Multi-wavelength second-harmonic generation in a double-clad high nonlinear fiber induced by multiple phase-matching.

In this study, multi-wavelength second-harmonic generation (SHG) based on self-phase modulation (SPM) broadband supercontinuum (SC) was observed by employing a double-clad high nonlinear optical fiber (HNLF) in conjunction with a femtosecond laser. At a wavelength of 1050 nm and an average pump power of 320 mW, multiple phase-matching conditions were achieved, and SH signals of central wavelengths ∼530.7 nm, ∼525.1 nm, ∼503.5 nm, and ∼478.7 nm were observed, with SHG efficiency reaching ∼1.34 × 10-4. The SHG in this experiment can be attributed to the utilization of a doped optical fiber, where dopants create defect states, facilitating optical-chemical transformation and enhancing second-order polarization susceptibility. Additionally, theoretical simulations were conducted, aligning closely with the experimental findings. To the best of our knowledge, this work marks the first demonstration of multi-wavelength SHG in optical fibers. It offers a distinctive avenue for customizing multi-wavelength ultrafast light sources, exhibiting great application potential in the fields of medical diagnostics and optical sensing.

Numerical analysis of optical confinement in silica and tellurite multicore fibers for near-infrared image transportation.

We analyzed light confinement in circular step-index cores of tellurite and silica fibers through numerical calculations and also examined crosstalk between the fundamental modes of cores in multicore fibers. Our analysis showed that tellurite fibers have a pixel density about 2.2 times higher and a brightness about 1.4 times brighter than silica fibers. As a result, tellurite multicore image fibers have the potential to provide improved resolution and brightness for near-infrared image transportation compared with silica fibers.

Multimode interferometric sensor based on the no-core tellurite optical fiber for cryogenic temperature detection.

In this paper, a no-core tellurite optical fiber (NCTOF)-based sensor was proposed for cryogenic temperature detection in refrigeration process. The ultraviolet adhesive (UVA) dual-curing method was operated to stablish a sandwich-like composite structure, in which a section of NCTOF was compactly sandwiched between two segments of silica fiber to form multimode interference. The temperature sensing characteristics in cryogenic range were experimentally investigated by monitoring the transmission spectral movement, where a high sensitivity of 105.6 pm/°C was achieved in the range of -20-0 °C and 51.6 pm/°C in the range of -20-25 °C. The excellent performance was consistent with the simulation analysis. The maximum repeatability standard deviation and stability wavelength error of the sensor are 0.9799 pm/°C and 0.1676 nm, respectively. To the best of our knowledge, this is the first report on using tellurite optical fibers for cryogenic temperature detection, and the UVA dual-curing method provides a reliable solution for the integration and practical application of tellurite optical fiber. The proposed sensor is simple in structure, easy in fabrication, low in cost and excellent in performance. It can be expected to be used in food refrigeration, air-conditioning engineering, medical and health, industrial production, etc.

Chalcogenide all-solid hybrid microstructured optical fiber with polarization maintaining properties and its mid-infrared supercontinuum generation.

In this paper, we report a successful fabrication of a highly nonlinear chalcogenide all-solid hybrid microstructured optical fiber with polarization maintaining properties and a mid-infrared SC generation. Up to 4.5 × 10-4 at 10 µm of the fiber birefringence can be realized by employing a single As2Se3 core and two As2S5 rods horizontally aligned in the AsSe2 cladding. The fiber possesses a near-zero and flattened all-normal chromatic dispersion profile over the wavelength range from 5 to 10 µm. The polarization maintaining properties of the fiber is experimentally confirmed and a broadband supercontinuum spectrum from 2 to 10 µm in the mid-infrared window was experimentally demonstrated.

Plug-in tip sensor based on upconversion fluorescence in Er3+/Yb3+ co-doped tellurite glass for thermal monitoring of a miniature winding coil.

We demonstrate a plug-in tip sensor with a maximum cross section diameter of only 1 mm for real-time thermal monitoring of a high-density miniature winding coil, which can meet the miniaturization development needs of electromagnetic actuators. Due to the high upconversion luminescence efficiency, tellurite glass with an optimized Er3+/Yb3+ doping ratio is adhered to the end face of silica fiber for a temperature-sensitive tip. Temperature information is demodulated using the fluorescence intensity ratio technique, yielding a nonlinear response with R2 up to 0.9978. Within a wide temperature range of 253.55-442.45 K, the tip sensor exhibits good repeatability, excellent stability, high sensitivity of 52.7 × 10-4 K-1, small absolute error within ±1 K, and fast time response of 2.03 s. It has been successfully proven to be a miniaturized device with strong anti-interference ability for the health management of high-density winding coils.

Frequency conversions of nine peaks based on dispersive waves and solitons in a tellurite microstructured optical fiber.

We demonstrate the generation of broadband dispersive waves (DWs) and solitons in an 80-cm tellurite microstructured optical fiber (TMOF) designed and fabricated with 78TeO2-5ZnO-12LiCO3-5Bi2O3 (TZLB) glass. A 1810-nm femtosecond laser is used as the pump source with an average pump power ranging from 33 mW to 175 mW, where the tunable frequency range is 211.1 THz, which corresponds to the tunable wavelength range of 1742.9 nm. At 175 mW, the trapped multiple DWs are located at 923.8 nm, 1039.2 nm, 1121.6 nm, and 1204.6 nm and the multiple solitons are located at 2666.7 nm, 2426.1 nm, 2165.9 nm, 1952.7 nm, and 1842.1 nm. The experimentally obtained maximum DW conversion efficiency is 14%, and the maximum soliton conversion efficiency is 43%. The experimental and theoretical results of pulse evolution in the TMOF agree very well. To the best of our knowledge, this is the first time that nine peaks of frequency conversions have been realized simultaneously in non-silicon fibers. The exceptionally high nonlinearity and broadband-tunable characteristics of the proposed TMOF are promising components for the development of compact and highly efficient tunable mid-infrared fiber lasers, wavelength converters, and time-frequency metrology.

Transverse Anderson localization of mid-infrared light in a chalcogenide transversely disordered optical fiber.

We successfully fabricate a transversely disordered optical fiber made of AsSe2 and As2S5 glasses for high-resolution mid-infrared image transport. By using the fabricated fiber, we experimentally observe transverse Anderson localization of mid-infrared light at the wavelength of 3 µm. Moreover, we numerically evaluate the localization in the fiber by using a cross-sectional image of the fiber.

Single-mode tellurite optical fiber for temperature measurement based on the self-phase modulation effect.

In this paper, the self-phase modulation (SPM) effect in a double-cladding single-mode tellurite optical fiber (DC-SMTOF) was exploited for temperature sensing. The DC-SMTOF was fabricated based on a TeO2-ZnO-Li2O-Bi2O3 (TZLB) glass material that has a thermo-optical coefficient as high as -16.4×10-6/°C. The temperature sensing performance was evaluated by detecting the 3-dB bandwidth of the SPM spectra with the variation of temperature at different pump wavelength and different average pump power. The temperature sensitivity was obtained to be -2.971 nm/°C with a resolution of 0.0168°C. Both simulation and experiment confirmed that a longer pump wavelength and higher average pump power will result in a higher temperature sensitivity. To the best of our knowledge, this is the first study concerning SPM-based temperature sensing in a tellurite optical fiber. The proposed temperature sensor has a compact structure, and it can realize temperature sensing of high sensitivity without any fiber modification. This work opens the road toward explorations of a novel temperature sensing technology combined with soft glass fibers and nonlinear phenomenon, and is expected to deepen our understanding in the application of these complex nonlinear phenomena.

Experimental investigation of supercontinuum generation in a birefringence tellurite microstructured optical fiber.

A four-hole birefringence tellurite microstructured optical fiber (BTMOF) was designed and fabricated based on 76.5T e O 2-6Z n O-11.5L i 2 O-6B i 2 O 3 glass, and its core (slow and fast axes were) measured to be approximately 4.74 µm and 4.29 µm, respectively. The experimentally measured results demonstrated that the maximum supercontinuum (SC) spectra extended from ∼914.1n m to ∼1885.1n m when the polarization state of the pump pulse was parallel to the fast axis at 1400 nm with an average power of 460 mW. We performed numerical simulations based on the nonlinear Schrödinger equation, which support the experimentally measured results. The SC generation in birefringent silica microstructured fiber with the same geometric parameters was simulated, and the results showed that the enhanced nonlinear refractive index of the BTMOF yielded a spectrum with a significantly larger bandwidth. Furthermore, the two polarization states along the fast axis and slow axis exhibit different dispersion characteristics, which provide a convenient way of tuning the properties of the generated SC. This work highlights BTMOF as a promising platform for the development of a SC light source, which can be widely used in food quality inspection, early cancer diagnostics, gas sensing, and high-spatial-resolution imaging.

Maintaining chromatic dispersion and signal gain performances in a chalcogenide buffer step-index optical fiber.

Aiming at maintaining the chromatic dispersion properties and fiber optical parametric amplification (FOPA) performance when fiber core fluctuation occurs, we propose a buffer step-index optical fiber. The AsSe2 chalcogenide glass is employed as the core material due to its high nonlinearity and broad transmission spectrum. The calculated results in this study show that the chromatic dispersion variation due to the change of core diameter can be greatly suppressed and a continuous and very broad FOPA signal gain spectrum can be obtained and maintained by carefully controlling the core, buffer and cladding properties such as refractive index and diameters. The calculated results in this study showed that by using the proposed 3-cm-long fiber pumped at 5.02 µm, a broad signal gain bandwidth from 3 to 14 µm at about 15 dB is attainable although the fiber core diameter Dc drastically fluctuated from 2 to 5 µm and the buffer diameter Db varies from 8.9 to 9.3 µm. Moreover, when Dc varies in smaller range from 3 to 4 µm, the FOPA signal gain spectra calculated at different fixed values of Db in the range from 8.9 to 9.3 µm are highly maintained. When Db is kept at 9.0 µm and Dc varies from 3 to 4 µm, the calculated FOPA signal gain spectra at different pump wavelengths from 4.98 to 5.02 µm are also nearly identical in the wavelength range from 3 up to 13 µm.

Mid-infrared cascaded stimulated Raman scattering and flat supercontinuum generation in an As-S optical fiber pump at 2 µm.

We demonstrate broadband mid-infrared cascaded stimulated Raman scattering (SRS) and flat supercontinuum (SC) generation in a chalcogenide optical fiber made from As2S5 glass. By using a 2 µm nanosecond laser as the pump source, mid-infrared cascaded SRS up to six orders ranging from 2149 to 3425 nm was experimentally observed, and this all-fiber Raman laser operating at 3.43 µm was realized for the first time to our knowledge. By introducing a 2 µm femtosecond laser as the excited source, the broadband flat mid-infrared SC with the spectral range of ∼10dB (from ∼1030 to 3441 nm) was observed. Our results verify that the As2S5 optical fibers possess promising applications for tunable mid-infrared Raman fiber lasers and SC light sources pumped by 2 µm pulsed lasers.

No-core optical fiber sensor based on surface plasmon resonance for glucose solution concentration and temperature measurement.

The accuracy of the surface plasmon resonance (SPR) optical fiber sensor is affected by the change of ambient temperature. Therefore, we propose a simple dual channel SPR optical fiber sensor, which can measure both glucose concentration and ambient temperature. The proposed sensor is a two-channel structure based on a no-core optical fiber (NCF): one channel is coated with gold film and polydimethylsiloxane (PDMS) to sense the ambient temperature, and the other is coated with silver film to sense glucose concentration. The experimental results show that the sensor's sensitivity for sensing glucose concentration is 2.882 nm / %, and for sensing temperature is -2.904 nm / °C. By monitoring the real-time temperature, the accuracy of glucose concentration detection was improved. The proposed sensor has a simple and compact structure, and it is suitable for sensing glucose solution or other analyte solutions that need temperature compensation.

Microstructured optical fiber temperature sensor based on the self-phase modulation effect.

In this paper, we proposed a highly sensitive temperature sensor based on self-phase modulation (SPM) in an in-house fabricated microstructured optical fiber (MOF) which had three rings of air holes. The temperature sensing performance was evaluated by detecting the 3 dB bandwidth of SPM spectrum with the variation of temperature at different pump wavelengths and average pump power. At the pump wavelength of 1400 nm with the average pump power of 600 mW, the temperature sensitivity was obtained to be as high as 1.296 nm/°C. Moreover, the theoretical simulation was carried out, the results of which corresponded well with the experiment. To the best of our knowledge, this is the first experimental study concerning SPM-based temperature sensing. This work proves experimentally and theoretically a new temperature sensing mechanism drawing on the SPM effect in optical fibers, which is expected to develop temperature sensors of low cost, simple structure and high sensitivity.

Supercontinuum-induced multi-wavelength third-harmonic generation in a suspended-core microstructured optical fiber.

In this paper, we reported a multi-wavelength third-harmonic generation (THG) induced by supercontinuum (SC) in an in-house fabricated suspended-core microstructured optical fiber (MOF). The adjustment of pump wavelength and pump power exerted an influence on SC which simultaneously emitted third harmonic (TH) waves in the visible light range. At the pump wavelength of 1220 nm and the average pump power of 450 mW, a multi-wavelength TH spectrum (373∼589 nm) with over twenty distinct peaks was observed under the phase matching (PM) condition between the fundamental mode and the higher-order modes. To the best of our knowledge, this is the first report on THG in optical fibers with so great a number of wavelengths. The maximal THG conversion efficiency ∼6.791 × 10-4 was obtained at 1480 nm, 350 mW, which is highly competitive compared with the values reported previously. Furthermore, theoretical simulation has been carried out, which corresponded well with the experimental observation. This multi-wavelength THG in the suspended-core MOF may provide a unique pathway towards tailored multi-wavelength ultrafast light sources for applications in sensing and imaging technologies.

Supercontinuum generation in a chalcogenide all-solid hybrid microstructured optical fiber.

We report the fabrication of a chalcogenide all-solid hybrid microstructured optical fiber and its application in supercontinuum generation for the first time, to the best of our knowledge. The fiber possesses all-normal and flattened chromatic dispersion, making it highly potential for broad and coherent supercontinuum generation. By pumping the fiber with a femtosecond laser at 3, 4, and 5 µm, broad supercontinua with good spectral flatness are generated. The broadest SC spectrum extending from 2.2 to 10 µm at -20 dB level was obtained when the fiber was pumped at 5 µm with an input power of 3.9 mW.

Intracavity supercontinuum generation in a mode-locked erbium-doped fiber laser based on the Mamyshev mechanism with highly nonlinear fiber.

An all-fiber supercontinuum laser source with a piece of highly nonlinear fiber inserted into a mode-locked fiber laser is experimentally demonstrated. This laser achieves mode-locking based on the Mamyshev mechanism and realizes supercontinuum generation spanning from 1330 nm to 2030 nm directly. Mode-locking based on the Mamyshev mechanism can be obtained easily, and the influence of the parameters of the laser cavity on the supercontinuum laser source is investigated. This supercontinuum laser source has a simple structure, and no amplifier stages are required. It demonstrates intracavity supercontinuum generation in mode-locked fiber laser based on the Mamyshev mechanism and exploits its operation further.

Mid-infrared wavelength conversion using dispersion-engineered As2S5 microstructured optical fiber pumped with an ultrafast laser at 2 µm.

We fabricate a dispersion-engineered As2S5 microstructured optical fiber for demonstration of frequency conversion in one of the atmospheric-transparent windows in the mid-infrared domain. The experimentally obtained results show that parametric wavelength conversion at 4.5 µm is obtained using fabricated microstructured optical fiber pumped with 200 fs laser pulses of average power of 20 mW at 2 µm. Obtained detuning frequency from the pump frequency was ∼84THz. To the best of our knowledge, the mid-infrared wavelength conversion at 4.5 µm in fiber configuration has been demonstrated for the first time. The experimentally observed result matches well with numerically simulated phase-matching conditions.

Theoretical Investigation of an Alcohol-Filled Tellurite Photonic Crystal Fiber Temperature Sensor Based on Four-Wave Mixing.

For this study, a temperature sensor utilizing a novel tellurite photonic crystal fiber (PCF) is designed. In order to improve the sensor sensitivity, alcohol is filled in the air holes of the tellurite PCF. Based on the degenerate four-wave mixing theory, temperature sensing in the mid-infrared region (MIR) can be achieved by detecting the wavelength shift of signal waves and idler waves during variations in temperature. Simulation results show that at a pump wavelength of 3550 nm, the temperature sensitivity of this proposed sensor can be as high as 0.70 nm/°C. To the best of our knowledge, this is the first study to propose temperature sensing in the MIR by drawing on four-wave mixing (FWM) in a non-silica PCF.

Coherent Mid-IR Supercontinuum Generation using Tapered Chalcogenide Step-Index Optical Fiber: Experiment and modelling.

Mid-infrared region of electromagnetic spectrum has increased a lot of scientific and technical interest because of its utility to figure out the molecular fingerprints. Current mid-infrared light sources including quantum cascade lasers, thermal-emitters, and synchrotron radiation are not suitable for various potential applications where we require coherent, portable and broadband light sources. During the current decade, several efforts have been put forwarded to extend the spectral range of the supercontinuum. However, the coherent mid-infrared supercontinuum spectrum in the mid-infrared region has been demonstrated rarely. Here, we demonstrate a coherent mid-infrared supercontinuum using a tapered chalcogenide fiber pumped at various wavelength ranging from 2 µm to 2.6 µm. Experimental observations show that the supercontinuum spectrum extending from ~1.6 µm to 3.7 µm can be achieved using a 3 cm long tapered chalcogenide step-index optical fiber pumped with femtosecond laser pulses at 2.6 µm. To the best of our knowledge, using short pump wavelengths at 2 µm to 2.6 µm in an all-normal dispersion engineered chalcogenide glass fiber, the coherent supercontinuum spectrum has been reported first time. Such coherent broadband light source has its key prominence for the various prospective applications in the fields of bio-medical, sensing, and multiplex coherent anti-Stokes Raman scattering microspectroscopy.

Mid-infrared transmission by a tellurite hollow core optical fiber.

We experimentally demonstrate for the first time a successful fabrication of a tellurite hollow core optical fiber which has a mid-infrared transmission range. The wall thickness of each cladding air-hole is about 2.8 µm and the outer diameter of the full air-hole structure D is approximately 110 µm. The results show that the measured transmission spectrum can expand up to 3.9 µm. In addition, it is expected that the transmission can extend to around 6 µm. When the input light is linearly polarized, it can be maintained after propagating through a 17-cm-long fiber.