can be used for real time monitoring contents in the blood. It is well known that in blood, the oxygen is carried by the hemoglobin. It uses the dual wavelength spectroscopy which can be performed on blood to determine the oxyhemoglobin saturation. The two sources used are of wavelength 632.8 nm and 830 nm. Two probes containing a bundle of fibers are designed out of which two are source fiber and one is detector fiber. Two finger holders are also designed to prevent any variation in intensity due to finger movement. The backscattered intensity and transmitted intensity of red light and near infrared light are measured. With the help of the ratio of the backscattered intensities and transmitted intensities of red light and near infrared light, oxyhemoglobin saturation is determined.

Research paper thumbnail of Effect of anisotropy on the spectral characteristics of one-dimensional porous silicon photonic crystal microcavity for optical sensing applications

Journal of Nanophotonics, 2019

Abstract. We present a numerical study of the effect of anisotropy on the spectral characteristic... more Abstract. We present a numerical study of the effect of anisotropy on the spectral characteristics of one-dimensional porous silicon microcavity (1D-PSMC) with single defect layer. These structures have strong potential applications in optical sensing of chemicals and bioanalytes. Bruggeman’s effective medium approximation (BEMA) and (4 × 4) general transfer matrix method are used for theoretical modeling of spectral response of anisotropic 1D-PSMC. The potential of this structure as a sensing material is illustrated by analyzing wavelength shift in the defect mode induced by infiltration of biochemical analytes of different refractive indices inside the pores. Observed wavelength shift is found to be linearly dependent on the refractive index of analytes. We propose two 1D-PSMC-based sensors with a microcavity wavelength around 800 and 1200 nm. An anisotropic sensor with an operating wavelength around 800 nm shows a maximum sensitivity of 190 while an isotropic sensor with the same design parameters displays a maximum sensitivity of 150. In the case of an anisotropic sensor designed around 1200 nm, the maximum sensitivity is 260; for the isotropic sensor with similar structure, maximum sensitivity of 210 is obtained. Increased sensitivity is observed in anisotropic structures as compared to the isotropic ones. Design parameters play an integral role to obtain desired sensitivity in 1D-PSMC structure for sensor applications. These sensors can be used for high precision optical sensing of chemical-analytes, bioanalytes, gases, and environmental pollutants.

Research paper thumbnail of Enhancement of omnidirectional bandgap in graphene based quasi-periodic one dimensional photonic crystal heterostructures

We study the omnidirectional reflection (ODR) in one dimensional photonic crystal (PC) structures... more We study the omnidirectional reflection (ODR) in one dimensional photonic crystal (PC) structures consisting of alternate layers of graphene as material of high refractive index and SiO 2 as material of low refractive index. The effects of the thickness of layers and incidence angles on the spectral reflectance have been investigated using transfer matrix method (TMM). The proposed structure gives high reflection within a wide range of wavelengths in the visible and near infrared region and can be used effectively in wavelength filters, optical resonators and mirrors. We also propose here the considerable enhancement of omnidirectional reflection band in near infrared region by changing the design parameters using a gradual constant. Due to considerable control of absorption and small dissipation of electromagnetic energy in graphene, the damping and skin effect in the PC are also obscured.

Research paper thumbnail of Broad inhibition of transmission frequency in multilayered dielectric one dimensional photonic crystal nanostructure

We report the omnidirectional reflection (ODR) in one dimensional photonic crystal (PC) structure... more We report the omnidirectional reflection (ODR) in one dimensional photonic crystal (PC) structure consisting of alternate layers of Cryolite (Na 3 AlF 6 ) as material of low refractive index and Germanium (Ge) as material of high refractive index. The effects of the thickness of layers and incidence angles on the spectral reflectance have been investigated using transfer matrix method (TMM). The proposed structure gives 100% reflection within a wide range of wavelengths in the visible-near IR region (600 nm- 850 nm) which can be tuned according to the design parameters. We observe that cryolite based photonic crystal structure can be used as a good candidate for wavelength filter or broad reflector in the near infrared spectrum which is very useful in many imaging sensors in the field of optical technology.