Fusion splicing of solid-core microstructured silica fibers has been one of the key enablers which opened practical applications of these structures in ultrafast light sources or fiber-based sensors. ...Anti-resonant hollow core fibers are special in this context, because their optical properties critically depend on single-micron or sub-micron thin wall membranes. This corresponds to high thermal isolation of their cladding structure and makes thermal processing of these fibers challenging. We investigate fusion splicing feasibility of a single capillary ring anti-resonant hollow core fiber made of silica glass. We begin by splicing pairs consisting of standard single mode and hollow core fibers, followed by pairs of polarization maintaining and hollow core fibers. Splice loss is determined within the 1450-2000 nm transmission window of the fiber at around 1-2 dB, depending on wavelength along the transmission window, in the transmission direction from the step index fiber into the hollow core fiber. Maintenance of polarization is verified and polarization extinction ratio of no less than 10 dB is recorded for the ARF spliced with a polarization maintaining fiber. Mechanical robustness of the fabricated splices is verified with standard pull tests returning damage thresholds of 140 g (32 kpsi) and 100 g (24 kpsi) for hollow core fibers spliced to single mode and polarization maintaining fibers, respectively.
We report an ultra-low noise, polarization-maintaining, ultrafast Thulium-doped all-fiber chirped pulse amplifier, seeded by a polarized all-normal dispersion (ANDi) supercontinuum (SC) driven by an ...ultrafast Erbium-fiber laser. The system comprises only polarization-maintaining fibers and delivers 96 fs pulses with 350 mW output power at 100 MHz, centered at 1900 nm. The integrated relative intensity noise (RIN) in the range of 10 Hz - 10 MHz is only 0.047% at the amplifier output, which is virtually identical to the RIN of the Erbium-fiber laser driving the SC. Therefore, neither the SC generation nor the amplification process introduce significant excess noise. The RIN of our system is an order of magnitude lower than similar systems previously seeded with Raman solitons. This highlights the superior noise properties of ANDi SC and their potential as ultra-low noise seed sources for broadband, high power ultrafast fiber amplifiers and frequency combs.
We report on experimental characterization of butt-coupling between a quantum cascade laser operating around the wavelength of 4.5 μm and a silica hollow core anti-resonant fiber. The used fiber has ...a single ring of non-touching capillaries surrounding a 42.5 μm dimeter air core and a mid-infrared transmission window in the wavelength range of 2.8 to 4.7 μm. A lens-less butt-coupling interconnection is established and coupling efficiency of 22% is achieved with over 100 mW of power at the fiber output. Bending losses in this test-bed system are verified depending on radius with the loss remaining below 1 dB/m for 20 mm loops, while bend losses exceeding 10 dB/m are observed when the fiber is bent down to a 5-mm radius. The presented coupling dramatically improves the output beam quality of the quantum cascade laser with a measured NA = 0.45. The beam at the fiber output has a circular shape, measured M 2 = 1.04 and uniform numerical aperture of NA = 0.13. Together with the hollow core fiber geometry, the proposed system would be suitable for simple implementations of absorption spectroscopy of popular atmospheric agents, like N 2 O.
We demonstrate birefringence enhancement in an optical fiber with artificial core anisotropy. A nanostructured fiber core in the form of a glass slab with layers of germanium-doped silica interleaved ...with the layers of fluorine-doped silica enabled an increase of the birefringence of 0.54×10 -4 without any stress zones. The experimental result confirms the numerical prediction of birefringence enhancement over previously presented fibers by increasing the refractive index contrast between the two core base glasses. Birefringence improvement has been achieved only by core material engineering and not by adding any stress zones or other approaches involving cladding shaping and core geometry design. The modification introduced to core had no impact on the guiding performance of the realized fiber, which remained perfectly matched to the SMF-28 standard in terms of its numerical aperture NA = 0.11 and the effective mode-field diameter MFD = 10.1 μm at the wavelength of 1550 nm.
We experimentally investigate the spectro-temporal characteristics of coherent supercontinuum (SC) pulses generated in several implementations of silica and soft-glass all-normal dispersion (ANDi) ...photonic crystal fibers optimized for pumping with Erbium (Er):fiber femtosecond laser technology. We characterize the resulting SC using time-domain ptychography, which is especially suitable for the measurement of complex, spectrally broadband ultrashort pulses. The measurements of the ANDi SC pulses reveal intricate pulse shapes, considerable temporal fine structure, and oscillations on time scales of < 25 femtoseconds, which differ from the smoothness and simplicity of temporal profiles obtained in numerical simulations and observed in previous experiments. We link the measured complex features to temporal sub-structures of the pump pulse, such as pre- and post-pulses and low-level pedestals, which are common in high pulse energy ultrafast Er:fiber systems. We also observe spectro-temporal structures consistent with incoherent noise amplification in weakly birefringent fiber samples. Our results highlight the importance of the pump source and polarization-maintaining (PM) fibers for high-quality SC generation and have practical relevance for many ultrafast photonics applications employing ANDi fiber-based SC sources.
In this work we discuss the effect of infiltration of different antiresonant fibers with low-refractive-index liquids, such as water and ethanol, on their optical properties. The fibers with single- ...and double-ring capillaries have been designed to show broad transmission bands in visible and near infrared range as it is required for optofluidics, in particular spectrophotometric applications. We show experimentally that their transmission windows shift toward shorter wavelengths and only modestly reduce their width. The transmission bands are located in the wavelength ranges of 533-670 nm and 707-925 nm, for the fibers when infiltrated with water. The two types of analyzed antiresonant fibers infiltrated with the liquids show similar light guidance properties when they are straight, but significantly lower bending loss can be achieved for the double-ring than for the single-ring antiresonant fiber. For this reason, the double-ring antiresonant fibers are more suitable as a compact solution for optofluidic applications, although transmission windows are reduced due to broader resonance peaks.
We report a silica glass nested capillary anti-resonant nodeless fiber with transmission and low bending sensitivity in the mid-infrared around 4000 nm. The fiber is characterized in terms of ...transmission over 1700-4200 nm wavelengths, revealing a mid-infrared 3500-4200 nm transmission window, clearly observable for a 12 m long fiber. Bending loss around 4000 nm is 0.5 dB/m measured over 3 full turns with 40 mm radius, going up to 5 dB/m for full turns with 15 mm radius. Our results provide experimental evidence of hollow-core silica fibers in which nested, anti-resonant capillaries provide high bend resistance in the mid-infrared. This is obtained for a fiber with large core diameter of over 60 um relative to around 30 um-capillaries in the cladding, which motivates its application in gas fiber lasers or fiber-based mid-infrared spectroscopy of COx or NxO analytes.
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