Optics: measuring and testing – By shade or color – With color transmitting filter
Reexamination Certificate
1999-08-06
2001-02-20
Evans, F. L. (Department: 2877)
Optics: measuring and testing
By shade or color
With color transmitting filter
C356S330000
Reexamination Certificate
active
06191860
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an optical shutter suitable for spectrometers, a spectrometer comprising such an optical shutter and to a method for special analysis of light radiation making use of the spectrometer.
BACKGROUND OF THE INVENTION
U.S. Pat. No. 4,193,691 refers to a spectrometer which comprises a slit assembly manufactured in file form of a liquid crystal cell. The electrodes of the cell can be selectively actuated for producing a pattern of so-called “slits” (temporarily transparent portions of the cell) which are arranged in a specific manner. Such a liquid crystal cell with a selectively actuatable pattern of “slits” capable of switching between clear and opaque optical states has acquired the name optical shutter. The spectrometer described in U.S. Pat. No. 4,193,691 comprises means for producing a spectrum of light under analysis, means for directing that spectrum on to the above-described slit assembly (where the slits have configurations appropriate to positions of specific spectral lines of interest in the spectrum), and also comprises detection means for detecting a portion of the spectrum which has passed the slit assembly at a specified time. The detected signal is then transmitted to so-called utilization means, i.e. the means by which the detected signal may be processed.
It should be emphasized that the concept of the above-described device resides in obtaining the spectrum of the light under analysis prior to directing radiation to the slit assembly. In accordance with this concept, the description specifically refers to a prism as the classic means for producing the spectrum. The conventional character of these means is further testified by the fact, that in all embodiments described in the specification the spectrum producing means are positioned before the slit assembly. However, such a configuration where the spectrum producing means precede the optical shutter cannot be considered as being the one the most compact and easy to manufacture.
U.S. Pat. No. 5,457,530 describes a “Spectrometer provided with an optical shutter” which follows the above-mentioned concept of first obtaining a light radiation spectrum and further directing it to an optical shutter array for selectively transmitting therethrough predetermined spectral lines (i.e. wavelength-dependent bands) at specified time intervals for further detecting and processing the intensity of these lines. The main involvement of the spectrometer of U.S. Pat. No. 5,457,530 in comparison with that of U.S. Pat. No. 4,193,691 is that, in the former, the optical shutter array includes a plurality of optical shutter elements arranged in correspondence with the lines in the obtained spectrum and being made of a material (PLZT) characterized by the increased switching speed of the optical state. Another difference is that the spectrum producing means constitutes a diffractor by which an incident light beam is diffracted according to wavelengths.
It is quite natural that methods of spectral analysis realizable by the known spectrometers which comprise optical shutters, are all based on the same approach in that the initial band of optical radiation must first be decomposed into a spectrum comprising a predetermined number of optical portions, each including predetermined wavelengths, which optical portions are then processed for further calculations. The optical shutter in the described methods (and devices) is used for high-speed switching between the mentioned optical portions of the spectrum. Such methods impose high requirements on the accuracy of the described optical equipment which is therefore expensive.
U.S. Pat. No. 5,424,545 describes a method for non-invasive non-spectrophotometric infrared measuement of blood analyte concentrations. The method includes either illuminating a sample with a plurality of radiation beams each covering a distinct portion of the spectrum and partially overlapping one another, or detecting radiation reflected or transmitted by the sample using a plurality of broadband detectors having at least partially overlapping responses. The obtained signals are coded and analyzed by analogy to colorimetry and visual processing and can be converted into concentration measurements. The computational method is based on implementation of the idea of color perception for a quantitative substrate analysis, which renders the method complex and time consuming.
OBJECT OF THE INVENTION
A principal object of the invention is the provision of a new concept of a known spectrometer incorporating an optical shutter, allowing for the development of a variety of compact and inexpensive novel spectrometers and to a new design of the optical shutter per se suitable for them. It is another object of the invention to provide a method of spectral analysis using the inventive device.
SUMMARY OF THE INVENTION
The concept of the present invention differs from that which has been acknowledged in the prior art and lies, briefly, in the recognition of the following fact: in a spectrometer with an optical shutter there is actually no need to obtain a spectrum in its conventional meaning, nor is it necessary to decompose the light radiation just before the optical shutter. Rather all that is required is to switch between a number of radiation portions each being wavelength-dependent in any predetermined way by means of the optical shutter.
Recognition of this idea has led the inventors to the conclusion that the conventional spectrum producing means may be replaced by an inexpensive device such as an attenuator comprising an assembly of attenuating zones having different wavelength-dependent attenuating characteristics, and being associated with switching segments (slits) of the optical shutter. Owing to such an exchange and, in accordance with the above-outlined idea, it becomes insignificant whether such a multi-zone attenuator is placed before or after the optical shutter, or is integrally combined therewith. These findings form a new concept of the invention which allows for various novel designs both of the spectrometer and of the optical shutter per se being suitable for spectral analysis purposes.
Thus in accordance with a broad aspect of the invention, there is provided an attenuating optical shutter for high speed spectral analysis of an optical radiation band so as to derive N wavelength-dependent portions thereof, said attenuating optical shutter incorporating:
an optical shutter body including N shutter segments, each selectably switchable between a first substantially transparent and a second substantially opaque optical state, and
a multi-zone attenuator comprising N optical attenuating zones each having a different predetermined wavelength-dependent attenuation characteristic;
wherein each of the shutter segments is optically interconnected with a respective one of the N optical attenuating zones of the multi-zone attenuator thus forming N respective cells of the attenuating optical shutter.
According to the simplest and most illustrative embodiment of the invention, the N segments of the optical shutter are capable of being successively actuated so that at any given moment only one of the N segments is in its transparent state.
It is understood that in such an attenuating shutter, each cell comprises one specific attenuation zone of the multi-zone attenuator optically interconnected to one corresponding segment of the shutter body. Thus, since only one optical segment is transparent at any given moment, only one specific wavelength-dependent portion of the optical band will pass through the attenuating shutter.
Alternatively, each of the N segments of the optical shutter may be switched from the first to the second state and vice versa at a different pre-selected frequency. In such an arrangement each optical radiation portion passing through a particular segment of the optical shutter is modulated at a frequency associated with this particular segment It is known to those skilled in the art that frequency modulation renders a signal noise resistant, and that the
Fine Ilya
Klinger Leonid
Evans F. L.
Fitch Even Tabin & Flannery
Orsense Ltd.
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