JPH0264922A - Automatic focusing device - Google Patents

Abstract

PURPOSE:To prevent focus dislocation from being generated and to stabilize the retrieval of an objective address by detecting a focus error signal with an optical detector arranged in the middle of the image forming position of second and third beams along the optical path of both beams, and detecting a tracking error signal with an optical detector to receive a first beam. CONSTITUTION:A reflected beam having a primary light generated in parallel to the track direction of a disk is transmitted by a first reflecting surface 19a and defined as a first beam and a beam to be samely reflected is transmitted by a send reflecting surface 19b and defined as a second beam. A beam to be reflected by the second reflected surface 19b is bent by 90 deg. to the channel direction of the disk on a third reflecting surface 19c and divided so as to be defined as a third beam reflected in the disk side. Then, an optical detector 13 is set in the middle of the image forming position of the second and third beams and the focus error signal is detected. Even when the centers of these second beam and third beam are dislocated from the center of the first beam, the focus error signal can be detected without being affected by a primary diffracting light. Thus, the retrieval of the purpose address can be made stable.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an optical reproduction device that optically reads information recorded on an information recording medium such as a video disk, or an optical reproduction device that optically reads information recorded on an information recording medium such as a video disk. An optical system that uses reflected light from an information recording medium to obtain servo signals and playback signals for applying various servos. The present invention relates to an automatic focus adjustment device used in a recording/reproducing device.

2. Description of the Related Art In general, in video discs and optical recording and reproducing devices, in order to record and reproduce information at high density, the tracks on the disc are fine, for example, with a width of 0.6 μm and a pitch of 1.6 μm. It has a spiral or concentric circle shape. The disc is irradiated with a minute spot of light having a diameter of 1 μm or less, and information on the disc is read from the reflected light.

In such a device, at least two servo techniques are required. One is that as the disk rotates, it causes surface wobble in the direction perpendicular to the direction of rotation, but the optical system is designed so that the minute spot light narrowed to φ1 μm or less can always be irradiated onto the disk in response to the surface wobbling. This servo is called a focus servo. On the other hand, as the disk rotates, the track moves in the radial direction of the disk due to eccentricity, etc., but this servo makes the optical system follow this so that the minute spot light always illuminates the track. It is called a tracking servo.

The servo signal (error signal) for performing the seven orcus and tracking servos is obtained from the reflected light of the disk, and the specific optical system is shown in Figs. 3, 4, 6, and 7, for example. An optical system as shown has been proposed.

FIG. 6(IL) shows a front view of the optical system, and FIG. 6(b) shows a side view of the optical system. In FIG. 6, reflected light from the disk 7 is imaged by a convex lens 8. In FIG. When the splitting prism 12 is tilted in the image-forming optical path, the first reflected light obtained from the upper surface '121L of the splitting prism and the second reflected light obtained from the lower surface 12b are separated, and each light is detected. Guided to Vessel 13. Here, the split prism is, for example, 1
The light reflectance of the top surface 121L is Ra
, when the light transmittance is Ta and the light reflectance of the lower surface 12b is Rb, if each light reflectance and light transmittance are selected so as to have the relationship shown in the following equation (1), then the first The intensity of the reflected light is equal to the intensity of the second reflected light.

Ra = Ta2x Rb ・・・・・・・・・Song・
...(1) Said No. 1. The imaging position of the second reflected light is the sixth
As shown in the figure, the positions p, , p2 are shifted in the X direction by the optical path difference caused by the splitting prism.

A photodetector 13 having a detection surface 13 &~13f divided into 6 parts when viewed from the light incident direction is placed approximately at the center of both the image forming positions P1 and P2, and the divided photodetector 1
3) 14.15 is the photodetector 1 which is wider than the detection surface 13+5, 13b and has approximately the same diameter.
3 is irradiated. If the output current of the detection surfaces 131L to 13f of the photodetector 13 divided into six parts is Ia-If,
Focus error signal PK is calculated from equation (2) as follows: FX= (Ib+Id+I f ) −(Ia+Ic+
4e )-・-・-@) Or, FIC=Ib-Is.

The principle by which the error signal is obtained will be described below.

FIG. 7 is a simplified diagram of FIG. 7 in order to explain only the method of obtaining the focus error signal, and the same signals are attached to the same components as in FIG. 6. 7th
In the figure, if the aperture lens 6 and the disk 7 surface are too close to each other than the desired distance, FIG.
is exactly the desired distance, that is, when the incident light is focused exactly on the disk surface (hereinafter referred to as being at the focus position), and Fig. 7 ((1) shows the case where the distance is longer than the desired distance). are shown respectively.

First, as shown in FIG. 7 (IL), when the diaphragm lens 6 and the disk 7 get too close to each other by the desired distance, the reflected light focused by the convex lens 8 is focused at the imaging position p1. p2
is further away from the photodetector 13. Therefore, in this case, the diameter of the light spot 16 of the second reflected light is smaller than the diameter of the light spot 14 of the first reflected light on the photodetector,
Based on the amount of light received by the detection surfaces 13&, 130, 136 of the photodetector 13, the detection surfaces 13b, 1311,
The amount of light received at 13f is greater. On the contrary, Figure 7 (
As shown in (1), when the aperture lens 6 and the disk 7 move away from the desired distance, the diameter of the light spot 16 becomes larger than the diameter of the light spot 14, and the detection surfaces 13b, 13d, 13f The amount of light received by the detection surfaces 131L and 130.1315 is greater than the amount of light received by the detection surfaces 131L and 130.1315.

Further, when the focus position is as shown in FIG. 7(b), the diameters of both the light spots 14 and 16 are approximately equal, and the amount of light received by the detection surfaces 13b, 13 (1, 13f) The amounts of light received by !L, 130, and 13e!1 are equal. Therefore, by taking the difference between the output currents of each photodetector shown in equation (2), the focus error signal FIC is obtained, and IN+IO+l15=Ib+Id+If. Focus servo can be achieved by applying the servo so that

In the configuration shown in FIG. 6, due to changes in environmental conditions such as temperature fluctuations and shocks, (1) the photodetector 13 is displaced in the Y and Z directions;

@) The parallel light incident on the convex lens 8 is shifted by an angle θ as shown by the dashed line.

(3 The light source 1 (Fig. 6) is displaced in the Y and Z directions.

When a displacement of an optical component or a movement of the optical axis occurs, both the optical spots (14 and 15) move in the Y and Z directions, but if the distance 2 between the two optical spots is sufficiently larger than the displacement,
) shown in the equation FK=(Ib+Id+If)−(Ia+Ic+Ie) are mutually canceled and have no influence.

An example of the above-mentioned cancellation will be explained with reference to a case where both optical sub-boards 14 and 15 are shifted in the Z direction. For example, both light spots are +2
If the direction is shifted, each detection surface 13a.

13(1), the amount of light received by the detection surface 13b increases.

The amount of light received at 13θ and 130, 13f decreases.

Since the shapes of both light spots are exactly the same, FK=((Ib−
α)+(Id+β)+(If'-γ))-[(Is-α
)+(xa+β)+(Io-7))=(Ib+Id+I
f) −(Ie+Ia+Ic), and no FK fluctuation (change in the position of the 7th occurrence) occurs.

The same principle applies when 1E=Ib-Ie.

Also, in the noise signal Ha-Nf' included in the output signals Ia to Xr of each photodetector, the receiver outputs light near the center of the optical axis, Nb and Ne, and the receiver outputs light far from the center of the optical axis. NIL, N(1 and Nc.

As mentioned above, the frequency characteristics are different from Nf'. 14.15 is just divided into two in terms of intensity, but the shapes are exactly the same, so Na=Nd and Nb=Ne.

Nc=Nf', noises cancel each other out in the focus error signal FK, and the S/N of the FIC signal becomes very good.

Also, the tracking error signal TKO detection is set to τ = (1aa
-z 3r) - (130+13(1). This means that the light beam emitted from the objective lens e & of the optical head is irradiated onto the track of the disk. The primary light generated at this time is the 8th order light on the photodetector. It will rain in the direction shown in the figure.

Therefore, the tracking error signal TI can be detected.

Problems to be Solved by the Invention However, in the above configuration, a focus shift may occur. In other words, when the centers of the two beams on the photodetector deviate from parallel to the center of the photodetector, in other words, when the photodetector cannot be adjusted properly, the beam emitted from the objective lens hits the disk track. If you are on track, you are in just focus, but when searching, for example, you will be crossing tracks on the disc. At this time, brightness and darkness of the primary light occur periodically as it traverses the tracks of the disk, and this causes a focus shift, and in severe cases, it becomes impossible to search for the target address.

Conventionally, in order to eliminate this problem, fine adjustments were made to the photodetector, which required a considerable amount of time and effort.

Means for Solving the Problems In order to solve the above problems, an optical head of the present invention transmits a reflected beam having primary light generated parallel to the track direction of an information recording medium through a first reflecting surface. The beam reflected by this first reflecting surface is transmitted through a second reflecting surface to become a second beam, and the beam reflected by this second reflecting surface is recorded on a third reflecting surface. The third beam is reflected toward the information recording medium side by 9o1 with respect to the track direction of the medium.
It is equipped with a splitting prism that splits the second and third beams into two beams, and a photodetector placed along the optical path of the second and third beams is placed midway between the imaging positions of both beams to detect a focus error signal. A tracking error signal is detected by a photodetector that receives light.

According to the present invention, with the above-described configuration, when detecting a focus error signal, the seven orcus photodetectors can be adjusted regardless of the intensity of the primary light that is the tracking error signal, and the number of adjustment steps can be shortened. Even when searching for the destination address, it can be pulled in with stable operation.

EXAMPLE Hereinafter, an example of the present invention will be described with reference to the drawings.

FIG. 1 is a front view, a plan view, and a side view of a main part of an optical system of an optical recording/reproducing apparatus according to an embodiment of the present invention;
FIG. 2 shows a split prism.

In each figure, the same parts as in FIGS. 1 and 2 are designated by the same numbers and their explanations will be omitted.

In FIG. 2, the reflective surfaces of the splitting prism 19 are coated with different coatings. The reflectance Ra of the pick reflective surface 191L was set to about 70%, the reflectance Rb of the reflective surface 19b was set to about 50%, and the reflectance of the reflective surface 1900 was set to about 100%. The optical head of this embodiment using this split prism will be explained.

FIG. 1 shows a schematic front view, plan view, and side view of the optical system of this embodiment. In FIG. 1, a semiconductor laser 1
The emitted light enters a polarizing beam splitter 17 via a collimating lens 2 and a beam shaping prism 16.

The laser beam incident on the polarizing beam splitter 17 is reflected and irradiated onto the disk 7 via the λ/4 plate 5 and the objective lens 61L. The reflected light from the disk 7 passes through the same path, is totally reflected by the total reflection prism 4, and enters the splitting prism 19 via the single lens 8. The split prism converts the incident light amount PG into a beam P1 for tracking error signal detection,
Beam P2 for focus error signal detection. Divide into P3. 7-occurrence error signal detection beam p2. p3 is detected in the direction shown below. In other words, a reflected beam having primary light generated parallel to the track direction of the disk is transmitted through the first reflecting surface 19& as a first beam, and a beam reflected by the first reflecting surface 191L is transmitted through the second reflecting surface 19b. The beam is reflected by the second reflecting surface 19b and is bent by 9 degrees with respect to the groove direction of the disk at the third reflecting surface 190 to form a third beam reflected toward the disk side. A shift focus error signal is detected by setting a photodetector 13 between the imaging positions of the second and third beams.

The detection method is FIC=(Ib+Id+If)-(Ia+Ia+Ie)
Alternatively, F]E=Zb-Is.

At this time, even when the centers of the second and third beams deviate from the center of the photodetector 13, the 1
Since the direction of the second-order diffracted light is 90 degrees different from that of the conventional method, the focus error signal can be detected without being affected by the first-order diffracted light.

The tracking error signal TIc is a current Ig obtained from the light receiving elements 20g and 20h of the photodetector 2°.

From Ih to Tic:Ig-processing. Since the tracking error signal is detected by a separate photodetector 2o in this way, the adjustment can be dramatically improved.

As described above, according to this embodiment, it is possible to complete the adjustment of the photodetector with high precision, and it is possible to obtain an optical head for an optical recording/reproducing device that is highly mass-producible.

Effects of the Invention As described above, the present invention bends the direction of the first-order diffracted light by 9 degrees when detecting a focus error, and
K signal detection and τ! By separating the signal detection, it is possible to simplify the adjustment of the optical system of the optical recording and reproducing device.
In addition, it is possible to stabilize the search for the destination address on the disk, which has a great practical effect.

[Brief explanation of the drawing]

FIG. 1 is a front view, an open plan view, and a side view of essential parts of an optical recording/reproducing device according to an embodiment of the present invention, FIG. 2 is a schematic diagram of a dividing prism of the same device, and FIG. 3 is a diagram of a conventional example. Main part front view,
4 is a schematic side view of the same, FIG. 5 is a front view of the detection surface, FIG. 6 is a front view of the conventional example, a side view thereof, FIG. 7 is a schematic side view thereof, and FIG. is a schematic diagram thereof. 1... Semiconductor laser, 2... Collimating lens, 4... Total reflection prism, 5...
...λ/4 plate, 6...Objective lens, 7...
... Disc, 8 ... Semi-convex lens 12 ...
...Division prism, 13...Photodetector, 16.
...Beam shaping prism, 1.....Polarizing beam splitter, 19.....Splitting prism,
20...Photodetector. Name of agent: Patent attorney Shigetaka Awano and 1 other person
Ichitan Ineshiji 8-Ichisha Convex Scene'. /Yl) No. 1 - Issute Sadai Hon & - The. Do-1-Colorist Nuns 4-= A, Female Ejaculation Asosism 6-7'A 6a-Kanumasu Synth Figure 17--J

Claims (2)

[Claims] (1) A light source, an objective lens that focuses a light beam emitted from the light source onto an information recording medium, and a reflected beam having an order diffracted light generated by a track of the information recording medium at a first beam splitting plane. The beam reflected by the beam splitting surface is transmitted as a second beam by the second beam splitting surface, and the beam reflected by the second beam splitting surface is transmitted by the third total reflection mirror. a splitting prism that is bent at right angles to the track direction of the information recording medium and split so as to be reflected as a third beam toward the information recording medium; and imaging of both beams along the optical path of the second and third beams. An automatic focusing device including a photodetector disposed at an intermediate position and a photodetector that receives a first beam. (2) In claim 1, the splitting prism divides the reflected light into two
a first beam splitter that splits the beam and transmits one beam as a first beam; a second beam splitter that divides the beam reflected by the first beam splitter into two and transmits one beam as a second beam; An automatic focus adjustment device that is integrated with a reflecting prism that totally reflects a beam reflected by a second beam splitter and reflects it in the same direction as the second beam to obtain a third beam.