Abstract:
An optical pathway selector is provided having a first direction selector, a second direction selector, and an actuator. The first direction selector is comprised of a substantially planar member having alternating reflecting and transparent portions. The first direction selector is disposed for rotation on an axle with the substantially planar member positioned askew to a first optical axis. The second direction selector has a configuration similar to that of the first direction selector and is disposed along the axle substantially parallel to the first direction selector. Additional direction selectors can be employed in a similar manner. A motor is connected to the axle for rotating the direction selectors. Alternatively, a motor moves the direction selector along a linear pathway in and out of the pathway of different light beams. The optical pathway selector is used to reflect a beam of light from the first optical axis to alternative optical axes or vice-versa. A retroreflector may be utilized in conjunction with the optical pathway selector to eliminate error due to non-planar surfaces or motion. The optical pathway selector may be used in epifluorescence imaging systems.

Description:
[0001]    This application is a continuation-in-part of U.S. patent application Ser. No. 09/733,575, filed Dec. 8, 2000, which is incorporated herein by reference. 
     
    
     
       FIELD OF INVENTION  
         [0002]    This invention relates to systems for optical imaging in wide-field epiflourescence microscopy, and particularly to the use of an optical pathway selector that directs a beam of light propagating along a first optical axis to propagate along a different optical axis, or directs several beams of light propagating along different optical axes to propagate along a single optical axis.  
         BACKGROUND OF THE INVENTION  
         [0003]    In the field of epifluorescence microscopy biochemical material samples that have been tagged with fluorescent markers are exposed to a beam of light that excites markers within the samples to fluoresce. The wavelength of the fluorescence light emitted from the sample depends on the markers that have been used with the sample. Typically, fluorescence light emitted from the sample is imaged onto an image detector, such as a CCD array or image tube in a camera, or is scanned point-by-point onto a detector whose output is processed by software, in order to determine the spatial distribution of emitted fluorescence light intensity. It is often desirable to use multiple excitation light sources, each producing a different wavelength of light, to excite a given sample. Therefore, it is necessary to be able to direct light from different sources toward the sample and to direct the resulting fluorescence light toward one or more detectors.  
           [0004]    U.S. Pat. No. 4,795,256 employs a reflective chopper to chop light from a laser so that the light propagates along two alternative optical pathways. A monochromator is disposed in each of the optical pathways to filter out two respective excitation wavelengths. However, this arrangement is limited in that it does not provide for switching between one and several bidirectional optical pathways so as to excite an epifluorescence sample with more than two wavelengths of light and detect the fluorescence light emitted therefrom.  
           [0005]    Consequently, there is a need to be able to switch between two or more light sources and direct them toward a given sample. In addition, there is a need to direct both the excitation and emitted fluorescence light along a selected one of a plurality of bidirectional pathways.  
         SUMMARY OF THE INVENTION  
         [0006]    The aforementioned need has been met in the present invention by providing an optical pathway selector having a first direction selector, a second direction selector, and an actuator. In two embodiments, the first direction selector is comprised of a substantially planar member having alternating reflecting and transparent portions. The first direction selector is disposed on an axle with the substantially planar member positioned askew to an optical axis, preferably 45 degrees. When the axle rotates so does the substantially planar member. The second direction selector has a configuration similar to that of the first direction selector. The second direction selector is mounted on the same axle and is coaxial with the first direction selector. The reflective surfaces are preferably perpendicular to the axle. Additional direction selectors can be employed in a similar manner. A motor is connected to the axle for rotating the direction selectors. In a third alternative embodiment, a motor moves the direction selector along a linear pathway in and out of the pathway of different light beams.  
           [0007]    When a light beam propagates along a first optical axis, the first direction selector may be inserted into its pathway. The light beam either hits the reflective portion and propagates along a second optical pathway or passes through the transparent portion and continues along the first optical pathway. If the light beam continues along the first optical pathway, the second direction selector may be inserted into the pathway. The light beam either hits the reflective portion of the second direction selector and propagates along a third optical pathway, or passes through the transparent portion and continues along the first optical pathway. Additional direction selectors disposed on the axle of the optical pathway selector can be utilized in a similar manner.  
           [0008]    Conversely, the optical pathway selector can be utilized to direct two or more light beams propagating along different optical pathways to propagate along the same optical pathway.  
           [0009]    In another embodiment of the invention the reflective surfaces can be comprised of wave-length selective mirrors to filter out a desired wavelength of light.  
           [0010]    In an additional embodiment of the invention, a retroreflector is utilized in conjunction with the optical pathway selector to eliminate angular path variations. The retroreflector returns a light beam that has been reflected from the optical pathway selector at the same angle that it was reflected, so that when it returns to the optical pathway selector it is reflected along a pathway that is parallel and opposite to its original pathway.  
           [0011]    In an embodiment directed to a specific application, the optical pathway selector is used in an epifluorescence microscope.  
           [0012]    Accordingly, it is a principal object of the present invention to provide a novel and improved method and apparatus for directing a beam of light along a selected optical pathway.  
           [0013]    It is another object of the invention to provide a method and apparatus for directing a beam of light along a selected one of a plurality of alternative pathways.  
           [0014]    It is a further object of the invention to provide a method and apparatus for selectively directing multiple beams of light along a single pathway.  
           [0015]    It is yet another object of the present invention to provide a method and apparatus for switching a beam of light between one and several bidirectional pathways.  
           [0016]    The foregoing and other objects, features, and advantages of the invention will be more readily understood upon consideration of the following detailed description of the invention, taken in conjunction with the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]    [0017]FIG. 1 is a perspective diagram of an optical pathway selector according to a first embodiment of the present invention.  
         [0018]    [0018]FIG. 2 is a side view of an optical pathway selector according to a second embodiment of the invention.  
         [0019]    [0019]FIG. 3 is a front view of the optical pathway selector of FIG. 2.  
         [0020]    [0020]FIG. 4 is a side view of an optical pathway selector according to a third embodiment of the invention.  
         [0021]    [0021]FIG. 5 is a side view of a fourth embodiment of an optical pathway selector employing a retroreflector.  
         [0022]    [0022]FIG. 6 is a view of a fifth embodiment of an optical pathway selector used in an epifluorescence microscope. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0023]    A first embodiment of an optical pathway selector according to the present invention is shown in FIG. 1. In this embodiment, an optical pathway selector  10  is provided with a first direction selector  12 , a second direction selector  14 , an axle  16  attached to direction selectors  12  and  14 , and a motor or actuator  18  for rotating the axle  16 .  
         [0024]    The first direction selector  12  is comprised of a substantially planar member  20  having reflective surfaces  22 . Disposed between the reflective surfaces  22  are transparent sections  24 , so that the reflective surfaces  22  alternate with the transparent sections  24 . The second direction selector  14  is configured similarly to the first direction selector  12  and is comprised of a substantially planar member  26  having reflective surfaces  28 . Disposed between the reflective surfaces  28  are transparent sections  30 . The reflective surfaces  22  and  28  are disposed normal to the axle  16  and are shown in FIG. 1 as being pie shaped. However, other configurations may be used without departing from the principles of the invention. In addition, while the preferred embodiment disclosed herein actually produces transparency by the absence of material between reflective surfaces, the selectors could employ solid material over the full 360° around the axis wherein the material is alternately reflective and transparent. The substantially planar members  20  and  26  of the direction selectors  12  and  14  are ordinarily disposed approximately 45 degrees to the optical axis. However, it is to be recognized that other angles may be used without departing from the principles of the invention.  
         [0025]    The optical pathway selector  10  can be used to divert a light beam traveling along an optical axis to propagate along a different optical axis. Alternatively, the optical pathway selector  10  can also be used to cause a plurality of light beams propagating along several optical axes to propagate along a single optical axis.  
         [0026]    [0026]FIG. 1 illustrates how the optical pathway selector  10  can be used to selectively direct light beams from one of two pathways along a third pathway. A light beam coming from a source such as a lamp or laser propagates along the optical axis  34  toward the optical pathway selector  10 . Depending on the rotational position of the first direction selector  12 , it will or will not encounter a reflective surface  22 . If it encounters a reflected surface  22 , it is diverted along the optical axis  32 . Similarly, a light beam that propagates along the optical axis  36  will or will not encounter a reflective surface  28 , depending on the rotational position of the first selector  14 . If it encounters a reflective surface  28 , it is diverted to propagate along the optical axis  32 . Thus, the optical pathway selector  10  of the present invention provides switching between one and several alternative bidirectional optical pathways.  
         [0027]    [0027]FIG. 2 illustrates another embodiment of an optical pathway selector  210 . Elements that are the same in both embodiments are given the same number. The optical pathway selector  210  has a first direction selector  212  having a reflective surface  222 , and a second direction selector  214  having a reflective surface  228 . The reflective surfaces  222  and  228  of the direction selectors  212  and  214  are substantially rectangular shaped; however, other shapes can be used without departing from the principles of the invention. The transparent portions could be from the absence of material, or they could be formed of an arc of material that passes light and is disposed between the reflective surfaces. As shown in FIG. 2, the second direction selector  214  has a larger lateral span than the first direction selector  212 . However, the second direction selector  214  can have a smaller lateral span, or both direction selectors  212  and  214  can have the same lateral span without departing from the principles of the invention. In this way, light can pass by the first direction selector  212  and encounter the second direction selector  214  when the optical pathway selector  210  is rotated in the desired position. The optical pathway selector  210  can be used to divert a light beam traveling along an optical axis to propagate along a different optical axis or, it can also be used to cause one of a plurality of light beams propagating along several optical axes to propagate along a single optical axis.  
         [0028]    [0028]FIG. 2 illustrates how the optical pathway selector  220  can be used to divert a light beam. A light beam coming from a light source such as a fluorescing sample propagates along the first optical axis  232  and encounters the first direction selector  212 . Depending upon the desired pathway, the first selector  212  is rotated so that the light beam either hits the reflective surface  222  and is reflected along a second optical axis  234 , or encounters a transparent section and continues along the first optical axis  232 . If the light beam continues along the first optical axis  232 , it encounters the second direction selector  214 . Depending upon the desired pathway, the second selector  214  is rotated so that the light beam either hits the reflective surface  228  and is reflected along a third optical axis  236 , or encounters a transparent section and continues along the first optical axis  232 .  
         [0029]    Although only two direction selectors are shown in FIGS. 1 and 2, additional direction selectors can be utilized to provide additional pathways. The reflective surfaces may comprise mirrors or other material having reflective properties. The mirrors may be of the kind that reflect essentially all wavelengths of light, or they may be dichroic mirrors that allow only certain wavelength of light to pass therethrough. One of the planar members can be dichroic and the other can be completely reflective. Additionally, one or both of the planar members can have alternating dichroic or completely reflective surfaces around its diameter. Dichroic mirrors are typically fabricated by multiple layers of dielectric material placed on a transparent substrate so that they reflect light of one or more wavelength regions yet transmit light of other wavelength regions, as is commonly understood in the art. These mirrors are substantially flat and relatively thin and, by appropriate selection of the dielectric layers, can be designed to reflect and transmit the desired wavelengths of light for a given application. However, it is to be recognized that other wavelength-selective devices which are physically compatible with the structure described and claimed herein may be used without departing from the principles of the invention.  
         [0030]    The motor  18  preferably is a stepper motor for moving the substantially planar members a discrete angular distance to move reflective surfaces in and out of the common optical pathway. However, a continuously rotating motor can be used where called for by the application. Also, preferably, the motor  18  is a dual purpose device that can operate either in a stepping mode or a continuously rotating mode. The direction selectors stay in the same plane when they are being rotated by the motor. In addition, other actuators or motors can be used, such as an elongated carriage that slides the direction selectors linearly into and out of a beam of light. Again, the direction selectors stay in the same respective planes when they are moved linearly.  
         [0031]    [0031]FIG. 4 shows a third embodiment of an optical pathway selector  310 . The optical pathway selector  310  comprises a first direction selector  312  having a planar reflective surface  322 , a second direction selector  314  having a planar reflective surface  328 , and a third direction selector  316  having a planar reflective surface  330 . A support structure  320  supports the direction selectors  312 ,  314  and  316 , and an actuator  318  moves the optical pathway selector  310  in and out of optical pathway  332 . Preferably, the direction selectors  312 ,  314  and  316  are of equal lengths, but other configurations can be used without departing from the principles of the invention. The reflective surfaces  322 ,  328  and  330  can be made from mirrors that reflect essentially all wavelengths of light, dichroic mirrors, or a combination thereof.  
         [0032]    In an example of how the optical pathway selector  310  can be used, the actuator  318  moves the optical pathway selector  310  in the direction of arrow A. A light beam is propagated along an optical axis  334  toward the first direction selector  312 . In addition, light beams are propagated along optical axis  336  and optical axis  338  toward the second direction selector  314  and the third direction selector  316 , respectively. The reflective surfaces  322 ,  328  and  330  are perpendicular to the plane of the drawing so that the actuator  318  and the support structure  320  are below the propagating beams of light and do not interfere with them. The direction selectors  312 ,  314  and  316  stay in the same plane while moving in out of the light beams.  
         [0033]    The first direction selector  312  is the first to encounter the light propagating along optical axis  334 , and the light is reflected to propagate along optical axis  332 . During this time, direction selectors  314  and  316  do not yet encounter the beams of light propagating along optical axes  336  and  338 , respectively. As the optical pathway selector  310  moves forward, the first direction selector  312  moves out of the pathway of the light and the light propagating along optical axis  334  is no longer reflected along optical axis  332 . Next, the second direction selector  314  encounters the light propagating along optical axis  336 , and the light is reflected to propagate along optical axis  332 . The light beams propagating along the optical axes  334  and  338  continues along their respective axes. Lastly, when the third direction selector  316  encounters the light propagating along optical axis  338 , that light is reflected to propagate along optical axis  332 .  
         [0034]    [0034]FIG. 5 shows another embodiment in which a direction selector  13  of an optical pathway selector having a rotational axle  17  is used in conjunction with a retroreflector  38 . Although the member  21  is substantially planar and rotates in a plane, in practice deviations from a plane may occur and wobbling of the member  21  may cause small positional errors that would cause angular variations in the path of a reflected beam. This error can be corrected with the retroreflector  38 . The retroreflector  38  is shown in FIG. 5 as being triangular, but it is to be understood that the retroreflector  38  may actually be a three dimensional device and that other shapes can be used that perform the same function. The retroreflector  38  has a first surface  40  that allows the light beam to pass through it. The retroreflector  38  further includes a second surface  42  and a third surface  44  which deflect the light beam. The third surface  44  is at a 90 degree angle to the second surface  42 .  
         [0035]    In the illustrated example, a light beam travels along a first optical axis  46  toward the substantially planar member  21  of the direction selector  13 . If the light beam encounters the reflective surface  23 , it is deflected along a second optical axis  48  to the retroreflector  38 . The light beam passes through the first surface  40 . Next, the light beam deflects off the second surface  42  along a third optical pathway  50  toward the third surface  44 . The third surface  44  deflects the light beam back toward the direction selector  13  along a fourth optical axis  52  that is parallel to the second optical axis  48 . The light beam then reflects off reflective surface  23 , so as to propagate along a fifth optical axis  54  that is parallel to the first optical axis  46 . Alternatively, a beam of light propagating in an opposite direction to the original light beam can pass through a transparent section of the planar member  21 , depending on the rotational position of the member  21 , so as to propagate along optical axis  54 .  
         [0036]    The retroreflector  38  corrects for any deviation in the angle that the beam makes with the reflective surface  23  by returning the light beam to the direction selector  13  along a parallel pathway, thus allowing the light beam to deflect off the direction selector  13  along a parallel axis, but opposite in direction to the original pathway of the beam of light.  
         [0037]    [0037]FIG. 6 shows an example of an epifluorescence microscope system  100  employing an alternative embodiment of an optical pathway selector  102 . The system  100  includes a slide  104  that contains a sample, a first laser  106 , a second laser  108 , a third laser  110 , a first lens  112  for focusing a beam of light on the sample, the optical pathway selector  102 , a first dichroic mirror  114 , a second dichroic mirror  116 , a third dichroic mirror  118 , a detector  120  and a larger second lens  122  for focusing the beam of light on the detector  120 .  
         [0038]    The optical pathway selector  102  in FIG. 6 is similar to the optical pathway selector of FIGS. 2 and 3, and like parts are given the same number. The optical pathway selector  102  further includes a third direction selector  124  that has a substantially planar surface  126  that has alternating reflective surfaces and transparent sections similar to the first and second direction selectors  12  and  14 . The third direction selector  124  has a larger lateral span than the first and second direction selectors  12  and  14 , but other configurations may be used without departing from the principles of the invention.  
         [0039]    In use, a laser directs excitation light toward its corresponding direction selector. For example, the third laser  110  directs an excitation light beam toward the third direction selector  124 . The light beam passes through the dichroic mirror  118  which is designed to pass excitation light while reflecting fluorescence light. If the excitation light beam encounters the reflective surface  126  of the third direction selector  124 , it is deflected toward the slide  104 . The excitation light passes through the first lens  112 , which focuses the excitation light on the slide  104 . The excitation light excites the sample, which causes the sample to emit fluorescence light back in the direction of the optical pathway selector  102 . The fluorescence light beam encounters the third direction selector  124  and is deflected back toward the third laser  110 . The fluorescence light has a different wavelength from the excitation light, and is reflected off the dichroic mirror  118  toward the detector  120 . The second lens  122  focuses the fluorescence light down to a spot at which detector  120  is located. The output of the detector  120  can be used to analyze the properties of the fluorescence light.  
         [0040]    As each of the beams reflected off dichroic mirrors  114 ,  116  and  118  are essentially parallel-ray beams, all of them will be focused at the detector  120  even though they are offset from one another. Similarly, fluorescence light stimulated by each of the excitation beams is directed by the pathway selector  102  back toward its respective excitation light source and by its respective dichroic mirror to the detector  120 .  
         [0041]    Although dichroic mirrors are most easily constructed so that they reflect higher wavelengths of light and pass lower wavelengths of light, they may be constructed to pass higher wavelengths of light and reflect lower wavelengths of light as shown in the drawings. An alternative to the dichroic mirrors is to use a geometric wavelength separator comprising a planar member having a reflective mirror with a small hole therethrough to separate the excitation light and the fluorescence light. The laser emits a small diameter excitation light beam that passes through the small hole, while the fluorescence light has a larger diameter. A small portion of the fluorescence light passes through the hole, but the majority is reflected towards the detectors.  
         [0042]    The terms and expressions which have been employed in the foregoing specification are used therein as terms of description and not of limitation, and there is no intention, in the use of such terms and expressions, of excluding equivalents of the features shown and described or portions thereof, it being recognized that the scope of the invention is defined and limited only by the claims which follow.