Patent Publication Number: US-6661512-B2

Title: Sample analysis system with fiber optics and related method

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to the coupling of selected input and output lines or channels through which optical signals are directed, and to the routing of optical signals to and from such lines or channels. More specifically, the present invention relates to an optical-based analysis system and method that utilizes a device adapted to effect selection and coupling through coordinated mechanical indexing movements and/or the use of optical fiber bundles whose ends are exposed to a detector. Such a device provides advantage in a wide variety of fields of application, particularly in applications involving the generation and transmission of analytical information. Specific fields of use include the preparation, sampling and analyzing of soluble materials as well as the testing of other fluids and solid materials exhibiting optical characteristics. 
     BACKGROUND OF THE INVENTION 
     Optical transport techniques are often utilized to direct a beam or pulse of light from a light source to a test site and, subsequently, to carry analytical information generated or measured at the test site to a suitable light receiving device. Analytical information transmitted by optical means can be chemical or biological in nature. For example, the analytical information can be used to identify a particular analyte, i.e., a component of interest, that is resident within the sample contained at the test site and to determine the concentration of the analyte. Examples of analytical signals include, among others, emission, absorption, scattering, refraction, and diffraction of electromagnetic radiation over differing ranges of spectra. Many of these analytical signals are measured through spectroscopic techniques. Spectroscopy generally involves irradiating a sample with some form of electromagnetic radiation (i.e., light), measuring an ensuing consequence of the irradiation (e.g., absorption, emission, or scattering), and interpreting of the measured parameters to provide the desired information. An example of an instrumental method of spectroscopy entails the operation of a spectrophotometer, in which a light source in combination with the irradiated sample serves as the analytical signal generator and the analytical signal is generated in the form of an attenuated light beam. The attenuated signal is received by a suitable input transducer such as a photocell. The transduced signal, such as electrical current, is then sent to a readout device. 
     As one example for implementing spectral analysis, a spectrophotometer uses ultraviolet (UV) and/or visible light, or in other cases infrared (IR) or near infrared (NIR) light, to scan the sample and calculate absorbance values. In one specific method involving the UV or UV-visible spectrophotometer, the UV sipper method, the sample is transferred to a sample cell contained within the spectrophotometer, is scanned while residing in the sample cell, and preferably is then returned to the test vessel. 
     The concentration of a given analyte in a sample through spectrochemical determination typically involves several steps. These steps can include (1) acquiring an initial sample; (2) performing sample preparation and/or treatment to produce the analytical sample; (3) using a sample introduction system to present the analytical sample to the sample holding portion of a selected analytical instrument (e.g., transferring the sample to the sample-holding portion of a UV spectrophotometer); (4) measuring an analytical signal (e.g., an optical signal) derived from the analytical sample; (5) establishing a calibration function through the use of standards and calculations; (6) interpreting the analytical signal based on sample and reference measurements; and (7) feeding the interpreted signal to a readout and/or recording system. 
     Conventional equipment employed in carrying out the above processes are generally known in various forms. Measurement of the analytical signal involves employing a suitable spectrochemical encoding system to encode the chemical information associated with the sample, such as concentration, in the form of an optical signal. In spectrochemical systems, the encoding process entails passing a beam of light through the sample under controlled conditions, in which case the desired chemical information is encoded as the magnitude of optical signals at particular wavelengths. Measurement and encoding can occur in or at sample cells, cuvettes, tanks, pipes, solid sample holders, or flow cells of various designs. 
     In addition, a suitable optical information selector is typically used to sort out or discriminate the desired optical signal from the several potentially interfering signals produced by the encoding process. For instance, a wavelength selector can be used to discriminate on the basis of wavelength, or optical frequency. A radiation transducer or photodetector is then activated to convert the optical signal into a corresponding electrical signal suitable for processing by the electronic circuitry normally integrated into the analytical equipment. A readout device provides human-readable numerical data, the values of which are proportional to the processed electrical signals. 
     For spectrophotometers operating according to UV-visible molecular absorption methods, the quantity measured from a sample is the magnitude of the radiant power or flux supplied from a radiation source that is absorbed by the analyte species of the sample. Ideally, a value for the absorbance A can be validly calculated from Beer&#39;s law:          A   =         -   log                   T     =         -   log          Ρ     Ρ   0         =   abc         ,                   
     where T is the transmittance, P 0  is the magnitude of the radiant power incident on the sample, P is the magnitude of the diminished (or attenuated) radiant power transmitted from the sample, a is the absorptivity, b is the pathlength of absorption, and c is the concentration of the absorbing species. 
     It thus can be seen that under suitable conditions, absorbance is directly proportional to analyte concentration through Beer&#39;s law. The concentration of the analyte can be determined from the absorbance value, which in turn is calculated from the ratio of measured radiation transmitted and measured radiation incident. In addition, a true absorbance value can be obtained by measuring a reference or blank media sample and taking the ratio of the radiant power transmitted through the analyte sample to that transmitted through the blank sample. 
     In some types of conventional sample testing systems, samples are transferred sequentially to one or more sample cells that are contained within the analytical instrument (e.g., spectrophotometer) itself. Samples are first taken from test vessels and, using sampling pumps, carried over sampling lines and through sampling filters. The samples are then transported to a UV analyzer, an HPLC system, a fraction collector, or the like. The analytical instrument may include a carousel that holds several sample cuvettes, such that rotation of the carousel brings each cuvette into position at the sample cell in a step-wise manner. The pulsing of the light source supplying the initial optical signal can be synchronized by control means with the rotation of the carousel. 
     Examples of UV-vis spectrophotometers are those available from Varian, Inc., Palo Alto, Calif., and designated as the CARY™ Series systems. In particular, the Varian CARY 50™ spectrophotometer includes a sample compartment that contains a sample cell through which a light beam or pulse passes. Several sizes of sample cells are available. In addition, the spectrophotometer can be equipped with a multi-cell holder that accommodates up to eighteen cells. A built-in movement mechanism moves the cells past the light beam. 
     Many conventional sample testing systems require either a plurality of active measurement beams, a plurality of active detectors, or both. For instance, U.S. Pat. No. 4,431,307 discloses a cuvette-set matrix containing an array of cuvettes adapted for use in measuring liquid samples using light beams. The cuvette-set matrix is adapted to receive a matrix of measurement beams such that one measurement beam is associated with each cuvette. A matrix of detectors is disposed on the side of the cuvettes opposite to the side at which the matrix of measurement beams is disposed. Thus, for each cuvette, the measurement beam emitted from the source passes through the liquid contained in the cuvette, and into the individual detector associated with that cuvette. 
     In other recently developed systems, fiber-optics are being used in conjunction with UV scans to conduct in-situ absorption measurements—that is, measurements taken directly in the sample containers of either dissolution test equipment or sample analysis equipment. Fiber optic cables consist of, for example, glass fibers coaxially surrounded by protective sheathing or cladding, and are capable of carrying monochromatic light signals. 
     One recent example of an in-situ fiber-optic method associated with dissolution testing is disclosed in U.S. Pat. No. 6,174,497. This method involves submerging a dip-type fiber-optic UV probe in test media contained in a vessel. Several probes can be operatively associated with a corresponding number of test vessels, with each probe communicating with its own UV spectrometer. A light beam (UV radiation) provided by a deuterium lamp is directed through fiber-optic cabling to the probe. Within the probe, the light travels through a quartz lens seated directly above a flow cell-type structure, the interior of which is filled with a quantity of the test media. The light passes through the test media in the flow cell, is reflected off a mirror positioned at the terminal end of the probe, passes back through the flow cell and the quartz lens, and travels through a second fiber-optic cable to a spectrometer. 
     Another recent example of an in-situ fiber-optic method associated with dissolution testing utilizes a U-shaped dip probe that is inserted into a test vessel. One leg of the U-shaped probe contains a source optical fiber and the other leg contains the return optical fiber. A gap between the ends of the fibers is defined at the base of the U-shape, across which the light beam is transmitted through the media of the test vessel. 
     For the previously described Varian CARY 50™ spectrophotometer, a fiber-optic dip probe coupler is available to enable in-situ sample measurement methods and effectively replace the need for a sipper accessory. This fiber optic coupler can be housed in the spectrophotometer unit in the place of the conventional sample cell. The coupler includes suitable connectors for coupling with the source and return optical fiber lines of a remote fiber-optic dip probe. The light beam from the light source of the spectrophotometer is directed to source line of the dip probe, and the resulting optical signal transmitted back to the spectrophotmeter through the return line. 
     Fiber optics have also been employed in connection with sample-holding cells. For example, U.S. Pat. No. 5,715,173 discloses an optical system for measuring transmitted light in which both a sample flow cell and a reference flow cell are used. Light supplied from a light source is transmitted through an optical fiber to the sample flow cell, and also through a second optical fiber to the reference flow cell. The path of transmitted light from each flow cell is directed through respective optical fibers toward an optical detector, and is controlled by an optical path switcher in the form of a light selecting shutter or disk. 
     It is acknowledged by persons skilled in the art that, when working with an array of flow cells, sample cells, cuvettes, probes, and other instruments of optical measurement, and particularly in connection with fiber-optic components, there remains a need for efficiently and effectively routing or distributing light energy to and from such sample containers. This need has been the subject of some developmental efforts. 
     For instance, U.S. Pat. No. 5,526,451 discloses a fiber-optic sample analyzing system in which a plurality of cuvettes each have a source optical fiber and a return optical fiber. A device is provided for selecting a source fiber to receive radiation for passage through a selected sample of one of the cuvettes, and for returning transmitted radiation from the selected cuvette through a selected return fiber to a spectrophotometer. The selection device includes a single rotatable retaining member supporting the respective ends of eight fiber-optic input lines and eight corresponding fiber-optic output lines. The respective ends of the fiber-optic lines are arranged in a ring around the central axis of the retaining member. The eight input lines define one half of the ring while the eight output lines define the other half. By this arrangement, each input line end affixed to the retaining member has a corresponding output line end affixed in diametrically opposite relation along the ring. Rotation of the retaining member determines which pair of input and output lines are respectively aligned with an input lens and an output lens disposed in spaced relation to the retaining member. A source beam passes through the input lens and into the selected input line at the end supported by the retaining member. The source beam then travels through the input line and into the sample cuvette associated with that particular input line. From the sample cuvette, the transmitted beam travels through the output line associated with the selected input line and sample cuvette. This output line terminates at its end supported by the retaining member. Since this output end is aligned with the output lens spaced from the retaining member, the transmitted beam passes through the output lens and is conducted to the analyzing means of the spectrophometer. 
     U.S. Pat. No. 5,112,134 discloses a vertical-beam photometric measurement system for performing enzyme-linked immunoabsorbent assay (ELISA) techniques. The system includes a light coupling and transmission mechanism utilizing a cylindrical rotor and a fiber-optic distributor. The mechanism receives light from a light assembly. The cylindrical rotor includes an optical fiber having an input end located at its center, and an output end located near its periphery. As the rotor rotates, the input end of the fiber of the rotor remains stationary with respect to the light assembly, while the output end moves around a circular path. The light output of the fiber of the rotor is received by a fiber optic distributor containing a multiplicity of optical fibers having their respective input ends arranged in a circular array. As the rotor is indexed about its axis, the output end of its fiber can be brought into alignment with successive fibers of the distributor. On the output side of the distributor, the multiplicity of fibers lead to a fiber manifold. The manifold aligns each fibers with a corresponding one of a multiplicity of assay sites. The assay sites are contained in a standard microplate consisting of an 8×12 array of optically transparent sample wells. Lens arrays are provided above and below the microplate to focus the beam of light passing through each individual sample well of the microplate. A detector board is located immediately below the lower lens array. The detector board contains an array of photodetectors corresponding to the array of sample wells. Thus, light from a selected fiber passes through a lens of the first lens array, the contents of the corresponding sample well, a corresponding lens of the second lens array, and into the corresponding photodetector of the detector board. In the conventional manner, the photodetector senses the intensity of the incident light that passed through the corresponding sample well and produces an electrical output signal proportional to the intensity. As in other vertical-beam systems adapted to scan samples contained in horizontally-oriented multi-well plates, this system requires a plurality of photedetectors and is not capable of routing the incident light from each sample well to a single detection means. 
     U.S. Pat. No. 6,151,111 also discloses a vertical-beam photometric system in which a plate carrier sequentially advances an 8×12 microplate through a measurement station. Each column of eight wells is scanned by light emitted from a bundle of eight corresponding distribution optical fibers. Light supplied from a light source passes through a monochromator to a rotor assembly. Each of the eight distribution fibers enables light from the rotor assembly to be sequentially directed by a corresponding mirror vertically through a corresponding aperture, lens, and microplate well, and subsequently into a corresponding photodetector lens. The rotor assembly consists of two mirrors positioned so as to bend light received by the rotor assembly 180 degrees, after which the light can be directed into one of the distribution fibers. The rotor can then be moved into alignment with another distribution fiber. 
     U.S. Pat. No. 4,989,932 discloses a multiplexer for enabling the sampling of a number of different samples. The multiplexer contains a stationary cylindrical outer body and a rotatable optical barrel disposed within the outer body. A primary inlet port is located on one side of the outer body through which light is introduced into the multiplexer. A primary exit port is located on an opposing side of the outer body through which light exits the multiplexer for transmission to an apparatus for optically analyzing a sample. Pairs of ancillary inlet and exit ports are disposed around the cylindrical wall of the outer body, and are oriented radially (or transversely) with respect to the longitudinal axis. The rotatable barrel contains a first mirror and lens associated with the ancillary exit ports, and a second mirror and lens associated with the ancillary inlet ports. A stepper motor is used to rotate the barrel to successively align the mirrors and lenses with a selected pair of ancillary inlet and exit ports. Light transmitted through the primary inlet port along the longitudinal axis of the multiplexer is turned at a right angle by the first mirror, passes through the first lens, and exits the multiplexer through the selected ancillary exit port. From the selected ancillary exit port, the light is transmitted through a fiber-optic bundle to a sample and returns to the multiplexer through the corresponding selected ancillary inlet port. From the selected ancillary inlet port, the light passes through the second lens, is turned at a right angle by the second mirror, and exits the multiplexer along the longitudinal axis. Other pairs of ancillary inlet and exit ports can be selected by rotating the barrel. In another embodiment disclosed in this patent, incoming light is received by an optical rod that has an angled mirrored surface at its end. Rotation of the rod by a stepper motor positions the angled mirrored surface to direct the light into a selected fiber-optic bundle. 
     U.S. Pat. No. 4,528,159 discloses a sample analysis system in which a belt containing a series of disposable reaction cuvettes is driven along a track so as to guide the cuvettes through several analysis stations. A separate photodetector tube is required for each analysis station. Light guides are used to transmit light from a light source, through filter wheels, through the reaction compartments of the cuvettes, and to the photodetectors. 
     U.S. Pat. No. 5,804,453 discloses a system in which a fiber-optic biosensor probe is inserted into a test tube. The probe receives a light beam from a light source and sends a testing signal to the photodetectors of a spectrometer. Time division multiplexing and demultiplexing is implemented to distribute light to and from several biosensors. Switching among inputs and outputs is controlled by an input control signal provided by an electronic clocked counter. 
     U.S. Pat. No. 5,580,784 discloses a system in which a plurality of chemical sensors are associated with several sample vials and arranged between a light source and a photodetector. Optical fibers are used to direct radiation into each sensor, as well as to direct emissions out from the sensors. A wavelength-tunable filter is combined with an optical multiplexer to direct radiation serially to each sensor through the fibers. 
     In view of the current state of the art, there is a continuing need for improved means for efficiently and effectively routing or distributing light energy to and from sample testing sites. It would be therefore be advantageous to provide a fiber-optic channel selection apparatus and method that utilize mechanical components to effect indexing among several optical input and/or output channels in an efficient and controlled manner without the need for costly optics-based switching components. In particular, it would be advantagous to provide an apparatus and method that enable analysis of multiple samples using only a single light source and a single detection means. Such an apparatus should be designed to minimize light loss and be compatible with a wide range of optical-based measurement systems. The present invention is provided to address these and other problems associated with the prior art. 
     SUMMARY OF THE INVENTION 
     According to one embodiment of the present invention, a sample measurement and analysis system comprises an optical channel selecting apparatus, a plurality of optical source lines, a plurality of optical return lines, a plurality of sample test sites, and an optical receiving device. 
     The optical channel selecting apparatus of the sample measurement and analysis system comprises an optical input selection device, an optical output selection device, and a controller element. The optical input selection device defines a first optical path running between a first input end and a first output end. The first output end is rotatable to a plurality of first index positions defined along a first circular path. The optical output selection device defines a second optical path running between a second input end and a second output end. The second input end is rotatable to a plurality of second index positions defined along a second circular path. The controller element communicates with the optical input selection device and the optical output selection device for selectively aligning the first optical path with the first index positions and the second optical path with the second index positions. 
     Preferably, the controller element comprises a rotatable coupling mechanism interconnecting the optical input selection device and the optical output selection device. Rotation of the coupling mechanism causes synchronized rotation of the first output end of the first optical path and the second input end of the second optical path. 
     In accordance with this embodiment, a light source can be optically coupled with the first input end of the first optical path. The plurality of optical source lines correspond to the plurality of first index positions and selectively communicate with the first optical path. The plurality of optical return lines correspond to the plurality of second index positions and selectively communicate with the second optical path. Each sample test site optically communicates with a corresponding one of the optical source lines and a corresponding one of the optical return lines. The optical signal receiving device optically communicates with the second output end of the second output path. 
     According to the invention, the sample test sites can take on various forms, depending on the particular function of purpose of the system in which the fiber-optic channel selecting apparatus is implemented. Non-limiting examples include sample containers, sample holders, sample cells, flow cells, optically transmissible multi-well plates, tanks, pipes, test vessels, cuvettes, test tubes, vials, and fiber-optic probes or dip probes. In one specific application of the invention, dip probes are insertable into test vessels containing the bulk media from which samples are taken or extracted. Insertion of the probes can be effected either manually or through automated means. The vessels can, for instance, contain dissolution media and be mounted on or otherwise supported by a dissolution test apparatus adapted to prepare the dissolution media. In other implementations, sample cells or flow cells are provided remotely in relation to the test vessels, and a suitable sample media transport system is provided for transferring samples to and from the cells and the vessels. 
     According to the invention, the optical signal receiving device can constitute any number of types of instruments, depending on the particular function of purpose of the system in which the fiber-optic channel selecting apparatus is implemented. In a specific exemplary embodiment of the invention, the optical signal receiving device is an optical detector such as a photodetector, phototube, photocell, or diode array. 
     According to another embodiment of the present invention, the fiber-optic channel selecting apparatus of the sample measurement and analysis system comprises an optical input selection device, an optical output selection device, and a rotatable coupling mechanism interconnecting the optical input selection device and the optical output selection device. The optical input selection device is rotatable about a first central axis, and comprises a first internal optical fiber having a first input end and a first output end. The first input end is disposed collinearly with the first central axis, and the first output end disposed at a radially offset distance from the first central axis. The optical output selection device is rotatable about a second central axis, and comprises a second internal optical fiber having a second input end and a second output end. The second input end is disposed at a radially offset distance from the second central axis, and the second output end disposed collinearly with the second central axis. Rotation of the coupling mechanism causes rotation of the first output end and the second input end. 
     In accordance with this embodiment, a light source can be optically coupled with the first input end of the first internal optical fiber. The plurality of optical source lines have respective source line input ends. Each source line input end is selectively optically alignable with the first output end of the first internal optical fiber. The plurality of optical return lines have respective return line output ends. Each return line output end is selectively optically alignable with the second input end of the second internal optical fiber. Each sample test site optically communicates with a corresponding one of the optical source lines and a corresponding one of the optical return lines. The optical signal receiving device optically communicates with the second output end. 
     According to an additional embodiment of the present invention, the sample measurement and analysis system comprises a fiber-optic channel selecting apparatus, a plurality of optical source lines, a mounting member, a plurality of optical return lines, a plurality of sample test sites, and an optical signal receiving device. 
     In this embodiment, the fiber-optic channel selecting apparatus comprising a rotary element rotatable about a central axis, and an internal optical fiber having an internal optical fiber input end and an internal optical fiber output end. The internal optical fiber input end is disposed collinearly with the central axis, and the internal optical fiber output end disposed at a radially offset distance from the central axis. A light source can be optically coupled with the first input end. The optical source lines have respective source line input ends. Each source line input end is selectively optically alignable with the internal optical fiber output end. The optical return lines have respective return line output ends. Each return line output end is fixedly supported by the mounting member. Each sample test site optically communicates with a corresponding one of the optical source lines and a corresponding one of the optical return lines. The optical signal receiving device is optically aligned with each return line output end. 
     According to a further embodiment of the present invention, a sample measurement and analysis system comprises an optical channel selection device, a plurality of optical source lines, a plurality of optical probes, and a plurality of optical return lines. The optical channel selection device defines an optical path running between an input end and an output end. The optical path is adjustable to a plurality of input channel positions. Each optical source line corresponds to a respective input channel position, and is selectively coupled to the optical path. Each probe is coupled to a respective source line. Each optical return line is coupled to a respective probe. 
     As described herein, the optical channel selecting apparatus of the inventive system can be provided as a mechanical, rotary fiber-optic multiplexer (and demultiplexer) apparatus for selecting channels through which a beam or pulse of light is routed in an indexing manner. The apparatus comprises one, two, or more rotary indexing devices. One of the rotary indexing devices demultiplexes a beam of light by distributing the light from a single, common outgoing or source line into a selected one of a plurality of outgoing or source channels. The selection is accomplished by rotating the demultiplexing device into a position at which the common outgoing or source line can optically communicate with the selected outgoing channel. The other rotary indexing device, when employed in the optical channel-selecting apparatus, multiplexes a beam of light for transmission into a single incoming or return line by selecting a selected one of a plurality of incoming or return channels. The selection is accomplished by rotating the multiplexing device into a position at which the common incoming or return line can optically communicate with the selected incoming or return channel. As an alternative to employing the multiplexing device, each incoming or return line can be optically aligned with a signal receiving means such as a photodetector, thereby eliminating the need for the second rotary indexing device and the common incoming or return line. 
     When two such rotary devices are provided in this manner, they can be mechanically interfaced so that rotation of one device concurs with rotation of the other device, with the result that the selection of a certain channel of the one device concurs with the selection of a corresponding channel of the other device. For instance, if each device includes twelve channels and thus twelve index positions, the selection of the channel at index position  1  of the one device simultaneously results in the selection of the channel at index position  1  of the other device. 
     According to an embodiment of the invention, each rotary device comprises two fixed components (i.e., first and second fixed components), a rotary component, and one or more bearings providing an interface between the fixed components and the rotary component. The rotary component is interposed between the two fixed components. Each fixed component faces a respective end of the rotary component. One of the fixed components (e.g., the first fixed component) has an optical aperture at its axial center. The other fixed component (e.g., the second fixed component) has a plurality of optical apertures oriented in a circular arrangement about its axial center. The number of optical apertures in the circular arrangement corresponds to the number of optical channels selectable by the apparatus of the invention. The rotary component has a light guiding path such as an optical fiber having one end located at the axial center of the rotary component and another end located radially outward with respect to the axial center. The centrally located end of the optical fiber of the rotary component is separated from the centrally located optical aperture of the first fixed component by a very small air gap. The offset end of the optical fiber of the rotary component is likewise separated from the plurality of optical apertures of the second fixed component by a very small air gap. These air gaps optimize light transmission while minimizing light loss, and avoid the necessity of using expensive additional optical components to couple the respective apertures and fiber ends of the fixed and rotary components. Indexed rotation of the rotary component with respect to the second fixed component results in selective coupling between the offset end of the optical fiber of the rotary component and each aperture of the second fixed component. 
     As indicated previously, the two rotary devices included with the optical channel selecting apparatus can be made to rotate together through a mechanical interface. This interface can be accomplished through a suitable set of gears arranged such that rotation of at least one gear results in rotation of both rotary devices. For example, each rotary device could be provided with its own gear, and each of these gears could be placed in meshing engagement with a third gear. While manual rotation of the third gear in order to rotate the other gears is possible, it is preferred that the third gear be powered through connection to a motor or similarly automated device. The motor could then be electronically controlled by suitable electronic hardware and/or software. As an alternative to providing gears with each rotary device, gear-like teeth could be formed on respective structures of the rotary devices to eliminate additional gearing. In either case, the rotary devices of the apparatus can be rotated continuously without the need to reverse rotation upon completion of the indexing of each channel provided. For instance, for a twelve-channel apparatus, the sampling interval from index position  1  to index position  2  is equivalent to the sampling interval from index position  12  to index position  1 . 
     As an alternative, the first rotary device utilized to select an outgoing channel is provided, but the second rotary device utilized to select an incoming channel is eliminated in favor of suitably collecting a bundle of optical return fibers constituting the incoming channels at a fixed position at which the ends of the fibers are optically aligned with the receiving window of a optical detection device. 
     The invention as just described offers advantages when incorporated into any system that includes one or more light sources and one or more devices adapted for receiving light energy from the light sources. In such systems, the mechanical multiplexing/demultiplexing functions realized by the present invention are useful in networking one or more light signals from selected light sources to selected receiver devices. The invention also offers advantages when incorporated into any system that uses optics to route optical signals over several lines or channels between a single light source and a single detector. An example of this latter system is a UV-vis spectrophotometer, which is generally designed to conduct UV scans on prepared samples. It is often desirable to scan a multitude of samples. In accordance with the present invention, each sample can be held in a test vessel or a suitable cell or well, or in any other suitable sample holding or containment means, and fiber-optic input and output lines can be brought into operative communication with each sample test site, or with each probe associated with the sample test site. In this manner, each cell, probe, vessel or test site respectively becomes associated with one of the channels of the apparatus of the invention, and hence becomes associated with the corresponding index positions of the rotary device or devices of the apparatus. Accordingly, the selection of index position  1  of each rotary device, for example, corresponds to the selection of test vessel  1 , cell  1 , and so on. 
     The fiber-optic channel selecting apparatus according to any of embodiments described herein can be directly integrated into the design of an optical-based sample measurement and/or analysis system or instrument, such as a spectroscopic apparatus. An example of a spectroscopic apparatus is a spectrophotometer. 
     According to another aspect of the present invention, a method for acquiring data from samples comprises the following steps. A plurality of samples are respectively disposed at a plurality of test sites. A plurality of optical source lines are provided such that each source line communicates with a corresponding one of the plurality of test sites. A plurality of optical return lines are provided such that each return line communicates with a corresponding one of the test sites. A test site and its corresponding source line and return line are selected by rotating a fiber-optic channel selecting apparatus to a position at which a light source is coupled to the selected source line. An optical signal of a first intensity is sent through the selected source line to the selected test site to expose the sample that is disposed at the selected test site. An optical signal of a second intensity is emitted from the selected test site and travels through the selected return line. This process can be repeated for additional samples of the plurality of samples provided. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a fiber-optic channel selection apparatus provided in accordance with the present invention; 
     FIG. 2 is a side elevation view of the apparatus illustrated in FIG. 1; 
     FIG. 3 is a top plan view of the apparatus illustrated in FIG. 1; 
     FIG. 4 is a rear elevation view of the apparatus illustrated in FIG. 1 showing the interconnection of rotary devices provided in accordance with one embodiment of the present invention; 
     FIG. 5A is a cross-sectional view of a rotary device for distributing a light beam or signal from a single input to one or more fiber-optic channels in accordance with the present invention; 
     FIG. 5B is a cross-sectional view of a rotary device for distributing light beams or signals from one or more fiber-optic channels to a single output in accordance with the present invention; 
     FIG. 6A is a cross-sectional view of an optical input selection device provided with the apparatus illustrated in FIGS. 1-4, including the rotary device illustrated in FIG. 5A; 
     FIG. 6B is cross-sectional view of an optical output selection device provided with the apparatus illustrated in FIGS. 1-4, including the rotary device illustrated in FIG. 5B; 
     FIG. 7A is a plan view illustrating either the input side of the optical input selection device illustrated in FIG. 6A or the output side of the optical output selection device illustrated in FIG. 6B; 
     FIG. 7B is a plan view illustrating either the output side of the optical input selection device illustrated in FIG. 6A or the input side of the optical output selection device illustrated in FIG. 6B; 
     FIG. 7C is a perspective view of either of the optical input selection device illustrated in FIG. 6A or the optical output selection device illustrated in FIG. 6B; 
     FIG. 8 is a schematic diagram of an analytical testing and data acquisition system in which the apparatus or portions thereof illustrated in FIGS. 1-7C is incorporated in accordance with the present invention; 
     FIG. 9 is a schematic diagram of a fiber-optic probe operating in conjunction with a test vessel and a spectrophotometer according to conventional methods; 
     FIG. 10 is a schematic diagram of an in-situ measurement system incorporating the use of the apparatus or portions thereof illustrated in FIGS. 1-7C in combination with fiber-optic probes or similar instruments; 
     FIG. 11 is a schematic diagram of an analytical testing and data acquisition system provided in accordance with another embodiment of the present invention; 
     FIG. 12A is a front elevation view of a fiber-optic bundle mounting component provided with the apparatus illustrated in FIG. 11; and 
     FIG. 12B is a cross-sectional side view of the mounting component illustrated in FIG.  12 A. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In general, the term “communicate” (e.g., a first component “communicates with” or “is in communication with” a second component) is used herein to indicate a structural, functional, mechanical, optical, or fluidic relationship between two or more components or elements. As such, the fact that one component is said to communicate with a second component is not intended to exclude the possibility that additional components may be present between, and/or operatively associated or engaged with, the first and second components. 
     As used herein, the term “multiplexer” is broadly defined to indicate a system or device that includes a plurality of independent, individual input lines or channels and a single output line or channel (i.e., a common path or bus). One of the input lines can be selected so that its value or signal is transmitted or routed over the output line. Thus, the multiplexer could also be referred to as a data selector. In addition, the term “demultiplexer” is broadly defined herein as implementing the converse function of the multiplexer. That is, a demultiplexer is a system or device that includes one input line or channel (i.e., a common path or bus) and a plurality of output lines or channels. One of the output lines is selected to receive the value or signal provided by the input line. Thus, the demultiplexer could also be referred to as a data distributor. These terms, as used herein, are therefore intended to have a broader meaning than, for instance, the meanings typically understood by persons associated with the communications or electronics industries, wherein the terms are often restricted to meaning a system in which all elements of a given signal are observed simultaneously. For convenience, the term “multiplexer” or “multiplexing apparatus” as used hereinafter is intended to cover a device or system that includes a multiplexer and/or a demultiplexer. 
     As used herein, the terms “beam,” “pulse,” and “optical signal” are intended to be interchangeable to indicate that the present invention is applicable to the transmission of light energy by both continuous and non-continuous methods. 
     As used herein, the terms “aperture” and “bore” are used interchangeably to denote any opening through which light energy can be transmitted with an acceptable degree of efficiency and an acceptable minimum of light loss. Such an opening can include an optical fiber for these purposes as well. Whether the term “aperture” or “bore” is more appropriate could, for instance, depend on the thickness of the structural body through which the opening runs, but in any case the two terms are considered herein to be interchangeable. 
     Referring now to FIGS. 1-4, an optical signal multiplexing apparatus, generally designated  10 , is illustrated in accordance with the present invention. Multiplexing apparatus  10  comprises an enclosure  12  mounted to a base  14 . Two rows of apertures (see FIG.  3 ), generally designated  16  and  18 , respectively, are formed on a top surface  12 A of enclosure  12 . Two corresponding rows of fiber optic cable ferrules or fittings generally designated  21  and  23 , respectively, (see FIG. 1) are mounted in these apertures  16  and  18 . Individual fiber-optic source lines OSL 1 -OSL n  (where, in the illustrated exemplary embodiment, n=8) extend through the respective fittings of row  23  (and apertures  18 ), and individual fiber-optic return lines ORL 1 -ORL n  extend through the respective fittings of the other row  21  (and apertures  16 ). In FIGS. 1 and 3, only the first pair of optical source and return lines, optical source line OSL 1  and optical return line ORL 1 , are shown. In FIG. 2, the respective bundles of optical source lines OSL 1 -OSL n  and optical return lines ORL 1 -ORL n  are schematically depicted by large arrows to indicate generally the direction of optical signals into and out from multiplexing apparatus  10 . 
     Portions of enclosure  12  are removed in FIGS. 1-4 to illustrate the interior components disposed within enclosure  12 . The primary operative interior components are two rotary indexing devices. One rotary device is referred to herein as an optical source line selector device, generally designated  80 , and the other rotary device is referred to as an optical return line selector device, generally designated  130 . 
     Source and return line selector devices  80  and  130  are situated adjacent to one another and are supported in fixed relation to each other, for example, by two axially spaced mounting blocks  26  and  28  that extend upwardly from base  14 . A ferrule or input fitting  31  is connected to an input end of source line selector device  80 . A circular array of fittings, generally designated  33 , are connected to an output end of source line selector device  80 . Another circular array of fittings, generally designated  35 , are connected to an input end of return line selector device  130 . A ferrule or output fitting  37  is connected to an output end of return line selector device  130 . A common source line or input bus IB is connected to input fitting  31 , and a common return line or output bus OB is connected to output fitting  37 . As just described, each individual fiber-optic source line OSL 1 -OSL n  runs through a corresponding fitting  23  of aperture row  18 , and each individual return line ORL 1 -ORL n  runs through fittings  21  mounted to aperture row  16 . Although not specifically shown in FIG. 1 for clarity, each individual fiber optic source line OSL 1 -OSL n  is connected to a corresponding one of fittings  33  of source line selector device  80 , and each individual return line ORL 1 -ORL n  is likewise connected to a corresponding one of fittings  35  of return line selector device  130 . As described more fully below, source line selector device  80  functions to select which one of the fiber-optic source lines OSL 1 -OSL n  is optically coupled to input bus IB over a given interval of time. Return line selector device  130  functions to select which one of the fiber-optic return lines ORL 1 -ORL n  is optically coupled to output bus OB over the same interval of time. 
     As best shown in FIGS. 3 and 4, multiplexing apparatus  10  further comprises a means for causing both source line selector device  80  and return line selector device  130  to rotate simultaneously and in an indexing fashion. Preferably, the means is provided in the form of a powered mechanism adapted to transfer rotational force through a force transmission mechanism. In the exemplary embodiment illustrated in FIGS. 1-4, the powered mechanism is a motor  40  (such as, for example, a DC stepper motor) that causes a shaft  42  to rotate through programmed increments. The transmission mechanism includes an arrangement of gear wheels  45 ,  47  and  49 . Gear wheel  45  is mounted to shaft  42  and thus rotates about the axis of shaft  42 . Gear wheel  47  is mounted to source line selector device  80  and rotates about an axis L 1  of source line selector device  80  (see FIG.  4 ). Gear wheel  49  is mounted to return line selector device  130  and rotates about an axis L 2  of return line selector device  130 . Gear wheels  47  and  49  are disposed in meshing engagement with gear wheel  45 . Accordingly, clockwise rotation of gear wheel  45  results in counterclockwise rotation of both gear wheels  47  and  49 . Conversely, counterclockwise rotation of gear wheel  45  results in clockwise rotation of both gear wheels  47  and  49 . Moreover, gear wheels  47  and  49  are similarly sized and have the same number of teeth. As a result, rotation of gear wheel  45  through a given incremental arc length causes rotation of both gear wheels  47  and  49  through another proportional incremental arc length. The arc length through which gear wheel  47  rotates is the same as the arc length through which gear wheel  49  rotates. 
     As appreciated by persons skilled in the art, multiplexing apparatus  10  can be provided with means for verifying the positions of the various rotating components. For example, primary position verification can be effected by providing an optical encoder (not shown) that is focused on shaft  42  of motor  40 . As a secondary mode of position verification, Hall effect sensors (not shown) can be provided to interface with a magnet (not shown) mounted on each gear wheel  47  and  49  respectively associated with source line selector device  80  and return line selector device  130 . With respect to each source line selector device  80  and return line selector device  130 , each corresponding set of Hall effect sensors would be mounted at each index position, such as by mounting the sensors in a circular array on a separate disks that rotates with corresponding barrel  85  or  135  in parallel with the magnet mounted to corresponding gear wheel  47  or  49 . 
     Referring now to FIGS. 5A-7C, details of source line selector device  80  and return line selector device  130  are illustrated. Referring specifically to FIG. 5A, source line selector device  80  comprises a rotary element or barrel  85  that is rotatable about its central axis L 1 . Barrel  85  includes an outer lateral surface  85 A, an input end surface  85 B, and an output end surface  85 C. Gear wheel  47  is fitted around the periphery of outer lateral surface  85 A. Gear wheel  47  is either a separate component or comprises teeth formed around barrel  85 . An internal bore  87  extends through the body of barrel  85 , and has an input bore end  87 A opening at input end surface  85 B and an output bore end  87 B opening at output end surface  85 C. Input bore end  87 A is coincident with axis L 1 , and thus the position of input bore end  87 A in relation to axis L 1  does not change during rotation of barrel  85 . Output bore end  87 B, on the other hand, is disposed at a location on output end surface  85 C that is offset from axis L 1  by a radial offset distance equal to radius R. Rotation of barrel  85  about axis L 1  therefore results in rotation of output bore end  87 B along a circular path of radius R, as defined on output end surface  85 C with respect to axis L 1 . An internal optical fiber  90  (see FIG. 6A) extends throughout internal bore  87 . Internal optical fiber  90  terminates at an input fiber end  90 A (see FIG. 6A) located at input bore end  87 A, and terminates at an output fiber end  90 B (see FIG. 6A) located at output bore end  87 B. Thus, input fiber end  90 A is coincident with axis L 1  and output fiber end  90 B is offset from axis L 1  by radial offset distance (or radius) R. Rotation of barrel  85  about axis L 1  does not affect the position of input fiber end  90 A, but results in a circumferential change in the position of output fiber end  90 B with respect to axis L 1 . 
     Referring to FIG. 6A, source line selector device  80  is designed to permit rotational indexing of barrel  85  about axis L 1 . Through this rotational movement, output fiber end  90 B can be selectively positioned at one of a plurality of equally spaced index locations around a circumference on output end surface  85 C. This circumference is swept out by the conceptual end point of radius R in relation to axis L 1 . In order to implement source fiber “channel” or line selection, barrel  85  rotates with respect to some type of stationary member that includes a number of fixed-position optical reception points corresponding to the plurality of index locations. In FIG. 6A, for example, the channel selection is implemented according to the invention by providing a stationary optical reception member. In the present embodiment, the stationary optical reception member is a bearing sleeve or cap  95  disposed at the output side of barrel  85 . A bearing  105  provides an interface between rotatable barrel  85  and stationary bearing sleeve  95 . As illustrated in FIG. 6A, bearing  105  can be a roller bearing of conventional design that includes an inner ring  105 A, an outer ring  105 B, and a series of balls  107  contacting the respective, opposing raceways of inner ring  105 A and outer ring  105 B. As understood by persons skilled in the art, balls  107  typically are interposed between inner ring  105 A and outer ring  105 B and in a circumferentially spaced arrangement through the use of a retaining element (not shown) forming some type of frame, cage, or carriage around each ball  107 . Inner ring  105 A firmly contacts (such as by press fitting) lateral outer surface  85 A of barrel  85 , while outer ring  105 B firmly contacts at least the inner surface of an annular section  95 A of bearing sleeve  95 . By this arrangement, inner ring  105 A rotates with barrel  85  while outer ring  105 B remains in a fixed position with stationary bearing sleeve  95 . It will be understood that bearing  105  could be either a ball bearing or a needle bearing, or some other type of bearing that permits barrel  85  to rotate in a stable manner with respect to bearing sleeve  95 . That is, rotatable needle elements could be substituted for balls  107  illustrated in FIG.  6 A. 
     In addition to its annular section  95 A, bearing sleeve  95  includes a plate section  95 B transversely oriented with respect to axis L 1  of source line selector device  80 . Plate section  95 B is immediately adjacent to output end surface  85 C of barrel  85 . Plate section  95 B includes a plurality of apertures  97  (only two of which are shown in FIG. 6A) arranged in a circular array of radius R with respect to axis L 1 . These apertures  97  constitute the previously described fixed-position optical reception points. The actual number of apertures  97  corresponds to the number of indices at which output fiber end  90 B of internal optical fiber  90  can be selectively positioned, and accordingly corresponds to the number of individual optical channels or lines into which an optical signal traveling through internal optical fiber  90  from input fiber end  90 A can be selectively directed through output fiber end  90 B. The specific number of apertures  97  (and hence the specific number of individual optical channels and index positions) will depend on the number of test sites to which optical source signals are to be sent. Besides the test sites that contain analytical samples, one or more of these test sites could hold reference or control samples (e.g., sources for obtaining blank or standard measurement data). In the example shown in FIG. 7B, plate section  95 B of bearing sleeve  95  includes an array of eight apertures  97  to handle eight separate optical channels or lines. It will be understood, however, that more or less apertures  97  could be provided, again depending on the number of separate optical channels. 
     The specific provision of bearing  105  and bearing sleeve  95 , in the arrangement and design illustrated in FIG. 6A, ensures that any light loss from the light conducting components of source line selector device  80  is negligible. The size of the air gap between output end surface  85 C of barrel  85  and plate section  95 B of bearing sleeve  95  is preset to provide optimal light transmission. Annular section  95 A and plate section  95 B of bearing sleeve  95  cooperatively form a shoulder around bearing  105  and output end surface  85 C to prevent light losses. In furtherance of the purpose of preventing light loss in this particular arrangement, it is preferable that the axial edges of inner ring  105 A and outer ring  105 B of bearing  105  facing plate section  95 B of bearing sleeve  95  be substantially flush with output end surface  85 C of barrel  85 . 
     Although source line selector device  80  and its barrel  85  are not expected to encounter axial thrust forces during the operation of multiplexing device  10 , source line selector device  80  can further include a second bearing  125  and corresponding bearing sleeve  115  mounted at the input side, as also shown in FIG.  6 A. The design and arrangement of input-side bearing  125  and bearing sleeve  115  can be similar to those of output-side bearing  105  and bearing sleeve  95 . Input-side bearing sleeve  115  thus includes an annular section  115 A and a plate section  115 B. As one principal difference, however, input-side bearing sleeve  115  includes only one aperture  117  formed in its plate section  115 B (see also FIG.  7 A). This single aperture  117  is situated coincident with axis L 1  and is immediately adjacent to input fiber end  90 A of internal optical fiber  90 . The inclusion of input-side bearing  125  and bearing sleeve  115  lends stability to the indexing movements of barrel  85  and overall operation of source line selector device  80 , and further facilitates the optical coupling of internal optical fiber  90  to input bus IB (see FIG.  1 ). Input-side bearing  125  can comprise balls  127  interposed between an inner ring  125 A and an outer ring  125 B. 
     Referring to FIG. 5B, return line selector device  130  comprises features similar to those of source line selector device  80  although, as shown in FIG. 1, the axial positions of the input and output sides of return line selector device  130  are reversed in comparison to those of source line selector device  80 . Specifically, return line selector device  130  comprises a rotary element or barrel  135  rotatable about its central axis L 2 . Barrel  135  includes an outer lateral surface  135 A, an input end surface  135 B, and an output end surface  135 C. Gear wheel  49  is fitted around the periphery of outer lateral surface  135 A. Gear wheel  49  is either a separate component or comprises teeth formed around barrel  135 . An internal bore  137  extends through the body of barrel  135 , and has an input bore end  137 A opening at input end surface  135 B and an output bore end  137 B opening at output end surface  135 C. Input bore end  137 A is disposed at a location on input end surface  135 B that is offset from axis L 2  by a radial offset distance equal to radius R. Rotation of barrel  135  about axis L 2  therefore results in rotation of input bore end  137 A along a circular path of radius R defined on input end surface  135 B with respect to axis L 2 . Output bore end  137 B, on the other hand, is coincident with axis L 2  such that its position in relation to axis L 2  does not change during rotation of barrel  135 . An internal optical fiber  140  extends throughout internal bore  137 . Internal optical fiber  140  (see FIG. 6B) terminates at an input fiber end  140 A located at input bore end  137 A, and terminates at an output fiber end  140 B located at output bore end  137 B. Thus, input fiber end  140 A is offset from axis L 2  by radial offset distance (or radius) R and output fiber end  140 B is coincident with axis L 2 . Rotation of barrel  135  about axis L 2  does not affect the position of output fiber end  140 B, but results in a circumferential change in the position of input fiber end  140 A with respect to axis L 2 . 
     Referring to FIG. 6B, return line selector device  130  enables rotational indexing of barrel  135  about axis L 2  in a manner analogous to source line selector device  80 . Through the rotational movement effected by return line selector device  130 , its input fiber end  140 A can be selectively positioned at one of a plurality of equally spaced index locations around a circumference of radius R defined on input end surface  135 B. In order to implement return fiber “channel” or line selection, return line selector device  130  includes a stationary bearing sleeve  145  disposed at the output side of barrel  135 . As in the case of source fiber selector device  80 , barrel  135  rotates with respect to bearing sleeve  145 . A bearing  155  provides an interface between rotatable barrel  135  and stationary bearing sleeve  145 . Bearing  155  can be provided in the form of a roller bearing that includes an inner ring  155 A, an outer ring  155 B, and a series of balls  157  or needles according to conventional designs. Inner ring  155 A rotates with barrel  135  while outer ring  155 B remains in a fixed position with stationary bearing sleeve  145 . 
     Bearing sleeve  145  of return line selector device  130  comprises an annular section  145 A coaxially disposed around bearing  155  and a plate section  145 B transversely oriented with respect to axis L 2  of return line selector device  130 . Plate section  145 B is immediately adjacent to input end surface  135 B of barrel  135  with an air gap therebetween, which is dimensioned for optimal optical transmission. Annular section  145 A and plate section  145 B of bearing sleeve  145  cooperatively form a shoulder around bearing  155  and input end surface  135 B. This arrangement of bearing  155  and bearing sleeve  145  ensures that any light loss from the light conducting components of return line selector device  130  is negligible. In furtherance of the purpose of preventing light loss in this particular arrangement, it is preferable that the axial edges of inner ring  155 A and outer ring  155 B of bearing  155  facing plate section  145 B of bearing sleeve  145  be substantially flush with input end surface  135 B of barrel  135 . 
     Plate section  145 B includes a plurality of apertures  147  (only two of which are shown in FIG. 6B) arranged in a circular array of radius R with respect to axis L 2 . These apertures  147  constitute fixed-position optical coupling points between the individual return fibers ORL 1 -ORL n  and input fiber end  140 A of internal optical fiber  140 . The actual number of apertures  147  corresponds to the number of indices at which input fiber end  140 A can be selectively positioned, and accordingly corresponds to the number of individual optical channels or lines from which an optical signal can be selectively directed into input fiber end  140 A. The specific number of apertures  147  (and hence the specific number of individual optical channels and index positions) will depend on the number of sites or detection areas from which optical return signals are to be received. 
     As also shown in FIG. 6B, return line selector device  130  can further include a second bearing  175  and corresponding bearing sleeve  165  mounted at the output side. The design and arrangement of output-side bearing  175  and bearing sleeve  165  can be similar to those of input-side bearing  105  and bearing sleeve  95 . Output-side bearing sleeve  165  thus includes an annular section  165 A and a plate section  165 B. Output-side bearing sleeve  165 , however, includes only one aperture  167  formed in its plate section  165 B. This single aperture  167  is situated coincident with axis L 2  and is immediately adjacent to output fiber end  140 B of internal optical fiber  140  and, on the other side, to output bus OB (see FIG.  1 ). Output-side bearing  175  can comprise balls  177  interposed between an inner ring  175 A and an outer ring  175 B. 
     FIG. 7A illustrates plate section  115 B and single aperture  117  of input-side bearing sleeve  115  of source line selector device  80 . FIG. 7B illustrates plate section  95 B and multiple apertures  97  of output-side bearing sleeve  95  of source line selector device  80 . FIG. 7C illustrates input-side bearing sleeve  115 , output-side bearing sleeve  95 , and bearings  105  and  125  assembled onto barrel  85  of source line selector device  80 . It will be understood that FIGS. 7A-7C are likewise representative of the structure of return line selector device  130 , but with the input and output sides reversed. That is, FIG. 7A could represent plate section  165 B and single aperture  167  of output-side bearing sleeve  165  of return line selector device  130 , and FIG. 7B could represent plate section  145 B and multiple apertures  147  of input-side bearing sleeve  145  of return line selector device  130 . Likewise, FIG. 7C can be considered as illustrating input-side bearing sleeve  145 , output-side bearing sleeve  165 , and bearings  155  and  175  assembled onto barrel  135  of return line selector device  130 . 
     According to another aspect of the invention, FIG. 8 illustrates the general features of an analytical testing and data acquisition system, generally designated  200 , in which multiplexer apparatus  10  can advantageously operate. In addition to multiplexer apparatus  10 , analytical testing system  200  comprises a light source, generally designated  210 , a data encoding or analytical signal generating system or arrangement, generally designated  220 , and an optical signal receiving device or system generally designated  230 . 
     Light source  210  can be any type of suitable continuous or non-continuous optical source. Non-limiting examples include deuterium arc lamps, xenon arc lamps, quartz halogen filament lamps, and tungsten filament lamps. In one specific example, a pulsed light source such as a xenon flash lamp could be employed to emit very short, intense bursts of light. This type of lamp flashes only when acquiring a data point, as compared to a diode array that exposes the sample to the entire wavelength range with each reading and potentially causes degradation of photosensitive samples. As described in commonly assigned U.S. Pat. No. 6,002,477, because it emits light on a non-continuous basis, the xenon flash lamp does not require a mechanical means such as a chopper for interrupting the light beam during measurement of a dark signal. One specific example of a xenon flash lamp that is capable of acquiring eighty data points per second is employed in CARY™ Series spectrophotometers commercially available from Varian, Inc, Palo Alto, Calif. 
     Data encoding or analytical signal generating system  220  can comprise any device or system adapted to contain and expose one or more samples to the light energy supplied by light source in order to encode information about that sample as the light passes through the sample and the sample is irradiated. For example, data encoding system could constitute an array of test sites F 1 -F n  such as sample measurement and/or holding sites. These test sites F 1 -F n  can be defined by a variety of sample measurement/containment components, such as solid sample holders, sample containers or cells, test vessels, flow cells, tanks, pipes, the wells of a quartz microtitre plate or similar microcells capable of transmitting light, and specially designed fiber-optic probes. 
     Signal receiving device or system  230  could be any type of instrument or system of instruments adapted to receive and process the optical signals supplied by data encoding device  220 . The specific property of the sample substance to be analyzed will dictate the type of equipment or instrumentation used to analyze samples taken from, for example, test vessels V 1 -V 8  shown in FIG.  10 . Moreover, the various components comprising signal receiving device  230  will depend on the type of analytical signal to be measured and detected. If the desired analytical signal is the intensity of light radiation absorbed by analytes at each test site F 1 -F n , absorbance values can be calculated in order to determine the concentration of the target substance (i.e., the analyte of interest). For this purpose, signal receiving device  230  in FIG. 8 can comprise a UV-vis spectrophotometer. The invention, however, is not limited to any specific design of spectrophotometer. Possible configurations for the spectrophotometer include those that utilize single detectors or multi-channel detectors, those that are adapted to perform single-beam or double-beam measurements, those that are adapted to perform horizontal-beam or vertical-beam measurements, and those that can perform measurements of fixed wavelength or of the entire absorption spectra for the sample. Moreover, for the purpose of the present disclosure, the terms “signal receiving device or system” and “sample analyzing system” are intended to encompass any analyzing equipment compatible with the systems and methods described herein. Such equipment may include, but is not limited to, HPLC, spectrometers, photometers, spectrophotometers, spectrographs, and similar equipment. In the case of a spectrophotometer, signal receiving device  230  typically includes light source  210 , a wavelength selector or similar device, a radiation detector such as a photoelectric detector or transducer, a signal processor, and a readout device. 
     Referring to the schematic depiction of analytical testing and data acquisition system  200  illustrated in FIG. 8, light source  210  optically communicates with source line selector device  80  of multiplexing apparatus  10  via input bus IB, and optical signal receiving device  230  optically communicates with return line selector device  130  via output bus OB. In the present embodiment, data encoding system  220  comprises a set of sample measurement components or test sites F 1 -F n  (e.g., flow cells, sample cells, test vessels, or the like), each of which is adapted to contain or provide a target for a sample to be analyzed. Source line selector device  80  optically communicates with sample measurement components F 1 -F n  via the set of optical source lines OSL 1 -OSL n , respectively, and return line selector device,  130  optically communicates with sample measurement components F 1 -F n  via a set of optical return lines ORL 1 -ORL n , respectively. For clarity, only four each of optical source lines OSL 1 -OSL n , sample measurement components F 1 -F n , and optical return lines ORL 1 -ORL n  are shown in FIG.  8 . By this arrangement, each sample measurement component F 1 -F n  can receive an incident light input of an initial intensity P 0  from light source over a corresponding optical source line OSL 1 -OSL n , and subsequently transmit a light output of an intensity P to optical signal receiving device for processing and readout over a corresponding optical return line OSL 1 -OSL n . As described previously, respective internal optical fibers  90  and  140  of source and return line selector devices  80  and  130  are rotatably indexed in mutual synchronization. As a result, the selection of optical source line OSL 1 , for example, to carry the source signal from internal optical fiber  90  of source line selector device  80  to sample measurement component F 1  concurs with the selection of optical return line ORL 1  to carry the attenuated signal transmitted from sample measurement component F 1  to internal optical fiber  140  of return line selector device  130 . 
     Referring back to FIG. 3, some of the features of the system described with reference to FIG. 8 are schematically shown in operative communication with multiplexing apparatus  10 . Light source  210  optically communicates with input bus IB, and output bus OB optically communicates with signal receiving device  230 . Sample measurement component F 1  optically communicates with optical source line OSL 1  and optical return line ORL 1 . In addition, sample measurement component F 1  is illustrated in the form of a liquid phase-containing sample holding cell, and accordingly is illustrated as fluidly communicating with a media sample line SL 1  and a media return line RL 1 . As described hereinabove, optical source line OSL 1  is connected to one of fittings  33  of source line selector device  80 , and optical return line ORL 1  is connected to one of fittings  35  of return line selector device  130 . It will be understood that other sample measurement components F 2 -F n  can be analogously interfaced with multiplexing apparatus  10  and other corresponding media sample lines and media return lines (not shown). 
     The operation of sample analysis system  200  with sample cells (e.g., sample cell or flow cell F 1  as shown in FIG. 3) will now be described. One or more samples of media are transferred from selected test vessels (which could be, for example, mounted in a dissolution test apparatus or other appropriate media preparation/testing apparatus) through media sample lines (e.g., sample line SL 1  in FIG. 3) to corresponding sample cells F 1 -F n . After optical measurements are taken, the samples can be, if the system is so configured, returned to the test vessels through media return lines (e.g., return line RL 1  in FIG.  3 ). Calibration operations can also be carried out prior to test runs as needed. 
     Multiplexing apparatus  10  is operated as described with reference to FIGS. 1-7C. Preferably, the movements of multiplexing apparatus  10  are coordinated with the operations of the other elements of sample analysis system  200  under the control of a suitable electronic processing device such as a computer (not shown). Accordingly, source line and return line selector devices  80  and  130  of multiplexing apparatus  10  are initially set to their respective home positions. At the home positions, one of the bundle of optical fiber source lines OSL 1 -OSL n  is positioned (e.g., at “index position  1 ”) in optical coupling relation with optical input bus IB, and a corresponding one of the bundle of optical fiber return lines ORL 1 -ORL n  is positioned (e.g., at a corresponding “index position  1 ”) in optical coupling relation with optical output bus OB. In effect, multiplexing apparatus  10  selects the sample measurement component F 1 -F n  corresponding to the selected index position of source and return selector devices  80  and  130 . 
     To take a measurement of the sample residing in the selected sample measurement component, light source  210  sends a beam of light of intensity P 0  into input bus IB. Source line selector device  80  is positioned such that the light is routed into the selected one of the bundle of source lines OSL 1 -OSL n . This source beam (or pulse) is thus transmitted into the particular sample measurement component F 1 -F n  that corresponds to the selected source line OSL 1 -OSL n  and return line ORL 1 -ORL n . Light source  210  and the sample residing in the selected sample measurement component can together be considered as a signal generator, in that light source  210  and the sample conjoin to generate the analytical signal in the form of an attenuated beam of light of intensity P as the beam of light passes through the sample. The analytical signal is transmitted through the selected one of return lines ORL 1 -ORL n  back to multiplexing apparatus  10  and, due to the position of return line selector device  130 , is routed into output bus OB. Output bus OB transmits the analytical signal to signal receiving device  230  for detection and processing, and the concentration of the measured sample is determined from the value obtained from its measured light absorbance, using calibration curves if necessary. 
     Within signal receiving device  230 , a wavelength selector is typically provided in the form of a filter or monochromator that isolates a restricted region of the electromagnetic spectrum for subsequent processing. The detector converts the radiant energy of the analytical signal into an electrical signal suitable for use by the signal processor. The signal processor can be adapted to modify the transduced signal in a variety of ways as necessary for the operation of signal receiving device  230  and the conversion to a readout signal. Functions performed by the signal processor can include amplification (i.e., multiplication of the signal by a constant greater than unity), logarithmic amplification, ratioing, attenuation (i.e., multiplication of the signal by a constant smaller than unity), integration, differentiation, addition, subtraction, exponential increase, conversion to AC, rectification to DC, comparison of the transduced signal with one from a standard source, and/or transformation of the electrical signal from a current to a voltage (or the converse of this operation). Finally, a readout device displays the transduced and processed signal, and can be a moving-coil meter, a strip-chart recorder, a digital display unit such as a digital voltmeter or CRT terminal, a printer, or a similarly related device. 
     As indicated previously, remote flow cells are but one type of means for encoding information that can be processed by signal receiving device  230 . Other examples of sample measurement components are fiber-optic probes, or dip probes, that are designed for insertion directly into a container holding an analyte-containing media. In some applications, the use of dip probes has been a substitute for the removal (and preferably the subsequent return) of samples from the media container and the transfer of the samples to the sample cell of a spectroscopic or other sample analyzing apparatus. 
     Referring now to FIG. 9, an example of a dip probe of conventional design, generally designated DP, is illustrated. In typical use, dip probe DP is inserted into a test vessel V so that the lower portion of its tip  371  is submerged in media held by test vessel V, thereby allowing absorbance measurements to be taken directly in test vessel V. Dip probe DP typically includes a detection area or cavity  373  similar to a flow cell that is defined by a gap between a fused silica or quartz lens or seal  375  and a mirror  377 . Dip probe DP is illustrated operating in conjunction with a spectrophotometer  380  that includes a light source  382  and a photodiode amplifier/detector  384 . A first, light-transmitting fiber-optic cable  386  runs between spectrophotometer  380  and glass seal  375 . A second, light-returning fiber-optic cable  388  runs between glass seal  375  back to spectrophotometer  380 , and usually includes an interference filter  391  or similar component. In use, a beam of light emitted by light source  382  is guided by first fiber-optic cable  386  along the direction of arrow A into detection area  373 . This beam of light passes through the media residing in detection area  373 , is reflected by mirror  377 , and thus is redirected into second fiber-optic cable  388  along the direction indicated by arrow B. The light beam then passes through interference filter  391  and returns to spectrophotometer  380  where the signal is processed by detector  384 . Preferably, the length of detection area  373  is half the optical pathlength, as the light passes through the solution twice before reaching detector  384 . 
     Referring now to FIG. 10, an in-situ measurement system, generally designated  400 , is illustrated as a specific application of analytical testing and data acquisition system  200  described hereinabove with reference to FIGS. 3 and 8. In-situ measurement system  400  comprises multiplexer apparatus  10 , light source  210 , and optical signal receiving device or system  230 . In this particular embodiment of the invention, in-situ measurement system  400  further provides a data encoding device or analytical generating system in the form of an array of dip probes DP 1 -DP 8  or similar instruments that are insertable into corresponding test vessels V 1 -V 8 . Hence, sample measurements are taken directly in test vessels V 1 -V 8 . One or more of vessels V 1 -V 8 , however, can serve as blank and/or standard media vessels. Each dip probe DP 1 -DP 8  is connected to a corresponding pair of optical source lines OSL 1 -OSL 8  (indicated by solid lines) and return lines ORL 1 -ORL 8  (indicated by dashed lines). Source and return line selector devices  80  and  130  of multiplexing apparatus  10  function in the manner described hereinabove to selectively couple each source line OSL 1 -OSL 8  with input bus IB and each corresponding return line ORL 1 -ORL 8  with output bus OB. As in previously described embodiments, light source  210  communicates with input bus IB and signal receiving device  230  communicates with output bus OB. As one alternative, each dip probe DP 1 -DP 8  could be mounted to the automated sampling assembly of a media preparation/testing apparatus  300 , such that each dip probe DP 1 -DP 8  could be inserted into its vessel V 1 -V 8  to take a measurement and thereafter removed according to a programmed, automated schedule. 
     In addition to the use of sample containment means such as flow cells, dip probes and the like as specified hereinabove, other means and accessories can be employed for generating analytical data in accordance with the invention. For example, instead of absorption probes, reflectance probes can be employed for undertaking reflectance measurements of samples. As appreciated by persons skilled in the art, a typical reflectance probe includes two fiber-optic bundles. One bundle forms a central core and delivers light to the sample. The other bundle surrounds the central core, and collects the light reflected from the sample and returns it to the detector of the associated sample analyzing instrument. Alternatively, a transmission probe can be employed to enable the measurement of solid samples. A typical transmission probe includes two single optical fibers. One fiber delivers light to the sample, and the other collects the light transmitted through the sample and returns the transmitted light to the sample analyzing instrument. The transmission probe is preferably used in conjunction with a sample holder adapted to position the sample for measurement. The nature of the sample (e.g., textile fabrics, sunglasses) dictates the design of the sample holder. Transmittance data can also be acquired from solid samples using an integrating sphere, which is a hollow sphere having an internal surface that is a non-selective diffuse reflector. Integrating spheres are often used to measure the transmission of turbid, translucent, or opaque refractory materials in situations where other techniques are inadequate due to loss of light resulting from the scattering effects of the sample. 
     Referring back to FIGS. 1-3, while input bus IB can be directly coupled to light source  210  and output bus OB directly coupled to signal receiving device  230 , this is not a requirement of the invention. The invention contemplates that various accessories and adaptations can be employed, such as those indicated hereinabove, and that multiplexing apparatus  10  can be integrated with existing analytical systems, in accordance with specific applications of multiplexing apparatus  10 . For example, in FIGS. 1-3, multiplexing apparatus  10  can additionally include a fiber-optic coupling unit, generally designated  425 , for routing light beams into and out from fiber-optic cables. Fiber-optic coupling unit  425  comprises an enclosure  431 , fittings  433  and  435  mounted to one or more walls of enclosure  431 , one or more internal optical mirrors  437  and  439  (see FIG. 3) disposed within enclosure  431  and positioned at desired angles, one or more apertures  441  and  443  (see FIGS. 1 and 2) formed in the walls of enclosure  431 , and various types of lenses (not shown) if needed. The input end of input bus IB is connected to fitting  433 , and the output end of output bus OB is connected to fitting  435 . As best illustrated in FIG. 3, a source signal from light source  210  enters enclosure  431  through aperture  441  (see FIG.  1 ), is reflected off internal mirror  437 , and is diverted into input bus IB. A return signal from output bus OB is reflected off internal mirror  439  and diverted toward signal receiving device  230  through aperture  443  (see FIG.  1 ). 
     Referring now to FIGS. 11,  12 A, and  12 B, another analytical testing and data acquisition system, generally designated  600 , is illustrated according to another embodiment of the present invention. In some cases, it may be desirable to eliminate either the multiplexing or the demultiplexing feature of the invention. Accordingly, this embodiment provides an alternative multiplexing apparatus, generally designated  10 ′, in which return line selector device  130  has been eliminated. Source line selector device  80  functions as described hereinabove. In the present embodiment, multiplexing apparatus  10 ′ comprises an output bus mounting assembly  630 . Output bus mounting assembly  630  includes an output aperture  632  in which a lens  634  is preferably disposed. Lens  634  can be situated at the terminal end of a cylindrical collar  636  or other suitable means for retaining and collecting optical return lines ORL 1 -ORL n  in a fixed-position bundle. In this embodiment, the bundle of optical return lines ORL 1 -ORL n  collected from, for example, aperture rows  16  or  18  (see FIGS. 2 and 3) is considered in effect to be a multi-channel output bus for analytical testing system  600 . The bundle of optical return lines ORL 1 -ORL n  could also include an extra test line that is connected to a reference source. In FIG. 12A, for example, a total of nine lines are illustrated. For another example, a 16-channel system would have seventeen lines (again assuming one test line were included). Output aperture  632  is optically aligned with the receiving window of a sample detector SD or other similar analyzing device or light-receiving component thereof. 
     In operation, a sample beam from light source  210  is directed through input bus IB into the input side of source line selector device  80  in the manner described hereinabove. As also described hereinabove, source line selector device  80  is indexed by motor  40 , shaft  42 , gear wheels  45  and  47 , and other associated components (see FIGS. 2 and 3) so as to select one of optical source lines OSL 1 -OSL n . The signal is transferred out from source line selector device  80  through the selected optical source line OSL 1 -OSL n  and associated fitting of one of aperture rows  16  and  18  to the selected sample container or other type of test site F 1 -F n  of encoding system  220 . The transmitted light beam P is then returned through the corresponding one of optical return lines ORL 1 -ORL n , through one of aperture rows  16  or  18 , to output bus mounting assembly  630  where all optical return lines ORL 1 -ORL n  are bundled at output aperture  632 . Transmitted light beam P emanating from selected optical return line ORL 1 -ORL n  is directed into the window of sample detector SD. This window is large enough to receive light from any of the ends of optical return lines ORL 1 -ORL n  bundled at output bus mounting assembly  630 . As an example, the window can be approximately 1 cm 2  in area, and the fiber ends of optical return lines ORL 1 -ORL n  can be positioned approximately 0.5 cm away from the window. 
     It will be noted that multiplexing apparatus  10 ′, in which either source line selector device  80  or return line selector device  130  is eliminated, and either including or not including the other features of spectrophotometer  600 , can be integrated into the various systems of the invention described with reference to FIGS. 3,  8  and  10  in the place of multiplexing apparatus  10 . 
     It is therefore seen from the foregoing description that the present invention provides a number of systems, devices, and methods benefiting from the use of fiber-optics coupled with sample measurement systems. The embodiments described herein result in high-quality analysis and quantification of analytical samples with decreased effort, and enable the efficient and controlled selection and routing of optical signals and signal paths with minimal light loss. 
     It will be understood that the spectrophotometers described hereinabove are generally of the type involving the transmission measurement of a sample, wherein a light beam passes through a sample cell or flow cell containing the sample to be analyzed. The invention, however, is equally applicable to spectrophotometers of the type in which the sample to be analyzed is subjected to reflectance measurement and consequently do not necessarily require a sample cell or flow cell for operation. 
     It will be understood that the embodiments described hereinabove can be modified without undue effort to utilize more than one multiplexing apparatus  10  or  10 ′, light source  210 , signal receiving device  230  or SD, and/or set F of sample measurement components. 
     It will be further understood that various details of the invention may be changed without departing from the scope of the invention. Furthermore, the foregoing description is for the purpose of illustration only, and not for the purpose of limitation-the invention being defined by the claims.