A MULTIPLE-PATH DICHROIC OPTICAL BEAM SPLITTER

Abstract: A dichroic beam splitter (13) design comprising a single unit assembly having a reduced number of components to provide for diminished weight and bulk, simplicity of alignment, greater optical efficiency and fewer steps in the assembly process to produce the device. The beam splitter includes two identical right triangular prisms (14, 17), a parallelogram shaped element (15), and a trapezoidal shaped element (16), all bonded together to form the single, L-shaped, beam splitter (13). High reliability, and ease of identification of component elements due to unique geometry, is provided by this approach. This device is especially useful for computer optical disk storage devices.

Description: A MULTIPLE-PATH DICHROIC OPTICAL BEAM SPLITTER BACKGROI ) OF THE INVENTION This invention relates to an optical light beam splitting device, and more particularly, to an optical beam splitting device for use in an optical data storage device. Even more particularly, the invention relates to an improved optical beam splitting device, wherein improved component alignment is achieved by special selection of optical component shapes and special optical coatings. The use of beam splitter devices for separating discrete beams of light within optical systems is well known in the prior art due to the need to conveniently combine and/or separate two discrete light beams having different wavelengths traveling the same optical path. This is basically accomplished through use of selective thin film coatings and cube or plate beam splitter components. In the prior art one such device is the cube cluster in which six identical prisms have optical thin film coatings applied to the prism hypotenuses. These prisms are bonded together to form three separate optical cubes, which in turn are then bonded onto -a planar surface carrier plate in precise alignment with respect to each other, forming the desired beam splitting device assembly. The- accuracy, of this assembly is predicated upon " the manufacturing tolerances of the individual prisms, and the placement and bonding of the prisms onto the carrier. Also, the placement of the individual prisms on the carrier is a lengthy and tedious procedure, adding to the cost of the device. Furthermore, precise identification of each individual prism must be maintained during assembly, due to the unique coating on the beam splitting surface in each prism, as misplacement of one of the cubes during assembly renders the device non-functional. While the use of special jigs for positioning purposes and special markings for identification minimizes these assembly obstacles, they also significantly add to the cost of the device. Also, precise tolerances are difficult to achieve when bonding the individual cubes onto the planar surface plant carrier, rendering the beam splitter device undesirable for the intended application. The present invention addresses this problem by providing a low cost, simple beam splitter design, wherein an accurate, reliable, easily assembled device is disclosed. SUMMARY OF THE INVENTION The present invention is a simplified dichroic optical beam splitter wherein all component elements are securely bonded together to form a single unit device. This allows for the physical reduction in size of the device and, further, diminishes light beam intensity losses by reducing the total number of interfaces through which the light beam must travel. Advantageously, the present invention is also a multi-function device. The optional path provides for combining discrete light beams which exit the device in a coaxial parallel fashion, and discrete light beams entering said exit point are separated and transmitted along selective discrete paths. The entire device . consists of four optical prism elements securely bonded together to form a single unit. The three junctions created by bonding the four elements together contain a discriminating coating substance, for selection of either polarization or wavelength of the incident light beams, thereby having either transmitting or reflecting characteristics with respect to the planar polarization or the wavelength of said incident light beams. OMP Unlike the prior art, the present invention requires fewer component elements for assembly, as all elements are bonded into a single unit. This also eliminates the air-to-glass interfaces, and therefore minimizes light intensity losses within the device. It is the object of the disclosed invention to provide a single-unit assembly optical beam splitter/combiner. It is a further object of the disclosed invention to provide a means for the more efficient assembly of optical beam splitter/combiner. BRIEF DESCRIPTION OF DRAWINGS FIGURE 1 is a schematic representation of a .prior art cube-cluster dichroic beam ' splitter showing the combining of two discrete light beams having different wavelengths, and further, depicting the separation of two light beams entering the cluster in a coaxial fashion, exiting in opposite directions. FIGURE 2 is a representative schematic diagram of the present invention, a single unit dichroic beam splitting device, with light beam combining and separating functions. DESCRIPTION OF PREFERRED EMBODIMENT The previously described objectives, features and other advantages of the. present invention will become more readily apparent in the following detailed description of the preferred embodiment which refers to the previously listed drawings. The following description sets forth the best presently assembled device model currently used to embody the present invention. This description is presented solely for the purpose of describing the essential principles of the present invention and should not be interpreted as limiting the true scope of the invention as set forth in the appended claims. OMP In order to better appreciate the features and advantages embodied in the present invention, FIGURE 1 shows a prior art light beam splitter 1 which is an optical cube cluster. The three optical cubes 2-4 shown are spatially separated a dimension convenient for assembly and alignment. The three said cubes 2-4 are assembled from identical right triangular prisms securely bonded together to form discriminating interfaces A, B and C. For instructive purposes, discriminating interfaces A § B are planar polarized such that each interface reflects planar S-Polarized light beams and transmits planar P-Polarized light beams. Discriminating interface C however, comprises a dichroic coating substance having sensitivity for transmitting light beams of a first wavelength (e.g., 835 nanometers) and reflecting light beams of a second wavelength (e.g., 633 nanometers). As shown in FIGURE 1 the above described beam splitter 1 constitutes a convenient device for combining or separating two discrete beams of light sharing the same optical path. A first S-Polarized light beam 5 impinging upon optical cube 4 is transmitted to interface B and reflected toward cube 3. Said first beam 5 upon impinging optical cube 3 is transmitted through to interface C and reflected, by interface C to exit cube 3 passing through quarter wave plate 9, which circularly polarizes the beam 5. Beam 5 is then reflected off planar reflector 10. Similarly, a second P-Polarized light beam 6 impinging upon optical cube 2 is transmitted through the discriminating interface A without deviation toward optical cube 3. Said second beam 6 upon impinging upon optical cube 3, is transmitted through the dichroic interface C, and exits the optical cube 3 coaxial with first light beam 5, also passing through quarter wave plate 9 and impinging reflector 10, thus completing the beam combining function of the -gtj E OMPI device 1. Upon passing through the quarter wave plate a second time, the circularly polarized beams 7 and 8 are again linerly polarized but now changed from P- to S- or S- to P- polarization respectively. Thus ' , the reflected beam 7 is still reflected off surface C but passes through surface B, while beam 8 still passes through surface C and is also reflected by surface A. This separates the reflected beam from the incident, which is part of the intended purpose of the invention. The above described optical relationships remain valid for light beams entering the device 1 from opposite direction 11. In the traditional triple cube beam splitter 1, the three component optical cubes 2-4 are not only spatially separated, but also separately mounted on a flat planar carrier plate 12. Each optical cube is securely bonded into its respective position on the plate 12 in order to form the single-unit device 1. FIGURE 2 is a schematic diagram of a dichroic beam splitter 13 configured according to the present invention. The current invention comprises a total of four discrete elements 14-17 securely bonded together forming a single unit. Elements 14 and 17 are identical right triangular prisms while elements 15, a parallelogram shape, and 16, a trapezoidal shape, are geometrically unique prisms having 45° interfaces with respect to the device. The interfaces A, B and C formed by securely bonding the four discrete • components 14-17 into a single unit replicate the interfaces previously described in FIGURE 1. As a result, the light beam combining and separating functions are repetitive of those previously described. The reduction to four discrete elements for the present invention can reduce the size of the assembled device 13. Bonding of the four discrete elements 14-17 into a single unit 13 fixedly -5- establishes the alignment of each element with respect to the device, without any need of additional alignment with respect to a carrier plate. As can be seen in FIGURE 2, optical prism 14 is securely bonded to prism 15 to form interface A oriented to create a polarizing beamsplitter surface. Additionally, interface A establishes the positioning, as well as the alignment, of the two prisms with respect to each other. Similarly, the dichroic light beam discriminating interface B is formed by the bonding of prisms 15 and 16, again establishing alignment and positioning of said elements. The fourth element, prism 17 in contact with prism 16 establish the polarizing interface C as well as providing alignment in order to complete the dichroic beam splitter device 13. Note that by bonding the elements together to establish alignment and positioning of the individual elements 14-17, the flat planar carrier plate 12 of prior art is eliminated as a component of the device assembly 13, thereby further reducing of the weight and bulk of the device. Also, elimination of air gaps within the optical path of the present invention reduces transmission losses. In the preferred embodiment of the present invention, two discrete light beams 5 and 6 are combined as previously described and exit the device 13 passing through external • quarter wave plate 9 onto reflecting surface 10. The two combined light beams 7 and 8 are then reflected back through the quarter wave plate 9, and finally exit the device after reflecting off surfaces C and A, respectively.

Claims: CLAIMS I claim: 1. A single-unit optical device for combining a first wavelength, S-Polarized, light beam and a second wavelength, P-Polarized, light beam onto a single, co-axial optical path, said device comprised of: a first means for selectively transmitting or reflecting the first wavelength, S-Polarized beam, said first means directing the first beam toward a third, wavelength selective, transmissive/reflective means; a second means for selectively transmitting or reflecting the second wavelength, polarized beam, said second means directing the second beam toward the third, wavelength selective, transmissive/reflective means, and; a third means for selectively reflecting the first wavelength beam and transmitting the second wavelength beam, such that upon exiting the device, the first and the second wavelength beams are combined, sharing a single, co-axial, optical path. 2. A single unit optical device of claim 1, wherein the first polarization selective means is comprised of a first, polarization sensitive, beamsplitter disposed within the light transmissive device in the path of the first beam and oriented at 45 degrees with respect to the optical path of the incident first beam, such that an incident S-Polarized beam is reflected by the first beamsplitter toward the third, wavelength sensitive means. OMPI -S- 3. A single unit optical device of claim 2, wherein the first, polarization sensitive, beamsplitter is comprised of: a first light transmissive prism having a right triangle cross section in the plane normal to the incident beam axis; a thin film coating deposited upon the hypotenuse face of the prism in such a thickness and oriented so as to reflect an S-Polarized incident beam, and; a second light transmissive prism having a 45 degree parallelogram shaped cross section in the plane normal to the incident beam axis, said second prism in intimate contact with the thin film coating so as to form a single unit beamsplitting device with said reflected beam traversing through said second prism toward the third wavelength selective means. 4. A single unit optical device of claim 3, wherein the second polarization selective means is comprised of a second polarization sensitive, beamsplitter disposed, within the light transmissive device, in the path of the second beam and oriented at 45 degrees with respect to the optical path of the incident second beam, such that an incident P-Polarized beam is reflected by the second beamsplitter toward the third, wavelength sensitive, means. 5. A single unit optical device of claim 4, wherein the second, polarization sensitive, beamsplitter is comprised of: a third light transmissive prism having a right triangle cross section in the plane normal to the incident beam axis; a thin film coating deposited upon the hypotenuse face of the prism in such a thickness and oriented so as to reflect an P-Polarized incident beam, and; a fourth light transmissive prism having a 45 degree parallelogram shaped cross section in the plane normal to the incident beam axis, said fourth prism in intimate contact with the thin film coating so as to form a single ' unit beamsplitting device with said reflected beam traversing through said fourth prism toward the third, wavelength selective means. 6. A single unit optical device of claim 5 wherein the third, wavelength sensitive means is comprised of a thin film plane of dichroic material disposed, within the light transmissive medium, said material positioned at 45 degrees with respect to both the first and the second beam, and having a thickness and orientation so as to reflect the first wavelength beam and transmit the second wavelength beam such that the first and the second beam emerge co-axial from the device. 7. A single unit optical device of claim 6 wherein the thin film dichroic material is deposited on the second surface of the first parallelogram and the second surface of the first parallelogram is in intimate contact with the thin film dichroic material, so as to form a single unit beam splitting device. 8. A single-unit optical device for splitting a first wavelength, S-Polarized, light -beam from a second wavelength , coaxially, P-Polarized, light beam, both beams sharing a single co-axial optical path, said device comprised of: a first means for selectively reflecting the first wavelength beam and transmitting the second wavelength beam, such that upon exiting the device, the first and the second wavelength beams are split, the first wavelength beam directed toward a second OMPI wavelength selective means and the second wavelength beam directed toward a third wavelength selective means. a second means for selectively transmitting or reflecting the first wavelength, S-Polarized beam, said second means directing the first beam out of the device along the path selected for said beam said path different from the path of an entering first beam. a third means for selectively transmitting or reflecting the second wavelength, polarized beam, said third means directing the second beam out of the device along the path selected for said beam said path different from the path of an entering second beam. 9. A single unit optical device of claim 8, wherein the second polarization selective means is comprised of a second, polarization sensitive, beamsplitter disposed within the light transmissive device in the path of the first beam and oriented at 45 degrees with respect to the optical path of the first beam, such that an incident S-Polarized beam is directed by the second beamsplitter out of the device along the preselected path. 10. A single unit optical device of claim 9, wherein the second, polarization sensitive, beamsplitter is comprised of: a first light transmissive prism having a right triangle cross section in the plane normal to the beam axis; a thin film coating deposited upon the hypotenuse face of the prism in such a thickness and oriented so as to reflect an S-Polarized beam, and; a second light transmissive prism having a 45 degree parallelogram shaped cross section in the plane normal to the beam axis, said second prism in intimate contact with the thin film coating so as to form a single unit beamsplitting device with said reflected beam traversing through said second prism out of the device along a preselected path. 11. A single unit optical device of claim 10, wherein the third polarization selective means is comprised of a third polarization sensitive, beamsplitter disposed, within the light transmissive device, in the path of the second beam and oriented at 45 degrees with respect to the optical path of the second beam, such that a P-Polarized beam is reflected by the second beamsplitter out of the device along a' preselected path. 12. A single unit optical device of claim 11, wherein the third, polarization sensitive, beamsplitter is comprised of: a third light transmissive prism having a right triangle cross section in the plane normal to the beam axis; a thin film coating deposited upon the hypotenuse face of the prism in such a thickness and oriented so as to reflect an P-Polarized beam, and; a fourth light transmissive prism having a 45 degree parallelogram shaped cross section in the plane normal to the beam axis, said fourth prism in • intimate contact with the thin film coating so as to fprm a single unit beamsplitting device with said reflected beam traversing through said fourth prism out of the device along a preselected path. 13. A single unit optical device of claim 12 wherein the first, wavelength sensitive means is comprised of a thin film plane of dichroic material disposed, within the light transmissive medium, OMΠ said material positioned at 45 degrees with respect to both the first and the second beam, and having a thickness and orientation so as to reflect the first wavelength beam and transmit the second wavelength beam such that the coaxial first and second beam emerge from the device along separate optical paths, the first beam toward the second polarization sensitive means and the second beam toward the third polarization sensitive means. 14. A single unit optical device of claim 13 wherein the thin film dichroic material is deposited on the second surface of the first parallelogram and the second surface of the first parallelogram is in intimate contact- with the thin film dichroic material, so as to form a single unit beam splitting device. OMPI

Inventors: REDDERSEN BRAD R, REDDERSEN, BRAD, R.
Applicants: STORAGE TECHNOLOGY PARTNERS, STORAGE TECHNOLOGY PARTNERS II
Application year: 1984
Main classification: G02B27
IPC codes: G02B27