A promising technique for inscribing long period fiber gratings (LPFGs) was demonstrated by only using a commercial splicer. The commercial splicer was developed secondarily to build up a new program for periodically tapering a single mode fiber. High-quality LPFGs with a low insertion loss of ∼1 dB and a large resonant attenuation of more than −30 dB were achieved. The achieved periodic tapers exhibited an excellent reproducibility with a small error of less than ±0.3 µm.To the best of our knowledge, it is the minimum reproducibility error of tapers achieved by arc discharge technique so far. Near mode fields of three LPFG samples with different pitches were observed to investigate the mode coupling in the taperinscribed LPFGs. In addition, the resonant wavelengths of our taper-inscribed LPFGs exhibited a blue shift first and then red shift with an increased number of grating periods, resulting from residual stress relaxation together with physical deformation.
We report a method for effective fabrication of Bragg gratings in all-silica photonic crystal fibers (PCF). The problem of cladding-hole scattering in PCF grating inscription is avoided by selectively inflating a section of PCF, resulting a locally suspended-core fiber (SCF) region with relatively simple cladding structure. Hence, the inscription laser can laterally access to the core region with little loss. In the SCF regions with core diameter ranging from 2 to 4.5 μm, first-order Bragg gratings are fabricated by use of a phase mask and a focused infrared femtosecond laser with pulse energy as low as ~200 μJ. For the same grating period, samples with different core sizes exhibit different resonant wavelengths and spectral properties, which would enable a range of applications in grating-integrated PCF sensors and devices.
Discriminating edible oils from gutter oils has significance in food safety, as illegal gutter oils cannot meet a variety of criteria such as the acid value, peroxide value and quality. To discriminate these illegal cooking oils, we propose an ultrasensitive optofluidic detection method based on a hybrid-waveguide coupler. Prior to the straight waveguide inscription in the cladding of the silica tube using a femtosecond laser, a section of coreless fibre is firstly spliced with the ST to supply a platform for the inscription of an S-band waveguide. Then a pair of microfluidic channels are ablated on the ST using the fs laser to enable liquid analytes to flow in and out of the air channel. In the transmission spectrum, a unique resonant loss dip can be observed, which is produced by coupling the light from the laser inscribed waveguide to the liquid core when the phase-matching condition is met. This hybrid-waveguide coupler with a simplified structure realizes dynamic optofluidic refractive index sensing with an ultrahigh sensitivity of -112 743 nm RIU, a detection limit of 2.08 × 10 RIU and a refractive index detection range from 1.4591 to 1.4622. This novel method can be used for food safety detection, specifically, for the discrimination of gutter oils.
Nanomechanical bolometers have proven to be well suited to the analysis of light. However, conventional wafer-based devices have limited practical applications because they require special vacuum chambers, cryogenic temperatures, bulky space optical components, and/or complex circuitry. The present work developed a nanoscale optomechanical bolometer intended for photothermal sensing using an all-optical actuation and measurement approach. The proposed bolometer is compact and has an integrated all-optical-fiber structure based on fabricating a Fabry− Perot interferometer incorporating multilayer graphene at the fiber tip and packaged in a small vacuum-sealed tube. This microscale vacuum packaging doubled the signal-to-noise ratio compared with that in air. This miniature all-fiber nanoscale optomechanical bolometer also exhibited a high resolution with photothermal sensitivities of approximately 6.23 and 6.44 kHz/μW when using the second-order mode at room temperature and 0 °C, respectively. This design could be beneficial for applications outside specialized laboratories with uses in the fields of medicine, industrial manufacturing, nanoscience, and astronomy.
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