High-Index-Contrast Grating (HCG) and Its Applications in Optoelectronic Devices

Abstract

Subwavelength High-Contrast Grating (HCG) and its Applications in Optoelectronic Devices Optical grating is a research topic with a long history. It has been extensively studied over the years due to its various applications in holography, spectroscopy, lasers, and many other optoelectronic devices. In this dissertation, we present a novel single-layer subwavelength high-index-contrast grating (HCG) which opens a new era in the study of grating. HCGs can serve as surface normal broadband (∆λ/λ ~35%), high-reflectivity (>99%) mirrors, which can be used to replace conventional distributed Bragg reflectors (DBRs) in optical devices. Different designs of HCGs can also serve as narrow band, surface emitting, high-quality (Q) factor optical resonators or shallow angle reflectors. In this dissertation, we will review the recent advances in high-index-contrast grating and its applications in optoelectronic devices, including vertical-cavity surface-emitting lasers (VCSELs), high-Q optical resonators, and hollow-core waveguides. We first present a novel HCG-based VCSEL where the conventional DBR mirror is replaced with a HCG-based mirror. A systematic and comprehensive review of the experimental and numerical simulation results is presented to demonstrate many desirable 2 attributes of HCG-based VCSELs, including polarization selection, transverse mode control and a large fabrication tolerance. Next, we present an ultra-fast tuning, HCG-based tunable VCSEL. By integrating a mechanically movable actuator with a single-layer HCG as the VCSEL top mirror, precise, wide continuous wavelength tuning (~18 nm) was achieved at room temperature. The small footprint of the HCG enables each of the mechanical actuator dimensions to be scaled down by at least a factor of 10, resulting in a greater than 1000 times reduction in mass, and an increase in the mechanical resonant frequency. It also allows for a record-fast, HCG-based tunable VCSEL with a tuning time in the ~10 ns range to be obtained. Besides the HCG-based VCSELs/tunable VCSELs, we also present a HCG-based surface normal high-Q resonator with a simulated Q-factor as large as 500,000 and an experimentally measured Q-factor of ~14,000. The unique feature of a high-Q with surface normal emission is highly desirable, as the topology facilitates a convenient and high output coupling with free-space or fiber optics. This feature is promising for array fabrication of lasers and filters, as well as high throughput sensor arrays. In addition, we propose a HCG-based hollow-core waveguide design with an ultralow propagation loss of <0.01dB/m, three orders of magnitude lower than the lowest loss of the state-of-art chip-scale hollow waveguides. This novel HCG hollow-core waveguide design will serve as a basic building block in many chip-scale integrated photonic circuits, enabling system-level applications including optical interconnects, optical delay lines, and optical sensors. ____________________________________ Professor Constance J. Chang-Hasnain Dissertation Committee Chair

Integration of GaAs-based VCSEL array on SiN platform with HCG reflectors for WDM applications

“…They have many interesting properties such as very broadband high reflectance and narrow high Q factor resonances [8]. In recent years, HCGs with broadband high reflectivity have been reported to replace top DBRs of VCSELs and tuning of the lasing wavelength have also been achieved by electrostatic actuation of the HCG [4].…”

A low-threshold high-index-contrast grating (HCG)-based organic VCSEL

“…Thus, it is a good candidate for replacing DBR reflectors in VCSELs. Not only is the HCG layer considerably thinner than a conventional DBR, but it also provides intrinsic polarization control to VCSELs [11]. One of the disadvantages of VCSELs is the propagation of higher order transverse modes.…”

Finite-size limitations on Quality Factor of guided resonance modes in 2D Photonic Crystals

“…Incoming light, with a real out-of-plane k-vector, can couple to in-plane propagating modes. This gives rise to properties that are useful in applications like vertically emitting light diodes [5][6][7], compact narrow fiber tip sensors [8,9] and highly sensitive optical sensors for environmental control and medical diagnosis [10,11].…”