Tip Of Single-mode Optical Fibers Research Articles

Excitation of Whispering Gallery Modes of a Microresonator Integrated in an Optical Fiber Axicon

We report novel designs to excite Whispering Gallery Mode (WGM) of spherical microresonator in an integrated single mode optical fiber tip probe, namely, Deep Seated Negative Axicon (DSNA). The empty DSNA and partially filled polymer DSNA are explored to host the Barium Titanate/Silica microresonator as WGM resonators. An SLD source with a central wavelength of 840 nm and bandwidth of 50 nm is used to excite the microresonator. Reflected spectra are recorded in a spectrometer through an optical circulator for different resonators at various locations. Experimentally the quality factor Q as high as ~ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$7\,\,\times10$ </tex-math></inline-formula> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> is achieved from the design. It is observed that spectral characteristics and Q value are affected by the resonator’s position, size and the material. The Finite Element Method (FEM) simulation results have also been included in support of the design.

Performance evaluation of a single mode optical fiber tip sensor for glucose detection

&lt;p&gt;Glucose must be carefully regulated to ensure its safety and quality. Nowadays, chemists often face difficulty to measure glucose concentrations as the current methods for the analysis are expensive and require complex procedures which have reduced the interest among chemists to use these techniques. This study evaluated the performance of a single mode optical fiber tip sensor for glucose detection. The sensing mechanism mainly depends on the Fresnel’s reflection that occurs at the flat fiber tip region while the sensor performance was evaluated based on its sensitivity and linearity. The sensor was tested in glucose solution at different concentration range; high range (0% - 14%), medium range (0% - 1.4%) and low range (0% - 0.14%). The sensor showed a good performance when sensing the glucose solution at high and medium concentration range with strong linearity of more than 90% and an average sensitivity of 0.0979 dBm/% and 0.1019 dBm/%, respectively. However, the low concentration range showed no significant changes during sensing. Based on the findings obtained in this study, the optical fiber tip sensor has the potential to be utilized for glucose detection and suitable for high and medium concentration range measurement.&lt;/p&gt;

Validation of an ultrasound transducer's generation and receiving function on one single-mode fiber

This paper presents the design, fabrication and testing of a single-mode fiber optic ultrasound transducer. This transducer can work as an ultrasound generator and a receiver, based on principles of photoacoustic (PA) effect and Fabry–Pérot (FP) interference. PA effect is a process in which ultrasound waves are generated from optical energy by a PA material, and an FP structure is used for ultrasound receiving. The transducer was manufactured by coating a material called gold nanocomposite directly onto a single-mode optical fiber tip. The gold nanocomposite acted as the PA material and formed the FP structure as well. The transducer had the same size as the single-mode fiber, whose diameter was only 125 μm. It demonstrated its ability to generate ultrasound signals with a bandwidth of 5.6 MHz at an efficiency of 3.2 × 10−5 and function as an ultrasound receiver with a sensitivity of 2.81 mV/MPa. The generator and receiver built together can currently only work separately. This new transducer has substantial potential to work in restricted space and harsh environments for non-destructive testing.

Grating-coupling-based excitation of Bloch surface waves for lab-on-fiber optrodes.

In this paper, we investigate the possibility to excite Bloch surface waves (BSWs) on the tip of single-mode optical fibers. Within this framework, after exploring an idealized, proof-of-principle grating-coupling-based scheme for on-tip excitation of BSWs, we focus on an alternative configuration that is more robust with respect to fabrication-related non-idealities. Subsequently, with a view towards label-free chemical and biological sensing, we present a specific design aimed at enhancing the sensitivity (in terms of wavelength shift) of the arising resonance with respect to changes in the refractive properties of the surrounding environment. Numerical results indicate that the attained sensitivities are in line with those exhibited by state-of-the-art plasmonic bioprobes, with the key advantage of exhibiting much narrower spectral resonances. This prototype study paves the way for a new class of miniaturized high-performance surface-wave fiber-optic devices for high-resolution label-free optical biosensing, and represents an important step forward in the "lab-on-fiber" technology roadmap.

Optical fiber tip-based quartz-enhanced photoacoustic sensor for trace gas detection

We reported the development of an evanescent-wave quartz-enhanced photoacoustic sensor (EW-QEPAS) using a single-mode optical fiber tip for sensitive gas detection in the extended near-infrared region. It is a spectroscopic technique based on the combination of quartz-enhanced photoacoustic spectroscopy with fiber-optic evanescent-wave absorption to achieve low optical noise, easy optical alignment, and high compactness. Carbon monoxide (CO) detection at 2.3 μm using a fiber-coupled, continuous-wave, distributed-feedback laser was selected for the sensor demonstration. By tapering the optical fiber down to 2.5 μm diameter using the flame-brushing technique, an evanescent field of ~0.6 mW around the fiber tip was absorbed by CO molecules. Besides an excellent linear response (R 2 = 0.9996) to CO concentrations, the EW-QEPAS sensor achieved a normalized noise-equivalent absorption (NNEA) coefficient of 8.6 × 10−8 cm−1W/√Hz for an incident optical power of 1.8 mW and integration time of 1 s. The sensor detection sensitivity can be further improved by enhancing the evanescent-wave power on the fiber tip.

Single-mode optical fiber connectors for optical accessing

With a view to improving the core illumination technique to confirm the optical fiber core in construction and maintenance, a structural design is presented for a single-mode optical connector with an optical accessing function that enables monitoring the illumination signal and with a capability of injecting the illumination signal externally. In this paper, an optical waveguide is placed from the single-mode optical fiber tip to contact with the latter. The other end of the optical waveguide is removed from the container. Next, the relationship between the connecting loss of the proposed connector and the monitoring efficiency, the one between the index of refraction of the UV epoxy for connecting the optical waveguide and the monitoring efficiency, and that between the connecting loss and the injection efficiency are studied so that the structural design of the present connector is established. Further, an optical connector was fabricated for trial. When the sum of the monitoring efficiency and the injection efficiency is −75.6 dB for the optical source wavelength of λ = 1.3 μm and is −80.8 dB for λ = 1.55 μm. Since the minimum receiving level of the receiver is −90 dBm and the maximum output power of the source is +10 dBm, it is confirmed that the illuminating signal light can be injection detected at an arbitrary connecting point.