High resolution compact spectrometer system based on scattering and spectral reconstruction.

In this Letter, we present a compact scattering spectrometer system based on fluorosilicate glass ceramics. By the algorithmic spectral calibration and reconstruction, we achieve wavelength detection with a resolution of 0.1 nm. Numerous nanocrystals embedded in the glass host in the glass ceramics result in a significant natural multilayer scattering medium, which can provide a 60% scattering efficiency for incident light while increasing the optical path of incident light transmitting in the medium. The glass ceramics scattering medium with a rather compact physical size is integrated with a low-cost camera to compose an optical spectral system, which has potential application in lab-on-a-chip optical spectroscopy.

Extruded TOPAS hollow-core anti-resonant fiber optimized for THz guidance at 0.9THz.

A hollow-core anti-resonant fiber for the THz regime is proposed and demonstrated. The proposed fiber is the hexagonal core shape which is directly extruded using a conventional 3D printer. Experimental results show that by using cyclic olefin copolymer (COC), the proposed fiber design provides a low attenuation of ∼3 dB∕m at ∼ 0.86 THz and ∼15 dB∕m at ∼ 0.42 THz.

Enhanced bandwidth distributed acoustic sensing using a frequency multiplexed pulse train and micro-machined point reflector fiber.

In this Letter, we present an enhanced bandwidth distributed acoustic sensor (DAS) that uses a frequency multiplexed interrogation system to probe a micro-machined point reflector fiber. The fiber contains a series of discrete point reflectors with reflectance as high as -48 dB, while the frequency multiplexed interrogator allows us to increase the effective pulse repetition rate by a factor of 10. Together, this enables a phase noise as low as -101 dB (re rad2/Hz) for a 2.5 km fiber with 10 m spatial resolution, corresponding to a strain noise of 0.095p ε/Hz. This scheme also enables a 10-fold increase in the sensor bandwidth without introducing noise due to interference fading. Finally, we demonstrate sensing at ranges up to 10 km using a fiber containing 1000 point reflectors, illustrating the scalability of this approach.

152 km-range single-ended distributed acoustic sensor based on inline optical amplification and a micromachined enhanced-backscattering fiber.

In this Letter, a distributed acoustic sensor (DAS) with a sensing range in excess of 150 km is reported. This extended sensing range is achieved by adding a low-loss enhanced-backscattering fiber at the far end of a standard single-mode fiber. A conventional DAS system along with inline optical amplifiers are used to interrogate the sensing fiber. The combined system exhibits a minimum detectable strain of 40 nε at 1 Hz over a spatial resolution of 5 m.

Anisotropic nanostructure generated by a spatial-temporal manipulated picosecond pulse for multidimensional optical data storage.

Anisotropic nanostructures can be generated in fused silica glass by manipulating the spatiotemporal properties of a picosecond pulse. This phenomenon is attributed to laser-induced interband self-trapped excitons. The anisotropic structures exhibit birefringent properties, and thus can be employed for multi-dimensional optical data storage applications. Data voxels generated by such short laser irradiation enable on-the-fly high-speed data recording.

Low-noise distributed acoustic sensing using enhanced backscattering fiber with ultra-low-loss point reflectors.

We present a low-noise distributed acoustic sensor using enhanced backscattering fiber with a series of localized reflectors. The point reflectors were inscribed in a standard telecom fiber in a fully automated system by focusing an ultra-fast laser through the fiber cladding. The inscribed reflectors provided a reflectance of -53 dB, significantly higher than the Rayleigh backscattering level of -70 dB/m, despite adding only 0.01 dB of loss per 100 reflection points. We constructed a coherent φ-OTDR system using a double-pulse architecture to probe the enhanced backscattering fiber. Using this system, we found that the point reflectors enabled an average phase noise of -91 dB (re rad2/Hz), 20 dB lower than sensors formed using Rayleigh backscattering in the same fiber. The sensors are immune to interference fading, exhibit a high degree of linearity, and demonstrate excellent non-local signal suppression (>50 dB). This work illustrates the potential for low-cost enhanced backscattering fiber to enable low-noise, long-range distributed acoustic sensing.

All-fiber sixth harmonic generation of deep UV: erratum.

This erratum corrects the mistyped pump repetition rate in Opt. Lett.42, 4671 (2017)OPLEDP0146-959210.1364/OL.42.004671.

Suspended-Core Microstructured Polymer Optical Fibers and Potential Applications in Sensing.

The study of the fabrication, material selection, and properties of microstructured polymer optical fibers (MPOFs) has long attracted great interest. This ever-increasing interest is due to their wide range of applications, mainly in sensing, including temperature, pressure, chemical, and biological species. This manuscript reviews the manufacturing of MPOFs, including the most recent single-step process involving extrusion from a modified 3D printer. MPOFs sensing applications are then discussed, with a stress on the benefit of using polymers.

Novel method for manufacturing optical fiber: extrusion and drawing of microstructured polymer optical fibers from a 3D printer.

Microstructured polymer optical fibers (MPOFs) have long attracted great interest due to their wide range of applications in biological and chemical sensing. In this manuscript, we demonstrate a novel technique of manufacturing MPOF via a single-step procedure by means of a 3D printer. A suspended-core polymer optical fiber has been extruded and directly drawn from a micro-structured 3D printer nozzle by using an acrylonitrile butadiene styrene (ABS) polymer. Near-field imaging at the fiber facet performed at the wavelength λ~1550 nm clearly indicates guidance in the fiber core. The propagation loss has been experimentally demonstrated to be better than α = 1.1 dB/cm. This work points toward direct MPOFs manufacturing of varieties of materials and structures of optical fibers from 3D printers using a single manufacturing step.

5.6 kW peak power, nanosecond pulses at 274 nm from a frequency quadrupled Yb-doped fiber MOPA.

A 2 W deep-ultraviolet (DUV) source at 274 nm with 5.6 kW peak power is demonstrated by frequency quadrupling a diode-seeded, polarization-maintaining (PM), Yb-doped fiber master oscillator power amplifier (MOPA) system delivering 1.8 ns pulses at a repetition rate of 200 kHz. The second harmonic generation (SHG) and the fourth harmonic generation (FHG) are achieved by using Lithium Triborate (LBO) crystal and ß-BaB2O4 (BBO) crystal in sequence, with an IR-to-green and green-to-UV conversion efficiency of up to 65% and 26%, respectively. This is the first kW peak power pulsed UV system reported at 274 nm which has great potential for machining insulators, 2D materials, isotopic separation of Calcium-48, and fluorescence analysis of biological molecules.

All-fiber sixth-harmonic generation of deep UV.

We simulate and experimentally demonstrate deep ultraviolet generation from a 1550 nm laser source in a fully fiberized system by cascading second- and third-harmonic generation using a periodically poled silica fiber and an optical sub-micron diameter fiber. Harmonic generation is achieved by harnessing intermodal phase matching in optical microfibers and a permanent χ(2) induced via thermal poling. As a result, efficient nonlinear processes can be observed, despite the low third-order nonlinear susceptibility of silica glass.

Void-nanograting transition by ultrashort laser pulse irradiation in silica glass.

The structural evolution from void modification to self-assembled nanogratings in fused silica is observed for moderate (NA > 0.4) focusing conditions. Void formation, appears before the geometrical focus after the initial few pulses and after subsequent irradiation, nanogratings gradually occur at the top of the induced structures. Nonlinear Schrödinger equation based simulations are conducted to simulate the laser fluence, intensity and electron density in the regions of modification. Comparing the experiment with simulations, the voids form due to cavitation in the regions where electron density exceeds 1020 cm-3 but is below critical. In this scenario, the energy absorption is insufficient to reach the critical electron density that was once assumed to occur in the regime of void formation and nanogratings, shedding light on the potential formation mechanism of nanogratings.

Tailored surface birefringence by femtosecond laser assisted wet etching.

Surface texturing is demonstrated by the combination of wet etching and ultrafast laser nanostructuring of silica glass. Using potassium hydroxide (KOH) at room temperature as an etchant of laser modified glass, we show the polarization dependent linear increase in retardance reaching a threefold value within 25 hours. The dispersion control of birefringence by the etching procedure led to achromatic behaviour over the entire visible spectral range. The mechanism of enhanced KOH etching selectivity after femtosecond laser exposure is discussed and correlated to the formation of various laser-induced defects, such as silicon-rich oxygen deficiency and color centers.

Airy beams generated by ultrafast laser-imprinted space-variant nanostructures in glass.

We demonstrate a technique to generate accelerating Airy beams with a femtosecond laser-imprinted space variant birefringent structure in silica glass. Our approach enables the generation of dual Airy beams with polarization sensitive beam deflection. The produced beam is used for the glass scribing. After the glass-breaking process, a spontaneous self-detachment of a fiber-like structure occurs that can be exploited as an alternative way for fabricating glass cantilevers.

Seemingly unlimited lifetime data storage in nanostructured glass.

We demonstrate recording and retrieval of the digital document with a nearly unlimited lifetime. The recording process of multiplexed digital data was implemented by femtosecond laser nanostructuring of fused quartz. The storage allows unprecedented parameters including hundreds of terabytes per disc data capacity, thermal stability up to 1000 °C, and virtually unlimited lifetime at room temperature. We anticipate that this demonstration will open a new era of eternal data archiving.

Stress distribution around femtosecond laser affected zones: effect of nanogratings orientation.

Under certain exposure conditions, femtosecond lasers create nanogratings in the bulk of fused silica for which the orientation is governed by the laser polarization. Such nanostructure induces stress that affects optical and chemical properties of the material. Here, we present a method based on optical retardance measurement to quantify the stress around laser affected zones. Further, we demonstrate stress dependence on the nanogratings orientation and we show that the stress within single nanogratings lamellae can locally be as high as several gigapascals.

Femtosecond versus picosecond laser machining of nano-gratings and micro-channels in silica glass.

The ability of 8 picosecond pulse lasers for three dimensional direct-writing in the bulk of transparent dielectrics is assessed through a comparative study with a femtosecond laser delivering 600 fs pulses. The comparison addresses two main applications: the fabrication of birefringent optical elements and two-step machining by laser exposure and post-processing by chemical etching. Formation of self-organized nano-gratings in glass by ps-pulses is demonstrated. Differential etching between ps-laser exposed regions and unexposed silica is observed. Despite attaining values of retardance (>100 nm) and etching rate (2 µm/min) similar to fs pulses, ps pulses are found unsuitable for bulk machining in silica glass primarily due to the build-up of a stress field causing scattering, cracks and non-homogeneous etching. Additionally, we show that the so-called "quill-effect", that is the dependence of the laser damage from the direction of writing, occurs also for ps-pulse laser machining. Finally, an opposite dependence of the retardance from the intra-pulse distance is observed for fs- and ps-laser direct writing.

Extraordinary anisotropy of ultrafast laser writing in glass.

The unusual dependence of femtosecond laser writing on the light polarization and direction of raster scanning is demonstrated in silica and chalcogenide glasses. Two different mechanisms contributing to the observed anisotropy are identified: the chevron-shaped stress induced by the sample movement and the pulse front tilt of ultrashort light pulse. Control of anisotropies associated with the spatio-temporal asymmetry of an ultrashort pulse beam and scanning geometry is crucial in the ultrafast laser machining of transparent materials.

Polarization sensitive camera by femtosecond laser nanostructuring.

A polarization imaging device based on a femtosecond laser nanostructured birefringent array is demonstrated. The device enables instant measurement of the distribution of the Stokes vectors in the visible spectrum. Polarimetric measurements with radially and circularly polarized light distributions are demonstrated.

Compact high-resolution FBG strain interrogator based on laser-written 3D scattering structure in flat optical fiber.

We demonstrate a fiber Bragg grating (FBG) strain interrogator based on a scattering medium to generate stable and deterministic speckle patterns, calibrated with applied strain, which are highly dependent on the FBG back-reflection spectral components. The strong wavelength-dependency of speckle patterns was previously used for high resolution wavemeters where scattering effectively folds the optical path, but instability makes practical realization of such devices difficult. Here, a new approach is demonstrated by utilizing femtosecond laser-written scatterers inside flat optical fiber, to enhance mechanical stability. By inscribing 15 planes of pseudo-randomized nanovoids (714 [Formula: see text] 500 voids per plane) as a 3D array in a 1 [Formula: see text] 0.7 [Formula: see text] 0.16 mm volume, the intrinsic stability and compactness of the device was improved. Operating as a wavemeter, it remained stable for at least 60 h with 45 pm resolution over the wavelength range of 1040-1056 nm. As a reflection mode FBG interrogator, after calibrating speckle patterns by applying tensile strain to the FBG, the device is capable of detecting microstrain changes in the range of 0-200 [Formula: see text] with a standard error of 4 [Formula: see text], limited by the translation stage step size. All these characteristics make it an interesting technology for filling the niche of low-cost, high-resolution wavemeters and interrogators which offer the best available trade-off between resolution, compactness, price and stability.