Abstract: A ring laser gyroscope (RLG) includes moveable minors and a Micro-Electro-Mechanical Systems (MEMS) actuator coupled to the moveable minors to cause a respective displacement thereof that induces a phase modulation on counter-propagating light beams relative to one another. The induced phase modulation creates an optical path difference between the counter-propagating light beams corresponding to a virtual rotation that reduces the lock-in of the RLG.

Abstract: Systems and methods for improved resonator fiber optic gyroscope intensity modulation control are provided. In one embodiment, a resonant fiber optic gyroscope (RFOG) having a residual intensity modulation (RIM) controller is provided. The controller includes an intensity modulator optically coupled to receive a light beam from a laser source modulated at a resonance detection modulation frequency, and an optical tap device optically coupled to the intensity modulator. The controller also includes a feedback servo coupled to the optical tap device and the intensity modulator, the demodulating feedback servo generating a sinusoidal feedback signal to the intensity modulator. The feedback servo adjusts an amplitude and phase of the sinusoidal feedback signal provided to intensity modulator based on a residual intensity modulation detected by the demodulating feedback servo.

Abstract: Methods and systems for improved fiber optic gyroscopes for operation in non-atmospheric environments are provided. In one embodiment, an integrated optical circuit for an interferometer subject to non-atmospheric conditions comprises: a first section of waveguide within a Lithium crystalline structure that is exposed to an electrical field, the first section of waveguide being a Titanium-diffused waveguide region; a second section of waveguide within the Lithium crystalline structure that is not within the first section of the waveguide, the second section of waveguide being a proton-exchange waveguide region; a stitch coupling the first section of waveguide to the second section of waveguide; and a third section of waveguide configured to combine reciprocal light beams to produce an interference pattern, wherein at least one of the reciprocal light beams pass through the first section of waveguide and the second section of waveguide prior to producing the interference pattern.

Abstract: A multiple nested interferometric fiber optic gyroscope system having varying functions may include a first fiber optic coil, a second fiber optic coil which is smaller than the first fiber optical coil and nested within and transversely to the first fiber optic coil, and a third fiber optic coil which is smaller than the second fiber optical coil and nested within and transversely to the second fiber optic coil.

Abstract: Interferometric fiber optic gyroscope. The gyroscope includes a pulsed light source for generating light pulses and a sense coil for receiving and trapping the light pulses travelling in clockwise and counter clockwise directions for a selected number of times around the sense coil. A detector receives the counter propagating light pulses to determine the phase shift between the two counter propagating light pulses, the phase shift being proportional to rotation rate of the sense coil.

Abstract: A hollow-core optical-fiber filter is provided. The hollow-core optical-fiber filter includes a hollow-core optical fiber having a first end-face and an opposing second end-face. The first end-face and the second end-face set a fiber length. The hollow-core optical-fiber filter also includes a first reflective end-cap positioned at the first end-face and a second reflective end-cap positioned at the second end-face. When an optical beam from a laser is coupled into one of the first end-face or the second end-face, an optical output from the opposing end-face has a narrow linewidth and low frequency noise fluctuations.

Abstract: A gyroscope and a method of detecting rotation are provided. The gyroscope includes a structure configured to be driven to move about a drive axis. The structure is further configured to move about a sense axis in response to a Coriolis force generated by rotation of the structure about a rotational axis while moving about the drive axis. The structure further includes at least one first torsional spring extending generally along the drive axis and at least one second torsional spring extending generally along the sense axis. The gyroscope further includes an optical sensor system configured to optically measure movement of the structure about the sense axis.

Abstract: An optical sensor includes at least a portion of an optical waveguide having a hollow core. The optical waveguide substantially confines a first optical signal and a second optical signal within the hollow core as the first optical signal and the second optical signal counterpropagate through the optical waveguide. Interference between the first optical signal and the second optical signal is responsive to perturbation of the at least a portion of the optical waveguide.

Abstract: An optical sensor, a method of configuring an optical sensor, and a method of using an optical sensor are provided. The optical sensor includes an optical waveguide having a length and a laser source optically coupled to the waveguide. The laser source has a coherence length. Light from the source is transmitted to the waveguide as a first signal propagating along the waveguide in a first direction and a second signal propagating along the waveguide in a second direction opposite to the first direction. The optical paths of the first signal and the second signal are substantially reciprocal with one another and the first signal and the second signal are combined together after propagating through the waveguide to generate a third signal. The coherence length is greater than 1 meter or is in a range between 200 microns and 10 centimeters.

Abstract: Solid-state gyrolaser having a device for stabilizing the intensities making it possible to maintain equilibrium of the two counter-propagating modes having at least a means for calculating a rotation measurement (?, I?) of the gyrolaser on the basis of the counter-propagating modes having a frequency difference (??mes) between them, by assuming that the frequency difference (??mes) between the two counter-propagating modes is induced only by the rotation of the cavity.

Abstract: A guided coherent atom source (1) includes elements for generating neutral atoms in a gaseous state (2), elements for cooling the atoms gas (3), elements for generating a magnetic field (4), including an electro-magnetic micro-chip (6) deposited on a surface (18) of a substrate (14), and capable of condensing the atoms in a magnetic trap, elements for generating an electro-magnetic RF field capable of extracting the condensed atoms, optical elements (10) for emitting and directing an optical coherent beam (12) toward the condensed atoms able to guide the condensed atoms, characterized in that the optical elements (10) and the electro-magnetic micro-chip (6) are integrated onto the same substrate (14). An atomic interferometer using such a source is also disclosed.

Abstract: A fiber-optic sensor includes an optical fiber coil and a laser source optically coupled to the coil. Light from the source is transmitted to the coil as a first optical signal and a second optical signal counter-propagating through the coil. The optical paths of the first optical signal and the second optical signal are substantially reciprocal with one another and the first optical signal and the second optical signal are combined together after counter-propagating through the coil to generate a third optical signal. The laser source is frequency-modulated or can have a coherence length longer than a length of the coil.

Abstract: A resonator fiber optic gyroscope (RFOG) is disclosed that reduces rotation rate error instability. In one embodiment, the RFOG comprises a resonator optical ring cavity, a first light source in optical communication with the ring cavity and configured to generate a clockwise optical signal, and a second light source in optical communication with the ring cavity and configured to generate a counter-clockwise optical signal. The RFOG also includes a first optical component in optical communication with the first light source and the ring cavity. The first optical component is configured to prevent the clockwise optical signal from being back-reflected to the first light source. A second optical component is in optical communication with the second light source and the ring cavity. The second optical component is configured to prevent the counter-clockwise optical signal from being back-reflected to the second light source.

Abstract: A Sagnac phase shift tracking method of fiber-optic gyroscopes comprises determining, for both a current time and a previous time, a value of a primary harmonic demodulated signal and a value of a secondary harmonic demodulated signal from a detector output in the fiber-optic gyroscope; and determining the Sagnac phase shift of the fiber-optic gyroscope for the current time based on the values of the primary harmonic demodulated signal and the secondary harmonic demodulated signal for both the current time and the previous time.

Abstract: A gyroscope and a method of detecting rotation are provided. The gyroscope includes a structure configured to be driven to move about a drive axis. The structure is further configured to move about a sense axis in response to a Coriolis force generated by rotation of the structure about a rotational axis while moving about the drive axis. The gyroscope further includes an optical sensor system configured to optically measure movement of the structure about the sense axis. In certain embodiments, the gyroscope is a microelectromechanical system (MEMS) gyroscope.

Abstract: A clamp-point active circuit is provided. The clamp-point active circuit includes a rate amplifier configured to receive an output from a device transitioning between at least two levels. The clamp-point active circuit has at least one switching device configured to receive an output from the rate amplifier. The at least one switching device is in at least one respective feedback loop of the rate amplifier. A switching of the at least one switching device causes the rate amplifier to amplify with high linearity in a desired operating range and to clamp outputs received from the transitioning device that are outside the desired operating range to a fixed level.

Abstract: An Interferometric Fiber Optic Gyro (IFOG) device for high accuracy sensing. An example IFOG includes an integrated optics chip (IOC) and a modulation component that modulates one or more light signals passing thru the IOC according to a bias-modulation waveform. A glitch pattern experienced at front-end components of the IFOG includes frequency content that has approximately zero amplitude at predefined sense harmonics. Frequency content of the bias-modulation waveform is below a predefined threshold value at the predefined sense harmonics.

Abstract: A telecommunications optical fiber is secured against intrusion by detecting manipulation of the optical fiber prior to an intrusion event. This can be used in a non-locating system where the detection end is opposite the transmit end or in a locating system which uses Fresnel reflections and Rayleigh backscattering to the transmit end to detect and then locate the motion. The Rayleigh backscattering time sliced data can be stored in a register until an intrusion event is detected. The detection is carried out by a polarization detection system which includes an optical splitter which is manufactured in simplified form for economic construction. This uses a non-calibrated splitter and less than all four of the Stokes parameters. It can use a polarimeter type function limited to linear and circular polarization or two linear polarizers at 90 degrees.

Abstract: An optical sensor includes at least a portion of an optical waveguide having a hollow core generally surrounded by a cladding. The cladding substantially confines a first optical signal and a second optical signal within the hollow core as the first optical signal and the second optical signal counterpropagate through the optical waveguide. Interference between the first optical signal and the second optical signal is responsive to perturbation of the at least a portion of the optical waveguide.

Abstract: A fiber-optic sensor, a method of configuring a fiber-optic sensor, and a method of using a fiber-optic sensor are provided. The fiber-optic sensor includes an optical fiber coil having a length and a laser source optically coupled to the coil. The laser source has a coherence length. Light from the source is transmitted to the coil as a first signal propagating along the coil in a first direction and a second signal propagating along the coil in a second direction opposite to the first direction. The optical paths of the first signal and the second signal are substantially reciprocal with one another and the first signal and the second signal are combined together after propagating through the coil to generate a third signal. The coherence length is greater than 1 meter or is in a range between 200 microns and 10 centimeters.

Abstract: Systems and methods for fiber-optic gyroscopes are provided. In one embodiment, a fiber-optic gyroscope comprises: a light source current servo coupled to a light source that transmits light through an optic path, wherein the light source current servo controls intensity of light through the optic path via a light source current drive that supplies current to power the light source; and an intensity control signal processor coupled to the optic path via a photo detector, wherein the intensity control signal processor outputs an intensity control signal to the light source current servo, wherein the intensity control signal is a function of intensity of light as received at the photo detector; wherein the light source current servo compares the intensity control signal against a stable analog voltage reference to adjust the light source current drive and drive optical power at the photo detector towards a constant level.

Abstract: The present invention relates to an interferometric path and/or rotation measuring device having a transducer unit (14), which has grating means, and which cooperates with a light conductor unit and a light pickup unit to detect a linear and/or rotational movement of the grating means in such a way that two partial beams (20, 22) of the light conductor unit which are aimed at the grating means, generate a superposition signal which is detectable by the light pickup unit and is a function of the linear or rotational movement and/or a position of the grating means, a modulation interferometer unit (10) being connected upstream from the light conductor unit, the modulation interferometer unit (10) having means for beam splitting into the two partial beams (20, 22) and first means for optical delay of one of the two partial beams (20, 22), which cause an optical delay route longer than an optical coherence length of the two partial beams (20, 22), the modulation interferometer unit (10) being connected via a fibe

Abstract: The invention relates to a sensor for the determination of the rotational speed of a shaft.

Abstract: Systems and methods for fiber-optic gyroscopes are provided. In one embodiment, a fiber-optic gyroscope comprises: a light source current servo coupled to a light source that transmits light through an optic path, wherein the light source current servo controls intensity of light through the optic path via a light source current drive that supplies current to power the light source; and an intensity control signal processor coupled to the optic path via a photo detector, wherein the intensity control signal processor outputs an intensity control signal to the light source current servo, wherein the intensity control signal is a function of intensity of light as received at the photo detector; wherein the light source current servo compares the intensity control signal against a stable analog voltage reference to adjust the light source current drive and drive optical power at the photo detector towards a constant level.

Abstract: A method for inhibiting zero drift of an all-fiber interferometric fiber optic gyroscope and a corresponding all-fiber interferometric fiber optic gyroscope are disclosed. The method comprises: reversing the polarity of an AC voltage applied to a PZT piezoelectric ceramic phase modulator according to a predetermined half-cycle time period, and making half of the difference between output rotation rates of the gyroscope in two adjacent half-cycle time periods as the output rotation rate of the gyroscope in a cycle. A phase reversal switch and a DSP chip are added to the all-fiber interferometric fiber optic gyroscope. The phase reversal switch is used for controlling the polarity of the AC voltage, and the DSP chip is used for outputting a square wave signal to control the phase reversal switch and for calculating the output rotation rate of the gyroscope according to the output signal of a demodulation/amplifier circuit.

Abstract: In an optical interferometer, polarization dependence attributable to the optical path difference has conventionally been eliminated by inserting a half-wave plate at the center of the interferometer. However, light induced by polarization coupling produced in directional couplers used in the optical interferometer causes interference having different interference conditions from those of the normal light. Polarization rotators that effect any one of 90° rotation and ?90° rotation of all states of polarization of incoming light are inserted in the optical interferometer, and thereby the interference conditions of light induced by polarization coupling are made the same as those of the normal light. Each of the polarization rotators is implemented by using two half-wave plates and by varying an angle of combination of these half-wave plates. Alternatively, each of the polarization rotators is implemented through a combination of one half-wave plate and a waveguide having birefringence properties.

Abstract: A small-size optical rotation measuring device for detecting an organism, a tissue, blood, or molecules having rotatory power and determining the content thereof with high accuracy and an optical rotation measuring method for detecting an organism, a tissue, blood, or molecules having rotatory power and determining the content thereof with high accuracy. A nonreciprocal optical system is disposed in a loop optical path of a ring optical interferometer, and thereby light beams of circularly polarized modes orthogonal to each other are propagated in opposite directions through a sample to be measured. The wavelength of the light beams from a light source is in a wavelength region where the loss by the nonreciprocal optical element is low. A signal processing technique for phase-modulation optical fiber gyro having the highest resolution among ring interferometers is applied.

Abstract: The present invention relates to an apparatus for real-time monitoring chemical reaction between various biomaterials. More particularly, the present invention directed to a real-time monitoring apparatus for biochemical reaction, which comprises parabolic mirror and/or an optical waveguide tube for effective irradiation of light over the whole plate with uniform intensity.

Abstract: A biaxial optical gyroscope is provided, which realizes mode separation using the waveguide devices with different material, and the biaxial optical gyroscope includes: a surface Plasmon Polariton Y-type mode splitter (1), a Y waveguide integrated optical device (2), a Y waveguide integrated optical chip (3), a first polarization-maintaining fiber coil (41), a second polarization-maintaining fiber coil (42), directional couplers (51, 52) and detectors (61, 62), wherein the two output ends of the surface Plasmon Polariton Y-type mode splitter (1) are respectively connected to the Y waveguide integrated optical device (2) and the Y waveguide integrated optical chip (3), and the output ends of the Y waveguide integrated optical device (2) and the Y waveguide integrated optical chip (3) are respectively connected to the first polarization-maintaining fiber coil (41) and the second polarization-maintaining fiber coil (42).

Abstract: A fiber optic gyroscope using a low-polarization and polarization-maintaining hybrid light path comprises an optical meter head and a circuit signal processing part, The optical meter head comprises: a light source, a multi-functional integrated optic chip, a detector, a coupler and a fiber coil, wherein the light source is a low polarization light source and single mode fiber pigtail coupling; the input terminal of multi-functional integrated optic chip uses a single mode fiber, and the output terminal of multi-functional integrated optic chip adopts a polarization-maintaining fiber; the input fiber pigtail of the said detector is a single mode fiber; the coupler is a 2×2 polarization independence single mode fiber coupler; the fiber coil is a polarization-maintaining fiber. By adopting the scheme of the low-polarization and polarization-maintaining hybrid light path and the signal processing methods such as all-digital closed loop control and random overmodulation etc.

Abstract: Determining linear modulator dynamics in an interferometric fiber-optic gyroscope may be accomplished by applying a stimulus at a point within the gyroscope, observing a response in an output of the gyroscope, and determining, from the observed response, the linear modulator dynamics.

Abstract: An all-fiber interferometric fiber optic gyroscope having a minimum reciprocal configuration is described. The gyroscope comprises a polarized light source, a light detector, a light source coupler, a fiber optic loop coupler, and a polarization maintaining fiber optic loop. A first port of the light source coupler is counter-axially coupled to an output end of the polarized light source, and a second port of the light source coupler on the same side as the first port is coupled to the light detector. A third port on the other side of the light source coupler is counter-axially coupled to the fiber optic loop coupler, and the fiber optic loop coupler is counter-axially coupled to the polarization maintaining fiber optic loop. The light source splits the input polarized light and polarizes the optical signal propagated along a transmission arm alone, where the first and third ports are on the same transmission arm.

Abstract: Systems and methods for optimizing input beam modulation for high gyro sensitivity and low bias errors. The present invention is a resonator optical gyroscope having an optimized phase-modulation amplitude (frequency) for a selected modulation frequency (amplitude) that maximizes the gyro signal-to-noise (S/N) sensitivity. For selected values of the phase modulation amplitude, the polarization cross-coupling induced intensity modulation can be nulled. By setting the phase modulation amplitudes substantially close to these nulling points (e.g. M=3.832 or 7.016 radians, which causes the first order Bessel function to be zero J1(M)=0) and then optimizing the modulation frequency, the intensity modulation induced bias is reduced to zero and gyro S/N sensitivity is maximized.

Abstract: One embodiment is directed to a power supply for a fiber optic gyroscope that comprises at least one main power supply, at least one demodulator local power supply to operatively couple the main power supply to a demodulator included in the fiber optic gyroscope, and at least one modulator local power supply to operatively couple the main power supply to a bias modulator included in the fiber optic gyroscope. The demodulator local power supply comprises a first current source to source current to the demodulator and a first shunt regulator coupled across a load associated with the demodulator. The modulator local power supply comprises a second current source to source current to the bias modulator and a second shunt regulator coupled across a load associated with the bias modulator.

Abstract: One embodiment is directed to a power supply for a fiber optic gyroscope that comprises at least one main power supply, at least one demodulator local power supply to operatively couple the main power supply to a demodulator included in the fiber optic gyroscope, and at least one modulator local power supply to operatively couple the main power supply to a bias modulator included in the fiber optic gyroscope. The demodulator local power supply comprises a first current source to source current to the demodulator and a first shunt regulator coupled across a load associated with the demodulator. The modulator local power supply comprises a second current source to source current to the bias modulator and a second shunt regulator coupled across a load associated with the bias modulator.

Abstract: An optical sensor includes an optical coupler configured to receive a first optical signal and to split the first optical signal into a second optical signal and a third optical signal. The optical sensor further includes a Bragg fiber in optical communication with the optical coupler. The second optical signal and the third optical signal counterpropagate through the Bragg fiber and return to the third port and the second port, respectively.

Abstract: A method for determining an accurate phase difference between a phase of a light beam in each of two light paths, the two light paths being in a rotating interferometric fiber optic gyro, by measuring a first phase difference due to angular velocity of the rotating interferometric fiber optic gyro, flipping axes of rotation of photons in the light loops of the rotating interferometric fiber optic gyro, and measuring a second phase difference due to angular velocity of the rotating interferometric fiber optic gyro.

Abstract: This application describes designs, implementations, and techniques for controlling propagation mode or modes of light in a common optical path, which may include one or more waveguides, to sense a sample.

Abstract: An optical fiber vibration sensor includes a light source, an optical receiver, an optical dividing/coupling portion, a signal processing unit, and a fiber loop portion made of an optical fiber. A part of an optical fiber composing the fiber loop portion is installed inside a housing of a main body of the optical fiber vibration sensor as an optical fiber for delay and another part of the optical fiber composing the fiber loop portion is installed outside the housing as a vibration detecting optical fiber.

Abstract: A resonator fiber optic gyroscope includes a first light source configured to generate a light signal. A resonator element is configured to generate a optical signal based on the light signal. A photodetector is configured to generate a first electrical signal based on the optical signal. The first electrical signal includes an oscillating signal, a direct-current (DC) signal, an even-harmonic signal including components at even harmonics of the oscillating signal, and an odd-harmonic signal including components at odd harmonics of the oscillating signal. A filtering element is configured to attenuate the DC signal, at least one even-harmonic component, and an odd-harmonic component to produce a second electrical signal. An amplifier is configured to amplify the second electrical signal. An analog-to-digital converter (ADC) is configured to digitize the amplified second electrical signal.

Abstract: The general field of the invention is that of rate gyros, of the matter-wave type, allowing the measurement of a speed of rotation in a given direction of measurement. This type of rate gyro works by the Sagnac effect and uses ultracold atoms to perform the measurement. It necessarily comprises an atom trap allowing a cloud of ultracold atoms to be immobilized in a given configuration and means for separation-displacement-recombination of the cloud into two packets of atoms so as to make them trace out a given area.

Abstract: A fiber optic gyroscope includes a light source, a coupler coupled to the light source, a photodetector coupled to the coupler, an integrated optic circuit (IOC) coupled to the coupler by a first element, and a sensing loop coupled to the IOC by second and third elements. At least one of the first, second and third elements includes a polarizing element.

Abstract: A fiber-optic interferometer comprising an optical fiber wound to form a fiber coil into which two partial light beams of a first light source can be coupled. The Bragg structure is integrated into the fiber coil. Said Bragg structure comprises an optical fiber having a periodically varying refractive index. In a method for determining physical state parameters in the interior of a fiber coil of a fiber optic interferometer information about physical state parameters in the interior of the fiber coil is obtained on the basis of the reflection wavelength of a Bragg structure comprising an optical fiber having a periodically varying refractive index is integrated into the fiber coil.

Abstract: An optical transmitter is disclosed having a temperature stabilization system for an optical filter for maintaining constant the frequency response of the filter. The filter is mounted within a housing having a substantially higher thermal conductivity. The housing may include a copper-tungsten alloy and extend along the optical axis of the filter. The housing is in thermal contact with a thermo-electric cooler (TEC) and a temperature sensor. The TEC and temperature sensor are electrically coupled to a controller which adjusts the temperature of the TEC according to the output of the temperature sensor.

Abstract: An evaluation method of an optical receiver of an optical communication system, including a DPSK (Differential Phase Shift Keying) signal modulated by a specific data series, a delay interferometer for performing delay detection on the DPSK signal, an optical receiver for receiving each of two optical outputs of the delay interferometer and outputting a difference signal, and a spectrum analyzer for measuring a spectrum of an output electrical signal of the optical receiver, comprising monitoring a specific frequency component of the spectrum analyzer and detecting a delay difference and a deviation in optical reception level between the two outputs of the delay interferometer and the optical receiver.

Abstract: Determining linear modulator dynamics in an interferometric fiber-optic gyroscope may be accomplished by applying a stimulus at a point within the gyroscope, observing a response in an output of the gyroscope, and determining, from the observed response, the linear modulator dynamics.

Abstract: An integrated interferometric gyroscope and accelerometer device. An example device includes a cantilever beam, a package having a post connected to one end of the beam, a piezoresistor driver, a piezoresistor sensor, and a semiconductor interferometric optical gyro. The piezoresistor driver is incorporated within the beam at a first area proximate to the post. The driver electro-thermally resonates the beam. The piezoresistor sensor is incorporated within the beam at the first area. The sensor piezoresitively senses a signal that relates to an acceleration force out-of-plane of the beam. The semiconductor interferometric optical gyro is also incorporated within the beam at a second area of the beam. The gyro senses rotational motion about an axis approximately equivalent to the acceleration force out-of-plane of the beam. The gyro includes a waveguide, a laser source and a light detector. The beam is formed from a semiconductor substrate.

Abstract: A gyroscope having photonic crystals for sensing rotation uses the Sagnac effect to determine angular motion. The gyroscope comprises a photonic crystal capable of guiding counter-propagating light beams in a closed path. A light source, coupling, and detection apparatus permits detection of phase changes between the counter-propagating beams, thereby permitting measurement of angular rotation. The photonic crystal comprises a periodic structure of pillars and voids which creates a photonic bandgap waveguide within which light waves in the proper wavelength range propagate with low loss.

Abstract: Solid-state gyrolaser having a device for stabilizing the intensities making it possible to maintain equilibrium of the two counter-propagating modes having at least a means for calculating a rotation measurement (?, I?) of the gyrolaser on the basis of the counter-propagating modes having a frequency difference (??mes) between them, by assuming that the frequency difference (??mes) between the two counter-propagating modes is induced only by the rotation of the cavity.

Abstract: An optical sensor includes an optical coupler. The optical sensor further includes a photonic bandgap fiber having a hollow core and an inner cladding generally surrounding the core. The photonic bandgap fiber is in optical communication with the optical coupler. Light signals counterpropagate through the photonic bandgap fiber and return to the optical coupler. The photonic bandgap fiber has a phase thermal constant S less than 8 parts-per-million per degree Celsius.