WO1996041335A2

WO1996041335A2 - Compact read/tracking system for optical tape recording

Info

Publication number: WO1996041335A2
Application number: PCT/IB1996/000718
Authority: WO
Inventors: Scott M. Hamilton; Billy C. Frederick; William D. Mccoy; James R. Boyd; Michael W. Montana
Original assignee: E-Systems, Inc.
Priority date: 1995-06-07
Filing date: 1996-06-06
Publication date: 1996-12-19
Also published as: WO1996041335A3; AU6315096A; ZA964613B

Abstract

A read/tracking system of an optical tape recorder for optically reading a data signal on light sensitive recording media (108) during a read function. A read beam is shaped to illuminate on the recording media a plurality of recorded data channels within a data track comprising the data signal. The read beam is modulated by data marks within the plurality of data channels to generate a reflected data modulated read beam. This reflected data modulated read beam is detected by detector (142) to recover the recorded data. The data image in the reflected data modulated read beam is detected to recover the recorded data. The data image in the reflected data modulated read beam is also used to generate an auto tracking control signal for electronics (156) which automatically adjusts the positioning of the objective lens (152) for proper positioning of the read beam on the recording media. The data track is, therefore, automatically tracked while the data track is being read during a read function.

Description

COMPACT READ/TRACKING SYSTEM FOR OPTICAL TAPE RECORDING

TECHNICAL FIELD

The present invention relates to optical tape recorders and, in particular, to a read/tracking system for retrieving data written on an optical media while automatically tracking the data recorded . on closely proximated data tracks.

BACKGROUND OF THE INVENTION

Optical systems are now commonly used in place of magnetic systems for recording and retrieval of digitized information. In optical recorders, the data is used to digitally modulate a light beam having a predetermined intensity necessary to mark a light sensitive recording media. The modulated beam is focused to a small spot and traced across the media to record the data as a fine optical pattern comprised of a number of closely spaced, microscopic dots (data marks) along a data track. A data track may contain a plurality of data channels depending on the number of write beams . To recover the recorded data from the optical media, a low intensity illumination beam is scanned along the data track and modulated by the optical pattern recorded therein. The modulated beam is reflected from the media to illuminate a light detector producing an electrical signal in accordance with the beam modulation for recovery of the recorded data.

Current optical read systems are capable of simultaneous reading of multiple data channels. An example of one such system is U.S. Patent No. 5,081,617 to Gelbart. This read system simultaneously reads a plurality of data channels with minimal optical cross-talk between the data channels. Reduction in cross-talk is achieved by choosing a numerical aperture (NA) for the imaging lens (or objective lens) to generate Airy pattern nulls at approximately double the spacing of the data channels. This system, therefore, requires an imaging lens having a specific NA for reducing the cross-talk. The problem with 5 this system is that while optimization of the NA of the read objective lens reduces the cross-talk, the read optimized objective lens may not be able to be used additionally as the objective (focusing) lens for a write system.

1.0 Accordingly, there is a need for an improved optical data storage and retrieval apparatus for reading data tracks that automatically tracks the recorded data tracks on the optical media to reduce cross-talk and maximize channel signal-to-noise ratio as data is retrieved from the

15 optical media. The system is capable of using the same objective lens for both the read function and additionally for a write function. Such a system will reduce data retrieval errors by automatically and accurately positioning the objective lens at an optimum read location

20 when reading data from the optical media.

SUMMARY OF THE INVENTION

A read/tracking system of an optical tape recorder for optically reading a data signal on light sensitive recording media comprises a light source for emitting a read beam and optics for shaping the read beam to illuminate a plurality of recorded data channels on the recording media within a data track storing the data signal. The read beam is modulated by data marks within the plurality of data channels to generate a reflected data modulated read beam. The data modulated read beam is detected to recover the recorded data and generates an auto tracking control signal for automatically adjusting the positioning of an objective lens to image the illuminated pattern on a read detector and position the read beam on the recording media in response to the auto tracking control signal. The read detector comprises two photosensing arrays, one for data detection and the other for tracking control.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the optical tape recorder of the present invention may be had by reference to the following detailed description in conjunction with the accompanying drawings wherein:

FIGURE 1 illustrates an optical tape recorder system using the read/tracking system according to the present invention;

FIGURE 2 is a schematic diagram of the read/tracking system for the optical tape recorder of FIGURE 1 showing the read/tracking subsystem and associated optics that couple a write function and an autofocus function into the optical tape recorder of FIGURE 1;

FIGURE 3A illustrates a partial^" view of the recording media showing data tracks, data channels, data marks and the layout of the read illumination beam at the surface of the recording media;

FIGURE 3B illustrates one embodiment of the spacing between adjacent data channels in the data track, the spacing between adjacent data marks in a data channel and the data mark size using pulse position modulation (PPM) with the distance between adjacent data marks in each data channel being determined by the encoding scheme; likewise, for pulse width modulation (PWM) , the length of each data mark is determined by the encoding scheme; FIGURE 4 is a block diagram of the read subsystem shown in FIGURE 2 illustrating the read beam source, read optics, read array and electronics module, and associated optics to retrieve data from the optical media and generate an autotracking signal;

FIGURE 5A illustrates the multi-beam illumination pattern as applied to the recording media;

FIGURE 5B illustrates an alternative multi-beam illumination pattern as applied to the recording media; FIGURE 6 is a schematic diagram illustrating the read array and electronics module shown in FIGURE 4;

FIGURE 7 is a more detailed diagram of the read array shown in FIGURE 6;

FIGURE 8 illustrates the read after write function at the surface of the recording media;

FIGURE 9 is a schematic diagram of the data array processing logic shown in FIGURE 7;

FIGURE 10 is a schematic diagram of the tracking array output logic and control shown in FIGURE 7; FIGURE 11 illustrates the spatial relationship between the data image on the recording media with respect to the linear photodiode arrays of the read array.

FIGURE 12 is a block diagram of an alternative embodiment of the read beam source shown in FIGURE 4; and - 7-

FIGURE 13 illustrates an alternative embodiment for the geometry of each linear photodiode array of the read array.

DETAILED DESCRIPTION OF THE DRAWINGS

Referring now to FIGURE 1, there is shown a block diagram of a read/tracking system 102 of an optical tape recorder 100. The read/tracking system 102 outputs an multi-beam illumination beam 104 and an actuator subsystem 106 for focuses and positions the multi-beam illumination beam 104 on light sensitive recording media 108. The multi-beam illumination beam 104 may include either or both a write beam and a read beam. The multi-beam illumination beam 104 may also include other beams, such as an autofocus beam, combined with the read and write beam as needed to perform the desired functions of an optical tape recorder. As will be discussed below, the read/tracking system 102 includes light sources and optics^" (see FIGURE 2) for generating and combining the included read and autofocus beams into the multi-beam illumination beam 104. Additionally, actuator subsystem 106 includes optics, actuator mechanisms and electronics for focusing and positioning the multi-beam illumination beam 104 onto recording media 108.

The present optical storage devices for which the read/tracking system 102 is designed includes multiple write beams that are focused and scanned across the recording media to record the data as a fine optical pattern, commonly referred to as a data track, comprised of multiple channels of closely spaced, microscopic dots (data marks) . A data track may contain any number of data channels depending on the number of write beams.

Referring now to FIGURE 2, the multi-beam illumination beam 104 output by the read/tracking system 102 is directed toward the actuator subsystem 106 comprised of objective lens 152, an actuator 154 and tracking-autofocus electronics 156. The objective lens 152, the actuator 154 and the tracking-autofocus electronics 156 of the autofocus subsystem 106 function in combination to accurately focus and position the multi-beam illumination beam 104 on the recording media 108 to provide the reading of a multiple data channel data track. In the preferred embodiment, the objective lens 152 is a 0.55 NA objective lens, but may have any desired value of NA to produce the desired results (i.e. resolving power) of the present invention.

The objective lens 152 is mounted to an actuator 154 controlled longitudinally (in response to the autofocus signal) and laterally (in response to the tracking signal) . As such, the positional movement of the objective lens to "track" the data channels (or data track) may be considered "medium" tracking of the data track. Additionally, the entire read head of the optical tape recorder is moved with respect to the optical media to read (or write) adjacent data tracks in serpentine fashion longitudinally along the optical media. This "coarse" tracking is usually accomplished by a stepper motor for positioning the read head.

The multi-beam illumination beam 104 output by the read/tracking system 102 comprises a plurality of spatially combined beams, including a collimated read beam 150 and a collimated autofocus beam 130. Additionally, a write beam or beams generated by a write subsystem (not shown) may be included in the multi-beam illumination beam 104. The read beam 150 is generated by a read/tracking module 140. The autofocus beam 130 is generated by an autofocus subsystem 120. Both beams, the read beam 150 and the autofocus beam 130, are combined together by combining optics 118 into the multi-beam illumination beam 104. The autofocus beam 130 is optional and will be discussed later.

Referring now to FIGURE 3A, there is illustrated a piece of recording media 108 having a plurality of data tracks 250. Each data track 250 is comprised of N channels of recorded data. Each channel of data is recorded on the recording media 108 as a data channel 252 within the data track 250. The number of data channels N depends on the number of write beams in a given optical tape recorder system. In the preferred embodiment, there are sixteen data channels 252 within a data track 250. With additional reference to FIGURE 3B, there is illustrated a piece of recording media 108, specifically a portion of a data track 250 as shown in FIGURE 3A, illustrating the marking of the light sensitive media by a write system as part of an optical tape recorder. Portions of two data channels 252 within a data track 250 are shown. The spacing (or channel pitch) between the centers of the adjacent data channels 252 in a data track 250 is typically about one and a half microns and may vary depending on the optics used to record the data marks on the recording media 108. The spacing between the centers of the adjacent data marks 254 in the along track direction depends on the encoding scheme. Further, the length of each data mark 254 in the along track direction may vary depending on if a pulse width modulation (PWM) encoding scheme is used. Typically, for pulse position modulation (PPM) the length of a data mark is about one micron, depending on writing wavelength and NA. While the spacing between the adjacent data channels 252 and the adjacent data marks 254 set forth above is preferred, other dimensions for this spacing can be used.

With reference to FIGURES 2 and 4 , the read/tracking module 140 includes a read beam source 146 for outputting a collimated read beam 150. The read beam source 146 includes a laser diode 166 for emitting a read beam 168, a -12- lens 170 for collimating read beam 168 and a deflector/translator 174. Preferably, the laser diode 166 has a wavelength of 680 nm.

The read beam 150 is output from the read beam source 146 and is reflected through a polarization beamsplitter 148. Additionally, the read beam 150 passes through a quarter-wave plate 178 to change the polarization of the read beam 150 from linear to circular before being combined into the multi-beam illumination beam 104. The deflector/translator 174 and a cylindrical lens

176 orient and shape the read beam 168 forming a substantially rectangular illumination* field 306 or 308 (see FIGURE 3A) as focused on the media 108 to illuminate across the data track 250 having multiple data channels 252. In the preferred embodiment, the read beam 150 as projected onto the recording media 108 is approximately 100 microns in length.

The deflector/translator 174 provides a mechanism 'or means to deflect the single read illumination beam 150 to either of the two read beam positions (illumination field 306 or 308 shown in FIGURE 3A) . Deflection may be accomplished by using a galvanometer. Alternatively, a translator 174 provides a means or mechanism for laterally translating the collimating lens 170. Now referring to FIGURE 5A, the recording media 108 is shown with an illumination pattern 300 of all constituent components of the multi-beam illumination beam 104 of an optical tape recorder. When the recording media 108 is traveling in the forward direction, the illumination pattern 300 comprises a forward read beam pattern 306 combined with a write beam pattern 302 and an autofocus pattern 304. When the recording media 108 is moving in the reverse direction and a read and/or write is being performed, the illumination pattern 300 comprises the write beam pattern 302, the autofocus pattern 304 and a reverse read beam pattern 308.

While only one read beam source may be sufficient, an alternative embodiment of the read be^"am source 146 shown in FIGURE 12 utilizes a first read beam source 164 and a second read beam source 165 and requires no deflection/translation mechanisms. The first read beam source 164 includes a laser diode 166a and a collimating lens 170a to produce a read beam 150a. The second read beam source 165 includes a laser diode 166b and a collimating lens 170b to produce a read beam 150b. The second read beam source 174 comprises the identical elements as the first read beam source 164, except that the positioning of the read beam with respect to the previously recorded data tracks is different (as discussed below) . The first read beam source 164 and the second read beam source 165 provide alternating beam sources for the read beam 150, depending on the direction of movement of the recording media 108. The read beam 150a and the read beam 150b are combined by a 50/50 beamsplitter 171 into the read beam 150. As such, the read beam 150 comprises the read beam 150a when the optical tape recorder 100 performs a read and/or write function when the recording media 108 is scanned in the +X direction. The read beam 150 comprises the read beam 150b when the recording media is scanned in the opposite direction, that is, the -x direction.

Now referring to FIGURE 5A and with continued reference to the alternative embodiment of the read beam source shown in FIGURE 12, the recording media 108 is shown with an illumination pattern 300 of all constituent components of the multi-beam illumination beam 104 of an optical tape recorder. When the recording media 108 is traveling in the forward direction, the illumination pattern 300 comprises a forward read beam pattern 306 combined with a write beam pattern 302 and an autofocus pattern 304. The forward read beam pattern 306 corresponds to the read beam 150a generated by the first read beam source 164. The second read beam source 174 is not activated when the recording media 108 is moving in the forward direction. When the recording media 108 is moving in the reverse direction and a read and/or write is being performed, the illumination pattern 300 comprises the write beam pattern 302, the autofocus pattern 304 and a reverse read beam pattern 308. The reverse read beam pattern 308 corresponds to the read beam 150b generated by the second read beam source 174. Likewise, the first read beam source 164 is not activated when performing a read and/or write in the reverse direction. As such, the first and second read beam sources 164, 174 alternate as the source for r;he read beam 150 depending on the direction of movement of the recording media 108 during a read and/or write cycle. Alternatively, the optical tape recorder may position individual write beams adjacent to one another to produce a write beam pattern 310 to create the illumination pattern 300 as shown in FIGURE 5B.

Referring now to FIGURES 3A and 4, the rectangular pattern 306, 308 of the read beam 150 is scanned along the longitudinal length of the data track 250 by movement of the recording media 108 either in the forward or reverse direction. Scanning of the read beam 150 in this manner causes the read beam 150 to be modulated by the data marks 254 of the multiple data channels 252 therein. The multi¬ channel modulated read beam 150 is reflected by the recording media 108 back through the actuator subsystem 106 -16- to the read subsystem 140. The polarization of the modulated read beam 150 is rotated from circular to a linear polarization orthogonal to the original polarization (from p- to s-polarization) by passing through the quarter- wave plate 178. The modulated read beam 150 is then reflected by the polarization beamsplitter 148 and directed through read optics 144 to a two-segment mirror 184 and directed to a read array and electronics module 142. The read optics 144 include a lens 180 and a lens 182 for shaping the modulated read beam 150 directed to the two- segment mirror 184. The two-segment mirror 184 focuses the reflected modulated read beam 150 (one of two possible read beams) onto the read array and electronics module 142.

Referring now to FIGURES 6 and 7, the modulated read beam 150 is imaged on a read array receiver 200, and more specifically, is imaged on a read array 206 (see FIGURE 7) that includes a data array 210 and a tracking array 208, with each array 208, 210 comprising a plurality of linear photodiodes 212. In the preferred embodiment, the photodiodes 212 of both the tracking array 208 and the data array 210 are located on the same integrated circuit chip. The distance B between the tracking array 208 and the data array 210 is generally (but not limited to) about 10 to 15 microns. -17- The read optics 144 (shown in FIGURE 4) dimensionally shape the modulated read beam 150 to illuminate both the tracking array 208 and the data array 210. The combining of the tracking array 208 and the data array 210 on the same chip allows tracking information, as well as data information, to be obtained from a single image of the recording media 108. While a single chip containing both the tracking array 208 and the data array 210 is preferred, multiple chips, multiple arrays or discrete photodiodes may be used but would require additional read optics to shape and properly position the modulated read beam on the photodiodes.

With reference to FIGURE 3A, there is shown a guardband area 256 between the adjacent data tracks 250 where no data is recorded. The distance between the adjacent data tracks 250 is a guardband distance 258. To increase the data storage density capabilities of the recording media 108, it is desired to have the guardband distance 258 as small as possible. The desired guardband distance 258 typically is about 4.5 microns (about equal to the width of 3 data channels 252) .

In order to obtain the desired guardband distance 258 of about 4.5 microns between the data tracks 250, the optical tape recorder system uses the tracking function of the read/tracking system 100 of the present invention. With reference to FIGURE 8, the tracking f nction provides for automatically tracking the position of data track 250 currently receiving data for recording with respect to an adjacent previously recorded data track 250a. As the data track 250 is written to the recording media 108 by the optical tape recorder, the read beam 150 scans/illuminates the data track 250 and, in addition, a portion of the adjacent data track 250a. The reflected modulated read beam 150 images the spatial relationship between the data track 250 and the adjacent data track 250a. From this spatial relationship, the objective lens 152 (shown in FIGURE 1) of the actuator subsystem 106 is positioned to provide the desired guardband distance 258 between adjacent data tracks 250 and 250a. During the^"recording of the data track 250, the actuator subsystem 106 continuously positions the data track 250 at the desired guardband distance 258 from the adjacent data track 250a. The read array and electronics module 142 (shown in FIGURE 6) comprises the read array receiver 200 and electronics for providing a tracking signal to the actuator subsystem 106 for positioning the objective lens 152 to position the multi-beam illumination beam 104 at the proper location on the recording media 108.

With reference to FIGURE 11, there is illustrated the relationship between the data image carried by the -19- modulated read beam 150 and the photodiodes of the read array 206 (both the tracking and data arrays 208, 210) . As shown, each data channel 252 is spatially divided so that the image of the data channel 252 covers four photodiodes 5 212. The number of photo diodes K for sampling the width of the data channel 252 is defined as the amount of Kx oversampling. In the preferred embodiment, four photodiodes are utilized resulting in 4x oversampling of each data channel 252. Alternative oversampling (e.g. 3x

10. or greater than 4x) may be used depending on the system parameters and impact on the integrity of the reconstructed data channels 252.

In the preferred embodiment, the tracking array 208 and the data array 210 each comprise one hundred twenty-

15 eight photodiodes. Preferably, the tracking array 208 comprises a serial output linear photodiode array and the data array 210 comprises a parallel output linear photodiode array. The number of photodiodes contained in arrays 208, 210 may be larger or smaller depending on the

20 amount of oversampling and amount of overlap (of adjacent data track 250a) necessary for imaging both the data track 250 and a portion of the data track 250a. The data array 210 (and its associated circuity) retrieves the data signals recorded in the data track 250 and outputs the DATA

25 OUT signal. The tracking array 208 (and its associated circuitry) retrieves tracking information from the data signals recorded in the data tracks 250 and 250a and generates the tracking feedback signal applied to the actuator subsystem 106. This tracking information is described as the relationship between the imaged data from the recording media 108 and each photodiode in the tracking array 208. The tracking array 208 integrates low energy signals over time allowing for accurate tracking information to be obtained from the edges of the read beam 150.

Referring now to FIGURE 9 and with continued reference to FIGURE 7, there is shown data array processing logic 214 receiving the signals generated by the photodiodes 212 of the data array 210 in response to the illumination of the photodiodes 212 by the reflected data modulated read beam 150. The signal outputs from the photodiodes 212 are amplified by a bank of amplifiers 218 for further processing. Next, the amplified signals are input to a comparator register 220 for converting the amplified signals into digital signals representing the data imaged from the reflected read beam 150. These amplified signals are compared with predetermined voltages to produce a digital signal "0" when the amplified signal is less than the predetermined voltage, otherwise a digital signal "1" will be output from the comparator register 220 corresponding to each photodiode 212 of the data array 210. In other words, the read array receiver 200 converts the data from an optical image to electronic digital data. In the preferred embodiment, the data array processing logic 214 comprises one hundred twenty-eight amplifiers and comparators, one each for each signal output by the photodiodes 212 of the data array 210.

The one hundred twenty-eight digital outputs from the comparator register 220 are then multiplexed by thirty-two 4 to 1 multiplexers 222. The four photodiodes 212 sampling each data channel width are multiplexed to select one of the four photodiodes to represent the data signal recorded on the recording media 108 (due to the 4x oversampling of each data channel) . The signal MUXSELECT determines which one of four detectors is selected for each channel. As such, thirty-two digital signals are output from the data array processing logic 214 representing the data signal recovered on the data modulated read beam 150.

With continued reference to FIGURE 6, the thirty-two digital outputs from the read array receiver 200 are input to a FPGA selector 204. The FPGA selector 204 selects the appropriate sixteen digital outputs to • represent the digital signal recorded in the sixteen data channels 252 of data track 250 in response to a SELECT signal from a digital signal processor 202. The digital processor 202 generates the appropriate SELECT signal from tracking information 201 received from the tracking array output logic and control module 216 of the read array receiver 200. The FPGA selector 204 selects sixteen of the thirty- 5 two digital outputs to represent the data signal recorded in the sixteen data channels 252 of data track 250. Control signals 203 allow for communication and control between the digital processor 202 and the read array receiver 200.

10. In the preferred embodiment shown in FIGURE 7, the read array 206 is designed for a data track comprising sixteen data channels. However, the read array 206 can be expanded or reduced to support a data track comprised of "N" data channels, with "N" being greater than or less than

15 sixteen.

Referring again to FIGURE 7, there is shown the tracking array output logic and control module 216 receiving signals generated by the photodiodes 212 of the tracking array 208 in response to the illumination of the

20 photodiodes by the reflected data modulated read beam 150. The tracking array 208 is a linear integrating photodiode array for time integrating the data image of the reflected read beam 150. This time integration provides tracking information 201 and is input to the digital signal

25 processor 202 (shown in FIGURE 6) . The tracking information obtained by the 4x oversampling and linear integrating photodiodes provides a method to electronically compensate for tracking offset during read and read-after- write functions. Tracking information is processed by the digital signal processor 202 to generate a TRACKING signal applied to the actuator subsystem 106. In response to the TRACKING signal, the actuator subsystem 106 positions the objective lens 152 transversely (see FIGURE 2) to track the data track 250 being read (either for a read or read-after- write function) .

Referring now to FIGURE 10, the tracking array output logic and control module 216 receives signals generated by each photodiode of the tracking array 208. The signals from each photodiode are amplified and accumulated by the amplifiers 224 and accumulators 226. The digital signal processor 202 (shown in FIGURE 6) provides control to the accumulators 226 thus controlling the duration of the time integration of the data image of the reflected read beam.

The time integrated signals are then provided to the multiplexers 228. By controlling the output of the multiplexers 228, the digital signal processor 202 views the time integrated signal from one or more photodiodes. In the preferred embodiment, the digital signal processor 202 will choose to read the time integrated signals from the one hundred and twenty-eight photodiodes of the tracking array 208 in a sequential fashion. It is also possible to choose a smaller subset of the photodiodes thus increasing the frequency of obtaining the tracking information 201. The output of the multiplexers 228 is analog or digital in format depending on the preference of the read/tracking system 100.

Referring again to FIGURE 8, there is illustrated a read-after-write function. The tracking information obtained from read array receiver 200 enables the digital signal processor 202 to locate the guardband 256 between adjacent data track 250a and data track 250. As the guardband distance 258 shrinks or grows, the digital signal processor 202 generates the TRACKING signal to position the actuator subsystem 106 to move slightly to maintain the guardband distance 258 at the desired guardband distance of approximately 4.5 microns. As such, the digital signal processor 202 generates the TRACKING signal to position the actuator subsystem 106 to insure the desired guardband distance between adjacent data track 250a and data track 250. Additional tracking information is then obtained from the read array receiver 200 to insure the actuator subsystem 106 is maintaining the desired guardband distance. Accordingly, a closed loop control mechanism is created. If the optical tape recorder 100 of the present invention performs a read-only function on the data track 250, the tracking information input to the digital signal processor 202 is used to locate the guardband 256 between adjacent data track 250a and data track 250. Knowing where the guardband 256 is, the digital signal processor 202 generates the tracking information necessary to position the actuator subsystem 106 so that the data image of data track 250 is positioned in the center of the read array 206. Further, the digital signal processor 202 will generate the SELECT signal to select the appropriate digital signals (see FIGURE 7) to represent the data recorded in data track 250.

The geometry and magnification ό^"f the read beam 150 as applied to the recording media 108 provide an illumination field that is orthogonal to the data channels, as shown in FIGURES 3A, 5A and 5B. Accordingly, it is advantageous for the data recorded in the data channels to have a parallel data front. As such, this provides for a less restrictive readout design.

However, in some write designs, the data recorded on the recording media may be purposely "skewed" when written, as shown in FIGURE 5A. This skewing may be accomplished by time-adjusting the data or by rotation of the read beams with respect to the data track length. In such a case, it would be advantageous to also skew the read beam to produce a parallel data front when the data is read. Now referring to FIGURE 13, there is illustrated an alternative read beam geometry providing a read illumination field 400 as applied to the optical media. The read beam is rotated at an angle with respect to the data track (or data channel) direction. Instead of changing the magnification of the read beam, the entire read beam source ^'is angularly rotated to produce the new read beam geometry. This new geometry effectively reduces optical crosstalk at the image plane and increases the resolution. Cross-talk is minimized because the read illumination and read detectors (photodiode arrays) are, in effect, reading data at a larger data channel pitch as shown. As such, the geometry of each linear photodiode array of the read array is different .

With reference again to FIGURE 2, the autofocus subsystem 120 includes an autofocus beam source 122 for outputting a collimated autofocus beam 13C. The autofocus beam 130 is reflected through the beamsplitter 126 and is passed through a quarter-wave plate 128 to change the polarization of the autofocus beam from linear to circular. The autofocus beam 130 is combined with multi-channel read beams 150 by combining optics 118 into the multi-beam illumination beam 104. The autofocus beam 130 is directed by the objective lens 152 onto the recording media 108. The autofocus beam 130 is reflected by the surface of the media 108 back through the objective lens 152 to the autofocus subsystem 120. As shown, the polarization of the reflected autofocus beam 130 is changed by the quarter-wave plate 128 from circular to linear for a total of a ninety degree change with respect to the original linear polarization (from p- to s-polarization) . The reflected autofocus beam 130 is then transmitted by the polarization beamsplitter 126 and directed to the autofocus beam receiver 124. Numerous well known techniques exist or generating an autofocus signal. Possible techniques may include astigmatic error correction, half-aperture, etc.

Although several embodiments of the read/tracking system of the present invention have^"been described in the foregoing detailed description and illustrated in the accompanying drawings, it will be understood that the invention is not limited to the embodiments disclosed, but is capable of numerous rearrangements, substitutions and modifications without departing from the spirit of the invention.

Claims

-28- CLAIMS: What is claimed is:

1. An apparatus for optically reading a data signal recorded on light sensitive media comprising: a radiation source for emitting a read beam; means for shaping the read beam to illuminate on the light sensitive media a plurality of recorded data channels within a data track recording the data signal, said read beam modulated by data marks within the plurality of data channels to generate a reflected data modulated read beam; means for detecting the reflected data modulated read beam to generate an auto tracking control signal; and a means for adjusting the position of the read beam on the light sensitive media in response to the auto tracking control signal.

2. An apparatus in accordance with Claim 1 wherein the radiation source comprises a laser diode having a lens for collimating the emitted light into the read beam.

3. An apparatus in accordance with Claim 1 wherein the radiation source comprises a plurality of laser diodes producing a plurality of laser read beams whereby a first read beam is selected for recovering the data signal when the light sensitive media travels in a first direction and a second read beam is selected to recover the data signal when the light sensitive media travels in a second direction.

4. An apparatus in accordance with Claim 1 wherein the means for detecting further comprises: a photo detector read array comprising a plurality of photodiodes for demodulating the data modulated read beam to recover the data signal and generate the auto tracking control signal.

- 30 -

5. An apparatus in accordance with Claim 4 wherein the photo detector read array further comprises: a data array comprising a plurality of photodiodes for recovering the data signal; a tracking array comprising a plurality of photodiodes for collecting tracking information from the reflected data modulated read beam for recovering the data signal; and a data signal processor for generating the autotracking control signal in response to the collected tracking information.

6. An apparatus in accordance with Claim 5 wherein the means for adjusting the position of the read beam comprises an actuator subsystem comprising a lens assembly for focusing the read beam on the light sensitive media in response to the auto tracking signal to position the reflected data modulated read beam corresponding to the data track being read onto the center of the data and tracking arrays.

7. An apparatus in accordance with Claim 5 wherein the data array is a parallel output linear photodiode array.

8. An apparatus in accordance with Claim 5 wherein the tracking array is a serial output linear integrating photodiode array.

9. An apparatus in accordance with Claim 5 wherein the data array and tracking array are combined on one integrated circuit chip and comprise a parallel output linear photodiode array and a serial output linear integrating photodiode array.

10. An apparatus in accordance with Claim 4 wherein the photo detector read array comprises: a data array comprising a parallel output linear photodiode array having a plurality of photodiodes for converting the data signal in the reflected data modulated read beam into signals for processing; a tracking array comprising serial output linear integrating photodiode array having a plurality of photodiodes for collecting information from the reflected data modulated read beam corresponding to the data signal recovered by the data array; a digital signal processor for controlling the tracking array and for generating the auto tracking control signal; and a means for converting the signals generated by the data array into digital signals to represent the recorded data signal.

-33- 11. An apparatus for optically reading a data signal recorded on light sensitive media comprising: a radiation source for emitting a read beam; means for shaping the read beam to illuminate a rectangular area on the light sensitive media across a data track having a plurality of data channels, said read beam being reflected from the light sensitive media to produce a reflected modulated read beam carrying an image of the illuminated data; means for detecting the reflected modulated read beam to recover the data image and generate an auto tracking signal; and an actuator controlled objective lens for adjusting the position of the read beam on the^"light sensitive media with respect to the data track being illuminated in response to the auto tracking signal.

12. An apparatus in accordance with Claim 11 wherein the radiation source comprises at least one laser light emitting diode and a lens for collimating the emitted light whereby a first read beam is selected for recovering the data image when the light sensitive media travels in a first direction and a second read beam is selected for recovering the data image when the light sensitive media travels in a second direction.

13. An apparatus in accordance with Claim 11 wherein the means for detecting further comprises: a photodetector read array comprising, a data array having a plurality of photodiodes, and a tracking array having a plurality of photodiodes whereby both said data and tracking arrays are concurrently illuminated by the reflected modulated read beam, said data array converting the data image carried by the reflected modulated read beam into signals, said tracking array converting the data image into tracking information; a means for converting the signals into digital signals representing the data signal recorded on the light sensitive media; and a signal processor for receiving the tracking information, controlling the tracking array and generating an autotracking signal in response to the tracking information.

14. An apparatus in accordance with Claim 13 wherein the data image illuminated on each photodiode of the data and tracking arrays corresponds to a predetermined length 1, as measured across the data track, on the recording media.

15. An apparatus in accordance with Claim 14 wherein data and tracking arrays provide spatial oversampling of each data channel.

16. An apparatus in accordance with Claim 13 wherein the data array comprises a parallel output linear photodiode array and the serial output linear integrating photodiode array whereby said parallel photodiode array and said serial photodiode array are both on one integrated circuit chip.