WO1987002499A1

WO1987002499A1 - Apparatus for recording and reading optical data marks on an optical medium

Info

Publication number: WO1987002499A1
Application number: PCT/US1986/002129
Authority: WO
Inventors: Dennis H. Rose
Original assignee: Opticon Technology Incorporated
Priority date: 1985-10-10
Filing date: 1986-10-09
Publication date: 1987-04-23
Also published as: EP0241537A1

Abstract

A data reading and writing system for optical tape (18) corrects curvature of field distortion and provides multidimensional scanning of the tape (18) by a light beam source (7). A telecentric optical arrangement of the data scanning galvanometer (16) and the objective lens (17) results in a stationary reflected beam, so that a fixed optical tracking control system (20-22) and an autofocus control system (23-28 and 36) may be used.

Description

APPARATUS FOR RECORDING AND READING OPTICAL DATA MARKS ON AN OPTICAL MEDIUM

TECHNICAL FIELD

This invention relates to apparatus for reading and writing digital data from and onto an optical data storage medium, and more specifically, to such apparatus operable with optical storage film. The invention includes a telecentric arrangement for the optical components utilized therein in order to eliminate movement of a reflected optical beam and thus to permit two dimensional scanning and increased efficiency of operation of the device.

BACKGROUND ART

Prior art devices for reading and recording optical data are well known. In such devices it is known to utilize relative movement between an optical beam and a recording medium in order to read optically encoded data written on a data track.

However, prior art devices typically contemplate one dimensional recording of information on a relatively rigid recording medium, such as an optical or video disc, as illustrated in Ito et al U.S. patent

4,422,168. Therein, an optical system is used to focus a light beam generated by a relatively fixed light source on a moving disc. in such systems, it is necessary to assure th>_.t the focussed light beam accurately tracks the recording medium and particularly the data track thereon.

Accordingly, there have been developed several tracking systems for optical data reading and recording devices. One such tracking and focusing control system is disclosed in Musha et al patent 4,4453,239.

The prior art systems are further typically constrained to read the one dimensionally recorded data sequentially, in a serial fashion as recorded on a spiral track along the record medium. Accordingly there is a need in optical information transfer technology for a multidimensional information storage and readout capability.

Moreover, because of the flat nature of the " recording medium and the curvature of field introduced by the optical system, there is introduced an inevitable distortion in the shape of a focussed light spot incident on the record medium.

There is thus a need to compensate for curvature of field introduced by focusing optics.

Additionally, there is a further need in the prior art to provide increased reading speed for optically recorded data.

Inasmuch as in the prior art a scanning light beam typically scans recorded data by single dimensional relative movement between the record medium and the light beam, it is difficult to increase data throughput utilizing the scanning technology of the prior art.

Accordingly, there is a need in the prior art to provide an improved method and apparatus for scanning of a record medium by a light beam, and otherwise to provide increased imaging capacity for optical data storage systems. There is thus also a need to provide improved . tracking control devices and au tof ocussing controls usable with the improved scanning and imaging techniques.

DESCRIPTION OF INVENTION

It is accordingly a primary object of the present invention to provide an improved optical data storage device overcoming the difficulties of the prior art.

It is yet another object of the invention to provide an optical data storage apparatus in which a light beam is scanned along a recording medium in a plurality of directions while the reflected light beam is maintained substantially fixed relative to the stationary optics of the system.

It is a more specific object of the invention to provide of a telecentric arrangement for optical components to permit multidimensional deflection of a light beam for scanning a record medium and to permit a congruent relationship between the reflected and scanning beams so that the reflected beam is fixed relative to the stationary optics it is another object of the invention to provide an optical data storage system in which a flexible storage medium is utilized and including sh.aping devices for adding curvature to the storage medium in order to compensate for curvature of field introduced by optical components of the system.

Yet another object of the invention is the provision of a multidimensional scan for data recorded on an optical storage medium, and particularly provision of a two dimensional scan for such data. it is an additional object of the invention to provide an optical scanning arrangement in which a beam of light scans data in a direction perpendicular to the direction of relative movement between a record medium and the light source. It is a further object of the invention to provide apparatus for scanning an optical data storage medium in two dimensions and for providing a stationary tracking control system therefor.

Still another object of the invention is the provision of apparatus for scanning an optical data storage medium in two dimensions and of a stationary focusing control therefor.

In accordance with these and other objects of the invention, there is provided an improved optical information device having a light source for producing a light beam and an optical arrangement for irradiating a- surface- of an optical data storage medium by the light, beam.. The improved structure includes a scanning device for: caursing the light beam to scan the surface ^' of the medium, as well as a device for fixing the reflected beam to impinge on stationary optics used therewith. Preferably, the beam fixing device includes a telecentric arrangement between an objective lens of the system, the medium, and the scanning device for the beam which includes a reflector therefor. The reflector may comprise a galvanometer causing displacement of the beam for scanning tracks perpendicularly to the direction of relative movement between the medium and the light source, the reflector being placed at a back focal point of the objective, thus providing two dimensional scanning^' of the stored optical data while maintaining the reflected beam substantially fixed.

According to a preferred embodiment of the invention, the storage medium is a flexible film. Rollers and vacuum devices are used to provide appropriate curvature to the film to conform the same to curvature of field introduced by the objective and by other- lenses in t .e optical system, thus compensating for the curvature of field.

In accordance with one embodiment of the invention, there are provided a number of linearly disposed photo detecting elements, in a linear array, to permit simultaneous reading of a number of data bits recorded along a single track perpendicularly to the direction of relative movement between the film and the beam. In accordance with another embodiment, the linear array is placed to permit simultaneous reading of corresponding data bits on a plurality of tracks recorded on the medium.

Yet another embodiment of the invention provides a two dimensional array of photo detectors for sim ltaneously reading data recorded along corresponding portions of a plurality of tracks along the record medium.

The improved apparatus is stabilized by a system utilizing a light beam reflected by the record medium to a substan ially fixed location relative to the stationary optics. The fixed reflected beam permits the utilization of simplified, stationary, detectors for autof ocuss i ng and tracking control devices even with multidimensional beam scanning and movement of the incident beam.

Preferably, a split photodetector arrangement is used for tracking control of the beam. An autofocus control is used in which the light beam reflected from the record medium is passed through a beam splitter and focussed by a pair of lenses. The two resultant light beams are passed through apertures to a pair of photodetecting elements. One aperture is preferably located in front of the focal point of the lens and the other aperture is located behind the focal point of the lens.

An acousto-optical scanner may be used to control tracking of the medium by the incident beam. Alternat ely, a motorized drive may be activated to displace a lens for proper positioning of the incident beam. BRIEF DESCRIPTION OF THE DRAWINGS

Other objects, features and advantages of the present invention will become readily apparent to those skilled in the art from the following description wherein there is shown and described a preferred embodiment of the invention, simply by way of illustration and not of limitation of one of the best modes- (and alternative embodiments) suited to carry out the invention. As will be realized upon examination of the specification and from practice of the same, the present invention is capable of still other, different, embodiments and its several details are capable of modifications in various obvious aspects, all without departing from the invention. Accordingly, the drawings and the descriptions provided herein are to be regarded as illustrative in nature and not as restrictive of the invention wherein

Figure 1 illustrates a preferred embodiment of the invention;

Figure 2 illustrates in block diagram form the control circuitry for the preferred embodiment of Figure 1;

Figure 3 shows an alternate embodiment of the invention;

Figure 4 shows a tracking control system for the embodiment of Figure 3; and

Figure 5 shows a focus control system for the alternate embodiment of Figure 3.^'

BEST MODE FOR CARRYING OUT THE INVENTION

Referring now to Figure 1, there is shown a preferred embodiment of the invention for writing and reading information onto and from an optical data medium, preferably a flexible optical tape.

Preferably, a laser diode 7 provides a light beam. The output beam, which may diverge, is collected and collimated by a collimating lens 8, which provides the laser beam to an anamorphic prism 9. The output beam from lens 8 has an elliptical gaussian cross section, which is changed to a round elliptical cross section by the prism 9. As will be seen in the following description, the beam provided by prism set 9 on the one hand is used both for tracking and focus control and, on the other hand, is used for writing of data on the optical tape. In the alternative embodiment described in connection with Figure 3, the laser beam is also used for reading data.

In a technique well known in the art, the collimated beam is provided to a polarizing beam splitter 10 and an associated quarter wave plate 11. Polarizing beam splitter 10 passes beams polarized in the P_ direction and reflects beams polarized in the S_ direction. However, as will be clear to one of ordinary skill in the art, the invention may also be practiced by utilizing a beam splitter which passes the S polarized portion of the beam and reflects the P_ polarized portion, when all other polarization sensitive components are similarly modified.

Quarter wave plate 11 converts the linearly polarized beam into a righthand circularly polarized beam, which is provided to a focussing lens 12 for focussing onto an acousto-optical deflector 13. Beam deflector 13 is preferably capable of scanning at least small angles at frequencies of up to 20 Khz, and is used to provide the desired tracking correction for the invention. Upon leaving the deflector, the circularly polarized beam expands and is passed through a dichroic beam splitter 14 and is collimated by a lens 15 which, together with focussing lens 12, functions as a telescope to expand the beam to a diameter of approximately 30 mm, which permits focussing of the beam to a 2 m spot on the optical tape.

The beam, as expanded by lens 15, is incident on a scanning galvanometer 16 for scanning the optical tape either to read or to write data thereon. Preferably, the scan frequency of galvo 16 is 275 Hz.

Although the preferred embodiment utilizes a garv.anαπreter, it is to be appreciated that a rotating prism scanning mirror, or any scanning device known in the art, may similarly be used without departing from the concept of the invention.

In a significant aspect of the present invention, the galvo 16 is telecentrically located with respect to an objective lens 17. That is, the galvanometer is located at the back focal length of objective lens 17 in order to provide telecentric scanning of the data on the optical film being scanned. Thus, the fulcrum of rotation of the scanning beam lies at the objective back focal length so that the beam is perpendicular to the tape at all times. In addition to minimization of aberrations, this arrangement causes the beam to be retroref lected to the objective, along the original axis, and without displacement of the reflected beam as a function of scan angle.

Thus, as a result of the telecentric arrangement, upon reflection by the optical tape and further reflection by galvanometer 16, the scanned light beam is congruent with the incident imaging beam output by acousto optical deflector 13 and lens 12. Thus, regardless of the scanning position of the incident beam on the optical medium, the reflected beam is substantially stationary at lens 12, and is provided to tracking control and focus control optics thereat.

The scanned beam, reflected by galvanometer 16, is focussed on the optical medium, flexible tape 18 through an optical window 19, which may be provided in a tape cartridge.

In accordance with the above described feature of the present invention, it is thus possible to scan an optical data bearing medium in two directions, or in a plurality of directions, without requiring any of the imaging optical elements, the track control optical elements, or the focus control optical elements to be moved or movable. In accordance with the invention, 0 the multidimensional scanning of the optical medium may thus be accomplished efficiently, utilizing essentially stationary tracking, focussing, and detecting optics. Moreover, the use of a flexible medium, and the curvature provided thereto provides compensation for 5 curvature of field introduced by the scanning optics. Moreover, the use of a flexible medium, and the curvature provided thereto, provides compensation for curvature of field introduced by the scanning optics.

As mentioned above, the scanning apparatus of the ϋ invention is telecentrically arranged. Such telecentricity assures that the central focussed ray will be perpendicular to the optical tape at all positions of the scan, so that the beam is reflected back directly through the path through which it came. 5 The reflected beam is thus stationary after leaving galvo 16, permitting the tracking and focus servo- optics, which utilize the reflected beam, to remain stationary.

The optical tape medium which is used in the n present invention may preferably form data mark pits in response to the concentrated focussed laser beam. The tape may be of a write-once only type of medium. The output power of laser 7 is preferably controlled to assure that no inadvertent writing takes place during a reading operation or as a result of tracking or focussing control. Accordingly, laser power is preferably reduced during a reading operation.

Preferably, the optical tape medium used in the present invention carries data arranged thereon as 5 frames formed of groups of tracks perpendicular to the direction of tape motion. In a reading operation an image of a portion of the tape, including a portion of aaframe or a plurality of frames, is imaged by a video camera 1. Alternatively, a scanning beam, similar to lϋ 'the beam focussed on the tape for tracking and focussing control purposed as hereinabove described, may be imaged on the tape as a reading beam. The reading beam may scan the tape perpendicularly to the direction of motion thereof to scan the various tracks 15. in each data frame, in accordance with the embodiment of Figure 3. However, if a plurality of tracks^" are provided which are parallel to the direction of movement of the tape, such a perpendicular scan will image a plurality of corresponding data bits from 0 corresponding points along the parallel data tracks. Where a frame or a portion of a frame of parallel tracks is imaged on the video camera, corresponding portions of a plurality of tracks are thus imaged and thus read out simultaneously. As will be apparent to 5 those skilled in the art, relative displacement of the tape 18 with respect to the objective lens 17 may occur on a continuous or on an indexed basis. In either case, whether complete images of a portion of the tape, are obtained by a video camera or whether a scanning 0 light beam is utilized, it is necessary to maintain a properly focussed and properly sized spot of the scanning beam on the tape.

It is thus necessary to control the size of the spot of the scanning beam both for writing operations, for both of the embodiments described herein, and for reading operations. For the reading operation described in connection with the preferred embodiment of Figure 1, control of the scanning beam is required in order to provide proper tracking and focussing. In connection with the embodiment of Figure 3, control of the scanning beam is necessary in order to assure that the data is properly read.

In order to maintain a relatively constant spot size on optical tape 18, the objective lens 17 is preferably provided with. a relatively large depth of focus, so that even if the optical tape to objective lens distance were to vary the spot size would remain fairly constant. However, as will be described below, the present invention includes autofocus control optics and circuitry, so that the spot size is maintained constant' and in sharp focus on the tape 18. In that regard, the tape cartridge or other tape conveying mechanism used in conjunction with the invention includes tape curving means for providing curvature to the optical tape in conformity with the curvature of field introduced by objective lens 17, thus further assuring constancy of focus and accuracy of the optical system. The tape may be shaped by rollers, by a capstan, or by vacuum hold-down devices in order to minimize the va^'riations in the focussed spot on the medium surface. Of course, the tape may be differently mounted, without using a cartridge.

The reflected beam, passing in a path congruent with the incident beam after reflection by scanning galvanometer 16, traverses lens 15 and is reflected by beam splitter 14 to the optical detecting system, which may consist of a single photodetec tor diode, a linear array of photodetectors which may be self scanned, a rectangular array, or a video imaging camera as shown in Figure 1.

In a situation wherein a single photodiode is used to read the data from the optical tape, the beam output by laser 7 may itself be used for reading the data, as well as to provide tracking and/or focus control, as described below. Additionally, it may be the same laser beam which is used to read the data and to provid optical control for a linear or rectangular array αf photodiodes. In such an arrangement, the galvo mirror may be designed to be at least partially transmissive, so that the image of the data tracks may be projected therethrough onto a linear CCD photodetector array as illustrated in Figure 3, for example. Such an array provides a parallel readout of the data tracks on the tape. Of course, in a further embodiment, the invention may be practiced by r e t r o r ef 1 ec t i on of the scanning beam to the photodetectors of the tracking or focus control optics to read the recorded data.

However, as will be clear to one of ordinary skill in the art, where a video imaging camera or an array, and preferably a two dimensional detecting array, is utilized, imaging may be efficiently obtained by utilization of a separate light source, such as shown at 29 in Figure 1. The imaging light, incident on optical tape 18, is reflected thereby and focussed on scanning galvanometer 16. The telecentric arrangement again permits the reflected viewing beam to be substantially stationary once reflected by galvanometer

16. Thus, the information bearing beam reflected by dichroic beam splitter 14 is essentially stationary and is provided to the imaging video apparatus.

In the preferred embodiment of Figure 1 the tracking optics, as well as focussing optics, receive the reflected laser beam and are responsive thereto. Tracking control is necessary to provide proper alignment between the imaging laser beam and the tape in a writing operation. Similarly, in a reading operation, where a single photodiode or a linear array of photodiodes is utilized, it is necessary to provide proper tracking between the reading laser beam and the data on the tape. Accordingly, the tape preferably includes preformed grooves, or other indicia, for detection by the tracking optics. Of course, where a self-scanned array is used, it may be possible to bypass a need for a tracking control. Nonetheless, for proper imaging of a complete frame or of a predetermined portion of a frame in a reading operation, or for proper location of a data track to be written, the embodiment of Figure 1 includes the tracking control optics.

In the laser beam reflected by the optical tape

18, righthanded circular polarization is converted to _„ lefthanded circular polarization. Additionally, after passing back through the quarter wave plate 11, the circular polarization is converted to S polarization.

Thus, the beam splitter 10 reflects the returning S- polarized beam to the tracking and focussing control optics. Preferably, a narrow band filter is provided at the reflecting output of polarizing beam splitter 10_/ in order to block any stray light or unrelated reflection from the beam provided to the control optics. Thus, an essentially pure data beam is provided to beam splitters 20 and 23 for the tracking and focussing optics, respectively. Beam splitter 20 utilizes a portion of the reflected beam to control tracking by reflecting that portion to a focussing lens 21, which in turn focusses the portion of the beam on a split photodiode detector

22. For an- optical tape in which the data tracks are provided perpendicularly to the direction of motion of the tape, and in which the preformed tracking grooves therein are similarly provided perpendicularly to the direction of tape motion, the present invention permits 5., the use. of. stationary tracking and focussing optics notwithstanding the necessity for scanning the laser beam. pexpe_ndicularly to to the direction of motion of thestape

In accordance with the invention, images of the

10. pregrooved data tracks are imaged on the split photodetector 22 which straddles the image thereof.

Any deviation of the image of the pregrooved track from the center of the split photodetector causes an unbalanced illumination of one side of the detector

15 with respect to the other. Thus, output signals A and

B Jrom the split photodetector 22 will be unbalanced if the reflection of the pregrooved data track is not directly imaged on the central portion of the photodetector. The resultant difference in 0 photosignals is provided as an error signal for amplification by amplifiers 41 and 42 and provision to a tracking servo mechanism 44 shown in Figure 2.

In the preferred embodiment the servo mechanism outputs a control signal 46 to an acousto-optical 5 deflector driving mechanism 48 , as shown in Figure 2, thus causing a deflection of the scanning laser beam by the AO deflector 13 in order to provide proper positioning . of the beam for properly tracking the pregrooved data tracks on the optical tape 18. 0 Another portion of the reflected beam, passed by beam splitter 20, is provided to beam splitter 23 in the focus control optics.

Beam splitter 23 provides the other portion of the reflected beam to a pair of lenses 24 and 36. The two lenses focus the respective components of the beam provided thereto at corresponding focal points. A pair of apertures 25 and 27 are provided, one aperture (25, for example) located between one lens (e.g., 24) and the focal point thereof, the other aperture (e.g., 27) being located outside the focal point, that is, further removed from the lens than its focal point. The light focussed by lenses 24 and 36, after passage through apertures 25 and 27, is detected by photodetectors 26 and 28, respectively.

As focus of the medium changes, the position of the focus created by the two lenses will similarly change, so that the two apertures block differing amounts of light. For example, under the assumption that aperture 25 is within one focal length of lens 24 while aperture 27 is outside one focal length of lens 36, the two apertures clearly block different amounts of light in a push-pull fashion. More particularly, as the focus moves away from the two lenses, more light ^J ' will be blocked by aperture 25 and less light will be blocked by aperture 27, and vice versa. Thus, as the focus moves toward lenses 24 and 36, less light will be blocked by aperture 25 and more light will be blocked by aperture 27 so that more light will impinge on photodetector 26 while less light will impinge on photodetector 28. Thus, the difference voltage between outputs C and D of photodetectors 26 and 28 is proportional to the focussing error. The outputs of photodetectors 26 and 28 are amplified by amplifiers 52 and 54, respectively, and are used to drive a focussing servo 56 as shown in Figure 2. A focus motor 58 may be mounted either on the objective lens 17 or on the focussing lens 12, for example. However, in view of the previously described advantageous features of the present invention obtained by properly curving the optical tape, for example, a separate focus control may not be necessary.

Thus, the light emitted by laser diode 7, upon reflection by the optical tape 18, is returned to the tracking and focus control optics to provide proper tracking of the preformed data tracks on the tape and to provide proper focussing of the scanning spot thereon.

Referring now to the data detection portion of the preferred embodiment, there is provide _*d a light source

29 for illuminating the portion of the optical tape being read. The reflected illumination is provided through objective 17 to the galvo 16 for reflection through collimating lens 15 and for further reflection by the dichroic beam splitter 14, which reflects white light and passes 830 nm laser beams. Video camera 1 thus receives and scans the detected image through a sequence of lenses 2, 4, 15 and 17 which magnify the reflected image by a factor of as much as 1000 times. Where necessary, the path of the reflected beam may be extended by use of further reflecting optics symbolized by a mirror identified by reference numeral 3 in Figure 1.

A pair of filters 5 and 6 may be provided to minimize laser power reflected to the video camera. More particularly, filters 5 and 6 may be a laser block and a neutral density filter, respectively. Referring now to Figure 2, there is shown a functional system block diagram for the preferred embodiment. Various elements of the system have previously been described. The remaining elements of the embodiment of Figure 2 include a monitor 60 for the data scanned by video camera 1. The detected data may be provided by the video camera to any utilization equipment, of which monitor 60 is only an illustration. Thus, for the embodiment of Figure 1 the data on tape 18 is detected by video camera 1 and may be decoded by computing or other devices receiving the detecjted data therefrom.

The preferred embodiment further provides for writing of optical data on the optical tape 18. Data to be written on the tape is provided from a data buffer 62 to a driver 64 for the laser diode 7. The data may be provided to the buffer 62 by a computer 66. Thus, data may be keyboard entered to computer 66, or may be received from other devices. The data is then provided to buffer 62 for controlling driver 64. Alternatively, a fast pulse generator 68 may be used to trigger the laser diode driver 64.

A synchronization circuit 70 is included for synchronizing the data to be written onto the tape with the scanning galvo 16 as well as with a tape drive 72. As previously mentioned, tape 18 may be provided in a cartridge so that tape drive 72 may include a cartridge drive. However, any means for displacing the tape relatively to the scanning beam of laser diode 7 in a main scanning direction is contemplated by the present invention. Synchronizing circuit 70 thus provides synchronizing signals to a galvo driver 74, to a tape drive 72, and to the data buffer 62. Preferably, phase lock loops are utilized in the synchronizing circuits to attain the desired synchronization. In response to- the signals output by the split photodetector 22, tracking servo 44 activates the acousto-optical deflector driving mechanism 48 in order properly to control the tracking acousto-optical deflector 13. Thus, the writing beam is properly positioned on the optical tape 18 to record the data in accordance with a predetermined position of the preformed data tracks.

As will be recognized by those of ordinary skill in the art, positioning of the written data may not necessarily rely on preformed data grooves. Other synchronizing marks may be provided on the optical tape. The synchronizing marks, such as sprocket holes or the like, may be detected by a different tracking optics system for controlling the tracking servo 44.

Referring now to the alternate embodiment of the Invention shown in Figure 3, like elements are identified by like reference numerals and will not be described. A number of differences characterize the embodiment of Fig. 3.

One difference between the embodiments of Figures 1 and 3 relates to the method for detecting and imaging the data, written on tape 18. Particularly, rather than using a video camera 1 and a separate high intensity light source therefor, the light beam generated by laser 7 is used both for reading, writing and optics control of the system. Thus, scanning galvo 16 is made partially transmissive so that the beam reflected by tape 18 is partially transmitted through galvo 16 to a photodetecting arrangement 80. The photodetecting arrangement 80 may comprise a single photodiode, a linear CCD array, or a rectangular array. The image of the data tracks may be projected through a further lens 82 onto the photodetecting structure. As previously mentioned herein, however, the reflected da_.ta may instead be provided to one of the photodetectors 22, 26 or 28. Thus, in the embodiment of Figure 3 the photodetecting arrangement shown at 80 is preferably a linear photodetecting array capable of providing simultaneous readout of multiple data channels, thus increasing the rate of data readout from the optical tape. Accordingly, the embodiment of Figure 3 is capable of writing one data mark at a time, while capable of reading a plurality of data marks simultaneously. In order to read simultaneously the plural data channels, however, a separate, non-scanned, illuminating source (not shown) may be provided. In either case, whether a single or plural photodetectors are utilized, the reflected beam provided by galvo 16 is stationary, and does not have lateral or angular shifts.

A further difference between the embodiments of Figures 1 and 3 relates to the tracking control mechanism. Rather than using an acousto-optical detector as shown in Figure 1, the present embodiment incorporates a linear motor 84 built into lens 17, the linear motor responding to the outputs of split photodetector 22 and the tracking servo 44 to cause the lens to oscillate as necessary to maintain proper tracking. In that regard, in the illustration of Figure.3 the scanning beam is controlled by galvo 16 to scan in a right-left orientation in the plane of the drawing figure. The linear motor 84 causes oscillation of lens 17 perpendicularly to the plane of the drawing, so that the scanning beam is controlled in movement perpendicular to the plane of the drawing, in order to track a pregrooved data track such as illustrated at 85, for example.

In yet another diversion from the embodiment of Figure 1, Figure 3 illustrates a single lens 86 in the focussing control optics. Thus, instead of providing the other portion of beam splitter 20 f rst to the beam splitter 23 and then to the two lenses 24 and 36 as shown in Figure 1, the embodiment of Figure 3 first provides the beam to lens 86 for subsequent beam splitting by the beam splitter 23. In this arrangement, the beam is focussed by lens 86 and the portion of the beam reflected by beam splitter 23 passes through aperture 25, within the focus, while the portion transmitted by beam splitter 23 passes through aperture 27, located outside the focus of lens 86.

Yet another difference between the embodiments of Figures 1 and 3 relates to the explicit illustration of a manner for focussing the scanning beam on the optical tape,- wherein a focussing motor may be provided in association with either the collimating lens 8 or the objective lens 17.

Finally, in the embodiment of Figure 3 there is provided a further degree of freedom for the imaging optics. More particularly, rotational motion is provided for a linear or rectangular array of photodetecting diodes 80 in order to correct for angular misalignment of the array with respect to the data tracks.

Referring to Figure 4, there is illustrated the manner in which both the tracking linear motor 84 and a rotating motor 88 for the linear array may be controlled by the output of split photodetector 22.

Particularly, the outputs of amplifiers 41 and 42 for the output signals of photodetector 22 are subtracted from one another in a difference amplifier 90 to provide a tracking error signal proportional to the tracking offset. The error signal output by amplifier

90 is provided to driver amplifiers 92 and 94 for respectively driving the linear motor 84 for the objective lens 17 and the rotating motor 88 for the photodetector array 80. Thus, the scanning optics for the scanning beam are maintained on track, and the array is maintained in alignment with the data tracks.

Referring now to Figure 5, the control system utilized in focussing servo 56 is illustrated in greater detail. More particularly, as shown therein the output signals of amplifiers 52 and 54 are provided to a difference amplifier 96 for generating a focussing error output signal. The focussing error output signal is provided to a focussing motor 97 associated with the collimating lens 8, or to a focussing motor 98 associated with the objective lens 17. In that, regard, it will be recognized that either of the focussing motors may be activated to move the associated lens along the optical axis thereof in order to change the focus of the scanning beam on the optical tape. Thus, the linear motor 84 associated with lens 17 provides movement perpendicular to the plane of the drawing in Figure 3 while the focussing motor associated with the same lens assembly provides vertical movement in the drawing Figure 3.

There has thus been illustrated and described a system for writing data on and reading data from an optical medium, and preferably from a flexible optical medium such as optical tape (which may be photographic film, for example), the tape advantageously being curved to compensate for curvature of field by the optical system. A telecentric system is used for control of the scanning beam to permit multidimensional displacement thereof along the tape without causing a corresponding displacement of the reflected beam. Thus, accurate tracking control and focussing control is provided utilizing optical systems which are not required to move with the reflected beam. The data may be read rfrom the tape by a video camera or by a photodetector arrangement comprising a single detector, or a l i near or a rec tangu lar a rray of de tectors. The tape may be scanned perpendicularly to the direction of tape motion or parallel thereto and plural data may be read simultaneously or consecutively.

T he f o reg o i ng d es c r i p t i on o f t he p r e f e r red embodiment of the invention has been presented for purposed of -illustration and description and is not intended to be exhaustive or to limit the invention to the precise forms disclosed, since many obvious modifications and variations are possible in the light of the above teaching. The embodiment was chosen and described in order best to explain the principles of the invention and its practical application, thereby to enable others skilled in the art best to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the claims appended hereto, when interpreted in accordance with the full breadth to which they are fairly and legally entitled.

Claims

1. In an optical information transfer device including a light source for producing a light beam, optical means for irradiating a surface of an optical information carrying medium by said light beam, and optical detecting means for detecting light reflected from the surface of the medium, the improvement comprising: scanning means for causing said light beam to scan the surface of the medium to traverse plural data locations thereon, and beam fixing means for causing the reflected light beam from the surface of the medium to be substantially stationary, independently of scanning movement of the light beam produced by said scanning means.

2. An improved optical information transfer device as recited in claim 1 wherein said beam fixing means comprises a telecentric arrangement of an objective lens, the medium, and said scanning means, whereby the reflected light beam is made stationary and substantially congruent with the scanning light beam.

3. An improved optical information transfer device as recited in claim 1 wherein said scanning means comprises scanning galvanometer means having a rotatably mounted reflecting means at a back focal point of an objective lens for scanning said light beam along said medium surface; said medium surface located at a front focal point of the objective lens.

4. An improved optical information transfer device as recited in claim 3 wherein said reflecting means comprises mirror means for reflecting the light beam to the medium surface and for transferring at least a portion of the light beam reflected by the medium to an optical detecting means.

5. An improved optical information transfer device as recited in claim 4 wherein said optical detecting means includes means for reading data from the medium surface..

6. An. improved optical information transfer device as recited in claim 4 wherein said optical detecting means is operable for controlling tracking of said light beam along said medium surface, and further comprising illuminating means separate from said light source for illuminating data recorded on said medium surface and imaging means for reading data from the medium surface responsive to light generated by said illuminating means and reflected by said medium surface.

7. An improved optical information transfer device as recited in claim 4 wherein said optical detecting means comprises optically driven control means for positioning the light beam in the improved device for predetermined proper optical operation in response to said portion of said light beam transferred by said mirror means.

8. 'An improved optical information transfer device as recited in claim 7 wherein said optically driven control means includes motor means responsive t signals generated by tracking control means receiving said portion of said reflected and transferred light beam, said motor means operable for displacing a lens structure positioning said light beam along said medium surface.

9. An improved optical information transfer device as recited in claim 7 wherein said optically driven control means includes acousto optical scanning means responsive to signals generated by tracking control means receiving said portion of said reflected and transferred light beam, said acousto optical scanning means operable for displacing said light beam for proper tracking position along said medium surface.

10. An improved optical information transfer^* device as recited in claim 1 further comprising optically driven control means for positioning components of the improved device for optical operation in response to light reflected by data tracks on said medium surface.

11. An improved optical information transfer device as recited in claim 10 wherein said control means includes tracking means for causing the scanning light beam to be properly located with respect to said data tracks oh the medium surface.

12. An improved optical information transfer device as recited in claim 11 wherein said control means further includes auto focus means for causing the scanning light beam to be focused on the medium surface.

13. An improved optical informatlion transfer device as recited in claim 12 wherein said scanning means further includes means for substantially simultaneously reading a plurality of data tracks from the medium surface.

14. An improved optical information transfer device as recited in claim 11 wherein said tracking means includes split photodetecting means, having said reflected light beam focused thereon, for generating control signals to maintain a predetermined relationship between intensities of light incident on plural photodetecting portions thereof, and motor means responsive to said control signals for displacing an objective lens to displace said light beam to a data track of said medium surface so that said light reflected thereby illuminates said plural photodetecting portions according to said predetermined relationship.

X5_.. An improved optical information transfer device as recited in claim 11 wherein said tracking means includes split photodetecting means, having said reflected light beam focused thereon, for generating control signals to maintain a predetermined relationship between intensities of light incident on plural photodetecting portions thereof, and acousto optical means responsive to said control signals for displacing said light beam to a data track of said medium surface so that said light reflected thereby illuminates said plural photodetecting portions according to said predetermined relationship.

16. An improved optical information transfer device as recited in claim 10 wherein said control means includes auto focus means for causing the scanning light beam to be focused on the medium surface.

17. An improved optical information transfer device as recited in claim 16 wherein said auto focus means includes a plurality of photodetecting means and lens means for focusing said reflected light beam, together with plural aperture means disposed between respective ones of said photodetecting means and said lens means, and wherein one of said apertures is disposed between said lens means and a focal point for the light focused thereby and another aperture is disposed between a focal point for the light focused by said lens and the corresponding photodetecting means.

18. In an optical information transfer device including a light source for producing a light beam, optical means for irradiating a surface of an optical information carrying medium by said light beam, and optical detecting means for detecting light reflected from the surface of the medium, the improvement comprising: a plurality of data tracks positioned perpendicularly to a direction of relative motion between said light source and said medium, scanning means for causing said light beam to scan the surface of the medium to traverse plural data locations thereon, and beam fixing means for causing the reflected light beam from the surface of the medium to be substantially stationary, independently of scanning movement of the light beam produced by said scanning means.

19. An improved optical information transfer device as recited in claim 18 wherein said scanning means comprises means for moving said scanning beam along said data tracks perpendicularly to said direction of relative motion between said light source and said medium.

20. An improved optical information transfer device as recited in claim 19 wherein said scanning means includes reading means for reading substantially simultaneously a plurality of data tracks from the medium surface.

21. An improved optical information transfer device as recited in claim 20 wherein said means for simultaneously reading a plurality of data tracks comprises photodetecting array means for simultaneously reading corresponding portions of said plurality of data tracks.

22. An improved optical information transfer device as recited in claim 21 wherein said array means comprises rectangular array means.

23. An improved optical information transfer device as recited in claim 19 wherein said beam fixing means includes a telecentric arrangement including a reflecting surface forming said scanning means and operable for reflecting light from said light source toward said medium, said scanning reflecting surface located at a back focus of an objective lens, said medium located at a front focus of said objective lens, thereby causing said reflected beam to be reflected by said reflecting surface and to be substantially congruent with said light beam from said light source and substantially fixed relative to said light source.

24. An improved optical information transfer device as recited in claim 18 wherein said scanning means comprises means for moving said scanning beam to scan a two-dimensional portion of said medium to read a two-dimensional block of data recorded thereon.

25. An improved optical information transfer device as recited in claim 18 wherein said medium is formed of flexible material curvedly positioned to compensate for field curvature introduced by said optical means.

26. An improved optical information transfer device as recited in claim 25 wherein said flexible material comprises optical tape.

27. An improved optical information transfer device as recited in claim 26 wherein said optical tape comprises a plurality of frames, each having a plurality of guide tracks preformed thereon.

28. An improved optical information transfer device as recited in claim 25 further comprising means for curving a portion of the surface of said flexible medium thereby to compensate for said field curvature.

29. An improved optical information transfer device as recited in claim 21 further comprising optically driven control means for positioning components of the improved device for optical operation in response to light reflected by data tracks on said medium surface,

" said control means including means for rotating said photodetecting array means to correct angular misalignment with said data tracks.