Jayanta Sarma - Academia.edu (original) (raw)
Papers by Jayanta Sarma
The Tenth International Conference on Advanced Semiconductor Devices and Microsystems, 2014
In the work reported here we use the finite-difference time-domain method to model an ordered nan... more In the work reported here we use the finite-difference time-domain method to model an ordered nanorod array incorporated in a vertical LED structure in place of the surface roughened region. The simulations reveal that diffraction dominates the far field emission when the emissive layer lies below the nanorod array, as might occur in a vertical LED structure with the NR layer used as a light extracting element in place of a roughened surface.
Multiwave mixing phenomena in semiconductor laser amplifiers is of interest both as a means for t... more Multiwave mixing phenomena in semiconductor laser amplifiers is of interest both as a means for the efficient generation of phase conjugate beams and also because of its practical importance in relation to co-channel interference in multiplexed optical communication systems. A description is given of a computationally efficient technique for solving the first order hyperbolic partial differential equations which model the temporal features of multiwave mixing in semiconductor optical amplifiers. >
2018 IEEE British and Irish Conference on Optics and Photonics (BICOP), 2018
In this paper we discuss the development of all-semiconductor photonic crystal surface emitting l... more In this paper we discuss the development of all-semiconductor photonic crystal surface emitting lasers. These devices offer novel routes to coherently coupled arrays which promise previously unachievable levels of brightness and a route to all-electronic beam steering from a single element device.
Conference on Lasers and Electro-Optics
In this paper we discuss the development of all-semiconductor photonic crystal surface emitting l... more In this paper we discuss the development of all-semiconductor photonic crystal surface emitting lasers. These devices offer novel routes to coherently coupled arrays and a route to all-electronic beam steering from a single element device.
IEEE Journal of Selected Topics in Quantum Electronics
We present a novel semi-analytical method utilising modal index analysis, for modelling the field... more We present a novel semi-analytical method utilising modal index analysis, for modelling the field resonances of photonic crystal surface emitting lasers (PCSELs). This method shows very good agreement with other modelling techniques in terms of mode calculations, with the added advantages of computational simplicity, the calculation of threshold gain, and rapid analysis of finite structures. We are able to model the effect of external lateral feedback and simulations indicate that the nearfield peak can be electronically displaced and the threshold as well as the frequency can be controlled through external in-plane feedback, paving the way to dynamic control of PCSELs.
IET Optoelectronics
The frequently sought after combination of characteristics in semiconductor lasers of high power ... more The frequently sought after combination of characteristics in semiconductor lasers of high power together with narrow beam divergence and monochromatic output is usually difficult to attain. The photonic crystal surface emitting laser (PCSEL) is one category of device, however, which tends to provide the above mentioned desirable output features. The PCSEL uses a large area optically active surface but with a 2-D periodic structure that enables it to generate high power in a narrow vertically emitted beam yet maintaining single wavelength operation. A primary requirement to model PCSELs is to obtain the optical field resonances that identify the lasing mode. This paper presents an alternative method for evaluating the resonances, based essentially on the transfer-matrix technique and wave propagation in multilayer medium, which is relatively easy to formulate, and has quite modest demands on computing requirements.
IEE Proceedings J Optoelectronics
The electromagnetic properties of optical disc resonators are analysed by the effective dielectri... more The electromagnetic properties of optical disc resonators are analysed by the effective dielectric constant method. The assumptions inherent in this method are clearly defined, thus enabling the requirements of a complete electromagnetic model to be stated. The present formalism is applicable to structures where the radial boundary is defined by index and/or gain changes. An eigenvalue equation is obtained for the complex resonant frequency of the structure. Analytic solutions to the eigenvalue equation are obtained using material and device parameters relevant to disc resonators fabricated in III-V heterostructure semiconductor materials. The complex eigenvalue gives not only the resonant frequency (wavelength), but also the Q-factor of that resonant mode. An outline is given of the applicability of the device to optoelectronic integrated circuits, and also a brief discussion is given of a number of methods for tuning the resonator.
IEEE Journal of Selected Topics in Quantum Electronics
Spie Proceedings Series, 1997
Recently a high level of in-plane emission in VCSELs has been reported [1]. Existence of the prob... more Recently a high level of in-plane emission in VCSELs has been reported [1]. Existence of the problem for vertical cavities has been previously demonstrated in connection with electron beam pumped lasers [2] and LED [3]. The effect results in increasing threshold and a reduction of efficiency of the devices [2]. Prilimenary estimation shows importance of the problem for large diameter VCSEL as well [4]. Thus, suppression of the in-plane emission gives a way of improvement of VCSEL operational characteristics. Features of the spontaneous emission (SE) pattern is a basis for simulation and modelling of the effect. In this paper the SE is considered for both λ- and λ/2- cavities in the framework of a planar multilayer structure model taking into account the QW optical spectrum. The model is suitable for large diameter VCSELs with weak radial boundaries and allows the consideration of both in-plane and vertical propagating modes. Besults of calculation show that, for a λ/2-cavity, all in-plane propagating modes have weak coupling to a dipole of the active region (QW), unlike the λ-cavity case where there is a mode having a field maximum in the position of QW and thus strong dipole coupling. This leads to a 2 - 4 times reduction of spontaneous emission in the in-plane direction for the λ/2-cavity. However, this is still comparable with the SE in vertical modes and therefore can not be neglected, as is usually assumed. The vertical modes in general propagate at different angles to the pure vertical direction and hence have an in-plane component of the propagation constant. Analysis shows the pure vertical part of the SE to be extremely small compared to the total. Thus, the in-plane component of the SE should be taken into account to improve VCSEL design.
Journal of Applied Physics, 2016
We report a broadband-gain superluminescent diode (SLD) based on self-assembled InAs quantum dots... more We report a broadband-gain superluminescent diode (SLD) based on self-assembled InAs quantum dots (QDs) for application in a high-resolution optical coherence tomography (OCT) light source. Four InAs QD layers, with sequentially shifted emission wavelengths achieved by varying the thickness of the In 0.2 Ga 0.8 As strain-reducing capping layers, were embedded in a conventional p-n heterojunction comprising GaAs and AlGaAs layers. A ridge-type waveguide with segmented contacts was formed on the grown wafer, and an as-cleaved 4-mm-long chip (QD-SLD) was prepared. The segmented contacts were effective in applying a high injection current density to the QDs and obtaining emission from excited states of the QDs, resulting in an extension of the bandwidth of the electroluminescence spectrum. In addition, gain spectra deduced with the segmented contacts indicated a broadband smooth positive gain region spanning 160 nm. Furthermore, OCT imaging with the fabricated QD-SLD was performed, and OCT images with an axial resolution of $4 lm in air were obtained. These results demonstrate the effectiveness of the QD-SLD with segmented contacts as a highresolution OCT light source. V
Novel In-Plane Semiconductor Lasers XV, 2016
We investigate the beam divergence in far-field region, diffraction loss and optical confinement ... more We investigate the beam divergence in far-field region, diffraction loss and optical confinement factors of allsemiconductor and void-semiconductor photonic-crystal surface-emitting lasers (PCSELs), containing either InGaP/GaAs or InGaP/air photonic crystals using a three-dimensional FDTD model. We explore the impact of changing the PC hole shape, size, and lattice structure in addition to the choice of all-semiconductor or void-semiconductor designs. We discuss the determination of the threshold gain from the diffraction losses, and explore limitations to direct modulation of the PCSEL.
Progress In Electromagnetics Research M, 2015
A terahertz (THz) antenna is proposed that offers high input resistance and gain in the presence ... more A terahertz (THz) antenna is proposed that offers high input resistance and gain in the presence of an electrically thick GaAs substrate. The antenna is centrally fed using two vertical probes connected to a photomixer on a thin low temperature grown gallium arsenide (LTG-GaAs) film which is supported by the GaAs substrate. An input impedance of ∼ 3.3 kΩ has been achieved using a dipole antenna that is printed on a thin dielectric slab, and isolated from the supporting substrate using a metal ground plane. A square aperture has been introduced to facilitate the illumination of the photomixer with two laser beams. Furthermore, a frequency selective surface (FSS) has been incorporated in the configuration, which results in a broadside gain of ∼ 19 dBi at a resonance frequency of 0.97 THz.
IEE Proceedings - Optoelectronics, 1997
The guiding properties of passive tapered rib-waveguides with a large output aperture have been m... more The guiding properties of passive tapered rib-waveguides with a large output aperture have been measured as a function of both rib-height and taper angle in the context of high power semiconductor optical sources. It is observed that the near-field (intensity) distribution at the output aperture can be much narrower than that expected from just the fundamental mode of the waveguide at that plane. A theoretical model of the structure, based on the step-transition approximation, has been developed to analyse experimentally measured near-field profiles. The experimental and theoretical results are found to be in good agreement over a wide range of taper angles and other waveguide parameters. Also presented are the corresponding far-field patterns which are so pertinent to high power device design.
IEEE Journal of Quantum Electronics, 2014
The Tenth International Conference on Advanced Semiconductor Devices and Microsystems, 2014
In the work reported here we use the finite-difference time-domain method to model an ordered nan... more In the work reported here we use the finite-difference time-domain method to model an ordered nanorod array incorporated in a vertical LED structure in place of the surface roughened region. The simulations reveal that diffraction dominates the far field emission when the emissive layer lies below the nanorod array, as might occur in a vertical LED structure with the NR layer used as a light extracting element in place of a roughened surface.
Multiwave mixing phenomena in semiconductor laser amplifiers is of interest both as a means for t... more Multiwave mixing phenomena in semiconductor laser amplifiers is of interest both as a means for the efficient generation of phase conjugate beams and also because of its practical importance in relation to co-channel interference in multiplexed optical communication systems. A description is given of a computationally efficient technique for solving the first order hyperbolic partial differential equations which model the temporal features of multiwave mixing in semiconductor optical amplifiers. >
2018 IEEE British and Irish Conference on Optics and Photonics (BICOP), 2018
In this paper we discuss the development of all-semiconductor photonic crystal surface emitting l... more In this paper we discuss the development of all-semiconductor photonic crystal surface emitting lasers. These devices offer novel routes to coherently coupled arrays which promise previously unachievable levels of brightness and a route to all-electronic beam steering from a single element device.
Conference on Lasers and Electro-Optics
In this paper we discuss the development of all-semiconductor photonic crystal surface emitting l... more In this paper we discuss the development of all-semiconductor photonic crystal surface emitting lasers. These devices offer novel routes to coherently coupled arrays and a route to all-electronic beam steering from a single element device.
IEEE Journal of Selected Topics in Quantum Electronics
We present a novel semi-analytical method utilising modal index analysis, for modelling the field... more We present a novel semi-analytical method utilising modal index analysis, for modelling the field resonances of photonic crystal surface emitting lasers (PCSELs). This method shows very good agreement with other modelling techniques in terms of mode calculations, with the added advantages of computational simplicity, the calculation of threshold gain, and rapid analysis of finite structures. We are able to model the effect of external lateral feedback and simulations indicate that the nearfield peak can be electronically displaced and the threshold as well as the frequency can be controlled through external in-plane feedback, paving the way to dynamic control of PCSELs.
IET Optoelectronics
The frequently sought after combination of characteristics in semiconductor lasers of high power ... more The frequently sought after combination of characteristics in semiconductor lasers of high power together with narrow beam divergence and monochromatic output is usually difficult to attain. The photonic crystal surface emitting laser (PCSEL) is one category of device, however, which tends to provide the above mentioned desirable output features. The PCSEL uses a large area optically active surface but with a 2-D periodic structure that enables it to generate high power in a narrow vertically emitted beam yet maintaining single wavelength operation. A primary requirement to model PCSELs is to obtain the optical field resonances that identify the lasing mode. This paper presents an alternative method for evaluating the resonances, based essentially on the transfer-matrix technique and wave propagation in multilayer medium, which is relatively easy to formulate, and has quite modest demands on computing requirements.
IEE Proceedings J Optoelectronics
The electromagnetic properties of optical disc resonators are analysed by the effective dielectri... more The electromagnetic properties of optical disc resonators are analysed by the effective dielectric constant method. The assumptions inherent in this method are clearly defined, thus enabling the requirements of a complete electromagnetic model to be stated. The present formalism is applicable to structures where the radial boundary is defined by index and/or gain changes. An eigenvalue equation is obtained for the complex resonant frequency of the structure. Analytic solutions to the eigenvalue equation are obtained using material and device parameters relevant to disc resonators fabricated in III-V heterostructure semiconductor materials. The complex eigenvalue gives not only the resonant frequency (wavelength), but also the Q-factor of that resonant mode. An outline is given of the applicability of the device to optoelectronic integrated circuits, and also a brief discussion is given of a number of methods for tuning the resonator.
IEEE Journal of Selected Topics in Quantum Electronics
Spie Proceedings Series, 1997
Recently a high level of in-plane emission in VCSELs has been reported [1]. Existence of the prob... more Recently a high level of in-plane emission in VCSELs has been reported [1]. Existence of the problem for vertical cavities has been previously demonstrated in connection with electron beam pumped lasers [2] and LED [3]. The effect results in increasing threshold and a reduction of efficiency of the devices [2]. Prilimenary estimation shows importance of the problem for large diameter VCSEL as well [4]. Thus, suppression of the in-plane emission gives a way of improvement of VCSEL operational characteristics. Features of the spontaneous emission (SE) pattern is a basis for simulation and modelling of the effect. In this paper the SE is considered for both λ- and λ/2- cavities in the framework of a planar multilayer structure model taking into account the QW optical spectrum. The model is suitable for large diameter VCSELs with weak radial boundaries and allows the consideration of both in-plane and vertical propagating modes. Besults of calculation show that, for a λ/2-cavity, all in-plane propagating modes have weak coupling to a dipole of the active region (QW), unlike the λ-cavity case where there is a mode having a field maximum in the position of QW and thus strong dipole coupling. This leads to a 2 - 4 times reduction of spontaneous emission in the in-plane direction for the λ/2-cavity. However, this is still comparable with the SE in vertical modes and therefore can not be neglected, as is usually assumed. The vertical modes in general propagate at different angles to the pure vertical direction and hence have an in-plane component of the propagation constant. Analysis shows the pure vertical part of the SE to be extremely small compared to the total. Thus, the in-plane component of the SE should be taken into account to improve VCSEL design.
Journal of Applied Physics, 2016
We report a broadband-gain superluminescent diode (SLD) based on self-assembled InAs quantum dots... more We report a broadband-gain superluminescent diode (SLD) based on self-assembled InAs quantum dots (QDs) for application in a high-resolution optical coherence tomography (OCT) light source. Four InAs QD layers, with sequentially shifted emission wavelengths achieved by varying the thickness of the In 0.2 Ga 0.8 As strain-reducing capping layers, were embedded in a conventional p-n heterojunction comprising GaAs and AlGaAs layers. A ridge-type waveguide with segmented contacts was formed on the grown wafer, and an as-cleaved 4-mm-long chip (QD-SLD) was prepared. The segmented contacts were effective in applying a high injection current density to the QDs and obtaining emission from excited states of the QDs, resulting in an extension of the bandwidth of the electroluminescence spectrum. In addition, gain spectra deduced with the segmented contacts indicated a broadband smooth positive gain region spanning 160 nm. Furthermore, OCT imaging with the fabricated QD-SLD was performed, and OCT images with an axial resolution of $4 lm in air were obtained. These results demonstrate the effectiveness of the QD-SLD with segmented contacts as a highresolution OCT light source. V
Novel In-Plane Semiconductor Lasers XV, 2016
We investigate the beam divergence in far-field region, diffraction loss and optical confinement ... more We investigate the beam divergence in far-field region, diffraction loss and optical confinement factors of allsemiconductor and void-semiconductor photonic-crystal surface-emitting lasers (PCSELs), containing either InGaP/GaAs or InGaP/air photonic crystals using a three-dimensional FDTD model. We explore the impact of changing the PC hole shape, size, and lattice structure in addition to the choice of all-semiconductor or void-semiconductor designs. We discuss the determination of the threshold gain from the diffraction losses, and explore limitations to direct modulation of the PCSEL.
Progress In Electromagnetics Research M, 2015
A terahertz (THz) antenna is proposed that offers high input resistance and gain in the presence ... more A terahertz (THz) antenna is proposed that offers high input resistance and gain in the presence of an electrically thick GaAs substrate. The antenna is centrally fed using two vertical probes connected to a photomixer on a thin low temperature grown gallium arsenide (LTG-GaAs) film which is supported by the GaAs substrate. An input impedance of ∼ 3.3 kΩ has been achieved using a dipole antenna that is printed on a thin dielectric slab, and isolated from the supporting substrate using a metal ground plane. A square aperture has been introduced to facilitate the illumination of the photomixer with two laser beams. Furthermore, a frequency selective surface (FSS) has been incorporated in the configuration, which results in a broadside gain of ∼ 19 dBi at a resonance frequency of 0.97 THz.
IEE Proceedings - Optoelectronics, 1997
The guiding properties of passive tapered rib-waveguides with a large output aperture have been m... more The guiding properties of passive tapered rib-waveguides with a large output aperture have been measured as a function of both rib-height and taper angle in the context of high power semiconductor optical sources. It is observed that the near-field (intensity) distribution at the output aperture can be much narrower than that expected from just the fundamental mode of the waveguide at that plane. A theoretical model of the structure, based on the step-transition approximation, has been developed to analyse experimentally measured near-field profiles. The experimental and theoretical results are found to be in good agreement over a wide range of taper angles and other waveguide parameters. Also presented are the corresponding far-field patterns which are so pertinent to high power device design.
IEEE Journal of Quantum Electronics, 2014