JPH0196831A - optical pickup device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

TECHNICAL FIELD The present invention relates to an optical pickup device that records and reproduces information by irradiating a recording medium with light from a semiconductor laser.

Prior Art A conventional optical pickup device will be explained with reference to FIG. In the optical pickup device 1, first, light from a semiconductor laser 2 is focused by a coupling lens 3 serving as a condensing lens to become parallel light, and the parallel light is transmitted through a polarizing beam splitter 4 and then transmitted through a 174-wave plate 5. The light is focused by an objective lens 6 and irradiated onto the surface of an optical disk 7 serving as an optical recording medium to form a minute spot of about 1 μm.

After the reflected light from the surface of the optical disk 7 is reflected by the polarizing beam splitter 4.

The light is focused by the objective lens 8. A prism 9 having a linear edge portion is provided at the optical axis position of this light beam. The light reflected by this prism 9 is irradiated onto a track light receiving element 10 having two divided light receiving surfaces A and B and is detected as a track error signal.
The light passing through the outside is irradiated onto a focus light receiving element 11 having two divided light receiving surfaces C and D, and is detected as a focus error signal.

In this case, especially if the focus light receiving element 11 deviates from its normal detection position, a focus error signal will be erroneously emitted, and as a result, accurate recording and reproduction of information may not be possible. This means that it is not possible.

Therefore, in order to check whether the focus light receiving element 11 is at a normal detection position, the following procedure has conventionally been carried out. In other words, when the distance from the surface of the optical disk 7 on which the spot is formed to the objective lens 6 is moved closer or further away within a range of several microns (μm), the amount of focus error signal when the spot is brought closer to the surface is calculated. .

Conversely, it is checked whether the focus light receiving element 11 is at a normal detection position by checking whether the amounts of the focus error signal when the focus light receiving element 11 is moved away from the surface are equal to each other.

However, in the case of such a conventional adjustment method of the focus light receiving element 11, the distance from the surface of the optical disk 7 to the objective lens 6 must be adjusted by moving it closer or further away within a range of several microns. There is a problem in that it requires a great deal of time and effort to adjust the detection position and verify (readjust) it afterward.

Purpose The present invention has been made in view of the above points, and provides an optical pickup device that allows easy adjustment of the detection position of a focus light receiving element and subsequent verification by forming a step in an optical recording medium. The purpose is to obtain.

Structure According to the present invention, at least one level difference is formed in the optical recording medium in order to adjust the deviation of the detection position of the focus light receiving element, so that a signal for adjusting the focus light receiving element can be easily generated using this level difference. Therefore, the configuration is such that adjustment of the detection position of the focus angle light receiving element and subsequent verification can be performed easily in a short time.

An embodiment of the present invention will be described based on the drawings.

Note that the structure of the optical pickup device and its basic operating principle have been explained in the prior art, so the explanation will be omitted here, and the same parts will be explained using the same reference numerals.

As shown in FIG. 1, the optical disc 7 as an optical recording medium has a recording track 12 called a pregroove formed in a spiral or concentric shape on its surface, and a part of the optical disc 7 on which the recording track 12 is formed is formed. A step 13 having a height H is formed on the surface.

In such a configuration, first, the track light receiving element 10
Fig. 9(a) shows the principle of detecting the track error signal by
b) Explain based on (c). Track light receiving element 10
The light-receiving surface is divided into two parts, A and B. As shown in FIG. 9(b), when the light focused by the objective lens 6 is normally irradiated onto the recording track 12, the light intensity distribution 14 on the light receiving surfaces A and B is Since it is irradiated symmetrically from the center position Q, the amount of received light is A=B, and the difference IA-Bl is not detected and becomes O, and as a result, no track error signal is detected.

On the other hand, as shown in FIGS. 9(a) and 9(c), when the light focused by the objective lens 6 is irradiated to a position shifted to the left or right from the position of the recording track 12 of the optical disc 7, In this case, the light intensity distribution 14 on the light-receiving surfaces A and B is irradiated at a position shifted from the center position Q, so the amount of received light becomes A>B or A<B, and the difference IA-
Bl is detected as a track error signal.

Next, the principle of detection of a focus error signal by the focus light receiving element 11 will be explained based on FIGS. 10(a), (b), and (c). The focus light receiving element 11 has a light receiving surface divided into two parts C and D. And the first
As shown in Fig. 0 (b), when the light focused by the objective lens 6 is irradiated onto the focal point P of the half disk 7, the amount of light received at the light receiving surfaces C and D is equal to the left and right. Since C=D is symmetrical, the difference IC-DI is not detected and becomes O, and as a result, no focus error signal is detected.

On the other hand, as shown in FIGS. 10(a) and 10(c), when the focus of the light condensed by the objective lens 6 is at the points X and Y, which are shifted from the position of the focused point P, The amount of light received at surfaces C and D is COD or COD, and the difference I
c-Dl is detected as a focus error signal.

Next, the principle of how the detection position of the focus light receiving element 11 is adjusted will be explained.

Generally, when a track error signal (IA-Bl) is detected, a track error signal (solid line) having a sinusoidal waveform as shown in the second @ is generated. At this time, when the distance between the optical disk 7 and the objective lens 6 changes and the spot is focused at a position shifted from the focused point P, the spot diameter increases, and as shown in FIG. The intensity distribution 14 (dashed line) is weakened, and as a result, the amplitude of the track error signal in FIG. 2 is reduced as shown by the dashed line.

However, at this time, even if the spot was at the focused point P, the detection position of the focus light receiving element 11 was slightly shifted from the normal detection position [Fig. 10(b)]
If the position is shifted by Δt], the focus error signal will be detected. Therefore, the position detection of the focus light receiving element 11 can be adjusted based on such a detection principle.

Next, a description will be given of how the position detection of the focus light receiving element 11 is adjusted using the step 13 of the optical disc 7, which is one aspect of the present invention. The step 13 is
As shown in FIG. 1, it is formed at a height H (several μm or less) on the surface of the optical disc 7. And now, the fourth
As shown in Figures (a), (b), and (c), when the optical disc 7 is reciprocated in the direction shown by the arrow with a spot irradiated on the step 13, the track error signal generated at that time is the fifth track error signal. It can be classified into waveforms as shown in Figures (a), (b), and (Q). That is, the waveform in FIG. 5(a) is obtained when the position of the focal point R in FIG. 4(a) is closer to the objective lens 6 than the height 1/2H. The waveform in FIG. 5(b) is obtained when the position of the focal point S in FIG. 4(b) coincides with the height 1/2H. The waveform in FIG. 5(c) is obtained when the position of the focal point T in FIG. 4(c) is farther from the objective lens 6 than the height 1/2H.

Therefore, first, the position of the focal point S is set at the height 1/
The distance between the objective lens 6 and the optical disk 7 is adjusted so that it is at the 2H position, and the amplitude of the track error signal is as shown in Figure 5 (
Keep it constant like b). Next, when the optical disc 7 is reciprocated in the direction of the arrow in this state, if the detection position of the focus light receiving element 11 is not shifted, the focus error signal will be vertically symmetrical as shown in FIG. 6(b). A rectangular wave should be obtained, and the difference IC-DI should be 0.

However, at this time, if the detection position of the focus light receiving element 11 shifts even slightly [Δ
If the position is shifted by t], then the focus error signal at that time will be an asymmetrical rectangular wave shifted either up or down as shown in Fig. 6 (a) (c), and the difference IC-DI will not be O. Detected.

Therefore, when the track error signal has a constant amplitude as shown in FIG. 5(b), the focus error signal changes as shown in FIG. 6(b).
In the case of an asymmetrical rectangular wave as shown in a) and (c), it means that the detection position of the focus light receiving element 11 has deviated from the normal position. If the detection position of the focus light receiving element 11 is adjusted so that the rectangular wave is vertically symmetrical as shown in Fig. 10(b), the positional deviation [the position shifted by Δt in Fig. 10(b)] can be eliminated and the normal It can be returned to the detection position.

Next, after the adjustment of the focus light receiving element 11 is completed, a focus error signal [vertically symmetrical rectangular wave in FIG. 6(b)]
Let us examine the defocus amount Q (focus light-receiving element setting error amount, unit: μm), that is, how much further adjustment is required after the adjustment is completed to completely eliminate the positional deviation (Δt).

After the adjustment of the focus light receiving element 11 is completed, the distance between the objective lens 6 and the optical disc 7 is adjusted so that the track error signal becomes as shown in FIGS. 4(b) and 5(b), and in this state, The optical disc 7 is moved again in the direction of the arrow. At this time, the focus error signal is shown in Fig. 6(a) (
If the waveform is vertically asymmetrical as shown in c), it means that the positional deviation (Δt) has not been completely eliminated.

Therefore, in order to completely eliminate this positional shift, the defocus amount Q is determined as follows. First, as shown in FIG. ) is γ.

The linear relationship shown in FIG. 7 is now replaced with that shown in FIG. 8, and the focus error signal F at that time is first determined. Δ
OAB and ΔOCD (Δ represents a triangle) have a similar relationship; In L, , L4, there is the following relationship. (However, L2=F) This (
1) Each coordinate point 0. When the focus error signal F is obtained by substituting the values of A, B, C, and D, F=(α−(α−β
)/2) ...(2). (However, α and β represent the magnitude of the pulse waveform in FIG. 7.) Thereby, the defocus amount Q can be determined as Q=F/γ (μm) (3).

Therefore, by moving the detection position of the focus light-receiving element 11 by the amount of defocus Q determined in this way, the positional deviation (Δt) can be completely eliminated in the end. Thereafter, after the final adjustment of the detection position of the focus light receiving element 11 that has been made in this way is completed, the focal point S of the spot [FIG. 4(b)] is moved by a height of 1/2H, and the optical disc 7 is again Ordinary information can be recorded and reproduced by irradiating the surface of the.

Effects In the present invention, since at least one step is formed on the optical recording medium in order to adjust the deviation of the detection position of the focus light receiving element, this step is used to adjust the detection position of the focus light receiving element. Since the signal can be easily generated, the detection position of the focus light receiving element can be adjusted and the subsequent verification can be easily performed in a short time.

[Brief explanation of the drawing]

Fig. 1 is a side view of a step showing an embodiment of the present invention, Fig. 2 is a waveform diagram of a track error signal, and Fig. 3 is a diagram showing the state of the light intensity distribution on the track light receiving element depending on the size of the spot diameter. 4 is an explanatory diagram showing the state when the spot is focused on a step, FIG. 5 is a waveform diagram of the track error signal at that time, FIG. 6 is a pulse waveform diagram of the focus error signal, and FIG. FIG. 8 is an explanatory diagram showing the relationship between the focus error signal and the defocus amount, FIG. 8 is an explanatory diagram for calculating the defocus amount mathematically, and FIG. 9 is an explanatory diagram showing the principle of detecting the track error signal. FIG. 10 is an explanatory diagram showing the principle of detecting a focus error signal, and FIG. 11 is a horizontal sectional view showing the overall configuration of the optical pickup device. 2... Semiconductor laser, 4... Polarizing beam splitter, 6... Objective lens, 7... Optical recording medium, 10...
・Track light receiving element, 11... Focus light receiving element,
13... Level difference applicant Ricoh Co., Ltd. -J3. !
Figure 3ZFigure 3, . Figure 3,, y3 γ Figure-3d Figure

Claims (1)

[Claims] Light from a semiconductor laser is transmitted through a polarizing beam splitter, and the transmitted light is focused by an objective lens to form a minute spot on an optical recording medium to record and reproduce information, as well as reflect light from the optical recording medium. In an optical pickup device that performs track control and focus control of the optical recording medium by reflecting light by the polarizing beam splitter and irradiating the light onto a track light receiving element and a focus light receiving element, a shift in the detection position of the focus light receiving element An optical pickup device characterized in that at least one step is formed on the optical recording medium to adjust the temperature.