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Photonic-crystal surface-emitting lasers (PCSELs), which utilize a two-dimensional (2D) optical resonance inside a photonic crystal for lasing, feature various outstanding functionalities such as single-mode high-power operation and arbitrary control of beam polarizations. Although most of the previous designs of PCSELs employ spatially uniform photonic crystals, it is expected that lasing performance can be further improved if it becomes possible to optimize the spatial distribution of photonic crystals. In this paper, we investigate the structural optimization of PCSELs via quantum annealing towards high-power, narrow-beam-divergence operation with linear polarization. The optimization of PCSELs is performed by the iteration of the following three steps: (1) time-dependent 3D coupled-wave analysis of lasing performance, (2) formulation of the lasing performance via a factorization machine, and (3) selection of optimal solution(s) via quantum annealing. By using this approach, we successfully discover an advanced PCSEL with a non-uniform spatial distribution of the band-edge frequency and injection current, which simultaneously enables higher output power, a narrower divergence angle, and a higher linear polarization ratio than conventional uniform PCSELs. Our results potentially indicate the universal applicability of quantum annealing, which has been mainly applied to specific types of discrete optimization problems so far, for various physics and engineering problems in the field of smart manufacturing., 16 pages, 3 figures

Flash light sources with a wide field of view (FOV) are indispensable in various fields such as light detection and ranging (LiDAR), optical wireless communication, and adaptive lighting. However, conventional flash light sources, which combine lasers with external optical elements, tend to suffer from high complexity, large size, and high cost. In this study, we investigate a new wide-FOV flash light source which does not require external optical elements, based on a dually modulated photonic crystal surface-emitting laser (PCSEL). First, we propose and design the concept of a photonic crystal into which information of gradually varying diffraction vectors is introduced in order to artificially broaden the divergence angle. We then experimentally demonstrate photonic crystals based on this concept. Finally, by arraying 100 such lasers with mutually different central emission angles and driving all of these lasers simultaneously, we successfully achieve optics-free, 4-W flash illumination over a FOV of 30° × 30° at a wavelength of 940 nm.

The photonic-crystal surface-emitting laser is a new-generation semiconductor laser capable of emitting a high-power, high-quality (i.e., high-brightness) beam, as well as on-chip two-dimensional beam steering, lasing in various wavelength regimes, and on-chip ultra-short self-pulsation, owing to their freedom of light-matter control. Here we introduce light detection as a new functionality, wherein the photonic-crystal laser is operated under reverse-bias conditions. We find that the photonic-crystal laser operated under reverse-bias conditions has a very high shunt resistance and a low dark current, which are essential qualities to achieve high detectivity. In addition, high responsivity is achieved by utilizing proper band-edge-modes and $Q$ -matching conditions for resonant light absorption. Furthermore, by employing photonic-crystal lasers as the detector as well as the laser source, a direct time-of-flight distance measurement is successfully demonstrated.

Realizing high-peak-power (tens to hundreds of watts or higher) short-pulse (tens of picoseconds or less) operation in semiconductor lasers is crucial for state-of-the-art applications including eye-safe high-resolution remote sensing and non-thermal ultrafine material processing. However, it has been challenging to introduce mechanisms that enable stable high-peak-power short-pulse operation in conventional semiconductor lasers. Here, we propose photonic crystal lasers that have two-dimensionally arranged gain and loss sections to enable high-peak-power short-pulse operation in the fundamental mode while suppressing lasing in higher-order modes to avoid laser instability. On the basis of this concept, we experimentally realize a high peak power of ~20 W and a short pulse width of ~35 ps with an injection current of only 3-4 A using a 400-μm-diameter device and theoretically predict that even higher peak power (>300 W) can be achieved in a 1-mm-diameter device. Our results will contribute to the realization of next-generation laser sources for the aforementioned applications. By using engineered gain and loss sections in a photonic crystal laser, pulses with a peak power of ~20 W and pulse width of ~35 ps have been experimentally demonstrated and even higher peak power operation (>300 W) has been theoretically predicted.

Photonic-crystal surface-emitting lasers (PCSELs) are attractive for a wide range of applications such as material processing and remote sensing owing to their advantage of broad-area coherent lasing supported by a 2-D photonic crystal. Recently, we proposed double-lattice photonic-crystal resonators and achieved 10-W-class high-power and high-beam-quality (namely, high-brightness) operation. To further increase the brightness, it is important to understand the lasing mode behavior of PCSELs in detail. In this article, we experimentally investigate the change in the lasing mode depending on the current injection levels and compare the results with a theoretical analysis that accounts for the change in refractive index and gain distributions due to the current injection. We observed a transition from single-mode lasing to two-mode lasing at high injection currents. We develop a technique for resolving the near-field profiles of individual lasing modes and show that these profiles coincide with theoretical predictions. A comparison of experimental and theoretical results reveals that high-order modes appear due to a bandgap confinement effect induced by a change in the refractive index in the carrier injection area. To effectively remove this confinement effect and suppress the oscillation of high-order modes, we incorporate an in-plane heterostructure into the PCSEL.

Photonic-crystal surface-emitting lasers (PCSELs) with modulated photonic crystals have attracted much attention for their unrivaled capabilities, such as broad area coherent resonance, and lens-free beam scanning and flash illumination. In this paper, we first explain the principles and the development of PCSELs with modulated photonic crystals toward non-mechanical two-dimensional (2D) beam-scanning applications. Then, we show PCSELs with modulated photonic crystals, whose modulation is designed based on an inverse Fourier transform to enable the emission of various beam patterns, such as flash patterns and multi-dot patterns, from a single photonic crystal without using external optical elements. This demonstration underscores the flexibility of PCSELs with modulated photonic crystals as compact, highly functional light sources for a wide range of applications, including not only beam-scanning-type, flash-type, and multidot-type light detection and ranging but also advanced object recognition and adaptive illumination.

We propose and develop a new type of non-mechanical three-dimensional (3D) light detection and ranging (LiDAR) system, which integrates a beam-scanning-type laser source and a flash-type laser source. Employing on-chip dually modulated photonic crystal lasers for both flash and beam-scanning sources, we develop a LiDAR system that is small enough to fit in the palm of the hand. This system is capable of measuring poorly reflective objects in the field of view (FoV) by selectively illuminating these objects with sufficient power by the beam-scanning laser, thereby overcoming the intrinsic issue affecting conventional flash-type 3D LiDAR systems. In addition, we develop and implement a program to have the LiDAR system automatically recognize poorly reflective objects in the FoV and measure their distances by selective illumination. Furthermore, we use the LiDAR system to perform long-distance ranging while including a poorly reflective object in the FoV.

Dually modulated photonic-crystal surface-emitting lasers (DM-PCSELs) are a new type of semiconductor laser that enable on-chip, mechanical-free, high-power, high-beam-quality 2D beam scanning over a wide field of view. These lasers are attracting attention for application in light detection and ranging, and the improvement of their slope efficiency is desired for this application. Thus far, the highest experimentally demonstrated slope efficiency is approximately 0.4 W/A at wavelengths of around 940 nm, which was limited by the fact that roughly half of the laser light was emitted toward and absorbed by the backside electrode. In this work, in order to improve the slope efficiency of DM-PCSELs, we utilize the light emitted toward the backside of the device by introducing a distributed Bragg reflector (DBR) as a backside reflector. In consideration of this laser’s ability to emit beams over a wide field of view, we design laser structures that facilitate a commensurate enhancement of efficiency at various emission angles. Next, we discuss the effect of the DBR on the confinement of transverse modes in thickness direction as well as the suppression of higher-order transverse modes. Then, we analyze the emission characteristics of a DM-PCSEL with a DBR and calculate that the theoretical slope efficiency is enhanced to 0.7–0.8 W/A, which is twice that of the device without a DBR, over a wide range of emission angles from 0° to 30°. We then fabricate the devices and experimentally demonstrate the emission of a single-lobed beam with a high slope efficiency of 0.7–0.8 W/A.

We develop a self-consistent theoretical model for simulating the lasing characteristics of photonic-crystal surface-emitting lasers (PCSELs) under continuous-wave (CW) operation that takes into account thermal effects caused by current injection. Our model enables us to analyze the lasing characteristics of PCSELs under CW operation by solving self-consistently the changes in the in-plane optical gain and refractive index distribution, which is associated with heat generation and temperature rise, and the change in the oscillation modes. We reveal that the lasing band-edge selectivity and beam quality of the PCSELs are affected by the spatial distribution of the band-edge frequency of the photonic crystal formed by the refractive index distribution, which depends on the temperature distribution in the resonator. Furthermore, we show that single-mode lasing with narrow beam divergence can be realized even at high current injection under CW operation by introducing a photonic-crystal structure with an artificially formed lattice constant distribution, which compensates such band-edge frequency distribution.

We demonstrate high-power continuous-wave (CW) lasing oscillation of 1.3-µm wavelength InP-based photonic-crystal surface-emitting lasers (PCSELs). Single-mode operation with an output power of over 100 mW, a side-mode suppression ratio (SMSR) of over 50 dB, and a narrow single-lobe beam with a divergence angle of below 1.2° are successfully achieved by using a double-lattice photonic crystal structure consisting of high-aspect-ratio deep air holes. The double lattice is designed to enhance both the in-plane optical feedback and the surface radiation effects in the photonic crystal. The coupling coefficients for 180 ∘ , +90 ∘ , and -90 ∘ diffractions are estimated from the measurements of the photonic band structure as κ1D = 417 cm−1, κ2D+ = 135 cm−1, and κ2D− = 65 cm−1, respectively. The stable single-mode, high-beam-quality operation is attributed to these large coupling coefficients introduced by the asymmetric double-lattice structure.

Light detection and ranging (LiDAR) is a key technology for smart mobility of robots, agricultural and construction machines, and autonomous vehicles. However, current LiDAR systems often rely on semiconductor lasers with low-quality, large-divergence, and asymmetric beams, requiring high-precision integration of complicated lens systems to reshape the beam. Also, due to the broad linewidth and the large temperature dependence of their lasing spectrum, a bandpass filter with broad bandwidth must be used in front of the detector, so the detected signal is affected by noise from background light such as sunlight. These critical issues limit the performance, compactness, affordability, and reliability of the LiDAR systems. Photonic-crystal surface-emitting lasers (PCSELs) have attracted much attention as novel semiconductor lasers that can solve the issues of conventional semiconductor lasers owing to their capability of high-quality, very-narrow-divergence, and symmetric beam operation supported by broad-area band-edge resonance in their two-dimensional photonic crystal. In this paper, we show the progress and the state of the art of broad-area coherent PCSELs and their application to a time-of-flight (ToF) LiDAR system. We first review the progress of PCSELs made so far. Next, we show recent progress based on PCSELs with a double-lattice structure that enables higher-power and narrower-divergence operation while keeping a symmetric beam shape. By optimizing the double-lattice photonic crystal and the reflective properties of a backside distributed Bragg reflector (DBR), we achieve a high peak power of 10 W while maintaining a nearly diffraction-limited beam divergence of ∼0.1° (FWHM) from a 500 µm diameter resonator. Using this PCSEL, we construct a LiDAR system that uses no external lens system in its light source and demonstrate highly spatially resolved ToF sensing (measurement range of ∼20 m), which is appropriate for autonomous robots and factory automation.

We report on photonic crystal lasers (PCSELs) with high power and high beam quality. The PCSELs have been developed with AI-assisted technologies. The developed devices with a 500µm diameter successfully oscillated with a high, 10W-class peak output power and a very narrow divergence angle of 0.1°. This fact indicates that the devices operate in a complete single lateral and longitudinal mode even over the large area of 500µm diameter. The devices have been installed in time-of-flight LiDAR system. Very high-resolution operation has been successfully realized even though a lens system is not utilized, clearly demonstrating the advantage of high-brightness PCSELs.

We report on electrically driven InP-based photonic-crystal surface-emitting lasers (PCSELs), which possess a deep-air-hole photonic crystal (PC) structure underneath an active region formed by metal-organic vapor-phase-epitaxial (MOVPE) regrowth. Single-mode continuous-wave (CW) lasing operation in 1.3-μm wavelength is successfully achieved at a temperature of 15°C. It is shown that the enhancement of lateral growth during the MOVPE regrowth process of air holes enables the formation of deep air holes with an atomically flat and thin overlayer, whose thickness is less than 100 nm. A threshold current of 120 mA (threshold current density = 0.68 kA/cm2) is obtained in a device with a diameter of 150 μm. A doughnut-like far-field pattern with the narrow beam divergence of less than 1° is observed. Strong optical confinement in the PC structure is revealed from measurements of the photonic band structure, and this strong optical confinement leads to the single-mode CW lasing operation with a low threshold current density.

Mechanical-free, high-power, high-beam-quality two-dimensional (2D) beam scanning lasers are in high demand for various applications including sensing systems for smart mobility, object recognition systems, and adaptive illuminations. Here, we propose and demonstrate the concept of dually modulated photonic crystals to realize such lasers, wherein the positions and sizes of the photonic-crystal lattice points are modulated simultaneously. We show using nano-antenna theory that this photonic nanostructure is essential to realize 2D beam scanning lasers with high output power and high beam quality. We also fabricate an on-chip, circuit-driven array of dually modulated photonic-crystal lasers with a 10 × 10 matrix configuration having 100 resolvable points. Our device enables the scanning of laser beams over a wide range of 2D directions in sequence and in parallel, and can be flexibly designed to meet application-specific demands., 電気的に2次元ビーム走査可能な新たなフォトニック結晶レーザーチップの開発に成功. 京都大学プレスリリース. 2020-07-22., Order from chaos. 京都大学プレスリリース. 2020-11-18.

Photonic-crystal surface-emitting lasers (PCSELs) use the two-dimensional (2D) resonance at the band-edge of a photonic crystal for lasing, and they feature various outstanding functionalities such as high-brightness lasing, arbitrary shaping of beam patterns and on-chip 2D beam steering. In this paper, to investigate the applicability of PCSELs for high-speed operation, we design PCSELs with enhanced in-plane optical feedback, which enable single-mode lasing inside a circular region the diameter of which is less than 10 µm. To realize a strong in-plane confinement of the lasing mode, we increase the one-dimensional coupling coefficients between counter-propagating waves through the careful design of the lattice points. We also introduce an in-plane heterostructure composed of two photonic crystals with different photonic bandgaps and utilize reflection at the boundary of the two photonic crystals in addition to the optical feedback at the band-edge of each photonic crystal. By using three-dimensional finite-difference time-domain method (3D-FDTD), we confirm that the proposed hetero-PCSELs can achieve single-mode lasing operation inside a 9-µm-diameter and possibly realize a 3-dB modulation bandwidth larger than 40 GHz.

We demonstrate the characteristics of photonic crystal lasers fabricated by air hole retained regrowth using metal-organic vapor-phase epitaxy based on an organic arsenic source [tertiary-butyl arsine (TBAs)]. TBAs has the advantage of high decomposition efficiency compared with AsH3, which enables us to achieve a unique air hole shape under the crystal regrowth. We demonstrate that photonic crystal lasers with an area of $200 \times 200~\mu \text{m}^{2}$ exhibit single-mode lasing with a low lasing threshold of ~0.5 kAcm−2. The effect of the unique shape of the air holes obtained by the TBAs-based regrowth on the laser performance is discussed using coupled-wave theory.

We investigate microcrystalline-silicon (μc-Si) solar cells with photonic crystals on the top surface, which exploit the large-area resonant effect in photonic crystals to enhance light absorption, for the first time. Guidelines for designing the surface photonic crystals are discussed, showing the importance of oblique leakage loss suppression. The influence of direct surface etching of the intrinsic μc-Si layer (or photovoltaic layer) is studied, and it is shown that unbalanced etching of the amorphous and crystalline components of the μc-Si layer deteriorates the electronic performance, in particular, the open-circuit voltage and fill factor. We then introduce photonic crystals under an adequate etching condition, and confirm that the light absorption (or the external quantum efficiency) is successfully enhanced by improving the incident light coupling to the resonant modes. Finally, we fabricate a few-micrometer-thick μc-Si solar cell with a photonic crystal on the top surface and demonstrate an active-area efficiency of 11%, resulting from enhancement of the short-circuit current density, while simultaneously suppressing the deterioration of open-circuit voltage and fill factor. The obtained efficiency is the highest reported for a category of μc-Si solar-cell in which all the n/i/p layers are composed of Si, excluding wide-gap materials such as silicon oxide.

We investigate the propagation of light in an ultra-thin gap in stacked-stripe three-dimensional (3D) photonic crystals operating in the near-infrared wavelength range. We fabricate 3D photonic crystals composed of 32 stacked layers with an artificially introduced gap (∼200 nm) in the center of the structure by using a wafer bonding method. In order to study the characteristics of the gap, we introduce oblique waveguides to connect the gap with the upper and lower sides of the photonic crystal. The observation of light output from waveguides that are distant from the waveguide used for incident light demonstrates for the first time that light propagates along the air gap and is distributed to multiple output waveguides. Moreover, we perform calculations that reveal the formation of a propagation mode resulting from introduction of the ultra-thin gap. We analyze the coupling between the propagation mode and the oblique waveguide mode and discuss the characteristics of light distribution via the gap.

We develop a self-pulsating photonic-crystal surface-emitting laser with a ring-shaped saturable absorber inside the current injection region, and realize self-pulsation with a peak power of 8W, a pulse width of less than 100ps, and a beam divergence angle of 0.5°.

Mechanical-free, high-power, high-beam quality two-dimensional beam scanning is strongly required for LiDAR systems for autonomous driving. Here, we propose and demonstrate a new, dually-modulated photonic crystal laser, with which we successfully emit a high-quality laser beam with watt-class power in any desired direction.

Thermal management for the continuous wave (CW) operation of large-area double-lattice photonic-crystal surface-emitting lasers (PCSELs) is discussed. Thermal analysis is conducted to calculate the temperature of PCSELs under CW operation with heat dissipation. We assemble a double-lattice PCSEL in a water-cooling package with a highly thermally conductive sub-mount for heat dissipation. We measure the device temperature by using a thermographic camera and compare the measured values with the calculations. Owing to proper heat dissipation, we successfully realize ∼ 8 W of output power under CW operation of a single-chip double-lattice PCSEL.

We develop double-lattice photonic-crystal surface-emitting lasers, which are designed to achieve high-power and high-beam-quality operation. CW output power of ∼7W is successfully achieved from a single-chip with a diameter of 800μm.

The passively Q-switched operation of a cryogenically cooled Yb:YAG/Cr:YAG microchip laser was demonstrated with end pumping by a photonic crystal surface emitting laser (PCSEL). This laser generated 70 μJ/1.7 ns/3.2 kHz pulses with near diffraction limited beam quality (M2=1.1) at 1029.4 nm. There were no coupling optics between the microchip laser crystal and PCSEL, which made the system simple and compact.

Achieving high brightness (where brightness is defined as optical power per unit area per unit solid angle) in semiconductor lasers is important for various applications, including direct-laser processing and light detection and ranging for next-generation smart production and mobility. Although the brightness of semiconductor lasers has been increased by the use of edge-emitting-type resonators, their brightness is still one order of magnitude smaller than that of gas and solid-state/fibre lasers, and they often suffer from large beam divergence with strong asymmetry and astigmatism. Here, we develop a so-called ‘double-lattice photonic crystal’, where we superimpose two photonic lattice groups separated by one-quarter wavelength in the x and y directions. Using this resonator, an output power of 10 W with a very narrow-divergence-angle (

We demonstrate self-pulsation with a pulse width of 100 ps and a beam divergence angle of 0.35° in a photonic-crystal surface-emitting laser by introducing a saturable absorber section and employing a new double-hole photonic crystal.

The radiation pattern and out-coupling efficiency of light from the end surface of interlayer (oblique) waveguides in stacked-stripe 3-D photonic crystals are numerically investigated. It is shown that the coupling to the surface mode of the 3-D photonic crystal decreases the out-coupling efficiency to free-space modes down to 60%, whereas the reflection at the surface is negligibly small. The efficiency can be improved to 90% by introducing a 2-D grating-like structure to create a surface-mode gap, where surface modes are prohibited.

Enhancing the absorption of thin-film microcrystalline silicon solar cells over a broadband range in order to improve the energy conversion efficiency is a very important challenge in the development of low cost and stable solar energy harvesting. Here, we demonstrate that a broadband enhancement of the absorption can be achieved by creating a large number of resonant modes associated with two-dimensional photonic crystal band edges. We utilize higher-order optical modes perpendicular to the silicon layer, as well as the band-folding effect by employing photonic crystal superlattice structures. We establish a method to incorporate photonic crystal structures into thin-film (~500 nm) microcrystalline silicon photovoltaic layers while suppressing undesired defects formed in the microcrystalline silicon. The fabricated solar cells exhibit 1.3 times increase of a short circuit current density (from 15.0 mA/cm2 to 19.6 mA/cm2) by introducing the photonic crystal structure, and consequently the conversion efficiency increases from 5.6% to 6.8%. Moreover, we theoretically analyze the absorption characteristics in the fabricated cell structure, and reveal that the energy conversion efficiency can be increased beyond 9.5% in a structure less than 1/400 as thick as conventional crystalline silicon solar cells with an efficiency of 24%. © 2015 The Authors. Progress in Photovoltaics: Research and Applications published by John Wiley & Sons Ltd.

In this paper, we demonstrate the operation of a photonic-crystal surface-emitting laser that has a double-hole two-dimensional photonic-crystal structure. We successfully fabricate this unique structure by employing air-hole retained crystal regrowth using metalorganic vapor phase epitaxy. Single-mode lasing having a narrow beam divergence of less than 0.2° is achieved with a large lasing area of 300×300 μm2.

A passively Q-switched Yb:YAG/Cr:YAG laser pumped by a photonic-crystal surface-emitting laser (PCSEL) was developed. Yb:YAG crystal was cryogenically cooled by liquid nitrogen at 77 K. Excellent Gaussian beam profile (M 2 = 1.02) and high slope efficiency of 58% were demonstrated without using a coupling optics between a laser material and PCSEL.

Photonic-crystal surface-emitting lasers (PCSELs) have attracted considerable attention as a novel semiconductor laser that surpasses traditional semiconductor lasers. In this review article, we review the current progress of PCSELs, including the demonstration of large-area coherent oscillation, the control of beam patterns, the demonstration of beam steering, and the realization of watt-class and high-beam-quality operation. Furthermore, we show very recent progress in the exploration of high brightness of more than 300 MW cm−2 sr−1, obtained with a high output power of about 10 W while maintaining a high beam quality M2 ~ 2. The PCSELs with such high performances are expected to be applied to a variety of fields, such as laser-based material processing, optical sensing (light-detection and ranging (LiDAR)), and lighting, as they retain the benefits of compact and high-efficiency semiconductor lasers.

Three-dimensional photonic crystals1,2,3,4,5,6,7,8,9,10 are expected to provide a fundamental building block for the realization of three-dimensional manipulation of photons. However, because of the lack of systematic design principles to precisely control bending and guiding in three dimensions, as well as advancements in the fabrication technology necessary for the realization of large-area, defect-free three-dimensional photonic crystals, the arbitrary three-dimensional manipulation of photons has yet to be demonstrated. Here, we develop a new design concept for three-dimensional waveguides and bends, and realize it experimentally in silicon three-dimensional photonic crystals. We demonstrate clear three-dimensional optical guiding phenomena, in which light is incident on the crystal from one side, is bent vertically and horizontally (and is even split into two or trapped by an intermediate nanocavity), and is finally emitted from the other side of the crystal. These results will open the door to the realization of three-dimensional optical chips with various functionalities. Researchers demonstrate the three-dimensional routing of light through a three-dimensional photonic crystal. Before transmission, the light is bent both vertically and horizontally, split and trapped.