High Thermo-optic Coefficient Research Articles

Ultrasensitive temperature sensor based on a urethane acrylate-coated off-axis spiral long period fiber grating

We propose and experimentally demonstrate an ultra-high sensitivity fiber-optic sensor to measure temperature changes in order to establish a high-precision temperature model in the bio-fermentation process. The proposed sensor based on off-axis spiral long-period fiber grating (OAS-LPFG) is fabricated in a single mode fiber (SMF) by arc discharge technology. This kind of grating is distinguished in the refractive index (RI) modulation, geometry changes, and shear stress of a spiral structure. Because the RI of the urethane acrylate is close to that of the SMF cladding and has a high thermo-optic coefficient, the resonant wavelength of the OAS-LPFG dip has a high sensitivity to the temperature measurement. The response of the OAS-LPFG to environmental RI is analyzed by full vector complex coupling mode theory. In the experiment, the temperature sensitivity of the proposed sensor can be reached ∼-108.69 nm/°C over a range of 25.0 °C to 25.5 °C. Compared with other all-fiber-based temperature sensors, the sensor has higher sensitivity.

Au Nanoparticles-Doped Polymer All-Optical Switches Based on Photothermal Effects.

This article demonstrated the Au nanoparticles-doped polymer all-optical switches based on photothermal effects. The Au nanoparticles have a strong photothermal effect, which would generate the inhomogeneous thermal field distributions in the waveguide under the laser irradiation. Meanwhile, the polymer materials have the characteristics of good compatibility with photothermal materials, low cost, high thermo-optical coefficient and flexibility. Therefore, the Au nanoparticles-doped polymer material can be applied in optically controlled optical switches with low power consumption, small device dimension and high integration. Moreover, the end-pumping method has a higher optical excitation efficiency, which can further reduce the power consumption of the device. Two kinds of all-optical switching devices have been designed including a base mode switch and a first-order mode switch. For the base mode switch, the power consumption and the rise/fall time were 2.05 mW and 17.3/106.9 μs, respectively at the wavelength of 650 nm. For the first-order mode switch, the power consumption and the rise/fall time were 0.5 mW and 10.2/74.9 μs, respectively at the wavelength of 532 nm. This all-optical switching device has the potential applications in all-optical networks, flexibility device and wearable technology fields.

Highly sensitive temperature sensor based on sagnac interferometer using photonic crystal fiber with circular layout

A temperature sensor based on Sagnac interferometer (SI) using photonic crystal fiber (PCF) with circular layout is proposed. Temperature measurement can be realized by filling the temperature sensitive liquid with high thermo-optic coefficient into the air holes. Considering the convenience of the experimental operation, three easy-to-operate liquid filling methods (FMs) were used to investigate the optical transmission characteristics of this sensor by the finite element method (FEM), the results show that two of which exhibit respective detection advantages in different aspects. One of the feasible methods is that all air holes are filled with temperature sensitive liquid. A single sensing interference dip with high detection sensitivity can be achieved, its average sensitivity reaches to 18.27 nm/°C. Another method is that only the large size air holes are filled with the temperature sensitive liquid. Two sensing interference dips with good linearity can be realized simultaneously. The linearity R2 are up to 0.99947 and 0.99877, corresponding average sensitivities are 9.47 and 8.57 nm/°C, respectively. Besides, these two proposed FMs are easier to be completed than FMs of some reported works. The proposed PCF temperature sensor with excellent detection performances, simple FMs and structural design has great application prospects to detect environmental temperature.

High efficiency four wave mixing and optical bistability in amorphous silicon carbide ring resonators

We demonstrate high efficiency wavelength conversion via four wave mixing in amorphous silicon carbide ring resonators with a loaded quality factor of 70 000. Owing to the high quality factor and high nonlinearity of amorphous silicon carbide, −21 dB conversion efficiency is achieved with 15 mW pump power. Moreover, the thermo-optic coefficient (TOC) of amorphous silicon carbide is measured to be 1.4 × 10−4/°C at telecommunication wavelengths. Taking advantage of the high TOC, we demonstrate optical bistability in the silicon carbide ring resonator. This work presents amorphous silicon carbide as a promising platform for applications in optical signal processing.

Liquid-Filled Highly Asymmetric Photonic Crystal Fiber Sagnac Interferometer Temperature Sensor

In this paper, we theoretically designed and numerically studied a high-resolution and ultrasensitive photonic crystal fiber temperature sensor by selective filling of a liquid with high thermo-optic coefficient in one of the airholes of the fiber. The finite element method was utilized to study the propagation characteristics and the modal birefringence of the fiber under different ambient temperatures. A large base birefringence value of 7.7 × 10−4 as well as a large birefringence sensitivity of almost 29% to a 10 °C temperature variation was achieved for the optimized fiber design with liquid chloroform between 15 °C and 35 °C. We also studied the performance of the proposed optical fiber in a temperature sensing Sagnac interferometer. An average linear temperature sensitivity of 17.53 nm/°C with an average resolution of 5.7 × 10−4 °C was achieved over a temperature range of 20 °C (15 °C to 35 °C).

Vanadium-Oxide-Based Thin Films with Ultra-High Thermo-Optic Coefficients at 1550 nm and 2000 nm Wavelengths.

In this paper, the temperature-dependent dielectric properties of vanadium-sesquioxide-based thin films are studied to assess their suitability for thermally tunable filters at optical communication wavelengths. Spectroscopic ellipsometry is utilized to measure the optical constants of vanadium oxide thin films at temperatures ranging from 25 °C to 65 °C. High thermo-optic coefficients (dn/dTs) were observed. The highest dn/dTs, measured at approximately 40 °C, were −8.4 × 10−3/°C and −1.05 × 10−2/°C at 1550 nm and 2000 nm, respectively.

Temperature Dependence of the Steering Angles of a Silicon Photonic Optical Phased Array

Silicon photonic optical phased arrays leveraging from the well established CMOS fabrication process have become promising candidates to realize miniaturized beam steering systems. While different implementations of optical phased arrays have been successfully demonstrated, no investigations on the influence of thermal distortions on the response of these systems have been performed so far. Due to the high thermo-optic coefficient of silicon, the refractive index and thus the functionality of silicon photonic components depend strongly on the temperature. In highly integrated systems, consisting of several photonic components, in which laser sources and control electronics are directly integrated on top of the photonic IC, heat dissipated by active components leads to temperature gradients and offsets, affecting the functionality of the photonic system. Optical phased arrays consisting of an array of phase sensitive components, are particularly sensitive towards temperature. Therefore, precise investigations of the temperature dependence of the OPA functionality are required. This article aims to expand the understanding of the influence of thermal distortions on the steering angles of optical phased arrays. Thereto, analytical expressions describing the temperature dependence of the steering angles are provided and experimentally validated. The expressions are provided in a general form so that they can be applied to any OPA system regardless of its implementation.

High-sensitivity temperature sensor based on Fano resonance in an optofluidic microcapillary resonator.

In this paper we demonstrate a high-sensitivity temperature sensor based on high-order Fano resonance (FR) in an optofluidic microcapillary resonator. High-order FR modes (Q∼3000) are excited in an ethanol-filled optofluidic microcapillary resonator for temperature sensing. Due to the high thermo-optic coefficient of ethanol and a large energy fraction of high-order modes in the core liquid, the sensitivity as high as -0.402nm/∘C and the detection limit of 0.026°C can be achieved. Also the sensitivity and free spectral range of different order radial modes are calculated theoretically. The experimental results agree well with the theoretical results. Through the comparison between the theoretical and experimental results, the radial order number of the mode used for temperature sensing is estimated to be 10.

Strain-Insensitive Biocompatible Temperature Sensor Based on DNA Solid Film on an Optical Microfiber

We demonstrated a biocompatible and highly sensitive temperature sensor using DNA-CTMA (DNA-Cetyl trimethyl ammonium) solid film deposited on micro-tapered fiber. The micro-tapered silica fiber provided a built-in interferometer that was inherently sensitive to the environment variation due to the enhancement of evanescent wave interaction. The tapered region was coated with DNA-CTMA film with a high thermo-optic coefficient enabling a high-temperature sensitivity higher than −0.9 nm/°C in the bio-medically important region from 35 to 80 °C in a water bath. The cross-sensitivity problem between the temperature-sensing and the strain-sensing was successfully resolved since the elastic properties of the DNA-CTMA film on the micro-tapered silica fiber resulted in a very low strain sensitivity of −7 pm/ $\mu \varepsilon $ . Detailed procedures for device fabrication and optical characterization of the proposed device were described.

High sensitivity temperature sensor based on liquid filled hole-assisted dual-core fiber

A high sensitivity temperature sensor is numerically and experimentally investigated in liquid filled eccentric hole-assisted dual-core fiber (EHADCF). The sensor is constructed by cascading two single mode fibers (SMFs) with an intermediate liquid filled EHADCF segment. The light couples periodically between the center and suspended cores due to small core distance. Refractive index (RI) matching liquid with high thermo-optic coefficient is filled into the air-hole of the EHADCF as the cladding of the suspended core. The dispersion curves of the center and suspended cores of the EHADCF change with the temperature, leading to the shift of the resonance peak. The measured temperature sensitivity of the sensor is −562.4 pm/°C. In addition, the stability of the sensor is also measured. Due to high sensitivity, good stability, compact size and large temperature range, the proposed sensor shows promising potentials for temperature sensing in environment monitoring.

Highly sensitive optical fiber temperature sensor based on resonance in sidewall of liquid-filled silica capillary tube**Project supported by the Scientific Research Project of Institutions of Higher Learning in Inner Mongolia Autonomous Region, China (Grant No. NJZY19214).

A highly sensitive optical fiber temperature sensor based on a section of liquid-filled silica capillary tube (SCT) between single mode fibers is proposed. Two micro-holes are drilled on two sides of SCT directly by using femtosecond laser micromachining, and liquid polymer is filled into the SCT through the micro-holes without any air bubbles and then sealed by using ultra-violet (UV) cure adhesive. The sidewall of the SCT forms a Fabry–Perot resonator, and loss peaks are achieved in the transmission spectrum of the SCT at the resonant wavelength. The resonance condition can be influenced by the refractive index variation of the liquid polymer filled in SCT, which is sensitive to temperature due to its high thermo-optical coefficient (−2.98 × 10−4 °C−1). The experimental result shows that the temperature sensitivity of the proposed fiber structure reaches 5.09 nm/°C with a perfect linearity of 99.8%. In addition, it exhibits good repeatability and reliability in temperature sensing application.

Temperature Sensor Based on Side-Polished Fiber SPR Device Coated with Polymer.

A highly sensitive temperature sensor based on surface plasmon resonance (SPR) of a side-polished single mode fiber is demonstrated. The sensor consists of a gold film coated side-polished fiber covered by a layer of UV-curable adhesive. Before introducing the UV-curable adhesive, the gold-coated fiber exhibits refractive index (RI) sensitivity of 1691.6 nm/RIU to 8800 nm/RIU in the range of 1.32 to 1.43. The resonant wavelength of the SPR sensor shifts to 650 nm when the adhesive is coated on the gold film, and is fixed at about 725 nm when the adhesive is cured. Due to the high thermo-optic and thermal expansion coefficient of the adhesive, the sensor structure achieves a temperature sensitivity of −0.978 nm/°C between 25 °C and 100 °C. The proposed optical fiber SPR sensor is simple, highly sensitive and cost effective, which may find potential applications for temperature measurements in the biomedical and environmental industries.

On-chip integrated optical switch based on polymer waveguides

Optical polymer is one of the promising materials for photonic integrated devices that can be processed with simple, flexible and semiconductor compatible technology. Especially, optical polymer with the advantages of high thermo-optic (TO) and electro-optic (EO) coefficients has been widely applied in optical waveguide switches. However, most of the current optical switches are independent with single function. It is essential to develop an on-chip integrated device with multilayer for signal manipulation. In this paper, we propose an on-chip 3-dimensional integrated optical switch based on the EO polymer-clad waveguide incorporate with the TO tunable vertical coupler. The proposed integrated optical switch could realize the function-integration of the adjustable 3D optical connection and the high-speed modulation. A typical fabricated switch shows an insertion loss of 16.3 dB and an extinction ratio of 16.0 dB at the driving power of 48.2 mW. The dynamic characteristics of TO and EO switching functions of the device were also measured in this work.

Lab-on-tip: Protruding-shaped all-fiber plasmonic microtip probe toward in-situ chem-bio detection

Lab-on-tip technology opens a new door for optical fiber surface plasmon resonance (SPR) sensors. In this paper, we first demonstrate an ultra-compact reflective SPR microtip probe on the flat fiber end in experiment, which has a length of tens of microns and a diameter of several microns. Simulations and experiments show that this new fiber SPR microtip probe coated with a nano-goldfilm has excellent refractive index (RI) sensing characteristic and great potential for biochemical detection at single cell level. Based on the high RI sensitivity, a bio-probe assembled with Chitosan/Polysodium Styrene Sulfonate (Cs/PSS) nano-polyelectrolyte film and the sheep anti-human IgG-HRP is prepared to recognize human IgG specifically. Due to the high surface sensitivity, the SPR microtip probe exhibits an ultra-low detection limit for human IgG. Due to the high bulk sensitivity and high thermo-optical coefficient (TOC) of polydimethylsiloxane (PDMS), a reference temperature probe based on SPR microtip is proposed, which is used to compensate for the temperature cross-sensitivity of the bio-probe. This new SPR microtip probe can be used not only in optical fiber sensor, but also in Tip-Enhanced Near-Field Raman Microscopy and Scanning Near-Field Optical Microscope.

Suppressing elaton drifts

suppressing elaton drifts

Hybrid Fiber Fabry–Perot Interferometer With Improved Refractometric Response

The reflectance of a hybrid fiber Fabry–Perot interferometer modulated by the Fresnel reflection at the fiber tip was used to assess the refractive index (RI) of liquid samples. Notwithstanding the closeness of RI values between samples and fiber core, well-defined interference spectra in Fourier domain were obtained after a robust signal processing algorithm. Then, the analysis of these spectra allowed us to derive a mathematical expression to obtain the RI value of the fiber tip surrounding media. Next, to assess the fiber refractometer measuring capability a series of liquid samples, typically used for RI calibration, with values ranging from 1.3924 to 1.5882 were measured. A standard deviation of 7 × 10−4 between the measured and actual RI values was estimated. Finally, the refractometer was used to monitor the RI of a sample, with a high thermo-optic coefficient, while it was heated. The accurate and compact all-fiber refractometer proposed here exhibited immunity to optical power fluctuations and one of the largest dynamic ranges reported. This set of combined features make it very attractive for real-time label-free biosensing applications.

Large thermal tuning of a polymer-embedded silicon nitride nanobeam cavity.

Tunable silicon nitride nanophotonic resonators are a critical building block for integrated photonic systems in the visible wavelength range. We experimentally demonstrate a thermally tunable polymer-embedded silicon nitride nanobeam cavity with a tuning efficiency of 44pm/°C and 0.13nm/mW in the near-visible wavelength range. The large tuning efficiency comes from the high thermo-optic coefficient of the SU-8 polymer and the "air-mode" cavity design, where a large portion of the cavity field is confined inside the polymer region. The demonstrated resonator will enable locally tunable cavity quantum electrodynamic experiments in the silicon nitride platform.

Isopropanol-sealed multimode microfiber for temperature sensing

Abstract This paper presents a low-cost and high-sensitivity temperature sensor based on an isopropanol-sealed multimode microfiber (MMMF). Isopropanol is a kind of material with a high thermo-optic coefficient. Refractive index (RI) of isopropanol changes with the surrounding temperature variation allowing high-sensitivity temperature sensing. By inserting the MMMF into an isopropanol-sealed capillary, a simple and highly sensitive fiber temperature sensor is implemented. Theoretical and experimental results demonstrate that the tapered multimode fiber can efficiently excite high-order cladding modes, the MMMF can enhance the multimode interference and increase the interaction between the evanescent wave and the isopropanol. The characteristics of the measured transmission spectra under different conditions are evaluated. Experimental results demonstrate that the temperature sensitivity increases with the decreasing diameter of MMMF. The maximum temperature sensitivity of −4.12 nm/°C is obtained over the range of 30 °C–50 °C. This packaging technology not only offers a more stable structure but also improves the temperature sensitivity for the thermo-optic effect of isopropanol and the thermal expansion effect of packaging materials.

Simultaneous Measurement of Temperature and Refractive Index Using an Exposed Core Microstructured Optical Fiber

We have demonstrated a novel scheme for simultaneous measurement of temperature and refractive index by using an exposed core microstructured optical fiber (ECF). The ECF allows for high sensitivity to refractive index due to the small exposed-core, while being supported by a standard fiber diameter cladding making it robust compared to optical microfibers. The sensor combines a fiber Bragg grating (FBG) inscribed into the core of the ECF and a multimode Mach-Zehnder interferometer (MZI). Both the FBG and MZI are sensitive to refractive index (RI) and temperature through a combination of direct access to the evanescent field via the exposed-core, the thermo-optic effect, and thermal expansion. The FBG and MZI respond differently to changes in temperature and RI, thus allowing for the simultaneous measurement of these parameters. In our experiment, RI sensitivities of 5.85 nm/RIU and 794 nm/RIU, and temperature sensitivities of 8.72 pm/°C and -57.9 pm/°C, were obtained for the FBG and MZI respectively. We demonstrate that a transfer matrix approach can be used to simultaneously measure both parameters, solving the problem of temperature sensitivity of RI sensors due to the high thermo-optic coefficient of aqueous samples.

Tunable Germanium-on-Insulator Band-Stop Optical Filter Using Thermo-Optic Effect

We demonstrate a tunable band-stop optical filter on a germanium-on-insulator photonic platform operating at 1.95 μ m wavelength. The band-stop filter is implemented using parallel-coupled microring resonators with the number of microring resonators varied from one to. three. Through the use of a heating stage, the thermo-optic coefficient of germanium is measured to be +3.55 × 10−4/°C. The high thermo-optic coefficient of germanium is exploited by including metal heating lines to provide localized on-chip tuning. As predicted by theoretical analysis, our experimental results show that when the number of microring resonators increases, the −3 dB bandwidth and extinction ratio of the optical filter increases. With the number of microring resonators increases from one to three, the −3 dB bandwidth of the filter increases from 0.283 to 0.661 nm and the extinction ratio from 9.56 to 22.10 dB.