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.

Apparatus and method for measuring optical characteristics of an object

New theoretical results for noise in cryogenic bolometers are derived. Johnson noise is reduced by as much as 60% by electrothermal feedback from the bias supply. Phonon noise in the thermal link is reduced by as much as 30% relative to the usual equilibrium formula. Photon noise in the Rayleigh-Jeans limit is computed with attention to the attenuation of the photon correlations in the light beam. Basic results on bolometer responsivity, time constant, and thermal properties are presented in a new and convenient form. Excess 1/f and contact shot noise are also discussed.

Bolometer noise: nonequilibrium theory

We demonstrate a 50-channel high-resolution arrayed waveguide grating microspectrometer with a 0.2 nm channel spacing on a silicon-on-insulator (SOI) platform. The chip size is 8 mm x 8 mm. High channel density and spectral resolution are achieved using high aspect ratio 0.6 mum x 1.5 mum waveguide apertures to inject the light into the input combiner and to intercept different spectral channels at the output combiner focal region. The measured crosstalk is <-10 dB, the 3 dB channel bandwidth is 0.15 nm, and the insertion loss is -17 dB near the central wavelength of lambda = 1.545 mum.

A high-resolution silicon-on-insulator arrayed waveguide grating microspectrometer with sub-micrometer aperture waveguides.

A vertical color filter detector group according to the present invention is formed on a semiconductor substrate and comprises at least six layers of alternating p-type and n-typed doped regions. PN junctions between the layers operate as photodiodes with spectral sensitivities that depend on the absorption depth versus wavelength of light in the semiconductor. Alternate layers, preferably the n-type layers, are detector layers to collect photo-generated carriers, while the intervening layers, preferably p-type, are reference layers and are connected in common to a reference potential referred to as ground. Each detector group includes a blue-sensitive detector layer at an n-type layer at the surface of the semiconductor, a green-sensitive detector layer at an n-type layer deeper in the semiconductor, and a red-sensitive detector layer at the n-type layer deepest in the semiconductor. The blue-sensitive detector layer at the surface of the semiconductor may have a reference layer only below it, while the red- and green-sensitive detector layers have reference layers above and below them. Three sets of active pixel sensor circuitry are coupled to the three detector layers, such that three active pixel sensors are formed using the group of three co-located detectors of the vertical color filter detector group.

Vertical color filter detector group and array

During the last decade there has been a rapidly growing interest in integrated optical (IO) sensors, expecially because many of them principally allow for sensitive, real time, label-free-on-site measurements of the concentration of (bio-)chemical species. This review aims at giving an overview of the most relevant developments in this area. After a general introduction into the field of IO sensors for the chemical domain, relevant aspects of integrated optics and chemical sensing are presented in short. A large variety of IO sensing platforms are introduced and discussed: interferometers, resonators, coupling-based devices such as grating couplers and surface plasmon resonance based sensors and finally a new class of sensors based on chemically induced field profile changes. Strong and weak points of principle and of configuration based on these principles are indicated and the main performance data of the IO sensing platforms, especially the obtained resolution, are indicated. Best resolutions of the chemically induced refractive indices on the order of magnitude $10^{-6}-10^{-8}RIU$ can be obtained, corresponding to a resolution of $10^{-3}-10^{-5}$nm in the chemically induced growth of layer thickness of chemo-optical transducer materials. Depending on the anlalyte and the type of transduction layer chemical concentrations down to some ppb or some pg $ml^{-1}$can be determined. Several IO sensing systems are commercially available. Extension of individual sensors to sensor arrays is treated and finally an outlook for the future is given.

Integrated Optical sensors for the chemical domain

Numerous applications, e.g., systems for chemical analysis by optical absorption and emission line characterization, will benefit from the availability of low-cost single-chip spectrometers. A single-chip CMOS optical microspectrometer containing an array of 16 addressable Fabry–Perot etalons (each one with different resonance cavity length), photodetectors and circuits for read-out, multiplexing and driving a serial bus interface has been fabricated. The result is a chip that can operate using only four external connections (including Vdd and Vss) covering the visible spectral range of the spectrum with FWHM=18 nm. Frequency output and serial bus interface allow easy multi-sensor, multi-chip interfacing using a microcontroller or a personal computer. Power consumption is 1250 μW for a clock frequency of 1 MHz.

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Single-chip CMOS optical microspectrometer

This paper reports on the IC-compatible fabrication of vertically tapered optical layers for use in linear variable optical filters (LVOF). The taper angle is fully defined by a mask design. Only one masked lithography step is required for defining strips in a photoresist with trenches etched therein of a density varying along the length of the strip. In a subsequent reflow, this patterned photoresist is planarized, resulting in a strip with a local thickness defined by the initial layer thickness and the trench density at that position before reflow. Hence a taper can be flexibly programmed by the mask design to be from 0.001o to 0.1o, which enables the simultaneous fabrication of tapered layers of different taper angles. The 3D pattern of resist structures is subsequently transferred into Si or SiO2 by appropriate etching. Complete LVOF fabrication involves CMOS-compatible deposition of a lower dielectric mirror using a stack of dielectrics on the wafer, tapered layer formation and deposition of the top dielectric mirror. Design principle, processing and simulation results plus experimental validation of the technique on the profile in the resist and after transfer of the taper into Si and SiO2 are presented.

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Vertically tapered layers for optical applications fabricated using resist reflow

The spectral resolution of a MEMS-based IR microspectrometer critically depends on the thermal cross-talk between adjacent TE elements in the detector array. Thermal isolation between elements is realized by using bulk micromachining directly following CMOS processing. This paper reports on the characterization results of bridge-shaped TE detector elements that are cut out of a membrane. Elements with dimensions of 650 × 36 ?m2 are separated by 10 ?m wide gaps in order to minimize the thermal cross-talk by heat conduction through the support structure. The static and dynamic aspects of thermal cross-talk have been evaluated with an emphasis on the effect of the thermal conductivity of air as a function of the package pressure.

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Characterization of thermal cross-talk in a MEMS-based thermopile detector array

This paper reports on an IC-Compatible process for the fabrication of Linear Variable Optical Filter (LVOF). The LVOF is integrated with a detector array to result in a micro-spectrometer. The technological challenge in fabrication of an LVOF is fabrication of a well-controlled tapered cavity layer. Very small taper angles, ranging from 0.001 degrees to 0.1 degrees. are fabricated in a resist layer by just one lithography step and a subsequent reflow process. The 3D pattern of resist structures is subsequently transferred into SiO2 by an appropriate etching. Complete LVOF fabrication involves CMOS-compatible deposition of a lower dielectric mirror using a stack of dielectrics on the wafer, tapered layer formation and the deposition of the top dielectric mirror. The design principle, IC-Compatible processing and the characterization results on fabricated LVOFs are presented. (C) 2010 Elsevier B.V. All rights reserved.

Fabrication and characterization of IC-Compatible Linear Variable Optical Filters with application in a micro-spectrometer

A silicon colour sensor can be realised based on the wavelength-dependent response of silicon photodiodes in the optical part of the spectrum rather than on the transmittance of dyes. Such a colour sensor has been reported before, however it lacked an output signal in a digital form. The wavelength dependence of the absorption coefficient causes a peaking of the response in silicon photodiodes. This is usually considered to be an undesirable effect and possibilities are explored for reducing the impact on silicon photodetectors. The opposite objective is pursued in the colour sensor and measures are taken to maximise the effect of this wavelength dependence in order to obtain colour sensors in silicon. A special read-out method has been used that allows the collection of only the charge carriers generated at certain depths. The ratio between the photocurrent that is due to charge carriers generated in a shallow layer of silicon and the total photocurrent, generated in this layer and the underlying silicon bulk, is used as the colour signal. The sensor operation can be combined with a dual-slope A/D converter for providing a digital output. The colour sensor has been tested against a set of Munsell colour cards and adjacent colours can be distinguished.

G. de Graaf

Papers

Single-chip CMOS optical microspectrometer

Vertically tapered layers for optical applications fabricated using resist reflow

Characterization of thermal cross-talk in a MEMS-based thermopile detector array

Fabrication and characterization of IC-Compatible Linear Variable Optical Filters with application in a micro-spectrometer

Performance of an integrated silicon colour sensor with a digital output in terms of response to colours in the colour triangle