Efficient Wavelength Conversion Research Articles

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 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.

Efficient and temperature-tunable second-harmonic generation in a thin film lithium niobate on insulator microdisk

The whispering-gallery-mode microcavities are important in fundamental science and practical applications, which also play an essential role in integrated photonic devices. Here, we prepared a 50 μm diameter thin film lithium niobate on insulator (TFLNOI) microdisk with a Q value of 1.88 × 105 through photolithography-assisted dry-wet etching. Then, we utilize the strong thermo-optic birefringence of TFLNOI to demonstrate the second-harmonic generation (SHG) and highly temperature-tunable SHG in a TFLNOI microdisk resonator, wherein the normalized conversion efficiency of the second harmonic is 140% W−1. Moreover, the tuning slope of spectral tuning is 1.68 nm 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.

Four-channel all-optical wavelength conversion unit based on nonlinear effect of three-section monolithically integrated semiconductor lasers.

A simple and highly efficient four-channel all-optical wavelength conversion based on four-wave mixing effect of the directly modulated three-section monolithically integrated semiconductor laser is proposed and experimentally investigated. For this wavelength conversion unit, the spacing of the wavelength can be adjusted by tuning the bias current of the lasers and setting it to be 0.4nm (50GHz) as a demonstration is this work. A 50Mbps 16-QAM signal centers at 4-8GHz is experimentally switched to a targeted path. Up- or downconversion depends on a wavelength-selective switch, and the conversion efficiency can reach up to -2 to 0dB. This work provides a new technology for photonic radio-frequency switching matrix and contributes to the integrated implementation of satellite transponders.

Ultrafast serrodyne optical frequency translator

The serrodyne principle enables an electromagnetic signal to be frequency shifted by applying a linear phase ramp in the time domain. This phenomenon has been exploited to frequency shift signals in the radiofrequency, microwave and optical regions of the electromagnetic spectrum over ranges of up to a few gigahertz, for example, to analyse the Doppler shift of radiofrequency signals for noise suppression and frequency stabilization. Here we employ this principle to shift the centre frequency of high-power femtosecond laser pulses over a range of several terahertz with the help of a nonlinear multi-pass cell. We demonstrate our method experimentally by shifting the central wavelength of a state-of-the-art 75 W frequency comb laser from 1,030 nm to 1,060 nm and to 1,000 nm. Furthermore, we experimentally show that this wavelength-shifting technique supports coherence characteristics at the few hertz-level while improving the temporal pulse quality. The technique is generally applicable to wide parameter ranges and different laser systems, enabling efficient wavelength conversion of high-power lasers to spectral regions beyond the gain bandwidth of available laser platforms.

Efficient four-wave mixing wavelength conversion in a hybrid silicon slot and polymer microring resonator.

We present a silicon slot microring resonator for efficient frequency conversion via four-wave mixing (FWM). The slot consists of a narrow silicon waveguide pair with a gap of 80 nm, which is filled with a nonlinear optical polymer. The group velocity dispersion for the microring is controlled by engineering the geometry of the slot structure. Because of the large buildup factor of the slot microring, an FWM conversion efficiency of -27.4 dB is achieved with an optical pump power of less than 1.0 mW. From the measured power dependence of FWM generation, a nonlinear refractive index coefficient of 1.31 × 10-17 m2 W-1 is obtained at a wavelength of 1562 nm. This work presents a hybrid silicon slot and polymer microring as a potential nonlinear device for applications in integrated photonic devices.

Wide Wavelength Selectable and High Frequency Precision of All-Optical Wavelength Conversion Using Pump Light Generated from Optical Combs and SSB Modulation

All-optical wavelength conversion based on four-wave mixing (FWM) in highly nonlinear fiber (HNLF) with wide wavelength selectivity and highly precise frequency controllability was investigated in combination with pump light generated from optical combs and single-side-band (SSB) modulation. Using multiple carriers, optical combs generated using LiNbO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> phase modulators and an SSB phase modulator, pump lights were precisely controlled with a frequency range of 580 GHz and frequency shift of 1.25 GHz. The frequency difference of the pump lights from the ideal one was less than the resolution of an optical spectrum analyzer FWM was performed for single-polarized 10 Gbaud NRZ-QPSK signals in combination with the generated pump lights, and clear eye-openings and constellations for idler signals were achieved. Moreover, a bit error rate (BER) of <3.8 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−3</sup> for all idler lights was achieved. Conversely, in the case of the 1.25 GHz controlled pump light, the constellation was distorted, and the BER was saturated at 2.0 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−4</sup> . In addition, the limit of wavelength convertible bandwidth was investigated to determine the condition for selecting the frequency of wavelength conversion applicable to wavelength defragmentation in the metro/core networks. From the experimental and analytical results, the maximum frequency spacing between the signal and pump was found to be 1403.125 GHz, limited by the wavelength conversion efficiency of the HNLF, whereas the minimum frequency spacing was found to be 25 GHz, restricted by the crosstalk between the signal and pump light that could not be eliminated using the bandpass filter.

Radially Polarized Second-Harmonic Generation from a Single-Element Nanoantenna via Dark Plasmon Coupling of Nonlinear Polarization

Controlling the process of second-harmonic (SH) generation at the nanoscale is important in photonic applications but remains challenging in nanophotonics. Herein, based on theoretical and experimental studies, we found that a cross-shaped single-element plasmonic nanoantenna resonating with bright and dark modes at the fundamental (excitation) and SH wavelengths, respectively, generates radially polarized ring-shaped SH radiations with axial symmetry by exciting the bright dipole mode with linearly polarized light. Mode expansion analysis of the generated SH radiation revealed that the radial polarization arises from a dark breathing mode in which coherent dipoles are radially distributed along the arms of the cross-shaped antenna. This study reveals that surface SH polarization generated by the electric near-field of the bright mode at the fundamental wavelength efficiently is coupled to the dark modes rather than the bright mode because its spatial distribution has the same symmetry as the dark modes. By engineering bright and dark modes at the fundamental and SH wavelengths, respectively, novel plasmonic nanodevices that simultaneously perform polarization control and efficient wavelength conversion are expected.

Second harmonic generation in GaN transverse quasi-phase-matched waveguide pumped with femtosecond laser

A wavelength conversion device with an input grating coupler that enables easy alignment was fabricated using a vertically polarity inverted GaN layer. The device was excited with a femtosecond laser, and a second harmonic wave with a peak wavelength of 438.4 nm was obtained. A normalized wavelength conversion efficiency of 4.7 × 10−4% W−1 and a spectral bandwidth of the second harmonic wave of 2.9 nm were comparable to the theoretical estimations taking into account serious walk-off and waveguide losses. High efficiency of 33%–34% W−1 can be expected under continuous-wave excitation.