Efficient Wavelength Conversion Research Articles

Free-Space to SMF Integration and Green to C-Band Conversion Based on PPLN.

In this study, we experimentally demonstrate a PPLN-based free-space to SMF (single-mode fiber) conversion system capable of efficient long-wavelength down-conversion from 518 nm, optimized for minimal loss in highly turbid water, to 1540 nm, which is ideal for low-loss transmission in standard SMF. Leveraging the nonlinear optical properties of periodically poled lithium niobate (PPLN), we achieve a wavelength conversion efficiency of 1.6% through difference frequency generation while maintaining a received optical signal-to-noise ratio of 10.4 dB. Our findings underscore the potential of integrating PPLN-based wavelength conversion with fiber optic networks, offering a viable solution for next-generation optical sensor systems that demand real-time, low-latency, and reliable data transmission. This work represents a significant advancement in developing robust and efficient optical sensor technologies, addressing the challenges associated with long-distance transmission and broad-linewidth light sources in optical remote sensing applications.

Dispersion-engineered InGaAsP/InP waveguide for high efficiency all-optical on-chip wavelength conversion

InGaAsP/InP waveguide platform offers superiority for all-optical on-chip wavelength conversion due to strong optical nonlinearity. However, a small refractive index difference between the core and cladding makes it challenging to achieve sufficient structural dispersion for phase matching. In this work, the InGaAsP multilayer waveguide and the SiN-cladded InGaAsP waveguide are investigated for optimized wavelength conversion at telecom wavelengths. Structural dispersion is effectively engineered through the incorporation of additional slot layers and a heterogeneous passivation layer. Through comparative analysis, the wavelength conversion efficiency of -4.7 dB is achieved by the SiN-cladded waveguide, which shows an improvement of 22 dB compared to traditional nanowire waveguide.

Metalorganic Vapor‐Phase Epitaxy of +c/−c GaN Polarity Inverted Bilayer for Transverse Quasi‐Phase‐Matched Wavelength Conversion Device

Photon‐pair generation based on optical parametric down‐conversion has attracted for the application as a light source for quantum information. Highly efficient wavelength‐conversion devices require a polarity‐inversion structure when using nitride semiconductors. A transverse quasi‐phase‐matching (QPM) polarity‐inverted GaN bilayer channel waveguide device is suitable for efficient wavelength conversion. This study designed a cross‐section device to satisfy the modal dispersion phase‐matching condition between the TM02 mode pump light and the TM00 mode signal/idler light. Moreover, an AlN oxidation interlayer fabricates the Ga‐polar/N‐polar (+c/−c) GaN layers via metalorganic vapor‐phase epitaxy (MOVPE). A 145 nm thick film layer with a macro‐step‐free surface is grown by optimizing the −c‐GaN growth conditions and reducing the substrate off‐angle to 0.2°. Next, the AlN layer is oxidized in an electric furnace and MOVPE is used to regrow a 1500 nm thick +c‐GaN layer. A macrosteps‐free surface can be achieved by reducing the off‐angle to 0.2° and optimizing the −c‐GaN growth conditions to avoid hillock formation. These results pave the way for improving the efficiency of GaN transverse QPM wavelength‐conversion devices.

199 nm vacuum-ultraviolet second harmonic generation from SrB4O7 vertical microcavity pumped with picosecond laser

We have proposed highly efficient microcavity wavelength conversion devices that do not utilize the birefringence or ferroelectricity of crystals. In this study, we utilized a low-birefringence paraelectric SrB4O7 crystal with significant potential for wavelength conversion and high transparency down to 130 nm and succeeded in achieving 199 nm vacuum-ultraviolet second harmonic generation (SHG) with a picosecond laser. The wavelength of 199 nm is shorter than the theoretical minimum for SHG in BaB2O4 of 205 nm. Our device could be a practical vacuum-ultraviolet SHG device, enabling significantly smaller and more efficient vacuum-ultraviolet laser sources compared to conventional systems.

Advancing large-scale thin-film PPLN nonlinear photonics with segmented tunable micro-heaters

Thin-film periodically poled lithium niobate (TF-PPLN) devices have recently gained prominence for efficient wavelength conversion processes in both classical and quantum applications. However, the patterning and poling of TF-PPLN devices today are mostly performed at chip scales, presenting a significant bottleneck for future large-scale nonlinear photonic systems that require the integration of multiple nonlinear components with consistent performance and low cost. Here, we take a pivotal step towards this goal by developing a wafer-scale TF-PPLN nonlinear photonic platform, leveraging ultraviolet stepper lithography and an automated poling process. To address the inhomogeneous broadening of the quasi-phase matching (QPM) spectrum induced by film thickness variations across the wafer, we propose and demonstrate segmented thermal optic tuning modules that can precisely adjust and align the QPM peak wavelengths in each section. Using the segmented micro-heaters, we show the successful realignment of inhomogeneously broadened multi-peak QPM spectra with up to 57% enhancement of conversion efficiency. We achieve a high normalized conversion efficiency of 3802% W−1 cm−2 in a 6 mm long PPLN waveguide, recovering 84% of the theoretically predicted efficiency in this device. The advanced fabrication techniques and segmented tuning architectures presented herein pave the way for wafer-scale integration of complex functional nonlinear photonic circuits with applications in quantum information processing, precision sensing and metrology, and low-noise-figure optical signal amplification.

Nonlinear Self‐Accelerating Pulses Shedding from Airyprime Pulses in Kerr Media

Herein, the propagation of truncated Airyprime pulses in nonlinear optical fibers with anomalous or normal dispersion is studied. Nonlinear self‐accelerating pulses generation, which is in sharp contrast to that of Airy pulses, is observed. Accelerating pulses have notable redshifted spectral notch (double peaks) or single blueshifted spectral peak depending on whether the dispersion is anomalous or normal. The emergent nonlinear self‐accelerating pulses are very sensitive to the truncated coefficient. The relationship between the characteristics of such accelerating pulses and the truncated coefficient is disclosed and compared in detail. The results not only shed new light on the nonlinear propagation of Airyprime pulses, but also provide a novel method to generate nonlinear self‐accelerating pulses as well as enable the realization of very efficient wavelength conversion based on the controlled frequency shift. Based on space–time duality, self‐accelerating spatiotemporal nonlinear light bullets can be envisaged from the propagation of spatiotemporal Airyprime wave packets in pure Kerr medium.

Design of an on-chip wavelength conversion device assisted by an erbium-ytterbium co-doped waveguide amplifier

In current documented studies, it has been observed that wavelength converters utilizing AlGaAsOI waveguides exhibit suboptimal on-chip wavelength conversion efficiency from the C-band to the 2 μm band, generally falling below −20.0 dB. To address this issue, we present a novel wavelength conversion device assisted by a waveguide amplifier, incorporating both AlGaAs wavelength converter and erbium-ytterbium co-doped waveguide amplifier, thereby achieving a notable conversion efficiency exceeding 0 dB. The noteworthy enhancement in efficiency can be attributed to the specific dispersion design of the AlGaAs wavelength converter, which enables an upsurge in conversion efficiency to −15.54 dB under 100 mW of pump power. Furthermore, the integration of an erbium-ytterbium co-doped waveguide amplifier facilitates a loss compensation of over 15 dB. Avoiding the use of external optical amplifiers, this device enables efficient and high-bandwidth wavelength conversion, showing promising applications in various fields, such as optical communication, sensing, imaging, and beyond.Graphical

Mitigating waveguide loss in Ge–Sb–Se chalcogenide glass photonics

Minimizing propagation loss within waveguides remains a central objective across diverse photonic platforms, impacting both linear lightwave transmission and nonlinear wavelength conversion efficiencies. Here, we present a method to mitigate waveguide loss in Ge28Sb12Se60 chalcogenide glass, a material known for its high nonlinearity, broad mid-infrared transparency, and significant potential for mid-IR photonics applications. By applying a sacrifical oxide layer to eliminate etching residues and a subsequent waveguide thermal reflow to smooth lithography-induced line edge roughness, we successfully reduced the waveguide loss down to 0.8 dB cm−1 at 1550 nm wavelength. This represents the best result in small-core and high-index-contrast Ge28Sb12Se60 channel waveguides. Our approach paves the way for low-loss, on-chip chalcogenide photonic devices.

Efficient second harmonic generation in a high-Q Fabry-Perot microresonator on x-cut thin film lithium niobate.

Microresonators facilitate enhanced light-matter interactions within a limited space, showing great promise for nonlinear optics. Here, we demonstrate a high-quality (Q) factor Fabry-Perot microresonator (FPR) for second harmonic generation (SHG) on an x-cut thin film lithium niobate (TFLN) platform. The FPR exhibits Q factors of Qpump = 1.09 × 105 and QSH = 1.15 × 104 at the 1560 nm pump wavelength and 780 nm second harmonic wavelength, respectively. Under low pump power, a normalized SHG efficiency of 158.5 ± 18.5%/W is attained. We experimentally verify that increased temperatures mitigate photorefractive effects that degrade SHG performance. This work highlights the immense capabilities of one-dimensional planar optical waveguide resonators for efficient on-chip nonlinear wavelength conversion.

Performance of Ce:YAG-MgO composite ceramics as high-power LED phosphor densified by non-reactive sintering

A novel white light converter has been successfully synthesized using a non-reactive sintering process to afford a fully densified Ce:YAG-MgO composite ceramic phosphor with high wavelength conversion efficiency under excitation at 450 nm. The composite obtained by HIP (hot isostatic pressing) treatment at 1080 ºC has no residual pores and the XRD (X-ray diffraction) analysis shows that there are no secondary phases other than Ce:YAG and MgO, moreover, the EDS (Energy-dispersive X-ray spectroscopy) analysis indicates no interdiffusion at the Ce:YAG-MgO contact interface. The thermal conductivity of 5–7.5 wt% Ce:YAG-added MgO composites is over 40 W/mK, nearly reaching the theoretical value. Due to the synergetic effect of “the difference in refractive index between MgO and Ce:YAG” and “MgO matrix with strong birefringence”, the excitation light (450 nm) is multiply scattered inside the composite medium, which provides efficient excitation even in a thin medium, resulting in the photoluminescence intensity that is 2.6 times higher than that of transparent Ce:YAG ceramics. This innovative white light converter combines a highly thermal conductive MgO matrix and Ce:YAG phosphor with high emission intensity.

Efficient polarization-insensitive all-fiber wavelength conversion in C-band using feedback in highly non-linear fibers

Efficient polarization-insensitive all-fiber wavelength conversion in C-band using feedback in highly non-linear fibers

Efficient and Broadband All-Optical Wavelength Conversion between C and O Bands in Nanophotonic Lithium Niobate Waveguides

Efficient and Broadband All-Optical Wavelength Conversion between C and O Bands in Nanophotonic Lithium Niobate Waveguides

Advances in Computational Fluid Dynamics Modeling for Biomass Pyrolysis: A Review

Pyrolysis, a process for extracting valuable chemicals from waste materials, leverages computational fluid dynamics (CFD) to optimize reactor parameters, thereby enhancing product quality and process efficiency. This review aims to understand the application of CFD in pyrolysis. Initially, the need for pyrolysis and its role in biomass valorization are discussed, and this is followed by an elaboration of the fundamentals of CFD studies in terms of their application to the pyrolysis process. The various CFD simulations and models used to understand product formation are also explained. Pyrolysis is conducted using both conventional and microwave-assisted pyrolysis platforms. Hence, the reaction kinetics, governing model equations, and laws are discussed in the conventional pyrolysis section. In the microwave-assisted pyrolysis section, the importance of wavelength, penetration depth, and microwave conversion efficiencies on the CFD are discussed. This review provides valuable insights to academic researchers on the application of CFD in pyrolysis systems. The modeling of pyrolysis by computational fluid dynamics (CFD) is a complex process due to the implementation of multiple reaction kinetics and physics, high computational cost, and reactor design. These challenges in the modeling of the pyrolysis process are discussed in this paper. Significant solutions that have been used to overcome the challenges are also provided with potential areas of research and development in the future of CFD in pyrolysis.

Towards efficient broadband parametric conversion in ultra-long Si3N4 waveguides.

Broadband continuous-wave parametric gain and efficient wavelength conversion is an important functionality to bring on-chip. Recently, meter-long silicon nitride waveguides have been utilized to obtain continuous-traveling-wave parametric gain, establishing the great potential of photonic-integrated-circuit-based parametric amplifiers. However, the effect of spiral structure on the performance and achievable bandwidth of such devices have not yet been studied. In this work, we investigate the efficiency-bandwidth performance in up to 2 meter-long waveguides engineered for broadband operation. Moreover, we analyze the conversion efficiency fluctuations that have been observed in meter-long Si3N4 waveguides and study the use of temperature control to limit the fluctuations.

Proton exchange thin film lithium niobate semi-nonlinear waveguides for highly efficient tunable second harmonic generation

The proton exchange thin film lithium niobate semi-nonlinear (PETFLN-SN) waveguides are a powerful platform for second harmonic generation (SHG). However, how to simultaneously generate second harmonic light and tunable second harmonic light output in PETFLN-SN waveguides has yet to be studied. Here, we propose a PETFLN-SN waveguide, which can efficiently generate second harmonic light and simultaneously realize temperature-tunable second harmonic light output. The highest normalized conversion efficiency of the second harmonic is 122.1 %W−1cm−2 at room temperature (25.9 ℃). Moreover, the tuning slope of spectral tuning is 79 pm K−1 for a telecom-band pump. Our device shows great promise for efficient on-chip wavelength conversion to produce highly tunable coherent visible light for broad applications.

Ultra-efficient second harmonic generation via mode phase matching in integrated lithium niobate racetrack resonators.

High-efficiency second harmonic generation (SHG) relying solely on intermodal dispersion engineering remains a challenge. Here, we realize highly efficient SHG using a double-waveguide coupled racetrack microring resonator on X-cut lithium niobate on insulator (LNOI), where both pump and second harmonic (SH) approach critical coupling. Through precise temperature tuning, simultaneous pump and SH resonance is attained in the resonator, dramatically enhancing SHG efficiency. With low pump power, a normalized conversion efficiency of 9972%/W is achieved. Moreover, the resonator provides a 25.73 dB enhancement in SHG efficiency compared to a 4 mm straight waveguide with identical phase matching in our experiment. This work enables efficient wavelength conversion and quantum state generation on integrated X-cut LNOI platforms.

2-μm short data pulse all-optical wavelength converter based on MXene microfiber

We demonstrate the all-optical wavelength conversion of short pulse signals at 2-μm using MXene-assisted microfiber. The process involves an actively mode-locked thulium-holmium co-doped fiber laser, which is synchronously modulated by a digital signal and coupled with continuous light for the conversion process. The converted light is generated via four-wave mixing (FWM) with in the MXene-assisted microfiber. The conversion efficiency reaches −38.98 dB. For a wavelength tuning range of 6.08 nm–1.04 nm, the conversion efficiency is increased by 10.44 dB. The wavelength conversion efficiency fluctuation during 130 min is only 0.512 dB. The converter enables the successful transmission of 489 Mb/s data carried by the converted light. The results show that the MXene-assisted microfiber carrier wavelength converter has a high conversion efficiency and excellent stability. This study aligns with the development trend of all-optical wavelength conversion and explores the characteristics of highly nonlinear optical materials. The utilization of MXene-assisted microfiber enables significant advancements in all-optical wavelength conversion, particularly in the context of processing 2-μm short data pulse signals for nonlinear optics applications.

Second harmonic generation from a-plane GaN vertical monolithic microcavity pumped with femtosecond laser

We have proposed highly efficient microcavity second harmonic generation devices. In this work, we designed and fabricated an a-plane GaN vertical monolithic microcavity second harmonic generation device pumped with a femtosecond laser and obtained normalized wavelength conversion efficiency of 0.15% W−1. The efficiency was comparable to the theoretical estimations taking into account the time evolution of fundamental wave intensity in the microcavity, second harmonic generation and even sum frequency generation. This result indicates the possibility of realizing ultra-compact and ultra-efficient devices pumped with long-pulsed or continuous wave lasers, in which the effect of resonance enhancement is even more pronounced.

Stable Hybrid Nanocapsules with Gold Nanorods and Cyanine Dyes for Near‐Infrared Photothermal Ablation of Subcutaneous Tumor

AbstractGold nanorods and cyanine dyes are promising to be widely used in photothermal therapy due to their adjustable absorption wavelength and excellent photothermal conversion efficiency. However, it is unclear how gold nanorods differ from cyanine dyes in therapeutic effects. Nanocapsules are synthesized from hybrid silica encapsulated gold nanorods (AuNRs@YSiO2, hereafter GNR@YS). Composite nanocapsules (hereafter GNR@YS‐CyN) are prepared from GNR@YS loaded with CyN to treat subcutaneous tumor. Cyanine dye (CyCl) with similar absorption to gold nanorods is also synthesized to match the existing commercial 808 nm laser. The results show that both materials have good therapeutic effect, but differ in healing scabs on skin tissue surface after tumor ablation. GNR@YS‐CyN are superior to CyCl in the treatment of subcutaneous tumor. This may be the size effect of GNR@YS‐CyN has permeability and retention enhancement effect at the tumor site. GNR@YS‐CyN have no obvious dye diffusion phenomenon, which reduces the damage to normal tissue.

Sum-frequency generation in a high-quality thin film lithium niobate microdisk via cyclic quasi-phase matching

Whispering-gallery-mode (WGM) microresonators can dramatically boost the interaction between light and matter, making them an ideal platform for studying nonlinear optics. Efficient wavelength conversion by nonlinear parametric processes is key to integrated optics in many applications, where WGM microresonators play an important role. Here, we demonstrate efficient second-harmonic generation (SHG) and sum-frequency generation (SFG) in an x-cut thin film lithium niobate microdisk with a high intrinsic quality factor over 106. The normalized conversion efficiency of cyclic quasi-phase-matched (CQPM) SHG and SFG is measured to be 1.53%/mW and 2.52×10−4/mW, respectively. Our work expands nonlinear optics applications of CQPM WGM microresonators as efficient wavelength convertors for light upconversion.