Supercontinuum generation in angle-etched diamond waveguides

The mid-infrared (MIR) wavelength coincides with various molecular resonances. In particular, a 13-20 µm wavelength window has fingerprints of unique groups such as organometallic, halogenated, and aromatic bonds. In this work, for the first time, to the best of our knowledge, an on-chip supercontinuum generation (SCG) source based on cadmium telluride (CdTe)/ cadmium sulfide (CdS)/ silicon heterostructure is proposed to extend the on-chip SCG beyond 13 µm (spanning 3.5 to 20 µm). CdTe has an ultra-broad transparent spectral range up to 25 µm, and almost the largest third-order nonlinear coefficient (n2∼ 5×10-17 m2/W at 1.55 µm, 1.3×10-17 m2/W at 9 µm, several times larger than that of silicon) among the MIR materials, making CdTe an excellent candidate for long-wavelength MIR on-chip SCG. The waveguide structure is designed with CdS as the intermediate cladding layer to achieve a low waveguide loss and high mode confinement. A large-core CdTe waveguide is tailored to generate a low and flat dispersion (< 30 ps/nm/km) in a spectral range spanning from 5 to 20 µm, while balancing the large effective nonlinearity and the convenience of coupling. The simulation results solved by the nonlinear Schrödinger equation manifest that the engineered large cross-section waveguide with only 2.5-mm propagation distance broadens the MIR spectrum covering 3.5 to 20 µm pumped by a 9 µm femtosecond laser. Moreover, it is found that good coherence is achieved from the designed MIR waveguide, before severe soliton fission breaks the temporal profile. 5-fold self-compression of the pump pulse down to 1.6 optical cycles is observed while propagating inside the CdTe waveguide. The detailed simulation of the CdTe/CdS/Si waveguide design with the various waveguide parameters, polarizations, pump wavelengths, and pump power are provided. With the SC spectrum covering almost the entire fingerprint regime and the excellent coherence generated from the designed CdTe waveguide, it provides abundant new opportunities for MIR microphotonics.

Supercontinuum (SC) generation in bulk materials offers a versatile, broadband coherent light source for ultrafast spectroscopy and nonlinear optics. The filamentation process underlying SC generation is primarily governed by three critical parameters: input pulse energy, focusing numerical aperture, and crystal thickness. Using femtosecond pulses and sapphire crystals, we systematically investigate how these parameters affect SC energy stability. Depending on the number of pulse-splitting events, filamentation can manifest in either single- or multi-filament regimes, with the latter leading to undesirable spectral modulation and thus requiring avoidance. Our study reveals that within the single-filament regime, two distinct dynamical states can arise: a critical state, in which pulse-splitting dynamics and SC spectra evolve rapidly with increasing input pulse energy, and a steady state, which ensures optimal stability. Experimental results show that steady-state SC generation yields the highest stability, exceeding that of the driving laser. These findings deepen the physical understanding of filamentation and provide clear guidelines for parameter selection to achieve stable SC in bulk media, offering practical insights for optimizing broadband coherent sources in ultrafast applications.

In this work we report the numerical results on the filamentation and supercontinuum (SC) generation of femtosecond flat-top pulses with different steep edges propagating in fused silica. Results show that the filamentation process is determined mainly by the self-steepening effect and ionization, and the SC generation is influenced mainly by the self-steepening effect. The filamentation onset and termination is determined by the leading edge and the tailing edge, respectively. The steeper the leading edge is, the earlier the filamentation onset is; the steeper the tailing edge is, the earlier the filamentation termination is. The cutoff wavelength in the blue-side region of the SC has no obvious difference for the pulses with different leading and tailing edges. But the spectral intensity of the blue extension is much stronger for the pulses with the steeper leading edges. The stronger spectral intensity results from the formation of more steep descending edges during filamentation.

Supercontinuum (SC) generation based on ultrashort pulse compression constitutes one of the most promising technologies towards ultra-wide bandwidth, high-brightness, and spatially coherent light sources for applications such as spectroscopy and microscopy. Here, multi-octave SC generation in a gas-filled hollow-core antiresonant fiber (HC-ARF) is reported spanning from 200 nm in the deep ultraviolet (DUV) to 4000 nm in the mid-infrared (mid-IR) having an output energy of 5 μJ. This was obtained by pumping at the center wavelength of the first anti-resonant transmission window (2460 nm) with ~100 fs pulses and an injected pulse energy of ~8 μJ. The mechanism behind the extreme spectral broadening relies upon intense soliton-plasma nonlinear dynamics which leads to efficient soliton self-compression and phase-matched dispersive wave (DW) emission in the DUV region. The strongest DW is observed at 275 nm which corresponds to the calculated phase-matching wavelength of the pump. Furthermore, the effect of changing the pump pulse energy and gas pressure on the nonlinear dynamics and their direct impact on SC generation was investigated. This work represents another step towards gas-filled fiber-based coherent sources, which is set to have a major impact on applications spanning from DUV to mid-IR.

We experimentally demonstrate record multi-octave supercontinuum (SC) generation spanning from 200 up to 4000 nm using a single Ar-filled hollow-core anti-resonant fiber pumped in the mid-IR region for the first time.

High power LP11 mode supercontinuum is generated from 25/250 large mode area (LMA) fiber. A mechanical long period grating (LPG) is utilized to control the transverse modes in the LMA fiber to realize the LP11 mode supercontinuum generation in a master oscillator power amplifier (MOPA) configuration. The generated LP11 mode supercontinuum covers the spectral range from ~900 nm to ~2100 nm with a -30-dB spectral width of ~1200 nm and 50% optical to optical conversion efficiency. The seed laser produces picosecond pulses with 1 MHz repetition rate at the wavelength of 1060 nm. After multi-stage amplification in ytterbium-doped fibers, the average output power is scaled to 54.51 W and 56.79 W respectively for LP11 and LP01 mode, accompanying supercontinuum generation. Obvious difference of supercontinuum generation between the LP01 and LP11 modes is experimentally observed due to the different dispersion characters.

A theoretical study of flat supercontinuum (SC) generation in a highly nonlinear photonic crystal fiber (PCF) is presented. We propose a chromatic dispersion profile of a highly nonlinear PCF for flatly broadened SC generation around 1550nm. The proposed chromatic dispersion profile of the fiber which is a convex function of wavelengths has small normal group-velocity dispersion at the pump wavelength and the dispersion slope around which is flat. It is found that the fiber with such dispersion characteristics is suitable for generating a relatively flat SC. The initial chirp of the input pulse also has a significant effect on SC generation in photonic crystal fiber. A flatter and wider spectrum can be obtained by the pulse with appropriate positive initial chirp.

Octave-spanning supercontinuum (SC) generation typically requires high input pulse energies and long fiber lengths. Achieving such high pulse energies is feasible only with low repetition rate lasers, operating in the kHz to MHz range. In contrast, high repetition rate lasers, such as microresonator-based frequency combs (microcombs), provide lower input pulse energy. This necessitates the use of fibers with high nonlinearity, high coupling efficiency with laser sources, and tailored dispersion properties for broadband supercontinua. In this work, we present tapered fibers fabricated from lead-bismuth-gallate (PBG) glass-a material with high nonlinearity-for octave-spanning supercontinuum generation spanning from 760 to 1860 nm at low input pulse energies (0.03-0.05 nJ). The untapered sections of these fibers feature a large core diameter (10 μm) to assure high coupling efficiency with standard single-mode fibers or laser sources. At the tapered waist, the core diameter is reduced to 1.5 μm, significantly enhancing the nonlinear coefficient and enabling octave-spanning supercontinuum generation. The supercontinuum spectra align well with the optical properties of periodically poled lithium niobate (PPLN-SHG6), making these tapered fibers ideal for f-2f interferometers to measure the carrier-envelope offset frequency of microcombs.

The conditions to obtain noise-like pulses (NLPs) from a figure-eight fiber laser (F8L) and their application for supercontinuum (SC) generation in the anomalous dispersion regime are reported. The F8L is designed to remove the undesired low-intensity background radiation from pulse emission, generating NLPs with a 3 dB spectral bandwidth of 17.43 nm at the fundamental repetition frequency of 0.8 MHz. After amplification, NLPs reach a maximum average power of 9.2 mW and 123.32 nm spectral bandwidth. By controlling the amplifier pump power, flat SC generation is demonstrated through both a 800 m long spool of SMF-28 fiber and a piece of 5 m long highly nonlinear optical fiber. The results demonstrate a satisfactory flatness of ~3 dB over a bandwidth of ~1000 nm in the range from 1261 to 2261 nm, achieving to the best of our knowledge, one of the flattest SC generated from noise-like pulses.

Supercontinuum (SC) generation has the important applications such as broadband light source, optical coherence tomography, ultra-short pulse compression, and optical frequency metrology, etc. Tellurite glass is transparent in the mid-infrared range, and has a higher n₂ than silica glass by at least one order of magnitude. We have fabricated the hexagonally shaped tellurite air-clad fiber with a core diameter of around 1 &mu;m through controlling the temperature field exactly in the process of fiber-drawing. Since the SC generation strongly depends on the chromatic dispersion, which is determined by the microstructure of fiber, it is interesting to investigate and demonstrate such dependence for such a small core fiber in detail. In this work by pumping a positive pressure of nitrogen gas into the holes of preform, we obtained 1 &mu;m core fibers with diameter ratio of holey region to core (DRHC) varied from 3.5 to 20. The dispersion was tailored effectively by the variation of DRHC. Dependences of SC on the microstructure and dispersion were demonstrated. The pump lasers were picosecond and femtosecond fiber lasers. One octave flattened SC generation was obtained for the fibers pumped by 1064 nm picosecond fiber laser with the pulse energy of several hundred pJ. Intense second and third harmonic generations were obtained under the pump of a 1557 nm femtosecond fiber laser. The correlation of dispersion and SC spectra was analyzed. Such tellurite microstructured optical fibers (MOFs) with high nonlinearity and controlled dispersion are significant in nonlinear applications.

We report on what we believe is the first demonstration of on-chip supercontinuum generation through dual-wavelength pumping of a nonlinear photonic integrated circuit, fabricated from high-index doped silica glass. In addition to the bandwidth enhancement through cross-phase modulation, we also observe multiple temporal reflections that help to extend the bandwidth further through far-detuned radiations. The experimental results show good agreement with the phase-matching theory and numerical simulations. Additionally, our real-time, pulse-to-pulse, spectral measurements through the dispersive Fourier transform technique reveal a significant increase in relative intensity noise for dual-wavelength pumping compared to the case of single-wavelength pumping.

Diamond is known from its strong single and narrow Raman line at 1332 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> . Our goal was to examine if the Raman response will noticeable influence the process of supercontinuum generation in diamond. We thus study experimentally the spectrum of the supercontinuum generated in a bulk diamond crystal as a function of the input energy. The 1 kHz regenerative amplifier was used as a source for 800 nm wavelength, 45 fs long input pulses. The advancing broadening of the blue side of supercontinuums spectrum is observed for energies below 26 μJ. The blue edge of supercontinuum has been found to be static for higher energies. The edge was found to be 615 nm. This limit is much higher than in case of commonly used shappire or CaF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> . It makes diamond not favourable as a material for supercontinuum generation for spectroscopic purposes in the visible light. The existence of the edge can be explained [1] by a 5-photon absorption over the band-gap. For energies over 31 μJ patterns characteristic for pulse splitting have been observed.

Spectral broadening of light and generating new frequencies are among the most interesting aspects of nonlinear optics. Supercontinuum generation (SCG) is a especial nonlinear process that occurs when pulses with narrow linewidth or continuous-wave (CW) lightwaves experience huge spectral broadening. In this paper, for the first time, SCG in the terahertz (THz) and Infrared (IR) ranges in a designed silicon-based rib waveguide is simulated by solving the generalized nonlinear Schrödinger equation (GNLSE). To this end, we first design a silicon waveguide with a zero-dispersion wavelength (ZDW) in the THz region and then determine the linear and nonlinear parameters of the waveguide. Subsequently, IR to THz SCG is simulated by means of the split-step Fourier transform (SSFT), where the influences of different parameters such as input pulse width, pulse power and waveguide length are investigated. By launching a 60-fs, 10-kW hyperbolic secant pulse into a 6-mm waveguide, a 1.3-octave SCG is obtained.

The femtosecond laser is crucial to the operation of the femtosecond optical frequency comb. In this paper, a passively mode-locked erbium-doped fiber laser is presented with 91.4 fs pulse width and 100.8 MHz repetition rate, making use of the nonlinear polarized evolution effect. Using a 976 nm pump laser diode, the average output power is 16 mW from the coupler and 27 mW from the polarization beam splitter at the pump power of 700 mW. The proposed fiber laser can offer excellent temporal purity in generated pulses with high power, and provide a robust source for fiber-based frequency combs and supercontinuum generation well suited for industrial applications.

Taking into account parameters such as input pulse duration, peak power and dimension and dispersion of the nanofiber etc., using a femtosecond laser as a pump source and a nanofiber as a nonlinear element, we numerically simulated the supercontinuum generation (SCG). The results show that tapering the common fiber to nanometer-scale fiber provides tight field confinement and diameter-dependent dispersion, and narrowing the input pulse width to femtosecond could observe SCG easier. The relation between the spectrum broadening and the diameter of nanofiber is not a direct proportion. According to our simulation the dimension of the nanofiber plays an important role in changing dispersion and then the generation of supercontinuum.