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Photonic Crystal Microcavity Filters Embedded in Ridge Waveguide Structures /

Record Type:	Electronic resources : Monograph/item
Title/Author:	Photonic Crystal Microcavity Filters Embedded in Ridge Waveguide Structures // Agnivesh Sharma Jugessur.
Author:	Jugessur, Agnivesh Sharma,
Description:	1 electronic resource (214 pages)
Notes:	Source: Dissertations Abstracts International, Volume: 81-09, Section: B.
Contained By:	Dissertations Abstracts International81-09B.
Subject:	Theory. -
Online resource:	https://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=27929328
ISBN:	9781658466813

Photonic Crystal Microcavity Filters Embedded in Ridge Waveguide Structures /
Jugessur, Agnivesh Sharma,

Photonic Crystal Microcavity Filters Embedded in Ridge Waveguide Structures /Agnivesh Sharma Jugessur. - 1 electronic resource (214 pages)

Source: Dissertations Abstracts International, Volume: 81-09, Section: B.

Highly confined optical systems can be used to reduce the size and power requirements of integrated optical components and, among other possible applications, compact optical filters can be designed that exhibit high quality factor and selective transmission that will be useful for wavelength division multiplexing (WDM) applications and densely integrated photonic circuits more generally. By the same token, compact photonic crystal (PhC) filters can be realised when light is confined in a microcavity formed by one-dimensionally or two-dimensionally periodic photonic crystal mirrors, realised in a ridge waveguide format. Confinement of light to small volumes also has important implications for optical emission properties: it changes the probability of spontaneous emission from atoms, allowing both enhancement and inhibition'. The PhC microcavities presented in the present work could potentially also be used in highly confined light sources. In this thesis, photonic crystal microcavity filters have been designed using the Finite Domain Time Difference (FDTD) method and fabricated using electron beam lithography (EBL) and reactive ion etching (RIE) on GaAs/AlGaAs epitaxial material. They were characterised using the end-fire coupling technique with a tunable Ti-Sapphire laser and a 1.5 μm tunable diode laser. The PhC filters were designed as an array of holes and also as several periods wide 2-D hole array PhC structures embedded in high lateral index contrast ridge waveguides. The lattice arrangements of the PhC holes that have been used were the square lattice and triangular lattice in the TM orientations. One of the main objectives of the present work was to reduce the mode mismatch at the waveguide-PhC interface - which causes substantial reflection and radiation losses. For efficient modal conversion between the waveguide and PhC sections, mode-matching features such as smaller size-graded holes were added on either side of the microcavity forming defect region, for most of the microcavity filters of the present work. The mode-matching method is based on a model2 whereby the gradual modal conversion is effected by the addition of smaller and graded-size holes at the PhC-waveguide interface. The smaller holes effectively generate artificial dielectric layers with progressively varying effective indices. In the present work, this model has been implemented in the photonic crystal microcavity filters to increase the optical throughput. It has been demonstrated experimentally that, by doing so, both the transmission at resonance increases significantly and, in some cases, the quality factor increases as well. Moreover, modal mismatch occurs within the cavity itself -and by adding smaller graded-size holes in the defect region, enhanced transmission has been demonstrated. In addition, since a Lorentzian filter response within a relatively broad base level is not ideal for many real applications, Bragg grating concepts have been applied to PhC filters to control the filter response. By appropriate choice of the phase shifts or microcavity size and their appropriate locations and magnitudes, a significant level of control over the filter response has been obtained. It has also been found that variation of the PhC hole size in the first and last rows at the input and output regions in a several periods wide, doubly-shifted, PhC square lattice filter can give another degree of freedom in engineering the filter response. Triangular-lattice PhC filters with tailored response have also been attempted. Nevertheless, precise tailoring of the response depends a great deal on the achievable fabrication accuracy, which poses both restrictions and challenges. Moreover, the idea of integrating the experimentally tested PhC filters with other photonic devices has been initiated and should be a stepping stone towards the realisation of dense, integrated and multifunctional photonic circuits. Experimental attempts have been made to integrate the several periods wide PhC filters embedded in 3 pun ridge waveguides with a PhC super-prism device with the idea of producing finer wavelength selectivity than obtainable with the super-prism alone. Furthermore, work has been initiated on the integration of the PhC mirrors into the ends of a ridge waveguide cavity structure to form a Distributed Bragg Reflected (DBR) laser, using the high reflectivity and inherent mechanical integrity of this type of PhC structure.

English

ISBN: 9781658466813Subjects--Topical Terms:

2142529
Theory.
Subjects--Index Terms:

Photonic crystals

Photonic Crystal Microcavity Filters Embedded in Ridge Waveguide Structures /
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520 $a Highly confined optical systems can be used to reduce the size and power requirements of integrated optical components and, among other possible applications, compact optical filters can be designed that exhibit high quality factor and selective transmission that will be useful for wavelength division multiplexing (WDM) applications and densely integrated photonic circuits more generally. By the same token, compact photonic crystal (PhC) filters can be realised when light is confined in a microcavity formed by one-dimensionally or two-dimensionally periodic photonic crystal mirrors, realised in a ridge waveguide format. Confinement of light to small volumes also has important implications for optical emission properties: it changes the probability of spontaneous emission from atoms, allowing both enhancement and inhibition'. The PhC microcavities presented in the present work could potentially also be used in highly confined light sources. In this thesis, photonic crystal microcavity filters have been designed using the Finite Domain Time Difference (FDTD) method and fabricated using electron beam lithography (EBL) and reactive ion etching (RIE) on GaAs/AlGaAs epitaxial material. They were characterised using the end-fire coupling technique with a tunable Ti-Sapphire laser and a 1.5 μm tunable diode laser. The PhC filters were designed as an array of holes and also as several periods wide 2-D hole array PhC structures embedded in high lateral index contrast ridge waveguides. The lattice arrangements of the PhC holes that have been used were the square lattice and triangular lattice in the TM orientations. One of the main objectives of the present work was to reduce the mode mismatch at the waveguide-PhC interface - which causes substantial reflection and radiation losses. For efficient modal conversion between the waveguide and PhC sections, mode-matching features such as smaller size-graded holes were added on either side of the microcavity forming defect region, for most of the microcavity filters of the present work. The mode-matching method is based on a model2 whereby the gradual modal conversion is effected by the addition of smaller and graded-size holes at the PhC-waveguide interface. The smaller holes effectively generate artificial dielectric layers with progressively varying effective indices. In the present work, this model has been implemented in the photonic crystal microcavity filters to increase the optical throughput. It has been demonstrated experimentally that, by doing so, both the transmission at resonance increases significantly and, in some cases, the quality factor increases as well. Moreover, modal mismatch occurs within the cavity itself -and by adding smaller graded-size holes in the defect region, enhanced transmission has been demonstrated. In addition, since a Lorentzian filter response within a relatively broad base level is not ideal for many real applications, Bragg grating concepts have been applied to PhC filters to control the filter response. By appropriate choice of the phase shifts or microcavity size and their appropriate locations and magnitudes, a significant level of control over the filter response has been obtained. It has also been found that variation of the PhC hole size in the first and last rows at the input and output regions in a several periods wide, doubly-shifted, PhC square lattice filter can give another degree of freedom in engineering the filter response. Triangular-lattice PhC filters with tailored response have also been attempted. Nevertheless, precise tailoring of the response depends a great deal on the achievable fabrication accuracy, which poses both restrictions and challenges. Moreover, the idea of integrating the experimentally tested PhC filters with other photonic devices has been initiated and should be a stepping stone towards the realisation of dense, integrated and multifunctional photonic circuits. Experimental attempts have been made to integrate the several periods wide PhC filters embedded in 3 pun ridge waveguides with a PhC super-prism device with the idea of producing finer wavelength selectivity than obtainable with the super-prism alone. Furthermore, work has been initiated on the integration of the PhC mirrors into the ends of a ridge waveguide cavity structure to form a Distributed Bragg Reflected (DBR) laser, using the high reflectivity and inherent mechanical integrity of this type of PhC structure.
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