CN1291399C - Optical reading/writing system - Google Patents

Abstract

An optical read/write system, which can record/reproduce signals of the first, second and third optical disc specifications, and the storage densities of the optical disc specifications increase sequentially, the optical read/write system includes three The second and third light sources of the incident light beam, three detection elements arranged opposite to the light source, a collimator lens, an objective lens and a prism unit with first, second, third light incident surfaces and a light exit surface, wherein the The wavelengths of the first, second and third incident light beams are the wavelengths stipulated by the first, second and third optical disc specifications respectively; The light incident surface enters the prism unit and is output from the same light exit surface; the prism unit is respectively provided with an aspheric surface in the optical path of the first and third incident light beams, and the collimating lens and the objective lens have the same specifications as the second optical disc. Matching optical parameters.

Description

Optical read/write system

【Technical field】

The present invention relates to an optical read/write system for a recording/reproducing device, especially an optical read/write system for a high-density recording/reproducing device compatible with various optical disc specifications.

【Background technique】

The optical read/write system uses an objective lens to focus a laser beam onto an optical disc to form a light spot, thereby recording information on the disc or reading information from the disc. The size of the focused light spot will determine the data recording density of the optical disc, thereby determining the recordable capacity of the optical disc. The smaller the light spot, the higher the recording capacity of the disc. In general, the size of the focused spot (S) is proportional to the wavelength (λ) of the laser beam and inversely proportional to the numerical aperture (NA) of the objective lens. It can be deduced from this that to form a small spot suitable for high-density recording media, the working wavelength (λ) of the laser beam must be reduced or the numerical aperture (NA) of the objective lens must be increased. Therefore, during the evolution of optical disc specifications, the operating wavelength (λ) and numerical aperture (NA) used by it are also constantly changing. The working wavelength used in the original CD specification is about 780nm, and the numerical aperture of the objective lens is 0.45; while the working wavelength used in the DVD specification has been reduced to 650nm, and the numerical aperture of the objective lens has been increased to 0.6; the new generation of HD-DVD specifications has adopted wavelength The short-wavelength blue light of about 405nm replaces the red light of CD and DVD, and the numerical aperture of the objective lens is above 0.6, up to 0.85. Since the optical parameters adopted by each specification are different, when recording/reading information of different optical disc specifications, the optical element of which specification is required to be read/recorded must meet the requirements of the specification.

In addition to the above differences, different optical disc specifications also have different thicknesses. The coma aberration will be generated due to the inclination of the optical disc, and the size of the coma aberration has a great relationship with the thickness of the optical disc. The thicker the optical disc, the greater the coma aberration will be. In order to control the coma aberration of the optical disc, the thickness of the optical disc has been gradually reduced, from 1.2mm of CD to less than 0.6mm of HD-DVD.

The high-density recording/reproducing device needs to be able to record/reproduce the disk of the corresponding recording standard, and also needs to be compatible with the existing low-density recording standard. Taking the HD-DVD recording/reproducing device as an example, it needs to be able to record/reproduce the specifications of HD-DVD discs, and also needs to be compatible with the specifications of CD and DVD discs which still occupy a large market. Therefore, an optical read/write system for an HD-DVD recording/reproducing device needs to have an optical system satisfying the three optical disc specifications. However, there are the above-mentioned differences in the working wavelength, the required numerical aperture of the objective lens, and the disc thickness among the specifications. Therefore, when the optical read/write system records/reproduces information, it needs to provide optical parameters that match the specifications of the optical disc it uses.

In the above-mentioned optical read/write system compatible with various optical disc specifications, an optical system can be deployed for each standard, and its optical parameters are respectively fully matched with the corresponding optical disc standards. In the aforementioned HD-DVD optical read/write system, there are three optical systems corresponding to HD-DVD standard, DVD standard and CD standard respectively. Each optical system is a complete optical path with corresponding light source, light receiving element and multiple optical path transmission elements. However, this design requires a large number of optical elements, which will directly lead to high cost of the optical read/write system. Moreover, the large number of optical components leads to a large package volume of the optical read/write system, which is contrary to the trend towards miniaturization of the current optical recording/reproducing device. Therefore, in the prior art, optical systems corresponding to different specifications share part of the optical path to reduce the number of optical elements, and usually share optical path transmission elements such as collimator lenses and objective lenses. However, the optical parameters of optical components are usually determined by shape, material, etc., which cannot be adjusted. For example, a collimator lens has the function of concentrating light, but only converts the divergent beam of a certain wavelength of light into a parallel beam, and the beams of other wavelengths can only be converted into approximately parallel beams. The same is true for the objective lens, which can only converge the input parallel beams of a specific wavelength to its corresponding position well, and converge other wavelengths to other positions, which means that there will be certain errors due to mismatch, such as aberrations Spherical aberration, chromatic aberration, or the area of the focused spot is too large, which affects the optical performance of the optical system and cannot correctly record/reproduce the information on the optical disc. For the optical read/write system of the above-mentioned HD-DVD recording/reproducing device, a light source and a light receiver are respectively provided for HD-DVD, DVD, and CD specifications, and an optical path coupling element needs to be provided in the optical read/write system so that different The light beams of the light source can share part of the light path. The shared collimator lens and objective lens can only be set for one of the specifications. If it is set for the HD-DVD specification, spherical aberration and chromatic aberration will appear in the optical paths of the DVD and CD specifications.

【Content of invention】

The technical problem to be solved by the present invention is to provide an optical read/write system that can record/reproduce three optical disc specifications, and the optical read/write system can not only reduce the package volume of the optical read/write system but also have good optics. performance.

An optical read/write system, which can record/reproduce signals of the first, second and third optical disc specifications, and the storage densities of the optical disc specifications increase sequentially, the optical read/write system includes three The light sources of the second and third incident light beams, three detection elements arranged opposite to the light source to receive the first, second and third incident light beams, a collimator lens, an objective lens and a first, second and third incident light beam A prism unit with a light surface and a light-emitting surface, wherein the wavelengths of the first, second, and third incident light beams are the wavelengths stipulated by the first, second, and third optical disc specifications; the first, second, and third The light incident surfaces are arranged opposite to the above-mentioned first, second and third light sources respectively, and the first, second and third incident light beams respectively enter the prism unit from the first, second and third light incident surfaces, and are transmitted by the same Output from the light output surface; the prism unit is respectively provided with an aspheric surface in the optical path of the first and third incident light beams. Optical parameters: the objective lens is set facing the surface of the optical disc and has optical parameters matching the specifications of the second optical disc.

Compared with the prior art, the optical read/write system of the present invention has the following advantages: first, the optical read/write system of the present invention adopts a prism unit with three light incident surfaces to automatically transmit different wavelength optical signals from different light sources Input from different light incident surfaces and output from the same light exit surface, so that different optical systems are coupled to share the optical components output from the prism unit, thereby reducing the number of optical components required for the optical read/write system compatible with three optical disc specifications , thereby reducing the packaging volume of the optical read/write system and reducing the cost of the optical read/write system. Furthermore, the objective lens of the collimating lens of the optical reading/writing system of the present invention and the optical parameters of the collimating lens all match with the standards established by the second optical disc specification, so when recording/reproducing the second optical disc specification data, the optical reading /Write system has good optical performance. And the optical reading/writing system of the present invention adds an aspheric optical element respectively in the optical paths passed by the first and third incident light beams, and the aspheric optical element can correct the optical parameters of the objective lens and the collimating lens and the first and third incident light beams respectively. The aberrations caused by the deviation of the standards set by the three optical disc specifications, therefore, the optical read/write system also has good optical performance when recording/reproducing the data of the first and third optical disc specifications.

【Description of drawings】

FIG. 1 is a schematic diagram of a first embodiment of an optical read/write system of the present invention.

FIG. 2 is a schematic diagram of part of the optical path of the first embodiment of the optical read/write system.

FIG. 3A is a front view of a wavelength selective mirror of the optical read/write system of FIG. 1. FIG.

Fig. 3B is a schematic diagram of the optical path of the wavelength selective mirror in Fig. 3A.

Fig. 4 is a schematic diagram of a second embodiment of the optical read/write system of the present invention.

Fig. 5 is a schematic diagram of a third embodiment of the optical read/write system of the present invention.

FIG. 6 is a schematic diagram of the optical path of the Pechan prism shown in FIG. 5 .

【Detailed ways】

Please refer to Fig. 1, the optical reading/writing system 100 of the present invention is suitable for recording/reproducing in the high-density recording/reproducing device of three kinds of optical disc specifications, and this embodiment can record/reproduce the optical disc of HD-DVD, DVD and CD standard Take the read/write system 100 as an example. The optical read/write system 100 includes three light sources 1a, 1b, 1c, three detection elements 2a, 2b, 2c, three holographic lenses 3a, 3b, 3c, a prism unit 4, a pentagonal prism 5, and a collimator lens 6 , a mirror 7, a wavelength selective mirror 8 and an objective lens 9, and the light source 1a, 1b, 1c, the detection element 2a, 2b, 2c, the holographic mirror 3a, 3b, 3c, and the prism unit 4 are packaged by semiconductor technology. The light sources 1a, 1b, and 1c are arranged in parallel and on the same plane. The light source 1a is set for the CD specification, and the working wavelength is 780nm; the light source 1b is set for the HD-DVD specification, and the working wavelength is 405nm; the light source 1c is set for the DVD specification, and the working wavelength is The wavelength is 650nm. The three detection elements 2a, 2b, 2c are respectively adjacent to the three light sources 1a, 1b, 1c and arranged parallel to receive CD, HD-DVD and DVD standard optical signals respectively. Each holographic lens 3a, 3b, 3c is set opposite to a pair of light sources 1a, 1b, 1c and detection elements 2a, 2b, 2c respectively, so as to refract the optical signals emitted by the light sources 1a, 1b, 1c or the optical signals of the optical path to the detection On elements 2a, 2b, 2c.

Please refer to Fig. 2, the prism unit 4 is located between the holographic sheet 3a, 3b, 3c and the pentagonal prism 5, and it includes first, second, third prisms 41, 42, 43, wherein the first prism 41 is a rectangular prism, its It has a light incident surface 410 and a light output surface 412 oppositely disposed. The light-incident surface 410 is the first light-incident surface of the prism unit 4 , which faces the holographic lens 3 a for transmitting CD-standard optical signals, and has an aspherical structure for converging the input optical signals. The aspheric structure can also be arranged on the light-emitting surface 412 in addition to being arranged on the light-incident surface 410 as described above. The second and third prisms 42 and 43 are composite prisms, respectively including rectangular prisms 420 and 430 and a parallelogram prism 422 and 432 . The rectangular prism 420 of the second prism 42 has a light incident surface 4200 adjacent to it at a right angle and a light exit surface 4202 opposite to the right angle. The light incident surface 4200 faces the holographic glass 3b to transmit HD-DVD standard light Signal. The parallelogram prism 422 of the second prism 42 has a light incident surface 4220 and a light exit surface 4222 oppositely disposed, and two reflective surfaces 4224 , 4226 . The light incident surface 4220 and the reflective surface 4226 form an angle of 45 degrees. The light incident surface 4220 is the third light incident surface of the prism unit 4, wherein the light incident surface 4220 is the third light incident surface of the prism unit 4, which is arranged facing the holographic lens 3c and has an aspherical structure to transmit DVD standard light Signal. The reflective surface 4224 is opposite to the light-emitting surface 4202 of the rectangular prism 420, and is coated with a film (not shown). The film reflects the incident 650nm optical signal and transmits the 405nm optical signal along its original transmission direction.

The rectangular prism 430 of the third prism has a light incident surface 4300 and a reflective surface 4324 at an angle of 45 degrees with the light incident surface 4300, wherein the light incident surface 4300 is opposite to the light exit surface 4222 of the parallelogram prism 422 of the second prism 42 . The parallelogram prism 432 of the third prism 43 has a light incident surface 4320 and a light exit surface 4322 arranged parallel to each other, and two reflective surfaces 4324 and 4326 respectively connected to the light incident surface 4320 and the light exit surface 4322 . The light incident surface 4320 is relatively parallel to the light exit surface 412 of the first prism 41 . The reflective surface 4324 is arranged opposite to the light-emitting surface 4322 of the rectangular prism 430, and a second film layer (not shown) is coated on its surface. The second film layer can reflect the incident 780nm optical signal and the incident 405nm and 650nm light The signal is transmitted in its original direction of travel. The light output surface 4322 is the output end surface of the prism unit 4 , and the 780nm, 650nm and 405nm optical signals respectively input from the first, second and third incident surfaces are output to the penta prism 5 through the output end surface.

The pentagonal prism 5 is a pentagonal columnar structure, which has a light incident surface 50 and a light output surface 51 , two reflective surfaces 52 , 53 and a connecting surface 54 arranged vertically adjacent to each other. Wherein, except that the included angle between the light incident surface 50 and the light output surface 51 is 90 degrees, the four included angles are all 112.5 degrees. The light incident surface 50 is opposite to the exit end surface 4322 of the prism unit 4 , and the two reflective surfaces 52 and 53 are respectively connected to the light incident surface 50 and the light exit surface 51 and coated with a total reflection film. The total reflection film is totally reflective to incident 405nm, 650nm and 780nm wavelength light signals.

The collimator lens 6 is arranged facing the light-emitting surface 51 of the pentaprism 5, and has optical parameters matching the HD-DVD standard. The surface reflector 7 is arranged obliquely, and has an included angle of 45 degrees with the horizontal direction to convert the optical signal transmitted horizontally to be transmitted along the vertical direction. The objective lens 9 is arranged facing the surface of the disc, and its optical parameters and positions are set according to the wavelength, numerical aperture and disc thickness of the HD-DVD standard adopted by the HD-DVD standard.

Please refer to FIG. 3A and FIG. 3B at the same time. The wavelength selection mirror 8 is disposed on one side of the objective lens 9 to select the optical signal passing through the objective lens 9 . The wavelength selective mirror 8 has a circular first area 81 at its center, an annular second area 82 surrounding the first area 81 , and a third area 83 outside the annular second area 82 . Among them, the first part 81 can pass 405nm, 650nm and 780nm wavelength optical signals; the second area 82 can pass 405nm, 650nm wavelength optical signals, and block 780nm wavelength optical signals; the third area 82 can only pass 405nm wavelength optical signals, And block 650nm and 780nm wavelength optical signals. Therefore, the actual numerical aperture of the objective lens 9 can be matched with HD-DVD, DVD, and CD specifications through the wavelength selective mirror 8 .

When recording or reading CD specification data, the light source 1a emits an optical signal with a wavelength of 780nm to form the first incident light beam, which enters the prism unit from the first incident surface 410 of the prism unit 4 after passing through the holographic lens 3a 4 of the first prism 41. Since the first light incident surface 410 has an aspherical structure, it has a light-condensing function for the input first incident light beam. The first incident light beam is condensed by the first light incident surface 410 for the first time and then output from the light exit surface 412 of the first prism 41 . Since the light-exiting surface 412 of the first prism 41 is opposite to the light-incident surface 4320 of the parallelogram prism 432 of the third prism 43, the first incident light beam output from the light-exit surface 412 enters the parallelogram prism of the third prism 43 through the light-incidence surface 4320 432. The first incident light beam entering the parallelogram prism 432 is first reflected by the reflecting surface 4326 to change its transmission direction, and the reflected first incident light beam is incident on another reflecting surface 4324. The 780nm wavelength optical signal has a reflection function, so the first incident beam is reflected again to restore the transmission direction of the first incident beam to the direction before entering the third prism 43, and it is output through the exit end surface 4322 of the prism unit 4.

The first incident light beam output from the prism unit 4 enters the fifth prism 5 through the light incident surface 50 of the pentagonal prism 5 , and is output from the light output surface 51 after being reflected twice by the reflective surfaces 52 and 53 . The first incident light beam output from the pentagonal prism 5 is condensed for the second time to form a near-parallel light beam after passing through the collimator lens 6 . After the near-parallel light beam is reflected by the surface mirror 7 , its transmission direction is changed from horizontal transmission to vertical transmission, and input to the wavelength selective mirror 8 . Since only the first area of the wavelength selective mirror 8 at the central position can pass the 780nm wavelength optical signal, the optical signal outside the first incident light beam is blocked by the wavelength selective mirror 8, and the optical signal inside it passes through the first area and then enters the objective lens9. The objective lens 9 converges the input near-parallel light beam with a wavelength of 780nm onto the data recording layer of the CD disc, and is reflected by the recording layer to form a first returning light beam. The first returning light beam returns to the holographic lens 3a along the optical path of the first incident light beam. The holographic lens 3a refracts and outputs the input first return light beam so that the light beam falls on the detection element 2a, and the detection element 2a converts the first return light beam into an electrical signal for output.

When recording or reading HD-DVD standard data, the light source 1b emits an optical signal with a wavelength of 405nm to form a second incident light beam. The second incident light beam enters the rectangular prism 420 of the prism unit 4 from the second incident surface 4200 of the prism unit 4 after passing through the holographic lens 3 b. The second incident light beam passes through the reflective surface 4224 of the parallelogram prism 422 when it is output from the light-emitting surface 4202 of the rectangular prism 420 . The reflective surface 4224 has a transmissive function for the input optical signal with a wavelength of 405nm, so the second incident light beam passes through the reflective surface 4202 along its original transmission direction, and then is output from the light output surface 4222 . The second incident light beam output from the second prism 42 enters the third prism 43 through the light incident surface 4300 of the rectangular prism 430 of the third prism 43 . The second incident light beam passes through the rectangular prism 430 and is input to the reflective surface 4324 of the parallelogram prism 432 . The reflective surface 4324 is transparent to the input optical signals with wavelengths of 405nm and 650nm, so the second incident light beam can be transmitted to the light output surface 4322 along its original transmission direction, and output from the light output surface 4322 to the pentagonal prism 5 . The transmission path of the second incident light beam from inputting the pentagonal prism 5 to outputting to the wavelength selective mirror 8 is exactly the same as the corresponding transmission path of the recording/reproducing CD standard, and will not be described in detail here. The second incident light beam is input to the wavelength selective mirror 8 after the above-mentioned transmission, because the first, second and third regions of the wavelength selective mirror 8 can pass through the 405nm wavelength optical signal, so the third incident light beam can be completely input to the objective lens 9, and converge to the data layer of the HD-DVD disc through the objective lens 9. The data layer reflects the incoming second incident light beam to form a second return light beam. The returning light path of the second returning light beam is substantially the same as the incident light path of the second incident light beam, the difference being that the second returning light beam is refracted when input to the holographic lens 3b and lands on the detection element 2b. The detection element 2b generates an electrical signal output according to the received second return light beam.

When recording or reading DVD standard data, the light source 1c emits an optical signal with a wavelength of 650nm to form a third incident light beam. Two prisms 42. Since the third light-incident surface 4220 is an aspheric surface, which has a light-condensing function for the input light beam, the third incident light beam converges the light beam through the third light-incident surface 4220 . The third incident light beam is totally reflected by the reflective surface 4226 of the parallelogram prism 422 of the second prism 42 to be transmitted to the reflective surface 4224 . The reflective surface 4224 has a reflective function for the incident 650nm wavelength optical signal, so the third incident light beam is reflected by the reflective surface 4224 to the light-emitting surface 4222 , and output to the third prism 43 through the light-emitting surface 4222 . The transmission path of the third incident light beam between entering the third prism and inputting to the wavelength selective mirror 8 is exactly the same as the corresponding optical path of the second incident light beam of recording/reading HD-DVD standard, please refer to the above section The description of the optical path of the second incident light beam will not be repeated here. The first and second regions of the wavelength selective mirror 8 transmit 650nm wavelength optical signals, and the third region blocks 650nm wavelength optical signals, so the third incident light beams input from the first and second regions of the wavelength selective mirror 8 can pass through the wavelength selective The mirror 8 is input to the objective lens 9, and converges on the data layer of the DVD disc through the objective lens 9. The data layer reflects the incident third incident light beam to form a third return light beam, and the transmission path of the third return light beam is basically the same as that of the third incident light beam, except that the third return light beam is input to the holographic The lens 3c is refracted and falls on the detection element 2c. The detection element 2c generates an electrical signal according to the third returned light beam, and outputs the electrical signal.

As can be seen from the above, the optical parameters of the collimator lens 6 and the objective lens 9 of the optical read/write system 100 are fully consistent with the parameters set by the HD-DVD standard, so when recording/reading of the HD-DVD standard, the optical read/write The system 100 does not produce phenomena such as aberration, and thus has good optical performance. When the optical read/write system 100 records/reproduces data according to DVD and CD standards, although the collimator lens 6 and the objective lens 9 do not completely match their standards, an aspheric correction mirror 4220 is added to the transmission optical paths of DVD and CD respectively. , 410, to correct the generated aberration. In addition, a wavelength selective mirror 8 is provided in the transmission optical path before the objective lens 9, which has different transmission ranges for different wavelength optical signals, so as to eliminate the influence of the excessively large numerical aperture of the objective lens 9 on DVD and CD standard optical signals. Therefore, the optical read/write system 100 has good optical performance for HD-DVD, DVD and CD standards.

Secondly, the prism unit 4 of the optical read/write system 100 has first, second, third light incident surfaces 410 , 4200 , 4220 and an output end surface 4322 . Optical signals from different optical paths can be input through the first, second, and third light incident surfaces 410 , 4200 , and 4220 , and output through the same output end surface 4322 after being transmitted inside the prism unit 4 . Thus, the coupling of multiple transmission optical paths is realized to fully utilize the optical components. Furthermore, the pentagonal prism 5 can be reflected between its surfaces, so that the transmission direction of the optical path can be changed, so that the actual size of the optical system can be reduced without reducing the length of the optical path, and the optical read/write system 100 can be fully utilized. The occupied space is to prevent the package volume of the optical read/write system 100 from being too long in a single direction and cannot be reduced.

Please refer to FIG. 4 , which is a second embodiment of the optical read/write system of the present invention. The optical read/write system 100 ′ is basically the same as the optical read/write system 100 of the above embodiment. However, the optical read/write system 100' omits the collimating lens 6 of the optical read/write system 100, but a pentagonal prism 5' is set in the optical read/write system 100', which is compatible with the optical read/write system 100 The pentagonal prism 5 is basically the same, the difference between the two is that the light-emitting surface of the pentagonal prism 5' is an aspherical structure. Therefore, the pentagonal prism 5 ′ not only has the function of the pentagonal prism 5 , but also has a light-condensing function instead of the collimating lens 6 .

Please refer to Fig. 5, which is the third embodiment of the optical read/write system of the present invention, the optical path design of the optical read/write system 100 "is basically the same as that of the optical read/write system 100 of the first embodiment, the two are different The difference is that the optical read/write system 100 "uses a Pechan prism 5" to replace the pentagonal prism 5 of the optical read/write system 100. Please refer to Fig. 6 at the same time, the Pechan prism 5 "is a compound prism, including first, oppositely arranged The second parts 51", 52", wherein the first and second parts 51", 52" have the same material. The first part 51" includes a light incident surface 510", and two reflective surfaces 511", 512" adjacent to the light incident surface 510". The two reflective surfaces 511", 512" are respectively coated with a total reflection film. The total reflection The film is totally reflective to incident 405nm, 650nm and 780nm wavelength light signals. The second part 52″ includes a light-emitting surface 520″ and two reflective surfaces 521″, 522″. The light-incident surface 510″ is parallel to the light-emitting surface 520″ set, and the reflective surface 511 ″ of the first part 51 ″ is combined with the second part 52 ″, and is partially coated with a reflective film, so that the reflective surface 511 ″ has a reflective function for the light beam incident on the coating area, The light beam incident on the outside of the reflective film has a transmission function.The basic parameters of the compound prism 5 are: a=4mm, b=4.828mm, =45 degrees, θ=112.5 degrees, β=67.5 degrees.

The incident light beam is input from the incident surface 510 ″ of the Pechan prism 5 ″, and transmitted to the coating area of the reflective surface 511 ″, and then reflected to the reflective surface 512 ″. The reflective surface 512" reflects the incident light beam, so that it falls on the uncoated area of the reflective surface 511", and then output to the second part 52" of the Pechan prism 5". The incident light beam output from the first part 51" enters the light output surface 520" of the second part 52" through the uncoated area of the reflective surface 521", and is totally reflected to the reflective surface 522", and then reflected to the total reflective coating area of 521". , so as to be reflected back to the light-emitting surface 520 ″ again, and output through the light-emitting surface 520 ″.

Claims (9)

1. optical read/write system, but its recoding/reproduction first, the signal of second and third CD specification, and the storage density of CD specification increases progressively successively, this optical read/write system comprises that three produce first respectively, the light source of second and third incident beam, three corresponding with light source to receive first, the detecting element of second and third incident beam, the light signal of three light signals that light source can be sent or light path reflects the holographic eyeglass on detecting element, one collimation lens and object lens, wherein this first, the wavelength of second and third incident beam is respectively first, the wavelength that second and third CD specification is formulated; It is characterized in that: this optical read/write system comprises that also one has the prism unit of first, second, third incidence surface and an exiting surface, an and wavelength-selective mirror, this first, second, third incidence surface is oppositely arranged with above-mentioned first, second, third light source respectively, this first, second and third incident beam enters this prism unit by first, second and third incidence surface respectively, and by same exiting surface output; This prism unit is in the first, the 3rd aspheric surface that incident beam is respectively equipped with in light path, and this collimation lens is arranged in the light path of prism unit exiting surface one side, and has the optical parametric that is complementary with second incident beam; This wavelength-selective mirror is located at the side that object lens deviate from optical disc surface, and be provided with first, second, third zone from inside to outside successively, wherein this first area is to all transmissions of first, second, third incident beam of incident, this second area stops first incident beam of incident and to second, third incident beam transmission, and the 3rd zone stops the first, the 3rd incident beam of incident and to the second incident beam transmission; These object lens are over against the optical disc surface setting and have the optical parametric that is complementary with the second CD specification.

2. as the described optical read/write of 1 of claim the system, it is characterized in that: this prism unit has first, second, third prism, this first, second prism is positioned at prism one side and parallel mutually the setting, this first prism has incidence surface and the exiting surface that is oppositely arranged, and this incidence surface is non-spherical structure and is first incidence surface of this prism unit, and this first incident beam is imported first prism and exported prism to via this exiting surface from incidence surface.

3. as the described optical read/write of 2 of claims the system, it is characterized in that: this second prism is a composite prism, it comprises a right-angle prism and parallelogram prism, wherein the hypotenuse of this right-angle prism combines with a wherein hypotenuse of this parallelogram prism, and this a right-angle prism wherein right-angle side is second incidence surface of this prism unit.

4. as the described optical read/write of 3 of claims the system, it is characterized in that: this parallelogram prism comprises parallel relative incidence surface and exiting surface and two parallel relative reflectings surface, and this incidence surface is non-spherical structure and is the 3rd incidence surface of this prism unit.

5. as the described optical read/write of 4 of claims the system, it is characterized in that: on this parallelogram prism and the reflecting surface that this right-angle prism combines a coating is arranged, this coating to second incident beam of input along its former transmission direction transmission and to the 3rd incident beam reflection of input.

6. as the described optical read/write of 2 of claims the system, it is characterized in that: this prism is a composite prism, it comprises a right-angle prism and parallelogram prism, wherein the hypotenuse of this right-angle prism combines with a wherein hypotenuse of this parallelogram prism, this first prism is oppositely arranged with a end away from this parallelogram prism of this right-angle prism, and this second prism and this right-angle prism are oppositely arranged.

7. as the described optical read/write of 6 of claims the system, it is characterized in that: this parallelogram prism has parallel relative incidence surface, exiting surface and two parallel relative reflectings surface, wherein this parallelogram prism is provided with first incident beam reflection of a pair of incident in the reflecting surface that combines with right-angle prism, and to second, third incident beam of input coating along its former transmission direction transmission.

8. as the described optical read/write of 7 of claims the system, it is characterized in that: the exiting surface of this parallelogram prism is the exiting surface of this prism unit, and first, second, third incident beam is all by this exiting surface output.

9. as the described optical read/write of 1 of claim the system, it is characterized in that: this optical read/write system also comprises a pentagonal prism, it is positioned on the light path between this prism unit and collimation lens, this pentagonal prism has an incidence surface, an exiting surface and at least two reflectings surface, angle is 90 degree between incidence surface and exiting surface, all the other of pentagonal prism four angles are all 112.5 degree, and at least two reflectings surface of this pentagonal prism are coated with total reflection film respectively.

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