JP4590660B2 - Optical pickup device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a reading device for an optical information recording medium such as an optical disk and a semiconductor laser device used as a light source of the optical pickup, and in particular compatible with DVD (Digital Versatile Disc) and CD-R (Compact Disc-write once). The present invention relates to a semiconductor laser device suitable for a reproduction system.
[0002]
[Prior art]
In recent years, higher density DVD systems have been proposed and commercialized for CDs, which are popular disk systems for consumer use, and have started to spread. In a DVD player as a playback device, compatible playback of a CD is indispensable in order to avoid duplication of devices and complicated use. Similarly, a compatible playback function is required for CD-R (Compact Disc-write once) that can be played back by a CD player. Therefore, various techniques for reproducing such optical discs of a plurality of types have been developed. Here, in particular, simplification of the configuration for realizing the above and cost reduction are problems.
[0003]
In particular, in the above-mentioned CD-R, since the reflectance of the recording medium has a large wavelength dependency, a semiconductor laser (laser light source) in a 780 nm band different from the 650 nm band for DVD is essential. Therefore, a pickup optical system incorporating the two-wavelength semiconductor laser is required.
[0004]
In view of the above, conventionally, two independent pickups are mechanically coupled, or a light receiving / emitting integrated element is independently attached to each wavelength and combined with the same optical axis by a dichroic prism, and some optical components such as an objective lens are combined. A system that shares the same system ("integrated DVD optical head": Mizuno et al., National Technical Report Vol.43 No.3 Jun. 1997 pp275-) has been developed. However, this type has the following problems: (1) the number of parts increases, (2) cannot be downsized, and (3) the position of each optical element needs to be adjusted.
[0005]
Therefore, in recent years, further attempts have been made to integrate the two-wavelength semiconductor lasers. That is, two types of semiconductor lasers that oscillate laser beams of the respective wavelengths are mounted in the same package, and other components are independent, but the optical axis is made common (1997 Autumn Applied Physics Society Preliminary Proceedings 4p-ZE). -5).
[0006]
In addition, proposals have been made in which not only two semiconductor lasers but also light receiving elements are integrated in the same package (Japanese Patent Application Laid-Open No. 10-21577 or Japanese Patent Application No. 10-297402).
[0007]
[Problems to be solved by the invention]
Among the pickups incorporating the above-mentioned two-wavelength semiconductor lasers, those in which both are integrated in the same package may be able to share all other optical systems, contributing to the downsizing of the pickup and the optical disk device. Possible and desirable.
[0008]
However, there is no semiconductor laser that emits two different wavelengths from the same emission point. Therefore, by placing two semiconductor lasers close and juxtaposed, both emission points are brought close to about 100 μm, and an attempt is made to ensure practical performance in such a way that the deviation from the ideal emission point position in the optical design is compromised. Attempts have been made to do this (1997 Autumn Fall Physics Society, 4p-ZE-5).
[0009]
As described above, when the emission point of the semiconductor laser is deviated from the ideal position, the following two types of problems occur.
[0010]
1. Problems with geometric optics (ray tracing) aberrations
In the lens design of the pickup optical system, the light beam emitted from the point light source is designed to converge again to one point on the disk surface at the design center. If the actual arrangement deviates from this condition, the light beam does not converge to one point strictly due to the occurrence of aberration. Therefore, a high-density optical disk system such as a DVD is designed so that almost no aberration occurs at least in ray tracing.
[0011]
In the optical disk system, only the objective lens normally has a movable range of about ± 0.5 mm because of a so-called tracking operation. Therefore, in the optical design, it is necessary to optimize the image height characteristics of the lens so that the aberration falls within a predetermined amount within this range.
[0012]
In the above optical system in which the two light emitting points are separated from each other by a certain distance, it is necessary to satisfy image height characteristics considering the distance in addition to the movable range of the objective lens. Although not detailed, this is possible by optical design.
[0013]
2. Problems related to misalignment of light intensity distribution
In a semiconductor laser, a light beam emitted from a light emitting point can be generally regarded as a spherical wave that diverges in all directions not shielded by the emission end face. However, the light intensity has an angular distribution, and generally shows a Gaussian distribution with a full width at half maximum of about 30 degrees × 10 degrees centering on the normal line of the emission end face.
[0014]
When the light emitting point of such a laser beam deviates from the optical ideal position, the light intensity distribution becomes asymmetric with respect to the center of the final exit pupil.
[0015]
3. These will be described in more detail as follows.
[0016]
FIG. 11 shows an example of an optical device including a semiconductor laser device in which two semiconductor lasers are placed close to each other and juxtaposed. More specifically, the optical device includes first and second semiconductor lasers 1 and 2 that are close to and juxtaposed with each other, and an objective lens 5 that converges the laser light from the semiconductor lasers 1 and 2 onto the optical disc 9. It is equipped with.
[0017]
Here, the light emitted from the light emission points 3 and 4 of the first and second semiconductor lasers is an extension of the geometrical central rays 7 and 8 connecting the light emission points 3 and 4 and the center 6 of the objective lens 5. It converges at two points 10 and 11 that intersect the 9 plane. As already described, the light emitting points 3 and 4 are close to, for example, about d = 100 μm.
[0018]
In the above-described geometric optical design, the deviation of light rays at the convergence points 10 and 11, that is, aberration is used as an index. That is, by performing an appropriate geometrical optical design, the aberration is suppressed within a practical range with respect to the deviation d of the light emitting points 3 and 4 to some extent.
[0019]
FIG. 12A shows an intensity distribution center ray (that is, a locus of the intensity distribution center) 14 of the emitted light 12 emitted from the second semiconductor laser 2 in FIG. As already described, the intensity distribution of the outgoing light 12 of the second semiconductor laser 2 has a center in the normal direction of the outgoing end face 2 a of the second semiconductor laser 2. Accordingly, the intensity distribution center ray 14 passes through a position deviated from the center of the objective lens pupil as shown in FIG. 12A, and reaches the condensing point at an angle different from the center ray 8 in FIG. .
[0020]
FIG. 12B shows the intensity distributions 15 and 16 of the emitted light from the first and second semiconductor lasers 1 and 2 with respect to the position of the objective lens pupil 51. As can be seen from this figure, the intensity distribution 15 of the emitted light from the first semiconductor laser 1 in which the geometric optical center ray and the intensity distribution center ray coincide with each other is symmetrical with respect to the center 51 a of the objective lens pupil 51. . On the other hand, the intensity distribution 16 of the emitted light 12 from the second semiconductor laser 2 in which the intensity distribution center ray does not coincide with the geometric optical center ray is asymmetrical with respect to the center 51a of the objective lens pupil 51. Become.
[0021]
FIG. 13A shows an optical device shown in FIG. 11 or FIG. 12, in which the objective lens 5 is moved from a position represented by a dotted line (position in FIGS. 11 and 12) to a position represented by a solid line. In this example, the geometrical optical central ray 8 and the intensity distribution central ray 14 coincide with each other. In the figure, reference numeral 18 denotes a convergence point of the emitted light from the second semiconductor laser 2.
[0022]
In this case, as shown in FIG. 13B, the intensity distribution 16 of the emitted light from the second semiconductor laser 2 is symmetrical with respect to the center 51a of the objective lens pupil 51, but the first semiconductor laser 1 The intensity distribution 15 of the emitted light from the lens is asymmetrical with respect to the center 51 a of the objective lens pupil 51.
[0023]
Thus, in the semiconductor laser device, when the intensity distribution of the emitted light is asymmetrical with respect to the center of the objective lens pupil, the following various problems (1) to (4) occur in the optical pickup using the same. . That is,
(1) The tracking error signal of the so-called push-pull method, in which the light beam is divided into two in the radial direction of the disk in the far field and the difference between them is taken, the intensity balance of the left and right components is lost and an offset occurs.
[0024]
(2) The tracking error signal of the so-called DPD (Differential Phase Detection) method in which the light beam is divided into four in the disk radial direction and the tangential direction in the far field, and the phase comparison is performed between the sums of the diagonal components. The intensity balance of components is lost, and signal quality and accuracy are degraded.
[0025]
(3) For example, in a recordable optical disk, the change in the amount of outgoing light emitted within the movable range of the objective lens is increased, so that the total light amount of the focused spot on the surface of the recording medium is reduced at the end of the movable range and sufficient recording power is obtained. In other words, the quality of the signal recorded at the time of moving the lens is deteriorated and the error rate is deteriorated.
[0026]
(4) A change in the amount of light reaching the light receiving element in the objective lens movable range becomes large. That is, the change accompanying the lens movement of the RF (reading) signal and the focus / tracking signal level increases. Thereby, the lens movable range in which stable operation is possible is narrowed, or the stability of the detection operation is deteriorated at the end of the movable range. In particular, since the light intensity center deviates from the pupil center as described above, the signal level is suddenly lowered on one side of the movable range, and thus the above-described problem occurs.
[0027]
In the two-wavelength semiconductor laser mounting system as described above, both semiconductor lasers are generally not used at the same time. Therefore, it can be considered that the problem of the intensity distribution center shift can be avoided by moving the reference position of the lens with respect to the semiconductor laser to be used.
[0028]
However, in an actual pickup optical device, the objective lens 5 is mounted on an actuator and is positioned at a mechanical neutral point with a driving voltage of 0, and a positive / negative voltage is applied in accordance with the tracking servo operation, and the neutral lens is neutralized accordingly. It can move in both directions. Therefore, in the method of changing the reference position depending on the semiconductor laser to be used, a DC voltage that always holds the reference position on at least one of them is always required, and there is a problem that the movable range cannot be made uniform. Absent.
[0029]
Therefore, in such a two-wavelength semiconductor laser juxtaposed optical system, it is desired to correct the light intensity distribution without depending on the movement of the lens reference position.
[0030]
  In other words, the object of the present invention is to make the intensity distribution centers of both lasers substantially coincide with each other even in an arrangement in which a certain amount of intervals between the emission points of two different wavelength semiconductor lasers exists.Optical pickupIs to provide a device.
[0031]
[Means for Solving the Problems]
  In order to achieve the above object, the present inventionOptical pickupThe deviceA first laser beam having a first oscillation wavelength is emitted from a first emission point.First semiconductor laserAnd a second laser beam disposed in the vicinity of the first semiconductor laser and having a second oscillation wavelength different from the first oscillation wavelength is emitted from a second emission point.Second semiconductor laserHaveSemiconductor laser deviceA collimating lens that collimates the first laser light emitted from the first light emitting point and the second laser light emitted from the second light emitting point, and the collimating lens that has passed through the collimating lens. An objective lens for condensing each of the first laser beam and the second laser beam.,The optical axis of the second laser beam that has passed through the collimating lens passes through the lens center of the objective lens and is parallel to the line connecting the second light emitting point and the lens center of the collimating lens. The optical axes of the second laser light emitted from the second light emission point and the optical axes of the first laser light emitted from the first light emission point are in the relationship. The optical axis of the second laser light emitted from the second light emitting point is inclined at a predetermined angle with respect to the optical axis of the objective lens so as to move away from the point. Is.
[0032]
  In addition, the present inventionOptical pickupThe apparatus is the second semiconductor laser.In the semiconductor laser device so that the optical axis of the second laser light emitted from the second light emitting point is inclined at the predetermined angle with respect to the optical axis of the objective lens.FixedHas beenIt is characterized by this.
[0033]
  Furthermore, the present inventionOptical pickupThe deviceThe second semiconductor laser is:Laser resonatorConstructionStripePartThePossess,In the stripe portion, the direction in which the stripe portion extends is the predetermined angle with respect to the optical axis of the objective lens.SlopeIt is tilted in the direction ofIt is characterized by this.
  Furthermore, the present inventionOptical pickupThe apparatus is the firstas well asSecond semiconductor laserEach have opposing surfaces facing each other, and the opposing surface of the first semiconductor laser and the opposing surface of the second semiconductor laser are parallel to each other.It is characterized by this.
[0034]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to FIGS. Note that similar drawing numbers are used for similar elements throughout the drawings.
[0035]
1 and 2 show a first embodiment of the present invention. As shown in FIG. 1, the semiconductor laser device according to the first embodiment includes first and second semiconductor lasers 1 and 2 that are close to and juxtaposed with each other. The optical pickup including the semiconductor laser device includes an objective lens 5 that converges the light emitted from the semiconductor lasers 1 and 2 onto the optical disk (optical information recording medium) 9. The first and second semiconductor lasers 1 and 2 emit first and second laser beams having first and second wavelengths (for example, 650 nm and 780 nm) which are different from each other.
[0036]
  Light emitting point 3 of the first semiconductor laser 1(First emission point)The central ray passing through the center 6 of the objective lens 5 is located on the optical axis L of the objective lens 5, and its emission end face 1a is also perpendicular to the optical axis L.
[0037]
  On the other hand, the second semiconductor laser 2 is disposed at a position away from the first semiconductor laser 1 by a certain distance (to the left in the drawing). The emission end face 2a is disposed so as to be inclined by an angle 20b with respect to the plane 53 orthogonal to the optical axis L. This inclination angle 20b is the light emitting point 4 of the second semiconductor laser 2.(Second light emission point)And the geometrical central ray 8 connecting the objective lens center 6 and the optical axis L of the objective lens 5 are set to be equal to an angle 20a. Thereby, the geometrical central ray 8 incident on the objective lens center 6 from the light emitting point 4 coincides with the normal line of the emission end face 2a.
[0038]
As described above, the distance between the first and second semiconductor lasers 1 and 2 is, for example, that the distance between the light emitting points 3 and 4 of the first and second semiconductor lasers 1 and 2 is about 100 μm. It will be.
[0039]
FIG. 2A shows an intensity distribution center ray 14 of emitted light emitted from the second semiconductor laser 2 in the arrangement of FIG. As shown in FIG. 2A, in the arrangement, the intensity distribution center ray 14 coincides with the geometric center ray 8 passing through the objective lens center 6.
[0040]
Therefore, as shown in FIG. 2B, in the arrangement, the intensity distribution 16 of the second semiconductor laser 2 is symmetric with respect to the center 51 a of the objective lens pupil 51. Of course, in the arrangement, the intensity distribution 15 of the first semiconductor laser 1 is symmetric with respect to the center 51a of the objective lens pupil 51 (this is the same as in the case of FIG. 11). Therefore, in this case, as illustrated, the center position of the intensity distribution 16 of the second semiconductor laser 2 coincides with the center position of the intensity distribution 15 of the first semiconductor laser 1.
[0041]
As described above, in the first embodiment, by adjusting the arrangement (orientation) of components, even when two different semiconductor lasers 1 and 2 are placed close to each other (with a predetermined distance apart), both semiconductor lasers are arranged. The light intensity distribution of the emitted light from 1 and 2 can be made symmetric with respect to the center 51a of the objective lens pupil 51, and the center positions can be made to coincide with each other.
[0042]
Incidentally, the optimum value of the inclination angle 20b is determined in more detail according to the selection of the system to be applied and the characteristics to be controlled. This will be described as follows.
[0043]
1. When solving “offset of tracking error detection signal of push-pull method” or “degradation of quality / accuracy of tracking error detection signal of DPD method” (problem described in the section of [Problems to be solved by the invention] ( (See 1) and (2))
In this case, the inclination angle 20b is determined so that the light intensity distribution in the objective lens pupil 51 is substantially symmetric with respect to the pupil center 51a.
[0044]
That is, in this case, the light intensity distribution 15 due to the light emitted from the first semiconductor laser 1 and the light intensity distribution 16 due to the light emitted from the second semiconductor laser 2 are both at the center 51 a of the objective lens pupil 51. On the other hand, at least one of the emission directions of the first and second semiconductor lasers 1 and 2 is inclined with respect to the optical axis L by a predetermined angle so as to be substantially symmetrical.
[0045]
2. When solving “degradation of signal quality / deterioration of error rate when moving objective lens on recordable optical disk” (see problem (3) described in [Problems to be solved by the invention])
In this case, the distribution in the pupil is not a problem. Rather, the total light amount after passing through the pupil (integrated value of the intensity distribution) and the change of the total light amount with respect to the movement of the objective lens are important. Therefore, from the standpoint of securing the allowance for the objective lens movement, the amount of emitted light at the center of the movable range of the objective lens 5 is determined to be maximum.
[0046]
In other words, in this case, at the center of the movable range of the final exit pupil 51, the final exit pupil light output by the first semiconductor laser 1 and the final exit pupil light output by the second semiconductor laser 2 are both substantially maximum. Thus, the inclination angle (with respect to the optical axis L) of at least one of the emission directions of the first and second semiconductor lasers 1 and 2 is determined.
[0047]
3. When solving the problem of “decrease in the level of RF (reading) signal and focus tracking signal (according to lens movement) due to a change in the amount of light reaching the light receiving element in the movable range of the objective lens” ([Problem to be Solved by the Invention] ] Refer to the problem (4) described in the section)
In this case, the change in the total amount of light is a problem as in the case 2 above, but the amount of light reflected from the medium reaches the light receiving element, that is, the “reciprocal” light path, not the light amount of the “outward path” to the recording medium. A change in the amount of light at the final stage becomes a problem.
[0048]
In the case where the central ray incident on the objective lens 5 is inclined as in the above-described embodiment, there is a “deviation” between the light beam position at the time of exiting the objective lens and at the time of re-incidence (after reflection by the medium), “Kerare” occurs only on the return path. Therefore, the slope optimum value at the center of the intensity distribution may be different from the former.
[0049]
Therefore, in this case, at the center of the movable range of the objective lens 5, the amount of light received by the photodetector from the optical disk (optical information recording medium) 9 by the first semiconductor laser 1, and the second semiconductor At least one of the emission directions of the first and second semiconductor lasers (optical axis L) so that the amount of light received by the photodetector with respect to the reflected light from the optical disk 9 by the laser 2 is substantially maximized. To determine the tilt angle.
[0050]
3 and 4 show a second embodiment of the present invention. As shown in FIG. 3, in this embodiment, the position of the objective lens 5 is shifted to the left from the optimum position (position indicated by the dotted line in FIG. 3) with respect to the light emitting point 3 of the first semiconductor laser 1. It is arranged at a substantially central position between 3 and 4 (position indicated by a solid line in FIG. 3).
[0051]
Further, as shown in FIG. 4, the first and second semiconductor lasers 1 and 2 are inclined so that the normal lines of the emission end faces 1a and 2a passing through the light emitting points 3 and 4 pass through the objective lens center 6. ing. More specifically, an optical axis L through which the geometrical central rays 7 and 8 connecting the emission points 3 and 4 of the first and second semiconductor lasers 1 and 2 and the objective lens center 6 pass perpendicularly through the objective lens center 6. Are 21a and 22a, and 21b and 22b are angles formed by the exit end faces 1a and 2a and the plane 53 orthogonal to the optical axis L, so that the angles 21b and 22b are equal to the angles 21a and 22b. The first and second semiconductor lasers 1 and 2 are tilted.
[0052]
As shown in FIG. 4B, also in this case, the intensity distributions 15 and 16 of the emitted light from the first and second semiconductor lasers 1 and 2 are symmetrical with respect to the objective lens pupil center 51a. In addition, the center positions of the respective intensity distributions coincide with each other.
[0053]
In the first embodiment, the geometric optical aberration is largely applied to the second semiconductor laser, whereas in the second embodiment, the arrangement is assigned to both. As described above, the positional relationship between each light emitting point and the objective lens can be freely arranged depending on the tolerance for aberration of the system (for example, DVD and CD) which each semiconductor laser is responsible for. One of them may be placed at the optimum position, or the “deviation amount” may be distributed at an appropriate ratio in consideration of each tolerance.
[0054]
Next, an example in which the present invention is applied to a so-called infinite optical system will be described.
[0055]
First of all, the problems of the infinite optical system in the prior art will be explained.
[0056]
5 and 6 show an example of an infinite optical system in the prior art.
[0057]
In general, an optical pickup such as a DVD that requires high density and high integration accuracy employs an infinite optical system in which a laser beam is once converted into a parallel light beam by a collimator lens and then a part of the light is condensed by an objective lens. There are many cases. In this method, even when the objective lens is moved by the above-mentioned actuator accompanying the tracking operation, the light beam incident on the objective lens is a parallel light beam whose inclination does not always change. There is an advantage that does not increase.
[0058]
FIG. 5 shows an example of an optical pickup of an infinite optical system in the prior art.
As shown in FIG. 5, this optical pickup is roughly composed of a first semiconductor laser 1, a second semiconductor laser 2, a collimator lens 26, and an objective lens 5. Reference numeral 9 denotes an optical disk.
[0059]
As shown in FIG. 5, in this example, the collimator lens 26 and the objective lens 5 are arranged with reference to the first semiconductor laser 1. That is, the light emitting point 3 of the first semiconductor laser 1 is arranged on the optical axis L passing through the center 26 a of the collimating lens 26 and the center 6 of the objective lens 5. Therefore, the central ray 7 from the light emitting point 3 also passes on the optical axis L.
[0060]
On the other hand, the light emitting point 4 of the second semiconductor laser 2 is arranged at a position shifted from the optical axis L (to the left in the drawing). Therefore, the emitted light from the second semiconductor laser 2 follows the inclination of a straight line connecting the light emitting point 4 and the center 26a of the collimating lens 26, and as shown in FIG. Is incident on. A geometrical central ray 8 with respect to the objective lens 5 is defined as a straight line 8 having the inclination and passing through the objective lens center 6, and a condensing point 11 is formed on an extension line of the straight line.
[0061]
FIG. 6 shows the behavior of the intensity distribution of the emitted light from the first and second semiconductor lasers 1 and 2 in this example.
[0062]
6A shows an intensity distribution center beam 14 of laser light emitted from the second semiconductor laser 2 in particular (13 is an intensity distribution of laser light emitted from the first semiconductor laser 1). Shows the central ray). As already described, the intensity distribution central ray 14 coincides with the normal line of the emission end face 2 a of the second semiconductor laser 2. Therefore, the intensity distribution central ray 14 that is the normal line of the second semiconductor laser emitting end face 2a is incident on the collimator lens 26 at a point 26b that is a fixed distance away from the collimator lens center 26a (equal to the emission point interval). After that, the intensity distribution center ray 14 enters the objective lens 5 following the inclination of the parallel light flux, and passes through the point 5b which is also away from the center 6 of the objective lens 5, and reaches the condensing point 11.
[0063]
FIG. 6B shows the intensity distribution 15 of the emitted light from the first semiconductor laser 1 and the intensity distribution 16 of the emitted light from the second semiconductor laser 2 with respect to the objective lens pupil 51. As shown in FIG. 6B, the intensity distribution 16 of the emitted light from the second semiconductor laser 2 is shifted from the center of the objective lens 6 by the deviation from the center 6 of the objective lens with respect to the center 51a. Left and right asymmetry. The intensity distribution 15 of the emitted light from the first semiconductor laser 1 is symmetrical with respect to the center 51a in the range of the objective lens pupil 51.
[0064]
In FIG. 5, since the light beam that has passed through the end of the collimator lens 26 is disposed so as to pass through the inside of the objective lens 5, so-called “vignetting” occurs in which light does not enter a part of the objective lens pupil 51. It has a configuration. However, although not described in detail, a design that avoids this is possible.
[0065]
When the behavior of the geometrical central ray 8 and the intensity distribution central ray 14 in such an infinite system is compared with the case of the finite system in FIGS. When the semiconductor laser 2 is shifted to the left in the drawing, the convergence point 11 on the optical disk 9 is shifted to the right in the drawing. However, in the finite system, the intensity distribution center ray 14 passes through a point shifted leftward in the drawing with respect to the objective lens center 6 (FIG. 12), whereas in the infinite system, the collimator lens and the objective lens. Is longer than the focal length of the collimator lens, it passes through a point shifted to the right in the drawing with respect to the center 6 (FIG. 6). Therefore, it can be seen that the deviation of the light intensity distribution to be corrected can occur in the opposite direction with respect to the objective lens pupil 51.
[0066]
In order to apply the present invention to such an infinite system, the following may be performed. That is, for example, in the configuration shown in FIG. 5, the geometrical central ray 8 passing through the objective lens center 6 is traced in reverse, and a point 27 where the central ray 8 passes through the collimating lens 26 is indicated as the semiconductor laser 2. The direction of the second semiconductor laser 2 is determined so that the central ray of the intensity distribution of the emitted light from the light passes through.
[0067]
7A and 7B show a third embodiment of the present invention. The third embodiment is an example in which the present invention is applied to the infinite system. FIG. 7 (b) is an enlarged view of a portion indicated by numeral 55 in FIG. 7 (a).
[0068]
As shown in FIG. 7A, the configurations of the first semiconductor laser 1, the collimator lens 26, and the objective lens 5 of the third embodiment are substantially the same as those shown in FIG.
The second semiconductor laser 2 is also adjacent to and juxtaposed on the left side with respect to the first semiconductor laser 1. However, the laser emission end face 2a of the second semiconductor laser 2 is inclined outward by an inclination angle 23b with respect to the surface 53 orthogonal to the optical axis L. Here, the inclination angle 23b is determined so that the geometrical central ray 8 between the light emitting point 4 and the collimator lens 26 is equal to the angle 23a formed with the optical axis L. More specifically, the geometrical central ray 8 is determined as a ray parallel to a straight line connecting the light emitting point 4 and the collimator lens center 26a and passing through the center 6 of the objective lens 5, as shown in FIG. Passes the point 27 on the collimating lens 26. Therefore, the geometrical central ray 8 overlaps with a straight line connecting the light emitting point 4 and the point 27 between the light emitting point 4 and the collimator lens 26. Therefore, when the angle formed by the straight line connecting the light emitting point 4 and the point 27 with the lens optical axis L is 23a, the tilt angle 23b is determined to be equal to the angle 23a.
[0069]
Thereby, the positions of the intensity distribution central ray 14 and the geometrical central ray 8 from the second semiconductor laser 2 coincide with each other. Accordingly, the laser light intensity distributions from the first and second semiconductor lasers 1 and 2 are symmetric with respect to the center of the objective lens pupil, as in the first and second embodiments, and Match each other.
[0070]
8 (a) and 8 (b) show a fourth embodiment of the present invention.
[0071]
In the case of the third embodiment, as shown in FIG. 7B, the first and second semiconductor lasers 1 and 2 are inclined in the direction in which the light emitting points 3 and 4 are separated from each other. Therefore, the clearance c between the two semiconductor lasers 1 and 2 is reduced (than the normal arrangement even at the same emission point interval), which may be disadvantageous in terms of assembly tolerance accuracy. The fourth embodiment solves the problem of the third embodiment (that is, the problem that the clearance c between the two semiconductor lasers 1 and 2 decreases). FIG. 8B is an enlarged view of a portion indicated by reference numeral 57 in FIG. 8A.
[0072]
In the fourth embodiment, the configurations of the first semiconductor laser 1, the collimator lens 26, and the objective lens 5 are substantially the same as the configurations of the first semiconductor laser, the collimator lens, and the objective lens of the third embodiment. It is. Further, the second semiconductor laser 2 is also close to and juxtaposed on the left side (in the drawing) with respect to the first semiconductor laser 1. However, in the fourth embodiment, instead of inclining the outer shape of the second semiconductor laser 2 including the emission end face 2a, only the waveguide stripe 28 of the semiconductor laser is set at a predetermined angle 24b with respect to the normal line of the emission end face 2a. It is tilted. The laser emission end face 2a of the second semiconductor laser 2 is made parallel to the surface 53 perpendicular to the optical axis L. The inclination angle 24b is determined so that the central beam 14 of the intensity distribution of the emitted light from the second semiconductor laser 2 passes through the point 27 on the collimator lens, as in the third embodiment.
[0073]
Specifically, the inclination angle 24b is determined as follows.
[0074]
Similarly to the third embodiment, the angle formed by the geometrical central ray 8 from the light emitting point 4 to the point 27 with the optical axis L is 24a.
[0075]
By the way, normally, both end faces of the first and second semiconductor lasers 1 and 2 are perpendicular to the waveguide stripe to form both reflection surfaces of the laser resonator. Here, if the angle formed by the end faces of the semiconductor lasers 1 and 2 and the stripe 28 is shifted from a right angle by a minute angle, the emission intensity center is shifted by a larger angle. That is, assuming that the emission angle deviation in the air is θ1, the stripe inclination angle is θ2, the air refractive index is n (= 1), and the semiconductor laser waveguide effective refractive index is N (= about 3 to 4). From Snell's law
n sin θ1 = N sin θ2 (1)
The relationship holds.
[0076]
Therefore, the stripe inclination angle 24b is obtained by calculating θ2 by substituting the geometrically obtained inclination angle 24a of the geometrical central ray 8 for θ1 in the above equation (1). Thus, the intensity distribution center ray 14 coincides with the geometric center ray 8.
[0077]
Such a semiconductor laser can be manufactured by the following method. That is, since the laser end face is generally formed by cleavage according to the crystal orientation, for example, a mask in which the stripe structure is inclined by the inclination angle obtained by the above calculation with respect to the crystal orientation indicated by the orientation flat. The laser structure is formed through processes such as crystal growth and patterning.
[0078]
If the stripe inclination angle 24b is increased, a loss occurs when the stripe is reflected at the end face and recombined as backward guided light, and there is a concern about performance deterioration in laser operation. However, as apparent from the equation (1), the stripe inclination angle 24b can be a fraction of the actual deviation angle 24a of the central ray of the intensity distribution. Therefore, a practical solution can be obtained by optimizing the entire optical design.
[0079]
9 (a) and 9 (b) show a fifth embodiment of the present invention. In the fifth embodiment, the clearance c between the first and second semiconductor lasers 1 and 2 is ensured without using the stripe inclination as in the fourth embodiment. FIG. 9B is an enlarged view of a portion indicated by numeral 59 in FIG. 9A.
[0080]
The configuration of the fifth embodiment is substantially the same as the configuration of the third embodiment. That is, in this embodiment, the optimal direction of the intensity distribution center ray 14 and the direction of the stripe 28 are made to coincide with each other, and the emission end face 2a is perpendicular to these. Therefore, it is optically equivalent to the third embodiment. More specifically, the direction of the stripe 28 of the second semiconductor laser 2 is formed perpendicular to the emission end face 2a, and the emission end face 2a is inclined by an angle 25b with respect to the plane 53 perpendicular to the optical axis L. Yes. The inclination angle 25b is determined so that the geometrical central ray 8 traveling from the light emitting point 4 to the point 27 on the collimator lens is equal to an angle 25a formed with the optical axis L.
[0081]
However, in this fifth embodiment, in order to ensure the clearance c between the first and second semiconductor lasers 1 and 2, the side surface 2s1 that does not include the front and rear emission points of the second semiconductor laser 2 is provided on the other side. The chip shape is determined so as to be substantially parallel to the side surface 2s2 of the semiconductor laser. In this case, when the inclination angle of the intensity distribution center is 25a, the outer shape is a parallelogram having four sides that intersect at an angle of ((90 degrees) ± (angle 25a)).
[0082]
In order to manufacture the first and second semiconductor lasers 1 and 2, a normal semiconductor laser manufacturing process is performed, front and rear emission end faces are formed by cleavage, and a bar in which a large number of chips are connected horizontally is manufactured. After that, dicing is performed in a direction inclined by a predetermined angle with respect to the end face to form a chip. In addition, chips may be formed by etching or the like without using dicing. Further, if the material has an appropriate crystal orientation, a method of cleaving after selecting a cutting angle of the wafer may be used.
[0083]
According to the fifth embodiment, there is no fear of laser characteristic deterioration as in the fourth embodiment, and the clearance between the semiconductor lasers does not decrease as in the third embodiment.
[0084]
As already described, in the case of the finite system as in the first and second embodiments, the inclination of the laser intensity central beam 14 is so-called inward (see FIGS. 1 to 4), and the front of the semiconductor laser. Since the light emitting points 3 and 4 are close to each other, the method as in the embodiment 3-5 (or claims 5 and 6) is practically unnecessary and can be dealt with only by the inclination of the semiconductor laser as described above. (See claim 4).
[0085]
In the above embodiment, the final exit pupil of the optical device is the exit pupil 51 of the objective lens 5. However, the final exit pupil of the optical device is not limited to this, and a mirror, a pinhole, a lens barrel, and the like used in the optical device can be the final exit pupil.
[0086]
In the embodiment, the tilt angles 20b, 21b, 22b, 23b, and 25b of the semiconductor lasers 1 and 2 are the geometric center ray 8 (in the case of including a collimator lens, the geometric distance between the collimator lens and the light emitting point). It is assumed that the optical center ray 8) is set to be equal to the angles 20a, 21a, 22a, 23a, and 25a formed by the optical axis L, but this does not necessarily have to be exactly the same. As long as it is practically achievable, it should be almost equal. Similarly, the stripe inclination angle 24b of the fourth embodiment does not have to be exactly equal to the value determined by the expression (1), and may be almost equal.
[0087]
Although not particularly shown, when mounting these semiconductor lasers 1 and 2, one of the semiconductor lasers is mounted first, its position / orientation is recognized by image processing or the like, and tilted by a predetermined angle based on it. One semiconductor laser may be mounted.
[0088]
Alternatively, a surface on which both semiconductor lasers are mounted, for example, a submount semiconductor laser mounting pattern may be formed by inclining in advance and then mounted based on this. Furthermore, it can also be mounted on this pattern by using a so-called self-alignment method in which positioning is performed automatically using the surface tension of the fusion material.
[0089]
According to the first to fifth embodiments described above, even if there is an interval between the light emitting points of the two semiconductor lasers, deterioration in detection characteristics due to this is avoided, and DVD and CD-R compatible reproduction are performed. Or, recording can be realized satisfactorily.
[0090]
FIG. 10 shows a configuration in which the above embodiment is mounted on an optical pickup.
[0091]
The first and second semiconductor lasers 1 and 2 are mounted on the same plane on the submount 101 at an inclining position according to the above-described embodiment, and the interval between the light emitting points is about 100 μm. The submount 101 is further die mounted on the light receiving element substrate 102. A mirror 103 is also bonded to the light receiving element substrate 102 so as to face the laser. Both the emitted lights of the first and second semiconductor lasers 1 and 2 are optically path-converted upward by the 45 ° reflecting surface of the mirror 103 and are emitted vertically upward. Both of these are in the objective lens 5
On the other hand, with respect to the position of the center 6 of the objective lens, the geometrical central rays 7 and 8 passing there coincide with the central beam of the intensity distribution by the action of the semiconductor lasers 1 and 2 mounted on the tilt. Accordingly, in the pupil range of the objective lens 5, the intensity distribution center of both of them coincides with the objective lens center 6, and the intensity distribution is symmetric. These light beams form spots on the information recording surface of the optical disc 9 at condensing points 10 and 11 that are slightly separated from each other. Here, the total amount of light (optical power) at the spot is maximized at the center of the movable range of the objective lens 5 with respect to both of the two semiconductor lasers 1 and 2 by the action of the inclined mounting of the semiconductor lasers 1 and 2. A light amount of a predetermined value or more can be secured over the movable range.
[0092]
After that, these light beams are reflected by the optical disk 9 and re-enter the objective lens 5 through the reverse path, and then the first laser light is diffracted by the hologram 105 formed on the upper surface of the hologram element 104, It receives the lens action and enters the light receiving area 109. Similarly, the second laser light is diffracted by the hologram 106 formed on the lower surface of the hologram element 104, undergoes beam branching and lens action, and enters the light receiving region 109. Here, by properly designing and dividing the holograms 105 and 106 and the light receiving area 109, it is possible to obtain focus and tracking error signals necessary for the pickup operation, but details are omitted here. However, since the light intensity distribution in the objective lens pupil and thus in the diffracted light beam is made symmetric by the action of the tilted mounting of the semiconductor laser, each signal can be obtained even in a design where an error signal is obtained by simple equal area division. The intensity balance is maintained and good signal detection is possible. In addition, even with respect to the displacement of the objective lens, the signal intensity decrease at both ends of the movable range is suppressed evenly and in the minimum (in both directions).
[0093]
In the drawing, each component is drawn at a position different from the actual one (for explanation). For example, the light receiving element substrate 102 is further bonded to the package 110 and electrically wired, and then the hologram element 104. May be adhered to the upper part and hermetically sealed to form an integrated light receiving and emitting device, or of course separate components. These are incorporated in the pickup housing 111 together with the objective lens 5 mounted on an actuator (not shown) to constitute one optical pickup.
[0094]
【The invention's effect】
As described above, according to the present invention, even in an arrangement in which a certain amount of intervals between the emission points of different two-wavelength semiconductor lasers exists, the two-wavelength laser beams emitted from the respective semiconductor lasers are reflected in the objective lens pupil. The intensity distribution centers can be virtually matched. Therefore, characteristic deterioration due to the deviation can be avoided, compatible reproduction or recording of DVD and CD-R can be realized satisfactorily, and the recording / reproducing apparatus can be greatly downsized and simplified as compared with the conventional one.
[Brief description of the drawings]
FIG. 1 shows a first embodiment of the present invention.
FIG. 2 shows a light intensity distribution of emitted light from the first and second semiconductor lasers in the first embodiment of the present invention.
FIG. 3 shows a second embodiment of the present invention.
FIG. 4 shows a light intensity distribution of emitted light from the first and second semiconductor lasers in the second embodiment of the present invention.
FIG. 5 shows a conventional example of an optical pickup of an infinite optical system.
6 shows a state of light intensity distribution in FIG. 5. FIG.
FIG. 7 shows a third embodiment of the present invention.
FIG. 8 shows a fourth embodiment of the present invention.
FIG. 9 shows a fifth embodiment of the present invention.
FIG. 10 shows a configuration in which any one of the first to fifth embodiments is mounted on an optical pickup.
FIG. 11 shows an example of a conventional semiconductor laser device.
12 shows an intensity distribution of emitted light from the first and second semiconductor lasers in the semiconductor laser device of FIG.
FIG. 13 shows the semiconductor laser device shown in FIG. 11, wherein the objective lens is moved from the first and second semiconductor lasers when the objective lens is moved so as to be optimal with respect to the emitted light emitted from the second semiconductor laser. The intensity distribution of the emitted light is shown.
[Explanation of symbols]
1: First semiconductor laser
2: Second semiconductor laser
3: Luminescent point
4: Luminescent point
5: Objective lens
9: Optical disc
15, 16: Light intensity distribution
26: Collimator lens
28: Waveguide stripe
51: Objective lens pupil
51a: objective lens pupil center

Claims (4)

A first semiconductor laser that emits a first laser beam having a first oscillation wavelength from a first light emitting point , and a first semiconductor laser that is disposed in the vicinity of the first semiconductor laser, differing from the first oscillation wavelength A semiconductor laser device having a second semiconductor laser that emits a second laser beam having a second oscillation wavelength from a second emission point ;
A collimating lens that collimates the first laser light emitted from the first light emitting point and the second laser light emitted from the second light emitting point, respectively;
An objective lens for condensing each of the first laser light and the second laser light that has passed through the collimator lens;
With
The optical axis of the second laser beam that has passed through the collimating lens passes through the lens center of the objective lens and is parallel to the line connecting the second light emitting point and the lens center of the collimating lens. The optical axes of the second laser light emitted from the second light emission point and the optical axes of the first laser light emitted from the first light emission point are in the relationship. The optical axis of the second laser beam emitted from the second light emitting point is inclined at a predetermined angle with respect to the optical axis of the objective lens so as to move away from the point.
An optical pickup device characterized by that. The second semiconductor laser is fixed to the semiconductor laser device such that the optical axis of the second laser light emitted from the second light emitting point is inclined at the predetermined angle with respect to the optical axis of the objective lens. it has an optical pickup apparatus according to claim 1, wherein. It said second semiconductor laser has a stripe portion forming the laser cavity structure,
2. The optical pickup device according to claim 1 , wherein the stripe portion is formed such that a direction in which the stripe portion extends is inclined in a direction inclined by the predetermined angle with respect to an optical axis of the objective lens . The first and second semiconductor lasers have opposing surfaces that face each other,
4. The optical pickup device according to claim 1 , wherein a facing surface of the first semiconductor laser and a facing surface of the second semiconductor laser are parallel to each other . 5.

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