Abstract:
An optical sensing head, which is for reading out an optical data memory, has a substrate with a main surface. An edge-emitting laser component is configured on the main surface of the substrate and has irradiation axis oriented essentially parallel to the first main plane. A deflection device is arranged on the main surface of the substrate and deflects the laser radiation in a direction that is essentially perpendicular to the main surface. At least one signal detector is provided for sensing the laser radiation that is reflected by the optical data memory. An optical element guides the deflected laser radiation to the optical data memory and guides reflected laser radiation to the signal detector. The optical element is connected to the substrate by at least one supporting element. The invention also includes a method for fabricating such a sensing head.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]    This application claims the benefit under 35 U.S.C. § 119(e) of copending provisional application No. 60/412,296, filed Sep. 20, 2002. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The invention relates to an optical sensing head, in particular for reading out an optical data memory, and to a method for fabricating such a sensing head.  
           [0004]    A conventional optical sensing head, such as is used for example in a CD (compact disk) player or a DVD (digital video disk) player, is generally composed of discrete active and passive components which are produced individually and installed in a hybrid fashion in a metal housing. Such a sensing head typically includes a laser source, optical components such as lenses and beam splitters, a deceleration plate, and detectors for monitor functions and signal functions. In order to measure the tracking, spacing and signal level, the signal detector senses the light that is emitted by the laser diode and reflected by the CD or DVD. The monitor detector is used to check the emitted laser power.  
           [0005]    The monitor detector is generally arranged in the vicinity of the laser source. For example it is possible to provide for some of the laser beam to strike a monitor photodiode directly behind a housed laser diode. The signal detector is typically mounted as a single component on the metal housing of the sensing head.  
           [0006]    Such a sensing head has a size of approximately 30 mm×40 mm and is relatively large and heavy as a result of the discrete design. The monitor detector and the signal detector are located in separate housings and must be individually adjusted.  
         SUMMARY OF THE INVENTION  
         [0007]    It is accordingly an object of the invention to provide an optical sensing head and a method for producing the optical sensing head, which overcome the above-mentioned disadvantages of the prior art apparatus and methods of this general type.  
           [0008]    In particular, it is an object of the invention to provide an optical sensing head that has a low weight and a small spatial requirement and whose components can easily be matched to one another. The intention is also to provide a fabrication method for such an optical sensing head, which permits cost-effective fabrication and mounting.  
           [0009]    With the foregoing and other objects in view there is provided, in accordance with the invention, an optical sensing head, which is of the type mentioned at the beginning, having a substrate with a main surface, and an edge-emitting laser component arranged on the main surface of the substrate. The irradiation axis of the edge-emitting laser is oriented essentially parallel to the first main plane. The optical sensing head also has a deflection device configured on the main surface of the substrate. The deflection device has the purpose of deflecting the laser radiation in a direction which is essentially perpendicular to the main surface. The optical sensing head also has at least one signal detector for sensing the laser radiation which is reflected by the optical data memory, and an optical element which guides the deflected laser radiation to the optical data memory and guides reflected laser radiation to the at least one signal detector. The optical element is connected to the substrate via at least one supporting element.  
           [0010]    By integrating a plurality of functions on a single substrate (submount), it is possible to achieve a very small size, and associated therewith, a sensing head with a low weight. This permits the sensing head to be used in particular for mobile applications such as cameras, music playback devices, games consoles, electronic books (eBooks), PDAs, laptops or computer peripherals. Furthermore, the integration permits cost-effective fabrication and mounting methods to be used so that the sensing head can be fabricated more cost-effectively than conventional pickup systems. Because of the low weight of the sensing head, faster access times than with conventional pickup systems can be achieved.  
           [0011]    In one preferred refinement of the optical sensing head, the deflection device is embodied simultaneously as a supporting element via which the optical element is connected to the substrate.  
           [0012]    An irradiation-direction signal detector is advantageously arranged on the main surface of the substrate on the irradiation axis of the laser component and downstream of the deflection device in the irradiation direction. The laser component, the deflection device and the irradiation-direction signal detector are thus arranged in this sequence one behind the other on a straight line.  
           [0013]    It is also preferred if an opposite-direction signal detector is arranged on the main surface of the substrate on the irradiation axis of the laser component and in the opposite direction to the irradiation direction of the laser component, as an alternative to or in addition to the irradiation-direction signal detector.  
           [0014]    A supporting element via which the optical element is connected to the substrate is advantageously arranged between the laser component and the opposite-direction signal detector. In this context it is preferred if the supporting element, which is arranged between the laser component and the opposite-direction signal detector, is provided with a metallic or a dielectric mirrored layer on its surface facing the laser component. As a result, it is possible to effectively counteract stray light of the laser component passing into the opposite-direction signal detector.  
           [0015]    Alternatively, the supporting element which is arranged between the laser component and the opposite-direction signal detector can be provided with an absorption layer on its surface facing the laser component. This also effectively suppresses stray light passing in.  
           [0016]    An even more wide-ranging reduction in stray light which passes in can be achieved by virtue of the fact that the supporting element which is arranged between the laser component and the opposite-direction signal detector is embodied as a deflection device which deflects away stray light of the laser component from the opposite-direction signal detector. The supporting element advantageously deflects the stray light in a direction essentially perpendicular to the main surface.  
           [0017]    The integration of an optical sensing head can be increased further by virtue of the fact that the signal detector (or more than one signal detector) is formed in the substrate. The signal detector preferably includes an array of PIN photodiodes that are formed in the substrate.  
           [0018]    In one preferred development of the optical sensing head, a monitor detector for checking the irradiated power of the laser component is also integrated on the substrate.  
           [0019]    In a further embodiment, the supporting elements are arranged to the side of the deflection mirror, and the detectors are installed between the mirror and the supporting elements. The optical element is mounted on the supporting elements.  
           [0020]    The substrate is advantageously formed by a silicon substrate. Cost-effective processes of the semiconductor industry can then be used for the fabrication and mounting method.  
           [0021]    The at least one supporting element and/or the deflection device are expediently produced from glass and are connected nondetachably to the substrate for example by bonding or anodic bonding.  
           [0022]    The main surface of the substrate preferably has an area of 10 mm 2  or less.  
           [0023]    With the foregoing and other objects in view there is provided, in accordance with the invention, a method for fabricating the optical sensing head described above. The method involves fabricating a deflection device. Fabricating the deflection device includes a step of sawing a glass wafer into individual strips. Fabricating the deflection device also includes a step of grinding surfaces onto the strips at a predetermined angle, in particular at an angle of approximately 45°. Fabricating the deflection device also includes a step of coating the ground surfaces with a highly reflective mirrored layer in order to obtain a deflection prism for the deflection of laser beams. Fabricating the deflection device also includes a step of orientating and nondetachably connecting the deflection prisms to the substrate.  
           [0024]    The deflection prisms are advantageously connected to the substrate by anodic bonding. Before the glass wafer is sawn, regions on the front side of the glass wafer are expediently metalized in order to provide soldering surfaces for connecting optical components to the substrate after the connection of the deflection prisms. It is also preferred to introduce trenches into the rear side of the glass wafer by sandblasting before the glass wafer is sawn.  
           [0025]    In a particularly advantageous refinement of the method, the supporting elements are fabricated from the glass wafer at the same time as the deflection device.  
           [0026]    An array of PIN photodiodes is preferably formed in the substrate as signal detector/detectors.  
           [0027]    Other features which are considered as characteristic for the invention are set forth in the appended claims.  
           [0028]    Although the invention is illustrated and described herein as embodied in an optical sensing head and a method for fabricating the sensing head, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.  
           [0029]    The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0030]    [0030]FIG. 1 is a schematic plan view of a first embodiment of a silicon submount before the glass prisms are mounted;  
         [0031]    [0031]FIG. 2 is a sectional view taken through the silicon submount in FIG. 1 after the glass prisms, the laser, and the optical components have been mounted;  
         [0032]    [0032]FIGS. 3A, 3B, and  3 C are schematic views showing three variants for suppressing laser stray light;  
         [0033]    [0033]FIG. 4 is a plan view of a second exemplary embodiment of a silicon submount;  
         [0034]    [0034]FIG. 5 is a sectional view taken through the silicon submount in FIG. 4;  
         [0035]    [0035]FIG. 6 is a plan view of a third exemplary embodiment of a silicon submount;  
         [0036]    [0036]FIG. 7 is a sectional view taken through the silicon submount in FIG. 6 after the glass prisms have been mounted;  
         [0037]    [0037]FIG. 8 is a sectional view taken through a fourth embodiment of a silicon submount;  
         [0038]    [0038]FIG. 9 is a plan view of a fifth exemplary embodiment of a silicon submount;  
         [0039]    [0039]FIG. 10 is a sectional view taken through the silicon submount in FIG. 9 after the glass prisms have been mounted;  
         [0040]    [0040]FIG. 11 includes a plan view of a sixth embodiment of a silicon submount and a sectional view taken through the same submount;  
         [0041]    [0041]FIGS. 12A, 12B,  12 C, and  12 D show four variants of the embodiment of the signal diodes in each of the silicon submounts; and  
         [0042]    FIGS.  13 A- 13 E show the intermediate steps of the method for fabricating the glass prisms and mounting the glass prisms on a silicon submount. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0043]    Referring now to the figures of the drawing in detail and first, particularly, to FIGS. 1 and 2 thereof, there is shown a first exemplary embodiment of the invention. FIG. 1 shows a plan view of a silicon submount, which is generally designated by  10 , before the glass prisms are mounted, and FIG. 2 shows the submount  10  after laser and optical components are mounted.  
         [0044]    The silicon submount  10  contains a silicon substrate  12  with a size of approximately 1.3 mm×4.8 mm, which has chip bonding surfaces  14  and  16 , two monitor photodiodes  18  and two signal diodes  20  and  22 . A heat sink  28  is mounted on the chip bonding surface  14 , and an edge-emitting laser diode  30 , which emits red laser radiation  32  along the irradiation axis  34  during operation, is mounted on the heat sink  28 . The chip bonding surface  16  has an integrated circuit  42 , for example, an amplifier circuit or a laser driver circuit.  
         [0045]    Two glass prisms  36  and  38  are connected nondetachably to the substrate  12  on the glass bonding surfaces  24  and  26  by anodic bonding. The glass prisms are used, on the one hand, as supporting elements on which an optical component  40  is mounted, for example by soldering. The glass prism  36  also serves as a deflection prism for deflecting the laser radiation  32 , which is emitted parallel to the surface of the substrate  12  along the irradiation axis  34 , by 90°.  
         [0046]    The optical component  40  guides the deflected laser radiation to an optical storage medium (not illustrated itself) and guides the laser radiation reflected there back to the signal diodes  20  and  22 . The signals which are modulated onto the storage medium in accordance with a dash pattern or dot pattern are used in a manner known per se for data transmission, and for tracking detection and tracking guidance, after they have been sensed by the signal diodes  20  and  22 .  
         [0047]    The surface of the glass prism  38  facing the laser diode  30  is mirror-coated with an aluminum layer  44  to prevent stray radiation from passing from the laser diode  30  to the signal diode  22 . Instead of an aluminum layer, it is also possible to provide the glass prism with a different metallic layer, for example, an AlSi layer, or with a dielectric mirror, for example, made of aluminum oxide/Si.  
         [0048]    [0048]FIGS. 3A, 3B and  3 C show simplified views of three further variants for suppressing laser stray light. In the variant in FIG. 3A, the glass prism  38 A is provided with an absorbent layer  44 A instead of with a mirror  44 . In the configuration in FIG. 3B, the glass prism  38 B is embodied as a 45° mirror whose mirrored surface  44 B reflects away laser stray light in the upward direction. The surface  44 B can be embodied as a standard mirror with a metallic or dielectric coating, or can be provided with an absorbent coating. FIG. 3C shows a refinement of the configuration of FIG. 3B in which the 45° mirrored surface  44 C of the glass prism  38 C is directed in the downward direction. That is to say, the mirrored surface  44 C deflects laser stray light into the substrate where it is absorbed. Here too, the surface  44 C can either be mirror-coated or can be provided with an absorbent layer.  
         [0049]    Again with respect to FIGS. 1 and 2, the silicon substrate  12  thus functions not only as a carrier for the glass prisms  36 ,  38  which are arranged on it, and as a carrier for the laser diode  30  and for the IC  42 , but also functions as a heat sink and as a substrate for a PIN photodiode array which includes the monitor photodiodes  18  and the signal diodes  20  and  22 . The monitor photodiodes  18  are arranged in the vicinity of the laser diode  30  and measure the backward reflection of one of the optical components in order to regulate the laser power.  
         [0050]    Another embodiment of a silicon submount  50  is illustrated in FIGS. 4 and 5. Here, identical reference symbols designate the same elements as in FIGS. 1 and 2. The silicon submount  50  differs from the silicon submount  10  in particular through the arrangement of the monitor photodiode  52 . The monitor photodiode  52  is arranged under the deflection prism  36  in this exemplary embodiment. The monitor photodiode  52  obtains, as a monitor signal, the part  54  of the laser radiation  32  that is let through by the mirror-coated surface of the deflection prism, and that is reflected in the direction of the monitor diode  52 .  
         [0051]    Furthermore, for reducing the stray light, the exemplary embodiment in FIG. 5 implements the variant shown in FIG. 3C in which the prism  38 C, which also serves as a supporting element, is embodied as a deflection element with a mirrored surface  44 C which is inclined at an angle of 45° with respect to the substrate  12 .  
         [0052]    [0052]FIGS. 6 and 7 show a further exemplary embodiment of a silicon submount  60 . Here too, identical reference symbols designate the same elements as in the silicon submount  10  shown in FIGS. 1 and 2. In the silicon submount  60 , instead of the pair of signal detectors  20  and  22  in FIG. 1, a single signal detector  62  performs all the functions for tracking, measurement of the signal level and focusing. The monitor diode  64  is arranged here directly downstream of the first chip bonding surface  14  in the direction that is opposite to the irradiation direction of the laser.  
         [0053]    [0053]FIG. 8 shows a refinement of the configuration in FIG. 7 in which the second supporting element  74  is bonded onto the substrate  12  in the irradiation direction, downstream of the single signal detector  62 . The arrangement of the other elements corresponds to that in FIG. 7.  
         [0054]    A further exemplary embodiment of the invention is illustrated in FIGS. 9 and 10. In the case of the silicon submount  80 , in addition to the glass bonding surface  82  which is used to hold the deflection prism  84 , a further glass supporting point is dispensed with. The deflection prism  84  thus constitutes the single supporting element for the optical component  40 . The arrangement and configuration of the signal diodes  20 ,  22  corresponds, in the exemplary embodiment shown, to that of FIG. 1, and the arrangement and configuration of the monitor diode  64  corresponds to that of FIG. 6.  
         [0055]    A further exemplary embodiment of the invention is illustrated in FIG. 11. The supporting elements  38 D,  38 E are arranged at the side of the deflection mirror  136 , and the detectors  20 ,  22  are installed between the mirror  136  and the supporting elements  38 D,  38 E. The optical element  40  is mounted on the supporting elements.  
         [0056]    [0056]FIGS. 12A, 12B,  12 C, and  12 D show four variants of the embodiment of a signal detector array  90 ,  92 ,  94  or  96 . Each of these arrays permits good measurement of the tracking, spacing and signal level of the reflected laser light and can be used for one of the signal detectors  20 ,  22  and  62  of the silicon submounts discussed above.  
         [0057]    The fabrication of the glass prisms and the mounting of the glass prisms on the silicon submount will now be explained with reference to FIGS.  13 A- 13 E. Here, the fabrication of the submounts is carried out in the wafer composite, for example, on 150 mm or 200 mm wafers. It is possible to arrange, for example, 1500 submounts on a 150 mm wafer.  
         [0058]    [0058]FIG. 13A is used to illustrate that in a first working step, regions  102  that will later be used as soldering surfaces for connecting the optical component  40  are metalized onto a glass wafer  100 . Then, approximately 20 μm-deep trenches  104  are made on the rear side of the glass wafer  100  by sandblasting. Then, the glass wafer  100  is sawn so that a multiplicity of individual strips  106  is produced, FIG. 13B.  
         [0059]    Then, as shown in FIG. 13C, surfaces  108  are ground to 45° jointly on a plurality of the strips  106 . These surfaces  108  are polished in the next working step and are coated with a highly reflective mirror for deflecting laser beams. The prisms are then oriented on a silicon wafer  110  and are anodically bonded as shown in FIG. 13D.  
         [0060]    Through various further sawing steps, the glass center part is respectively cut out so that a deflection prism  36  and a further supporting element  38  are produced from each glass strip  106 . The individual submounts  112  are also separated from one another as shown in FIG. 13E. Here, the submounts  112  are first still held on a film and are then placed in the sensing head housing using a pick &amp; place in a manner known per se.  
         [0061]    The explanation of the invention with reference to the exemplary embodiments should of course not be understood as a restriction to the exemplary embodiments. Instead, the invention includes the disclosed features both individually and in any combination with one another, even if these combinations are not explicitly specified in the claims.