Wavelength Conversion Devices Research Articles

Tunable Intracavity Coherent Up-Conversion with Giant Nonlinearity in a Polar Fluidic Medium.

The study has demonstrated a novel microcavity-based flexible photon up-conversion system using second harmonic generation (SHG) from a polar nematic fluidic medium doped with a laser dye. The idea is based on coherent light generation via stimulated emission (lasing) and simultaneous frequency doubling inside a microcavity. The polar nematic fluid equips very high even-order optical nonlinearity due to its polar symmetry and large dipole moment along the molecular long axis. At the same time, its inherent fluidic nature allows to easily functionalize the media just by doping, in the present case, with an emissive laser dye. The demonstrated system exhibits a giant nonlinear optical response to input light, while enabling spectral narrowing and multiple-signal output of up-converted light, which is not attainable through the simple SH-conversion of input light. Furthermore, the susceptibility of the liquid crystal offers dynamic modulation capabilities by an external stimulus, such as signal switching by the application of electric field or wavelength tuning through temperature variation. Such a brand-new type of simple coherent flexible up-conversion system must be promising as a new principle for easily accessible and down-scalable wavelength conversion devices.

Polarity Inversion of GaN via AlN Oxidation Interlayer Using Metal–Organic Vapor Phase Epitaxy

The polarity inversion of GaN films grown on vicinal sapphire substrates is demonstrated using the metal–organic vapor phase epitaxy (MOVPE) method via an AlN oxidation interlayer for application in wavelength conversion devices. By annealing the N‐polar AlN surface at 900 °C in air, the pit‐free Ga‐polar GaN layer can be regrown. Anisotropic etching in KOH and transmission electron microscopy confirms the formation of a GaN polarity‐inverted structure. X‐ray diffraction measurements reveal an increase in threading dislocations due to the nucleation island formation by low‐temperature GaN layer and strain relaxation at the regrown interface. The simple fabrication process of the GaN polarity‐inverted structure using an AlN oxidation interlayer will pave the way for applications in new devices that require polarity‐controlled and/or polarity‐inverted stacking structures.

Epitaxial Junction of Inversion Symmetry Breaking AlN and Centrosymmetric NbN: A Polarity Control of Wide-Bandgap AlN

The polarity control of AlN by epitaxial growth can enable the fabrication of wavelength conversion devices and innovative electronic devices based on nitride semiconductors. Conventional techniques for controlling the AlN polarity are based on oxygen-mediated growth mechanisms. In contrast, this study reports a technique to invert the polarity of wurtzite-type AlN using lattice-matched centrosymmetric NbN. The surface of AlN grown by sputtering on NbN/Al-polar AlN was atomically flat and highly crystalline. Structural analysis with scanning transmission electron microscopy revealed that the AlN grown on NbN/Al-polar AlN was N-polar. The proposed all-nitride epitaxial N-polar AlN/NbN/Al-polar AlN heterostructure did not contain oxide materials, which typically degrade the optical and electrical properties of AlN. Furthermore, the stability of the N-polar AlN/NbN interface was clarified by density functional theory calculations. These findings can contribute to the fabrication of structural defect-free vertical- and lateral-polarity structures based on AlN.

Fabrication and evaluation of rib-waveguide-type wavelength conversion devices using GaN-QPM crystals

A GaN crystal comprises two polar structures along the c-axis direction, and functions as a quasi-phase-matching (QPM) crystal by fabricating a periodic inversion structure. We fabricated GaN-QPM crystals to design rib-waveguide-type devices for achieving highly efficient wavelength conversion. The QPM period required for wavelength conversion was calculated in the design phase of the device structure. GaN-QPM crystals with the obtained period were fabricated using double-polarity selective-area growth (DP-SAG). The GaN-QPM crystal was then used to fabricate a second-harmonic generation (SHG) device with a rib waveguide structure. Optical measurements revealed that the device achieved wavelength conversion from 840 to 420 nm. Further, the SHG device exhibited a wavelength conversion efficiency of 1.5 × 10–4% W−1. These results indicated that GaN-QPM crystals fabricated by DP-SAG can be used for wavelength conversion.

DUV coherent light emission from ultracompact microcavity wavelength conversion device.

A unique design of our ultracompact microcavity wavelength conversion device exploits the simple principle that the wavelength conversion efficiency is proportional to the square of the electric field amplitude of enhanced pump light in the microcavity, and expands the range of suitable device materials to include crystals that do not exhibit birefringence or ferroelectricity. Here, as a first step toward practical applications of all-solid-state ultracompact deep-ultraviolet coherent light sources, we adopted a low-birefringence paraelectric SrB4O7 crystal with great potential for wavelength conversion and high transparency down to 130 nm as our device material, and demonstrated 234 nm deep-ultraviolet coherent light generation, whose wavelength band is expected to be used for on-demand disinfection tools that can irradiate the human body.

Quasi-phase-matching stack of 25 GaAs plates with high transmittance for high-power mid-infrared wavelength conversion fabricated by use of room-temperature bonding

A quasi-phase-matching (QPM) stack of 25 GaAs plates with better surface flatness and reduced internal loss has been successfully fabricated using the room-temperature-bonding technique, which is for a high-power and highly efficient wavelength-conversion device in the mid-infrared region. This is accomplished owing to an improved process in which GaAs plates are set on Y 3 A l 5 O 12 crystals with the flat surfaces polished to laser grade. The loss coefficient and the loss per interface of the fabricated 2.1 mm long, 25-plate-stacked GaAs QPM device are 2.1 c m − 1 and 1.8%, respectively, which are 70% smaller than those of a 0.92 mm long, 11-plate stack fabricated with the previous process.

Monolithic microcavity second harmonic generation device using low birefringence paraelectric material without polarity-inverted structure

We proposed a monolithic microcavity wavelength conversion device without a polarity-inverted structure. The device consists of a low birefringence paraelectric material and a dielectric material. A fundamental wave intensity is enhanced significantly in the microcavity with two distributed Bragg reflectors, and a second-harmonic wave is efficiently generated in a very short region close to a coherence length. As a first step of this study, we used GaN as a device material, and succeeded in the blue second harmonic generation with a wavelength of 428 nm.

Wavelength down-conversion study of Ba3Y1-X (BO3)3: x Tb3+& Eu3+ [0.005 ≤ X ≤ 0.05] phosphor for solid state lighting applications

In this work, we synthesized the Tb3+ and Eu3+ doped α-Ba3Y(BO3)3 phosphor using the solution combustion method. Using the powder XRD pattern and FTIR low-temperature phase of α-Ba3Y1-X(BO3): xTb3+& Eu3+ was confirmed. Element composition with percentage was verified by FE-SEM-EDS. Stoke’s shift values were calculated which confirms the high thermal stability of the phosphor& its use in high power WLED. Photoluminescence study at room temperature was done. Intrinsic absorption due to the 4f-4f transition of Eu3+ results intense red emission from α-Ba3Y1-X(BO3): xEu3+ makes it suitable for pc-WLED and confirms the Centro-inversion symmetry site of Eu3+ in the host. Green emission at NUV excitation from Ba3Y1-X(BO3): xTb3+ results from cross-relaxation of Tb3+ in a host. The concentration quenching reason for both activators was investigated by calculating and comparing critical distance. The purity of luminescence color was confirmed by plotting CIE-chromaticity co-ordinates on CIE-Color gamut. The entire work confirms the importance of synthesized phosphor along with previously reported same host materials. The reported phosphor may be suitable for NUV converted WLED, wavelength conversion devices, and high power RGB –WLED.

Silicon-Based Group-IV O-E-O Devices for Gain, Logic, and Wavelength Conversion

Using the strip-guided “manufacturable” SOI/GeSn group-IV integrated-photonics platform operating at 1550 nm, we propose an optical-to-electrical-to-optical (O-E-O) device that can work either as a...

Electrically Poled, MNA-Microstructured Optical Fibers for Second Harmonic Generation

A hybrid, microstructured optical fiber (MOF) comprised of a silica glass, endlessly single mode optical fiber infiltrated with 2-methyl, 4-nitroaniline (MNA) is subjected to electric field poling for enhancing non-linear wavelength conversion properties. Different poling conditions (temperature, and electric field) are applied, resulting in significant changes manifested in the transmittance and second harmonic generation (SHG) behavior of this hybrid optical fiber. The origins of material and guidance changes induced by the electric poling are investigated by scanning electron microscopy, backscattered SHG microscopy and modal imaging as a function of the polarization state of a 1064 nm, pulsed laser pump. Results show that the improved crystallinity, induced by the poling of the MNA material infiltrated into the MOF capillaries surrounding the optical fiber core, play a dominant role in both SHG efficiency and the transmission performance of these hybrid optical fibers, opening new prospects in the development of in-fiber light switching and wavelength conversion devices.

Effect of composition and temperature on the second harmonic generation in silver phosphate glasses

We herein employ nonlinear laser imaging microscopy to explicitly study the dynamics of second harmonic generation (SHG) in silver iodide phosphate glasses. While glasses of this family have gained extensive scientific attention over the years due to their superior conducting properties, considerably less attention has been paid to their unique nonlinear optical characteristics. In the present study, firstly, it is demonstrated that SHG signal intensity is enhanced upon increasing silver content due to the random formation of silver microstructures within the glass network. Secondly, the SHG temperature dynamics were explored near the glass transition temperature (Tg) regime, where significant glass relaxation phenomena occur. It is found that heating towards the Tg improves the SHG efficiency, whereas above Tg, the capacity of glasses to generate second harmonic radiation is drastically suppressed. The novel findings of this work are considered important in terms of the potential employment of these glasses for the realization of advanced photonic applications like optical-switches and wavelength conversion devices.

Mid-infrared pulsed laser ultrasonic testing for carbon fiber reinforced plastics

Laser ultrasonic testing (LUT) can realize contactless and instantaneous non-destructive testing, but its signal-to-noise ratio must be improved in order to measure carbon fiber reinforced plastics (CFRPs). We have developed a mid-infrared (mid-IR) laser source optimal for generating ultrasonic waves in CFRPs by using a wavelength conversion device based on an optical parametric oscillator. This paper reports a comparison of the ultrasonic generation behavior between the mid-IR laser and the Nd:YAG laser. The mid-IR laser generated a significantly larger ultrasonic amplitude in CFRP laminates than a conventional Nd:YAG laser. In addition, our study revealed that the surface epoxy matrix of CFRPs plays an important role in laser ultrasonic generation.

GaAs/AlAs triple-coupled cavity with InAs quantum dots for ultrafast wavelength conversion devices

We have investigated a GaAs/AlAs triple-coupled multilayer cavity structure with InAs quantum dots for an ultrafast wavelength conversion device. Three cavity modes with the resonance frequencies ω1, ω2, and ω3 were used for efficient wavelength conversion via a four-wave mixing (FWM) process. Identical frequency separation between two adjacent modes (ω1 − ω2 = ω2 − ω3) was successfully realized using a controlled lateral thickness variation across the wafer. Time-resolved FWM signals from the triple-coupled multilayer cavity were measured using 100 fs laser pulses. The incident laser pulses were divided into two pulses and each of them was spectrally shaped individually so that the input and control pulses only covered the ω1 and ω2 modes, respectively. The wavelength-converted FWM signal with a frequency of ω3 (= 2ω2 − ω1) was clearly observed when the sample was simultaneously irradiated with the input and control laser pulses.

Fabrication of 0.7 µm2 ridge waveguide in ion-sliced LiNbO3 by proton-exchange accelerated chemical etching

We fabricated low-loss ridge waveguides of 1.0 × 0.7 µm2 cross-sectional area in ion-sliced LiNbO3 crystals by chemical etching accelerated in proton-exchanged regions. Strong light confinement was obtained at 1.55 µm wavelength. The waveguides are effective in implementing efficient and compact nonlinear-optic wavelength conversion devices.

Four-wave mixing in GaAs/AlAs triple-coupled cavity with InAs quantum dots

We have investigated a GaAs/AlAs triple-coupled multilayer cavity structure for an ultrafast wavelength conversion device. We found that significant improvement in the wavelength conversion was realized by introducing good nonlinear materials in the cavity layer, and that the precise control of the cavity modes was important to obtain stronger frequency conversion signals. We grew a triple coupled multilayer cavity structure with self-assembled InAs quantum dots (QDs) by molecular beam epitaxy and investigated the frequency separations of the cavity modes in relation to the cavity layer thickness using on the basis of the reflection spectra. Clear four-wave mixing (FWM) signals were demonstrated by time-resolved FWM measurements were performed at room temperature using a femtosecond laser system.

周期双晶構造を有する四ホウ酸リチウムの作製と波長変換素子への応用

周期双晶構造を有する四ホウ酸リチウムの作製と波長変換素子への応用

Four-wave mixing in a GaAs/AlAs triple-coupled multilayer cavity for novel ultrafast wavelength conversion devices

Four-wave mixing (FWM) in a GaAs/AlAs triple-coupled multilayer cavity has been studied for novel planar wavelength conversion devices. Three half-wavelength cavity layers are connected in series using GaAs/AlAs distributed Bragg reflector multilayers to yield three cavity modes with equal frequency separation. Efficient and ultrafast wavelength conversion via nondegenerate FWM can be realized even in the normal incidence configuration because of the enhanced internal electric fields of the three cavity modes. The triple-coupled cavity sample was grown by molecular beam epitaxy and wavelength conversion was successfully demonstrated by measuring the spectrum of time-resolved FWM signals generated by spectrally shaped laser pulses. We found that precise control of the layer thickness is particularly important because the structural asymmetry due to the thickness inhomogeneity produces a nondegenerate FWM signal with low intensity. The temporal response was extremely fast and was almost limited by the photon lifetime (∼1 ps) of each cavity mode.

Wavelength conversion via four-wave mixing in a triple-coupled multilayer cavity

Four-wave mixing in a triple-coupled multilayer cavity has been investigated for planar-type wavelength conversion devices. Three half-wavelength cavity layers are connected in series using GaAs/AlAs distributed Bragg reflector multilayers to yield three cavity modes with equal frequency separation. The enhanced internal electric fields of the three cavity modes indicate that efficient ultrafast wavelength conversion via four-wave mixing can be achieved even in the normal incidence configuration. Wavelength conversion was experimentally demonstrated using spectrally shaped laser pulses. A clear converted wavelength signal was observed in the measured spectrum. The temporal response was almost limited by the photon lifetime of each cavity mode.

Research on ultrafast wavelength conversion device by using tellurite glass

In the wavelength-division multiplexing network, high-performance optical wavelength converters are desired. This article will report very stable second harmonic generation by using tellurite glasses, second harmonic generation comparison in glass materials, and time-dependent change of second harmonic generation. We obtained 9 times larger second harmonic generation using TeO2 (60 mol%)–WO3 (30 mol%)–Bi2O3 (10 mol%) than using TeO2 (60 mol%)–WO3 (30 mol%)–PbO (10 mol%) glass. This value corresponds to 4.6 times higher than d11 constant of Y-cut quartz (0.4 pm/V). We have succeeded permanent poling by measurement of time-dependent change of second harmonic generation because there could not be found second harmonic generation intensity change after 6 months of poling at room temperature, and there was no decay of second harmonic generation intensity after 4 h of heating at 100°C.

Second-harmonic generation in silicon waveguides strained by silicon nitride

Silicon photonics meets the electronics requirement of increased speed and bandwidth with on-chip optical networks. All-optical data management requires nonlinear silicon photonics. In silicon only third-order optical nonlinearities are present owing to its crystalline inversion symmetry. Introducing a second-order nonlinearity into silicon photonics by proper material engineering would be highly desirable. It would enable devices for wideband wavelength conversion operating at relatively low optical powers. Here we show that a sizeable second-order nonlinearity at optical wavelengths is induced in a silicon waveguide by using a stressing silicon nitride overlayer. We carried out second-harmonic-generation experiments and first-principle calculations, which both yield large values of strain-induced bulk second-order nonlinear susceptibility, up to 40 pm V(-1) at 2,300 nm. We envisage that nonlinear strained silicon could provide a competing platform for a new class of integrated light sources spanning the near- to mid-infrared spectrum from 1.2 to 10 μm.