Search query: Thermo-Optic Coefficients

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abstract: Unconventional thermo optic responses of CH3NH3PbCl3 enable phase shift compensators and tunable retarders for visible light. Lead halide perovskites are promising semiconductors for high performance photonic devices. Because the refractive index determines the optimal design and performance limit of the semiconductor devices, the refractive index and its change upon external modulations are the most critical properties for advanced photonic applications. Here, we report that the refractive index of halide perovskite CH3NH3PbCl3 shows a distinct decrease with increasing temperature, i.e. a large negative thermo optic coefficient, which is opposite to those of conventional inorganic semiconductors. By using this negative coefficient, we demonstrate the compensation of thermally induced optical phase shifts occurring in conventional semiconductors. Furthermore, we observe a large and slow refractive index change in CH3NH3PbCl3 during photoirradiation and clarify its origin to be a very low thermal conductivity supported by theoretical analysis. The giant thermo optic response of CH3NH3PbCl3 facilitates efficient phase modulation of visible light.
author_names: Taketo Handa

Hirokazu Tahara

Tomoko Aharen

Yoshihiko Kanemitsu
title: Large negative thermo optic coefficients of a lead halide perovskite
venue: Science Advances
year: 2019

abstract: Abstract Chalcogenide glasses have attracted much attention for the realization of photonic components owing to their outstanding optical properties in the mid infrared (MIR) region. However, relatively few refractive index dispersion data are presently available for these glasses at MIR wavelengths. This paper presents a mini review of methods we have both used and developed to determine the refractive indices and thermo optic coefficients of chalcogenide glasses at MIR wavelengths, and is supported by new results. The mini review should be useful to both new and established researchers in the chalcogenide glass field and fields of MIR optics, fiber optics and waveguides. Three groups of methods are distinguished: (1) spectroscopic ellipsometry, (2) prism based methods, and (3) methods using Fourier transform infrared (FTIR) transmission data. The mini review is supported by a brief discussion of refractive index models.
author_names: Y Fang

David Furniss

Dinuka Jayasuriya

Harriet Parnell

Z Q Tang

Daniel J Gibson

Shyam S Bayya

Jas S Sanghera

Angela B Seddon

T M Benson
title: (INVITED) Methods for determining the refractive indices and thermo optic coefficients of chalcogenide glasses at MIR wavelengths
venue: Optical Materials: X
year: 2019

abstract: A new method (FTIR continuous dn dT method, n is refractive index and T temperature) for measuring the continuous thermo optic coefficients of thin transparent films in the mid infrared (MIR) spectral region is introduced. The technique is based on Fourier transform infrared (FTIR) transmission spectra measured at different temperatures. It is shown that this method can successfully determine the thermo optic coefficient of chalcogenide glass thin films (of batch compositions Ge20Sb10Se70 at. (atomic and Ge16As24Se15.5Te44.5 at. over the wavelength range from 2 to 25 um. The measurement precision error is less than 11.5 ppm degC over the wavelength range from 6 to 20 um. The precision is much better than that provided by the prism minimum deviation method or an improved Swanepoel method.
author_names: Yuanrong Fang

David Furniss

Dinuka Jayasuriya

Harriet Parnell

Zhuoqi Tang

Angela B Seddon

Trevor M Benson
title: Determining the continuous thermo optic coefficients of chalcogenide glass thin films in the MIR region using FTIR transmission spectra.
venue: Optics express
year: 2019

abstract: Abstract Terahertz time domain spectroscopy has been used to measure the temperature dependent absorption coefficients and refractive indices of different polymers in 0.2 1.8 THz spectral frequency. The coefficients of temperature dependent Sellmeier equation for all these polymers have also been evaluated by statistical fitting the measured data, which will be helpful for the evaluation of dispersion properties of the material. Additionally, the thermo optic coefficients have been evaluated to be the range of 1.230 x 10 4 to 2.50 x 10 4 K 1 for 298 373 K. This data would be helpful for the applications of polymers as THz waveguide and other temperature sensitive devices. These results provide a temperature dependent database of optical properties of different polymers for their efficient utilization in THz technology.
author_names: Muhammad Bilal Mumtaz

M Ahsan Mahmood

Sabih D Khan

M Aslam Zia

Mushtaq Ahmed

Izhar Ahmad
title: Experimental measurement of temperature dependent sellmeier coefficients and thermo optic coefficients of polymers in terahertz spectral range
venue: Optical Materials
year: 2019

abstract: We have measured mass densities, thermo optic coefficients, and electronic polarizability of MoO3 thin films and of HxMoO3 and LixMoO3 bronze thin films over the temperature range from 100 K to 373 K using ellipsometry. The mass densities of MoO3 and molybdenum bronzes with different concentrations (x) changed from 3.76 g/cm3 to 2.45 g/cm3 during the heating and cooling cycles. Thermo optic coefficients (TOCs) or dn/dT and dk/dT values of the molybdenum bronzes were found to have anomalous dispersion in the heating cycles over the range 295 373 K. On the other hand, the values of dn/dT for MoO3 thin films and for ZxMoO3 bronzes were found to be negative and positive, respectively over the temperature range 100 295 K and were on the order of 10 4 K 1. The respective values of dk/dT were found to be positive and negative and were on the order of 10 4 K 1 in the same temperature range. A little increase in the values of TOCs for the molybdenum bronzes is due to small increase in electronic polarizability, which was calculated in the range from 8.20 to 8.22 x 10 24 cm3 over the temperature range 100 373 K. All these small values are due to creation of more amorphousness in the MoO3 structure during the cooling cycles. The n and k data and TOCs values of molybdenum bronzes are explained using analytical model. The reported ellipsometric data is also interpreted in terms of small polarons and bipolarons using configurational coordinate model.
author_names: Zahid Hussain
title: Ellipsometric Investigations of Electronic Polarizability and Thermo optic Coefficients of ZxMoO3 (Z H+ Li+ Bronzes
venue: Journal of Electronic Materials
year: 2019

abstract: The values of dn/dT for thermally evaporated WO3 thin films were found to be negative either in the heating cycle (295 373 K) or in the cooling cycle (100 300 K) and were found to be of order of 10 5 K 1. On the other hand thermo optic coefficients (TOCs: dn/dT and dk/dT values) of tungsten bronzes (H+ Li+ Na+ with different concentrations were found to be positive and negative, respectively in both the heating and cooling cycles and they were found to be in the order of 10 4 K 1. Heating cycles show hysteresis loops of n and k for tungsten bronzes, which are good for electrochromic devices. On heating the bronzes at temperature higher than 400 K, there might be a reduction in the porosity but an irreversible disordering of hydrogen, lithium or sodium atoms could occur because of anomalous dispersions produced in the optical data. For cooling cycles, the calculated TOCs were again of the order of 10 4 but there was an increase in dn/dT and a decrease in dk/dT values due to more amorphousness built up in the bronzes during the cooling cycles. This change in the values of TOCs for tungsten bronzes created small decrease in electronic polarizabilities (ae) which were calculated in the range from 8.003 to 8.02 x 10 24 cm3 in the cooling cycles.
author_names: Zahid Hussain
title: Thermo Optic Coefficients and Electronic Polarizabilities of Tungsten Bronzes Using Ellipsometry
venue: IEEE Photonics Journal
year: 2019

abstract: Abstract The development of thermo optic modulator elements for midwave infrared (MWIR) and longwave infrared (LWIR) electro optic systems, and the development of resistive thermometer elements for infrared imaging microbolometers require materials with high thermo optic coefficients (TOC) and high temperature coefficients of resistance (TCR) respectively. In this paper, we synthesize novel vanadium oxide (VxOy) thin film structures and measure their MWIR/LWIR thermo optic coefficients (TOCs) and their temperature coefficients of resistance (TCRs) The VxOy thin film are synthesized by sputter depositing interchanging, 5 nm thick, layers of vanadium sesquioxide (V2O3) and vanadium (V) reaching a final thin film thickness of 95 nm. The sputter deposited multilayer structures are then ex situ annealed in N2 and O2 atmospheres at 300 degC for 30 min. Infrared spectroscopic ellipsometry was used to measure the optical constants of the thin films as a function of temperature across the MWIR and LWIR bands (3000 14000 nm) The synthesized VxOy thin films exhibited high TOCs and high TCRs when operated in their semiconducting phase. A high TOC was measured reaching a maximum of 0.0278 degC 1 and 0.119 degC 1 at l 4000 nm for N2 and O2 annealed VxOy thin films respectively; and reaching a maximum of 0.0634 degC 1 and 0.139 degC 1 at l 10,000 nm for N2 and O2 annealed VxOy thin films respectively. Moreover, sheet resistance versus temperature measurements were conducted revealing room temperature sheet resistances of 1.495 k O/sq. and 1.516 k O/sq. and TCRs of 3.54%/degC and 3.46%/degC for N2 and O2 annealed VxOy thin films respectively.
author_names: Mohamed R Abdel-Rahman
title: Vanadium oxide thin films with high midwave longwave infrared thermo optic coefficients and high temperature coefficients of resistance
year: 2018

abstract: A microcavity fiber Fabry Perot interferometer (MFFPI) that is based on dual hollow core fibers (HCFs) is developed for measuring the thermo optic coefficients (TOCs) of liquids. The proposed MFFPI was fabricated by fusion splicing a tiny segment of the main HCF with a diameter D of 30 mm and another section of feeding HCF with a diameter of 5 mm. Then, the main HCF was filled with liquid by capillary action through the feeding HCF by immersing the MFFPI in the liquid. The TOCs of the Cargille liquid (n(D)=1.3) deionized (DI) water, and ethanol were accurately determined from the shift of the interference wavelength, which was due to the temperature variation. Our experimental results were also compared with other published studies to investigate the effectiveness of the proposed sensing scheme. The major advantage is that the miniature MFFPI can achieve the measurement of the TOCs of the liquids with picoliter volume, and the measured liquids also can be sealed off and stored inside the HCF to prevent contamination.
author_names: Cheng-Ling Lee

Hsuan-Yu Ho

Jheng-Hong Gu

Tung-Yuan Yeh

Chung-Hao Tseng
title: Dual hollow core fiber based Fabry Perot interferometer for measuring the thermo optic coefficients of liquids.
venue: Optics letters
year: 2015

abstract: We report a method for compensation of errors caused by temperature fluctuations in refractive index measurements using Silicon photonic microring sensors. The method involves determination of resonance wavelength shifts caused by thermal fluctuations using real time measurement of on chip temperature variations and thermo optic coefficient (TOC) of analyte liquids. Resistive metal lines patterned around Silicon microrings are used to track temperature variations and TOC of analyte is calculated by measuring wavelength shifts caused by controlled increments in device temperature. The TOC of de ionized water is determined to be 1.12 x 10 4/degC, with an accuracy of 8.26 x 10 6/degC. In our system, chip surface temperature variations were measured with an instrument limited precision of 0.004 degC yielding a factor of 16 enhancement in tracking accuracy compared to conventional, bottom of chip temperature measurement. We show that refractive index detection limit of the microring sensor is also improved by the same factor.
author_names: Prashanth R Prasad

Shankar Kumar Selvaraja

Manoj M Varma
title: Real time compensation of errors in refractive index shift measurements of microring sensors using thermo optic coefficients.
venue: Optics express
year: 2018

abstract: Seventeen glasses in the Ge As Se ternary glass forming region have been fabricated and analyzed to provide input for optical design data and to establish composition and structure based relationships to aide development of novel chalcogenide glasses with tailored optical functionality. While known that Ge addition to binary As Se glasses enhances the mean coordination number (MCN) of the network and results in increased Tg and decreased CTE, this work highlights the impact on optical properties, specifically mid wave (l 4.515 mm) index and thermo optic coefficient (dn/dT) Trends in property changes were correlated with an excess or deficiency of chalcogen content in the glassy network as compared to stoichiometric compositions. Transitions in key optical properties were observed with the disappearance of Se Se homopolar bonds and creation of As As homopolar bonds which are associated with the Se rich and Se deficient regions near the stoichiometry, respectively. A second transition was observed with the creation of GeSe ethane like structures, which are only present in strongly Se deficient networks. Fitting dn/dT values with a simplified version of the thermal Lorentz Lorenz formulation yielded a linear relation between the quantity (n 3dn/dT) and the CTE, which can be used to predict compositions with the near zero dn/dT required for athermal optical systems.
author_names: Benn Gleason

Kathleen Richardson

Laura Sisken

Charmayne E Smith
title: Refractive Index and Thermo Optic Coefficients of Ge As Se Chalcogenide Glasses
year: 2016