JP4160476B2 - Optical head - Google Patents

Description

  The present invention relates to an optical head used for recording or reproducing information on an optical recording medium.

  In recent years, DVDs are rapidly spreading as high-density optical recording media. On the other hand, optical disks such as CDs, CD-ROMs, and CD-Rs are already widely used in the market. Furthermore, a semiconductor laser called a blue laser has also been developed, and an optical disc apparatus capable of recording and reproducing higher-density information by using short-wavelength irradiation light having a wavelength of about 400 nm from the blue laser has been developed. ing. Therefore, future optical disc apparatuses are strongly required to have compatibility with these various optical discs to obtain recording and reproducing functions.

  However, a DVD uses a semiconductor laser having a wavelength of 660 nm, and a CD-R includes a disc whose light source wavelength for recording and reproducing information is limited to 780 nm to 790 nm.

  Therefore, in order to perform recording or reproduction on these plural different discs with the same optical disc apparatus, it is necessary to mount semiconductor lasers that emit light of three types of wavelengths.

  As a method of configuring such an optical disc device having compatibility, for example, a technique using two optical heads disclosed in Patent Document 1 described later is adopted. For example, a semiconductor laser having a wavelength of 660 nm and a wavelength of 785 nm are used for one optical head. It is conceivable to mount two types of semiconductor lasers, i.e., a semiconductor laser, and a blue laser on the other optical head. One optical head on which two types of semiconductor lasers are mounted is selected from these semiconductor lasers by synthesizing the outgoing optical axes of the two types of semiconductor lasers with a dichroic prism as disclosed in, for example, Patent Document 2 below. The optical recording medium is irradiated with the optically emitted light beam using the same objective lens, the reflected light from the optical recording medium is separated again by the dichroic prism, and the servo signal and the information signal are detected. .

  As another configuration method, three semiconductor lasers having different wavelengths are mounted on one optical head, and the output optical axes of these semiconductor lasers are synthesized by applying the technique of Patent Document 2 and adding a dichroic prism. As a result, the optical recording medium is irradiated with the light flux from each semiconductor laser using the same objective lens, and the reflected light from the optical recording medium is separated again by the dichroic prism, and the servo signal and the information signal are detected. It is conceivable to configure as follows.

JP-A-10-27369 JP 2002-329346 A

  However, as in the former case, when two optical heads are used, an independent optical system and drive system are required for the two optical heads, which increases the size of the apparatus and increases the cost. There is concern.

  On the other hand, as in the latter case, when a dichroic prism is added to form a single optical head, the size and cost can be reduced as compared with the former case. However, as the dichroic prism is added, The number of parts increases, leading to an increase in size and cost of the apparatus.

  Accordingly, an object of the present invention made in view of such a point is to provide a small and inexpensive optical head equipped with three semiconductor lasers having different wavelengths.

The invention according to claim 1, which achieves the above object, includes a first laser light source that oscillates at a first wavelength, a second laser light source that oscillates at a second wavelength, and a third laser that oscillates at a third wavelength. And recording, erasing or reproducing information by irradiating the optical recording medium with a light beam selectively emitted from the first to third semiconductor lasers through one common objective lens. In the optical head,
Refraction that combines at least two of the light beams emitted from the first to third laser light sources into substantially the same optical axis in the optical path between the first to third laser light sources and the objective lens. An optical path synthesizing unit having a surface is disposed, and the return light of the first to third wavelengths reflected by the optical recording medium is reflected by the refractive surface of the optical path synthesizing unit. A second refracting surface is provided that refracts the first to third wavelength return light reflected by the refracting surface, and the optical axis of the first to third wavelength return light is separated by the second refracting surface. It is characterized by having comprised so.

  According to a second aspect of the present invention, in the optical head according to the first aspect, the first collimator that converts the light beam emitted from the first laser light source and the light beam emitted from the second laser light source into parallel light. It has a lens and a second collimator lens that makes the light beam emitted from the third laser light source parallel light.

  The invention according to claim 3 is the optical head according to claim 1, characterized in that it has one common collimator lens that collimates the light beams emitted from the first to third laser light sources. It is.

  According to a fourth aspect of the present invention, in the optical head according to the first, second or third aspect, the beam shape of the incident light beam is shaped and guided to the objective lens by the refracting surface of the optical path synthesizing unit. It is characterized by.

  According to a fifth aspect of the present invention, in the optical head according to any one of the first to fourth aspects, the first to third laser light sources are accommodated in the same package.

  The invention according to claim 6 is the optical head according to claim 3, wherein the first laser light source and the second laser light source are accommodated in the same package, and the collimator lens, the package, and the third laser light source are accommodated. Among the laser light sources, at least two of the laser light sources are provided so as to be position-adjustable in the optical axis direction.

  According to a seventh aspect of the present invention, in the optical head according to the third aspect, the first laser light source and the second laser light source are accommodated in the same package, and between the collimator lens and the package or the above A lens is disposed between the collimator lens and the third laser light source.

The invention according to claim 8 is the optical head according to any one of claims 1 to 7, wherein the first to third wavelengths are: first wavelength> second wavelength> third wavelength. Yes,
The first to first angles are set so that the incident angle of each wavelength on the refractive surface of the optical path synthesizing unit is the incident angle of the first wavelength <the incident angle of the second wavelength <the incident angle of the third wavelength. 3 laser light sources are arranged.

The invention according to claim 9 is the optical head according to claim 3, wherein the first to third wavelengths are first wavelength> second wavelength> third wavelength,
The first laser light source and the second laser light source are arranged so that light beams emitted from these laser light sources are incident on the collimator lens from the off-axis,
The third laser light source is characterized in that the light beam emitted from the laser light source is arranged so as to be incident on the collimator lens almost on the axis.

According to the invention according to claim 1, of each of the different wavelengths of light flux emitted from the first to third laser light sources, as well as synthetic substantially the same optical axis by the refracting surface of the optical path combining portion at least two light beams , the first to third wavelength of the return light reflected by the optical recording medium, after being reflected by the refractive surface, since as to separate the optical axis is refracted by the second refracting surface of the optical path combining portion, A dedicated beam separation element is not required, and the number of components can be reduced, and a small and inexpensive optical head equipped with first to third laser light sources having different wavelengths can be provided.

  According to the second aspect of the present invention, since two collimator lenses are provided, a collimator lens is used as a parallel light for two light beams having a small wavelength difference and a small separation angle on the refracting surface. Is possible.

  According to the invention of claim 3, since one collimator lens is shared for the light beams of the first to third wavelengths, the optical head can be made smaller and less expensive.

  According to the fourth aspect of the invention, since the refracting surface has a beam shaping function, a dedicated beam shaping element is not required, the number of parts can be reduced, and the optical head can be made smaller and less expensive.

  According to the fifth aspect of the present invention, since the first to third laser light sources are accommodated in the same package, the light emission directions of the light beams from the laser light sources can be aligned in substantially the same direction, and the optical head can be downsized. I can expect.

  According to the invention of claim 6, the position adjustment in the optical axis direction of the collimator lens common to the package containing the first and second laser light sources, the third laser light source, and the first to third laser light sources. Can be easily performed.

  According to the invention which concerns on Claim 7, with respect to the collimator lens common to the 1st-3rd laser light source, the arrangement | positioning position of the package which accommodates the 1st, 2nd laser light source, or the 3rd laser light source is arbitrary with a lens Therefore, the layout design of the optical component is facilitated.

  According to the invention which concerns on Claim 8, it becomes possible to synthesize | combine each light beam from the 1st-3rd laser light source reliably on a refracting surface.

  According to the ninth aspect of the present invention, since the light flux from the third laser light source having the shortest wavelength is incident on the collimator lens common to the first to third laser light sources from the substantially on-axis, the occurrence of aberration is generated. Thus, recording, erasing or reproducing performance can be improved.

Hereinafter, it will be explained the embodiment of the optical head according to the present invention.

Figure 1 is a diagram showing a schematic configuration of an optical system of an optical head according to an embodiment of the present invention.

  The optical head includes a blue semiconductor laser 1 as a third laser light source that emits light having a wavelength of 405 nm as a third wavelength, and a laser as a second laser light source that emits light having a wavelength of 650 nm as a second wavelength. A hybrid semiconductor laser 2 in which two laser chips, a chip 2a and a laser chip 2b as a first laser light source that emits light having a wavelength of 780 nm as a first wavelength, are housed in one package, a collimator lens 3, and an optical path From the beam shaping prism 4, the wavelength selection filter 5, the objective lens 6, the detection lens 7, the photodetector 8 that receives the light emitted from the blue semiconductor laser 1, and the hybrid semiconductor laser 2. It has a photodetector 9 that receives the emitted light, a monitoring photodetector 10, and a mirror 11. The hybrid semiconductor laser 2 may be a monolithic semiconductor laser that emits light having a wavelength of 650 nm and light having a wavelength of 780 nm from a single chip.

  First, a light beam having a wavelength of 405 nm emitted from the blue semiconductor laser 1 will be described.

  The light beam emitted from the blue semiconductor laser 1 is converted into parallel light by the collimator lens 3. Here, since the light flux from the blue semiconductor laser 1 with the shortest wavelength has the greatest influence of aberration, it is preferable to arrange the blue semiconductor laser 1 on the axis of the collimator lens 3 to suppress aberration deterioration.

  The parallel light transmitted through the collimator lens 3 is incident on the shaping surface 4a of the beam shaping prism 4 which is a refracting surface. Here, the shaping surface 4a is designed so that a part of the reflected light is generated, and the reflected light is incident on the monitoring photodetector 10 and the emitted light quantity of the blue semiconductor laser 1 is monitored.

  The parallel light transmitted through the shaping surface 4a of the beam shaping prism 4 is shaped into a substantially circular intensity distribution of the elliptical light beam due to the astigmatic difference of the blue semiconductor laser 1 by the beam shaping function of the shaping surface 4a.

  Here, in this embodiment, BSL7 (manufactured by OHARA) is used as the glass material of the beam shaping prism 4 in order to set the beam shaping ratio to 2.55. In this case, since the refractive index n1 of the BSL 7 at the wavelength 405 nm of the blue semiconductor laser 1 is 1.52972, when the refraction angle (θ0) at the shaping surface 4a of the beam shaping prism 4 is 38.47 deg, the beam As the shaping ratio = cos θ0 / cos θ1, the incident angle (θ1) with respect to the shaping surface 4a of the beam shaping prism 4 is 72.11 deg.

  The light beam shaped by refraction of the shaping surface 4a of the beam shaping prism 4 at a refraction angle (θ0) of 38.47 deg is emitted from the beam shaping prism 4, and the optical path is bent 90 degrees by the mirror 11. In FIG. 1, for the convenience of explanation, the beam shaping prism 4 and the mirror 11 are displayed by being rotated 90 degrees around the optical axis.

  The light beam reflected by the mirror 11 passes through the wavelength selection filter 5. The wavelength selection filter 5 is set so as to limit the aperture according to the numerical aperture of the objective lens 6 with respect to the light beam emitted from the blue semiconductor laser 1. The light beam that has passed through the wavelength selection filter 5 is condensed by the objective lens 6 onto the optical disk 12 that is an optical recording medium, and information is erased, recorded, or reproduced.

  On the other hand, the return light from the optical disk 12 passes through the objective lens 6 and the wavelength selection filter 5 again, the optical path is bent 90 degrees by the mirror 11, and enters the shaping surface 4 a of the beam shaping prism 4 again. Here, as described above, since the shaping surface 4a is designed so that a part of the reflected light is generated, the return light incident on the beam shaping prism 4 is partially reflected by the shaping surface 4a and beam shaped. The light enters the surface 4b, which is the second refracting surface of the prism 4, and refracts and transmits the surface 4b. In the present embodiment, the surface 4b is set so that the incident angle of the return light is 36.94 deg and the refraction angle is 66.83 deg.

  The return light emitted from the beam shaping prism 4 is collected on the photodetector 8 by the detection lens 7, and a signal for controlling the light spot on the optical disk 12, such as a focus error and a track error, is detected based on the output. Alternatively, the information signal recorded on the optical disk 12 is reproduced.

  As a signal detection method for controlling the light spot on the optical disc 12, various conventionally known methods can be used, and the shape of the light receiving surface of the photodetector 8 is not limited to a specific shape.

  Next, a light beam having a wavelength of 650 nm emitted from the laser chip 2a of the hybrid semiconductor laser 2 will be described.

  A light beam having a wavelength of 650 nm emitted from the laser chip 2a of the hybrid type semiconductor laser 2 passes through the collimator lens 3 and becomes parallel light and enters the shaping surface 4a of the beam shaping prism 4, and a part of the light is reflected here. Then, when the reflected light is received by the monitoring photodetector 10, the amount of light emitted from the hybrid semiconductor laser 2 at a wavelength of 650 nm is monitored.

  The incident angle of the beam shaping prism 4 on the shaping surface 4a is such that the refraction angle at the shaping surface 4a is θ0, that is, 38.47 deg., At the wavelength 650 nm of the glass material BSL7 (manufactured by OHARA) of the beam shaping prism 4. From the refractive index n2 = 1.51405, it is set to 70.37 deg by Snell's law.

  Thus, by setting the arrangement of the laser chip 2a of the hybrid semiconductor laser 2 and the angle of view to the collimator lens 3 so that the refraction angle at the shaping surface 4a of the beam shaping prism 4 becomes θ0, the laser chip 2a The optical axis of the light beam having a wavelength of 650 nm emitted from the laser beam can be combined with the optical axis of the light beam emitted from the blue semiconductor laser 1 after refracting the shaping surface 4 a of the beam shaping prism 4.

  The light beam having a wavelength of 650 nm emitted from the beam shaping prism 4 is shaped into an approximately circular intensity distribution of the elliptical light beam with a beam shaping ratio of 2.33 by the beam shaping function by the shaping surface 4 a of the beam shaping prism 4. Is bent 90 degrees.

  The light beam reflected by the mirror 11 passes through the wavelength selection filter 5. The wavelength selection filter 5 is set so as to limit the aperture in accordance with the numerical aperture of the objective lens 6 with respect to the light beam having a wavelength of 650 nm, and the light beam transmitted through the wavelength selection filter 5 is collected on the optical disk 12 by the objective lens 6. The light is erased, recorded or reproduced.

  On the other hand, the return light having a wavelength of 650 nm from the optical disk 12 is transmitted again through the objective lens 6 and the wavelength selection filter 5, the optical path is bent by 90 degrees, and is incident on the shaping surface 4 a of the beam shaping prism 4 again. As described above, the shaping surface 4a is designed so that a part of the reflected light is generated. Therefore, the return light is partially reflected by the shaping surface 4a and is incident on the surface 4b of the beam shaping prism 4 at an incident angle of 36.94 °. And is emitted at a refraction angle of 65.49 deg (n2 = 1.51405).

  In this way, by refracting the surface 4b of the beam shaping prism 4, the optical axis of the return light having a wavelength of 650 nm can be separated from the optical axis of the return light having a wavelength of 405 nm.

  The return light having a wavelength of 650 nm emitted from the beam shaping prism 4 is condensed on the photodetector 9 by the detection lens 7, and a signal for controlling the light spot on the optical disk 12 such as a focus error and a track error is output based on the output. The information signal detected or recorded on the optical disc 12 is reproduced.

  Various known methods can be used as the signal detection method for controlling the light spot on the optical disc 12 for the light beam having a wavelength of 650 nm, and the light receiving surface shape of the photodetector 9 is limited to a specific shape. It is not something.

  Next, a light beam having a wavelength of 780 nm emitted from the laser chip 2b of the hybrid semiconductor laser 2 will be described.

  A light beam having a wavelength of 780 nm emitted from the laser chip 2b of the hybrid semiconductor laser 2 passes through the collimator lens 3 to become parallel light, and is incident on the shaping surface 4a of the beam shaping prism 4 and is partially reflected here. Then, when the reflected light is received by the monitoring photodetector 10, the amount of light emitted from the hybrid semiconductor laser 2 with a wavelength of 780 nm is monitored.

  The incident angle of the beam shaping prism 4 on the shaping surface 4a is such that the refraction angle at the shaping surface 4a is θ0, that is, 38.47 deg., At the wavelength 780 nm of the glass material BSL7 (manufactured by OHARA) of the beam shaping prism 4. From the refractive index n3 = 1.51062, it is set to 70.01 deg according to Snell's law.

  Thus, by setting the arrangement of the laser chip 2b of the hybrid semiconductor laser 2 and the angle of view to the collimator lens 3 so that the refraction angle at the shaping surface 4a of the beam shaping prism 4 becomes θ0, the laser chip 2b The optical axis of the light beam having a wavelength of 780 nm emitted from the laser beam can be combined with the optical axis of the light beam emitted from the blue semiconductor laser 1 after refracting the shaping surface 4 a of the beam shaping prism 4.

  The light beam having a wavelength of 780 nm emitted from the beam shaping prism 4 is shaped into a substantially circular intensity distribution of the elliptical light beam with a beam shaping ratio of 2.29 by the beam shaping function by the shaping surface 4a of the beam shaping prism 4, and the optical path by the mirror 11 Is bent 90 degrees.

  The light beam reflected by the mirror 11 passes through the wavelength selection filter 5. The wavelength selection filter 5 is set so as to limit the aperture in accordance with the numerical aperture of the objective lens 6 with respect to the light beam having a wavelength of 780 nm, and the light beam transmitted through the wavelength selection filter 5 is collected on the optical disk 12 by the objective lens 6. The light is erased, recorded or reproduced.

  On the other hand, the return light having a wavelength of 780 nm from the optical disk 12 is transmitted again through the objective lens 6 and the wavelength selection filter 5, the optical path is bent 90 degrees by the mirror 11, and enters the shaping surface 4 a of the beam shaping prism 4 again. As described above, the shaping surface 4a is designed so that a part of the reflected light is generated. Therefore, the return light is partially reflected by the shaping surface 4a and is incident on the surface 4b of the beam shaping prism 4 at an incident angle of 36.94 °. And is emitted at a refraction angle of 65.21 deg (n3 = 1.61062).

  In this way, by refracting the surface 4b of the beam shaping prism 4, the optical axis of the return light having a wavelength of 780 nm can be separated from the optical axis of the return light having a wavelength of 405 nm.

  The return light having a wavelength of 780 nm emitted from the beam shaping prism 4 is condensed on the photodetector 9 by the detection lens 7, and a signal for controlling a light spot on the optical disk 12 such as a focus error and a track error is output based on the output. The information signal detected or recorded on the optical disc 12 is reproduced.

  Various known methods can be used as the signal detection method for controlling the light spot on the optical disc 12 for the light beam having a wavelength of 780 nm, and the shape of the light receiving surface of the photodetector 9 is limited to a specific shape. It is not something.

  Here, as described above, when one common collimator lens 3 is used for each of the light fluxes having a wavelength of 780 nm, a wavelength of 650 nm, and a wavelength of 405 nm, the incident angle of view on the collimator lens 3 is set for each light flux. If equal, the shorter the wavelength, the greater the aberration. For this reason, in the present embodiment, the angle of view incident on the collimator lens 3 is reduced as the wavelength is shortened to reduce the degree of influence on the aberration characteristics.

  Thus, according to the present embodiment, by using one beam shaping prism 4 and utilizing the refraction of the shaping surface 4a, the optical axes of the three light beams having different wavelengths are made coincident with each other, and the surface 4b By utilizing refraction, the return light from the optical disk 12 is separated according to the wavelength, so that optical components can be reduced, and a small and inexpensive optical head can be obtained.

  In addition, this Embodiment is not limited to the said structure, A various deformation | transformation or change is possible. For example, in the above-described embodiment, the wavelength of the light beam emitted from the blue semiconductor laser 1 is greatly different from the wavelength of the light beam emitted from the hybrid semiconductor laser 2. Since the difference in the light receiving sensitivity of the detectors is also greatly different, the photodetector 9 for receiving the return light from the optical disk 12 of the light beam having a wavelength of 650 nm and the light beam having a wavelength of 780 nm emitted from the hybrid semiconductor laser 2 is made common, and the blue semiconductor The photodetector 8 that receives the return light from the optical disk 12 with a light beam having a wavelength of 405 nm emitted from the laser 1 has a different configuration, but the photodetector 9 and the photodetector 8 are used as a common photodetector. It is also possible to configure.

  In addition, instead of using one common collimator lens 3 for each of the light beams having a wavelength of 780 nm, a wavelength of 650 nm, and a wavelength of 405 nm, an independent collimator lens is arranged for each light beam, or a blue semiconductor laser is used. It is also possible to arrange two collimator lenses: a collimator lens for a light beam having a wavelength of 405 nm from 1 and a common collimator lens for a light beam having a wavelength of 650 nm and a light beam having a wavelength of 780 nm from a hybrid semiconductor laser.

  Further, the optical axes of the light beams directed toward the mirror 11 do not necessarily have to coincide with each other as long as a good spot can be formed on the optical disk 12 by the objective lens 9.

  Further, as shown in FIG. 1, a light beam having a wavelength of 650 nm and a wavelength of 780 nm oscillated from the hybrid semiconductor laser 2 and a light beam having a wavelength of 405 nm oscillated from the blue semiconductor laser 1 are passed through a collimator lens 3 to form a beam shaping prism. 4 is incident obliquely on the shaping surface 4a, the distances between the hybrid semiconductor laser 2 and the blue semiconductor laser 1 and the collimator lens 3 must be adjusted in units of μm.

  For this reason, preferably, two or more of the hybrid semiconductor laser 2, the blue semiconductor laser 1, and the collimator lens 3 are provided so that the position thereof can be adjusted in the optical axis direction. When it is difficult to provide the hybrid semiconductor laser 2 and the blue semiconductor laser 1 so that the position of the hybrid semiconductor laser 2 and the blue semiconductor laser 1 can be adjusted in the direction of the optical axis, as shown in FIG. 2, the hybrid semiconductor laser 2 or the blue semiconductor laser is used. 1 is arranged between the collimator lens 3 and the collimator lens 3 and the lens 14 can be adjusted in the direction of the optical axis, so that the hybrid semiconductor laser 2 and the blue semiconductor laser 1 and the collimator lens 3 can be adjusted. Adjust the distance in μm units.

  In FIG. 1, the single beam shaping prism 4 is configured. However, as shown in FIG. 3, the beam shaping prism 4 may be configured using two beam shaping prisms 401 and 402. As described above, when the beam shaping prism 4 is configured by using the two beam shaping prisms 401 and 402, the beam shaping prism 402 can cancel the optical axis change of the emitted light of the beam shaping prism 401 with respect to the wavelength variation. it can.

FIG. 4 is a diagram showing a schematic configuration of an optical system of an optical head according to a reference example developed together with the present invention.

In this reference example , a blue semiconductor laser chip 201 as a third laser light source that emits light having a wavelength of 405 nm as a third wavelength, and a second laser light source that emits light having a wavelength of 650 nm as a second wavelength. A laser chip 202, a laser chip 203 as a first laser light source that emits light having a wavelength of 780 nm as a first wavelength, and a photodetector 204 are arranged in the same package, and a laser / photodetector unit 20 is constituted.

  Hereinafter, in FIG. 4, light oscillating in a direction parallel to the paper surface will be referred to as P-polarized light, and light oscillating perpendicular to the paper surface will be referred to as S-polarized light.

  First, the light beam emitted from the blue semiconductor laser chip 201 in the laser / photodetector unit 20 will be described.

  The light beam emitted as P-polarized light from the blue semiconductor laser chip 201 is converted into parallel light by the collimator lens 3 and enters the beam shaping prism 4. Here, the shaping surface 4a of the beam shaping prism 4 is designed so that part of the P-polarized light and all of the S-polarized light are reflected with respect to light having a wavelength of about 405 nm. The reflected P-polarized light is received by the monitoring photodetector 10 and the amount of light emitted from the blue semiconductor laser chip 201 is monitored.

  The parallel light transmitted through the shaping surface 4a of the beam shaping prism 4 is shaped into an approximately circular intensity distribution of the elliptical light beam due to the astigmatic difference of the blue semiconductor laser chip 201 by the beam shaping function of the shaping surface 4a.

Here, in the present embodiment, since the beam shaping ratio is 2.55, as the glass material of the beam shaping prism 4, as with the above embodiment using BSL7 (by OHARA Inc.). In this case, since the refractive index n1 of the BSL7 at the wavelength 405 nm of the blue semiconductor laser chip 201 is 1.52972, when the refraction angle (θ0) at the shaping surface 4a of the beam shaping prism 4 is 38.47 deg. Since the beam shaping ratio = cos θ0 / cos θ1, the incident angle (θ1) with respect to the shaping surface 4a of the beam shaping prism 4 is 72.11 deg.

  The light beam shaped by refraction of the shaping surface 4a of the beam shaping prism 4 at a refraction angle (θ0) of 38.47 deg is emitted from the beam shaping prism 4 and is incident on the quarter-wave plate 21. The quarter-wave plate 21 has a function of converting linearly polarized light in the vicinity of a wavelength of 405 nm into circularly polarized light. A light beam converted from linearly polarized light of P-polarized light into circularly polarized light by the quarter-wave plate 21 is The optical path is bent 90 degrees by the mirror 11. In FIG. 4, for convenience of explanation, the image is rotated 90 degrees around the optical axis between the quarter-wave plate 21 and the mirror 11.

  The light beam reflected by the mirror 11 passes through the wavelength selection filter 5. The wavelength selection filter 5 is set so as to limit the aperture according to the numerical aperture of the objective lens 6 with respect to the light beam emitted from the blue semiconductor laser chip 201. The light beam that has passed through the wavelength selection filter 5 is condensed on the optical disk 12 by the objective lens 6, and information is erased, recorded, or reproduced.

  On the other hand, the return light from the optical disk 12 passes through the objective lens 6 and the wavelength selection filter 5 again, and the optical path is bent 90 degrees by the mirror 11, and is incident on the quarter wavelength plate 21 again to change from circularly polarized light to linearly polarized light. Converted. Here, since the return light is transmitted through the quarter wavelength plate 21 a total of two times in the forward path and the return path, the direction of the linear polarization in the return light transmitted through the quarter wavelength plate 21 is the linear polarization in the forward path. Is converted to S-polarized light orthogonal to the direction of.

  The return light converted into S-polarized light by the quarter wavelength plate 21 enters the shaping surface 4 a of the beam shaping prism 4. Here, since the shaping surface 4a is designed so as to reflect all the S-polarized light as described above, all the return light incident on the beam shaping prism 4 is reflected by the shaping surface 4a to be reflected by the beam shaping prism 4. The light is emitted from the surface 4b.

  The return light emitted from the surface 4b of the beam shaping prism 4 is collected on the photodetector 8 by the detection lens 7, and the light spot on the optical disk 12 such as a focus error and a track error is controlled based on the output. A signal is detected or an information signal recorded on the optical disk 12 is reproduced.

  As a signal detection method for controlling the light spot on the optical disc 12, various conventionally known methods can be used, and the shape of the light receiving surface of the photodetector 8 is not limited to a specific shape.

  Next, a light beam having a wavelength of 650 nm emitted from the laser chip 202 in the laser / photodetector unit 20 will be described.

  The P-polarized light beam having a wavelength of 650 nm emitted from the laser chip 202 passes through the collimator lens 3 and becomes parallel light and enters the shaping surface 4 a of the beam shaping prism 4. Here, the shaping surface 4a is designed to partially reflect P-polarized light and transmit all S-polarized light with respect to light having a wavelength of about 650 nm. P-polarized light that is partially reflected by the shaping surface 4a. Is received by the monitoring photodetector 10 and the amount of light emitted from the laser chip 202 is monitored.

  The incident angle of the beam shaping prism 4 on the shaping surface 4a is such that the refraction angle at the shaping surface 4a is θ0, that is, 38.47 deg., At the wavelength 650 nm of the glass material BSL7 (manufactured by OHARA) of the beam shaping prism 4. From the refractive index n2 = 1.51405, it is set to 70.37 deg according to Snell's law.

  Thus, by setting the arrangement of the laser chip 202 and the angle of view to the collimator lens 3 so that the refraction angle at the shaping surface 4a of the beam shaping prism 4 becomes θ0, the wavelength of light emitted from the laser chip 202 is 650 nm. It is possible to combine the optical axis of the luminous flux with the optical axis of the luminous flux emitted from the blue semiconductor laser chip 201 after refracting the shaping surface 4 a of the beam shaping prism 4.

  The light beam having a wavelength of 650 nm emitted from the beam shaping prism 4 is shaped into a substantially circular shape by the beam shaping function by the shaping surface 4a of the beam shaping prism 4 so that the intensity distribution of the elliptical light beam is shaped into a substantially circular shape with a beam shaping ratio of 2.33. Incident on the plate 21.

Here, as described above, the quarter wavelength plate 21 is configured to function as a quarter wavelength plate with respect to a light flux in the vicinity of a wavelength of 405 nm, and thus the wavelength transmitted through the quarter wavelength plate 21. A light beam of 650 nm is in an arbitrary polarization state. In this reference example , the light beam having a wavelength of 650 nm that is transmitted through the quarter-wave plate 21 is not set to a specific polarization state. However, by setting the thickness d of the quarter-wave plate 21 appropriately, It can also be polarized or linearly polarized.

  The light beam transmitted through the quarter-wave plate 21 passes through the wavelength selection filter 5 after the optical path is bent 90 degrees by the mirror 11. The wavelength selection filter 5 is set so as to limit the aperture in accordance with the numerical aperture of the objective lens 6 with respect to the light beam having a wavelength of 650 nm, and the light beam transmitted through the wavelength selection filter 5 is collected on the optical disk 12 by the objective lens 6. The light is erased, recorded or reproduced.

  On the other hand, the return light having a wavelength of 650 nm from the optical disk 12 is transmitted again through the objective lens 6 and the wavelength selection filter 5, the optical path is bent 90 degrees by the mirror 11, and again transmitted through the quarter wavelength plate 21. The light again enters an arbitrary polarization state and enters the shaping surface 4 a of the beam shaping prism 4. Here, as described above, the shaping surface 4a is designed to partially reflect P-polarized light and transmit all S-polarized light with respect to light having a wavelength of about 650 nm. The return light incident on 4a is partially reflected by the shaping surface 4a, but almost all of it is emitted from the shaping surface 4a at a refraction angle of 70.37 deg.

  The return light having a wavelength of 650 nm emitted from the shaping surface 4a is condensed by the collimator lens 3 onto the photodetector 204 disposed inside the laser / photodetector unit 20, and the focus error and the error are determined based on the output. A signal for controlling a light spot on the optical disk 12 such as a track error is detected, or an information signal recorded on the optical disk 12 is reproduced.

  Various known methods can be used as the signal detection method for controlling the light spot on the optical disc 12 for the light beam having a wavelength of 650 nm. The shape of the light receiving surface of the photodetector 204 is limited to a specific shape. It is not something.

  In general, a so-called three-spot method is used as a track error signal detection method. In this case, as shown in FIG. 4, a diffraction grating 22 is arranged on the upper part of the laser / photodetector unit 20 to provide a light beam. Is divided into three to form three spots for track error signal detection.

  Next, a light beam having a wavelength of 780 nm emitted from the laser chip 203 in the laser / photodetector unit 20 will be described.

  The P-polarized light beam having a wavelength of 780 nm emitted from the laser chip 203 passes through the collimator lens 3 and becomes parallel light and enters the shaping surface 4 a of the beam shaping prism 4. Here, the shaping surface 4a is designed to partially reflect P-polarized light and transmit all S-polarized light with respect to light having a wavelength of about 780 nm. P-polarized light partially reflected by the shaping surface 4a. Is received by the monitoring photodetector 10 and the amount of light emitted from the laser chip 203 is monitored.

  The incident angle of the beam shaping prism 4 on the shaping surface 4a is such that the refraction angle at the shaping surface 4a is θ0, that is, 38.47 deg., At the wavelength 780 nm of the glass material BSL7 (manufactured by OHARA) of the beam shaping prism 4. From the refractive index n3 = 1.51062, it is set to 70.01 deg according to Snell's law.

  Thus, by setting the arrangement of the laser chip 203 and the angle of view to the collimator lens 3 so that the refraction angle at the shaping surface 4a of the beam shaping prism 4 is θ0, the wavelength of light emitted from the laser chip 203 is 650 nm. It is possible to combine the optical axis of the luminous flux with the optical axis of the luminous flux emitted from the blue semiconductor laser chip 201 after refracting the shaping surface 4 a of the beam shaping prism 4.

  The light beam having a wavelength of 780 nm emitted from the beam shaping prism 4 is shaped into a substantially circular shape by the beam shaping function by the shaping surface 4a of the beam shaping prism 4, and the intensity distribution of the elliptical light beam is shaped into a substantially circular shape with a beam shaping ratio of 2.29. Incident on the plate 21.

Here, as described above, the quarter wavelength plate 21 is configured to function as a quarter wavelength plate with respect to a light flux in the vicinity of a wavelength of 405 nm, and thus the wavelength transmitted through the quarter wavelength plate 21. The light beam of 780 nm is in an arbitrary polarization state as in the case of the light beam having a wavelength of 650 nm. In this reference example , the light beam having a wavelength of 780 nm transmitted through the quarter-wave plate 21 is not in a specific polarization state, but by appropriately setting the thickness d of the quarter-wave plate 21, Circularly polarized light or linearly polarized light can also be used.

  The light beam transmitted through the quarter-wave plate 21 passes through the wavelength selection filter 5 after the optical path is bent 90 degrees by the mirror 11. The wavelength selection filter 5 is set so as to limit the aperture in accordance with the numerical aperture of the objective lens 6 with respect to the light beam having a wavelength of 780 nm, and the light beam transmitted through the wavelength selection filter 5 is collected on the optical disk 12 by the objective lens 6. The light is erased, recorded or reproduced.

  On the other hand, the return light having a wavelength of 780 nm from the optical disk 12 is transmitted again through the objective lens 6 and the wavelength selection filter 5, the optical path is bent 90 degrees by the mirror 11, and again transmitted through the quarter wavelength plate 21. The light again enters an arbitrary polarization state and enters the shaping surface 4 a of the beam shaping prism 4. Here, as described above, the shaping surface 4a is designed to partially reflect P-polarized light and transmit all S-polarized light with respect to light having a wavelength of around 780 nm. The return light incident on 4a is partially reflected by the shaping surface 4a, but almost all of it is emitted from the shaping surface 4a at a refraction angle of 70.01 deg.

  The return light having a wavelength of 780 nm emitted from the shaping surface 4a is condensed by the collimator lens 3 onto the photodetector 204 disposed inside the laser / photodetector unit 20, and the focus error and the error are determined based on the output. A signal for controlling a light spot on the optical disk 12 such as a track error is detected, or an information signal recorded on the optical disk 12 is reproduced.

  Various known methods can be used as the signal detection method for controlling the light spot on the optical disc 12 for the light beam having a wavelength of 780 nm, and the shape of the light receiving surface of the photodetector 204 is limited to a specific shape. It is not something.

  In general, a so-called three-spot method is used as a track error signal detection method. In this case, as shown in FIG. 4, a diffraction grating 22 is arranged on the upper part of the laser / photodetector unit 20 to provide a light beam. Is divided into three to form three spots for track error signal detection.

Thus, according to this reference example, using a single beam shaping prism 4, by utilizing the refraction of the shaping surface 4a, are respectively emitted from the blue semiconductor laser chip 201, the laser chip 202 and the laser chip 203 Since the luminous fluxes are synthesized with substantially the same optical axis, these blue semiconductor laser chip 201, laser chip 202 and laser chip 203 can be easily accommodated in the same package, and a small and inexpensive optical head is obtained. be able to.

It is a figure which shows schematic structure of the optical system of the optical head which concerns on one embodiment of this invention. It is a figure for demonstrating the modification of FIG. Similarly, it is a figure for demonstrating the modification of FIG. It is a figure which shows schematic structure of the optical system of the optical head which concerns on the reference example developed with this invention.

Explanation of symbols

1 Blue semiconductor laser (third laser light source)
2 Hybrid semiconductor laser 2a Laser chip (second laser light source)
2b Laser chip (first laser light source)
3 Collimator lens 4 Beam shaping prism (light path synthesis means)
4a Shaped surface (refractive surface)
4b surface (second refracting surface)
DESCRIPTION OF SYMBOLS 5 Wavelength selection filter 6 Objective lens 7 Detection lens 8, 9 Photo detector 10 Photo detector for monitor 11 Mirror 12 Optical disk (optical recording medium)
14 Lens 401, 402 Beam shaping prism 20 Laser / photodetector unit 201 Blue semiconductor laser chip (third laser light source)
202 Laser chip (second laser light source)
203 Laser chip (first laser light source)
204 Photodetector 21 1/4 wavelength plate 22 Diffraction grating

Claims (9)

A first laser light source that oscillates at a first wavelength; a second laser light source that oscillates at a second wavelength; and a third laser light source that oscillates at a third wavelength. In an optical head that records, erases, or reproduces information by irradiating a light beam selectively emitted from the semiconductor laser through an optical recording medium through one common objective lens,
Refraction that combines at least two of the light beams emitted from the first to third laser light sources into substantially the same optical axis in the optical path between the first to third laser light sources and the objective lens. An optical path synthesizing unit having a surface is disposed, and the return light of the first to third wavelengths reflected by the optical recording medium is reflected by the refractive surface of the optical path synthesizing unit. A second refracting surface is provided that refracts the first to third wavelength return light reflected by the refracting surface, and the optical axis of the first to third wavelength return light is separated by the second refracting surface. An optical head characterized in that the optical head is constructed .   A first collimator lens that converts the light beam emitted from the first laser light source and the light beam emitted from the second laser light source into parallel light; and the light beam emitted from the third laser light source into parallel light. The optical head according to claim 1, further comprising: a second collimator lens.   2. The optical head according to claim 1, further comprising a common collimator lens that collimates the light beams emitted from the first to third laser light sources.   4. The optical head according to claim 1, wherein the refractive path of the optical path synthesizing unit shapes the shape of an incident light beam and guides it to the objective lens.   The optical head according to any one of claims 1 to 4, wherein the first to third laser light sources are accommodated in the same package.   The first laser light source and the second laser light source are accommodated in the same package, and at least two of the collimator lens, the package, and the third laser light source are provided so as to be positionally adjustable in the optical axis direction. The optical head according to claim 3.   The first laser light source and the second laser light source are accommodated in the same package, and the lens is disposed between the collimator lens and the package or between the collimator lens and the third laser light source. The optical head according to claim 3. The first to third wavelengths are first wavelength> second wavelength> third wavelength,
The first to first angles are set so that the incident angle of each wavelength on the refractive surface of the optical path synthesizing unit is the incident angle of the first wavelength <the incident angle of the second wavelength <the incident angle of the third wavelength. The optical head according to claim 1, wherein three laser light sources are arranged. The first to third wavelengths are first wavelength> second wavelength> third wavelength,
The first laser light source and the second laser light source are arranged so that light beams emitted from these laser light sources are incident on the collimator lens from the off-axis,
4. The optical head according to claim 3, wherein the third laser light source is disposed so that a light beam emitted from the laser light source is incident on the collimator lens from substantially on the axis.

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