The diffraction tomography theorem is adapted to one-dimensional length measurement. The resulting spectral interferometry technique is described and the first length measurements using this technique on a model eye and on a human eye in vivo are presented.

Measurement of intraocular distances by backscattering spectral interferometry

Apparatus and method for increasing the sensitivity in the detection of optical coherence tomography and low coherence interferometry (“LCI”) signals by detecting a parallel set of spectral bands, each band being a unique combination of optical frequencies. The LCI broad bandwidth source is split into N spectral bands. The N spectral bands are individually detected and processed to provide an increase in the signal-to-noise ratio by a factor of N. Each spectral band is detected by a separate photo detector and amplified. For each spectral band the signal is band pass filtered around the signal band by analog electronics and digitized, or, alternatively, the signal may be digitized and band pass filtered in software. As a consequence, the shot noise contribution to the signal is reduced by a factor equal to the number of spectral bands. The signal remains the same. The reduction of the shot noise increases the dynamic range and sensitivity of the system.

Apparatus and method for ranging and noise reduction of low coherence interferometry LCI and optical coherence tomography OCT signals by parallel detection of spectral bands

An apparatus and method are provided. In particular, at least one first electro-magnetic radiation may be provided to a sample and at least one second electro-magnetic radiation can be provided to a non-reflective reference. A frequency of the first and/or second radiations varies over time. An interference is detected between at least one third radiation associated with the first radiation and at least one fourth radiation associated with the second radiation. Alternatively, the first electro-magnetic radiation and/or second electro-magnetic radiation have a spectrum which changes over time. The spectrum may contain multiple frequencies at a particular time. In addition, it is possible to detect the interference signal between the third radiation and the fourth radiation in a first polarization state. Further, it may be preferable to detect a further interference signal between the third and fourth radiations in a second polarization state which is different from the first polarization state. The first and/or second electro-magnetic radiations may have a spectrum whose mean frequency changes substantially continuously over time at a tuning speed that is greater than 100 Tera Hertz per millisecond.

Method and apparatus for performing optical imaging using frequency-domain interferometry

A system and method for imaging of a sample, e.g., biological sample, are provided. In particular, at least one source electro-magnetic radiation forwarded to the sample and a reference may be generated. A plurality of detectors may be used, at least one of the detectors capable of detecting a signal associated with a combination of at least one first electro-magnetic radiation received from the sample and at least one second electro-magnetic radiation received from the reference. At least one particular detector may have a particular electrical integration time, and can receive at least a portion of the signal for a time duration which has a first portion with a first power level greater than a predetermined threshold and a second portion immediately preceding or following the first portion. The second portion may have a second power level that is less than the predetermined threshold, and extends for a time period which may be, e.g., approximately more than 10% of the particular electrical integration time.

System and method for optical coherence imaging

Piezoelectric sensing is of increasing interest for high-temperature applications in aerospace, automotive, power plants and material processing due to its low cost, compact sensor size and simple signal conditioning, in comparison with other high-temperature sensing techniques. This paper presented an overview of high-temperature piezoelectric sensing techniques. Firstly, different types of high-temperature piezoelectric single crystals, electrode materials, and their pros and cons are discussed. Secondly, recent work on high-temperature piezoelectric sensors including accelerometer, surface acoustic wave sensor, ultrasound transducer, acoustic emission sensor, gas sensor, and pressure sensor for temperatures up to 1,250 °C were reviewed. Finally, discussions of existing challenges and future work for high-temperature piezoelectric sensing are presented.

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High-Temperature Piezoelectric Sensing

An agile optical sensor based on scanning optical interferometry is proposed. The preferred embodiment uses a retroreflective sensing design while another embodiment uses a transmissive sensing design. The basic invention uses wavelength tuning to enable an optical scanning beam and a wavelength dispersive element like a grating to act as a beam splitter and beam combiner to create the two beams required for interferometry. A compact and environmentally robust version of the sensor is an all-fiber in-line low noise delivery design using a fiber circulator, optical fiber, and fiber lens connected to a Grating-optic and reflective sensor chip.

Agile high sensitivity optical sensor

An optical sensing probe includes a tube having a tip portion configured for placement in an environment in which conditions are to be sensed and an etalon having a known characteristic disposed proximate the tip portion. The tube also includes a head portion remote from the tip portion containing a light directing element for directing light beams at the etalon and receiving reflected light beams from the etalon wherein the received reflected light beams are used for determining an environmental condition proximate the tip portion. A method for measuring a thickness of the etalon may include directing a light beams at different frequencies at the etalon and receiving the light beams from the etalon. The method may also include identifying conditions of the respective light beams condition received from the etalon and then calculating a first thickness of the etalon responsive to the respective conditions and the known characteristic.

Optical sensor for extreme environments

Accuracy, reliability, and long lifetimes are critical parameters for sensors measuring temperature in gas turbines of clean coal-fired power plants. Greener high efficiency next generation power plants need gas turbines operating at extremely high temperatures of 1500°C, where present thermocouple temperature probe technology fails to operate with reliable and accurate readings over long lifetimes. To solve this pressing problem, we have proposed the concept of a new hybrid class of all-silicon carbide (SiC) optical sensor, where a single crystal SiC optical chip is embedded in a sintered SiC tube assembly, forming a coefficient of thermal expansion (CTE) matched all-SiC front-end probe. Because chip and host material are CTE matched, optimal handling of extreme thermal ramps and temperatures is possible. In this article, we demonstrate the first successful industrial combustor rig test of this hybrid all-SiC temperature sensor front-end probe indicating demonstrated probe structural robustness to 1600°C and rig test data to ~1200°C. The design of the rig test sensor system is presented and data are analyzed.

Hybrid Wireless-Wired Optical Sensor for Extreme Temperature Measurement in Next Generation Energy Efficient Gas Turbines

To the best of our knowledge, for the first time, a single-crystal silicon carbide (SiC)-based minimally invasive smart optical sensor suited for harsh environments has been designed and demonstrated. The novel sensor design is based on an agile wavelength source, instantaneous single-wavelength strong two-beam interferometry, full optical power cycle data acquisition, free-space targeted laser beams, multiple single-crystal-thick SiC optical front-end chips, and multiwavelength signal processing for unambiguous temperature measurements to form a fast and distributed smart optical sensor system. Experiments conducted using a 1550-nm eye-safe band-tunable laser and a 300-mum coating-free thick SiC chip demonstrate temperature sensing from room temperature to 1000degC with an estimated average 1.3degC resolution. Applications for the proposed sensor include use in fossil fuel-based power systems, aerospace/aircraft systems, satellite systems, deep-space exploration systems, and drilling and oil mining industries

Harsh environments minimally invasive optical sensor using free-space targeted single-crystal silicon carbide

6H single-crystal silicon carbide (SiC) is an excellent optical material for extremely high temperature applications. Furthermore, the telecommunication infrared band (e.g., 1500–1600 nm) is an eye safe and high commercial maturity optical technology. With this motivation, the thermo-optic coefficient ∂n∕∂T for 6H single-crystal SiC is experimentally measured and analyzed from near room temperature to a high temperature of 1273 K with data taken at the 1550 nm wavelength. Specifically, the natural etalon behavior of 6-H single-crystal SiC is exploited within a simple polarization-insensitive hybrid fiber-free-space optical interferometric system to take accurate and rapid optical power measurements leading to ∂n∕∂T data. The reported results are in agreement with the previously reported research at the lower <600K temperatures.

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6-H single-crystal silicon carbide thermo-optic coefficient measurements for ultrahigh temperatures up to 1273 K in the telecommunications infrared band

Frank Perez

Papers

Agile high sensitivity optical sensor

Optical sensor for extreme environments

Hybrid Wireless-Wired Optical Sensor for Extreme Temperature Measurement in Next Generation Energy Efficient Gas Turbines

Harsh environments minimally invasive optical sensor using free-space targeted single-crystal silicon carbide

6-H single-crystal silicon carbide thermo-optic coefficient measurements for ultrahigh temperatures up to 1273 K in the telecommunications infrared band