Chalcogenide Step-index Fiber Research Articles

Low-loss Ge-As-Se-Te fiber for high-intensity CO2 laser delivery

High-purity Ge-As-Se-Te glasses have been well prepared via an effective double-distillation method. These glasses exhibit robust characteristics, withstanding input power levels as high as 12 W (68 kW/cm2). Utilizing extrusion-based fabrication, a large-core chalcogenide step-index fiber has been produced with a core diameter of 200 µm and a low optical loss of 0.78 dB/m at 7.25 µm. The fiber mode field area exceeded 26522 µm2. The fiber exhibits excellent transmittance in the whole mid and far infrared region of 2-12 µm, and its loss has been also certificated to be 1.85 dB/m at 10.6 µm by a CO2 laser. Further, the fiber is capable of high-intensity laser delivery of 16.13 kW/cm2, even under a high temperature of 150°C. At last, a high transmission efficiency of 44.9% has been recorded in this fiber, and the output power density is as high as 4.01 kW/cm2. All these results show that the fiber has the potential to be used in far-infrared laser machining and medical operation.

1.7–18 µm mid-infrared supercontinuum generation in a dispersion-engineered step-index chalcogenide fiber

We demonstrate 1.7–18 µm mid-infrared coherent supercontinuum generation by means of the full transmission window of a unique dispersion-engineered step-index Ge-Se-Te fiber. Our study thus opens the entire molecular fingerprint region to future chalcogenide fiber platforms.

Power threshold reduction and laser efficiency improvement of Brillouin fiber laser based on an As[formula omitted]S[formula omitted] Chalcogenide fiber via a mode field adaptor

A Brillouin fiber laser with low power threshold and high laser efficiency based on a 4.2-m-long As2S3 chalcogenide step-index fiber is presented in this work. Due to the free-space system between the As2S3 and single mode fiber (SMF), a high coupling efficiency is required to reduce the ring cavity loss and laser threshold, and hence improve the laser conversion efficiency. Compared with the lensed fiber and ultrahigh numerical aperture (UHNA) fiber which are commonly used as butt-coupling devices, the mode field adaptor (MFA) employed in this work can better match the mode field diameter and numerical aperture of the As2S3 and SMF, exhibiting a total coupling loss of only 1 dB. A low Brillouin laser threshold of 14 mW is achieved benefiting from the high cavity feedback of 16%. A Stokes power of ∼50 mW is generated for an injected pump power of 120 mW, showing a high laser efficiency of 42%. Furthermore, the Brillouin laser with the MFA butt-coupling exhibits lower relative intensity noise and phase noise and hence narrower laser linewidth than that with the lensed fiber and UHNA fiber butt-coupling. These results suggest the significance of the MFA which can reduce the cavity loss for a Brillouin laser with good performance based on As2S3 chalcogenide fiber.

Low-noise octave-spanning mid-infrared supercontinuum generation in a multimode chalcogenide fiber.

We demonstrate the generation of a low-noise, octave-spanning mid-infrared supercontinuum from 1700 to 4800 nm by injecting femtosecond pulses into the normal dispersion regime of a multimode step-index chalcogenide fiber with 100 µm core diameter. We conduct a systematic study of the intensity noise across the supercontinuum spectrum and show that the initial fluctuations of the pump laser are at most amplified by a factor of three. We also perform a comparison with the noise characteristics of an octave-spanning supercontinuum generated in the anomalous dispersion regime of a multimode fluoride fiber with similar core size and show that the normal dispersion supercontinuum in the multimode chalcogenide fiber has superior noise characteristics. Our results open up novel perspectives for many practical applications such as long-distance remote sensing where high power and low noise are paramount.

Mid-IR supercontinuum generation in birefringent, low loss, ultra-high numerical aperture Ge-As-Se-Te chalcogenide step-index fiber

This work reports on the fabrication and subsequent supercontinuum generation in a Ge-As-Se-Te/Ge-As-Se core/clad chalcogenide step-index fiber with an elliptical-core and an ultra-high numerical aperture of 1.88 ± 0.02 from 2.5 - 15 µm wavelength. The fiber has very low transmission loss of < 2 dB/m from 5-11 µm and a minimum loss of 0.72 ± 0.04 dB/m at 8.56 µm. Supercontinuum spanning from 2.1 µm to 11.5 µm with an average power of ∼6.5 mW was achieved by pumping a ∼16 cm fiber with a minor/major axis core diameter of 4.2/5.2 µm with 250 fs pulses at 4.65 µm wavelength and a repetition rate of 20.88 MHz. The effect of the elliptical-core was investigated by means of mechanical rotation of the fiber relative to the linear pump polarization, and it was found to cause a shift in the supercontinuum spectral edges by several hundred nanometers.

Chalcogenide glass fibers with a rectangular core for polarized mid-infrared supercontinuum generation

A step-index chalcogenide fiber with a rectangular core and a circular cladding was fabricated through an approach that combines an extrusion technique and a multiple-stage rod-in-tube method. This fiber has a Ge12As24Se64 glass core with a size of ~2.8 μm × 5.9 μm, and a Ge10As24S66 glass cladding with a diameter of ~220 μm, and shows a relatively large birefringence. When ~10 cm long fiber was pumped at 4.0 μm with 330 fs pulses, ~2.2–9.5 μm supercontinuum with a flatness of 20 dB and a polarization extinction ratio of ~10 dB was generated.

Broadband high-power mid-IR supercontinuum generation in tapered chalcogenide step-index optical fiber

We report a design, analysis, and numerical modeling of a tapered chalcogenide step-index fiber for broadband high-power mid-infrared supercontinuum extending from the 1.5–14.5 µm molecular ‘fingerprint region’. The reported tapered chalcogenide fiber structure is able to generate a broadband supercontinuum spectrum with output average power of 82 mW (27.7 mW for the wavelengths >5 µm) when it is pumped with 200 fs laser pulses with a repetition rate of 76 MHz and average power of 200 mW at 3.5 µm. Such a bright and broadband mid-infrared supercontinuum light source covering both the 3–5 µm and 8–13 µm atmospheric windows and most of the molecular fingerprint spectral region has practical applications in various fields, including mid-infrared spectroscopy, imaging, and biomedical diagnostics.

Prospective use of a normally dispersive step-index chalcogenide fiber in nonlinear pulse reshaping.

In this work, several normally dispersive highly nonlinear chalcogenide optical fibers (NDHNCFs) with a step-index profile have been designed and optimized in view of efficient parabolic pulse (PP) generation. A typical NDHNCF is selected such that the group velocity dispersion is highest among them and the corresponding nonlinearity is also very high. The input pulse parameters are optimized to find the lowest possible optimum length (Lopt) of the fiber where the linearly chirped PP is obtained. Further, it is found that for a shorter input pulse width, PP can be generated at a sufficiently smaller length of the NDHNCF with a slight compromise for its misfit parameter. A detailed analysis of the effect of pre-chirping helps to identify the suitable amount of initial chirp for different chalcogenide fibers with a choice of input pulse parameters. Although no improvement in PP generation is found for normal and initially chirped hyperbolic secant pulses, a highly efficient triangular pulse is achieved for a particular value of input pulse energy and the initial chirp parameter. Finally, the comparative study substantiates that our optimized NDHNCF is capable enough to generate quality PP at a length almost 70% shorter than a standard silica-based fiber.

Broadband mid-infrared supercontinuum generation in novel [formula omitted] step-index fibers

We experimentally demonstrate the mid-infrared supercontinuum generation in a chalcogenide step-index fiber consisting of an As2Se3 core and an As2Se2S cladding. The fiber with the core diameter of 21μm was fabricated through the rod-in-tube technique and fiber-drawing process. The effect of pump wavelength, fiber length, and pump power on the spectral bandwidth and output power of the supercontinuum spectra generated from the fiber pumped by the ultrashort pulses of ∼150 fs with a repetition rate of 1000 Hz was systematically investigated. When pumping a 12-cm-long fiber at a wavelength of 6.5μm with 14 mW pump laser power, a broadband supercontinuum spanning from 2.0μm to 12.7μm with an output power of 300μW was obtained.

Mid-infrared supercontinuum generation spanning from 1.9 to 5.7 μm in a chalcogenide fiber taper with ultra-high NA

We report a broadband supercontinuum generation in a chalcogenide fiber taper with an ultra-high numerical aperture. The chalcogenide step-index fiber consisting of As2Se3 core and As2S3 cladding was fabricated by using the isolated stacked extrusion method. The fiber taper with a core diameter of 1.75μm was prepared by employing a homemade tapering setup. By pumping the fiber taper with a femtosecond laser pulses at 3.3μm, a broadband supercontinuum generation spanning from 1.9 to 5.7μm was achieved.

Toward High-Power All-Fiber 2–5 μm Supercontinuum Generation in Chalcogenide Step-Index Fiber

In this paper, a high-power spectrally flat 2-5 μm supercontinuum (SC) laser is reported in a piece of As2S3 chalcogenide step-index fiber. A fluoride fiber-based SC laser which spans from 2-4.2 μm is used as the pump light. Two pump coupling systems between the fluoride and As2S3 fibers, one based on aspheric lens coupling and the other using all-fiber mechanical splicing are investigated. With the setup of aspheric lens coupling, the obtained SC laser has a 10 dB spectral bandwidth of 3000 nm spanning from 2050 to 5050 nm, corresponding to an average power of 57.6 mW. While with the all-fiber mechanical splicing, the 10 dB spectral bandwidth of the SC laser shrinks slightly, spanning from 2140 to 4980 nm range, but the average output power is further scaled to a record power of 97.1 mW. It is found that the dominant nonlinearities for continuous spectral broadenings in the As2 S3 fiber are self-phase modulation and stimulated Raman scattering in the normal dispersion regime. This paper presents an all-fiber mid-infrared SC laser with spectrum beyond 5 μm for the first time. It also offers a practical solution for robust and reliable high power 2-5 μm broadband fiber laser.

Numerical investigation of highly coherent mid-infrared supercontinuum generation in chalcogenide double-clad fiber

Abstract It is shown that chalcogenide double-clad fibers (Ch-DCFs) have large potential to realize the highly coherent mid-infrared (MIR) supercontinuum generation. We design the Ch-DCFs with flatter chromatic dispersion and smaller effective mode diameter than chalcogenide step index fibers in the MIR region. We numerically investigate MIR supercontinuum generation in designed Ch-DCFs. It is numerically demonstrated that highly coherent MIR supercontinuum extending from 3.3 to 10.4 μm in the Ch-DCFs can be generated by pumping with hyperbolic secant pulse at 6 μm, the peak power of 2 kW, and the full width at half maximum of 300 fs.

1.5-14 μm midinfrared supercontinuum generation in a low-loss Te-based chalcogenide step-index fiber.

We have experimentally demonstrated midinfrared (MIR) supercontinuum (SC) generation in a low-loss Te-based chalcogenide (ChG) step-index fiber. The fiber, fabricated by an isolated extrusion method, has an optical loss of 2-3 dB/m at 6.2-10.3 μm and 3.2 dB/m at 10.6 μm, the lowest value reported for any Te-based ChG step-index fiber. A MIR SC spectrum (∼1.5 to 14 μm) is generated from the 23-cm fiber pumped by a 4.5 μm laser (∼150 fs, 1 kHz). To the best of our knowledge, this is the first SC experimental demonstration in Te-based ChG fiber and the broadest MIR SC generation pumped in the normal dispersion regime in the optical fibers.

Supercontinuum generation in a step-index chalcogenide fiber with AsSe2 core and As2S5 cladding

We demonstrate the supercontinuum (SC) generation in a chalcogenide step-index fiber with AsSe2 core and As2S5 cladding. The characteristics of fiber are analyzed using the full-vectorial mode solver technique. The fiber has two zero-dispersion wavelengths at 2898 and 5140 nm. The evolving of SC spectra with fiber length and pump wavelength is investigated experimentally. The maximum SC range covering one octave from 1550 to 3300 nm is obtained when the 20 cm long fiber is pumped by 2000 nm pulses in normal dispersion region. The fiber can push forward the nonlinear application based on the stimulated Raman effect, stimulated Brillouin effect, four-wave mixing, supercontinuum generation, and so on in the mid-infrared waveband. The SCs are simulated by the nonlinear Schrödinger equation. The simulated results agree well with the experiments.

Mid-infrared supercontinuum generation spanning 2.0 to 15.1 μm in a chalcogenide step-index fiber.

We experimentally demonstrate mid-infrared (MIR) supercontinuum (SC) generation spanning ∼2.0 to 15.1 μm in a 3 cm-long chalcogenide step-index fiber. The pump source is generated by the difference frequency generation with a pulse width of ∼170 fs, a repetition rate of ∼1000 Hz, and a wavelength range tunable from 2.4 to 11 μm. To the best of our knowledge, this is the broadest MIR SC generation observed so far in optical fibers. It facilitates fiber-based applications in sensing, medical, and biological imaging areas.

High-power mid-infrared high repetition-rate supercontinuum source based on a chalcogenide step-index fiber.

We demonstrate a tunable and robust femtosecond supercontinuum source with a maximum output power of 550 mW and a maximum spectral width of up to 2.0 μm, which can cover the mid-infrared region from 2.3 μm up to 4.9 μm by tuning the pump wavelength. As2S3 chalcogenide step-index fibers with core diameters of 7 and 9 μm are pumped at different wavelengths from 2.5 μm up to 4.1 μm with femtosecond pulses by means of a post-amplified optical parametric oscillator pumped by an Yb:KGW laser. The spectral behavior of the supercontinuum is investigated by changing the pump wavelength, core diameter, fiber length, and pump power. Self-phase modulation is identified as the main broadening mechanism in the normal dispersion regime. This source promises to be an excellent laboratory tool for infrared spectroscopy owing to its high brilliance as demonstrated for the CS2-absorption bands around 3.5 μm.

1.8-10 μm mid-infrared supercontinuum generated in a step-index chalcogenide fiber using low peak pump power.

By pumping an 11-cm-long step-index chalcogenide fiber with ∼330 fs pulses at 4.0μm from an optical parametric amplifier, mid-infrared supercontinuum generation spanning from ∼1.8 to ∼10 μm within a dynamic range of ±15 dB has been demonstrated at a relatively low power threshold of ∼3000 W.

1.9 octave supercontinuum generation in a As₂S₃ step-index fiber driven by mid-IR OPCPA.

Using a 3.1-μm optical parametric chirped-pulse amplifier (OPCPA), we generate a supercontinuum in a step-index chalcogenide fiber that spans from 1.6 to 5.9 μm at the -20 dB points. The rugged step-index geometry allows for long-term operation, while the spectral bandwidth is limited by the transmission of the As2S3 fiber.

Fused taper infrared optical fiber couplers in chalcogenide glass

We have fabricated low loss, high coupling ratio bidirectional optical couplers for infrared light using multimode step-index chalcogenide fiber. Using a fusion technique similar to that commonly employed with silica fibers, we have found a temperature regime where fusion can occur while interdiffusion of the core and cladding materials will not. The resultant device has a roughly 3:1 coupling ratio, less than 0.3 dB of excess insertion loss, and preserves the guided modes of the fiber intact.