Abstract:
In an optical recorder and/or player the lens system of the scanning device focuses the light beam into a scanning spot on the information carrier. The lens system includes a main or objective lens and an auxiliary or solid immersion lens to provide the large numerical aperture required for scanning information carriers with a high information density, such as high-density compact discs. At least one lens, in particular the main lens, is suspended in a housing in a direction parallel to the optical axis of the lens system by two elastically deformable mounting elements. When viewed parallel to the optical axis, the mounting elements are distal from each other, and each allow tilting movements of the lens about tilt axes perpendicular to the optical axis, and are substantially undeformable in directions perpendicular to the optical axis. During manufacture of the lens system, the lenses are aligned relative to each other by shifting at least one of the mounting elements in directions perpendicular to the optical axis. The lenses may be positioned parallel to each other by shifting one of the mounting elements in a direction perpendicular to the optical axis, and centered relative to each other by shifting the non-suspended lens in a direction perpendicular to the optical axis. Thus, allowing accurate alignment of the lenses relative to each other using a simple manipulator with limited positioning possibilities.

Description:
FIELD OF THE INVENTION 
     The invention relates to optical disk drives for reading and writing information in tracks of a rotating disk and is most closely related to optical lens systems for focusing the scanning beam into a spot on the disk in such optical disk drives. 
     BACKGROUND OF THE INVENTION 
     The invention relates to a method of manufacturing an optical lens system including a housing, a first lens element having a first optical axis, and a second lens element having a second optical axis. According to the method, the lens elements, before being secured to the housing, are aligned relative to each other such that the optical axes of the lens elements coincide. 
     The invention further relates to an optical scanning device for scanning an information track of an optically scannable information carrier. The scanning device includes a radiation source, an optical lens system having an optical axis for focusing a radiation beam supplied, in operation, by the radiation source into a scanning spot on the information carrier, and a first actuator for displacing the lens system in a direction parallel to the optical axis. The lens system includes a first lens element, a second lens element and a second actuator for displacing the first lens element and the second lens element relative to each other. 
     The invention also relates to an optical player including a table which can be rotated about an axis of rotation, an optical scanning device for scanning an information track of an optically scannable information carrier which can be arranged on the table, and a displacement device which displaces the scanning device, in operation, relative to the axis of rotation, predominantly in a radial direction. 
     An optical lens system manufactured in accordance with a method of the type mentioned in the opening paragraph, as well as an optical scanning device and an optical player of the types mentioned in the opening paragraphs are known from U.S. Pat. No. 5,712,842. The known optical lens system used in the known optical scanning device includes an objective lens and a relatively small, so-called solid immersion lens, which is arranged between the objective lens and the information carrier to be scanned. By using the solid immersion lens, the known lens system has a relatively large numerical aperture, so that a relatively small scanning spot on the information carrier to be scanned is obtained. As a result, the known scanning device can suitably be used to scan information carriers having relatively small elementary information characteristics, i.e. information carriers having a relatively high information density, such as a high-density CD. Using the first actuator of the known scanning device, the lens system is displaced parallel to the optical axis, thus enabling the scanning spot to be focused on the information layer of the information carrier. Using the second actuator of the known scanning device, the solid immersion lens is displaced relative to the objective lens in a direction parallel to the optical axis, thus enabling a spherical aberration of the radiation beam in a transparent protective layer of the information carrier between the information layer and the scanning device to be corrected. 
     The objective lens of the known optical lens system is secured to the housing of the lens system in a fixed position, while the solid immersion lens is secured to the housing via a leaf spring. For a good optical operation of the lens system, the optical axes of the objective lens and the solid immersion lens must coincide as much as possible. To achieve this, in the course of the manufacture of the lens system, the objective lens and the solid immersion lens are aligned relative to each other, before being secured to the housing of the lens system, in such a manner that the optical axes of the objective lens and the solid immersion lens coincide as much as possible. 
     The above citations are hereby incorporated in whole by reference. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to provide a method of the type mentioned in the opening paragraphs, by which the lens elements of the lens system to be manufactured can be accurately aligned relative to each other by simple auxiliary apparatus, before they are secured to the housing of the lens system. 
     To achieve this, at least the first lens element is secured to the housing via two elastically deformable mounting elements. The mounting elements, when viewed parallel to the first optical axis, are arranged at some distance from each other and each individually allow tilting of the first lens element about tilting axes extending perpendicularly to the first optical axis. The mounting elements, when viewed in directions at right angles to the first optical axis, are substantially undeformable. At least one of the mounting elements is displaced, before being secured to the housing, in a direction transverse to the first optical axis to bring the lens elements into mutually parallel positions. In order to bring the lens elements of the lens system into a position in which the optical axes of the lens elements coincide, at least one of the lens elements must be tilted, during the aligning process, about a tilt axis directed at right angles to its optical axis, so that the lens elements are brought into mutually parallel positions, and, during aligning, at least one of the lens elements must be displaced at right angles to its optical axis, so that the lens elements are centered relative to each other. If, before being secured to the housing, at least one of the mounting elements is displaced in a direction transverse to the first optical axis, the first lens element is tilted about a tilt axis directed perpendicularly to the first optical axis, thereby elastically deforming the two mounting elements. Because the lens elements are brought into mutually parallel positions, in the manner described above, by displacing at least one of the mounting elements only in a linear direction transverse to the first optical axis, and that such linear displacements can be carried out with great accuracy, the lens elements can be very accurately brought into mutually parallel positions by a simple manipulator having limited possibilities of displacement. Since, viewed in directions perpendicular to the first optical axis, the mounting elements are substantially undeformable, after securing the mounting elements to the housing, viewed perpendicularly to the first optical axis, a very rigid support of the first lens element relative to the housing is obtained, while the cooperation between the two mounting elements secured to the housing additionally provides for a very high tilt resistance of the first lens element relative to the housing about tilt axes directed at right angles to the first optical axis. In this manner, the mutual positions of the two lens elements obtained during aligning are accurately maintained after securing the mounting elements to the housing. 
     In a particular embodiment of the method in accordance with the invention, before being secured to the housing, the second lens element is displaced in a direction transverse to the second optical axis in order to center the lens elements relative to each other. Because the lens elements are centered relative to each other, as described above, by displacing the second lens element exclusively in a linear direction transverse to the second optical axis, and that such linear displacements can be carried out with great accuracy, the lens elements can also be very accurately centered relative to each other by a simple manipulator having limited possibilities of displacement. 
     In a further embodiment, before being secured to the housing, the mounting elements are displaced over equal distances and in a same direction transverse to the first optical axis in order to center the lens elements relative to each other, and over equal distances, in mutually opposite directions transverse to the first optical axis in order to bring the lens elements into mutually parallel positions. The first lens element is displaced at right angles to the first optical axis by displacing both mounting elements over equal distances and in an equal direction transverse to the first optical axis, while the first lens element is tilted about a tilt axis directed at right angles to the first optical axis, by displacing the two mounting elements over equal distances, in opposite directions transverse to the first optical axis. Because the lens elements are, respectively, mutually centered and brought into mutually parallel positions by two different methods of displacing the mounting elements, the lens elements are univocally and accurately brought into positions in which the optical axes of the lens elements coincide. 
     In a particular embodiment, the second lens element is secured to a first part of the housing, while a first mounting element is secured to a second part of the housing and a second mounting element is secured to a third part of the housing, the first part, second part and third part of the housing being fixed with respect to each other after the lens elements are aligned relative to each other. By using the three parts of the housing, the aligning of the lens elements is further simplified because the parts can be coupled in a simple manner to a manipulator necessary for aligning. In addition, after aligning the lens elements, the parts can be fixed relative to each other in a simple manner. 
     In a further embodiment, the first part of the housing is provided with a sliding surface which extends transversely to the second optical axis. The second part of the housing is provided with a first sliding surface which extends transversely to the first optical axis and with a second sliding surface which extends transversely to the first optical axis and serves to co-operate with the sliding surface of the first part. The third part of the housing is provided with a sliding surface, which extends transversely to the first optical axis and serves to co-operate with the first sliding surface of the second part. By using the sliding surfaces which extend transversely to the optical axes, a further simplification of the alignment of the lens elements is achieved because, during the aligning process, the three parts of the housing can be mutually slided over the co-operating sliding surfaces in directions transverse to the optical axes. 
     In yet another embodiment, the first part, the second part and the third part of the housing are fixed relative to each other by glued joints. By using the glued joints, the three parts of the housing are fixed relative to each other in a simple manner. The glued joints are preferably formed between the co-operating sliding surfaces of the three parts, because shrinkage or expansion of the glued joints formed there occurs predominantly in a direction parallel to the optical axes of the lens elements and hence substantially does not affect the mutual alignment of the lens elements. 
     In a particular embodiment, the mounting elements are each provided with a first, substantially ring-shaped part which is secured to the housing, and with a second, substantially ring-shaped part, which is secured to the first lens element. The ring-shaped parts of a first mounting element is interconnected by at least three bendable bridges which are arranged at regular intervals and which extend in a plane transverse to the first optical axis, while the ring-shaped parts of a second mounting element are interconnected by at least two bendable bridges which extend in a plane transverse to the first optical axis. If the first mounting element is provided with three bendable bridges, and the second mounting element is provided with two bendable bridges, a so-called statically determined, i.e. substantially stress-free suspension of the first lens element in the housing is obtained, and the first lens element can only be displaced in a direction parallel to the first optical axis. If a larger number of bendable bridges is used, a suspension of the first lens element in the housing is obtained which, although not statically determined, still enables the first lens element to be displaced parallel to the first optical axis. 
     In a further embodiment, the mounting elements are each made from a single plate of a material. Also, the mounting elements are made in a simple and accurate manner by, for example, an etching process. 
     In yet another embodiment, the first mounting element and the second mounting element are each provided with three bendable bridges which are placed at regular intervals. Also, the lens system is provided with two identical mounting elements, so that the construction of the lens system is further simplified. 
     In a particular embodiment, the bendable bridges of the mounting elements are each provided with a uniformly bendable spoke which extends substantially in a tangential direction relative to the optical axis of the first lens element. By using the uniformly bendable spokes, a simple and robust construction of the mounting elements is obtained. 
     In a further embodiment, the bendable bridges of the mounting elements are each provided with a relatively rigid strip which extends substantially in a tangential direction relative to the optical axis of the first lens element and is connected, by two flexible joints, to the two ring-shaped parts of the relevant mounting element. By using the strips and flexible joints, the mounting elements can be manufactured in a simple manner by providing a number of incisions. 
     A further object of the invention is to provide an optical scanning device and an optical player of the types mentioned in the opening paragraph, in which the lens elements of the optical lens systems employed therein are accurately aligned relative to each other, and in which the mutual positions of the lens elements obtained by aligning them relative to each other can be accurately maintained. 
     To achieve this, in the optical scanning device in accordance with the invention, the housing of the lens system can be displaced in a direction parallel to the optical axis by the first actuator, while the first lens element of the lens system can be displaced relative to the housing by the second actuator, in a direction parallel to the optical axis. 
     An optical player in accordance with the invention uses an optical scanning device in accordance with the invention as described above. 
     These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the drawings: 
     FIG. 1 schematically shows an optical player in accordance with the invention, 
     FIG. 2 schematically shows an optical scanning device in accordance with the invention, which is used in the optical player in accordance with FIG. 1, 
     FIG. 3 shows an optical lens system manufactured in accordance with a method in accordance with the invention, which is used in the optical scanning device in accordance with FIG. 2, 
     FIG. 4 shows an elastically deformable mounting element of the optical lens system in accordance with FIG. 3, 
     FIGS. 5 a  and  5   b  schematically show how two lens elements of the lens system shown in FIG. 3 are aligned using a method in accordance with the invention, 
     FIGS. 6 a  and  6   b  schematically show how two lens elements of the lens system shown in FIG. 3 are aligned using an alternative method in accordance with the invention, and 
     FIG. 7 shows an alternative elastically deformable mounting element of the optical lens system shown in FIG.  3 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 schematically shows an optical player in accordance with the invention, which includes a table  1  which can be rotated about an axis of rotation  3  and can be driven by an electric motor  5  which is secured onto a frame  7 . On table  1 , an optically scannable information carrier  9 , such as a CD, can be arranged which is provided with a disc-shaped support  11  and a transparent protective layer  13 . A side of the support  11  bordering on the protective layer  13  forms an information layer  15  of the information carrier  9  on which a spiral-shaped information track is present. The optical player further includes an optical scanning device  17  for optically scanning the information track of the information carrier  9 . 
     The scanning device  17  can be displaced by a displacement device  19  of the optical player relative to the axis of rotation  3  predominantly in two opposite radial directions X and X′. To this end, the scanning device  17  is secured to a slide  21  of the displacement device  19  which is further provided with a straight guide  23  provided on the frame  7  and extending parallel to the X direction, over which guide the slide  21  is guided in a displaceable manner. Device  19  also includes an electric motor  25  which displaces the slide  21  over the guide  23 . In operation, an electrical control unit of the optical player, not shown in the Figures, controls the motors  5  and  25 , causing the information carrier  9  to rotate about the axis of rotation  3 , and simultaneously, the scanning device  17  to be displaced parallel to the X-direction, in such a manner that the spiral-shaped information track present on the information carrier  9  is scanned by the scanning device  17 . During the scanning, information present on the information track can be read by the scanning device  17  or information can be written on the information track by the scanning device  17 . 
     The optical scanning device  17  in accordance with the invention, used in the optical player in accordance with the invention is schematically shown in FIG.  2 . The scanning device  17  is provided with a radiation source  27 , for example a semiconductor laser, with an optical axis  29 . The scanning device  17  further includes a radiation beam splitter  31  which includes a transparent plate  33  which is arranged at an angle of 45° relative to the optical axis  29  of the radiation source  27  and which includes a reflective surface  35  facing the radiation source  27 . The scanning device  17  further includes an optical lens system  37  with an optical axis  39  and a collimator lens  41  arranged between the radiation beam splitter  31  and the lens system  37 . The optical axis  39  of the lens system  37  and the optical axis  29  of the radiation source  27  include an angle of 90°. The scanning device  17  further includes an optical detector  43  which, relative to the lens system  37 , is arranged behind the radiation beam splitter  31 , said optical detector being of a type which is known per se and customarily used. In operation, the radiation source  27  generates a radiation beam  45  which is reflected by the reflective surface  35  of the radiation beam splitter  31  and focused by the lens system  37  into a scanning spot  47  on the information layer  15  of the information carrier  9 . 
     The radiation beam  45  is reflected by the information layer  15  into a reflected radiation beam  49  which is focused on the optical detector  43  via the lens system  37 , the collimator lens  41  and the radiation beam splitter  31 . For reading information present on the information carrier  9 , the radiation source  27  generates a continuous radiation beam  45 , and the optical detector  43  supplies a detection signal which corresponds to a series of elementary information characteristics on the information track of the information carrier  9 , which elementary information characteristics are successively present in the scanning spot  47 . For writing information on the information carrier  9 , the radiation source  27  generates a radiation beam  45  which corresponds to the information to be written, in the scanning spot  47  a series of successive elementary information characteristics being generated on the information track of the information carrier  9 . 
     As is also shown in FIG. 2, the scanning device  17  includes a first actuator  51  which displaces the lens system  37  over relatively small distances parallel to the optical axis  39  of the lens system  37 , and over relatively small distances parallel to the X-direction. By displacing the lens system  37  using the first actuator  51  in a direction parallel to the optical axis  39 , the scanning spot  47  is focused with a desired degree of accuracy on the information layer  15  of the information carrier  9 . By displacing the lens system  37  using the first actuator  51  in a direction parallel to the X-direction, the scanning spot  47  is maintained with a desired accuracy on the information track to be followed. To this end, the first actuator  51  is driven by the above-mentioned control unit of the optical player, which receives both a focus-error signal and a track error signal from the optical detector  43 . 
     The optical lens system  37  used in the optical scanning device  17 , which lens system is manufactured in accordance with a method of the invention, is shown in detail in FIG.  3  and includes a first lens element  53  and a second lens element  55 . The first lens element  53  is an objective lens and constitutes a main lens of the lens system  37 . The second lens element  55  is a so-called solid immersion lens, which is arranged between the objective lens and the information carrier  9  to be scanned, and which constitutes a relatively small auxiliary lens of the lens system  37 . By employing, apart from the main lens  53 , the auxiliary lens  55 , the lens system  37  has a relatively large numerical aperture, so that the scanning spot  47  on the information layer  15  of the information carrier  9  is relatively small. As a result, the scanning device  17  is suitable for scanning optical information carriers having relatively small elementary information characteristics, i.e. optical information carriers having a relatively high information density, such as a high-density CD. As shown in FIG. 3, the auxiliary lens  55  is secured in a fixed position to a housing  57  of the lens system  37 , which housing  57  is secured to the first actuator  51  and hence can be displaced parallel to the optical axis  39  of the lens system  37  using the first actuator  51 . The main lens  53  is secured to a substantially ring-shaped holder  59  which, viewed parallel to the optical axis  39 , is elastically suspended in the housing  57  an elastically deformable mounting unit  61 , which will be described in greater detail hereinbelow, the main lens  53  being displaceable, parallel to the optical axis  39 , relative to the housing  57 , thereby elastically deforming the mounting unit  61 . As shown in FIG. 3, the lens system . 37  further includes a second actuator  63 , which will be described in greater detail hereinbelow, by means of which the main lens  53  can be displaced, parallel to the optical axis  39  of the lens system  37 , relative to the housing  57  and the auxiliary lens  55 . By displacing the main lens  53  relative to the auxiliary lens  55 , in a direction parallel to the optical axis  39 , using the second actuator  63 , a spherical aberration of the radiation beam  45  in the transparent protective layer  13  of the information carrier  9  is corrected. Such a spherical aberration is predominantly caused by fluctuations in the thickness t of the protective layer  13 . The second actuator  63  is also driven by the control unit of the optical player, which receives an error signal from a sensor of the scanning device  17 , not shown in the Figures for the sake of simplicity, by which sensor, for example, the thickness t of the protective layer  13  near the scanning spot  47  can be measured. 
     As shown in FIG. 3, the mounting unit  61  includes two mounting elements  65 ,  67  which, viewed parallel to the optical axis  39 , are arranged at a distance from each other and extend transversely to the optical axis  39 . The mounting elements  65 ,  67 , which are identical and shown in detail in FIG. 4, are, viewed at right angles to the optical axis  39 , substantially undeformable and, viewed parallel to the optical axis  39 , elastically deformable. For this purpose, as shown in FIG. 4, the mounting elements  65 ,  67  are each provided with a first, predominantly ring-shaped portion  69  which is secured to the housing  57  of the lens system  37 , and a second, predominantly ring-shaped portion  71  which is secured to the holder  59  of the main lens  53 , the ring-shaped portions  69  and  71  being interconnected by three bendable bridges  73  which extend in a plane transverse to the optical axis  39  and are mutually placed at regular intervals. By using the two mounting elements  65 ,  67 , the main lens  53  is given, viewed parallel to the optical axis  39 , a freedom of displacement, while, viewed at right angles to the optical axis  39 , a relatively rigid bearing of the main lens  53  relative to the housing  57  is obtained. The mounting elements  65 ,  67  each individually allow tilting movements of the main lens  53  about every tilt axis directed at right angles to the optical axis  39 , but the co-operation between the two mounting elements  65 ,  67  provides the mounting unit  61  with a relatively high tilt resistance about every tilt axis directed perpendicularly to the optical axis  39 , so that tilting of the main lens  53  relative to the housing  57  about tilt axes directed at right angles to the optical axis  39  is precluded as much as possible. By virtue thereof, it is achieved that a mutual alignment of the main lens  53  and the auxiliary lens  55  relative to each other, which is obtained during the manufacture of the lens system  37 , and as a result of which the optical axes of the main lens  53  and the auxiliary lens  55  coincide as much as possible is maintained in operation to the extent possible. 
     As shown in FIG. 3, the second actuator  63 , viewed parallel to the optical axis  39 , is arranged between the two mounting elements  65 ,  67  of the mounting unit  61 , so that the space available between the two mounting elements  65 ,  67  is efficiently used and a compact construction of the lens system  37  is obtained. The actuator  63  has two ring-shaped permanent magnets  75 ,  77  which, viewed parallel to the optical axis  39 , are arranged one beside the other and secured to a substantially ring-shaped closing yoke  79 , which is made of a magnetizable material and constitutes a separate part of the housing  57  of the lens system  37 . The actuator  63  further includes two ring-shaped electric coils  81 ,  83  which are secured to the holder  59  of the main lens  53 . Viewed parallel to the optical axis  39 , the coils  81 ,  83  are also arranged next to each other, the coil  81  being arranged opposite the magnet  75  and the coil  83  being arranged opposite the magnet  77 , while a ring-shaped air gap  85  is present between the magnets  75 ,  77  and the coils  81 ,  83 . As shown in FIG. 3, the magnets  75 ,  77  are magnetized, relative to the optical axis  39 , in opposite radial directions R and R′. The coils  81 ,  83  are wound in opposite directions relative to each other, so that, in operation, an electric current in the coil  81  and an electric current in the coil  83  flow in opposite directions. In this manner, it is achieved that the electromagnetic forces which, in operation, are exerted on the coils  81  and  83  by an interaction between a magnetic field of the magnets  75 ,  77  and the electric current in the coils  81 ,  83  are substantially equally directed. The holder  59  is made of a non-magnetizable material, so that the magnets  75 ,  77  do not exert magnetic forces on the holder  59 , and mechanical loads on the mounting elements  65 ,  67 , which are directed at right angles to the optical axis  39 , are limited as much as possible. 
     In accordance with a method according to the invention of manufacturing the optical lens system  37 , the auxiliary lens  55  is secured, in a fixed position, to a first part  87  of the housing  57 , while the ring-shaped part  69  of the mounting element  65  is secured to a second part  89  of the housing  57 , and the ring-shaped part  69  of the mounting element  67  is secured to a third part  91  of the housing  57 . The three parts  87 ,  89 ,  91  of the housing  57  are shown in FIG.  3 . In accordance with the method, the first part  87  of the housing  57  is provided with a ring-shaped sliding surface  93  which, in a situation shown in FIG. 3 in which the auxiliary lens  55  is secured to the first part  87 , extends transversely to an optical axis  95  of the auxiliary lens  55 . The third part  91  of the housing  57  is also provided with a ring-shaped sliding surface  97  which, in the situation shown in FIG. 3 in which the main lens  53  is secured to the third part  91  via the mounting element  67 , extends transversely to an optical axis  99  of the main lens  53 . The second part  89  of the housing  57  is provided with a first ring-shaped sliding surface  101  for co-operation with the sliding surface  97  of the third part  91 , and with a second ring-shaped sliding surface  103  for co-operation with the sliding surface  93  of the first part  87 . The sliding surfaces  101  and  103  of the second part  89  extend transversely to the optical axis  99  of the main lens  53 , in the situation shown in FIG. 3 in which the main lens  53  is secured to the second part  89  via the mounting element  65 . 
     As schematically shown in FIGS. 5 a  and  5   b , in accordance with the invention, the three parts  87 ,  89 ,  91  of the housing  57 , including the main lens  53  and the auxiliary lens  55  attached thereto, are arranged on top of each other via the co-operating sliding surfaces  93 ,  103  and the cooperating sliding surfaces  97 ,  101 . The first part  87  is coupled to a reference  105  of a manipulator  107 , the second part  89  is coupled to a first effector  109  of the manipulator  107 , and the third part  91  is coupled to a second effector  111  of the manipulator  107 . Using manipulator  107 , which for simplicity&#39;s sake is not shown in detail in the Figures, the main lens  53  and the auxiliary lens  55  of the lens system  37  to be manufactured are aligned relative to each other in such a manner that the optical axis  99  of the main lens  53  and the optical axis  95  of the auxiliary lens  55  coincide and hence constitute the optical axis  39  of the lens system  37 . In order to align the optical axes  95  and  99  of, respectively, the auxiliary lens  55  and the main lens  53 , the main lens  53  is displaced over a necessary distance relative to the auxiliary lens  55  by manipulator  107  in a direction transverse to the optical axis  99  of the main lens  53 , so that the main lens  53  and the auxiliary lens  55  are centered relative to each other, and the main lens  53  is tilted through a necessary angle relative to the auxiliary lens  55  by the manipulator  107  about a tilt axis directed transversely to the optical axis  99  of the main lens  53 , so that the optical axes  95  and  99  of the auxiliary lens  55  and the main lens  53  are brought into mutually parallel positions. 
     In order to enable the main lens  53  to be displaced relative to the auxiliary lens  55  in a direction transverse to the optical axis  99  of the main lens  53 , the effectors  109  and  111  of the manipulator  107  are displaced over equal distances in a same direction transverse to the optical axis  99  of the main lens  53 , as shown in FIG. 5 a . Here, the second sliding surface  103  of the second part  89  of the housing  57  slides over the sliding surface  93  of the first part  87  of the housing  57 . In order to be able to tilt the main lens  53  relative to the auxiliary lens  55  about a tilt axis C directed transversely to the optical axis  99  of the main lens  53 , the effectors  109  and  111  of the manipulator  107  are displaced over equal distances, in opposite directions, transverse to the optical axis  99  of the main lens  53 , as shown in FIG. 5 b . Here, the second sliding surface  103  of the second part  89  of the housing  57  slides over the sliding surface  93  of the first part  87  of the housing  57 , while the first sliding surface  101  of the second part  89  of the housing  57  slides over the sliding surface  97  of the third part  91  of the housing  57 . The tilt axis C is situated between the two mounting elements  65  and  67 . Since, as shown in FIGS. 5 a  and  5   b , the main lens  53  and the auxiliary lens  55  are, respectively, centered relative to each other and brought into mutually parallel positions by two mutually different methods of displacing the second part  89  of the housing  57  with the mounting element  65  attached thereto and the third part  91  of the housing  57  with the mounting element  67  attached thereto, the main lens  53  and the auxiliary lens  55  are aligned relative to each other in a simple and accurate manner. Since the alignment of the main lens  53  and the auxiliary lens  55  takes place exclusively by displacing the second part  89  and the third part  91  of the housing  57  in directions transverse to the optical axis  99  of the main lens  53 , the manipulator  107  may be of a simple type. 
     The three parts  87 ,  89 ,  91  of the housing  57  can be coupled to the manipulator  107  in a simple manner, for example by a clamp coupling, which leads to a further simplification of the alignment of the main lens  53  and the auxiliary lens  55 . By using co-operating sliding surfaces  93  and  103 , and the co-operating sliding surfaces  97  and  101 , the main lens  53  and the auxiliary lens  55  can be readily handled during the aligning process, so that the alignment of the main lens  53  and the auxiliary lens  55  is further simplified. 
     After the main lens  53  and the auxiliary lens  55  are aligned relative to each other as described above, the three parts  87 ,  89 ,  91  of the housing  57  are fixed relative to each other. In the example of a method in accordance with the invention, as shown in the Figures, the three parts  87 ,  89 ,  91  are fixed relative to each other by providing an adhesive between the co-operating sliding surfaces  93  and  103  and between the co-operating sliding surfaces  97  and  101 , which adhesive is cured after the alignment of the main lens  53  and the auxiliary lens  55 . Since shrinkage or expansion of the adhesive provided between the co-operating sliding surfaces  93 ,  103  and between the co-operating sliding surfaces  97 ,  101  occurs mainly in a direction parallel to the optical axis  39  of the lens system  37 , such shrinkage or expansion leads to hardly any relative displacements of the three parts  87 ,  89 ,  91  of the housing  57  in directions transverse to the optical axis  39  of the lens system  37 , so that the alignment of the main lens  53  and the auxiliary lens  55  relative to each other is hardly disturbed by such shrinkage or expansion. It is noted that, in accordance with the invention, the three parts  87 ,  89 ,  91  of the housing may alternatively be fixed relative to each other in a different manner, such as by laser-welded joints. 
     In accordance with the alternative method of the invention schematically shown in FIGS. 6 a  and  6   b , the first part  87  of the housing  57  with the auxiliary lens  55  secured thereto, is coupled to the first effector  109  of the manipulator  107 , the second part  89  of the housing  57  with the mounting element  65  secured thereto, is coupled to the reference  105  of the manipulator  107 , and the third part  91  of the housing  57  with the mounting element  67  secured thereto is coupled to the second effector  111  of the manipulator  107 . In this alternative method in accordance with the invention, the main lens  53  and the auxiliary lens  55  are brought into mutually parallel positions, as in the method shown in FIGS. 5 a  and  5   b , by tilting the main lens  53  about a tilt axis C′ which is directed perpendicularly to the optical axis  99  of the main lens  53 . For this purpose, as schematically shown in FIG. 6 a , only the second effector  111  of the manipulator  107  is displaced in a direction transverse to the optical axis  99  of the main lens  53 , so that only the mounting element  67  is displaced in a direction transverse to the optical axis  99  of the main lens  53 . The tilt axis C′ is consequently situated, for example, near the mounting element  65  or near the surface of the main lens  53  facing the auxiliary lens  55 . Here, the first sliding surface  101  of the second part  89  of the housing  57  slides over the sliding surface  97  of the third part  91  of the housing  57 . 
     In the alternative method in accordance with the invention, the main lens  53  and the auxiliary lens  55  are centered relative to each other by displacing the auxiliary lens  55  in a direction transverse to the optical axis  95  of the auxiliary lens  55 . For this purpose, as schematically shown in FIG. 6 b , only the first effector  109  of the manipulator  107  is displaced in a direction transverse to the optical axis  95  of the auxiliary lens  55 , so that only the first part  87  of the housing  57  with the auxiliary lens  55  attached thereto is displaced in a direction transverse to the optical axis  95  of the auxiliary lens  55 . Here, the sliding surface  93  of the first part  87  of the housing  57  slides over the second sliding surface  103  of the second part  89  of the housing  57 . Since, in the alternative method, during aligning the main lens  53  and the auxiliary lens  55 , tilting of the main lens  53  and displacing the auxiliary lens  55  take place by displacing, respectively, only the second effector  111  of the manipulator  107  and only the first effector  109  of the manipulator  107 , a very simple embodiment of the method in accordance with the invention is obtained. 
     As described hereinabove, the mounting elements  65 ,  67  of the lens system  37  each include three bendable bridges  73  which are arranged at regular distances from each other and extend in a plane transverse to the optical axis  39 . As shown in FIG. 4, the bendable bridges  73  each include a uniformly bendable spoke which extends mainly in a tangential direction relative to the optical axis  39  of the lens system  37 . By virtue thereof, a simple and robust construction of the mounting elements  65 ,  67  is obtained. FIG. 7 shows an alternative mounting element  65 ′,  67 ′, which may be used in the lens system  37  instead of the mounting element  65 ,  67  shown in FIG.  4 . In accordance with the invention, the alternative mounting element  65 ′,  67 ′ is provided, like the mounting element  65 ,  67 , with a first, predominantly ring-shaped portion  69 ′, which is secured to the housing  57  of the lens element  37 , and with a second, predominantly ring-shaped portion  71 ′ which is secured to the holder  59 . The ring-shaped portions  69 ′,  71 ′ of the alternative securing element  65 ′,  67 ′ shown in FIG. 7 are interconnected by three bendable bridges  73 ′ which are arranged at regular distances from each other and extend in a plane transverse to the optical axis  39 , each bridge being provided with a relatively rigid strip  113  which extends predominantly in a tangential direction relative to the optical axis  39  and is connected via two flexible joints  115 ,  117  to the two ring-shaped portions  69 ′,  71 ′. By using strips  113  and flexible joints  115 ,  117 , the mounting elements  65 ′,  67 ′ can be manufactured in a simple manner by providing a relatively small number of incisions in a plate of a material. 
     The mounting elements  65 ,  67  and the alternative mounting elements  65 ′,  67 ′ can be manufactured from a single plate of a material by, for example, a cutting or etching process. Since the mounting elements  65 ,  67  and  65 ′,  67 ′ are identical, a simple construction of the lens system  37  is obtained. It is noted that in accordance with the invention also lens systems  37  can be manufactured in which the mounting elements  65 ,  67 ,  65 ′,  67 ′ used therein include a different number of bendable bridges  73 ,  73 ′. In accordance with the invention, however, a first one of the mounting elements  65 ,  67 ,  65 ′,  67 ′ should be provided with at least three bendable bridges  73 ,  73 ′ which are arranged at regular intervals and extend in a plane transverse to the optical axis  39 , and a second one of the mounting elements  65 ,  67 ,  65 ′,  67 ′ should be provided with at least two bendable bridges  73 ,  73 ′ which extend in a plane transverse to the optical axis  39 . 
     If the first mounting element  65 ,  67 ,  65 ′,  67 ′ is provided, as described above, with three bendable bridges  73 ,  73 ′, and the second mounting element  65 ,  67 ,  65 ′,  67 ′ is provided, as described above, with two bendable bridges  73 ,  73 ′, a so-called statically determined, i.e. substantially stress-free suspension of the main lens  53  in the housing  57  is obtained, in which case the main lens  53  can only be displaced in a direction parallel to the optical axis  39  of the lens system  37 . This is based on the recognition that each individual, bendable bridge  73 ,  73 ′ predominantly serves as a mechanical rod with which substantially exclusively forces directed parallel to a longitudinal direction of the bendable bridge  73 ,  73 ′ are transmitted. If a larger number of bendable bridges  73 ,  73 ′ extending in a plane transverse to the optical axis  39  of the lens system  37  are used in the mounting elements  65 ,  67 ,  65 ′,  67 ′, then the main lens  53  is suspended in the housing  57  in a manner which is not statically determined, but which also enables the main lens  53  to be displaced in a direction parallel to the optical axis  39 . 
     The above-described optical player in accordance with the invention can be used, during scanning the information track of the information carrier  9 , to read information present on the information track or write information on the information track. It is noted that the invention also relates to optical players which can only be used to read information present on an information track of an information carrier. 
     In accordance with the above-described methods according to the invention, the main lens  53  and the auxiliary lens  55  are aligned relative to each other by tilting the main lens  53  about a tilt axis C, C′ which is directed at right angles to the optical axis  99  of the main lens  53 , and by displacing the main lens  53  or the auxiliary lens  55  in a direction transverse to the optical axis  99 ,  95  of the main lens  53  or the auxiliary lens  55 . It is further noted that the invention also includes methods in which, during alignment, the main lens  53  and the auxiliary lens  55  are only brought into mutually parallel positions by tilting the main lens  53  about a tilt axis which is directed transversely to the optical axis  99  of the main lens  53 . It is further noted that, in accordance with the invention, the main lens  53  and the auxiliary lens  55  can also be brought into mutually parallel positions by securing the auxiliary lens  55 , instead of the main lens  53 , to two similar mounting elements and displacing at least one of the mounting elements in a direction transverse to the optical axis  95  of the auxiliary lens  55 . The invention further includes methods of manufacturing a lens system, in which the two lens elements employed therein are each secured to the housing by two similar mounting elements. During aligning the lens elements of such a lens system relative to each other, one of the two lens elements may be manipulated in a manner shown in FIGS. 5 a ,  5   b  or  6   a ,  6   b , or both lens elements may be manipulated each in a manner shown in FIGS. 5 a ,  5   b  or  6   a ,  6   b.    
     It is further noted that the invention also relates to a method of manufacturing a lens system in which the two lens elements employed therein cannot be displaced relative to each other by an actuator. 
     In the above-described methods in accordance with the invention, two of the three parts  87 ,  89 ,  91  of the housing  57  are manipulated during aligning the main lens  53  and the auxiliary lens  55  relative to each other. It is noted that in accordance with a method according to the invention, in general, at least one of the two mounting elements of one of the lens elements is manipulated during the alignment and, subsequently, secured to the housing of the lens system. The fixation relative to each other of the three parts  87 ,  89 ,  91  of the housing  57  in the above-described examples of the method in accordance with the invention should consequently be construed as securing the mounting elements  65 ,  67  to the housing  57 . 
     The invention has been disclosed with reference to specific preferred embodiments, to enable those skilled in the art to make and use the invention, and to describe the best mode contemplated for carrying out the invention. Those skilled in the art may modify or add to these embodiments or provide other embodiments without departing from the spirit of the invention. Thus, the scope of the invention is only limited by the following claims: