Performance comparison of Zn-MOF and Nb2CTx/Co3O4 coatings on side-polished fibers for enhanced four-wave mixing at 1.5 µm

We demonstrated temperature sensing of a fiber with nanostructured cladding, which was constructed by titanium dioxide TiO2 nanoparticles self-assembled onto a side polished optical fiber (SPF). Significantly enhanced interaction between the propagating light and the TiO2 nanoparticles (TN) can be obtained via strong evanescent field of the SPF. The strong light-TN interaction results in temperature sensing with a maximum optical power variation of ~4dB in SPF experimentally for an external environment temperature varying from -7.8°C to 77.6°C. The novel temperature sensing device shows a linear correlation coefficient of better than 99.4%, and a sensitivity of ~0.044 dB/°C. The TN-based all-fiber-optic temperature sensing characteristics was successfully demonstrated, and it is compatible with fiber-optic interconnections and high potential in photonics applications.

A high sensitive volatile organic compounds (VOCs) gas sensor using side-polished optical fiber was developed in this study. The surface of the side-polished optical fiber coupled with the coated solvatochromic dye which has charge-transfer (CT) characters. Dimethylamine, acetic acid, toluene, benzene, and ethanol 5-types of VOCs gases were detected in this study. The different polarities of the VOCs gases cause different CT and different effective refractive index changings of the sensing membrane, which can lead to the resonance wave length of the side-polished optical fiber changed. According to the results, we found that the side-polished optical fiber sensor has good selectivity and high sensitivity properties.

We have developed a novel approach for fabricating and testing optical ring resonators. Using a side-polished optical fiber and fabricating a ring waveguide directly over its core, an efficient and passive signal filter in the 1.55 um telecommunication band is created. A standard single mode optical fiber is permanently secured in an arcing groove in quartz and is side polished proximally to its core. The ring resonator is fabricated using two-photon initiated free-radical polymerization of tri-functional acrylate on low-index quartz substrate with a 100 femtosecond pulsed Ti/sapphire laser. The quartz substrate is inverted and vacuum mounted to an X-Y-Z stage so that the polymer ring waveguide can be positioned directly above the core of the fiber forming a vertically coupled ring resonator. Our technique allows infinite variation of the width, height, diameter and location (therefore the coupling strength between the fiber and the ring) of the ring resonator waveguide. This approach enables resonators to be fabricated, tested and subsequently removed multiple times on the same side-polished fiber, refining both the ring resonator geometry and materials. Because it is a fiber-based device, it possesses negligibly low optical insertion loss and can be used for fixed and tunable wavelength filters, intensity modulators, and fiber-optic sensors. Both theoretical analysis and experimental data will be presented.

Application of micro-electro-mechanical system (MEMS) technology for controlling the evanescent field is attractive because the dimension of the evanescent field is of the same order as that of the movement distance of the MEMS device. Two different types of MEMS-based devices are proposed and developed for controlling the evanescent field generated at the surface of the side-polished optical fiber. The first one is a hybrid type and the other is a monolithic type. Both devices have merit and demerit from the aspects of process ease and alignment. The hybrid-type of device has a problem of close contact of the diaphragm with the side-polished optical fiber. The monolithic-type of device is a pre-aligned structure but has a difficulty in terms of polishing depth control on the single mode fiber. A change in the transmission spectrum due to device operation (movement of diaphragm with respect to polished optical fiber surface) has been noticed. However, the extent of change in transmission has to be improved. Fine control of polishing depth and parallel alignment of side-polished fiber with a diaphragm are the critical factors for effective interaction of the diaphragm with an evanescent field.

In this report, we investigate the effects of Ag/TiO2 integrated in side polished optical fiber. Several layers of Ag thickness has been deposited on glass substrates using electron beam (e-beam) evaporation technique in order to determinate the influence of silver with combination of TiO2 on final properties of the sensor. Several thicknesses of Ag NPs were sets to 5 nm, 7 nm, 12 nm, and 16 nm. Another layer of metal oxide, specifically titanium oxide (TiO2) is introduced, covering the Ag layer to study the effect of metal oxides toward the performance of the device. The morphology of the samples was observed using a field-emission scanning electron microscope (FESEM), Raman UV–Vis spectroscopy and Raman photoluminescence (PL) spectroscopy. A CST Microwave used to observe the electric field distribution for all the samples to support the experimental findings. Based on the simulation analysis, two thicknesses of Ag layers (7 nm and 16 nm) were selected to be coated on a side polished optical fiber and tested as a humidity sensor. TiO2 layer was introduced to see the enhancement in the sensing measurements as a suitable material for trapping the photo generated electrons and avoiding charge recombination. From this observation, it can be conclusively shows that the sensitivity of the sensor is improved with integration of Ag NPs and TiO2. Based on the experimental results, the sensor of Ag/TiO2 with 7 nm of Ag layers shows the best characteristics in humidity sensing with good sensitivity and linearity of 0.9201% and 13.4 mW/% RH, respectively.

Side-polished optical fiber has long been used to build fiber sensors in a range of applications. In this work, we demonstrate a biochemical sensor application leading to sodium nitrate solutions enhanced by the interaction of multi-walled carbon nanotubes (MWCNTs) with evanescent field of propagating light in a side-polished optical fiber. Insertion loss of this sensor was estimated to be around 5 dB, which is quite high and close to the core index of the polished fiber. The influence of MWCNTs film, particularly on its sensitivity to sodium nitrate, was investigated by coating single drop of MWCNTs on a side-polished single mode fiber. It is observed the improvement of sensitivity with MWCNTs coated side-polished optical fiber has reached 0.125 dBm/°C near the resonant wavelength of 1550 nm. The experimental results clearly verify the present of MWCNTs on side-polished optical fiber has slightly influence the performance of the fiber. The output power values and shifting of the spectral positions were observed during the sensor tests by exposure of the sodium nitrate solutions with increasing concentration from 1 to 7%.

Application of micro-electro-mechanical system (MEMS) technology for controlling the evanescent field is attractive because the dimension of the evanescent field is of the same order as that of the movement distance of the MEMS device. Two different types of MEMS-based devices are proposed and developed for controlling the evanescent field generated at the surface of the side-polished optical fiber. The first one is a hybrid type and the other is a monolithic type. Both devices have merit and demerit from the aspects of process ease and alignment. The hybrid-type of device has a problem of close contact of the diaphragm with the side-polished optical fiber. The monolithic-type of device is a pre-aligned structure but has a difficulty in terms of polishing depth control on the single mode fiber. A change in the transmission spectrum due to device operation (movement of diaphragm with respect to polished optical fiber surface) has been noticed. However, the extent of change in transmission has to be improved. Fine control of polishing depth and parallel alignment of side-polished fiber with a diaphragm are the critical factors for effective interaction of the diaphragm with an evanescent field.

A temperature fiber sensor with nanostructured cladding composed ted by titanium dioxide (TiO2) nanoparticles was demonstrated. The nanoparticles self-assembled onto a side polished optical fiber (SPF). The enhancement of interaction between the propagating light and the TiO2 nanoparticles (TN) can be obtained via strong evanescent field of the SPF. The strong light–TN interaction gives rise to temperature sensing with a optical power variation of ~4dB in SPF experimentally for an environment temperature ranging from -7.8°C to 77.6°C. The novel temperature sensor shows a sensitivity of ~0.044 dB/°C. The TN-based fiber-optic temperature sensor is facile to manufactured, compatible with fiber-optic interconnections and high potential in photonics applications.

A side-polished plastic optical fiber is proposed as the line source of a linear fiber array in a liquid level sensor. We hope the leakage light power of side-polished plastic optical fiber along the axial direction is constant. To that end, the transmission characteristics of the line source is investigated, and a formula describing the relationship between the polished depth and the side leak light power is developed with a simple method. A 300 mm long gradient side-polished plastic optical fiber is fabricated according to the theoretical conclusion, its side-leak light power is measured and the measurement results are discussed.

One important use of molybdenum disulfide (MoS2) could be in making sensing and detection devices with optical chip or fiber. Here, MoS2 nanosheets coated on side-polished optical fiber (SPF) is proposed, which can enhance the localized interaction between evanescent light of fiber core and MoS2 nanosheets, this can motivate greatly sensing and detection performance. Moreover, the MoS2 nanosheet possesses exceedingly high surface/volume ratio. By combining the MoS2 nanosheets and the side-polished fiber, humidity sensing characteristics has been demonstrated. The optical transmitted power (OTP) of the MoS2-based SPF changes with a negative correlation to the variation of relative humidity (RH) in experiments. The OTP changes of the MoS2-based SPF as an exponential function can reach ~13.5dB (~54 fold enhancement) when the RH ranges from 40%RH to 85%RH. Furthermore, experiments on the monitoring of human breath have also been conducted to evaluate the response time (0.85 s) and the recovery time (0.85 s). The performance comparison between this proposed device and the other recent-developed fiber-optic humidity sensing devices in literature illustrates the superiority of the MoS2-based SPF in humidity sensing and monitoring of human breath, which paves a path for the MoS2 nanosheets to integrate in lab-on-fiber sensing and detection devices.

Optical resonance coupling between a side-polished fiber and thin film waveguides has been investigated in the presence of biochemical adsorbates. The shift of the resonance wavelengths was found to be highly sensitive to the capture of target DNA recognition elements with Au nanoparticle markers, allowing for a sensitivity limit of 10 particles on the side-polished fiber core area (2000 μm²) during on-line measurements using a polychromator spectrometer.

A novel fiber optical device based on microring resonators fabricated on side-polished fiber is proposed. The compact size and light weight device structure can be useful for various fiber-optic sensors, fixed and tunable wavelength filters, and intensity modulators. Since the device is directly fabricated on the optical fiber, many issues associated with fiber-to-chip coupling and attachment can be avoided. A preliminary experiment using polymer microring resonators made by two-photon polymerization has proved this new device concept.

Ultrasound generators have been studied for ultrasound non-destructive testing (NDT) and biomedical ultrasound imaging. Fiber-optic ultrasound generators, based on photoacoustic (PA) principle, are promising devices for these applications. Their compact sizes enable them to work in restricted space; the acoustic properties of the ultrasound signal can be easily tailored by the optical signal. This paper demonstrates a novel structure with which the ultrasound signal is generated on a side-polished fiber. The fiber was mounted on a steel plate and the ultrasound signal was detected on the back surface of the steel plate. The fiber's ability of generating ultrasound was verified and the distribution of the acoustic signal along the fiber was measured.

A theoretical presentation by using a three-dimensional finite difference beam propagating method (3-D FD-BPM) for the evanescent coupling is offered with respect to the refractive indexes between a side-polished optical fiber and an infinitely planar waveguide with a conductor cladding (PWGCC). The PWG is suspended at a constant distance from an unclad fiber core and attached with a perfect conductor (PEC) on one side. The coupling and propagation of light are found to depend on both the relationship between the refractive index values of two structures and the configuration of the side-polished fiber used in the PWGCC. The spreading of light in the unconfined direction of a PWGCC is presented with the distribution of electric fields in xy - plane and the absolute amplitude of electric fields along the x and y axis. The power of the light propagation in a fiber decreases exponentially along the fiber axis as it is transferred to the PWGCC, where it is carried away.

Analysis of the four wave mixing effect (FWM) in a dispersion decreasing fiber (DDF) for a WDM system