JPH08153330A - Optical recording and reproducing device - Google Patents

Abstract

PURPOSE: To suppress an effect by a side lobe of a super-high resolution spot without providing a minute slit in an optical system. CONSTITUTION: An information recording part of an optical disk A is irradiated with a beam spot 12 having a narrow main lobe in width in the middle and a large side lobe, formed from a beam emitted from a semiconductor laser 1 by an apodize element 4 and an objective lens 6. A detecting signal obtained by transducing a reflected light beam 13 from the information recording part into an electric signal by a photodetector 7 is sent to an equalizer circuit 9 for suppressing an effect of the side lobe in the beam spot and error decision circuit 10 for adjusting an equalizing coefft. of the equalizer circuit. Consequently, an effect of the side lobe in a regenerative waveform is suppressed, and equalization to a partial response waveform is realized.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical recording / reproducing device using an optical disc or the like.

[0002]

2. Description of the Related Art As a conventional optical recording / reproducing apparatus, a central portion of light emitted from a light source such as a semiconductor laser is attenuated by using a light-shielding band, condensed by a lens, and a beam spot with a narrow main lobe width ( Hereinafter referred to as a super-resolution spot.)
And irradiate the information recording portion of the optical recording medium with the reflected light to form a minute slit (slit width 10 to 20 μm).
m), the reflected light component due to the side lobes is suppressed and guided to the photodetector, and the recorded information is reproduced by detecting the change in the light intensity or the polarization direction of the reflected light (for example, application. Physics, Vol. 61, No. 3, 1992, "Next Generation Optical Head Technology for Magneto-Optics").

[0003]

However, the above-mentioned conventional optical recording / reproducing apparatus has a problem that it is necessary to accurately provide minute slits in the optical system for signal detection. Further, by providing a slit in the optical system for signal detection, not only the reflected light component due to the side lobe but also the reflected light component due to the main lobe is suppressed, and the light amount of the detected signal light is reduced to reproduce information with good S / N. There was a problem that I could not do it.

An object of the present invention is to provide an optical recording / reproducing apparatus capable of suppressing the influence of the side lobes of the super resolution spot without providing a minute slit in the optical system.

[0005]

In order to achieve the above object, the present invention condenses light emitted from a light source to form a beam spot, which is irradiated onto an information recording portion of an optical recording medium. In an optical recording / reproducing apparatus for detecting reflected light or transmitted light and reproducing recorded information, an apodizing element that changes the intensity distribution of light so that the beam spot diameter becomes small,
An equalization circuit that suppresses the influence of side lobes in the beam spot from the detection signal of reflected light or transmitted light and an error determination circuit that adjusts the equalization coefficient of the equalization circuit are provided.

[0006]

According to the present invention, a super-resolution spot can be formed on the information recording portion of the optical recording medium by the apodization element, and the influence of the side lobe of the super-resolution spot included in the detection signal of the reflected light or the transmitted light can be reduced. This can be suppressed by the equalization circuit, which makes it possible to extract reproduction information with improved resolution of the main lobe of the super-resolution spot. Further, by adjusting the equalization coefficient of the equalization circuit by the error determination circuit, the reproduced waveform can be equalized into a partial response waveform (PR waveform), and more accurate information reproduction can be performed.

[0007]

1 shows an embodiment of an optical recording / reproducing apparatus of the present invention, in which 1 is a light source, here a semiconductor laser,
2 and 3 are collimating lenses, 4 is an apodizing element, 5 is a beam splitter, 6 is an objective lens, 7 is a photodetector, and 8
Is an amplifier, 9 is an equalization circuit, 10 is an error determination circuit, A is an optical recording medium, here an optical disk.

The apodizing element 4 changes the intensity distribution of light so that the beam spot diameter after focusing becomes small, and more precisely attenuates the central part of the light beam. Here, a strip-shaped light-shielding band is formed on a glass plate. 4a is used.
The shape of the light-shielding band may be a strip-like shape, a shape having a circular or curved edge, or the like, and it is also possible to use a rhombus prism, a wedge-shaped prism, or the like outside the light-shielding band.

The equalization circuit 9 suppresses the influence of side lobes in the beam spot from the detection signal as described later. The error determination circuit 10 adjusts the equalization coefficient of the equalization circuit 9 as described later.

In the above structure, the light 11 emitted from the semiconductor laser 1 is shaped into parallel light by the collimator lens 2, passes through the apodizing element 4, and the light intensity at the central portion is attenuated by the light shielding band 4a. The light passing through the apodizing element 4 is changed in direction by the beam splitter 5, is condensed by the objective lens 6 to form a beam spot 12, and is irradiated onto the information recording portion of the optical disc A.

At this time, the beam spot 12 has a narrower main lobe in the center and a larger side lobe than in the case where there is no light-shielding band (broken line in FIG. 2) as shown in FIG. It becomes a spot.

The reflected light 13 from the information recording portion of the optical disc A by the beam spot 12 passes through the objective lens 6 and the beam splitter 5, is received by the photodetector 7 through the collimator lens 3, is converted into an electric signal, and is amplified. Amplified by 8. The electric signal after the amplification, that is, the detection signal is processed by the equalization circuit 9 and the error determination circuit 10 and output.

A known quarter wave plate may be inserted between the beam splitter 5 and the objective lens 6 in order to pass the beam splitter 5, or a polarization beam splitter may be used as the beam splitter 5. Although omitted here, a well-known method may be used for detecting and controlling the focus signal and tracking signal necessary for actual information reproduction.

Here, the interval between the main lobe and the side lobe in the beam spot 12 is ± L (= ± v · τ /
β; where v is the speed, τ is the delay time, and β is a constant), the optical disc A by the main lobe is detected from the photodetector 7.
A signal corresponding to the recording information at the upper one point and a signal corresponding to the recording information at the points ± L before and after the one point on the optical disc A by the side lobes are detected.

Therefore, assuming that the optical disk A is rotating at the speed v, the signal from the photodetector 7 is i (t) = i ₀ (t) + i ₁ (t + τ) + i ₁ (t−τ). It can be approximated as (1). However, i ₀ (t) represents the detection signal by the main lobe, and i ₁ (t + τ) and i ₁ (t−τ) represent the detection signal by the side lobe.

If this function is Fourier transformed, it can be approximated as I (ω) = I ₀ (ω) {1 + K ₀ [exp (jωτ) + exp (-jωτ)]} (2). However, I (ω) is the reproduced waveform spectrum,
I ₀ (ω) represents the spectrum of the detection signal i ₀ (t) by the main lobe, and I ₀ (ω) · K ₀ represents the spectrum of the two side lobes.

Here, when the spectrum of the output of the equalization circuit 9 is O (ω), the transfer function H (ω) of the equalization circuit 9 is H (ω) = O (ω) / I (ω) = O (Ω) / I ₀ (ω) {1 + K ₀ α [exp (jωτ) + exp (-jωτ)]} (3)

If O (ω) = I ₀ (ω), H (ω) is approximately H (ω) = 1 / {1 + K ₀ α [exp (jωτ) + exp (-jωτ) )]} = 1-2K ₀ αcos (ωτ) ... (4)

Therefore, the equalization circuit 9 which satisfies the above equation (4)
By allowing the signal from the photodetector 7 to pass through, the influence of the side lobes in the beam spot 12 can be suppressed, and the reproduction information with the improved resolution of the main lobe can be extracted.

Here, K ₀ is the size of the side lobe with respect to the main lobe, and τ is τ = βL / v. β is a constant, 0.5 <β <1.5 is preferable, and 0.8 <β <
1.2 is optimal. L is the peak interval between the main lobe and the side lobe, and v is the velocity. α is the error determination circuit 1
It is a constant adjusted by 0, and 0 <α <1 / K ₀ is preferable.

Further, the resolution of the main lobe is equalized by the equalizing circuit 9.
In order to further improve, the transfer function of O (ω) / I ₀ (ω) = exp (aω ² ) ... (5) should be realized. However, a is a waveform slimming coefficient.

Assuming that the wavelength of the actual beam spot is λ ₁ and the target equalization wavelength is λ ₂ , the waveform slimming coefficient a is a = γ [(λ ₁ ) ² − (λ ₂ ) ² ]. 6) Here, γ is a constant determined by the configuration of the optical system.

[0023] Therefore, by substituting equation (5) into equation (3), is modified approximation, the transfer function H (omega) is H (ω) = {1 / (1-3K 1/2)} [1- _{2K 1 α 1 cos (ωτ /} 2) -2 (K 0 -K 1/4) α 2 cos (ωτ)] becomes ... (7). However, K ₁ = 2aπ ² / (3aπ ² + 8τ ² ) (8).

FIG. 3 shows an example of an equalization circuit which realizes the transfer function, here, a 5-tap transversal type equalization circuit, in which 21-1, 21-2, 21-3,
21-4 is a τ / 2 delay circuit, 22-1, 22-2, 22
-3, 22-4 and 22-5 are multipliers and 23 is an adder. Here, in order to realize the transfer function, each constant is set to C.
_{0 = 1, C 1 = -α} 1 K 1, C -1 = -α -11 K 1, C 2
_{= -Α 2 (K 0 -K 1} /4), C -2 = -α -22 (K 0 -
K _1/4) and may be set. That is, as shown in FIG.
Input waveform of equalizer 9 (a) (tap output of constant C ₀ )
Is corrected with a correction waveform (b) (combined output of taps of constants C ₁ , C _-1 , C ₂ , and C _-2 ), an output waveform (c) with improved resolution can be obtained.

Here, K ₀ is the size of the side lobe with respect to the main lobe, and τ is τ = βL / v. β is a constant, 0.5 <β <1.5 is preferable, and 0.8 <β <
1.2 is optimal. L is the peak interval between the main lobe and the side lobe, and v is the velocity. α ₁ , α _-11 , −α
₂ , −α ₋₂₂ are constants adjusted by the error determination circuit 10, and 0 <α ₁ <1 / K ₁ , 0 <α ₋₁₁ <1 /
_{K 1, 0 <-α 2 <} 1 / (K 0 -K 1/4), 0 <-α
_{22 <1 / (K 0 -K} 1/4) are preferred.

FIG. 5 shows an example of the error judgment circuit.
In the figure, 31 is a determination circuit, 32 is a feedback filter, 33 is a control circuit, and 34 and 35 are adders. Here, the partial response class 1 {PR (1,
1)} shows an example of equalization. The waveform of the detection signal shown in Fig. 4 (a) and the correction waveform shown in Fig. 4 (b) are output from taps other than the center of the equalization circuit of Fig. 3. The aim is to form a Nyquist waveform whose output is “1” at 0 and T on the time axis of FIG.

However, in reality, the input waveform of the equalizing circuit 9 varies due to variations in the optical system, shape errors in the recording section due to differences in optical disc sensitivity, various conditions during recording and reproduction, and the like. Therefore, the error determining circuit 10 adjusts the gain in the equalizing circuit 9 to equalize the ideal Nyquist waveform. The output of the equalization circuit 9 is input to the error determination circuit 10, and the determination circuit 31 determines "0" or "1". The judgment result is returned to the front of the judgment circuit 31 by the feedback filter 32. The characteristic of the feedback filter 32 may be 1-P (D) =-D by utilizing the characteristic of PR (1,1) represented by P (D) = 1 + D. Further, since an error in the equalization circuit 9 is generated due to the difference between the input and the output of the determination circuit 31, the gain of the equalization circuit 9 may be adjusted by the control circuit 33 using the value.

In the control circuit 33, with respect to the gain of each tap, it is determined by correlation detection which pulse of the waveform following the error causes the error. Thereby,
The weighting of taps causing intersymbol interference is sequentially controlled and changed to suppress the above-mentioned error. Then, reproduction information having no error can be obtained.

Therefore, the waveform compensation of the super-resolution spot and the equalization to the partial response waveform can be performed by one equalizing circuit, and the circuit scale can be reduced and highly accurate information reproduction can be realized.

FIG. 6 shows another example of the error judgment circuit, in which the coefficient weighting in the feedback filter is also changed. That is, in the figure, 3
Reference numeral 2a is a feedback filter, which sequentially changes the weighting of the coefficient based on the output of the adder 35, that is, the difference between the input and the output of the determination circuit 31. With this configuration, it is possible to perform correction based on the determination result once, and more stable reproduction information can be obtained without incorporating noise or interference included in the detection signal into the equalized waveform. The other configurations and operations are similar to those of the circuit of FIG.

FIG. 7 shows still another example of the error determination circuit, and here, an example is shown in which the information reproduction is performed by another circuit. That is, in the figure, numeral 36 is a maximum likelihood determination circuit (Viterbi decoding method), which determines and outputs the reproduction information with the highest probability based on the amplitude information of the reproduced waveform equalized to the Nyquist waveform. With this configuration, the reproduction information having the highest probability can be determined by the state transition (the transition of the reproduction information), and the error can be determined based on the encoding characteristic and the format characteristic at the time of recording by using this. The waveform equalization is performed by the determination circuit 31, the feedback filter 32, etc., as in the case of the circuit of FIG. 5 or 6.

In FIG. 3, the time constant of the delay circuit is τ.
/ 2 shows the case _{but, τ 1 = (1 / n} ) even tau ₁ satisfying the relationship of tau good. However, n is a positive integer,
τ is τ = βL / v. β is a constant, 0.5 <β
<1.5 is preferable, and 0.8 <β <1.2 is optimal.
L is the peak interval between the main lobe and the side lobe, and v is the velocity.

With the above arrangement, the number of delay circuits is 2n or more, but 4n or less is preferable. Further, this τ ₁ is preferably the same as the cycle of the reproduction information or an integral multiple thereof.

[0034]

As described above, according to the present invention, the light emitted from the light source is condensed to form a beam spot, which is irradiated to the information recording portion of the optical recording medium and the reflected light or In an optical recording / reproducing apparatus that detects transmitted light and reproduces recorded information, an apodizing element that changes the intensity distribution of light so that the beam spot diameter becomes small, and a side lobe in the beam spot from a detection signal of reflected light or transmitted light. Since an equalization circuit that suppresses the influence of the above and an error determination circuit that adjusts the equalization coefficient of the equalization circuit are provided, the influence of the side lobes of the super-resolution spot is suppressed without providing a minute slit in the optical system. Therefore, it is possible to reproduce information with high resolution and high accuracy. Further, by adjusting the equalization coefficient of the equalization circuit so that the waveform of the detection signal becomes the partial response waveform by the error determination circuit,
It is possible to reproduce information with higher accuracy.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of an optical recording / reproducing apparatus of the present invention.

FIG. 2 is a diagram showing a light intensity distribution of a beam spot with which an information recording portion of an optical disc is irradiated.

FIG. 3 is a configuration diagram showing an example of an equalization circuit.

FIG. 4 is a diagram showing a state of waveform equalization by an equalization circuit.

FIG. 5 is a configuration diagram showing an example of an error determination circuit.

FIG. 6 is a configuration diagram showing another example of an error determination circuit.

FIG. 7 is a configuration diagram showing still another example of the error determination circuit.

[Explanation of symbols]

1 ... Semiconductor laser, 2, 3 ... Collimating lens, 4 ... Apodizing element, 4a ... Shading band, 5 ... Beam splitter,
6 ... Objective lens, 7 ... Photodetector, 8 ... Amplifier, 9 ... Equalization circuit, 10 ... Error determination circuit, A ... Optical disk.

Claims (5)

[Claims] 1. A light spot emitted from a light source is condensed to form a beam spot, which is applied to an information recording portion of an optical recording medium, and reflected light or transmitted light thereof is detected to reproduce recorded information. In an optical recording / reproducing apparatus, an apodizing element that changes the intensity distribution of light so that the beam spot diameter becomes small, an equalization circuit that suppresses the influence of side lobes in the beam spot from a detection signal of reflected light or transmitted light, An optical recording / reproducing apparatus provided with an error determination circuit for adjusting the equalization coefficient of the equalization circuit. 2. The optical recording / reproducing apparatus according to claim 1, further comprising an error determining circuit for adjusting an equalization coefficient of the equalizing circuit so that the waveform of the detection signal becomes a partial response waveform. 3. A judgment circuit for judging whether the output of the equalization circuit is "0" or "1", a feedback filter for feeding back the output of the judgment circuit to its input side, and an input and an output of the judgment circuit. 3. The optical recording / reproducing apparatus according to claim 2, further comprising an error determination circuit including a control circuit that adjusts the equalization coefficient of the equalization circuit based on the difference. 4. The optical recording / reproducing apparatus according to claim 3, wherein the coefficient of the feedback filter is adjusted based on the difference between the input and the output of the determination circuit. 5. A maximum likelihood judgment circuit for reproducing recorded information from the output of the equalization circuit is provided.
The optical recording / reproducing apparatus described.