JPS58150146A - Optical pickup for optical disc - Google Patents

Abstract

PURPOSE:To reduce the weight of the optical system part of an optical pickup to be driven by an actuator to about 1/5 the weight of conventional optical pickups and to reduce the size thereof by separating a laser light source and a photodetector from said optical system part, connecting both by means of optical fibers and transmitting light beams between the same. CONSTITUTION:The exit light 5 from the 1st optical fiber 4 passes through a calcite plate 6 of which the polarizing direction of ordinary rays is matched to the direction of the linear polarizing direction thereof, whereafter the light is converted to parallel beams with the 1st combined lens 7. The parallel beams are focused with the 2nd combined lens 9, and the focused light is made incident to an optical disc 10. Incident light 11 is reflected as signal light 12 having recording information by the disc 10, and returns to the lens 9 and a 1/4 wavelength plate 8. The polarizing direction of the signal light 12 past the plate 8 intersects orthogonally the polarizing direction of the light 5 and since the signal light 12 propagates as abnormal rays in the plate 6, the light is separated from the optical path of the light 5 and is coupled to the 2nd optical fiber 13. The 2nd optical fiber 13 has the 1st-4th core parts, and the 1st- the 4th coupled beams of light are made incident to a photodetector 26 having the 1st-4th photodetecting surfaces.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical pickup used in an optical recording/reproducing disk device.

The optical system used in optical recording and reproducing disk devices consists of an optical polarization beam splitter, a light receiving element, etc., and a lens system that irradiates a focused light beam to the desired location on the optical disk surface. It consists of an actuator system that moves the. In order to operate the actuator system with low power consumption and to obtain good drive characteristics, the optical system to be operated must be small and lightweight. However, in conventional optical pickups, even when a semiconductor laser is used as a laser light source, it is necessary to install a heavy electric current for fMlk as a heat dissipation member and a large-volume metallic material 1R semiconductor laser, and the semiconductor laser, Each photodetector has a diameter of 4 mm and a length of 4 to 5 m.
The disadvantage was that the optical system could not be made sufficiently small or had a lid, as it had to be used in a hermetically sealed package of about 1.5 m in size.

The object of the present invention is to overcome these drawbacks and provide an optical pickup in which the optical system portion driven by the actuator can be made smaller and lighter.

According to the present invention, there is provided a laser source, a first optical fiber for transmitting the output light of the laser light source, and a first optical fiber for transmitting the output light of the laser light source; Light beam minute [element and.

A 1/4-wavelength detector, a condensing lens, and the output light focused by the condensing lens is reflected on the original disk surface and is then connected to the condensing lens, the 174-wave plate, and the polarization-dependent light beam separation element. An optical tiff-moonlight pickup is obtained that includes a second optical fiber that is coupled after passing through the second optical fiber tube, and a light receiving element that detects the output light emitted from the second optical fiber tube.

In the present invention, a laser light source and a light receiving element are separated from the optical system part of an optical pickup, and a gold optical fiber is connected between them to transmit a light beam.

Since the optical fiber is flexible, only a portion of the optical fiber close to the optical system or all together with the optical system is driven by the actuator. Moreover, the optical fiber is small in diameter and lightweight. For this reason.

The heavy electric power in the optical system portion driven by the actuator can be reduced to about 5 times the conventional size.

Next, the optical disc moonlight pickup according to the present invention will be explained in detail with reference to the drawings.

FIG. 1A is a sectional view for explaining a first embodiment of an optical pickup for an optical disk according to the present invention.

The first BIQ is a perspective view of the light receiving element, and the second BIQ is a perspective view of the light receiving element. FIG. 3 is a cross-sectional view of the first original fiber 4 and the second optical fiber 13, respectively, and FIGS. 4A, 4B, 2, and 5A-5F are cross-sectional views of the first source fiber 4 and the second optical fiber 13, and FIGS. FIG. 2 is a diagram illustrating the principle of obtaining information.

Directly spun polarized output light 2i1t of the semiconductor laser 1 used as a laser light source is coupled to a first optical fiber 4KM having polarization preservation property by a first coupling lens 3.

The emitted light 5 from the first optical fiber 4 adjusts the polarization direction of the enriched light beam to the direction of the linearly polarized light, passes through a friend calcite plate 6 (polarization-dependent light beam separation element), and then passes through a first combination lens 7 is converted into a parallel beam.

1mIII11 polarized light is converted into a circularly polarized beam with 174 wavelengths 8, and the second combination lens 9 (focusing lens)
The light is focused and incident on the original disk 10.

The incident light 11 is reflected as a signal light 12 that waits for recording information on the original disk 10 and passes through the second combination lens 9. Return to '74 wavelength plate 8. Signal light 12 is 1/4 long plate 8 and Takahi Nao? Returning to 1M polarization, when the incident light 11 is reflected by the optical disk 10, the direction of rotation of the circularly polarized light is reversed with respect to the traveling direction of the light, so the polarization direction of the signal light 12 that has passed through the quarter-wave plate 8 is orthogonal to the polarization direction of the emitted light 5. Therefore, the signal light 12 propagates as an extraordinary ray in the calcite plate 6, and is separated from the optical path of the incident light 5, and is connected to the second optical fiber 1.
Combine to 3.

The second original fiber 13 has the first to fourth core parts 14°15
．． 16,171-, each of the first to fourth core portions 1
4, 15, 16. 1st to 4th coupled light 18°1 to 17
9. 20 and 21 are expanded by the coupling lens 14 of group 2 after propagating through the second optical fiber 13, and are connected to the first to fourth light receiving surfaces 22.
．． The light is incident on the light receiving element 26 (photodiode) K provided at 23, 24, and 251.

Note that the first to fourth combined lights 25, 26, 27.28 are incident on the first to fourth light receiving surfaces 22, 23, 24.25, respectively ◎ Diameter of first and sg2 combination lenses 7.9 is 3 mm.

The lengths are 1.5 mm and 2.5 mm, respectively. The thickness of the calcite plate 6 is 2 mm, and the thickness of the quarter wavelength plate 8 is 1 mm.
So, these optical parts, and the first. second optical fiber 4
, 13 has a diameter of 4.5 mm and a length of 18 mm. The original head section 28 including these optical parts and the reference case 27t is driven by the actuator 29, and its storage weight is at most 4g.
It is lighter and smaller than the conventional example.

The core part 30 of the first optical fiber 4Fi as shown in FIG.
．． +'Ii 1-circle cladding part 31. It consists of a jacket part 32 made of quartz glass and a nylon shaft part 33. The diameter of the core portion 30 is 6 μm, the outer diameter of the jacket portion 32 is 125 μm, and the outer diameter of the covered portion 33 is 9.
It is 5mm. Since the circular cladding part 31 has a horizontally inner shape, stress is applied to the core part 30Kl, and as a result, it exhibits swimming refraction, and as a result, m and i polarized light are preserved.

The second original fiber 13 is as shown in FIG.

The first to fourth core parts 14.15, 16.17 and the surrounding cladding s34. and a nylon cracked transverse portion 33, the first to fourth core portions 14, 15° 16.1
The outer pole of the whole 7 is about 60 μm, and the outer diameter of the cladding part 34 is 1
The outer diameter of the transverse portion 33 is 9.5 mm. 1st
~The fourth core part 14.15, 16.17 and the cladding part 34 are made of quartz glass, and such a cross-sectional shape is 1
For example, it can be obtained by placing four core materials and a quartz plate separating them into a quartz tube with a diameter of 2 cIL and an inner diameter of 1 crrL, creating a preform similar in shape to the second optical fiber 13, and spinning the preform.

A method generally referred to as a track deviation detection method is used. 4A and 4B illustrate the principle of this method, and FIG. 4A is a plan view of the input end 39 of the second optical fiber 13.

FIG. 4B is a sectional view of the optical disc 10. Here, when the incident light 11 entering the information recording surface 35 of the optical disc 10 hits the information pit 36, the first . Second diffracted light 37.3
8 is generated as a side component of the signal light 12, and this first .
This takes advantage of the fact that the balance of the intensity of the second diffracted lights 37 and 38 changes depending on the track deviation. For example, in FIG. 4B, when the incident light 11 shifts in the positive direction of X, the second diffracted light component 38 becomes stronger, and as a result, the second optical core ino (
13 2nd. The sum of the intensities of the signal lights 12 coupled to the fourth core 1s15.17 increases. On the other hand, the incident light 11 is
If it shifts in the negative direction, the first. Third core part 14.1
The sum of the intensities of the signal lights 120 coupled to 6 becomes larger.

A method commonly called the Naifetsu method was applied to detect out-of-focus. Figures 5A to 5F are diagrams explaining the principle of this method, and Figures 5A and 5C.

5E is a plan view of the input end 39 of the optical fiber 13 of the sliding door 2, 5B, 5L), and ssE is a sectional view of the original disk 10 and the input end 13 of the original fiber 13. Also 8g5
Figures A and 5B are when the defocus is normal, Figures 5C and 5D
The figure shows a case in which the optical head section 28 is too far away from the optical disk 10, and conversely, a case in which the 5B and 5F sections are too close.

7JyI6 Sekii 6 has a refractive index for extraordinary rays smaller than that for ordinary rays, so the 58th rI! As shown in J%, the signal light 12 is transmitted to the second source fiber 13 from the fiber 11.
An image is formed in the negative direction of the Z axis by approximately 150 μm from the first surface 39. A knife 41 was placed near this imaging point 40. When the position of the information recording surface 35 of the optical disc 10 shifts in the Z-axis direction from the position of the imaging point 42 of the incident light 11, the imaging point 40 of the signal light 12 also shifts in the Z-axis direction. In this case, depending on the direction of the shift, the portion of the signal light 12 that is cut by the knife 41 changes as shown in Figures 5B, 5D, and 5F, and as a result, as shown in Figures 5A, 5C, and 5E. Each core portion 14, 15° 16 of the second optical fiber 13
．． The intensity ratio of the signal light 120 coupled to the signal light 17 changes.

That is, when the position of the information recording surface 35 deviates from the position of the imaging point 42 of the incident light 11 in the negative direction of the Z axis as shown in FIG. 5D, the first . Second core part 14.1
The components of the signal light 12 incident on the signal light 5 are traced, and the sum of their light intensities decreases. On the other hand, information recording side 35. is shifted in the positive direction of ZI11] as shown in FIG. 5F, the 3rd. The components of the signal light 12 incident on the fourth core portions 16 and 17 are blocked, and the sum of their light intensities is reduced.

Since the combinations of the core parts 14, 15, 16, 17 for detecting each deviation are different, the output laminate from each light receiving surface 22, 23, 24, 25 of the light receiving element 26 is detected for track deviation and defocus. By processing them separately, they can be detected independently of each other.

Figure WJ6 shows the second optical fiber 12 in the first embodiment.
It is a sectional view for explaining a modification of .

In this modification, an optical fiber east 43'f, which is a bundle of first to fourth small-diameter optical fibers 44, 45, 46, and 474 having a single core, is used instead of the second original fiber 13. ing. First to fourth circular core portions 48, 49, 50
．． 51 is the first to fourth cores gt4.51 in the second optical fiber 13. t5. Exactly the same function as xe and t7! Do t.

The outer diameters of the first to fourth small-diameter optical fibers 44, 45, 46, and 47 are each 50 μm, and the first to fourth circular core portions 48, 4
9,50.51 has an outer diameter of 40 μm.

All of them are quartz fiber glass fissures. The original fiber bundle 43 is covered with a bonded portion 33 made of nylon.

Although the optical fiber bundle 43 of this modification is easier to manufacture than the second optical fiber 13 in the first embodiment, the difference between the 48.49° and 50.51°
Since the distance between them is somewhat large, there is a drawback that the coupling loss of the signal light 12 is large.

Figure $7 is a sectional view for explaining the second embodiment of the present invention.

Second! j! In the example, the distance from the central axis it
has a refractive weight of 15 which decreases in proportion to the square of the first .
The second converging light transmitting bodies 52 and 53 were used in place of the first combination lens 7 and the second combination lens 9 in the first embodiment. As the second optical fiber 13, an optical fiber having a single core with a core diameter of 50 μm and whose input end 39 was rounded into a hemispherical shape was used. The light-receiving element 26 also had a single light-receiving surface. Other parts are the same as in the first embodiment.

In the second embodiment, the first. Second focusing optical transmission body 52.
The diameter of case 53 is 2mm, and the diameter of gold-woven case 27 is 3.9m.
m, the length is 12 mm, the weight of the optical head section 28 is 2 g, and the first! ! Compared to the embodiment, the original head portion 28 is further reduced in weight and size.

In the second embodiment, the method for detecting track deviation and defocus sound is based on the quabbling method. In other words, the optical head section 28' is moved slightly and at high speed in the ftJ direction and in two directions, and control is performed so that the light receiving element 26 of the signal light 12 has the highest manual power and the extinction ratio of the signal light 12 is maximized. In addition, as the actuator 29, φ Seiko was used for 1.

Input into the source fiber 13 of @2: Ia39e The reason why the signal light 12 is rounded into a hemispherical shape is that the signal light 12 concluding at a point in the negative direction of about 150 μmz from the input end 39 is most efficiently converted into the second source in that state. This is to enable coupling to the fiber 13.

As a result, due to the defocus K.

When the position of the imaging point 40 of the signal light 12 shifts in two directions, the amount of signal light 120 coupled to the optical fiber 13 of II2 decreases, regardless of the sign or negative of the shift, so it can be seen that only a focus shift has occurred. .

In addition to one or more embodiments of the invention, various modifications are possible. As a laser light source, a He-Ne laser may be used in addition to the σ semicircular laser. In addition to the calcite plate 6, lower prisms and quarastons can be used as polarization-dependent original beam splitting elements. Any device that can change the propagation direction of the light beam depending on the polarization direction can be used, such as a prism or a polarizing beam splitter.

Regarding the detection method of track deviation and focus deviation.

A second optical fiber 1 having a core cross-sectional shape similar to that of the light-receiving surface is placed at the light-receiving surface of the light-receiving element in the prior art.
By simply arranging the entrance surface 39, the method 1υ1 for detecting track deviation and defocus in the prior art can be applied as is. Therefore, in addition to the *m example above, for example, if the second optical fiber 13 used in the first embodiment is sandwiched between two single-core fibers, the track is called a three-beam method. A shift detection method can be applied.

The optical pickup of the present invention can be used not only for reading signals but also for writing signals.

As described in detail above, in the present invention, a single fiber is used to connect the optical system part of the optical pickup and the laser light source.
By separating the photodetector.

The optical head driven by the actuator can be made smaller than the IA of the conventional example by @1°, and can be made smaller.

[Brief explanation of the drawing]

FIG.
GR plane view and FIG. 1B are enlarged perspective views of the light receiving element. 2 and 3 are used in the first embodiment, respectively. Second optical fiber 4', 1, 1.7) Cross-sectional view, 4th
Figures A, 4B, and 5A to 5F are diagrams showing the principles by which track deviation and defocus are detected in the first embodiment, respectively. 1m7 is a sectional view showing a modification of No. 11! for explaining the second embodiment. It is an IT view. In the figure, 1... Semiconductor laser, 2...
・Light light of semiconductor laser 1, 4...first optical fiber, 28...former head section, 5...
@1 Output light from original fiber 4, 6... Calcite plate (polarization dependent light beam separation element), 8...1/
Two-wavelength plate, 7.9... Each 1st. 2nd combination lens, 52.53... each first. Second focusing optical transmission body, 10... Optical disk, 3
5... Information recording surface of optical disc 10, 12...
...Signal light, 13...Second source fiber,
14゜15.16.17... First to fourth core portions of second optical fiber 13, 43... Original fiber bundle, 26... Light receiving element be.

Claims (1)

[Claims] (11) A laser light source, a first optical fiber that transmits the output light of this laser light source, and polarized light arranged in order on the optical path of the optical output light emitted from this first optical fiber. a dependent beam separation element, a quarter-wave plate, a condenser lens, and the output light focused by the condenser lens is reflected by the optical disk surface and returned to the condenser lens, J!
II 174 wave plate, said polarization-dependent light beam 111 minutes
1. An optical pickup for an optical disk, comprising: a second optical fiber that is coupled after passing through the second original fiber; and a light-receiving element that detects the output light t emitted from the second original fiber. 12) The optical disc light output pickup according to claim 1, wherein a polarization preserving optical fiber is used as the first optical fiber. (3) An optical pickup for an optical disk according to claim 1 or 2, which uses an optical fiber having a plurality of cores as the second optical fiber. (41) Optical pickup for optical disks according to claim 1 or 2, using an optical fiber bundle consisting of a plurality of optical fibers as the second original fiber. (5) Polarization-dependent optical beam separation An optical pickup for an optical disk according to claim 3 or 4, wherein a birefringent crystal plate is used as a resistor.