All-silica Fibers Research Articles

3D-Printed Ultracompact Multicore Fiber-Tip Probes for Simultaneous Measurement of Nanoforce and Temperature.

Optical fiber force sensing has attracted considerable interest in biological, materials science, micromanipulation, and medical applications owing to its compact and cost-efficient configuration. However, the glass fiber has an intrinsic high Young's modulus, resulting in force sensors being generally less sensitive. While hyperelastic polymer materials can be utilized to enhance the force sensitivity, the thermodynamic properties of the polymer may weaken the sensing accuracy and reliability. Herein, we demonstrate ultracompact three-dimensional (3D)-printed multicore fiber (MCF) tip probes for simultaneous measurement of nanoforce and temperature with high sensitivity. The sensor is highly sensitive to force-induced deformation due to the special geometric features of the polymer microcantilever, and the high-temperature sensitivity can be implemented through the poly(dimethylsiloxane) (PDMS) microcavity on the same fiber facet. Moreover, the sensitivities of the fiber interferometers are remarkably enhanced by introducing the optical analogue of the Vernier effect. Such a device exhibits a force sensitivity of 56.35 nm/μN, which is more than 103 times that of all-silica fiber force sensors. The PDMS microcavity provides a temperature sensitivity of 1.447 nm/°C, measuring the local temperature of the probe and compensating for temperature crosstalk of the force detection. The proposed compact MCF-tip sensor can simultaneously measure nanoforce and temperature with high sensitivity, facilitating multiparameter sensing in a restricted space environment and showing the potential in miniaturized all-fiber multiparameter sensors.

Efficient tunable cascaded Raman source with all-silica fibers based on 2-µm DSR pulse pumping.

We present an efficient tunable all-silica-fiber 2nd-order cascaded Raman pulse laser utilizing 2-µm dissipative-soliton-resonance (DSR) rectangular pulses for pumping and highly GeO2-doped silica fiber as Raman gain medium. When pumped at 1966.5 nm, the maximum 1st-order Raman optical conversion efficiency is up to 64.4% at 2153 nm, with 92.4% spectral purity and 0.39-W average power. The maximum 2nd-order Raman optical conversion efficiency is 19.3% at 2370 nm, with 39.2% spectral purity and 0.25-W average power. To our knowledge, these conversion efficiencies and spectral purities represent the highest levels achieved in a mid-infrared all-silica-fiber cascaded pulsed Raman laser. Additionally, by adjusting the central wavelength of the DSR seed pulse, the 2nd-order Raman light can be tuned within a range of 41 nm (2354∼2395 nm). Our system provides a simple and easy-to-implement solution for realizing efficient tunable cascaded pulsed Raman lasers in the 2.4-µm band.

NIR to MIR ultra-broadband supercontinuum laser source based on all-silica fibers.

We demonstrated an ultra-broadband supercontinuum (SC) laser source with a wavelength range spanning the near-infrared (NIR) to mid-infrared (MIR) region. The SC spectrum was generated in a very short piece of highly nonlinear silica fiber (HNLF) which has a zero-dispersion wavelength (ZDW) of 1.55 µm. The pump source used has a spectral coverage of 1.5∼2.4 µm which covers the ZDW of HNLF, resulting in a dramatic blue and red shift of the spectrum through strong non-linear effects. As the pump laser pulse launched into HNLF, a SC spectrum with broadband range of 0.92∼2.92 µm and maximum average power of 5.09 W was achieved, which sets record coverage of HNLF-based watts magnitude SC laser sources for now, to the best of the authors' knowledge. The setup consists of silica fiber that can be considered easy-to-implement and with a cost-effectiveness scheme for ultra-broadband SC generation that could be easily applied to optical fiber sensing and spectral imaging technology.

All-Silica Fiber Ultra-Flat 2-3 μm Supercontinuum Source Based on Highly Nonlinear Silica Fiber

In this letter, we demonstrated an all-silica fiber 1.5- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$3.2 ~\mu \text{m}$ </tex-math></inline-formula> supercontinuum (SC) source based on germanium-doped highly nonlinear fibers (HNLF). By optimizing the length of HNLF, as the pump injected into the HNLF increased to 6 W, a 4.12 W broadband SC source extending from 1516 to 3182 nm was obtained. The 3 dB spectrum bandwidth was up to 1022 nm ranging from 1855 nm to 2877 nm, and the 1 dB bandwidth was up to 878 nm covering from 1959 nm to 2837 nm. To the best of our knowledge, this is the flattest SC in the 2- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$3 ~\mu \text{m}$ </tex-math></inline-formula> region based on doped silica fiber to date.

High-power, high-efficiency single-frequency DBR fiber laser at 1064 nm based on Yb3+-doped silica fiber.

A high-power, high-efficiency single-frequency fiber laser at 1064 nm was demonstrated based on a distributed Bragg reflector (DBR) all-silica-fiber configuration. A single-frequency laser with an output power of 642 mW and slope efficiency of 66.4% with respect to absorbed pump power was achieved from a 1.2-cm-long commercially available Yb3+-doped silica fiber. To the best of our knowledge, this is the highest single-frequency laser power and efficiency obtained from the DBR all-silica fiber laser. The work presented here paves the way for the development of high-power, robust, and cost-effective single-frequency Yb3+-doped all-silica fiber lasers.

Single-frequency distributed Bragg reflector Tm:YAG ceramic derived all-glass fiber laser at 1.95 μm

A 135 mW single-frequency distributed Bragg reflector fiber laser at 1.95 μm was obtained based on a Tm:YAG ceramic-derived all-glass fiber. The fiber laser achieved an optical signal-to-noise ratio of ∼ 77 dB. Moreover, the threshold and linewidth of the single-frequency laser were measured to be 15.4 mW and 4.5 kHz, respectively. In addition, the measured relative intensity noise was less than –140 dB⋅Hz−1 at frequencies of over 10 MHz. The results show that the as-drawn Tm:YAG ceramic-derived all-glass fiber is highly promising for ∼ 2 μm single-frequency fiber laser applications.

All-silica optical fiber bonding.

In this work, we demonstrate a spot-welding method for fabrication of all-silica fiber components. A CO2 laser was used to locally sinter sub-micron silica powders, enabling rigid bonding of optical fiber to glass substrates. The bonding was achieved without inducing any fiber transmission losses. The components showed no sign of deterioration or structural change when heated up to 1100 °C. These single material assemblies are therefore well suited for use in harsh environments where high stability and robustness is required.

Orders of magnitude loss reduction in photonic bandgap fibers by engineering the core surround.

We demonstrate how to reduce the loss in photonic bandgap fibers by orders of magnitude by varying the radius of the corner strands in the core surround. As a fundamental working principle we find that changing the corner strand radius can lead to backscattering of light into the fiber core. Selecting an optimal corner strand radius can thus reduce the loss of the fundamental core mode in a specific wavelength range by almost two orders of magnitude when compared to an unmodified cladding structure. Using the optimal corner radius for each transmission window, we observe the low-loss behavior for the first and second bandgaps, with the losses in the second bandgap being even lower than that of the first one. Our approach of reducing the confinement loss is conceptually applicable to all kinds of photonic bandgap fibers including hollow core and all-glass fibers as well as on-chip light cages. Therefore, our concept paves the way to low-loss light guidance in such systems with substantially reduced fabrication complexity.

Simulation Study on Supercontinuum Generation at Normal Dispersion Regime of a Carbon Disulfide-core Photonic Crystal Fiber

A photonic crystal fiber with a hollow core filled with carbon disulfide (CS2) is proposed as a new source of supercontinuum light. We numerically study guiding properties of modeled fibers including the dispersion and the effective mode area of the fundamental mode. As a result, octave spanning of the SC spectrum was achieved in the wavelength range of near-IR from 1.25 μm to 2.3 μm with 90 fs pulse and energy of 1.5 nJ at a pump wavelength of 1.55 μm. The proposed fibers are fully compatible with all-silica fiber systems, in particular, could be used for all-fiber SC sources and new low-cost all-fiber optical systems.

Tapered fiber radiation sensor based on Ce/Tb:YAG crystals for remote γ-ray dosimetry.

A novel tapered fiber-optic radiation sensor (TFRS) based on cerium (Ce) and terbium (Tb) co-doped YAG scintillation crystals is demonstrated for the first time. Using the CO2 laser-heated method, a Ce/Tb:YAG crystal is well embedded into silica glass cladding without any cracks. The scintillation light emitted from the YAG scintillation crystal can be directly coupled into the derived silica optical fiber by the tapered region. The loss of the derived optical fiber is 0.14 dB/cm, which is one order of magnitude lower than the 1.59 dB/cm of the YAG crystal in the TFRS. Subsequently, strong photo- and radio-luminescence of Tb3+ (5D4→7F5) ions in TFRS are achieved under ultraviolet light and high-energy ray excitation, respectively. In particular, a prominent remote radiation response of the TFRS is presented under excitation by γ-rays through fusion splicing with multimode optical fibers. The response is approximately four times larger than that of a plastic scintillation fiber (BCF-12) sensor. Furthermore, the results possess high stability as well as a good linearity between the radiation dose rate and the response intensity. The TFRS in combination with an all-silica fiber system is a promising candidate for remote radiation detection.

Sensitivity amplification of bubble-based all-silica fiber liquid-pressure sensor by using femtosecond laser exposure

We proposed an efficient and universal sensitivity amplification method for most kinds of sensors based on fiber in-line two-beam Fabry–Perot interferometers (FPIs) by using the femtosecond laser exposure. As an example of two beam FPI, a liquid-pressure sensor based on a micro-bubble at the end of the single mode fiber (SMF) was fabricated. To improve the sensitivity, a third refection mirror in SMF near the bubble at a certain distance was fabricated by using femtosecond laser exposure. As a result, the Vernier effect is generated, which improves the pressure sensitivity from −0.414 nm/MPa to −3.973 nm/MPa. Besides, the synchronous measurement of liquid-pressure and temperature can be achieved by monitoring the interference peak and the Vernier envelope at the same time.

Silica-based photonic crystal fiber for the generation of broad band UV radiation

We report a small-core UV-grade silica multimode photonic crystal fiber for nonlinear frequency conversion in the ultraviolet spectral region. The fiber has been fabricated using F110 UV-Grade glass from Heraeus, which features excellent transmission and low solarization in the UV window. Pumping the fiber core at 355 nm with picosecond laser pulses, we observe the appearance of parametric sidebands in several spatial modes up to 380 nm. We modelled this process using intermodal phase-matching conditions and obtained excellent agreement between calculations and the measured data. We further report frequency conversion pumping into the fiber microstructured cladding where broadband cascaded Raman scattering spanning up to 391 nm is observed. These results represent a significant step towards the efficient and stable generation of UV supercontinuum spectra in an all-silica fiber platform.

1.8 µm passively Q-switched thulium-doped fiber laser

This work demonstrates a simple and reliable passively Q-switched thulium-doped fiber laser capable of generating an output with a peak wavelength at 1.8 µm. Lasing is realized from the shorter wavelength region of a thulium-doped silica fiber gain medium by suppressing lasing at longer wavelengths in combination with a tunable bandpass filter. The laser is modulated by a single-walled carbon nanotube film saturable absorber. The generated Q-switched laser is capable of achieving a high repetition rate of 67.9 kHz and a narrow pulse width of 1.2 µs. As most work on the 1.6–1.8 µm waveband focuses on continuous-wave and mode-locked lasers, to the best of the author’s knowledge, this is the first demonstration of a passively Q-switched thulium-doped fiber laser operating at 1.8 µm with an all-silica fiber setup. The demonstrated laser has potential for various applications including biomedical surgery and polymer-based welding applications.

Low-Attenuation Variable Mode Control Using Twist Processing for Step-Index Optical Fiber Loops

We propose a method of variable mode control that generates an equilibrium modal distribution (EMD) in step-index multimode fibers. The proposed method can control the modal power distribution variably from a low-order mode distribution to a high-order mode distribution (including EMD) by twisting fiber loops. The attenuation of the controller for EMD generation is five times smaller than those of conventional EMD generation methods. As a reference light source with high measurement reproducibility, the EMD light source obtained by the variable mode control method can be used to evaluate hard polymer cladding fiber link systems. The proposed method is applicable to all types of step-index multimode optical fibers, including all-glass fibers, hard polymer cladding fibers, and plastic optical fibers.

Broadband 2 μm amplified spontaneous emission of Ho/Cr/Tm:YAG crystal derived all-glass fibers for mode-locked fiber laser applications

Broadband ∼2 μm amplified spontaneous emissions with a full width at half-maximum (FWHM) varying from ∼206 to ∼234 nm were obtained from the Ho/Cr/Tm:yttrium aluminum garnet (YAG) crystal derived fibers, which were drawn using a molten core method. The core-cladding structure of the as-drawn fibers was preserved completely, and the core was found to be amorphous. What is more, an all-fiber-integrated passively mode-locked laser based on an 8cm long Ho/Cr/Tm:YAG crystal derived all-glass fiber was built which, to the best of our knowledge, is the first demonstration of a mode-locked fiber laser in a similar YAG derived fiber. The mode-locked pulses operate at 1.95μm with duration of ∼118 ps, and the repetition rate is ∼9.5 MHz. Limited by the bandwidth of the fiber grating used in the laser cavity, the mode-locking spectrum has a relatively narrow FWHM of ∼0.09 nm. These results suggest that the broadband YAG crystal derived all-glass fibers are promising for ultrafast fiber lasers applications.

Highly Sensitive Miniature All-Silica Fiber Tip Fabry–Perot Pressure Sensor

This letter presents the design, fabrication, and testing of a diaphragm-based, all-silica fiber tip pressure sensor. A piece of 1.2- $\mu \text{m}$ -thick silica diaphragm was thermally bonded to the end face of an etched fiber with an outer diameter (OD) of 125 $\mu \text{m}$ to form a Fabry–Perot (FP) interferometer. The diameter of the etched FP cavity is $105~\mu \text{m}$ , enabling the sensing area to be large, and thus, a static pressure sensitivity of 12.4 nm/kPa (85.3 nm/psi) is accomplished without the need for any post polishing or etching. The sensor also shows a low-temperature cross sensitivity during tests, owing to its all-silica structure. It is suitable for extensive production, and it has a great potential to work in applications, where miniature size and high sensitivity are essential such as medical applications.

Supercontinuum source based on all-silica fibers with optimized spectral power from 1100 up to 2300 nm

The authors present here an attainable fiber supercontinuum source with competitive characteristics in the near infrared range. The proposed system is based on a highly nonlinear silica fiber, with nominal zero-dispersion wavelength at 1550 nm. A mode-locked fiber laser was used as the seed. The pump wavelength was shifted to match the zero-dispersion wavelength of the nonlinear fiber, achieving a better performance of the spectral emission. The supercontinuum emission was characterized between 1100 nm and 2300 nm, showing a flat and wide spectrum with a conversion efficiency over 80%. The set-up consists only in silica fiber and can be considered, therefore, as a cost-effective alternative for supercontinuum generation in the near infrared range, which can be easily implemented in any photonics laboratory, where commercial amplifiers are usual devices.

Miniature All-Silica Microbubble-Based Fiber Optic Fabry-Perot Pressure Sensor with Pressure Leading-In Tube

A novel all-silica fiber optic Fabry-Perot (FP) pressure sensor with pressure leading-in tube based on microbubble structure is developed and experimentally demonstrated. The FP cavity is formed by fixing the end face of the single-mode fiber (SMF) parallel to the outer surface of the microbubble, in which the microbubble with a diameter of about 318 μm is constructed at the end of silica hollow tube. When external pressure is transmitted on the inner surface of the microbubble by the pressure leading-in tube, the FP cavity length changes with the diameter of microbubble. Experimental results show that such a sensor has a linear sensitivity of approximately 4.84 nm/MPa at room temperature over the pressure range of 1.1 MPa; the sensor has a very low temperature coefficient of approximately 2 pm/°C from room temperature to 600°C. The sensor has advantages of extremely low temperature coefficient, compact structure, and small size, which has potential applications for measuring pressure in high-temperature environment.

Optimization of optical properties of photonic crystal fibers infiltrated with carbon tetrachloride for supercontinuum generation with subnanojoule femtosecond pulses.

A photonic crystal fiber (PCF) made of fused silica glass, infiltrated with carbon tetrachloride (CCl4), is proposed as a new source of supercontinuum (SC) light. Guiding properties in terms of effective refractive index, attenuation, and dispersion of the fundamental mode are studied numerically. As a result, two optimized structures are selected and verified against SC generation in detail. The dispersion characteristic of the first structure has the zero-dispersion wavelength at 1.252μm, while the dispersion characteristic of the second structure is all-normal and equals -4.37 ps·nm-1·km-1 at 1.55μm. SC generation was demonstrated for the wavelengths 1.064μm, 1.35μm, and 1.55μm. We prove the possibility of coherent, octave-spanning SC generation with 300fs pulses with only 0.8nJ of energy in-coupled into the core with each of the studied structures. Proposed fibers are fully compatible with all-silica fiber systems and PCFs with wide mode area, and can also be used for all-fiber SC sources. The proposed solution may lead to new low-cost all-fiber optical systems.

The importance of translaminar fracture toughness for the penetration impact behaviour of woven carbon/glass hybrid composites

The impact resistance of fibre-reinforced composites is vital in many applications, and can be improved by exploiting synergies in fibre-hybridisation. These effects are however not sufficiently well understood in the literature. Penetration impact tests were hence performed on carbon/glass hybrids, and the results were linked to the flexural behaviour and translaminar fracture toughness. The results revealed large synergetic effects of up to 40% compared to the linear rule-of-mixtures. The results are also the first to reveal that creating a translaminar fracture surface can strongly contribute to the energy absorbed during penetration impact: 56% for an all-carbon fibre composite and 13% for an all-glass fibre composite. These results prove that strategies for maximising the translaminar fracture toughness can also be exploited to maximise the penetration impact resistance of fibre-hybrids. In carbon fibre composites in particular, ply blocking, using larger yarns and introducing micro-cuts should therefore increase the penetration impact resistance.