JPS63183625A - Optical disk device - Google Patents

Abstract

PURPOSE:To obtain an optical disk device having a high CN ratio by detecting a reproducing signal by a differential detecting method for offsetting a noise caused by a relative fluctuation of an optical system or an electric system. CONSTITUTION:Only a 1/4 circular light part 14a of a circular luminous flux 14 is allowed to pass through a phase difference plate 3 and a phase is delayed by theta and the luminous flux of this circular light part 14a and the luminous flux of the remaining 3/4 circular light part 14b are projected to a light recording surface 7, and a reflection and a diffraction are generated therein. When the optical amplitude of a 0-th order diffracted light 15b of the 3/4 circular light part is denoted as Ao, the optical amplitude of a 0-th order diffracted light 15a of the 1/4 circular light part becomes AoEXP(jtheta), and also, as for the primary diffracted light, the primary diffracted light 16b of the 3/4 circular light part and the primary diffracted light 16c of the 1/4 circular light part having a phase delay are superposed, and as for the -primary diffracted light, it becomes only the -primary diffracted light 16a of the 3/4 circular light part. In such a way, the luminous flux to which the 0-th order diffracted light and the + or -primary diffracted light have been superposed is led to an optical system split mirror 9, made incident on a differential amplifier through a photosensor 10, and a desired reproducing signal is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an optical disc device for recording or reproducing information on an optical disc.

2. Description of the Related Art The configuration of a conventional optical disc device will be described below with reference to the drawings. As shown in FIG. 4, the light emitted from the semiconductor laser 1 is focused by a condensing lens 2, and focused onto the optical disk recording surface 7 by a deflection beat splitter 4, a quarter-wave plate 5, and an aperture lens 6. . The light reflected from the optical disc recording surface 7 passes through the fringe lens 6 and the quarter-wave plate 5 again, reaches the deflection beam splitter 4, travels straight through this, and is condensed by the convex lens 8.

A part of this light is reflected by the focus error detector 21, and the remaining light is reflected by the splitting mirror 9 and received by the tracking error detector 20.

Figure 5 (a
) and (b). (a) is a distribution diagram of light received by the tracking error detector 20, and similarly, (b) is a light distribution diagram of the focus error detector 21.

(a) As shown in the figure, a tracking error detector 20
The splitting mirror 9 receives semicircular light 23a, which is approximately 1/2 of the reflected light from the optical disc recording surface 7. The distribution of this semicircular light 23a is such that the 0th-order diffracted light 24 is reflected from the track surface that the scanning light is following, the 1st-order diffracted light 24a and the The light distribution is such that the folded lights 24b are superimposed.

Here, O-order diffracted light 24, first-order diffracted light 24a and -1
The optical amplitude of the order diffracted light 24b is as follows: Optical amplitude of the O-order diffracted light = A0 Optical amplitude of the 1st-order diffracted light = A +EXP[jlφ-2z(
x/p)l]-light amplitude of first-order diffracted light = A+EXP[j
It can be expressed as l φ+2π(x/p)II (jr imaginary unit).

However, (x/p) is the deviation of the scanning light from the groove center on the optical disc recording surface 7! ! It represents the ratio between Lx and the groove pitch p. AOlAI and φ are uniquely determined by the groove shape of the optical disk recording surface 7, and when groove depth; d1 groove width; w1 groove pitch; p, the wavelength of the laser is λ.
Then, Ao=w/p+ (1-w/p)EXP(-j
4πd/λ)AIEXP(jφ) = l 1-EXP
(-j4πd/λ)l +5IN(πw/p)/π).

This light distribution is divided into two by a dividing line 25 corresponding to the track center of the hollow photo sensor 20a, 2.
0b, and is amplified by a differential amplifier 26 to obtain a tracking error signal (TE). For this reason,
The tracking error signal (TE) is proportional to the following equation (A) obtained by subtracting the light amount of the 1st-order diffracted light from the light amount of the 1st-order diffracted light.

1 l Ao+A+EXP[jlφ−2π(x/pN]
l2-IA.

+A+EXP[jlφ+2π(x/p)II l 21
--- (A) Therefore, when the scanning light is controlled to the drag center (when x / p = O), the above 1.
Since the amplitude and phase of the second-order diffracted light 24a and the first-order diffracted light 24b are equal, no tracking error signal (TE) is output. However, when the scanning light deviates from the center of the track, the first-order diffracted light 24a and the first-order diffracted light 24b
A phase difference occurs, and a difference in light amount due to this phase difference is amplified by the differential amplifier 26 to obtain a tracking error signal (TE).

Furthermore, the reproduced signal (RF) is detected as a sum signal of the optical signals received by these two divided photosensors 20a and 20b, and at the time of just tracking (when x/p=o), the following equation (B ) will be proportional to

21 l AOlt+ l A+EXP(j;6) l
21--(B) Therefore, if α is the change in the amount of reflected light due to recording dots or recording or address bits formed on the optical disk recording surface 7, the amplitude of the reproduced signal due to the recorded data is proportional to the following equation (C). It becomes what it is.

2 (1-a) (I AO12+ I A+EXP
(jφ) IB---(C) Furthermore, the semicircular light 23b that is narrowed down by the convex lens 8 and focused on the focus error detector 21 is a further narrowed semicircular light that forms the bare semicircular light 23a. It is something. Therefore, the distribution is such that the first-order diffracted light 27a and the first-order diffracted light 27b are superimposed on the O-order diffracted light 27. This light distribution is divided into 1 m parallel to the cutting diameter of the semicircular light 23b.
Photosensors 21a and 21b divided into two by 28
The signal is photoelectrically converted and then amplified by a differential amplifier 29 to obtain a focus error signal (FE).

Problems to be Solved by the Invention However, in the above configuration, the reproduced signal (RF) is detected as a sum signal of the signals received by the two photosensors 20a and 20b forming the tracking error detector 20. Therefore, there is a problem in that the reproduced signal (RF) is vulnerable to relative signal fluctuations due to deviations in the optical system, scattered light, or noise in the circuit system.

In view of these problems, the present invention has newly developed a reproduction signal (
RF) with an optical system configuration obtained by differential signals, and has sufficiently good carrier-to-noise (C/N) characteristics even against relative signal fluctuations due to deviations in conventional optical systems, scattered light, or circuit noise. An object of the present invention is to provide an optical disc device that can obtain a reproduction signal (RF) of

Means for Solving the Problems The present invention provides a scanning light emitting means, a phase delaying means for uniformly delaying the phase of a part of the scanning light, and a phase delaying means for delaying the phase of the scanning light by the phase delaying means. a condensing means for condensing the light beam A of the scanning light and the other light beam B of the scanning light which has not been phase-delayed on an optical disk recording surface; A first photoelectric conversion means photoelectrically converts a superimposed light beam of the 1st-order diffracted light of the light flux B, and charges and converts the superimposed light flux of the 1st-order diffracted light of the light flux A and the 0th-order diffracted light of the light flux B from the optical disk recording surface. a second photoelectric conversion means, a differential amplifier that obtains a signal difference between the second photoelectric conversion means and the first photoelectric conversion means, and a reproduced signal output means that uses the signal from the differential amplifier as a reproduced signal. This is an optical disc device comprising:

By means of the operational phase delay means, it is possible to uniformly delay the phase of only a portion of the scanning light. Among the diffracted lights from the optical disk recording surface of this partially phase-delayed scanning light, the 0th-order diffracted light of the phase-delayed light beam A and the part 1 of the light beam B whose phase is not delayed.
The superimposed portion of the next-order diffracted light can be received by the first photoelectric conversion means. Further, the superimposed portion of the first-order diffracted light of the light beam A whose phase has been delayed and the O-th order diffracted light of the light beam B whose phase has not been delayed can be received by the second photoelectric conversion means. Furthermore, a differential amplifier is used to connect the first photoelectric conversion means and the second photoelectric conversion means.
Take the difference signal of the signals output by the photoelectric conversion means,
A reproduced signal can be obtained by the reproduced signal output means that outputs the signal.

EXAMPLES Hereinafter, examples of the present invention will be described based on the accompanying drawings. Note that components that are the same as those of a conventional optical disc device are given the same numbers.

FIG. 1 shows an embodiment of the present invention. As shown in FIG. 1, the scanning light emitted from the semiconductor laser 1 is condensed by a condensing lens 2, a polarizing beam splitter 4, and a quarter-wave plate 5.
The aperture lens 6 focuses the light onto the optical disc recording surface 7 . However, a feature is that a part of the scanning light condensed by the condenser lens 2 passes through the retardation plate 3.

A part of the scanning light that passes through the retardation plate 3 and another part of the scanning light that does not pass through are focused on the optical disk recording surface 7, reflected and diffracted, and then passed through the aperture lens 6 and the quarter-wave plate 5 again. The beam passes through the beam, reaches the deflection beam splitter 4, and then travels straight ahead to be reflected by the convex lens 8. A part of this focused light is separated into two beams by a splitting mirror 9,
One is a reproduction signal (RF) detector 10 and the other is a half mirror.
It is branched into 11. Further, the half mirror 11 divides the light into reflected light, which is received by a tracking error detector 12, and transmitted light, which is received by a focus error detector 13.

Photodistribution diagrams of the main parts of these optical system configurations are shown in FIGS. 2(a) to 2(g), and the operation of the optical system of this embodiment will be specifically explained based on these diagrams.

As shown in FIG. 2(a), only the 1/4 circular light portion 14a of the circular light beam 14 is passed through the retardation plate 3, and its phase is delayed by θ. For convenience of explanation, the 0th-order diffracted light and the ±1st-order diffracted light due to reflection diffraction from the optical disk recording surface 7 of the light beam of the 1/4 circular light portion 14a with a phase delay of θ and the remaining 3/4 circular light portion 14b are respectively referred to. It is shown separately in Figure (b) and Figure (C).

(b) In the figure, if the optical amplitude of the O-order diffracted light 15b in the 3/4 circular part is AO, then the O-order diffracted light 15 in the 1/4 circular part is
The optical amplitude of a is AOEXP (jθ). Also, (C
) As shown in the figure, for the first-order diffracted light, the first-order diffracted light 16b of the 3/4 circular light part and the first-order diffracted light 16c of the 1/4 circular light part having a phase delay are superimposed, and for the -1st-order diffracted light, the first-order diffracted light 16b of the 1/4 circular light part is superimposed. It is only the 1st-order diffracted light 16a of the /4 circular light portion.

The O-order diffracted light shown in these figures (b) and (c) and ±
The light beam in which the first-order diffracted light is superimposed is sent to the split mirror 9 of the optical system.
, resulting in a full distribution as shown in figure (d). That is, the light distribution has six regions 15a, b and 16a to d. These luminous fluxes are split into two by the edge 9a of the splitting mirror 9, and the reproduced signal (RF) detector 10 receives (e
) As shown in the figure (the right semicircular light 23c of this circular luminous flux is received by two divided photosensors 10a and 10b, and further amplified and outputted by a differential amplifier 30 to obtain a reproduction signal (RF).

Here, the light amplitude of each light distribution area of the semicircular light 23c is 16 c ; Ao+A+EXP[jlθ+φ−2π
(x/p)Ill 6 d; AOEXP[jl θ
l] 10 AIEXP [jlφ+2π(x/p)l] 15
a; AoEXP[Nθ)1 15b;AO(j; imaginary unit), and the amount of light for each is 16 c; l Ao+A+EXP[jlθ+φ−2
π(x/p)11 l 216 d ; l AoEX
P[l e l]+ A+EXP[jl ψ+2π(x
/p)l] l 2 = l EXP[jl θl] l 2 l Ao+A
tEXP[jl-θ+φ+2π(x/p) 1112 = l Ao+A+EXPl-θ+φ+2π(x/p)
)] l 2 (1EXP[jlθl]12=1yori) 1
5 a; l AoEXP[jlθ)]1215
b: 1AO12.

Also, l Ao l 2= l AoEXPlθ111
21', and the light amount of 15a and 15b are equal, so the light is received by the two divided photosensors 10a and 10b, and the reproduced signal (RF) obtained from the differential signal is proportional to the following equation (Dl) do.

l Ao+A+EXP[jlθ+φ−2π(x/p)l
] l 2- l AO+A+EXP[jl-θtenφ+
2z(x/p)l] l 2 --- (Dl) Here, when the scanning light is focused on a track on the recording surface of the optical disk, (x/p)=O. Therefore, the above equation (Dl) becomes the following equation (D2).

l Ao+ A+EXP[jl e, +φ1112-
I Ao+A+EXP[j(-θ+φll1g---
(D2) The value of the reproduced signal (RF) expressed by this equation (D2) will be specifically examined below.

Figure 3 shows the optical amplitude IAO+A with respect to the phase delay amount θ.
+EXP[jl e+φ111 z(7) value shown Lr 1st), ti1 width W = 0, 8 μrn N Groove depth d = λ/8, groove pitch P = 1.6 μm These are the results calculated for an optical disc.

Now, in the optical disc under the above conditions, φ=π/2, and if the phase delay amount θ of the retardation plate 3 is set to π/2, l Ao
+A+EXP[jl θ+φl] l2c is point P in Figure 3, and lAo+A+EXP[jl-θ+φ11+2 is point Q. That is, the differential output is proportional to the maximum amplitude H in FIG. Further, if α (>1) is the change in the amount of reflected light due to recording dots, addresses, or recording bits formed on the optical disk recording surface 7, the differential output is proportional to αH. Therefore, the reproduced signal (RF) amplitude is (α-1)
It becomes H.

The width of this reproduced signal (RF) 8 is about the same as the conventional reproduced signal amplitude, but since a differential detection method is employed, it is resistant to relative fluctuations in the signal. Further, optical noise and electrical noise are also canceled out, and the reproduced signal characteristics (CZN ratio) can be dramatically improved.

The other semicircular beam 23d that is not reflected by the splitting mirror 9 is separated into two beams by the half mirror 11, and each is received by a tracking error detector 12 and a focus error detector 13. These light distributions are shown in FIGS. 2(f) and (g). The light distribution received by the tracking error detector 12 is as shown in FIG. ±1st order diffracted light of the part 16
This is a distribution in which a and 16b are superimposed. The amplitude of each optical signal is as follows.

16 a; Ao+ A+EXP[jlφ−2π(x
/p) 1116 b; Ao+ A+EXP(Nφ+
2r(x/p)f] 15b; AO (j: imaginary unit) Here, the tracking error signal (TE) is received by the two divided photosensors 12a and 12b, and is obtained by the differential signal thereof. Its size is exactly the same as the conventional one, and is not affected by the insertion of the retardation plate 3 at all. Furthermore, the distribution of light received by the focus error detector 13 shown in FIG. 3(g) is also exactly the same as that of the conventional one.

As described above, in this embodiment, the tracking error signal (TE
) or the focus error signal (FE) are exactly the same as those of conventional optical disc devices. Reproduction signal (RF
), inserting a retardation plate 3 in a part of the optical path of the optical system enables differential amplification, suppresses relative signal fluctuations due to optical system noise and electrical system noise, and is extremely stable. Strong against noise (sufficient reproduction signal ratio (C/N ratio)
A reproduced signal having . Therefore, it provides an extremely effective means for stabilizing the performance of an optical disc device.

Effects of the Invention As described above, according to the present invention, the relative relationship between the optical system and the electrical system can be improved without changing the conventional stable tracking error signal (TE) detection method and focus error signal (FE) detection method. It is possible to detect reproduced signals using a differential detection method that cancels out noise caused by fluctuations.

Therefore, it is extremely useful for stabilizing reproduction signals and improving performance of optical disc devices.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing the basic structure of an optical disk device according to an embodiment of the present invention, Fig. 2 is a distribution diagram of light flux in the main parts of the device, and Fig. 3 is a retardation plate inserted in the device. FIG. 4 is a diagram showing the principle of construction of a conventional optical disk device, and FIG. 5 is a photovoltaic diagram on a detector of the same device. DESCRIPTION OF SYMBOLS 1... Semiconductor laser, 3... Retardation plate, 4... Polarizing beam splitter, 6... Aperture lens, 7... Optical disk recording surface, 8... Convex lens, 9... Dividing mirror , 10... Reproduction signal (RF) detector, 12... Tracking error detector, 13... Focus error detector Name of agent Patent attorney Toshio Nakao and one other person I
-4 hands laser? - Straight front lens 3 - a phase nose 4 - 1 - Preparation - Musbuzofuku 5 - lmu λ Nagami 6 - Hagi Riren χ 7 - Optical disc recording surface 8 - Convex lens 9 ~ Divided mirror 10 - RF ( IT detector 11-8-Full mirror Fig. 1 !2-Tracking error detector 13-1-Focus error detector h Fig. 3?O-Trough error pincher Fig. 5 --Four Nuewo horizontal $6 nb---r next riJ latitude 2B ・+ tl u η−・− difference increase incest (b)

Claims (1)

[Claims] a scanning light emitting means, a phase delaying means for uniformly retarding the phase of a part of the scanning light, and a beam A of the scanning light whose phase has been delayed by the phase delaying means, and a beam A of the scanning light whose phase has been delayed by the phase delaying means. a condensing means for condensing the other light beam B of the scanning light that has not been detected on the optical disk recording surface; and a superimposed light beam of the 0th-order diffracted light of the light beam A and the -1st-order diffracted light of the light beam B from the optical disk recording surface. a first photoelectric conversion means for photoelectrically converting the light beam; a second photoelectric conversion means for photoelectrically converting a superimposed light beam of the first-order diffracted light of the light beam A and the zero-order diffracted light of the light beam B from the optical disk recording surface; An optical disc device comprising: a differential amplifier that obtains a signal difference from the second photoelectric conversion means and the first photoelectric conversion means; and a reproduced signal output means that uses the signal from the differential amplifier as a reproduced signal.