Microfiber Loop Resonator Research Articles

Optical microfiber loop resonator for gas pressure sensing

Based on theoretical modeling of optical microfiber loop resonator (MLR) and Hauf-Grigull relation, we have combined the ability of MLR in the sensing of ambient refractive index to the linear dependence of the refractive index of gases to the pressure and introduced the MLR structure for gas pressure sensing. The simulation results show the reduction in the microfiber radius increases the sensitivity of the sensor. Also, due to the significant difference between the sensitivities of some gases such as O2 and CO2, we have proposed this sensor to detect the type of such gases.

ZnO nanorods coated microfiber loop resonator for relative humidity sensing

This paper reported a new humidity sensor, employing microfiber loop resonator (MLR) coated with Zinc Oxide (ZnO) as a probe. The MLR was constructed from a silica tapered fiber with a waist diameter of 7 µm, which was prepared using flame brushing technique. The self-touching loop was coated by ZnO using sol–gel method. A significant response to humidity changes from 35%RH to 85%RH was observed due to the changeable refractive index of the ZnO coating material which modified the light propagation at the output of the MLR. The result shows that the sensitivity of the proposed sensor increases by a factor of 2 as compared to the uncoated MLR. The output power of the ZnO coated MLR drops linearly from −29.3 dBm to −43 dBm when relative humidity increases from 35%RH to 85%RH. The linearity and resolution of the ZnO coated MLR also outperformed the uncoated MLR with 99.4% and 0.013%RH respectively.

Microfiber loop resonator for formaldehyde liquid sensing

This work employed the whispering gallery mode (WGM) of microfiber loop resonator (MLR) for formaldehyde (CH2O) liquid sensing application. A significant sensing response to different concentrations of formaldehyde liquid from 0% to 5% was observed due to the surface absorption and changeable refractive index resulting in different light attenuation in the silica microfiber. As the concentration increases, the output power of the MLR decreased linearly from −18.9 dB m to −36.2.dBm with sensitivity increased by a factor of 2.5 as compared to straight microfiber (SmF). As for resolution, the MLR improved by a factor of 3.28 as compared to SmF.

Optical characterization of microfiber loop resonator towards humidity sensing

Microfiber loop resonator (MLR) fabricated by using silica fiber for relative humidity (RH) sensing application is reported. The silica fiber was tapered to achieve waist diameter of 5 µm using flame brushing technique. The MLR with a 300 µm diameter loop microfiber was formed by manually twisted the tapered fiber. Initially, the effect of whispering gallery modes (WGMs) on the MLR was observed. Transmission mode spectra were observed to determine the number of resonated wavelength and quality factor (Q-factor). The Q-factor for MLR is observed to be > 105 which is a good attribution for sensing application. A significant response to RH from 35% to 85% was observed due to the change of resonating behaviour of MLR across the RH range. The sensing sensitivity increased by a factor of 8.15 in MLR compared to the straight microfiber (SF) structure. As the RH increased, the output power of the MLR decreased linearly from -43.05 dBm to -46.81 dBm with linearity and resolution of 95.91% and 0.153% RH respectively.

Optical characterization of different waist diameter on microfiber loop resonator humidity sensor

In this paper, the effect of different waist diameter on silica microfiber loop resonator (MLR) relative humidity (%RH) sensor is reported. The silica fiber was tapered to vary the waist diameter to 3 μm, 4 μm, 5 μm,7 μm, 8 μm and 10 μm using flame brushing technique. The MLR with a 300 μm diameter loop was formed by manually twisted the tapered fiber under an optical microscope into a self-touching loop. Initially, the effect of whispering gallery modes (WGMs) on the MLR was observed. Transmission mode spectra were observed to determine the number of resonated wavelength and quality factor (Q-factor). The Q-factor is observed to be >105 for all samples and MLR with 3 μm diameter achieve the highest Q-factor value. A significant response to %RH from 35% to 85% was observed due to the change of refractive index between the MLR and the surrounding medium resulting different light attenuation in the microfiber. The sensitivity increased by a factor of 12.2 for the MLR with diameter of 7 μm as compared to the smaller diameter MLRs and a factor of 13.7 as compared to straight microfiber (SmF). As for resolution, the MLR with waist diameter of 7 μm improve by a factor of 5 as compared to the smaller waist diameter and a factor of 6.5 as compared to SmF. The proposed humidity sensor employs the microfiber loop resonator without any sensitive material coated on it which reduced the complexity during the fabrication and manufacturing process. The reported results may contribute to the optimal waist diameter of microfiber loop resonators for humidity sensing application.

LeTrungThanh Optical Biosensors Based on Multimode Interference and Microring Resonator Structures

LeTrungThanh Optical Biosensors Based on Multimode Interference and Microring Resonator Structures

A Review of Microfiber-Based Temperature Sensors.

Optical microfiber-based temperature sensors have been proposed for many applications in a variety of industrial uses, including biomedical, geological, automotive, and defense applications. This increasing demand for these micrometric devices is attributed to their large dynamic range, high sensitivity, fast-response, compactness and robustness. Additionally, they can perform in-situ measurements remotely and in harsh environments. This paper presents an overview of optical microfibers, with a focus on their applications in temperature sensing. This review broadly divides microfiber-based temperature sensors into two categories: resonant and non-resonant microfiber sensors. While the former includes microfiber loop, knot and coil resonators, the latter comprises sensors based on functionally coated/doped microfibers, microfiber couplers, optical gratings and interferometers. In the conclusions, a summary of reported performances is presented.

PMMA microfiber loop resonator for humidity sensor

A PMMA microfiber loop resonator (PMLR) coated with zinc oxide (ZnO) nanostructure is proposed and demonstrated for the monitoring of relative humidity. The PMLR has a loop diameter of 56μm and was fabricated using direct drawing technique using a 6μm diameter PMMA microfiber. The results showed an increase in the sensitivity of the sensor with the additional coating of ZnO nanostructure on the surface of the PMMA fiber. The working mechanism of the device is based on the observed decrement in the transmission of the sensor that was carefully placed in a sealed chamber. As the relative humidity level varies from 20% to 80%, the output power of the PMLR with ZnO nanostructure coating decreases linearly from −9.57dBm to −20.19dBm with a maximum sensitivity, linearity and resolution of 0.1746dBm/%, 94% and 6.17%, respectively. This work is highly beneficial as it combines the high sensitivity obtained by using traditional silica fibers but with the ruggedness and flexibility of PMMA fibers, making them highly suitable for continuous monitoring of relative humidity in compact areas.

A PMMA microfiber loop resonator based humidity sensor with ZnO nanorods coating

Abstract A Polymethyl methacrylate (PMMA) microfiber loop resonator (PMLR) coated with zinc oxide (ZnO) nanorods is proposed and demonstrated for the monitoring of relative humidity (RH) of the surrounding air. Relative humidity refers to the amount of moisture in the air relative to the total amount of moisture that the air can contain. The PMLR has a loop diameter of 42 μm and was fabricated using a direct drawing technique using an 8 μm diameter PMMA microfiber. The results showed an increase in the sensitivity of the sensor with the additional coating of the ZnO nanorods on the surface of the PMMA fiber. The working mechanism of the device is based on the observed increment in the transmission of the sensor that was carefully placed in a sealed chamber. As the relative humidity level increases from 50%RH to 80%RH, the output power of the PMLR with ZnO nanorods coating decreases linearly from −37.77 dBm to −52.99 dBm with a maximum sensitivity, linearity and resolution of 0.5221 dBm/%RH, more than 99% and 0.4094%RH, respectively. This work is highly beneficial as it combines the high sensitivity of traditional silica fibers with the ruggedness and flexibility of PMMA fibers, making them highly suitable for continuous monitoring of relative humidity in compact areas.

PMMA microfiber coated with ZnO nanostructure for the measurement of relative humidity

PMMA microfibers coated with zinc oxide (ZnO) nanostructure are demonstrated for relative humidity monitoring. The fabrication of two different microfiber structures, namely the straight PMMA microfiber and the PMMA microfiber loop resonator (PMLR) were performed by using the direct drawing technique. The sensitivities of the PMMA microfibers were compared and analyzed. The results implied that the PMLR is more sensitive than the straight PMMA microfiber and the sensitivity of the sensors were further increased with the additional coating of ZnO nanostructure on the surface of the PMMA fiber.

Highly Sensitive Current Sensor Based on an Optical Microfiber Loop Resonator Incorporating Low Index Polymer Overlay

A highly sensitive current sensor based on an optical microfiber loop resonator (MLR) incorporating low index polymer is proposed and experimentally demonstrated. The microfiber with a waist diameter of 2 μm is wrapped around the nichrome wire with low index polymer overlay to realize the MLR as the highly sensitive current sensor. Low index polymer overlay can successfully reduce round-trip fractional loss resulting in the improvement of the Q-factor ( Q ) and the finesse ( F ) of the MLR around the nichrome wire. The use of the microfiber with a waist diameter of 2 μm and low index polymer with high thermal property can effectively improve the current sensitivity of the proposed MLR to be 437.9 pm/A2.

Resonantly enhanced third harmonic generation in microfiber loop resonators

We theoretically study third harmonic generation in silica microfiber loop resonators wherein the large resonant field strength is exploited to increase the efficiency and reduce the required pump power, with a focus on the influence of loop parameters such as loss and coupling. For a 3 mm length loop, the conversion can reach several percent, that is, 640 times greater than an equivalent straight microfiber, for input powers as low as 100 W. The harmonic signal can be toggled between a high- and low-output state due to hysteresis at higher powers, and the efficiency can be further enhanced if the harmonic light is recirculated and coresonant with the pump.

Relative Humidity Sensor Based on Microfiber Loop Resonator

A novel relative humidity (RH) sensor based on a microfiber loop resonator (MLR) is proposed and experimentally demonstrated. As refractive index of the microfiber in the MLR is modified by environmental humidity, resonant wavelength of the MLR changes with RH level. By detecting this wavelength shift, RH measurement is realized with a linear response sensitivity of 1.8 pm/% RH. The obvious advantage of this technique over others is that no coating of humidity-sensitive material is required.

Nonlinear microfiber loop resonators for resonantly enhanced third harmonic generation

We model and demonstrate resonantly enhanced third harmonic generation in microfiber loop resonators, in which the large pump field intensity is exploited to improve the conversion on resonance. Silica microfibers were fabricated with waist diameters near 0.76 μm to ensure intermodal phase matching. When pumped with λ=1.55 μm 4 ns pulses at 100 W peak power, the conversion efficiency is 3×10(-6) over an estimated interaction length of ∼1 mm near the waist. The resonator is then formed by manually translating and twisting the microfiber ends to produce loop diameters down to 6 mm and resonant enhancements up to 7.7 dB for the same pump parameters.

Modeling optical microfiber loops for seawater sensing

Based on resonant and waveguiding properties of optical microfiber loops, we theoretically investigated silica microfiber loop resonators (MLRs) for refractive index (RI) and salinity sensing of seawater. Dependences of sensitivity and detection limit on probing wavelength, fiber diameter, and ring diameter are calculated with typical parameters of seawater. Our results show that the sensitivity of MLRs increases with the increasing wavelength and the decreasing diameter of the microfiber. Bending loss and absorption loss are both important factors to determine the detection limit. By optimizing the parameters of the sensing system, RI sensitivity and salinity detection limit can reach 10(-6) RI units (RIU) and 10(-2) ‰ (10 ppm), respectively. The model presented here may be helpful for developing microscale fiber sensors for seawater detection with high sensitivity, low detection limit, and miniaturized sizes.

MICROFIBER STRUCTURES FOR SENSOR APPLICATIONS

Microfiber loop resonator (MLR) and microfiber knot resonator (MKR) are fabricated using melt-stretching method for applications in temperature and current sensor, respectively. The MLR is embedded into low refractive index polymer for robustness. Although the spacing of the transmission comb spectrum of the MLR is unchanged with temperature, the extinction ratio of the spectrum is observed to decrease linearly with temperature due to induced changes in the material's refractive index. The slope of the extinction ratio reduction against temperature is about 0.043dB/°C. With the assistance of a copper wire that is wrapped by the MKR, resonant wavelength can be tuned by varying the electric current delivered to the wire. The resonant wavelength change is based on the thermally induced optical phase shift in the MKR due to the heat produced by the flow of electric current over a short transit length. It is shown that the wavelength shift is linearly proportional to the square of current in the copper wire with a tuning slope of 46 pm/A2.

Microfiber loop resonator based temperature sensor

A microfiber loop resonator (MLR) is fabricated by coiling a microfiber which is fabricated using a flame heating technique, into itself. A temperature response on a comb spectrum of a fabricated MLR, which is embedded in a low refractive index polymer, is investigated. The spacing of the transmission comb spectrum of the MLR is observed to be unchanged with the temperature. However, the extinction ratio of the spectrum is observed to be linearly decreased with the temperature. The slope of the extinction ratio reduction against temperature was about 0.043dB/°C. The dependence of the extinction ratio on temperature is due to the change in the material’s refractive index.

Polarization Effects in Microfiber Loop and Knot Resonators

We theoretically investigate the polarization effect of three-dimensional (3-D) microfiber/nanofiber (MNF) loop resonators and knot resonators. Due to the lack of circular symmetry, the coupling at the joint regions of loop resonator and knot resonator are highly polarization-dependent. Using Jones matrices to express coupling coefficients, we suggest a matrix formula to describe the propagation of arbitrary polarized incidence through the resonator. Thereby, the polarization effect of 3-D loop resonators and knot resonators can be comprehensively investigated. We find that the polarization properties of the resonance spectrum and Q -factor are strongly dependent on the parameters of the twisted region. Results obtained in this work may serve as helpful guidelines for MNF resonator design and fabrication.

Novel high sensitivity accelerometer based on a microfiber loop resonator

An optical accelerometer with a bulk-micromachined silicon proof mass and a microfiber loop resonator (MLR) sensor was developed. The MLR was fixed on the surface of the cantilever beam. The proof mass and cantilever beam were fabricated with a two-mask process. An accelerometer with a range of ±20 g and output sensitivity 624.7 mV/g was fabricated. The design, simulation, fabrication, and preliminary results are presented.

A tunable all-fiber filter based on microfiber loop resonator

In this paper, a tunable high finesse microfilter is described, which is based on microfiber loop resonator (MLR). The length of microfiber loop could be controlled by a small cylindrical piezoelectric ceramic. As we calculated, this resonator has the maximum Q factor of 2400 and the finesse of 4.3. MLR filter was demonstrated that the maximum extinction ratio is about 10dB, and the free spectral range variation range could be more than 100GHz. This device could also be integrated into a smaller size due to the bigger radius of curvature of the microfiber.