High Thermo-optic Coefficient Research Articles

Tilted Bragg grating in a glycerol-infiltrated specialty optical fiber for temperature and strain measurements.

In this Letter, we propose an in-line tilted fiber Bragg grating sensor for temperature and strain measurements. The grating is inscribed in a specialty optical fiber using tightly focused femtosecond laser pulses and the line-by-line direct writing method. Beside the central core in which the grating is produced, a hollow channel filled with glycerol aqueous solution significantly improves the sensitivity of the fiber cladding modes due to its high thermo-optic coefficient. We show that the temperature sensitivity of the core mode is 9.8 pm/°C, while the one of the cladding modes is strongly altered and can reach -24.3 pm/°C, in the investigated range of 20-40°C. For the strain measurement, sensitivities of the core mode and the cladding modes are similar (∼0.60 pm/με) between 0 and 2400 με. The significative difference of temperature sensitivity between the two modes facilitates the discrimination of the dual parameters in simultaneous measurements.

Improvement of Temperature Sensitivity of Long-period Fiber Gratings Using Liquids with High Thermo-optic Coefficients

Improvement of Temperature Sensitivity of Long-period Fiber Gratings Using Liquids with High Thermo-optic Coefficients

Easy-to-Fabricate UV-Glue-Based Cascaded Fabry–Perot Fiber Sensor Probe for Temperature Measurement

In this paper, we propose an in-line fiber sensor probe based on UV-glue-assisted cascaded Fabry–Perot cavities for temperature measurement. The UV-curable adhesive in the sensing cavity plays an important role due to its high thermo-optic coefficient. We show that the temperature sensitivity depends on the optical path length difference between both cavities. We report a maximum value of 12.57 nm/°C in the range of 20 to 30 °C. This original sensor architecture features a low cost and simple structure that can be straightforwardly manufactured with readily available materials and a short production time.

Highly sensitive temperature and refractive index sensor based on no-core fiber cascaded with a balloon-shaped bent single-mode fiber

A highly sensitive temperature and refractive index (RI) sensor based on no-core fiber (NCF) cascaded with a balloon-shaped bent single-mode fiber (BSBSF) is proposed and demonstrated. The NCF can excite higher-order modes which will be concentrated and transmitted into the BSBSF due to the characteristic of self-imaging effect. The BSBSF has an excellent temperature performance due to the high thermo-optical coefficient and thermal expansion coefficient of the polymer coating. The NCF and BSBSF are both conducive to the excitation of higher-order modes, which induces the sensitivity of the sensor with an efficiency improvement. The experimental results show that the maximum temperature sensitivity is −3.19nm/∘C in the range of 22°C–83°C, which is the highest temperature sensitivity in the cascaded BSBSF structure to our best knowledge. In addition, the maximum RI sensitivity is 232.16 nm/RIU when the RI changes from 1.3234 to 1.3512. Compared with other cascaded BSBSF structures, this sensor has a higher temperature sensitivity and can be applicated in the prospects of food, biology, and environmental monitoring.

Polymer and Hybrid Optical Devices Manipulated by the Thermo-Optic Effect.

The thermo-optic effect is a crucial driving mechanism for optical devices. The application of the thermo-optic effect in integrated photonics has received extensive investigation, with continuous progress in the performance and fabrication processes of thermo-optic devices. Due to the high thermo-optic coefficient, polymers have become an excellent candidate for the preparation of high-performance thermo-optic devices. Firstly, this review briefly introduces the principle of the thermo-optic effect and the materials commonly used. In the third section, a brief introduction to the waveguide structure of thermo-optic devices is provided. In addition, three kinds of thermo-optic devices based on polymers, including an optical switch, a variable optical attenuator, and a temperature sensor, are reviewed. In the fourth section, the typical fabrication processes for waveguide devices based on polymers are introduced. Finally, thermo-optic devices play important roles in various applications. Nevertheless, the large-scale integrated applications of polymer-based thermo-optic devices are still worth investigating. Therefore, we propose a future direction for the development of polymers.

Pressure and temperature dual-parameter optical sensor based on the MIM waveguide structure coupled with two T-shaped cavities.

This paper elaborates on the design and simulation of a multifunctional optical sensor that features simultaneous detection of pressure and temperature, which is based on the metal-insulator-metal waveguide structure with two T-shaped resonant cavities. Depending on the simulation findings, pressure and temperature can be measured separately by two T-shaped cavities at different Fano resonance wavelengths. As the pressure applied to the upper T-shaped cavity increases, the resonance wavelength first shifts linearly due to the slight deformation of the cavity, and the maximum pressure sensitivity reaches 12.48nm/MPa. After the pressure exceeds a threshold, the relationship between pressure and resonance wavelength transforms into a quadratic polynomial. In the lower T-shaped cavity, solid polydimethylsiloxane is sealed as a thermal-sensitive material, effectively preventing material overflow brought on by structural micro-vibration under pressure, and its high thermo-optical coefficient prompts a temperature sensitivity of 0.36nm/°C. Furthermore, by optimizing the choice of Fano resonances, pressure and temperature can be sensed independently without mutual interference. The designed sensor provides extensive application possibilities for scenarios where multiparameter monitoring is required.

Ultra-sensitive all-optical phase modulation based on a fiber optic interferometer combined with Ti3C2Tx MXene-incorporated PDMS.

This study proposes an all-optical phase modulator based on a compact fiber optic interferometer combined with Ti3C2Tx MXene-incorporated PDMS. Due to the high photothermal conversion efficiency of MXene and the high thermo-optic coefficient of PDMS, changes in pump power can be effectively converted into refractive index (RI) variations in the PDMS. Then, by employing a fiber optic interferometer with a high RI response, ultra-sensitive all-optical phase modulation can be realized. The experimental results demonstrate that the resonant wavelength shift of the modulator with MXene-incorporated PDMS is 126 times higher than that of a modulator with single MXene deposition. Also, a maximum wavelength sensitivity of 14.57 nm/mW is achieved (equivalent to a phase sensitivity of 0.33π/mW); this excellent modulation performance is a great improvement on that of a previously reported fiber-based all-optical phase modulator. Furthermore, PDMS is also employed as a packaging layer to strengthen the device structure and restrict the heat in an enclosed space, which improves the heat utilization efficiency. The proposed device shows great potential in optical communication, optical filtering, sensing, and modulation applications.

Realization of a wide steering end-fire facet optical phased array using silicon rich silicon nitride.

The design, fabrication, and characterization of a 16-element optical phased array (OPA) using a high index (n = 3.1) silicon-rich silicon nitride (SRN) is demonstrated. We present one-dimensional beam steering with end-fire facet antennas over a wide steering range of >115° at a fixed wavelength of 1525 nm. A beam width of 6.3° has been measured at boresight, consistent with theory. We demonstrate SRN as a viable material choice for chip-scale OPA applications due to its high thermo-optic coefficient, high optical power handling capacity [negligible two-photon absorption (TPA)], wide transparency window, and CMOS compatibility.

Highly Sensitive and Specific Detection of Myoglobin in the Urine Based on Enhanced Photothermal Effect

Acute myocardial infarction can be diagnosed by measurement of myoglobin concentration in urine. In this article, a label-free sensor is proposed based on the photothermal effect of biomolecules, which is used for the immediate detection of myoglobin concentration in urine. The sensor was fabricated by a tapered microfiber (TMF) coated with the ultraviolet-curable polymer (UVCP) that has a high thermo-optical coefficient. The photothermal signal of biomolecules is only related to their selective absorption, while the scattering and reflection losses do not generate the photothermal signal. Therefore, specific identification could be realized by detecting the photothermal signal of myoglobin biomolecules. The results showed that the UVCP could enhance the detection sensitivity of photothermal signal due to the high thermo-optic coefficient. The sensitivity of the device is −267.652 nm/(mg/mL) in the concentration range of 0.0001–0.10 mg/mL, the limit of detection (LOD) is 74.7 ng/mL, and the response time is only 30 s. It can meet the demand for detecting the myoglobin concentrations in the urine analysis of related diseases, which has potential applications in the early diagnosis and quantitative analysis of conditions.

Photonic-enabled beam steering at 300 GHz using a photodiode-based antenna array and a polymer-based optical phased array.

For wireless networks beyond 5G, directivity and reconfigurability of antennas are highly relevant. Therefore, we propose a linear antenna array based on photodiodes operating at 300 GHz, and an optical phased array based on polymer waveguides to orchestrate the antennas. Due to its low thermal conductivity and high thermo-optical coefficient, the polymer chip enables highly efficient and crosstalk-free phase shifting. With these, we demonstrate purely photonic-controlled beam steering across 20°. Compared to a single emitter, the 3-dB beam width is reduced by 8.5° to 22.5° and the output power is >10 dB higher. Employing Snell's law for coupling into air, we can precisely predict the radiation patterns.

Ultrahigh-sensitivity SPR fiber temperature sensor based Ge2Sb2Te5 and cyclohexane

High-sensitivity fiber optic temperature sensors are essential analytical tools in biological and chemical fields. To increase the temperature sensitivity of the surface plasmon resonance sensors, we decide to employ a stable material, Ge2Sb2Te5 (GST). When GST is deposited on the gold film's surface, SPR is excited at lower frequency, this indicates that the resonance dips are red-shifted. At long wavelengths, the evanescent field is greatly enhanced, and the penetration depth is increased, which increases the interaction volume. In other words, the sensitivity is greatly improved. The fiber optic is encapsulated in cyclohexane with a high thermo-optic coefficient and a high refractive index. The sensitivity improves further because the fiber is placed in a high refractive index environment. The sensor's average temperature sensitivity is 14.7 nm/°C, with a measurement range of 5 °C to 80 °C, according to the output spectra. The maximum temperature sensitivity can reach 25.7 nm/°C. As a result, the suggested temperature sensor might be useful in various industries that need high measurement precision.

Highly Sensitive Curvature and Temperature Sensor Based on Double Groove Structure and Hollow Core Fiber

In this paper, we propose a curvature and temperature sensor based on two symmetrical grooves and a hollow core fiber (HCF) filled with polydimethylsiloxane (PDMS). The two grooves are produced by splicing both ends of the polished HCF with two multimode fibers (MMFs). The proposed groove structure is sensitive to curvature, and the PDMS, with a high thermo-optical coefficient, makes the sensor highly sensitive to temperature. The experimental results show that the sensor exhibits a high sensitivity of −6.833 nm/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−1</sup> in the curvature range of 0 m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−1</sup> to 45.97m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−1</sup> , and a high sensitivity of 4.278 nm/°C in the temperature range of 25°C to 95°C. The proposed sensor can monitor curvature and temperature simultaneously in real-time, and has potential application prospects in industrial production, biomedicine, structural health monitoring, and other fields.

High-performance all-fiber Mach-Zehnder interferometer based on D-shaped two-mode fiber coated with polydimethylsiloxane for temperature sensing

A novel fiber sensor, an all-fiber Mach-Zehnder interferometer based on D-shaped two-mode fiber (DTMF-MZI) coated with polydimethylsiloxane (PDMS), is proposed and demonstrated. When light is incident from a single-mode fiber (SMF) to a two-mode fiber (TMF), two modes will be excited in the TMF and interfere with each other, just like a two-beam fiber Mach-Zehnder interferometer (MZI). Due to the high negative thermo-optical coefficient, the proposed sensor is sensitive to temperature. Our theoretical analysis and experimental results prove that as the temperature increases, the dips in the transmitted spectrum of DTMF-MZI will blue-shift. Furthermore, we demonstrate the influences of the distance from the center of the fiber core to the polished plane (parameter h) and the length of the polished area (parameter Lpo) of TMF on the temperature sensitivity. In the experiments, the maximum temperature sensitivity of the proposed sensor reaches −305.6 pm/°C in the temperature range of 30 ∼ 80 °C, and the linearity is as high as 0.9890. In addition, the sensor shows good stability at 30 °C and 80 °C in 60 min with the maximum variations of 0.16 nm. The proposed sensor has many advantages, such as being highly temperature-sensitive, compact, and stable.

A Temperature Sensor Based on Composite Optical Waveguide

We propose a temperature sensor, which consists of a composite optical waveguide (COW) sandwiched between two single mode fibers (SMFs). The COW is formed by side polishing a capillary optical fiber (COF) and filling with polydimethylsiloxane (PDMS). Unlike the conventional fixed sensing structure, the Mach-Zehnder interferometer (MZI) and multimode interferometer (MMI) can be selectively formed by adjusting different fusion splicing parameters, so as to produce a blunt or sharp tapered fusion structure between the SMF and the COF. Because of the high thermo-optic coefficient of PDMS and the high-order modes excited by the tapered fusion structure, the MZI and MMI sensors are very sensitive to temperature. The experimental results show that within the temperature measurement range from 16 °C to 80 °C, several resonance wavelengths of the MZI and MMI sensors exhibit a remarkable blue shift with the increase of temperature. The maximum temperature sensitivities of the MZI and MMI sensors can reach −0.50 nm/ °C and −0.88 nm/ °C, respectively. The humidity sensitivity of the sensor is −0.10 nm/%RH. However, in the process of temperature measurement, humidity has little influence on the sensitivity of the sensor. Due to the advantages of compact size, flexible structure, and high sensitivity, the sensor has great application potential in monitoring the changes of environment and living temperature.

Cascaded Dual-Channel Fiber SPR Sensor Based on Ge2Sb2Te5

We propose and demonstrate a cascaded dual-channel fiber surface plasmon resonance (SPR) sensor based on a phase change material, Ge <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Sb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Te <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sub> (GST). This material may modulate the sensing bands of SPR to the infrared bands. We configure channel I with a 50 nm Au film and configure channel II with a 50 nm Au film and a 30 nm GST film. The experimental results show that the sensing bands of channel I are 596 nm - 793 nm, and the refractive index (RI) sensitivity is 2781 nm/RIU. The sensing bands of channel II are 1045 nm - 1421 nm, and the RI sensitivity reaches 5226 nm/RIU. The RI measuring range is 1.333 - 1.403. The sensing bands of the two channels are completely separated. We coat polydimethylsiloxane (PDMS) on the surface of Au-GST film. Since PDMS is a heat-sensitive material with a high thermo-optical coefficient (TOC), channel II responds to temperature. Therefore, the sensor can also be used to measure the TOC of unknown liquid samples. The temperature sensitivity reaches 5.88 nm/°C. The sensor has high sensitivity, high resolution, good stability, and strong toughness. These advantages meet the requirements of biochemistry for high-precision and harsh experimental environments. We believe that the sensor has bright application prospects.

Cr-=SUP=-2+-=/SUP=-:CdSe-лазер с мощностью непрерывной генерации более 20 W

Strong thermal lensing limits cw power of Cr2+:CdSe laser about ~ 1 W level due to unfavorable active media properties: low thermal conductivity and high thermo optical coefficient. Shifting from conventional approach to moving active media scheme allowed us to achieve over 20 W of cw generation in Cr2+:CdSe crystal

Simultaneous Measurement of Seawater Temperature and Pressure With Polydimethylsiloxane Packaged Optical Microfiber Coupler Combined Sagnac Loop

In the field of physical oceanography, the temperature and pressure of seawater are important fundamental parameters. In order to realize the simultaneous measurement of the temperature and pressure in seawater, a reflective optical fiber sensor based on polydimethylsiloxane (PDMS)-sealed optical microfiber coupler combined with a sagnac loop (OMCSL) is proposed. Benefiting from the high thermo-optical coefficient and large elasticity of PDMS, and the large-scale swift field transmission characteristics of optical microfiber coupler (OMC), the sensitivity and structural stability of our sensor is largely improved. The response performance of the sensor is further analyzed by numerical simulation calculations and theoretical modeling. Experimental results show that the temperature and pressure sensitivity of the sensor could reach &#x2212;2.133 nm&#x002F;&#x00B0;C and 3.416 nm&#x002F;Mpa, respectively, about one order higher than that of bare fiber OMCSL. Furthermore, via inversely calculating the cross-sensitivity matrix, the temperature and pressure sensing can be demodulated simultaneously, and the average errors of the preliminary experimental settlements are 1.61&#x0025; and 5.02&#x0025;, respectively. Due to the merits of compact structure, easy fabrication, high sensitivity, fast response speed and high stability, the basic performance of this dual parametric sensor is comparable to the existing electrical temperature-depth (TD) sensor, which is expected to meet the practical application requirements of marine environmental monitoring and ocean dynamics research.

Effects of Thermally Induced Phase Transition on the Negative Thermo-Optic Properties of Atomic-Layer-Deposited TiO2 Films

The negative thermo-optic properties of TiO2 have been considered promising for athermal photonic devices that can mitigate the optical-performance instability due to temperature variations. When temperature increases, its negative thermo-optic coefficient (TOC) can compensate for the unfavorable increase in refractive index exhibited by widely used optical materials such as Si, which have positive TOCs. Herein, the structure–property relationship of TiO2 is thoroughly investigated to understand the negative thermo-optic behaviors of TiO2. Through atomic layer deposition and mild thermal annealing, the obtained negative TOC values are as high as −2.30 × 10–4/°C in the visible to the near-infrared regime. X-ray diffraction/reflectivity and temperature-dependent refractive index measurements identify that the higher crystallinity of anatase TiO2 leads to greater negative TOC values due to its higher density and lower porosity, compared to those of amorphous or weakly crystalline states. The Prod’homme model and band gap analysis reveal that the effect of volume expansion is more dominant on the enhanced negative TOC of TiO2, rather than the polarizability. Photoelectron spectroscopy measurements suggest an amorphous relaxation process during annealing that further supports the amorphous-to-crystalline transformation in TiO2. The findings of the structure and chemical properties governing the negative TOC of TiO2 for athermal applications may be of significant relevance to many photonic devices showing strong performance instability due to the high positive TOCs.

Microstructured optical fiber filled with glycerin for temperature measurement based on dispersive wave and soliton

A nonlinear temperature sensor was proposed drawing on dispersive wave (DW) and soliton in an in-house made silica microstructured optical fiber (MOF). Glycerin with high thermo-optical coefficient was filled into the MOF air holes as the thermal medium. Using a 1050 nm femtosecond laser as the pump source, DW and soliton were experimentally and theoretically explored for temperature sensing by detecting their central wavelength shift of 3-dB bandwidth. The results showed that the higher the average pump power, the higher the temperature sensitivity of DW and soliton. When the DW blue-shifted relative to the soliton, the temperature sensitivity of DW was higher than that of soliton, and the experimental maximum values were 0.928 nm/℃ (DW) and -0.923 nm/℃ (soliton). Our work explored the nonlinear phenomenon for optical fiber-based sensing technology and verified that both DW and soliton can be used to realize temperature sensors of high sensitivity and good mechanical strength. The sensing characteristic difference of DW and soliton revealed in this work might provide a new way for solving the cross-sensitivity of dual-parameter sensing in biological engineering, disease detection and environmental monitoring without introducing extra structural complexity.

Mode transition induced enhanced temperature sensitivity in long period waveguide gratings near dispersion turning point

We propose a highly sensitive temperature sensor based on long period grating inscribed high index coated ridge waveguide in which the unique feature of mode transition (MT) phenomenon combined with the high thermo optic coefficient (TOC) polymer ambient elevates the differential thermal dependence between the participating modes. Using the dual resonance behavior, the temperature sensitivity is found to be ∼100 nm/°C near the dispersion turning point (DTP) at around room temperature with good tolerances with respect to waveguide’s width and grating period. A judicious grating design has also been formulated to operate the proposed structure near the DTP for temperatures other than room temperature including human body temperature, making the device an excellent choice for different bio and chemical applications. A comparative study of temperature sensitivity near the DTP with a conventional ridge waveguide is used to show the importance of the MT in obtaining high sensitivity near the turning point.