United States Patent 1191
`Van Sant
`
`[11] Patent Number:
`
`4,856,871
`
`[45] Date of Patent:
`
`Aug. 15, 1989
`
`[54] REPLACEABLE LASER AND LENS
`ASSEMBLY
`
`[75]
`
`Inventor: Glen J. Van Sant, Penndel, Pa.
`
`[73] Assignee: General Electric Company,
`Moorestown, N.J.
`
`[21] Appl. No.: 91,132
`[22] Filed:
`Aug. 31, 1987
`[51]
`Int. c1.4 ..............................................., G02B 7/02
`[52] U.S. C1. . .....
`.. . ... 350/253; 369/122
`[58] Field of Search . ..
`350/502, 571, 417, 252,
`350/253; 369/122
`
`
`
`..
`
`.
`
`arrangement which can be readily replaced without
`complex realignment of the recorder. The module in-
`cludes a cylindrical outer housing/heat-sink, and a tilt-
`able yoke within the outer housing/heat-sink. A heat
`pump such as a thermoelectric element has a hot side
`coupled to the yoke, and also has a cold side. A combi-
`nation mount is at least thermally cantilevered from the
`cold side of the thermoelectric element, and is thermally
`isolated from adjacent structures. A laser diode is
`bonded to a structure within the combination housing,
`and a lens is loosely mounted at the light-emitting end of
`the combination housing. The module is prealigned by
`operating for a period sufficient to achieve thermal
`stability in a fixture which is dimensionally identical to
`the optical recorder with which the module is to be
`used. When thermal stability has been achieved, the
`yoke is tilted, and the position of the lens is adjusted in
`order to achieve focus at a selected location relative to
`the refeience plane. The lens is then secured in the
`selected position. That position will remain constant or
`substantially constant
`as
`the ambient
`temperature
`changes. This enables the optical recorder to be oper-
`ated at any ambient temperature needing virtually no
`adjustment to the optical alignment.
`
`20 Claims, 6 Drawing Sheets
`
`[56]
`
`References Cited
`U.S. PATENT DOCUMENTS
`
`3/1985 Jansen ................................. 358/213
`4,504,935
`.. 358/213
`4.55l,760 ll/1985 Bendell .
`
`4,587,563
`5/1986 Bendell
`369/32
`8/1987 Branc et al.
`..
`369/19 x
`4,685,303
`3/1989 Nakayama et al.
`........ 369/45
`4,815,059
`
`
`Primary Examz‘ner—Frank Gonzalez
`Attorney, Agent, or Firm—-Raymond E. Smiley; William
`H. Meise
`
`ABSTRACT
`[57]
`An optical recorder such as a data recorder has an
`interchangeable, prealigned laser diode/lens module
`
`
`
`Apple 1038
`
`U.S. Pat. 9,189,437
`
`Apple 1038
`U.S. Pat. 9,189,437
`
`

`
`U.S. Patent
`
`Aug. 15, 1989
`
`Sheet 1 of2
`
`4,856,871
`
`

`
`U.S. Patent
`
`Aug. 15,1989
`
`Sheet 2 of2
`
`4,856,871
`
`

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`1
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`4,856,871
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`REPLACEABLE LASER AND LENS ASSEMBLY
`
`This invention was made with Government support
`under Contract No. F30602-85-C-0193 awarded by the
`Air Force. The Government has certain rights in this
`invention.
`This invention relates to an assembly of a light-emit-
`ting device such as a laser diode with a focussing lens,
`which is arranged as a modular unit which focusses the
`light emitted at a predetermined distance from a refer-
`ence plane.
`Modern data techniques may require the handling
`and storage of large amounts of high-rate data. For
`example, data processing and storage at rates in excess
`of tens of megabits per second may be required. Optical
`disc recorders have been devised for recording and
`reproducing data at such high data rates by means of
`focussed light beams. Permanent optical storage discs
`for archival purposes are known in which recording is
`accomplished by a high-intensity focussed data-
`modulated light beam, which forms a permanent pat-
`tern of data-representative pits on the record track. The
`pits have a reflectivity which differs from that of the
`surrounding surface of the disc medium, and their pres-
`ence or absence may be detected by the changes in the
`magnitude of the light reflected by the recorded and
`unrecorded portions of the disc in response to a low-
`intensity read light beam. Reusable recording media are
`also known in which a data-modulated high-intensity
`light beam makes reversible changes in the polarization
`characteristics of the medium surface. Such media may
`be erased by the annealing effect of a gradual1y-decreas-
`ing intensity erase light beam. Reading is accomplished
`in one such system by comparing the polarization of the
`reflections from recorded and unrecorded portions of
`the surface of the medium when illuminated by a low-
`intensity read light beam.
`In optical data recorders, the light-emitting device is
`often a solid-state laser diode or array of laser diodes. At
`the present state of the art, such laser diodes have light-
`emitting characteristics as a function of drive current
`which change from time to time as the diodes age. Also,
`probably because of the relatively high electrical drive
`required to achieve the intense light required for re-
`cording onto the record medium or for erasing erasable
`media, the laser diodes are subject to failure. When a
`laser diode of a laser diode array fails, it may be possible
`to switch to an unused diode of the array. Ultimately,
`however, the laser diode or laser diode array must be
`replaced.
`When the laser diode or laser diode array of a re-
`corder is replaced, the light-emitting point of the re-
`placement diode(s) must be placed in precisely the same
`position as that of the previous diode in order to achieve
`focus at the surface of the disc, or the optical system
`must be realigned in order to achieve the desired perfor-
`mance. Exact placement of the laser diode is difficult to
`accomplish because the laser diode, when in operation,
`may produce a great deal of heat, which changes its
`temperature and that of the surrounding support struc-
`tures. As known, the dimensions of the support struc-
`tures may change under the influence of temperature,
`thereby affecting the point of focus. Realignment of the
`optics may require specialized test fixtures, and may
`also require the changing of lenses.
`The recorder may be used at a location at which
`specialized optical alignment gear and techniques are
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`not readily available. In that event, the data recorder in
`which the laser diode has failed must be returned to the
`factory for installation of a new laser diode(s) and for
`realignment. As a result, the data recorder is unavail-
`able to its user for a protracted period, or the user must
`keep on hand spare units, which may be a considerable
`expense, as well as requiring inventory control.
`It is desirable to arrange an optical data recorder with
`a light-emitting module which can be readily inter-
`changed by relatively unskilled personnel.
`SUMMARY OF THE INVENTION
`
`A data recorder/playback apparatus (recorder) using
`a light-sensitive medium includes means for generating
`relative motion between the medium and a light beam.
`A mutually orthogonal reference plane and reference
`axis are provided in the recorder, and an optical system
`accepts light leaving the reference plane parallel with
`the reference axis and translates it to the medium. A
`modular combination of a light-emitting device and a
`lens includes a second mutually orthogonal reference
`plane and axis, and is prealigned to cause the light to
`leave parallel with the second axis, and to focus at a
`predetermined distance from the reference plane. The
`reference plane and axis of the modular combination are
`readily made congruent with the reference plane and
`axis of the recorder, so that any prealigned modular
`combination may be used with the recorder, without
`further complex alignment.
`According to another aspect of the invention, the
`modular combination includes a focussing lens and a
`light-emitting device which may require cooling during
`operation. A heat pump including a cold surface and a
`hot surface is adapted to be energized for cooling the
`light-emitting device. A first mechanical and thermal
`coupler is coupled to the cold surface of the heat pump,
`to the light-emitting device, and to the lens, for holding
`the lens in a selectable position on the axis and before
`the light-emitting device, at least thermally cantilevered
`from the cold surface of the heat pump. The first me-
`chanical and thermal coupler is constructed from mate-
`rials, dimensioned and thermally isolated from adjacent
`structures such that, during operation, a substantially
`uniform temperature is maintained over the entirety of
`the first mechanical and thermal coupler. A second
`mechanical and thermal coupler is connected to the hot
`side of the heat pump for holding the first mechanical
`and thermal coupler and its associated lens and light-
`emitting device, and the heat pump, at least thermally
`cantilevered in position with the axis substantially or-
`thogonal to a reference plane, and for sinking heat re-
`ceived from the hot side of the heat pump. The select-
`able position of the lens is selected, and the lens is fixed
`in the selected position, under normal operating condi-
`tions, with the light beam focussed at a predetermined
`distance before the reference plane.
`
`DESCRIPTION OF THE DRAWING
`
`FIG. 1 is a simplified schematic View of an optical
`recorder including an optical disc recording medium, a
`motor for spinning a turntable, a recorder housing, a
`common reference plane and common axis, a modular
`light source, and an optical system;
`FIGS. 2a and 2b, referred to jointly as FIG. 2, illus-
`trate in FIG. 2a a simplified schematic view, partially
`exploded, of the optical system including a common
`reference plane and axis, the recorder housing and the
`modular light source of FIG. 1, and in FIG. 2b illus-
`
`

`
`3
`trates a cross-section of the recorder housing illustrating
`the reference surface and axis;
`FIG. 3 is an exploded perspective or isometric view
`of the modular light source of FIGS. 1 and 2, illustrat-
`ing a cylindrical module housing which mates with the
`recorder housing of FIGS. 1 and 2 to make the refer-
`ence planes and axes congruent, first and second me-
`chanical and thermal coupling elements coupled to the
`cold and hot sides, respectively, of a thermoelectric
`cooler, a laser diode and mount, and a lens and lens
`mount;
`FIGS. 4a, 4b and 4c, referred to jointly as FIG. 4, are
`cross-sections of the module housing of FIG. 3;
`FIGS. 511, 5b and 5c, referred to jointly as FIG. 5, are
`elevation, cross-sectional and plan views, respectively,
`of the second mechanical and thermal coupling element
`of FIG. 3;
`FIGS. 6a and 6b, referred to jointly as FIG. 6, are
`axial and cross-sectional views, respectively, of the first
`mechanical and thermal coupling element of FIG. 3;
`FIGS. 7a, 7b and 7c, referred to jointly as FIG. 7, in
`FIGS. 7:: and 7b are laser-side and rear, respectively,
`perspective or isometric views of the laser diode mount
`of FIG. 3, and an end view of the laser diode illustrating
`its relationship to the axis; and
`FIGS. 8a and 8b, referred to jointly as FIG. 8, are
`axial and cross-sectional views, respectively, of the lens
`mount of FIG. 3.
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`DESCRIPTION OF THE INVENTION
`
`FIG. 1 is a simplified schematic representation of an
`optical disc recorder/playback arrangement (recorder)
`10. Recorder 10 of FIG. 1 includes a turntable 12 driven
`by a motor 14 for rotary motion. Motor 14 is fixed to the
`housing 18 of the recorder. A photosensitive disc 16 is
`mounted on turntable 12 for rotation therewith. Also
`fixed to housing 18 of the recorder is an optical system
`including beam expanding prisms 20 and 22, a further _
`prism 24 having a mirrored face for reflecting a light
`beam or beams, illustrated as a line 26, toward the disc,
`spectrum limiting wave plates and gratings illustrated
`together as 28, and other optics represented as 27 re-
`quired to translate a light beam 26 entering the optical
`system along or parallel with an optical axis 30 to the
`disc. Translation of the light beam(s) may include con-
`trol of the polarization, focussing or defocussing in
`response to operating mode, beam expansion or con-
`traction, control of the cross-sectional dimensions,
`beam splitting or combining, offset position and other
`functions required for operation of the recorder.
`In FIG. 2, elements corresponding to those of FIG. 1
`are designated by corresponding reference numerals.
`FIG. 2a illustrates recorder housing 18, with a remov-
`able modular light source 200 insertable into a cavity
`212 therein. FIG. 2b is a cross-section of the arrange-
`ment of FIG. 1a, with module 200 removed, taken in
`the direction of section lines 2b—2b. Modular light
`source 200 has the general shape of a right circular
`cylinder and it fits fully into a right circularly cylindri-
`cal cavity 212. Cavity 212 has a central axis 30. Since
`modular light source 200 has an external shape which is
`cylindrical to match the shape of cavity 212, modular
`light source 200 is also symmetrical about axis 30 when
`inserted into cavity 212, and may be rotated about the
`axis for adjustment. A cavity dust cover 218 covers the
`right end of cavity 212 and is held in place by screws,
`one of which is illustrated as 219. In operation, modular
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`light source 200 emits light beam(s) 26 congruent with
`or parallel with axis 30.
`The left end of modular light source 200 as illustrated
`in FIG. 2a includes a flat reference surface illustrated as
`220 which is orthogonal to axis 30. Surface 220 is con-
`gruent with a reference plane, and is hereafter referred
`to as reference plane 220 for modular light source 200.
`Cavity 212 includes matching flat reference surface or
`reference plane 220’, against which reference plane or
`surface 220 mates when modular light source 200 is
`fully inserted into cavity 212. When assembled, there-
`fore, the axes 30 are congruent and the, reference planes
`220 of cavity 212 and of modular light source 200 are
`congruent.
`Also illustrated in FIG. 2 is a lever 230 fitted into a
`sectional notch 232 cut into recorder housing 18 to a
`depth, as viewed in FIG. 2b, below reference surface
`220’. The inner end of lever 230 is attached to an optical
`grating 28’ to permit small rotary positional adjustments
`thereof, for controlling polarization-sensitive character-
`istics of the light beam. A spectrum-limiting waveplate
`is illustrated as 28" in FIG. 2.
`FIG. 3 is an exploded perspective or isometric view
`of modular light source 200 of FIGS. 1 and 2. In FIG.
`3, an outer housing 410 of modular light source 200 has
`the exterior shape of a right circular cylinder centered
`on axis 30. At the left end of module housing 410 of
`FIG. 3, reference surface 220 defined by the end of
`module housing 510 can be seen to be annular, and
`coincident with a reference x—y plane which is orthogo-
`nal to axis 30. Housing 410 is formed from a thermally
`conductive material such as aluminum. As described
`below, housing 410 provides mechanical and thermal
`support for structures supporting the light emitting
`device, which may be a laser diode.
`Housing 410, which is illustrated in axial and side
`cross-sectional views in FIGS. 4a and 4b, includes a
`through central cavity 412 having a cross-section over
`the principal portion of its length which includes mutu-
`ally opposed first and second straight sides 414 and 416.
`Other portions 415, 417 of the interior of cavity 412 are
`curved or circular. Housing 410, as illustrated in FIG. 3,
`is partially cut away to reveal interior details. At the
`extreme rear end of housing 410 is a circular aperture
`418 having a smaller diameter than the diameter be-
`tween circular surfaces 415 and 417. A dust cover 320 is
`affixed to the rear of housing 410 by a plurality of
`screws, one of which is illustrated as 322, for covering
`aperture 418.
`Referring to FIGS. 3 and 4, a pair of coaxial apertures
`424, 426 are defined through the walls of housing 410,
`centered between the upper and lower sides of flat
`portions 414, 416. A further pair of curved through slots
`428, 429 penetrate the walls of housing 410 with a radius
`centered on the axis of apertures 424, 426. As illustrated
`in the cross-section of FIG. 4c, the outer portion of the
`walls of housing 410 in the region around slots 428, 429
`is undercut by depressions 427, 430, respectively, for the
`purpose of countersinking the heads of screws de-
`scribed below. A pair of coaxial jackscrews 332, 332’,
`with their common axis disposed parallel with the Y
`axis, are threaded into threaded through holes 434, 434’,
`respectively, formed in the sides of housing 410, as
`illustrated in FIG. 3.
`In FIG. 4a, threaded apertures 422’ formed in the
`back wall of housing 410 are visible. Threaded aper-
`tures 422’ accept screws 322 (FIG. 3) for holding dust
`cover 320 (FIG. 3) onto housing 410.
`
`

`
`.5
`A furcated copper yoke, designated generally as 540
`in FIG. 3, is illustrated in three views in FIG. 5. As
`illustrated in FIGS. 3 and 5, yoke 540 includes a thick,
`flat baseplate 542 having an approximately octagonal
`peripheral shape. A pair of yoke arms 544 and 546 ex-
`tend in a forward direction from baseplate 542. A pair
`of smooth-sided coaxial apertures 548, 550 are formed
`through the sides of yoke arms 544 and 546, respec-
`tively. Apertures 548 and 550 have the same dimensions
`as apertures 524 and 526 formed in housing 410, as
`illustrated in FIG. 3, and are adapted to receive trun-
`nion pins, one of which is illustrated as 352 in FIG. 3.
`Arms 544 and 546 are also penetrated by threaded holes
`554, 554', respectively, which are adapted to receive a
`pair of screws, illustrated as 356, 356' in FIG. 3.
`Baseplate 542 of yoke 540 has formed therein a set of
`four apertures 558——558”’, best seen in FIG. 5b. Aper-
`tures 558 are clearance holes for screws, one of which is
`illustrated as 360 in FIG. 3. Screws 360 are used for
`holding in place, as described below, a thermoelectric
`or Peltier-effect heat pump or cooler illustrated as 362
`in FIG. 3. Heat pump 362 pumps heat from a cold plate
`or cold surface 364 to a hot plate or hot surface 365. A
`suitable thermoelectric cooler is type FCO.6-32-06L
`manufactured by Melcor Corporation. The pattern of
`apertures 558 in baseplate 542 is selected in conjunction
`with the dimensions of cooler 352. Thermoelectric
`cooler 362 is energized by electrical power applied
`thereto through electrical leads 363, 363’. Leads 363,
`363’ are led from housing 310 in any convenient man-
`ner. As described below, a temperature sensor may be
`used in conjunction with thermoelectric cooler 362 for
`feedback control of the temperature of cold face 364.
`A pair of conical recesses 566, 566' are formed in
`upper and lower flat edges of baseplate 542 of yoke 540.
`When assembled, yoke 540, together with thermoelec-
`tric cooler 362 fastened thereto, fits within cavity 412
`defined by housing 410, with yoke arms 544 and 546
`fitted snugly to flat surfaces 414 and 416 in the interior
`of housing 410. Trunnion pin 352 passes through aper-
`tures 426 and 550, and another trunnion pin (not illus-
`trated) passes through apertures 424 and 548, and both
`are fastened in any convenient manner, for permitting
`yoke 540 and the attached thermal cooler 362 to pivot
`slightly within housing 410. When so assembled, the
`ends of jackscrews 332, 332’ fit into conical recesses
`566, 566’ formed in baseplate 542 of yoke 540. Jack-
`screws 332, 332’, when alternately loosened and tight-
`ened, allow fine control of the exact position of yoke
`540 within housing 410, and also secure it in position
`when the desired position has been achieved. Locking
`screws 356 and 356’, extending through slots 429 and
`428, respectively, and into threaded holes 554’, 554,
`respectively, prevent
`inadvertent misadjustment. As
`mentioned, the heads of screws 356 are allowed to sink
`below the outer surface of housing 410 because of the
`undercutting illustrated as 427, 430 in FIG. 4c.
`Referring to FIG. 3, a combination mounting illus-
`trated as 600 for a light-emitting device and a lens in-
`cludes relatively thick copper walls 603 with a circu-
`larly cylindrical outer surface 605. As illustrated in
`FIG. 3, combination mounting 600 is partially cut away
`to illustrate interior details. Combination mounting 600
`is further illustrated in FIG. 6. A cavity or chamber 606
`is defined within walls 603, with interior surface 612
`also in the form of a right circular cylinder. Integral
`with walls 603 is a floor 608 closing off one end of
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`cavity 606. Floor 608 has a relatively flat exterior sur-
`face 609, clearly visible in FIG. 6b.
`Referring now to FIGS. 3, 6a, and 6b, floor 608 of
`mounting 600 can be seen to be penetrated by four
`threaded apertures designated 628—628”’. The pattern
`of holes 628 matches the pattern of holes 558 formed in
`baseplate 542 of yoke 540. Screws, two of which are
`illustrated as 360, 360’ in FIG. 3, pass through clearance
`holes 558, 558’ in yoke 540, and thread into threaded
`apertures 628, 628’ of mounting 600, in order to draw
`bottom surface 609 of floor 608 of combination mount-
`ing 600 toward baseplate 542 of yoke 540, with thermo-
`electric element 362 sandwiched therebetween. Thus,
`thermoelectric element 362 is held in place with its cold
`surface 364 flat against bottom surface 609 of floor 608,
`and with its hot surface 365 flat against a surface of yoke
`baseplate 542. The mating surfaces between surface 609
`of mounting 600 and cold plate 364, and between hot
`plate 365 and base plate 542 of yoke 540 may be coated
`with a thermally conductive grease to enhance thermal
`conductivity, as known in the art. Such thermally con-
`ductive grease may also be advantageously used at the
`interface between yoke arms 544, 546 and flat surfaces
`414, 416 in the interior of module housing 410.
`While it might appear that the screws which hold
`mounting 600 to base plate 542 constitute a thermal
`short-circuit between the cold and hot sides of thermo-
`electric element 362, their relatively great length with
`relation to their diameter reduces the thermal conduc-
`tion by this path to a relatively negligible level. By
`selecting a material for the screws which has a rela-
`tively low thermal conductivity, such as stainless steel,
`the thermal conduction may be further reduced. From a
`thermal point of view, therefore, mounting 600 is con-
`nected only to cold plate 364 and is effectively ther-
`mally “cantilevered” from cold plate 364, even though
`it is not mechanically cantilevered from cold plate 364.
`In this context, thermal cantilevering means that there
`are no structures affixed to or connected tothe struc-
`tures attached to cold plate 364 which conduct ther-
`mally to any structures connected to hot plate 365 of
`cooler 362.
`Bottom floor 608 of mounting 600 is bored part-way
`through to form a depression, illustrated by 616 and best
`seen in FIG. 6, for accepting a mounting stud of a laser
`diode mount. Bore 616 encompasses axis 30. At the
`center of bored portion 616 is a smaller through aper-
`ture 618, dimensioned to clear a screw (illustrated as 750
`in FIG. 3) for fixing the laser diode mount (700 of FIG.
`1) within chamber 606 of combination mount 600. A
`further bored portion 619 is formed in rear surface 609
`of floor 608 of combination mount 600 for countersink-
`ing the head of screw 750.
`A pair of apertures 614, 614’ (FIG. 6a) is formed at a
`convenient location through floor 608. These locations
`are selected for convenient passage therethrough of
`conductors for the energization of the laser diode.
`A laser mounting element 700 is affixed to a laser
`diode 740 as illustrated in FIG. 3, and the combination
`fits within cavity 606 of combination mount 600. Details
`of laser diode mounting 700 are illustrated in FIG. 7.
`FIG. 7a is a perspective view of laser diode mounting
`arrangement 700, illustrating its relationship with laser
`diode 740. Laser diode mounting 700 is generally disc-
`shaped, with a diameter only slightly less than the inner
`diameter of chamber 606 of combination mount 600. As
`illustrated in FIG. 7a, laser diode mounting 700 includes
`a steel disc 710, the edge of which includes a plurality of
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`7
`steps 712 having no significance to the invention, and a
`further copper-tellurium alloy (ASTM B301) stud 714
`swaged into a bore through disc 710. Stud 714 includes
`a flat 716 to which laser diode 740 is bonded, as by
`soldering or welding. Stud 714 penetrates through disc
`710 as illustrated in FIG. 7b, and extends beyond rear
`surface 716 of disc 710. A threaded aperture 718 is cen-
`trally located in, and accessible from the rear of stud
`714. A screw illustrated as 750 fits threaded aperture
`718 and, as mentioned in conjunction with FIG. 3, holds
`stud 714 of laser diode mount 700 fixedly in place
`against the inner surface of floor 608 of mounting 600.
`Referring once again to FIGS. 7a and 7b, power for the
`laser diode is provided by a pair of conductive rods 730,
`732 which pass through copper disc 710 and are insu-
`lated therefrom by glass inserts 740, 742, respectively.
`Conductive rods 730 and 732 are coupled to the laser
`diode by bond wires (not illustrated).
`Laser diode 740 is bonded to flat 716 with the lasing
`portion centered, insofar as possible, at a height above
`flat 716 selected to place the lasing portion congruent
`with axis 30, as illustrated in FIG. 7c. The x and y axes
`are illustrated in FIG. 7c for reference only, as the las-
`ing surface is to the rear of the reference x—y plane in
`the assembled modular light source 200.
`Referring once again to FIG. 3, the open end of cav-
`ity 606 of mounting 600 is closed by a lens holder 800 in
`the general form of a disc with a central aperture. De-
`tails of lens holder 800 are illustrated in FIG. 8.
`In FIG. 8, central aperture 812 can be seen together
`with an annular depression 814 concentric with central
`aperture 812. A radial hole 816 communicates with
`depression 814. A plurality of clearance holes 818 are
`dimensioned to clear mounting screws, one of which is
`illustrated as 370 in FIG. 3, for mounting lens holder
`800 over the open end of cavity 606 of combination
`mount 600, with the body of screws 370 threaded into
`apertures 630 in walls 603 of combination mount 600.
`A focussing lens illustrated in FIG. 3 as 372 includes
`a cylindrical portion 374 dimensioned to fit within cen-
`tral aperture 812 of lens mount 800. When the final
`position of lens 372 has been selected, a hardenable
`liquid is injected through hole 816 in the edge of lens
`mount 800, and runs through depression or groove 814
`to completely surround portion 374 of lens 372. The
`hardenable liquid is then allowed to harden to fix lens
`372 in the selected position. The hardenable liquid may
`be an epoxy resin.
`When modular light source 200 has been assembled
`and tested for operation, but before the position of lens
`372 is fixed, modular light source 200 is mounted in a
`test fixture which is dimensionally identical to that of an
`operating recorder such as that illustrated in FIG. 1.
`The laser diode 740 and thermoelectric cooler 362 are
`
`then energized, with feedback control of the tempera-
`ture, if such is used in the final recorder, and operation
`is allowed to continue until the temperature stabilizes.
`Once the temperature has
`stabilized, combination
`mount 600, because of its thick walls and the thermal
`conductivity of the materials of which it is constructed,
`and because it is thermally isolated from adjacent heat-
`sinking structures (except for screws 360, which are
`negligible), assumes a substantially constant tempera-
`ture, without thermal gradients thereacross. Similarly,
`laser diode mount 700 and lens mount 800 are at the
`same temperature as that of combination mount 600.
`Since the combination mount, laser diode mount, and
`lens mount 800 are at the operating temperature without
`
`8
`thermal gradients thereacross, the dimensions are the
`same as those which occur during normal operation,
`except for variations due to room ambient. If a tempera-
`ture sensing element (not illustrated) is affixed to cold
`plate 364 or to any portion of mounting 600, and used
`for control of the gemperature thereof, the cold temper-
`ature will be stabilized. Consequently, the dimension of
`the combination mount, laser diode mount, lens mount
`and lens will be identical to those used during initial
`alignment, regardless of the ambient temperature.
`the
`Similarly, after the temperature has stabilized,
`temperature of yoke 540 and housing 410 will be essen-
`tially at room temperature, with very small thermal
`gradients which might result in indeterminate dimen-
`sions. Consequently, after thermal stabilization,
`laser
`diode 740 will be at the same distance from the refer-
`ence X—Y plane as it will be during normal operation in
`a recorder. Thus, one mounting requirement is thereby
`fulfilled.
`As mentioned, the light beam emitted by laser diode
`740 may not be exactly parallel to axis 30, because of
`slight
`imperfections in the_ mounting procedure. An
`alignment is performed to produce a light beam parallel
`with axis 30 which is focussed at a precise distance from
`the X—Y reference plane by loosening lock screws 356,
`and adjusting jackscrews 332, 332’ in order to tilt the
`yoke 540,
`thermoelectric element 362, combination
`mount 600, laser diode mount 700, lens mount 800, and
`lens 372 to bring the beam of light emitted by laser
`diode 740 parallel with axis 30. The axial position of lens
`372 is then adjusted to produce focus at the precise
`desired distance from the reference x—y plane, and the
`liquid epoxy is injected as by a syringe, illustrated in
`FIG. 3 as 376, into hole 816 to fill depression 814 and
`thereby hold lens 372 in the selected position.
`Other embodiments of the invention will be apparent
`to those skilled in the art. For example, instead of con-
`necting combination mount 600 to base plate 542 of
`yoke 540 with screws, bottom surface 609 of combina-
`tion mount 600 may be bonded, as by use of a thermally
`conductive epoxy, to cold plate 364, and hot plate 365
`of thermoelectric element 362 may be attached by
`screws to base plate 542, thereby mechanically cantilev-
`ering, as well as thermally cantilevering the combina-
`tion mount, laser diode mount, lens mount, and lens
`from cold plate 364. Also,
`instead of stainless steel
`screws such as 360, 360’ of FIG. 3, screws of materials
`such as nylon could be used for even lower thermal
`conduction.
`What is claimed is:
`
`1. A replaceable assembly including a light-emitting
`device for an optical apparatus requiring a focussed
`light beam at a predetermined distance from a reference
`plane, said assembly comprising:
`a light-emitting device for emitting light in a for-
`wardly direction parallel with an axis, said light
`emitting device requiring cooling during normal
`operation;
`a lens to focus said light;
`a heat pump including a cold surface and a hot sur-
`face;
`first mechanical and thermal coupling means coupled
`to said light-emitting device, to said lens, and at a
`heat transfer surface to said cold surface of said
`heat pump, for forming a mechanical combination,
`said first mechanical and thermal coupling means
`being arranged for holding said lens in a selectable
`position before said light-emitting device, said first
`
`l0
`
`15
`
`20
`
`25
`
`30
`
`35
`
`45
`
`50
`
`55
`
`60
`
`65
`
`

`
`9
`mechanical and thermal coupling means being con-
`structed from"a material dimensioned and ther-
`mally isolated from adjacent structures such that,
`in operation, said lens and said light emitting device
`are at least thermally cantilevered from said cold
`surface of said heat pump, and a substantially uni-
`form temperature is maintained over the entirety of
`said first mechanical and thermal coupling means,
`second mechanical and thermal coupling means, said
`second mechanical and thermal coupling means
`being at least thermally coupled at a heat transfer
`surface to said hot surface of said heat pump and
`mechanically coupled to at least said first mechani-
`cal and thermal coupling means for holding said
`mechanical combination of said light emitting de-
`vice, said lens, said flrst mechanical and thermal
`coupling means, and said heat pump in a position
`with said axis substantially orthogonal relative to a
`reference plane, said second mechanical and ther-
`mal coupling means being thermally coupled for
`sinking heat transferred thereto by said hot surface
`of said heat pump; and
`wherein said selectable position of said lens relative to
`said light-emitting device is selected at normal
`operating temperature and condition of said lens,
`light-emitting device, heat pump, and first and
`second mechanical and thermal coupling means to
`produce focus at said predetermined distance from
`said reference plane, whereby the positions of said
`lens and said light emitting device relative to said
`reference plane are repeatable at said operating
`temperature and condition, and said assembly may
`be freely substituted for another like assembly for
`producing focussed light at said predetermined
`distance from any reference plane.
`2. An assembly according to claim 1, wherein said
`light emitting device comprises a lase