Not applicable.
Many optical systems utilize spectrum separation techniques and light diversion systems to select one or more wavelength bands of light and to direct the selected light to a sensing device. In many different types of instrumentation, often a specific spectrum of light is what is selected, because the signal sought to be detected is spectrum limited. For example, in many chemical analytical instruments, the distinguishing characteristics of a chemical mixture are detected by sampling the wavelengths or wavelength bands of light originating from a chemical or biological sample. In a simple example, a single distinct species of molecule that emits light in a characteristic wavelength can be identified by a detection system that selectively collects and transmits that wavelength band to a photodetector. When mixtures of chemicals, each with a specific light-emitting characteristic, are mixed, it then becomes necessary to enable multi-color transmission and detection, as well as separation.
Instrument designs to accomplish multi-color detection rely on optical elements such as color filters, gratings and dichroic mirrors to separate an incident light signal into one or more light signals that each encompasses a characteristic wavelength band. Light signals contained within selected wavelength bands can then be analyzed by photodetectors to determine the intensity of light present in the incident light beam in one or more wavelength regions. Such analysis can reveal the chemical components of the sample under study.
Multi-color systems are known which use dichroic mirrors to define the wavelength regions to be analyzed. FIG. 1 illustrates a simple system, known to the prior art, that uses three dichroic mirrors in a row to separate incident light into three primary colors. This system is used in electronic color imaging such as described in U.S. Pat. No. 4,654,698 to Longworthy. FIG. 2, also illustrating a prior art system, illustrates the type of system used in U.S. Pat. No. 3,7944,407 to Nishimura that includes two dichroic mirrors and three photodetectors. This systems uses an additional filter in front of each photodetector to further define the wavelength region being detected. Systems using three dichroic mirrors and four photodetectors, exemplified by U.S. Pat. No. 4,776,702 to Yamaba and U.S. Pat. No. 5,538,613 to Brumley, are illustrated schematically in FIGS. 3 and 4 respectively.
In all of these systems, the dichroic mirrors are used to reflect a desired wavelength band of light to a detector or group of detectors while the non-selected wavelength bands are directed to other dichroic mirrors. In all of these designs, the dichroic mirrors are fixed in place, thus limiting the instrument to the detection of light patterns of certain defined characteristics. In short, the instruments are dedicated to a defined type or pattern of light sensing.
In some applications, notably for the detection of fluorescently tagged DNA molecules, it would be desirable in different applications to be able to filter and detect different wavelength bands. For DNA sequencing procedures, a set of fluorescent dyes are commonly used to tag the DNA molecules so that the sequence of the DNA molecule can be detected by optical reading. For other DNA analysis procedures, for a variety of reasons not important here, the use of different fluorescent tags which have a different spectral characteristic, are more desirable. Therefore, an instrument which is capable of altering its optical characteristics for the particular application would be adapted for use in more applications, as contrasted to one that was invariable in it optics.
The present invention is summarized in an apparatus using light signals to test chemical properties of a sample, that the apparatus includes a reasonable filter module which includes a plurality of dichroic mirrors each of which is fixed in place relative to the other mirrors in the filter module, so that filter modules can be changed in the instrument to permit the optical characteristics of the instrument to be changed without the need for mirror adjustments of the mirrors relative to each other.
It is an advantage of the present invention that it enables devices intended for analysis of DNA molecules to be used for a variety of different applications which use a variety of fluorescent tags.
It is a feature of the present invention that it enables optical instruments of greater versatility for chemical or biochemical analysis.
Other objects, advantages, and features of the present invention will be apparent from the following specification, when taken in conjunction with the accompanying drawings.
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