Coherent Supercontinuum Generation Research Articles

Retraction Note: Design and analysis of inverse tapered silicon nitride waveguide for flat and highly coherent supercontinuum generation in the mid-infrared

Retraction Note: Design and analysis of inverse tapered silicon nitride waveguide for flat and highly coherent supercontinuum generation in the mid-infrared

Highly coherent mid-infrared wideband supercontinuum generation by a silica cladded silicon nitride core buried waveguide

Abstract Optical waveguides with semiconductor cores are drawing considerable research interest in the domain of supercontinuum (SC) generation in recent times. In this work, we design a square-core silicon nitride buried waveguide with a silica-clad, aiming for a wideband spectrum generation in the mid-IR region when operated at the standard telecommunication wavelength of 1550 nm. Among different such silicon nitride square-core buried waveguides, we propose a typical design with dimensions of 400 nm × 400 nm along its height and width, capable of producing a highly coherent broadband intensity spectrum ranging from 810 nm to 5441 nm after propagating through just a few millimeters of the waveguide. The group velocity dispersion maintains minimal value over a broad wavelength range in the mid-IR region, while the nonlinear coefficient is estimated to be sufficiently high. The nonlinear pulse propagation through such a waveguide leads to achieving an SC spanning over 2.76 octaves, sufficiently broader than previously reported silicon nitride-based waveguides. Furthermore, our calculations confirm the highly coherent nature of the generated SC. To the best of our knowledge, this is the first report of SC generation maintaining a high degree of coherence over such a wide wavelength range in the mid-IR zone using a square-core silicon nitride buried waveguide.

Inverse design of coherent supercontinuum generation using free-form nanophotonic waveguides

Many key functionalities of optical frequency combs, such as self-referencing and broad spectral access, rely on coherent supercontinuum generation (SCG). While nanophotonic waveguides have emerged as a compact and power-efficient platform for SCG, their geometric degrees of freedom have not been fully utilized due to the underlying complex nonlinear and noise-dependent stochastic physics. Here, we introduce inverse design to unlock free-form waveguides for coherent SCG. The efficacy of our design is numerically and experimentally demonstrated on Si3N4 waveguides, producing flat and coherent spectra from visible to mid-infrared wavelengths. Our work has direct applications in developing chip-based broadband light sources for spectroscopy, metrology, and sensing across multiple spectral regimes.

Mid-infrared gas absorption spectroscopy using a silicon germanium waveguide based chirped supercontinuum

We report the simulations of coherent supercontinuum generation from 2.63 to 8.04 μm in a silicon germanium photonic waveguide. The influence of input quantum noise pulses on coherence of the generated spectra was investigated. A high value of first order degree of coherence (i.e. 0.98) on supercontinuum spectra was predicted numerically. Our mid-infrared simulated coherent chirped supercontinuum source was then used as the input light source in absorption spectroscopy of carbon dioxide and methane gases. The simulated absorbance spectra for these greenhouse gases have high molecular contrast, thanks to the intense, chirped supercontinuum used.

Design of ultra-broadband and highly coherent MIR supercontinuum generation using a photonic crystal fiber

Design of ultra-broadband and highly coherent MIR supercontinuum generation using a photonic crystal fiber

RETRACTED ARTICLE: Design and analysis of inverse tapered silicon nitride waveguide for flat and highly coherent supercontinuum generation in the mid-infrared

RETRACTED ARTICLE: Design and analysis of inverse tapered silicon nitride waveguide for flat and highly coherent supercontinuum generation in the mid-infrared

Super-flat coherent mid-infrared supercontinuum in all-normal dispersion As39Se61 chalcogenide photonic crystal fiber

We numerically demonstrated the generation of super-flat coherent mid-infrared supercontinuum in all-normal dispersion (ANDi) As39Se61 chalcogenide photonic crystal fiber (PCF). The PCF with flat-ANDi and high nonlinearities is obtained by optimizing the structural parameters of the fiber. When pumping a 50 fs pulse width and 6 kW peak power laser pulses at 3.35 μm, under 3dB spectral flatness the super-flat coherent mid-infrared supercontinuum extended from 2.17 to 7.47 μm is obtianed. Such coherent mid-infrared supercontinuum are enormously required for optical coherence tomography, biological imaging and frequency metrology.

Numerical simulation of coherent mid-infrared supercontinuum generation based on carbon chloride core tapered photonic crystal fibers

We numerically studied coherent mid-infrared (MIR) supercontinuum (SC) generated by filling carbon chloride (CCl4, C2Cl4) into the tapered photonic crystal fiber (PCF). The mechanism involves nonlinear soliton compression, Raman soliton self-frequency shift and dispersive wave generated in a carbon chloride core tapered PCF pumped by a 1.98 μm femtosecond laser. Numerical solution of the generalized nonlinear Schrodinger equation shows that 1.15–5.5 μm (CCl4-core tapered PCF) and 1.15–5.7 μm (C2Cl4-core tapered PCF) coherent MIR-SC sources can be realized. Our results show that the above liquid-core tapered PCFs are promising nonlinear media for constructing broadband coherent MIR-SC light sources.

Coherent mid-infrared supercontinuum generation in tellurite all-solid microstructured optical fibers with anomalous and normal dispersion property

Tellurite all-solid hybrid microstructured optical fibers (ASHMOFs) can be used to generate supercontinua with broad bandwidths in both anomalous and normal dispersion regimes. In the anomalous dispersion regime, a supercontinuum spectrum from 1.1 to 6.7 μm can be generated with a pump power of 10 kW and a pump wavelength of 3.5 μm. In the normal dispersion regime, a supercontinuum spectrum from 2.0 to 4.4 μm can be generated with the same pump power and wavelength. The simulations of supercontinuum generation in ASHMOFs show promising results for applications such as broadband infrared spectroscopy and enviromental monitoring. The all-solid nature of these fibers also makes them more robust and easier to handle than conventional soft-glass fibers.

Photonic molecule state transition by collision.

We investigate the impact of collisions with two-frequency photonic molecules aiming to observe internal dynamic behavior and challenge their strong robustness. Versatile interaction scenarios show intriguing state changes expressed through modifications of the resulting state such as temporal compression and unknown collision-induced spectral tunneling. These processes show potential for efficient coherent supercontinuum generation and all-optical manipulation.

All-fiber 2–6 [formula omitted] coherent supercontinuum source based on chalcogenide fibers pumped by an amplified mid-IR soliton laser

We numerically and experimentally investigate an all-fiber configuration of coherent mid-infrared supercontinuum generation in the femtosecond pumping regime. In particular, we demonstrate the advantageous combination of various dispersion-engineered chalcogenide (Ge-Se-Te glass) fibers with a turn-key amplified femtosecond fiber laser delivering 175-fs soliton pulses around 3.4 μm and developed from the erbium-doped fluoride fiber technology. Our results show that compact and coherent octave-spanning fiber supercontinuum sources centered on the 2–5 μm infrared atmospheric window can be obtained with a maximum average power of 50 mW at 25 MHz repetition rate.

Ultra-wideband and coherent supercontinuum generation (near and mid-infrared) in dispersion flattened ZnGeP2 photonic crystal fiber

Transmission window is a major concern in selecting the background material of photonic crystal fiber for supercontinuum generation. In this work, Zinc-Germanium Diphosphide (ZnGeP2) based single material photonic crystal fiber has been proposed with high nonlinearity and low confinement loss for near and mid-infrared supercontinuum generation. As single material is used, hence the concerned difficulties for choosing separate materials for core and cladding is eliminated. Again, the light transmission window of ZnGeP2 is very large (700 nm – 13000 nm). Optical properties like dispersion, numerical aperture, effective area, nonlinearity and confinement loss are analyzed and demonstrated for a wavelength range of 1000 – 5000 nm. COMSOL software is used to design the fiber and finite element method (FEM) is adopted for numerical analysis. The proposed fiber presents low and flattened dispersion in the range of 2250 – 5000 nm, nonlinearity of the order of 104 W–1km−1 and confinement loss of the order of 10–9 dB/m. The fiber is then used for supercontinuum generation in both near and mid-infrared range and an unprecedented bandwidth of 31000 nm has been achieved which may be pragmatic for outstanding medical applications.

Sub-100 fs Kerr-lens mode-locked femtosecond Yb:CaYAlO<sub>4</sub> laser with GHz repetition rate

Femtosecond lasers with GHz repetition rate play an important role in scientific and industrial applications such as spectroscopy, optical frequency combs and GHz-Burst pulse trains for micro-machining in the ablation-cooled regime. Kerr-lens mode-locked (KLM) technique and passively mode-locking based on semiconductor saturable absorber mirror (SESAM) are the primary methods to generate GHz femtosecond all-solid-state lasers (ASSLs). Kerr-lens mode-locked Ti:Sapphire lasers have made significant progress benefited from the high-power green pump lasers, and repetition rate up to 10 GHz has been obtained with the average power of 1.2 W. In the early 21st century, ytterbium ion (Yb<sup>3+</sup>) doped laser crystals and ceramics with emission wavelengths near 1 μm received attention due to their high conversion efficiency and broad gain-bandwidth. Combining the customized SESAM and high-power multimode fiber-coupled laser diodes (LDs), GHz Yb-doped ASSLs with watt-level average power may be easily attained and have made rapid progress. However, GHz KLM lasers have strict requirements for the cavity design and pump sources. For satisfying mode matching and enhancing the soft aperture effect within the gain medium, a high-brightness pump source with excellent beam quality (<i>M</i><sup> 2</sup> ～ 1) is desired, such as the single-mode fiber coupled LD, however, the maximum pump power of which is only ～1 W. As a result, the average power of GHz KLM femtosecond laser is typically limited to few tens of milliwatts, which limits the further applications. In this work, we report the first GHz high-power KLM Yb:CaYAlO<sub>4</sub> laser by using a high-power single-mode fiber laser instead of the low-power single-mode fiber coupled LDs as the pump source. On the basis of <i>ABCD</i> matrix, a simple four-mirror bow-tie ring cavity is built so that the laser mode can match well with the focused pump spot in the crystal. At the pump power of 8 W, stable unidirectional KLM is achieved, the laser has the average power of 2.1 W with a pulse duration of 88 fs and a repetition rate of 1.8 GHz, corresponding to the peak power of 11.57 kW. The high peak power and extremely short pulse duration are crucial for coherent octave-spanning supercontinuum generation. The powerful GHz KLM laser with sub-100 fs pulse duration provides an attractive source for realizing the optical frequency combs and micro-machining applications.

Soft glass based specialty optical fibers and their applications - INVITED

This paper describes a prospect for broadband mid-infrared (mid-IR) highly coherent supercontinuum generation. Tellurite and chalcogenide glass with high transparency up to the mid-IR range are used as fiber materials. We successfully develop all-solid hybrid microstructured optical fibers made of tellurite and chalcogenide glass to control chromatic dispersion and demonstrate that highly nonlinear soft glass microstructured optical fibers are promising media for broadband mid-IR highly coherent supercontinuum generation.

Highly coherent supercontinuum generation in circular lattice photonic crystal fibers using low-power pulses

Two structures of circular lattice Photonic Crystal Fibers (PCFs) based on Ge20Sb15Se65 (GSS) material have been proposed for a highly coherent broadband supercontinuum generation (SCG) in the mid-infrared region. Numerical studies using the Finite Difference Eigenmode (FDE) solver on both structures show that the fundamental modes are well confined in the core while the confinement losses are very low. Also, the high nonlinear coefficient of 22.01 W−1m−1 and 17.99202 W−1m−1 for the two structures ensure that these structures can accomplish high nonlinear activity. It has been found that broadband supercontinuums (SCs) spanning from 0.45 μm to 5.3 μm and 0.48 μm to 6.5 μm can be generated using a hyperbolic secant pulse of 0.5 kW. The proposed structures also show very good structural tolerance to optical properties that prevents any radical shift in SC spectra owing to potential fabrication mismatch.

Fabrication of Step−Index Fluorotellurite Fibers with High Numerical Aperture for Coherent Mid—Infrared Supercontinuum

We demonstrate the fabrication process and coherent supercontinuum (SC) generation of fluorotellurite step−index fibers with a high numerical aperture (0.56 and 0.64 at 1552 nm). Two compatible fluorotellurite glass pairs were first explored for fiber fabricating with built−in casting and rod−in−tube techniques in a glovebox. Coherent SC sources from 1200 nm to 2400 nm were generated from the fluorotellurite step−index fibers pumped by a femtosecond fiber laser at 1560 nm. Owing to the excellent dehydration of the fluoride, such fibers are available and promising nonlinear media for achieving coherent mid−infrared (MIR) SC.

High coherent supercontinuum generation in nitrobenzene liquid-core photonic crystal fiber with elliptical air-hole inner ring

A nitrobenzene liquid-core photonic crystal fiber (NLC-PCF) with eight elliptical air-holes in the innermost ring of the cladding is proposed in this work, and this fiber structure can contribute to flexibly adjusting dispersion and constraining the fiber core. The appreciable dispersion is realized by adjusting the structural parameters of NLC-PCF, which is characterized by three zero-dispersion wavelengths (ZDWs), flat dispersion with the fluctuation of fewer than 40 ps nm−1 km−1, and high nonlinearity as high as 5500 W−1 km−1. The propagation of femtosecond pulse and supercontinuum generation (SCG) in NLC-PCF is studied numerically when the pump wavelength is located in the normal and abnormal dispersion region near different ZDW through solving the generalized nonlinear Schrödinger equation (GNLSE) by the split-step Fourier method. The numerical results show that a highly coherent supercontinuum (SC) spanning from 1.3 to 2.8 µm is obtained when the pump pulse with the center wavelength of 1810 nm, the peak power of 1000 W, and pulse width of 50 fs propagated in the 5 cm long NLC-PCF. This research can find applications in the fields of novel liquid-core PCF design and ultrashort pulse propagation.

Numerical investigation of coherent supercontinuum generation via soliton implosion in ZBLAN photonic crystal fiber

We numerically investigate coherent supercontinuum (SC) generation extending from the deep ultraviolet to the mid-infrared spectral region using few-cycle optical pulses, pumped into a ZBLAN photonic crystal fiber. The finite difference method is used to optimize the fiber structure and achieve two zero dispersion wavelengths, with a broad anomalous dispersion region. The propagation of ultrashort pulses and their nonlinear dynamics is accurately modeled by employing the forward unidirectional propagation equation for the analytic signal of the pulse electric field. We show that by pumping in the anomalous regime of dispersion, the high-order solitons undergo an implosion process and spectral broadening is achieved via the contribution of self-phase modulation, self-steepening, and shock formation, along with a strong transfer of energy into a nonsolitonic resonant Cherenkov-like radiation in the normal dispersion region. Furthermore, numerical results indicate that broadband supercontinua spanning the region from 0.22 to 4.6 μm is successfully achieved with a pulse having a soliton order and duration of 12 and 6 fs, respectively. In addition, the deterministic feature of the implosion mechanism exhibits very low sensitivity to the input quantum noise and achieves excellent coherence properties. The proposed multioctave SC source is found promising for various potential applications, such as two-photon excited autofluorescence, bioimaging, spectroscopy, optical signal processing, and medicine.

Semiconductor material photonic crystal fiber for mid-infrared supercontinuum generation

In this paper, Al0.24Ga0.76As based holey optical fiber is designed for coherent supercontinuum generation. It is mainly simulated for optical characteristic of lattice microstructures. For computational studies, the introduced design is composed of five loops of air vents with circular and elliptical structures. Flat and anomalous dispersion in the mid-infrared range has been achieved by obtaining a high nonlinear Kerr coefficient 5402 W−1 km−1 at the pump wavelength of 3.25 µm from the proposed microstructure fiber. Thereby, the expansion of the supercontinuum spectrum from 1.70 µm to 8.5 µm has been obtained. With the help of the high effective refractive index at the pump wavelength and the small effective mode region, proper supercontinuum spectrum (SC) is generated. The range of the spectrum of supercontinuum based on fiber length, pump duration and pump energy is simulated. Applications of this work will be advantageous in bio-medical, optical sensing, and wavelength conversion.

Coherent Supercontinuum Generation in Step-Index Heavily Ge-Doped Silica Fibers With All Normal Dispersion

Coherent Supercontinuum Generation in Step-Index Heavily Ge-Doped Silica Fibers With All Normal Dispersion