Abstract:
An optical head for an optical signal recorder includes a nonpolarizing beam combiner for combining the light beams from two like-frequency, sic wavelength, lasers along one light path. The combined beams travel slightly diverging paths so that a first one of the beams can record signals on a disk while a second beam follows the first beam on the disk for direct reading-after-recording. Intermediate the combiner and the disk are a polarization type beam splitter and a focuser. One or more detectors receive reflected light from the disk via the beam splitter for detecting focus, sensed recorded signals and for tracking the beams to tracks of the disk. The combiner and splitter are preferably secured together as a single unit. The combiner uses refraction and internal reflection properties to combine the two like-frequency beams without polarization changes of either beam.

Description:
FIELD OF THE INVENTION 
     The present invention relates to optical signal recorders, particularly of the disk type, and optical data recorders of the present invention can be a compact unit with a lightweight optical head movable with respect to an optical record medium. 
     BACKGROUND OF THE INVENTION 
     1. Discussion of the Prior Art 
     Optical data recorders have been noted for their high areal recording density. One of the drawbacks on many of the optical data recorders is the inability to instantaneously verify that signals being recorded have been, in fact, recorded. Verification of such recording is referred to as &#34;direct-read-after-write&#34; (DRAW). Such DRAW requires that two light beams simultaneously impinge on the optical record medium in a predetermined spaced-apart relationship. A first light beam that records the signals onto the record medium is a high power, or high intensity, beam which alters the optical properties of the recording surface. In immediate trailing juxtaposition to the recording beam for scanning the recording created by the recording beam just after it is recorded is a second reading or sensing beam. The physical separation on the record member along a track being recorded by the recording beam is in the order of 20-60 microns. Any optical signal recorder that is to provide the DRAW capability requires the efficient generation of these two beams for simultaneously recording and readback of signals being recorded and then the separaticn of the light reflected from the record member of both beams. Other applications of multi-beam heads include erase-before-write (rewriteable media) and a three-beam head for erase-before-write then read-after-write. 
     U.S. Pat. No. 4,100,577 shows a single-laser (gaseous type), two-beam system providing the DRAW function. While the function is performed, the number of optical elements and the character of those optical elements work against providing an extremely compact optical signal recorder. Note the two extended light paths required in the beam splitting operation. Rather than provide a single laser, which requires an extremely high-power laser for providing both recording energy and sensing energy; two-laser systems have been employed. A two-laser system is attractive, particularly when semiconductive lasers are used. One widely-known prior art technique is to cross-polarize the read and write beams. This arrangement has proven not to be satisfactory because of the known problems of beam separation of the light reflected from the record member by the read and write beams. Accordingly, two lasers have been selected having significantly different frequencies such that dichroics can be used to isolate the read and write beam reflections. For example, U.S. Pat. No. 4,085,423 shows a two-laser system. One of the lasers operates at a high power, which is reflected by a dichroic mirror. That laser beam is also provided for tracking and data sensing. A second laser source of low power and of different frequency projects its beam through the dichroic mirror such that its beam is reflected to a focus-controlling photodetector. Other configurations of two laser-two frequency optical signal recorders are known. When the lasers have widely different frequencies, the thermal characteristics and focus control of the lasers becomes complicated adding to the weight and space required for implementing such a signal recorder. 
     U.S. Pat. No. 4,225,873 shows two gas lasers, which are extremely large and mounted on a frame rather than on a head arm which is movably across the face of an optical record disk. Because of the size of the components, including a Glan prism, mirrors and several other components, this system requires not only two lasers having different frequencies of operation which emit light having different wavelength, but results in a relatively large signal recorder. 
     Many diverse optical systems employ prisms for combining and separating light beams using cross-polarized light. The above-mentioned Glan prism requires that the two beams being optically processed be orthogonally polarized to achieve beam separation and combination. Other beam combiners and beam splitters have been employed using such cross-polarization of light. See IBM TECHNICAL DISCLOSURE BULLETIN, entitled &#34;Light Beam Combiner&#34; by J. J. Winne, Vol. 15, No. 4, September 1972, pp. 1399-1400. As mentioned earlier, initial cross or orthogonal polarization of the beams does not provide separation between the beams for satisfactory optical signal processing. 
     For good optical isolation, physical separation of the beams, as by diverging beams, is desired. The Glan prism employs refractive and reflective techniques, such as described in analytical form by Hect &amp; Zajak in their bock &#34;Optics&#34; published by Addison Wellsley, 1974, pp. 72-84. This publication defines the mathematics of optical refraction and internal reflection and tends to explain the operation of a Glan prism. This publication is incorporated by reference for defining the theory of operation of the present invention. Additional refractive optical signal processing is shown in the USSR Pat. No. 289465, wherein two optical members are separated by an air slot for providing an optical attenuator. A refractive optical beam combiner is shown in U.S. Pat. No. 3,743,383. This combiner is designed for high power laser beams, apparently, much more powerful than desired for optical signal recorders. It appears that these optical components and their spacing, operate because the input signals have different wavelengths. As mentioned earlier, it is desired to have both lasers, if possible, operate at the same frequency. The temperature characteristics of identical lasers tend to prevent differential focus errors between the write and read beams, such that a single focus control is easily applicable to both the reading and recording. If both lasers can electrically and optically track in a similar fashion with respect to temperature changes, then the optical signal recorder may exhibit a wider range of tolerance to temperature variations, as well as exhibiting a greater degree of stability of operation during turn on and subsequent operations. 
     Another aspect of providing a compact optical signal recorder is to reduce the amount of electronics involved in processing the optical signals. By reducing the electronics and taking advantage of large scale integration, electronics can be conveniently mounted on the head arm along with the optical elements. U.S. Pat. No. 4,059,841 shows a single photodetector system that responds to the reflected light beams found in the optical signal record member to provide not only data information, but also focus and tracking information. In many instances, two photodetectors are employed--one for providing tracking, and a second one for providing focus and data detection. With efficient semiconductive photodetectors, either one or two photodetectors can be employed for providing a compact optical signal recorder. 
     Accordingly, it is desired that an optical signal recorder be provided that uses multiple lasers of the same frequency with a minimal of optical components for minimizing optical path lengths and yet provide a recording beam of high power and a read beam of low power. 
     SUMMARY OF THE INVENTION 
     In accordance with one aspect of the invention, two identical semiconductive lasers emit beams preferably on parallel paths which are combined into a third path such that the beam from a first, or read, laser is attenuated, while the beam from a second, or write, laser is not attenuated. The two beams have a predetermined diverging relationship, such that when the beams impinge upon a record member, they are separated a predetermined distance for enabling recording and direct-read-after-write. Polarization-sensitive optics are interposed between the beam combiner and the record member for redirecting a reflected read beam to a detectcr such that read-after-write verification occurs. The reflected read beam may also be employed for tracking and focus control. 
     In another aspect of the invention, two lasers (preferably substantially identical) emit their beams into a nonpolarizing or a polarization insensitive combiner and thence projected in a slightly diverging relationship to a record member for enabling recording and read-after-write. Polarization optics are interposed between the combiner and the optical disks for separating a reflected read beam for enabling data detection including direct-read-after-write verification, focus detection, and tracking control. In a variation, a dichroic element is employed in the combiner; then the lasers must have differing output wavelengths. 
     It is preferred that the two lasers be mounted with high thermal conductivity therebetween such that both lasers operate at the same temperature. The polarization of emitted light beams of the two lasers in any of the embodiments are preferably colinearly polarized for maximizing efficiency of the optical system. Cross-polarized or other angularly-polarized beams may also be employed. 
     In yet another aspect of the invention, the beam combiner, beam splitter and polarization optics are a composite but unitary member having a major light path axis parallel to the disk. A mirror optically couples the composite member through a focusing element allowing a path orthogonal to the major axis of the composite member. A detector system is mounted immediately adjacent the focuser and intermediate the major optical axis of the optical composite for minimizing the axial depth of the optics with respect to the axis of rotation of the disk. Integrated circuits are mounted on the head arm adjacent the detector, preferably intermediate the optical composite and the disk for making a compact optical signal recorder. The lasers are preferably mounted remote from the focuser and emit light beams parallel to the planar extent of the disk. 
     The beam combiner is preferably a refraction-internal-reflection type, wherein the read beam from a first laser is optically directed using optical properties of the beam combiner such that it can be used as a sensing beam. A beam from a second laser, which is to be a recording, or write, laser is internally reflected with insignificant attenuation. The arrangement in the beam combiner, allows a path carrying a read beam and a write beam at a slightly diverging relationship, such as one-half degree. The write beam precedes the read beam on an optical record member for enabling direct-read-after-write verification. For maintaining a desired beam cross-section of the refracted read beam an optical wedge is disposed in a slightly-spaced relationship from the surface of the beam combiner used to refract the read beam and internally reflect the write beam. In a preferred embodiment, the write beam has two internal reflections for making a more compact optical apparatus. 
     The foregoing and other objects, features, and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention, as illustrated in the accompanying drawings. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a simplified side-elevationed view of an optical head disposed adjacent to an optical record disk. 
     FIG. 2 is a combined diagrammatic and plan view of the FIG. 1 illustrated apparatus with the head arm being viewed along a plane intermediate the FIG. 1 record disk and the illustrated head arm assembly. 
     FIG. 3 diagrammatically illustrates a preferred optical composite member for use in the FIG. 1 illustrated apparatus for achieving a compact optical signal recorder. 
    
    
     DETAILED DESCRIPTION 
     Referring now more particularly to the drawings, like numerals indicate like parts and structural features in the three figures. FIGS. 1 and 2 illustrate a first embodiment, while FIG. 3 illustrates a portion of a preferred, or second, embodiment. The optical signal recorder, generally denominated by numeral 10, is constructed using known techniques as represented by other circuits and elements 11. Optical disk 13 is mounted for rotation on a suitable spindle, which is controlled in accordance with using known techniques as represented by numeral 12. Such spindle speed control can either be a constant angular speed or an angular speed that varies with the radial position of the head arm 17 mounted for radial translation with respect to the record disk 13 in the usual manner. Information processing and control circuits 14 are connected to a host processor, communication line or other utilization device as indicated by the double-headed outline arrow 14A. The electrical connections of signal circuits 14 to various circuitry in the recorder are indicated by the plurality of lines 14B. Included in signal recorder 10 are the usual tracking circuits 15 and focusing control circuits 16. Circuits 14, 15 and 16 employ electrical signals derived from a detector, later described, for analyzing the informational content of the reflected light beams for providing optical signal data functions based upon the informational content contained on a recording coating (not shown) of the optical record disk 13. For example, data can be recorded as a series of holes, series of reflective and nonreflective areas, a series of bumps, which tend to scatter the impinging light with intermingled planar areas which tend to reflect the light, and the like. All of the informational content is arranged in a series of concentric tracks or a single spiral track on the coating surface of the optical record disk, as is well known. The function of tracking circuits 15 is to ensure that head arm 17 precisely positions the optical head over a record track being scanned. Focus circuits 16 detect the focus of a light beam to maintain good focus at the recording surface of the optical record disk 13. In FIG. 1, the recording surface is represented by the lower surface of the disk 13. 
     The optical head assembly employing the present invention is mounted on frame 19, which in turn is suitably mounted in head arm 17. Included in frame 19 is a highly thermal conductive portion 20, which suitably thermally connects first laser 21 and second laser 22. The first and second lasers are of the semiconductive type preferably operating at the same frequency for emitting identical wavelength light beams, the first laser 21 emitted light beam for sensing information recorded on disk 13, while the laser 22 emitted light beam is modulated for recording information on optical record disk 13. In one embodiment, the optics of the invention attenuate the energy of the first laser 21 emitted light beam such that it is suitable for reading; the power output of the first laser 21 power output is also adjustable to achieve suitable read beam power levels. The two lasers being thermally connected together tend to operate at the same temperature and therefore tend to emit light beams that vary identically with temperature changes occurring during operation of the optical signal recorder 10. This feature adds stability to the operation of the recorder and applies to those aspects of the inventions employing lasers emitting light of differing wavelengths or emitting different wavelength light. 
     The lasers 21 and 22 supply their light beams, respectively, through collimating optics 23 and 24. A polarization insensitive beam combiner 25 receives the beams from lasers 21 and 22 and supplies the combined beams, as later detailed, to half-wave plate 26. As will become apparent, plate 26 is desired only for making the assembly more compact for facilitating optical efficiencies of the assembly. The effect of the half-wave plate is to rotate the polarization of both beams 41, 50 simultaneously. This rotation enables beam splitter to be oriented for positioning detector 31 as shown in FIG. 1--between the disk 13 and splitter 27--for minimizing the size of the optical assembly, as will become apparent. Half-wave plate 26 is suitably bonded to combiner 25. The next optical element in the light path from the lasers to the disk is polarization-sensitive beam splitter 27 of usual construction. Beam splitter 27 is suitably bonded to the half-wave plate 26. Mounted on the output face of beam splitter 27 is one-fourth wave length polarization plate 28 which retards the polarization of both beams by 45 degrees, as is well-known. The light reflected from record member 13 is further rotated 45 degrees, such that the beam splitter rather than transmitting the light back to the splitter into the lasers, reflects the disk 13 reflected light to detector 31, which is disposed on frame 19 intermediate the major optical axis of elements 25, 26, 27 and 28, and record disk 13. Quarter-wave plate 28 is suitably bonded to splitter 27 for making a composite optical assembly consisting of combiner 25, half-wave plate 26, splitter 27 and quarter-wave plate 28. 
     The diverging laser beams leaving quarter-wave plate 28 are reflected by mirror assembly 29, which includes planar pivotally mounted mirror 29M which directs the diverging beams through focus element 30, an objective lens system, onto the recording surface of optical record disk 13. Mirror system 29 may be made responsive to tracking circuits 15 for providing tracking functions of the diverging beams with respect to the track defined on optical record disk 13. Alternately, focus unit 30 may flexibly mount its objective lens (not shown) to provide the tracking function using known tracking apparatus employed in combination with such focusing elements. 
     Inspection of FIGS. 1 and 2 shows that frame 19 provides support for a compact optical system having a simple optical path and that all of the elements mounted on the frame are in close proximity for minimizing the size of frame 19 and head arm 17. Electrical integrated circuits may be mounted on frame 19 adjacent to detector 31. 
     An element important to the present invention is the polarization insensitive beam combiner 25. For maximal efficiency, it is preferred that the polarization of the emitted light beams from lasers 21 and 22 be in the plane of the drawing as best seen in FIG. 2. A first optical element (amorphous glass or plastic, for example) 35 of beam combiner 25 includes a first angled surface 36. Surface 36 in a preferred embodiment provides an air-to-optical element interface which refracts the read beam 42 emitted from laser 21 and internally reflects the emitted write beam 40 received from laser 22. In a second embodiment, a known dichroic coating is included in surface 36. For the second embodiment, laser 21 emits light having a wavelength that passes through the dichroic coating (not separately shown but is represented by the surface 36) while laser 22 emits light having a wavelength that is reflected by the dichroic coating. Semiconductive lasers having similar thermal characteristics and operating at different frequencies are known. 
     Beam 40 enters optical element 45 through input surface 37, which is disposed substantially orthogonal with respect to output surface 38. The term &#34;substantially orthogonal&#34; means that the angle between beam 40 and surface 37 is near ninety degrees; the angle differs from ninety degrees in the preferred embodiment by the small angle of divergence desired between the light beams 41 and 50, such as one-half of one degree. The angle of divergence between beams 41 and 50 can be obtained by changing the angle of surface 36 with respect to the output surface 38 rather than altering the angle between beam 40 and surface 37. For avoiding refraction, it is preferred that the angle between beam 40 and surface 37 be kept close to ninety degrees. Output surface 38 pauses the diverging read and write beams to be transmitted through halfwave plate 26 as beams 41 and 50, respectively. The angle of divergence between beams 41 and 50 for the illustrated embodiment is approximately one-half degree. Surface 36 in refracting read beam 42 reduces the beam energy content by approximately 25 percent; therefore the surface acts as an optical attenuator having internal reflection properties. 
     The laser 21 emitted beam 42 has a predetermined cross-sectional shape, such as circular or slightly ellipsoid. When such a beam impinges upon an angled surface 36, because of the angle of incidence, the beam cross-sectional shape is distorted along one axis of the beam. To keep the beam shape from distorting, input optical element 43 is disposed upon surface 36 and spaced therefrom a short distance. In the preferred embodiment, the spacing can vary from a few microns to about one-fourth of a millimeter. The spacing should be at least about one-tenth wavelength of the lasers 21, 22 for effecting internal reflectance. As the spacing increases, the size of the optical combiner 26 gets larger. This increase in size is caused by the surface 45 refracting beam 42 away from a line extending normal or ninety degrees with respect to parallel surfaces 36 and 45, or upwardly as viewed in FIG. 2. It is desired that beam 50 extend parallel to beam 42, after being refracted by surface 36. For a large spacing, annular ring 46 can be a metallic shim; while for a micron spacing, ring 46 may consist of a suitable coating of adhesive. Coating 46 preferably bonds input optical member 43 to optical element 35. The laser 21 emitted beam 42 passes through orthogonally disposed input surface 44 of the input optical member 43. At the output surface 45 of input optical member 43, the beam 42 is refracted by the glass-to-air surface 45 away from a line normal to surface 36. It is important that the surfaces 36 and 45 be substantially planar and be disposed in a closely parallel relationship for maintaining the output beam 50 substantially parallel to input beam 42. The spacing is preferably small because the relatively large upward (FIG. 2) refractive angle of the beam 42 at surface 45. When surface 36 includes a dichroic, then surfaces 36 and 45 can be in contact. 
     The resultant diverging beams 41 and 50, which are still identically polarized in a preferred environment, then travel through beam splitter 27, then through quarter-wave plate 28, to be reflected to disk 13 by mirror 29M. The laser 22 emitted beam 41 is internally reflected at surface 36 as write beam 51 which goes via components 27 and 29 to optical disk 13. Read beam 50 goes through focus unit 30 as read beam 52 to optical record disk 13. The record disk 13 rotates into the plane of the drawing as viewed in FIG. 1 and as represented by arrow 13R. Write beam 51 scans a track on disk 13 immediately ahead of read beam 52. The spacing of the beams 51 and 52 on record disk 13 is preferably between 20 and 50 microns, no limitation thereto intended. The read beam is shown as a heavy dashed line while the write beam is shown as a light dashed line. These lines represent the respective optical axes of the illustrated beams, it being understood that the optical components are designed to optically process most of the energy of the illustrated beams. As best seen in FIG. 2, write beam 51 is represented by an upper &#34;X&#34; while read beam 52 is represented by an &#34;X&#34; below and space from the write beam 51. This view is looking into the focuser 30 from the disk 13. The relative motion of disk 13, as viewed in FIG. 2, is toward the top of the figure. 
     Optical record disk 13 reflects the beams 51 and 52, as is well-known, back along paths 51 and 52, respectively. Mirror 29M, in turn, directs the reflected beams to polarization-sensitive beam splitter 27 after passing through quarter-wave plate 28 a second time. As is well known, the polarization of the reflected beams are rotated ninety degrees with respect to the laser 21, 22 beams, respectively, beam splitter 27 then reflects both of the reflected beams toward detector 31, as beams 53 and 54, respectively, for the reflected write and read beams. Remember, the reflected write beam will have a greater intensity than the reflected read beam. While various configurations may be employed for isolating the reflected read and write beams, shown is a mask 56M disposed between detector 31 and lens 56, having an aperture 56A for passing reflected read beam 54 while blocking out reflected write beam 53. Lens 56 passes the reflected beams toward mask 56M and detector system 31. Detection system 31 can be of any known optical detector design. Alternatively, the lens and detector system can be sufficiently small such that it only receives reflected read beams; the divergence of beams 53 and 54 providing physical isolation. 
     The lasers 21 and 22, being of the semiconductor type, can be modulated directly by signal circuits 14 using known techniques; in particular modulating write laser 22 provides information modulation in write beam 40. Read beam 21 can be of the constant intensity type or can be intensity modulated for provided additional tracking and focusing functions. 
     The electronic circuits supported on head arm 17 are best understood with respect to FIG. 2. Detector 31 provides a data output signal derived from reflected read beam 52 over line 57 to signal circuits 14. This means that the data detector, preferably a single integrated-circuit chip, is suitably mounted as a part of detector system 31. Tracking information, which can be derived by detector system 31 from either the reflected write or read beam, provides tracking error information signals over line 58 to tracking circuit 15. Tracking circuit 15 analyzes the tracking error signals and provides control signals over line 59 either to tracking mirror system 29 or to the focus unit 30, whichever does the tracking function. Detector system 31 also provides focus error signals over line 60 to focus circuit 16 which, in turn, provides focus error control signals over line 61 to focus unit 30. Operations of the tracking and focus circuits 15 and 16 are well-known and not described for that reason. 
     The FIGS. 1 and 2 illustrated beam combiner 25 requires that lasers 21 and 22 be disposed to emit substantially orthogonal beams (the angle between the laser 21, 22 beams is ninety degrees plus or minus the angle of divergence cf beams 41, 50). FIG. 3 illustrates a preferred embodiment wherein the lasers 21 and 22 emit substantially parallel beams such that thermal conduction mount 20A is smaller, hence lighter and the lasers are closer together. This means that the lasers 21 and 22 operate at a much closer temperature and therefore operate more consistently with temperature changes. Thermal conduction unit 20A is diagrammatically shown for illustrating the close proximity of the two lasers. Read laser 21 cooperates with the preferred beam combiner 25A as described with respect to FIGS. 1 and 2. The other elements of the optical composite, including the described optical components, are suitably bonded as described for FIGS. 1 and 2. The write or second laser 22 is mounted coplanar with laser 21 on thermal conduction mount 20A such that its emitted write or recording beam 76 is substantially parallel to the emitted read beam 42. In a preferred arrangement; the laser beams diverge at about the desired angle of divergence; such small divergence is defined as substanially parallel. 
     This preferred mounting requires additional optical processing for effecting the desired diverging beam combination. For the additional processing, beam combiner 25 includes a depending portion for changing the direction of the laser 22 beam 26. The input surface 74 of beam combiner 25A for the write beam 76 is also angled with respect to the input plane including input surface 44 of optical input element 43. For the illustrated embodiment, this angle 75 is less than one degree for corresponding to the desired angle of divergence and for receiving the laser 22 emitted light beam orthogonally to its surface plane. When the laser 22 beam is parallel to laser 21 beam, hence not orthogonal to surface 74, input surface 74 slightly refracts the write beam 76 along optical axis 77 to internal reflective surface 78. Otherwise, the laser 22, already at a small angle of precise orthogonality, is not refracted by surface 74, but is already aligned with path 77. The refracted or internal beam 77 is internally reflected by surface 78 along optical axis 79 onto input-reflective surface 72, which corresponds to surface 36 shown in FIGS. 1 and 2. The output write beam diverges from the read beam 50 at an angle of less than one degree. Other than the above-described changes, operation of an optical head in the preferred embodiment is identical to that described for FIGS. 1 and 2. As seen in FIG. 3, looking at combiner 25A from a record disk 13, detector system 31 is mounted on the face of splitter 27 facing the viewer; mirror 29 is disposed to reflect the beams 49, 50 toward the viewer. Rather than dispose surface 74 at a light angle 75 with respect to output surface 73, surface 74 can be parallel to surface 73 requiring laser 22 be mounted at an angle thereto such that beam 76 is refracted to beam 77. Other geometric variations can also be employed. 
     In an additional alternate embodiment, surface 72 includes dichroic characteristics. Lasers 21, 22 emit different wavelength light such that the dichroic version of surface 72 passes the laser 21 wavelength light and reflects the laser 22 wavelength light. 
     The optical members 35,43 of combiner 25 and optical members constituting combiner 25A consist of amorphous optical glass. Other optical amorphous materials, such as plastic materials, can be readily substituted for the optical glass. Such materials are not birefringent; such as crystalline materials of many beam combiners. The index of refraction of the materials and the wavelength of the laser beams emitted by lasers 21,22 affect the angles required for constructing the described polarization insensitive beam combiners. The indices of refraction of various materials are empirically determined in a usual manner. The indices of refraction of many commercially available optical materials are published by the various manufacturers. As one example, optical glass used in constructing one embodiment of the invention has an index of refraction of 1.511. Using the known wavelength of the emitted radiation of lasers 21,22 and the index of refraction, the equations, particularly equation (4.63) on page 80, of the &#34;Optics&#34; article, supra, can be used to calculate the angles necessary for constructing a beam combiner using the present invention. Such calculations also lead to a desired spacing between surfaces 36 (or 72) and 45 as described earlier. The angle 75 of surface 74 with respect to the plane of output surface 73 will also vary with the above-described parameters and can be calculated as well using the teachings of the above-cited article. The calculations are simplified when all of the members of the combiner have the same index of refraction; such a selection is not required to practice the present invention. Also, when lasers 21,22 supply beams of light having the same wavelength, design and construction of the combiner 25,25A is simplified. 
     One spacing selected for a constructed embodiment was abcut ten-thousands of one inch. In one embodiment, spring-shaped spacer 46 consisted of deposited spacer, such as a metal or a glass. Norland 61 adhesive, a commercially available adhesive, may be used to bond all of the optical components of the described optical composite. The approximate axis of beam 50 is deemed to be the major axis of the optical composite and is preferably disposed parallel to the plane of optical record disk 13 as best seen in FIG. 1. This arrangement tends to minimize the axial depth of the optical disk recorder 10. While it is not necessary for the beams to enter the combiner orthogonally to the various input surfaces, for desired power transfer and beam direction to obtain diverse angles of divergence in between beams 41, 50, this orthogonal relationship should be maintained. 
     Using the above criteria, one embodiment of the beam combiner 25A surface 72 was disposed at 41 degrees, 15 minutes with respect to surface 73, surfaces 74 and 72 subtended an angle of about 137 degrees, 46 minutes and the gap between surfaces 72 and input optical wedge 43 was about 0.25 millimeters. The output surface 73 was parallel to input surface 44, the latter surface was orthogonal (to the axis of beam 42). Combiner 25A consisted of amorphous glass having an index of refraction of 1.511 and an objective lens and focal length of objective lens in focuser 30, such that an angle of divergence subtended by the axes of light beams 41 and 50 resulted in a separation of about 20 microns on the optical disk 13. 
     While the invention has been particularly shown and described with reference to preferred embodiment thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention.