Abstract: A method for testing inkjets for defects in an inkjet device includes determining, based on the likelihood that one or more inkjets are defective, whether to perform an inkjet defect test, The method may also include, identifying, if it is determined to perform an inkjet defect test, which inkjets to test based on properties of the inkjets, the number of identified inkjets being less than a total number of inkjets in the inkjet device; and testing the identified inkjets for defects using an image sensor.

Abstract: A spectroscopic device that can suppress the occurrence of cross-talk when light beams of different wavelength ranges are optically received is provided. Detected light is made incident to a dichroic minor (hereinafter referred to as “mirror”) DM1 along the perpendicular direction of a photoelectric surface 7. Accordingly, light transmitted through the mirror DM1 is made incident substantially perpendicular to the photoelectric surface 7. On the other hand, light reflected from the mirror DM1 is reflected from a main mirror surface 23. At this time, the dichroic mirror array 21 is inclined so that the mirror DM8 side having the minimum shortest wavelength is nearer to the photoelectric surface 7 than the minor DM1 side having the maximum shortest wavelength and substantially parallel to the main minor surface 23a, so that light reflected from the main mirror surface 23a is made incident to the mirror DM2 along the perpendicular direction of the photoelectric surface 7.

Abstract: Methods and apparatuses for determining a color calibration for different spectral light inputs in an imaging apparatus measurement are disclosed herein. In one embodiment, for example, a method for determining a color calibration for different spectral light inputs in an imaging apparatus measurement can include creating a reference color calibration and a reference luminance scaling calibration for each of a plurality of colors. The method can also include measuring a reference gray value R, G, B for each color in an image measurement of the light source. The method can further include calculating an R, G, B gray value for a first pixel in each of three filtered image measurements. The method can then include calculating pixel ratio values from each of the three first pixel gray values and comparing the reference gray values to the pixel ratio values to determine which one or more reference gray values are closest to the pixel ratio values.

Abstract: A tristimulus colorimeter on a single semiconductor chip having at least three detectors, each detector being coated by colorant filters, each filter having at least one layer and at least one filter having a double layer is provided. The colorimeter determines CIE tristimulus values of an incident light from inputs to the filters and detectors. Colorimeters having integral dye filters may be constructed on a single silicon chip embodying all the detectors and electronics, coated over each detector by a deposited filter layer. Colorants may be directly deposited on the detectors, rather than using a plastic substrate for a filter.

Abstract: A method for determining the optimal colorant thicknesses and linear combinations for integral illuminant-weighted CIE color-matching filters is provided. A reflectance colorimeter for configuring printers may be designed using this method.

Abstract: A light filter includes exactly one partially reflective layer having a top and a bottom and a wedge-shaped profile defining a wedge direction. First and second transparent layers are disposed on the top and bottom, respectively, of the partially reflective layer, each transparent layer including at least two dielectric layers of two different materials, each dielectric layer having a wedge-shaped profile oriented in the wedge direction. A photospectrometer including a light filter with the wedge-shaped profile is also disclosed.

Abstract: A method for inspecting a color filter includes a first step of disposing the color filter so that the color filter is opposed to a light source, a second step of outputting, from the light source, monochromatic light of a color corresponding to one of the colors of color layers of the color filter and entering the light into the plurality of color layers, and a third step of inspecting for display unevenness in each of the color layers with light transmitted through the color layers.

Abstract: A vehicle-mounted imaging device that is mounted in an automobile and performs color imaging has been provided with a plurality of two-dimensionally arranged pixel cells. In each of the pixels, a color filter separates incident light by a multilayer interference filter. The multilayer interference filter is composed of two ?/4 multilayer films and a spacer layer sandwiched therebetween. The multilayer interference filter transmits light in a wavelength region that corresponds to an optical thickness of the spacer layer. The ?/4 multilayer films and spacer layer are composed of inorganic materials.

Abstract: An optical system comprising an optical instrument and a processing unit. The optical instrument may comprise an illumination source and a sensor. The processing unit may comprise a data storage having stored thereon a characterization of the illumination source and a characterization of the sensor. The processing unit may also comprise a computer configured to calculate a system response of the illumination source and the receiving element considering the characterization of the illumination source and the characterization of the receiving element.

Abstract: An optical assembly is disclosed that includes an illumination source, a detection sensor, a monitor sensor, and an optical piece having a first side adapted to face a sample. The optical piece defines an illumination channel extending from the illumination source toward the first side, a detection channel extending from the first side toward the detection sensor, and a monitor channel extending from the illumination channel toward the monitor sensor. A spectrophotometer is also disclosed that includes a circuit board, illumination source and one or more sensors. The circuit board includes an optically transparent region, wherein the illumination source is mounted and situated relative to a first surface of the circuit board, so as to direct light through the optically transparent region. Each sensor is mounted and situated relative to a second surface of the circuit board opposite the first surface.

Abstract: A system for applying pigment to a substrate includes a spectrophotometer integral to the system. Light received from the substrate is spectrally analyzed by a spectrometer. One or more pigment discharges apply one or more pigments to the substrate. The spectrometer spectrally analyzes the one or more pigments applied to the substrate. The spectrometer includes an optical sensing circuit having thereon a plurality of optical sensors and one or more processing elements. A plurality of filter elements are fixedly positioned over at least a first group of the optical sensors, and an optical manifold having a plurality of exit windows and at least one entrance port is fixedly positioned with respect to the plurality of filter elements.

Abstract: This invention discloses an illumination method and an illumination control method. An embodiment of the illumination system includes two light detection modules for detecting a light produced by a light emitting diode and an ambient light, calculating a reference spectral distribution based on a detection result of the ambient light, comparing the detection result of the light emitting diode with the reference spectral distribution, and driving the illumination module to emit a light matching with the reference spectral distribution based on a comparison result. Another embodiment of the illumination system includes a light detection module for periodically switching the light emitting diode to emit light and stop emitting light. When the light emitting diode stops an illumination period, the light detection module detects an ambient light, and when the light emitting diode continues an illumination period, the light detection module detects a light produced by the light emitting diode.

Abstract: Spectrometric apparatus that include an array of detector elements and exhibits a number of capabilities is disclosed. The elements can be responsive to incident radiation to produce an output signal that includes information from the incident radiation. A spectrally selective element can be located in an optical path between the radiation source and the array, with an analysis module responsive to the output signal operative to analyze spatial distribution of spectral information received by the array. The apparatus can also correct for differences in intensity and spectral variability for spectral image signals and/or compare the spectral image signals with a pattern in spatial-spectral coordinate space. Detector elements can be responsive to scattering, and spatial information in their output can be analyzed.

Abstract: A scanning device for photoelectrically measuring a measurement object in the form of a printed sheet on the basis of image elements comprises a measuring table (MT) for supporting the measurement object, a measuring device which can be moved above the surface of the measuring tables for scanning image element lines of the measurement object, a drive system for moving the measuring device above the measurement object, a measurement and drive control system for the measuring device and drive system, and a processing unit, for processing and evaluating the measurement signals generated by the measuring device from the scanned image elements of the measurement object (S). The measuring device comprises a lighting system, a photoelectric receiver unit and optical means. The lighting system applies light to image elements disposed in strip-shaped lighting regions (15) at a standardized angle of incidence range.

Abstract: A spectrometer for use with a desired wavelength range includes an array of filters. Each filter outputs at least two non-contiguous wavelength peaks within the desired wavelength range. The array of filters is spectrally diverse over the desired wavelength range, and each filter in the array of filters outputs a spectrum of a first resolution. An array of detectors has a detector for receiving an output of a corresponding filter. A processor receives signals from each detector, and outputs a reconstructed spectrum having a second resolution, the second resolution being higher than any of the first resolution of each filter. Filters and detectors may be arranged into a plurality of imaging units, each imaging unit including first and second filters and first and second photosensing regions. A processor receives signals from each imaging unit, and generates a reconstructed spatial image comprised of discrete spatial units corresponding to each imaging unit.

Abstract: An electromagnetic energy measurement apparatus and method for measuring first, second, and third wavelength components includes first and second coated optical elements having non-parallel surfaces. Proper selection of the parameters of the optical elements reduces the level of coma and astigmatism in the apparatus. Additionally, filters pass the first, second, and third wavelength components to first, second, and third sensors. Improvement in the alignment of the field of view between sensors is realized by applying an adjustable compressive force on the filters to individually adjust the field of view.

Abstract: A tristimulus colorimeter for measuring reflective or transmissive materials is provided. The colorimeter measures a sample under a calibrated light source, receives inputs to detectors, and determines CIE tristimulus values of the same sample as they would occur under a reference light source. The colorimeter includes a calibrated light source and a single silicon chip that includes three or more detectors. Each detector is permanently coated by a different mix of dyes or other colorants that form a wavelength-selective filter. A single silicon chip embodies all the detectors and electronics, with each detector coated over by deposited filter layers.

Abstract: An absorption detection system is provided. The system includes a plurality of monochromatic light sources and a separator for separating the light from the plurality of monochromatic light sources into a plurality of wavelengths. A plurality of detectors, receives light of a single wavelength to measure absorption of light in a biological sample.

Abstract: In this spectral instrument, a plurality of interference filters 31, 32 . . . with transmitting wavebands different from each other are arranged in order so that light reflected by a specific interference filter 31 is made incident on the interference filter 32 on the next stage, and at positions on which light transmitted through each interference filter is made incident, photodetecting devices 41, 42 . . . are provided, wherein a silver thin film 31a with a thickness of 20 to 200 nm is provided on the light incidence surface side of the interference filter 31 on the first stage.

Abstract: A spectrometer for use with a desired wavelength range includes an array of filters. Each filter outputs at least two non-contiguous wavelength peaks within the desired wavelength range. The array of filters is spectrally diverse over the desired wavelength range, and each filter in the array of filters outputs a spectrum of a first resolution. An array of detectors has a detector for receiving an output of a corresponding filter. A processor receives signals from each detector, and outputs a reconstructed spectrum having a second resolution, the second resolution being higher than any of the first resolution of each filter.

Abstract: Aspects of the present invention encompass the collection of multispectral images from a population of objects, and the analysis of the collected images to measure at least one characteristic of the population, using photometric and/or morphometric features identifiable in the collection of images. In an exemplary application, the objects are biological cells. In a particularly preferred, but not limiting implementation, the plurality of images for each individual object are collected simultaneously. In an empirical study, the characteristic being measured involves the synapse between conjugated cells. The conjugated cells may represent a subpopulation of the overall population of objects that were imaged. In a particularly preferred, yet not limiting embodiment, the present invention enables the quantization of the redistribution of cellular molecules due to the conjugation of different biological cells. Significantly, such quantization is not feasible with standard microscopy and flow cytometry.

Abstract: A system (10) for multispectral imaging includes a first optical filter (24) having at least two passbands disposed in different spatial positions on the first optical filter, a second optical filter (20) having another at least two passbands, and processor (32) adapted to identify an intensity of light in the at least two passband of the second optical filter (20).

Abstract: A hyperspectral imager that achieves accurate spectral and spatial resolution by using a micro-lens array as a series of field lenses, with each lens distributing a point in the image scene received through an objective lens across an area of a detector array forming a hyperspectral detector super-pixel. Spectral filtering is performed by a spectral filter array positioned at the objective lens so that each sub-pixel within a super-pixel receives light that has been filtered by a bandpass or other type filter and is responsive to a different band of the image spectrum. The micro-lens spatially corrects the focused image point to project the same image scene point onto all sub-pixels within a super-pixel.

Abstract: Method and apparatus for generating an output signal that represents light with a desired color profile. A first sensor is provided to receive light and based thereon to generate a first signal with a first color profile. A color sensor is also provided that receives light and based thereon generates a second signal with a second color profile. A signal generation mechanism that is coupled to the first sensor and the color sensor and receives the first signal with a first color profile, receives the second signal with a second color profile, and performs a predetermined operation on the first signal and the second signal to generate the output signal with the desired color profile.

Abstract: An integrated circuit includes a photosensor array with subrange cells that photosense within respective subranges of an energy range. An optical signal and the array move relative to each other, and, for segments of their relative movement, sets of subrange cells photosense within subranges that are different. For example, a scanning device can cause relative scanning movement. The optical signal can be produced by illuminating a two-dimensional object. The photosensed quantities for a part of the optical signal can be used to produce spectral information for the part.

Abstract: Systems and techniques for multi-spectral imaging. Light may be received at a multi-spectral optical module, which transmits a plurality of wavelength band portions of the received light, each having a pre-selected bandwidth between about two nanometers and about forty nanometers. The pre-selected bandwidths may be between about ten nanometers and about thirty nanometers. Each of the wavelength band portions may have the same pre-selected bandwidth, or may have different pre-selected bandwidths.

Abstract: This invention discloses a spectroscopic sensor that is integrated with a mobile communication device, such as a mobile phone. The spectroscopic sensor is capable of measuring the optical spectra of a physical object for purposes of detection, identification, authentication, and real time monitoring. Through the mobile communication device, the obtained spectral information can be transmitted, distributed, collected, and shared by utilizing all the functions of the known or existing wireless communication networks.

Abstract: The disclosure relates to method and apparatus for obtaining a multimodal hyperspectral image of a sample for widefield spectral analysis. An apparatus according to one embodiment may include a plurality of optical lenses configured to interchangeably receive photons and focus the photons; a plurality of tunable filters positioned in a filter housing, each tunable filter selectively receiving the focused dispersed photons from one of the plurality of optical lenses, each tunable filter providing wavelength-selective filtered photons; a first optical camera and a second optical cameras for selectively receiving the wavelength-selective filtered photons from each of the plurality of tunable filters and combining said filtered photons to form a hyperspectral spatially accurate, wavelength-resolved image of the sample.

Abstract: A method for determining the optimal colorant thicknesses for integral CIE color-matching filters is provided. According to a computational study, a four band filter of the present invention provides a best approximation to the CIE XYZ color-matching functions with the least cost.

Abstract: A method for remotely detecting whether a subject is alive, comprising the steps of determining a calibration spectral signature for light reflectance from living skin, normalizing the calibration spectral signature values to the calibration reflectance value at a reference wavelength, storing the normalized calibration spectral signature, determining a subject spectral signature of the light reflectance of a region of skin of the subject whose liveness is to be determined, normalizing the subject spectral signature values to the subject reflectance value at the reference wavelength, comparing the normalized subject spectral signature with the normalized calibration spectral signature for at least one wavelength, generating a subject liveness signal based on the comparison of the normalized subject spectral signature with the normalized calibration spectral signature, and emitting the subject liveness signal.

Abstract: An apparatus for photometrically testing several specimens each irradiated by a light source, the light altered by the specimens being detected by an optical device and analyzed, the apparatus including a light source, a plurality of sample holders configured adjacent to one another on a support, a detector that receives altered light from sample within the sample holders, the detector including a filter for eliminating interfering light, a sensor having a sensor face and a diffusing optical member located between the filter and the sensor, wherein light is diffused and shines on a greater portion of the sensor surface, and with a more homogeneous brightness as compared to when the light is not diffused.

Abstract: In one embodiment, light having a first spectrum is filtered from a mixed light. Light having a second spectrum, different from the first spectrum, is also filtered from the mixed light. An intensity of the light having the first spectrum, and an intensity of the light having the second spectrum, are then sensed. From the sensed intensities of the lights having the first and second spectrums, an intensity of light having a third spectrum is estimated.

Abstract: Color measuring systems and methods are disclosed. Perimeter receiver fiber optics are spaced apart from a central source fiber optic and receive light reflected from the surface of the object being measured. Light from the perimeter fiber optics pass to a variety of filters. The system utilizes the perimeter receiver fiber optics to determine information regarding the height and angle of the probe with respect to the object being measured. Under processor control, the color measurement may be made at a predetermined height and angle. Various color spectral photometer arrangements are disclosed. Translucency, fluorescence and/or surface texture data also may be obtained. Audio feedback may be provided to guide operator use of the system. The probe may have a removable or shielded tip for contamination prevention.

Abstract: A method for determining spectral characteristics of an object is disclosed. A probe is positioned in proximity relative to the object and provides light to a surface of the object and receives light from the object. One or more critical heights are defined below which no specularly refelcted light is received and propagated. Prior to positioning the probe in proximity relative to the object, a plurality of position-sensitive calibration/normalization reference and a plurality of calibration/normalization measurements are taken with the probe at a plurality of predetermined positions with respect to the calibration/normalization reference. The intensity of light received is determined in a plurality of spectral bands with one or more measurements. The spectral characteristics of the object are determined based on the one or more measurements and based on data taken from one or more of the calibration/normalization measurements.

Abstract: Color/optical characteristics measuring systems and methods are disclosed. Perimeter receiver fiber optics/elements are spaced apart from a central source fiber optic/element and received light reflected from the surface of the object is measured. Light from the perimeter fiber optics pass to a variety of filters. The system utilizes the perimeter receiver fiber optics to determine information regarding the height and angle of the probe with respect to the object being measured. Under processor control, the color measurement may be made at a predetermined height and angle. Various color spectral photometer arrangements are disclosed. Translucency, fluorescence and/or surface texture data also may be obtained. Audio feedback may be provided to guide operator use of the system. The probe may have a removable or shielded tip for contamination prevention.

Abstract: Ambient light analysis methods, imaging devices, and articles of manufacture are described. According to one aspect, an ambient light analysis method includes emitting light using a source, first filtering the light of the source providing first filtered light, first receiving the first filtered light using an imaging device, providing a first response of the imaging device to the first filtered light, second filtering ambient light providing second filtered light, second receiving the second filtered light using the imaging device, providing a second response of the imaging device to the second filtered light, and determining information regarding a spectral power distribution of the ambient light using the first response and the second response.

Abstract: The present invention features a fiber optic imaging system for generating a customized spectral response comprising (a) an optional optical source for generating optical energy, (b) an optical system for focusing multi spectral optical energy to form a focal surface; (b) a fiber optic element for conveying the optical energy, wherein the fiber optic element has an input end optically coupled to the focal surface to receive the optical energy and an output end to transmit the conveyed optical energy; and (c) a spectral filter optically coupled to at least one of the input and output ends of the fiber optic element, wherein the spectral filter has a filter passband configured to provide the fiber optic element with a pre-determined wavelength transmittance capacity, such that only pre-determined wavelengths of the optical energy are transmitted through the output end, thus achieving a customized spectral response.

Abstract: Apparatus and methods for wavelength-dependent detection are provided. A detector includes a hybrid filter having unpatterned and patterned filter layers and at least one light-detecting sensor that detects light in first and second wavelength bands from the patterned filter layer of the hybrid filter. The unpatterned filter layer passes light in two nonoverlapping wavelength bands relative to light in wavelength bands between or among the nonoverlapping wavelength bands. The patterned filter layer includes first and second regions configured respectively to pass light in the first and second wavelength bands of the nonoverlapping wavelength bands passed by the unpatterned filter layer.

Abstract: A calorimeter for measuring a color of light includes a color sensing device, a suspension means and a counterweight. The suspension means suspends the color sensing device in an operative relationship relative to a color producing device, while the counterweight is secured to the suspension means and balances the color sensing device in the operative relationship relative to the color producing device.

Abstract: The present invention provides an optical sensor having one or more filter-photodetector pairs and feedback to monitor the intensity and chromaticity of the white light generated by an illumination system. According to the present invention, filter-photodetectors are configured into pairs thereof, wherein a first filter-photodetector of a pair is configured and arranged so as to be sensitive to a predetermined region of the electromagnetic spectrum, while a second filter-photodetector of the pair is configured and arranged to be sensitive to a substantially complementary region of the electromagnetic spectrum. The spectral responsivity of the first filter-photodetector and the second filter-photodetector overlap in a predetermined region of the electromagnetic spectrum.

Abstract: A system and method for distinguishing a first light source from other light sources utilizes an image receiver that can selectively engage and disengage a filter. The filter can be configured to either block bands of light corresponding to the light being emitted by either the first source or the other sources. By sequentially engaging and disengaging the filter from the image receiver, the first light source may be distinguished from other light sources.

Abstract: An imaging optical instrument for acquiring images of a sample area is disclosed. The instrument includes a spatial detector with aligned detector elements and a variable filter having filter characteristics that vary in at least one direction and are located in an optical path between the sample area and the spatial detector. An actuator is operatively connected between the variable filter and the spatial detector and is operative to move the variable filter along the direction in which the filter characteristics vary.

Abstract: A spectroscopic sensor for measuring flat sheet product is disclosed. The disclosed sensor uses a combination of spectrometers and single-channel detectors and filters together with a broadband source of illumination to optimally measure multiple properties of a flat sheet product. A spectrometer is used to measure over a spectral range where an easily configurable set of wavelength channels is needed and where the signal-to-noise ratios and spectral resolutions of the channels are consistent with the spectral range and number of pixels of the spectrometer; while one or more single channel detector and filter combinations are used to measure, with high signal-to-noise ratio, at specific wavelengths within or outside the spectral range of the spectrometer(s).

Abstract: The present invention relates to the production of instantaneous or non-instantaneous multi-band images, to be transformed into multi- or hyperspectral images, comprising light collecting means (11), an image sensor (12) with at least one two dimensional sensor array (121), and an instantaneous colour separating means (123), positioned before the image sensor array (121) in the optical path (OP) of the arrangement (1), and first uniform spectral filters (13) in the optical path (OP), with the purpose of restricting imaging to certain parts of the electromagnetic spectrum. The present invention specifically teaches that a filter unit (FU) comprising colour or spectral filter mosaics and/or uniform colour or spectral filters mounted on filter wheels (114) or displayed by transmissive displays (115), is either permanently or interchangeably positioned before the colour separating means (123) in the optical path (OP) in, or close to, converged light (B).

Abstract: A colorimeter method and apparatus is described. The colorimeter includes a plurality of sensors/filter systems with non overlapping spectral responses, adequate for providing data capable of translation into standard coordinates system such as, CIE XYZ, CIE L*a*b*, or CIE Luv, as well as non-standard operable coordinate systems. The field of view of the colorimeter is chosen to closely track the response of the human eye using an optical path configured to select and limit the field of view in a manner that is insensitive to placement of the colorimeter on the source image. The optical path from the source image to the sensor is configured to select preferred light rays while rejecting undesirable light rays to maximize the signal/noise ratio. A rearward facing sensor channel is included to simultaneously measure ambient light impinging on the source image and feedback means to provide status and/or change of information.

Abstract: A two-dimensional spectroradiometer has an optical system such as an objective optical system 2 and a relay lens 6 for receiving light rays La from a two-dimensional light source L to form an optical image i.e. a first image 2a and a second image 6a, a WBPF 12 as a transmittance wavelength variable filter having a spectral transmittance characteristic that transmittance wavelengths of the light rays La differ from each other depending on transmittance sites of the filter where the respective light rays La pass, a scanning WBPF 10 which scannably holds the WBPF 12 on an optical path forming the optical image, and an image sensor 7 for capturing the second image 6a composed of the light rays La passing through the WBPF 12 at a position corresponding to each of scanning steps of the WBPF 12 to acquire a plurality of images each having a different spectral sensitivity among pixels of the image at the position corresponding to the each of the scanning steps.

Abstract: The present invention provides an apparatus and method for high resolution spectroscopy (approximately 10 picometer wavelength resolution) using a tunable optical filter (TOF) for analyzing a formation fluid sample downhole and at the surface to determine formation fluid parameters. The analysis comprises determination of gas oil ratio, API gravity and various other fluid parameters which can be estimated after developing correlations to a training set of samples using a neural network or a chemometric equation.

Abstract: Disclosed is an apparatus and method for a compact, rugged, and inexpensive spectrometer that will make possible a range of new applications for optical spectroscopy including point-of-care medical devices, personal monitors, and ubiquitous environmental sensing. Embodiments of the disclosure include silicon photodetectors where incident light passes through a layer of an inexpensive, absorbing thin film. In one embodiment, one or more photodetectors may be used where a series of absorbing thin film layers are passed over the photodetectors. In another embodiment, an absorbing thin film layer is placed over one or more photodetectors where the absorptivity of the thin film layer is different for each photodetector.

Abstract: A spectrophotometric optical system of a microplate reader and a filter wheel thereof are disclosed. The filter wheel comprises a pivotable wheel body, at least one narrow-band filter with a relatively long central wavelength mounted to the wheel body, and at least one narrow-band filter with a relatively short central wavelength mounted to the wheel body. The narrow-band filter with a relatively long central wavelength is provided with a diaphragm on a front surface thereof The diaphragm is formed with a plurality of apertures. A ratio of a total effective area of the plurality of apertures to an effective area of the narrow-band filter with a relatively short central wavelength is equivalent to a ratio of energy amounts of shorter wavelength light passed through the narrow-band filter with a relatively short central wavelength to energy amounts of longer wavelength light passed through the narrow-band filter with a relatively long central wavelength when the diaphragm is not disposed.

Abstract: A broadband light source, such as a light-emitting diode (LED), such as a superluminescent light-emitting diode (SLED), has its mean wavelength stabilized by using a filter to pass a characteristic of the output of the source, detecting the filtered output, and adjusting a parameter affecting the wavelength of the source, such as drive current or temperature. A Gaussian or near-Gaussian filter can be used to obtain an intensity detection, or two narrowband filters can be used where one filter passes a wavelength greater, and one passes a wavelength less, than the desired mean wavelength.