Abstract: A strain sensor includes an optical fiber with at least one optical fiber, a reflector body with a reflective surface, a housing affixed to the optical fiber probe and to the reflector body. The reflective surface is spaced apart at a distance d from the ends of the probe's fibers and receives light from the end of the fiber and to reflect at least a portion of the light into the end of the fiber. The housing is attached to the fiber probe at a first end of the housing and attached to the reflector body at a second end of the housing. The housing is affixed to the material to be measured, and in the material causes a change in gap between the fiber end and the reflective surface, modulating the amount of light received in the receiving fiber, detectable by a photodetector connected to the receiving fiber.

Abstract: This disclosure generally pertains to a method for manufacturing a distributed optical fiber scrim comprising a functional optical fiber, the functional optical fiber scrim thus manufactured, and composites in which an optical fiber scrim is incorporated. The present disclosure describes a variety of textile scrims, particularly adhesively bonded nonwoven scrim materials, each comprising at least one optical fiber with a continuous path across at least the length or width of the fabric. Such optical fiber scrims may be useful as sensor components (for example, as a detector of breakage, strain, pressure, or torque), as illumination components (for example, in a variety of light-providing applications), or as data-distribution components, either alone or in combination with other materials, such as fabrics, films, foams, and the like.

Abstract: A modulated optical radiation field (I) whose modulation amplitude and temporal phase depend on the local position can be detected with a plurality of pixels 1. Each pixel 1 consists of a transducing stage (T) that converts incoming light (I) into a proportional electric signal, a sampling stage (S), two subtraction/summation stages (SUB1, SUM1; SUB2, SUM2), and an output stage. Each pixel can be addressed individually. The optical radiation field (I) is locally sensed and sampled at a frequency that is four times the wavefield's modulation frequency. The subtraction/summation stages (SUB1, SUM1; SUB2, SUM2) accumulate differences of two samples per modulation period, separated by half the period, during several averaging periods; the two stages are time shifted with respect to each other by a quarter period. The resulting two output signals are employed for the determination of the local envelope amplitude and the temporal phase.

Abstract: A physical quantity measuring system includes an optical fiber in which plural fiber Bragg gratings having different reflection wavelength changing bands are formed along the optical fiber in a longitudinal direction, a light source which outputs a broadband light into the optical fiber, an arrayed waveguide grating and an operating portion. The arrayed waveguide grating divides a light reflected by the fiber Bragg grating and outputted from the optical fiber into plural divisional wavelength bands. The arrayed waveguide grating outputs the divided lights to output channels. The operating portion detects a change of a reflected center wavelength of each fiber Bragg grating by a change of an output of each light-receiving element, operates a physical quantity and a position thereof given to the optical fiber, and is capable of detecting light from adjacent output channels.

Abstract: An optical sensor comprises a sensing element comprising a waveguide grating with a response that varies with an effective modal index experienced by light propagating in the grating and a sample window for receiving fluid which affects the effective modal index to modify the response, the sensing element arranged to receive light from a light source and to output the light after filtering; and an analyzing element comprising a second waveguide grating having a second response, and arranged to receive light output by the sensing element and to output the light after filtering for detection by an optical power detector. The combination of the two gratings converts changes in the wavelength of light output by the sensing element in response to the sample of fluid to changes in the amount of light, allowing the fluid index to be deduced from a measurement of optical power. The two elements may be fabricated on a single substrate to reduce errors from environmental disturbances such as temperature changes.

Abstract: Devices for monitoring structural health conditions of host structures. A device includes at least one optical fiber sensor and an electronic module. The optical fiber sensor includes a rolled optical fiber cable operative to generate a frequency shift of a light signal passing therethrough and a coating layer applied to the rolled optical cable. The frequency shift is commensurate with vibration of the host structure. The electronic module sends an input light signal to the optical fiber sensor, receives a sensor signal from the optical fiber sensor, and processes the sensor signal.

Abstract: The present invention discloses a method for detecting dispersion, overcoming disadvantages of complex configuration and insensitivity to a tiny dispersion of the method and device for detecting dispersion in the prior art. The inventive method includes: obtaining a signal within a predetermined bandwidth range from an optical signal received; obtaining an operated value of power via an operation on the signal within the predetermined bandwidth range; and obtaining amount of system dispersion according to a corresponding relation between the operated value of power and the amount of system dispersion. A device for detecting dispersion is disclosed, including a photoelectric filter operational unit and a processing unit, where an output of the photoelectric filter operational unit is connected to an input of the processing unit. The device for detecting dispersion of the present invention is applicable to an adaptive dispersion compensation system. An optical signal transmission system is further disclosed.

Abstract: An intensity modulated broadband optical signal source is arranged to produce optical signals in a plurality of wavelength bands. A demultiplexer/multiplexer pair receives optical signals from the optical signal source and produces a separate optical signal for each wavelength band. An optical coupler is arranged to receive the separate optical signals. Optical fiber loops connected to the optical coupler guides both clockwise and counter clockwise waves for each of the separate optical signals. The optical signals propagate through a sensor in each loop and then combine in the optical coupler to form a plurality of interference signals in each wavelength band. A multiplexer is optically coupled to the optical coupler to receive the interference signals therefrom, and a detector array having a selected detector corresponding to the each of the plurality of wavelength bands is arranged to provide an electrical signal that indicates the interference signals for each wavelength band.

Abstract: An optical fiber strain-temperature sensing system includes first and second optical sources respectively generating first and second light signals having different wavelengths. Optical circulators direct the light signals to an external sensing cable for the respective generation of first and second Brillouin scattered light signals. First and second frequency mixers have a first input respectively coupled to the first and second optical light sources. The optical circulators direct the first and second Brillouin scattered light signals respectively to second inputs of the first and second frequency mixers. First and second transducers are respectively coupled to an output of the first and second frequency mixers and are respectively configured for generating first and second electrical signals indicative of a Brillouin frequency shift of the first and second light signals.

Abstract: Accelerometers for determining acceleration and methods of fabricating an accelerometer are disclosed. In one embodiment, the accelerometer includes a frame, a mass movably suspended on the frame, a fixed element having a rounded surface that does not move with respect to the frame, a movable element having a rounded surface that moves with the mass, and a sensing coil of optical waveguide wrapped around the rounded surfaces to detect movement of the mass in response to acceleration based on interferometric sensing of a change in length of the sensing coil. A method of fabricating the accelerometer includes suspending the mass in the frame and wrapping the optical waveguide around the rounded surfaces. Sensitivity and low fabrication cost of the accelerometers enables their use for integration within an ocean bottom seismic cable. Further, the accelerometer may be an in-line or a cross-line accelerometer depending on the arrangement within the frame.

Abstract: A method and apparatus for monitoring one or more environmental parameters using interferometric sensor(s), a cross-correlator, a two-dimensional photosensitive array and optical focusing means are described. The method and apparatus allows for near simultaneous monitoring of the parameter(s) of interest.

Abstract: A fiber optic perimeter detection system includes a receiver to receive output light signals from sensors positioned at different regions, each sensor including a sensing fiber. Each sensor generates an output light signal having a specified wavelength, the output light signal having a property that varies when stress is induced in the sensing fiber. The perimeter detection system includes a memory to store information related to a mapping between the wavelengths of the output light signals and the regions where the sensors are positioned.

Abstract: An optical interrogation system and a method are described herein that enable the interrogation of one or more biosensors which can be located within the wells of a microplate. In one embodiment, the optical interrogation system has a tunable laser, N-fiber launches, N-lenses and N-detectors that are set-up to interrogate N-biosensors. In another embodiment, the optical interrogation system has a tunable laser, N-fiber launches, N+1 lenses and N-detectors that are set-up to interrogate N-biosensors.

Abstract: A multimode optical transmission system reduces a deterioration of a noise characteristic and a distortion characteristic caused by an interference between modes. In an optical transmitter, a signal output section outputs a predetermined signal based on an inputted electrical signal. A control section controls the signal output section so as to adjust a frequency component of the signal outputted by the signal output section based on group delay information of modes which propagate in a multimode optical transmission line. An electric-optic conversion section converts, into an optical signal, the signal outputted by the signal output section, and transmits the optical signal via the multimode optical transmission line.

Abstract: A multi-layer sensor (10) and a use for the sensor (10) are described. This sensor is multi-layered in construction. 5 An optical wave guide (18) is passed through the sensor (10) such that in the event of an external application of force the force acts on the optical wave guide.

Abstract: Plasmons on a waveguide may deliver energy to photocatalyze a reaction. The waveguide or other energy carrier may be configured to carry electromagnetic energy and generate plasmon energy at one or more locations proximate to the waveguide, where the plasmon energy may react chemically with a medium or interaction material.

Abstract: A biological agent detector for detecting predetermined biological agents. The biological agent detector includes an optical fiber, a cladding that clads a length of the optical fiber and a bioindicator disposed within the cladding. The biological agent detector also includes a coherent light source that excites the optical fiber and a biological agent signature detector that detects the presence of a biological agent based upon a change in a resonance characteristic of the optical fiber caused by absorption of the predetermined biological agent into the cladding of the fiber.

Abstract: The present invention measures the strain caused by the shrink and expansion from the corrosion and examines the corrosion of a tendon for a long term with high sensitivity to improve the accuracy of the examination.

Abstract: Plasmons on a waveguide may deliver energy to photocatalyze a reaction. The waveguide or other energy carrier may be configured to carry electromagnetic energy and generate plasmon energy at one or more locations proximate to the waveguide, where the plasmon energy may react chemically with a medium or interaction material.

Abstract: A physical quantity measuring system, includes an optical fiber in which plural fiber Bragg gratings having different reflection wavelength changing bands are formed along said optical fiber in a longitudinal direction, a light source which outputs a broadband light covering the reflection wavelength changing bands of all of the fiber Bragg gratings into the optical fiber, an arrayed waveguide grating which divides a light reflected by the fiber Bragg gratings and outputted from the optical fiber into plural divisional wavelength bands having a constant wavelength interval, and which outputs the divided lights to output channels, respectively, and an operating portion which detects a change of a reflected center wavelength of each fiber Bragg grating by a change of an output of each light-receiving element, and which operates a physical quantity and a position thereof given to the optical fiber, and which is capable of detecting light from adjacent output channels.

Abstract: A method and device are presented for use in determining a rate of rotation of an object. The device comprises a light guide comprising an arrangement of a plurality of coupled optical resonators arranged along a curvilinear optical path. This allows for determining a change in at least one of the light phase and frequency affected by the light propagation through the curvilinear path during the device rotation, said change being indicative of the rotation rate of the light guide.

Abstract: Disclosed is an impact detection system including: an optical fiber including a plurality of sensor sections to reflect light, a wavelength band of the reflected light vibrates depending on an elastic wave propagating through a subject to be inspected; a light source to input light into the optical fiber; optical filters each connected to an output terminal of the optical fiber; and an arithmetic processing unit to detect the impact from output values of sensor sections, wherein the wavelength bands of the sensor sections in the optical fiber are distributed such that the vibration bands caused by the impact to be detected do not overlap with each other, and a pass band of the optical filter corresponding to one of the sensor sections is distributed in the vibration band caused by the detection object, and is distributed in both sides of a center of the wavelength band of the one sensor section.

Abstract: A multi-core distributed temperature sensing optical fiber is described, wherein the arrangement and construction of at least two cores provides a spectral attenuation corrected (e.g., corrected for hydrogen and/or stress on the fiber) temperature measurement.

Abstract: Apparatus and method are provided for chemical and biological agent sensing. The sensing apparatus includes a resonator having a resonance frequency and one or more optical fiber coils. The optical fiber coil has a permeable cladding and an indicator embedded in the cladding that reacts to an agent (e.g., a chemical or biological substance). The resonator circulates light through the coil and produces a resonance shape centered at the resonance frequency and measured via the input light. A predetermined change in the resonance shape indicates a presence of the agent in the environment.

Abstract: A high-voltage component, having a first end and a second end, whereby the first end is on a high-voltage potential with respect to the second end. An insulating part, is arranged between the first end and the second end, and an optical fiber is integrated in the high-voltage component and extends from the first end to the second end. A capillary extends from the first end to the second end and is arranged within the insulating part. The inside diameter of the capillary exceeds the outside diameter of the fiber, and the fiber is arranged within the capillary. The capillary includes a protective medium to achieve a dielectric strength in the capillary, which dielectric strength is suitable for the operating conditions.

Abstract: Plasmons on a waveguide may deliver energy to photocatalyze a reaction. The waveguide or other energy carrier may be configured to carry electromagnetic energy and generate plasmon energy at one or more locations proximate to the waveguide, where the plasmon energy may react chemically with a medium or interaction material.

Abstract: An optical accelerometer includes means for changing the length of at least one optical fiber in response to acceleration functionally coupled to the at least one optical fiber. The fiber and the means for changing length are enclosed in a pressure compensated housing. The housing is filled with a substantially incompressible fluid or gel.

Abstract: A wear determination device for determining vibration in a turbine engine component to reduce wear in a turbine engine. The wear determination device may be capable of measuring vibrations in a turbine engine component. The vibration measurement may be used to determine vibrations in a turbine engine to identify wear locations and sources of wear. The wear determination device may be configured such that multiple locations in a turbine engine may be monitored on a single turbine engine by moving the wear determination device from location to location.

Abstract: Light to be sensed is spreaded across an entry surface of a transmission structure with a laterally varying energy transmission function. For example, the light could be output from a stimulus-wavelength converter, provided through an optical fiber, or it could come from a point-like source or broad area source. Output photons from the transmission structure can be photosensed by photosensing components such as an array, position sensor, or array of position sensors. Wavelength information from the light can be obtained in response to the photosensing component. Spreading can be performed by air, gas, transparent material, or vacuum in a gap, by a region or other part of a lens, or by an optical fiber end surface. If the light comes from more than one source, a propagation component can both spread the light and also keep light from the sources separate.

Abstract: The present invention relates to a determination of a physical state of an optical device by measuring a response signal. At least two subsequent measurements are executed. Therefore, a first optical signal is transmitted to the optical device, wherein a first optical property of said first signal is varied according to a first function of the time. A second optical property of a first response signal returning from the optical device is measured over the time and a first result function of the second optical property of the first response signal over the first optical property of first optical signal is established. Further, a second optical signal is transmitted to the optical device, wherein the first optical property of said signal is varied according to a second function of the time that is different from the first function of time.

Abstract: Plasmons on a waveguide may deliver energy to photocatalyze a reaction. The waveguide or other energy carrier may be configured to carry electromagnetic energy and generate plasmon energy at one or more locations proximate to the waveguide, where the plasmon energy may react chemically with a medium or interaction material.

Abstract: Interrogation systems for monitoring structural health conditions. An interrogation system includes at least one wave generator for generating a wave signal and optical fiber sensors applied to a structure. The interrogation system also includes at least one electronic module for generating an input sensor signal and sending the input sensor signal to the optical fiber sensors. Each optical fiber sensor impresses the wave signal onto the input sensor signal to generate an output sensor signal that is frequency shifted from the input sensor signal. The electronic module generates an information signal in response to the output sensor signal. The interrogation system also includes a signal processing unit and a relay switch array module that has relay switches. Each relay switch relays the information signal to the signal processing unit and the signal processing unit generates a digital sensor signal that is subsequently sent to a computer.

Abstract: Accelerometers for determining acceleration and methods of fabricating an accelerometer are disclosed. In one embodiment, the accelerometer includes a frame, a mass movably suspended on the frame, a fixed element having a rounded surface that does not move with respect to the frame, a movable element having a rounded surface that moves with the mass, and a sensing coil of optical waveguide wrapped around the rounded surfaces to detect movement of the mass in response to acceleration based on interferometric sensing of a change in length of the sensing coil. A method of fabricating the accelerometer includes suspending the mass in the frame and wrapping the optical waveguide around the rounded surfaces. Sensitivity and low fabrication cost of the accelerometers enables their use for integration within an ocean bottom seismic cable. Further, the accelerometer may be an in-line or a cross-line accelerometer depending on the arrangement within the frame.

Abstract: A chemical sensing device comprises a fiber core and a fiber cladding. The fiber core comprises an index-modulated grating region having an apodized profile configured for increasing shedding of light into the fiber cladding, and the fiber cladding of the chemical sensing device is configured for reflecting at least some of the deflected light back towards the fiber core. The sensing device is applicable in methods and systems for sensing chemicals.

Abstract: Sensors and systems for monitoring structural health conditions. The present invention provides a device for monitoring structural health conditions including a dielectric substrate, a piezoelectric device for actuating and/or sensing Lamb waves, a molding layer deposited over the piezoelectric device, a cover layer deposited over the molding layer and a hoop layer surrounding the piezoelectric device and being attached to the substrate. The device further includes an optical fiber coil sensor attached to the dielectric substrate, where the coil sensor has a rolled optical fiber cable and a coating layer applied to the rolled optical fiber cable. The present invention also provides a diagnostic patch network that includes a plurality of patch sensors attached to a host structure and a bridge box connected to the patch sensors. The bridge box sends information of structural health conditions to and receive power from a ground control system using a wireless communication technique.

Abstract: An optical wavelength readout system for application in optical sensing systems is disclosed. The system includes a Master unit including a wavelength swept optical source for launching light into a string of optical sensors, and a detection and processing unit for detecting and processing the light emitted by the source. The system also includes a Slave unit including a light coupling device for coupling light from the light source into the string of sensors and for coupling light reflected from the string of sensors to a detection and processing unit arranged to detect and process the reflected light. The Master unit includes a wavelength reference unit adapted to make a reference signal available to other parts of the sensing system. The reference signal represents a generally exact relation between the wavelength of the light emitted from the source and time.

Abstract: An optical fiber sensor array is disclosed which includes a first sensor fiber and a first reference fiber coupled at one end thereof to one side of a first optical coupling. A first wavelength selective reflector is coupled to the other end of each of the first sensor fiber and the first reference fiber. A second sensor fiber is coupled at one end to one side of a second optical coupling. The other side of the second optical coupling is coupled to an opposite side of one of the first wavelength selective reflectors coupled on one side to the first sensor fiber and the first reference fiber. The array also includes a second wavelength selective reflector coupled to the other end of each of the second sensor fiber and the second reference fiber. The second wavelength selective reflectors are operative at a wavelength different from an operative wavelength of the first wavelength selective reflectors.

Abstract: A surface sensing system including at least two sensors located on the end of the same optical fiber. The sensors are configured such that they exhibit resonant frequencies or Q-factors that are distinguishable from each other, where the Q-factor is defined as the resonant frequency divided by the resonance spectrum at full-width half maximum (FWHM). Because the sensors have distinguishable resonant frequencies or Q-factors and are located on the end of the same optical fiber, they can be monitored in parallel with little or no optical interference.

Abstract: The present invention relates to a method and a device for determining the cut-off wavelength of an optical fiber. A first aspect of the present invention is to provide a method for determining the cut-off wavelength of an optical fiber, which method provides a stable measurement, which measurement is substantially independent of the exact fiber position.

Abstract: A optical fiber sensor for measuring temperature and/or pressure employs temporally created long period gratings. The gratings may be produced by a periodic change in the refractive index of the fiber along the fiber longitudinal axis caused by periodically spaced compressive and/or expansive forces or by spaced-apart unbalanced forces that cause periodic fiber micro-bending. Pressure and temperature are determined by measuring changes in both the wavelength at which light is coupled from a mode guided by a core to a different mode and an amount of such coupling. The gratings are created intrinsically and extrinsically. Single and multiple core fibers are used.

Abstract: Fiber Bragg gratings (FBG) seismic activity sensors coupled in sensor arrays provide increased sensitivity to seismic activities, lower strain values and an absence of EMI allowing detection of troop and vehicle movements based on ground vibrations generating seismic signals. The FBG sensor head features a spring-mass configuration with a head surface, fiber optic cable and the FBG sensor attached to a spring that stretches during the acceleration of the mass. Waves propagating inside the earth and along the ground arriving at the sensor locations cause movement of the seismic activity sensors embedded in the ground and this movement induces an acceleration-dependent change in the FBG gratings placed on the sensors. In multiple sensor configurations, the cable will be connected to the other sensors in the network. FBG sensors, sensor arrays and sensor methods are provided in several embodiments.

Abstract: A method for aligning the spectral responses of two comb-like optical filters is provided. This method does not necessitate the use of spectrally-resolved equipment, as it uses the optical power correlation profile of a broadband light signal representative of the combined spectral responses of the two filters. In one embodiment, the power correlation profile is compared to a pre-stored profile. A tuning method for tuning two filters using this alignment method is also provided. The two filters are first relaxed to an unstretched position, and the second filter is stretched and aligned with the first. The first filter is also stretched and aligned with the other. Both filters are then stretched at a calibrated value.

Abstract: A highly stable broadband light source includes a semiconductor light source having a specific emission spectrum, an optical filter having a specific bandpass filtering function and a predetermined bandwidth and a coupling element, to which the light emissions of the semiconductor light source and of the optical filter are fed. The light emission of the broadband light source occurs at the output of the coupling element. The spectrum of the light emission of the broadband light source is composed of the emission spectrum of the semiconductor light source and the bandpass filtering function of the optical filter. The wavelength of the optical filter is temperature-stabilized so that the spectrum of light emission of the broadband light source is essentially determined solely by the filtering function of the optical filter.

Abstract: A method and apparatus for quickly and accurately determining optical wavelengths using multiple features of an optical spectrum produced by an optical element that is configured to produce an optical spectrum having multiple resolvable features. Finding the mean of the measured values of the multiple resolvable features may provide an improved characterizing measurement of the element. Examples of optical elements suitable for use in the present invention include, but are not limited to, super-structured fiber Bragg gratings, multiple fiber Bragg gratings, Fabry-Perot etalons and gas cells.

Abstract: A scanning optical monitoring system and method are appropriate for high speed scanning of a WDM signal band. The system and method are able to identify dropped channels or, more generally, discrepancies between the determined or detected channel inventory and a perpetual inventory for the WDM signal, which perpetual inventory specifies the channels that should be present in the WDM signal assuming proper operation of the network. The system includes a tunable optical filter that scans a pass band across a signal band of a WDM signal to generate a filtered signal. A photodetector then generates an electrical signal in response to this filtered signal. A decision circuit compares the electrical signal to a threshold and a controller, which is responsive to the decision circuit, inventories the channels in the WDM signal.

Abstract: An apparatus and method generating an optical pulse of picosecond class (having a high duty ratio), which accurately and stably operates at an arbitrary repetition frequency, has a high OSNR, and is not restricted by an RF modulation frequency, are provided. New modulation spectrum components are generated by performing phase modulation for light output from a single wavelength laser light source with an optical phase modulator. The phases of the modulation spectrum components are aligned by a phase adjuster, so that a pulse wave in a time domain is generated.

Abstract: A patch-type extrinsic Fabry-Perot interferometric fiber optic sensor and a real-time structural vibration monitoring method using the same are disclosed. The patch-type extrinsic Fabry-Perot interferometric fiber optic sensor is provided by combining the existing EFPI (Extrinsic Fabry-Perot Interferometer) fiber optic sensor with a direction-detecting sensor which can acquire direction information of a strain of a structure, which can solve a signal distortion problem occurring in the existing EFPI fiber optic sensor through a simple signal process. The patch-type extrinsic Fabry-Perot interferometric fiber optic sensor includes a piezoelectric material which can apply a control force to the existing EFPI fiber optic sensor, and a self-sensing bridge circuit for extracting the direction information when the piezoelectric material is used as an actuator, so that the sensible range of strain can be extended and the piezoelectric material can directly be used as the actuator based on the sensed signal.

Abstract: The method and the device are used for compensating for interfering variables in an optical sensor (50), which is at least sensitive with respect to a measured variable (M), a wavelength (?) of the optical signal (S1) fed in and an interfering variable (T). The optical signal (S1) also passes through a compensation element (40) which, together with the optical sensor (50), is located in a common interfering variable effect range (60) with the same effect of the interfering variable (T). In the compensation element (40), the interfering variable (T) changes the wavelength of the optical signal (S1) in such a way that the partial influences that take place in the optical sensor (50) on account of the changed wavelength and on account of the interfering variable (T) cancel one another out.

Abstract: An optical wavelength readout system for application in optical sensing systems is disclosed. The system includes a Master unit including a wavelength swept optical source for launching light into a string of optical sensors, and a detection and processing unit for detecting and processing the light emitted by the source. The system also includes a Slave unit including a light coupling device for coupling light from the light source into the string of sensors and for coupling light reflected from the string of sensors to a detection and processing unit arranged to detect and process the reflected light. The Master unit includes a wavelength reference unit adapted to make a reference signal available to other parts of the sensing system. The reference signal represents a generally exact relation between the wavelength of the light emitted from the source and time.

Abstract: Sensor arrays utilizing standard 1×2 couplers reduce the differences in the returned optical power levels by appropriate selection of the coupling ratios. Preferred embodiments are described that comprise 6 distribution fiber lines and 16 return fiber lines. One embodiment includes 16 sensor groups in which each sensor group has a dedicated return line. In another embodiment, 8 sensor groups are configured so that no two adjacent sensors have either a common distribution fiber line or a common return fiber line.