Lih-Ren Chen

Bio: Lih-Ren Chen is an academic researcher from National Chiao Tung University. The author has contributed to research in topics: Laser & Photonic crystal. The author has an hindex of 2, co-authored 10 publications receiving 10 citations.

Improvement of output efficiency of p-face up photonic-crystal surface-emitting lasers.

Abstract: We optimized the p-side emission device configuration of photonic-crystal surface-emitting laser (PCSEL) to facilitate the easier chip process and wafer level testing as well as the feasibility of lasing at shorter wavelength. Typically, in order to obtain uniformly distributed current for larger emission area of PCSELs, laser output is designed through the n-side window due to the low hole mobility and thin p-side cladding layer. However, the substrate as well as the epi-layers have to be isolated before the test of each single die on the wafer, which compromised the advantage of wafer-level test of surface emitters. On the other hand, for lasers with emission photon energy higher than the bandgap energy of GaAs substrate, the power will be entirely attenuated. In this study, the optimized p-side emission by applying the transparent conduction layer on top of the p side contact layer to enhance the current distribution and breaking the symmetry of conventional circle pattern in a unit cell to boost the output efficiency is investigated. Through this approach, a high efficiency p-side up PCSEL platform with lower fabrication cost is developed, which is also applicable for short wavelength PCSELs.

Photonic integrated multiwavelength laser arrays: Recent progress and perspectives

Abstract: With the significant technology advancement in photonic integration and the demands of compact light sources of multiple wavelengths, multiwavelength laser arrays (MWLAs) can play important roles in high-capacity optical signal transmission, photonic switching, and optical sensing. Manufacturing with semiconductor foundries and the integration with electronic integrated circuits bring not only advanced technologies but also new concepts for realizing MWLAs. This paper will first overview the existing technology development and then discuss the challenges and possible solutions for enabling photonic-integrated MWLAs. The overview will cover monolithically and hybrid-integrated MWLAs. The wavelength registration for both in-plane and vertical-cavity MWLAs will be discussed and compared.

Study of an Epitaxial Regrowth Process by MOCVD for Photonic-Crystal Surface-Emitting Lasers

Abstract: We study a metal organic chemical vapor deposition regrowth process for electrically driven photonic-crystal surface-emitting lasers (PCSELs). The photonic-crystal (PC) structure consisting of air ...

Impact of Air-Hole on the Optical Performances of Epitaxially Regrown P-Side Up Photonic Crystal Surface-Emitting Lasers

Abstract: Optical performances of 950 nm p-side up photonic crystal surface emitting lasers (PCSELs) with different types of air holes are numerically and experimentally investigated. Simulation results show an obvious distinction between effective index method and three dimensional finite-element method (FEM). Measured experiments including wavelength, threshold, and slope efficiency can well meet the FEM numerical predictions. It further reveals that the B mode dominates the laser action and the PCSELs accompanying with equilateral triangle and right isosceles triangle holes possess a lower threshold current and higher radiation than symmetric circle holes. The output power can be further enhanced by increasing the filling factor of air holes before the regrowth process.

Vertically integrated diffractive gratings on photonic crystal surface emitting lasers.

Abstract: We designed and fabricated a photonic crystal surface emitting laser (PCSEL) with vertically integrated diffractive optical elements on their top to study the mechanism of static beam steering on a single chip. The deflected output beam by the self-formed periodic ITO cladding layer of the PCSEL can be further steered by changing the grating period and azimuthal angle of the diffractive gratings relative to the photonic crystal. Through the analysis of photonic band structure and lasing characteristics, the periodic ITO structure is coupled to the photonic crystal band, whereas the integrated grating serves the diffractive function only. The findings pave the way for the design of PCSELs enabling single or multiple output beam with varying direction capability. This type of laser is regarded as an ideal light source for various applications, such as light detection and ranging and three-dimensional sensing systems.

Design and analysis of extended depth of focus metalenses for achromatic computational imaging

Abstract: Metasurface optics have demonstrated vast potential for implementing traditional optical components in an ultracompact and lightweight form factor Metasurfaces, however, suffer from severe chromatic aberrations, posing serious limitations on their practical use Existing approaches for circumventing this involving dispersion engineering are limited to small apertures and often entail multiple scatterers per unit cell with small feature sizes Here, we present an alternative technique to mitigate chromatic aberration and demonstrate high-quality, full-color imaging using extended depth of focus (EDOF) metalenses and computational reconstruction Previous EDOF metalenses have relied on cubic phase masks, where the image quality suffers from asymmetric artefacts Here we demonstrate the use of rotationally symmetric masks, including logarithmic-aspherical, and shifted axicon masks, to mitigate this problem Our work will inspire further development in achromatic metalenses beyond dispersion engineering and hybrid optical–digital metasurface systems

Perovskite random lasers: A tunable coherent light source for emerging applications

Abstract: Metal halide perovskites have attracted increasing attention due to their superior optical and electrical characteristics, flexible tunability, and easy fabrication processes. Apart from their unprecedented successes in photovoltaic devices, lasing action is the latest exploitation of the optoelectronic performance of perovskites. Among the substantial body of research on the configuration design and light emission quality of perovskite lasers, the random laser is a very interesting stimulated emission phenomenon with unique optical characteristics. In this review article, we first comprehensively overview the development of perovskite-based optoelectronic devices and then focus our discussion on random lasing performance. After an introduction to the historical development of versatile random lasers and perovskite random lasers, we summarize several synthesis methods and discuss their material configurations and stability in synthesized perovskite materials. Following this, a theoretical approach is provided to explain the random lasing mechanism in metal halide perovskites. Finally, we propose future applications of perovskite random lasers, presenting conclusions as well as future challenges, such as quality stability and toxicity reduction, of perovskite materials with regard to practical applications in this promising field.

Improvement of output efficiency of p-face up photonic-crystal surface-emitting lasers.

Abstract: We optimized the p-side emission device configuration of photonic-crystal surface-emitting laser (PCSEL) to facilitate the easier chip process and wafer level testing as well as the feasibility of lasing at shorter wavelength. Typically, in order to obtain uniformly distributed current for larger emission area of PCSELs, laser output is designed through the n-side window due to the low hole mobility and thin p-side cladding layer. However, the substrate as well as the epi-layers have to be isolated before the test of each single die on the wafer, which compromised the advantage of wafer-level test of surface emitters. On the other hand, for lasers with emission photon energy higher than the bandgap energy of GaAs substrate, the power will be entirely attenuated. In this study, the optimized p-side emission by applying the transparent conduction layer on top of the p side contact layer to enhance the current distribution and breaking the symmetry of conventional circle pattern in a unit cell to boost the output efficiency is investigated. Through this approach, a high efficiency p-side up PCSEL platform with lower fabrication cost is developed, which is also applicable for short wavelength PCSELs.

Double-Resolved Beam Steering by Metagrating-Based Tamm Plasmon Polariton

Abstract: We consider Tamm plasmon polariton in a subwavelength grating patterned on top of a Bragg reflector. We demonstrate dynamic control of the phase and amplitude of a plane wave reflected from such metagrating due to resonant coupling with the Tamm plasmon polariton. The tunability of the phase and amplitude of the reflected wave arises from modulation of the refractive index of a transparent conductive oxide layer by applying the bias voltage. The electrical switching of diffracted beams of the ±1st order is shown. The possibility of doubling the angular resolution of beam steering by using asymmetric reflected phase distribution with integer and half-integer periods of the metagrating is demonstrated.

Color‐Tuning Mechanism of Electrically Stretchable Photonic Organogels

Abstract: In contrast to nano‐processed rigid photonic crystals with fixed structures, soft photonic organic hydrogel beads with dielectric nanostructures possess advanced capabilities, such as stimuli‐responsive deformation and photonic wavelength color changes. Recenlty, advanced from well‐investigated mechanochromic method, an electromechanical stress approach is used to demonstrate electrically induced mechanical color shifts in soft organic photonic hydrogel beads. To better understand the electrically stretchable color change functionality in such soft organic photonic hydrogel systems, the electromechanical wavelength‐tuning mechanism is comprehensively investigated in this study. By employing controllable electroactive dielectric elastomeric actuators, the discoloration wavelength‐tuning process of an electrically stretchable photonic organogel is carefully examined. Based on the experimental in‐situ response of electrically stretchable nano‐spherical polystyrene hydrogel beads, the color change mechanism is meticulously analyzed. Further, changes in the nanostructure of the symmetrically and electrically stretchable organogel are analytically investigated through simulations of its hexagonal close‐packed (HCP) lattice model. Detailed photonic wavelength control factors, such as the refractive index of dielectric materials, lattice diffraction, and bead distance in an organogel lattice, are theoretically studied. Herein, the switcing mechanism of electrically stretchable mechanochromic photonic organogels with photonic stopband‐tuning features are suggested for the first time.