JPS61150148A - Reproducing device of composite signal recording medium - Google Patents

Abstract

PURPOSE:To separate both signals without increasing the number of components of the optical system by reproducing an photomagnetic signal and an optical intensity signal based on the difference and sum of outputs of a photoelectric converting element photoelctric-converting two-split lights respectively. CONSTITUTION:A linearly polarized output from a laser light source L is irradiated to a composite signal recording medium recorded by the photomagnetic signal and the optical intensity signal on a disk D via a beam splitter BS. The reflected light is made incident to a polarized beam splitter PBS via the splitter BS and a lambda/2 plate J, and divided into the S and P deflections. The luminous flux shared by the splitter PBS is converted into a current in response to the photo intensity by photoelectric converting elements T1, T2 and converted into a voltage signal by buffer amplifiers Amp1, Amp2. The amplifiers Amp1, Amp2 are connected respectively to a differential amplifier M and a summing amplifier N, and an excellent photomagnetic signal whose noise component is suppressed is outputted from the amplifier M and the in-phase component, i.e., the optical intensity signal is outputted from the amplifier N.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field of the Invention) The present invention relates to a reproducing apparatus for reproducing a magneto-optical signal and an optical intensity signal recorded on the same track or different tracks of the same recording medium.

(Background of the Invention) The applicant of the present application proposed in a patent application filed in 1983 that the recording density could be increased by alternately arranging magneto-optical signal tracks and optical intensity signal tracks on one recording medium. 1913◆0, a reproduction system known as the 45° differential method was used as a reproduction device for reproducing a recording medium in which signals were recorded using such a magneto-optical signal and an optical intensity signal. The 45° differential method, which can be considered as shown in FIGS. 11 and 12, is a type of differential method known as a reproduction method that can remove common mode noise. In FIGS. 11 and 12, D is a disk-shaped recording medium C (hereinafter referred to as a disk) recorded using both magneto-optical and optical intensity signals, L is a laser light source, and 10 is an objective lens that is used to detect light from the laser light source. The disk D is irradiated with light as a beam spot. BS is beam splitter, PB
S is polarizing beam splitter, Jl-1'/2 plate, T1~
T3 is a photoelectric conversion element, Amp1 to Amp3i is a buffer amplifier, M is a differential amplifier, and Sl is a differential amplifier.

is a reproduced signal of the magneto-optical signal, and S11 is a reproduced signal of the optical intensity signal.

However, as shown in FIG. 11, since two beam splitters BSI and BS2 are inserted in the reproduction optical system, the amount of light to the photoelectric conversion elements T and T3 is reduced.

Particularly in the reproduction of magneto-optical signals, if the amount of light decreases, the S/N ratio of the reproduced signal may become insufficient. Also the first
According to FIG. 2, since the beam splitter BSI is inserted in the optical path from the laser light source to the disk D, the amount of light to the disk D is reduced. Therefore, as described above, there is a possibility that the S/N ratio of the reproduced signal, especially the magneto-optical signal, may be reduced.

In addition, in both FIGS. 11 and 12, the components of the magneto-optical reproducing device include a beam splitter BS2 and a photoelectric conversion element T.
This has the disadvantage that the number of elements increases, resulting in an increase in cost.

In particular, an increase in the number of components of the optical system also results in an increase in the size of the device.

It is clear that even if the above-mentioned technique is applied to reproduction using a differential method other than the 45° differential method in which the amount of light is not divided into equal parts, the same drawbacks will occur.

(Objective of the Invention) The present invention provides a magneto-optical signal and an optical intensity signal that can obtain a reproduction signal (especially a reproduction signal of a magneto-optical signal) with a sufficiently high S/N ratio without increasing the number of components of an optical system. It is an object of the present invention to obtain a reproducing apparatus using a differential method, which is suitable for reproducing signals from a composite signal recording medium on which signals are recorded.

(Embodiment) FIG. 1 is an enlarged partial plan view of a composite signal recording medium (disc) in which a magneto-optical signal and a light intensity signal are recorded in an overlapping manner on the same spiral or concentric track.

In FIG. 1, the pit array indicated by a solid line represents a light intensity signal, for example, an uneven pit array, and the pit array indicated by a dotted line represents a magnetic pit due to perpendicular magnetic recording. The magnetic pits are formed by reversing the magnetization direction of a perpendicular magnetization layer that has been previously magnetized in a certain direction.

Figure 1 T P a , ~ Pats and Pb , ~ P
b and 6/fi are the uneven pit row and magnetic pit row of the first track, respectively. Also, Pa2. ~Pa25 and pb
2. -pb27 are a concavo-convex pit row and a magnetic pit row of the second track, respectively.

Fig. 2 Fi is a cross-sectional view taken along the line A-A in Fig. 1. In Fig. 2, 1 is a signal formed by an uneven pit row on one surface of a transparent plastic disk by a known method such as injection molding. The transparent substrate 2Fi is a perpendicular magnetization layer laminated on the surface of the transparent substrate 1 on which the uneven pit array is formed by a known method such as sputtering. The protective layer is formed by laminating the 3Fi perpendicular magnetization layer by a known method such as sputtering, and is made of, for example, SiO2 or AIN.

Reference numeral 4 denotes a highly rigid disc-shaped substrate made of glass, plastic, aluminum, or the like, which is adhered and integrated with an adhesive 5 to form a disc-shaped recording medium. The magneto-optical recording medium configured in this manner can record, reproduce, erase, and re-record magneto-optical signals in the same way as conventional magneto-optical recording media, completely independent of the concavo-convex pit array. Of course, since the light intensity signal is a concave and convex pit array, it can only be reproduced and recorded.

It is impossible to erase or re-record.

FIG. 3 shows an embodiment of the reproducing circuit for the recording medium described above, and is an example in which a reproducing method known as the 45 differential method is used. In FIG. 3, the disk D is rotationally driven by a drive device (not shown). The disk DK is a linearly polarized light output from a laser light source using a conductor laser, part of which is reflected by a beam splitter BS, the rest transmitted, and the beam is narrowed down to the diffraction limit by an objective lens 10. The recording medium is irradiated as a spot. The reflected light from the disk D includes a light intensity signal due to the uneven pit array and a magneto-optical signal due to the magnetic pit array due to perpendicular magnetic recording, that is, a rotation of the plane of polarization due to the Kerr effect. The reflected light passes through the beam splitter BS and enters the λ/2 plate J (where λ is the wavelength of the optical output of the laser light source). The λ/2
Plate J is an optical element that has the function of rotating the plane of polarization, and its rotation rotates the plane of polarization of the light beam incident on the polarizing beam splitter - PBS, and the rotation angles on both sides relative to the reference plane are adjusted to 45°. The photoelectric conversion elements, for example, the PIN photodiodes T1 and T2 are configured to distribute the light so that the average amount of light is equal. Here, the polarizing beam splitter - PBS is an optical element that has the function of total reflection of S-polarized incident light and total transmission of P-polarized incident light. It is an optical element that converts light intensity. The light flux distributed by the polarizing beam splitter-PBS is transferred to the photoelectric conversion element T
, , T2 converts it into a current according to the light intensity and outputs it, and converts it into a voltage signal at a buffer amplifier. The output S2 of the buffer amplifier Am p 2 is an output of P-polarized light and is applied to the + terminal of the differential amplifier M and the middle terminal of the summing amplifier N.
The output S1 of pl is an output of S-polarized light, and is applied to one leaker of the differential amplifier M and the other + terminal of the summing amplifier N.

In this reproduction optical system, the λ/2 plate J and the polarization beam 7'
The function of distributing light according to the plane of polarization of the reflected light beam by the Ritter PBS will be explained in detail below.

First, the light incident on the disk D as linearly polarized light changes the polarization plane force θkf of the reflected light due to the fluoro effect depending on the direction of magnetization (upward or downward) in the disk D.

Varies within the range of .

Furthermore, since a light intensity signal based on a concavo-convex pit array is recorded on the disc D, the amount of reflected light 9 also changes.

That is, if shown in the vector diagram of Fig. 8, the incident linearly polarized light is Or
Then, when the amount of reflected light from the disk D is large, the plane of polarization becomes the vector OK or OF depending on the magnetization direction.
As shown in , it rotates within the range of ±θ, and when the amount of reflected light is small, the plane of polarization changes to the vector OE/, depending on the direction of magnetization.
Rotate as shown in OF/. In this way, for the incident light,
The reflected light beam whose polarization plane changes within the range of ±θ and whose amount of reflected light changes is incident on the λ/2 plate J. As mentioned above, the polarization plane is changed from the reference plane by the λ/2 plate J. 4 on both sides
Since the angle is adjusted to 5°, the average amount of light to the photoelectric conversion element TInT2 is distributed equally. At this time, on the photoelectric conversion element T2, light that changes between the large amount of reflected light and QC, OD, which is the projection of the vectors OE and OF on the OH axis in FIG. Above are vectors OE, O
Light that changes between OA and OH, which is a projection of F on the OG wheel axis, is irradiated. Furthermore, when the amount of reflected light is small, the vectors OE/, O in FIG.
The light that changes between QC' and OD', which are the projections of F' on the OH axis, is on the photoelectric conversion element T, and the vector OE',
Light that changes between OA/ and 087, which is a projection of OF' on the OG wheel axis, is irradiated.

FIG. 4 is a diagram of signal waveforms at various locations in the reproducing circuit shown in FIG. 3. (a) is the output signal waveform of buffer amplifier Aml) 2, (b) is the output signal waveform of buffer amplifier Ampl, (C) is the output signal waveform of differential amplifier M, (d)
shows the output signal waveform of the summing amplifier N.

In the reproducing circuit shown in FIG. 3, photoelectric conversion element T2. T.

contains a magneto-optical signal due to magnetic pits of perpendicular magnetic recording and a light intensity signal of changes in the amount of reflected light due to uneven pits, respectively, and buffer amplifier Amp2 includes
, is converted into a voltage signal by Amp 1, and is shown in Fig. 4 (&
), (b) The output signal waveform is shown as K. Fourth
Although the figure shows a case where the magneto-optical signal is a higher frequency signal than the optical intensity signal, it is of course not limited to this.
There are no restrictions on the frequency bands of both signals. In the differential amplifier M, the two input signals of the optical intensity signal are in phase, so they are canceled out, and only the opposite phase component, that is, the magneto-optical signal is fi! J4 diagram (c)
Also, at this time, noise components proportional to the average light amount (for example, light source noise, light amount fluctuation noise due to dust or scratches on the disk D), Fi, are in phase, so they are suppressed by the differential amplifier M. and a high-quality magneto-optical signal is reproduced.

Although the in-phase component slightly AM-modulates the magneto-optical signal, this does not pose any problem in detecting and determining the presence or absence of magnetic pits or the length of the pits.

On the other hand, in the summing amplifier N, the two input signals of the magneto-optical signals are of opposite phases and are therefore canceled out, and only the in-phase component, that is, the optical intensity signal is outputted as shown in FIG. 4(d).

In this way, if a magneto-optical reproducing device such as the embodiment shown in Fig. 3 is used, the magneto-optical signal and the optical intensity signal can be separated very easily with a good S/N ratio without increasing the number of components in the optical system. can do.

FIG. 5 shows another embodiment of the invention. In Figure 5, λ/
The setting angle of the two plates J is different from that shown in Fig. 3, and the rotation angles on both sides with respect to the reference plane are not 45 degrees, so that the amount of light to the photoelectric conversion elements T, , T3 is equal. In this embodiment, where no distribution is made, the set angle θ of the λ/2 plate J is set to, for example, θ=10°, as shown in the vector diagram of FIG.

Also, one of the photoelectric conversion elements T3 uses an avalanche photodiode (hereinafter referred to as APD), and unlike in Fig. 3, an summing amplifier 40 is not provided. In the reproduction optical system shown, the behavior of the reflected light beam from the disk D is similar to that of the optical system shown in FIG. 3 of the previous embodiment. That is, when the amount of reflected light is large, The light that changes between QC and OD, which are the projections of the vectors OE and OF on the OH axis in FIG. In addition, when the reflected light is 1 small, the projections of the vectors OE/ and OF/ in FIG. 9 on the OH axis are shown on the APDT3.
c'.

The light that changes between OD/ is on the photoelectric conversion element T1 as OA', which is the projection of vector OE/, OF' on the OG thin axis.
.

Light that changes between OB' is irradiated.

Here, Z10E=ZIOF=θ.

At this time, in the embodiment shown in FIG. 5, unlike the embodiment shown in FIG. 3, the average light amount on the APDT T and on the photoelectric conversion element T1 are not equal. Therefore, even if you convert the current to voltage with Amp2 and Ampl with the buffer amplifiers and take the differential with the differential amplifier M, the magnitude of the common-mode noise component proportional to the average light intensity will not be equal between the two inputs. Since the noise is not suppressed, a high-quality magneto-optical signal cannot be reproduced. Therefore, in order to exhibit the noise suppression effect, in this embodiment, the one with the smaller average light amount is amplified using the APDT 3. At this time, in order to exhibit the noise suppression effect, both photoelectric conversion elements T3. What should we do so that the asymmetric photocurrents output from T are equal? Using θ in Figure 9, AP
The DO multiplication factor may be set as below. In other words, since the average light amount on the APDT3 side th2θ and the average light amount on the photoelectric conversion element T1 side 41 cas2θ, for example, if θ=10° is chosen, m=”/210° will be 32.2 s I .

FIG. 6 shows signal waveform diagrams at various points in the reproducing circuit when the multiplication factor m of the APDT 3 is set in this manner. Similarly to Fig. 4, (a) Fi buffer core amplifier Ar11p
2 output signal waveform, (b) Fi buffer core amplifier Amp
The output signal waveform of No. 1 is shown. In the differential amplifier M, the multiplication factor m of the APDT 3 is set so that the magnitude of the common-mode noise component is equal, so the optical intensity signal, which is the common-mode component, is also canceled, as shown in FIG. 6(e). Output. Here, due to the in-phase component, the polar (slightly magneto-optical signal becomes AM
Although it is modulated, there is no problem in detecting and determining the presence or absence of magnetic pits or the length of the pits. - The tip strength signal is shown in FIG. 6 ('b), and the signal SI which is the output of the buffer amplifier 38 may be used. Unlike the embodiment shown in FIG. 3, the embodiment shown in FIG. 5 In this case, the summing amplifier N is not provided. This is λ/2 board JK
Since the distribution ratio of the amount of light caused by the magneto-optical effect is equal to 1, the signal shown in FIG. 6(b) actually includes a component due to the magneto-optical signal.
This is because it is possible to ignore optical intensity signals that have a large degree of modulation and can reproduce high-quality signals. Therefore, compared to the embodiment shown in FIG. 3, there is an advantage that the addition amplifier N can be omitted.

As described above, the embodiment shown in FIG. 5 is more suitable than the embodiment shown in FIG. 3 when the degree of modulation of the magneto-optical signal component is lower, that is, when the Kerr rotation angle θk of the magneto-optical reproduction signal is small. It can be said that In addition, in actual use, the differential amplifier used is ideal and has a common mode rejection ratio (CMRR: C
ommonModeRejectionRatio
) is infinite, it is possible to completely remove the common-mode noise component or the common-mode signal component, which is balanced in size. However, in an actual differential amplifier, the common-mode signal rejection ratio (CM
RR) does not become infinite, and in this case, θ shown in FIG.
= 45, rather than making the amount of light the same, the distribution is the 9th
As shown in the figure, when θ is set to 45 degrees or less and the amount of light distributed on the APDT3 side is reduced, the proportion of the common-mode component in the reproduced signal on the APDT3 side will be smaller, and the removal of the common-mode component by differential amplification will be easier. It's advantageous.

Of course, if the degree of modulation of the magneto-optical signal becomes high enough that it cannot be ignored with respect to the optical intensity signal, it is sufficient to provide a summing amplifier to suppress the magneto-optical signal component with respect to the optical intensity signal. As shown in the figure, in addition to the summing amplifier N, a one-novel adjustment mechanism K must be provided to equalize the magnitudes of the magneto-optical signal components at the two inputs of the summing amplifier N.

Specifically, it may be used as an amplifier for the output signal SI of IdAmp1, or as an attenuator for the output signal S2 of ArrIp2. In some cases, both may be used.

In the embodiment shown in FIG. 5, an APD is used as a photoelectric conversion element having an amplification function, but a normal photoelectric conversion element (for example, a PIN photodiode) and an amplifier may be used.

In that case, there is a possibility that a sufficient S/N ratio of the noise reproduction signal generated by the APD itself cannot be ensured. Also,
Each of the two separated lights may be photoelectrically converted by an APD. When photoelectric conversion is performed using two APDs in this manner, a temperature compensation circuit for the APDs can be made unnecessary by installing the circuit so that the temperature conditions for the two APDs are the same. That is, since the temperature conditions of the two APDs are the same, the same amplification factor changes with respect to temperature, and as a result, there is no relative difference in the common mode components contained in the two input signals at the input of the differential amplifier M, and the APD Even if the temperature conditions change, the common mode components input to the differential amplifier M can always be matched.

In addition, in the embodiments shown in FIGS. 3, 5, and 10, λ/2
The combination of Plate J and Polarizing Beam Splitter-PBS rotates the polarization plane of the reflected light and distributes it into two optical paths.By rotating the Polarizing Beam Splitter-PBS itself around the optical axis, a λ/2 plate is created. J can be omitted.

FIG. 7 shows another example of a medium that can be used in the present invention, in which a magneto-optical signal I/'i by perpendicular magnetic recording is recorded between optical intensity signal tracks by concave and convex bit strings previously recorded in a spiral or concentric manner. It is. In the case where the optical intensity signal track and the magneto-optical signal track are separately provided in this way, the optical intensity signal is not formed by a concave-convex pit array, but for example, the perpendicular magnetization layer is made of an amorphous material, and a high-output laser beam is irradiated. By crystallizing the irradiated portion, the reflectance of light may be varied, thereby obtaining a light intensity signal.

It can also be used as a reproducing circuit when reproducing a disc in which such optical intensity signals and magneto-optical signals are recorded on separate tracks.
The embodiments described above are applicable.

In a medium such as this example in which magneto-optical signals and optical intensity signals are arranged alternately, it is not possible to reproduce both signals at the same time. However, since the magneto-optical signal and the optical intensity signal can be separated as in the previous embodiment, the pitch of the track of the magneto-optical signal track and the optical intensity signal is set to 1/1/2 of the track pitch of the same type of signal. 2. This makes it possible to double the density of the information signal compared to a conventional optical system using the same beam spot.

In the above embodiments, all disc-shaped recording media are shown, but the external shape of the image is not limited to this, and may be any shape as long as the recording/reproducing light beam and the medium can move relative to each other. Alternatively, the recording/reproducing light beam and the medium may be configured to move relatively linearly.

(Effects of the Invention Joqin) As described above, according to the present invention, a composite signal recording medium in which a magneto-optical signal and an optical intensity signal are recorded on the same or different tracks of the same recording medium can be realized by increasing the number of optical members. Therefore, it is possible to obtain a reproduced signal with a sufficiently high S/N ratio.

[Brief explanation of drawings]

FIG. 1 is an enlarged partial plan view of a composite signal recording medium, FIG. 2 is a sectional view taken along the line A-A in FIG. 1, FIG. 3 is an embodiment of the present invention, and FIG. Signal waveform diagrams at various points in the embodiment shown in the figures, No. 5 A is another embodiment of the present invention, and FIG.
FIG. 7 is an enlarged partial plan view of a composite signal recording medium according to another example; FIG. 8 is a vector diagram illustrating reproduction operation using the 45° differential method. ,
FIG. 9 is a vector diagram explaining the reproducing operation when the amount of light is divided unevenly, FIG. 10 is another embodiment of the present invention, and FIG.
12 shows a reproducing apparatus for a composite signal recording medium. (Explanation of symbols of main parts) D... Disk 10... Objective lens BS... Beam splitter J... λ/2 plate PBS... ...Polarizing beam splitter T, , I
'2...Photoelectric conversion element Amp1, Amp
2...Buffer amplifier M...Differential amplifier N...Additional amplifier L...Laser light source T3...APD

Claims (2)

[Claims] (1) Laser light source; an optical system that irradiates the laser light source in a spot shape onto a composite signal recording medium recorded with a magneto-optical signal and a light intensity signal; An optical path splitting member that splits the light into two optical paths; two photoelectric conversion elements that photoelectrically convert the light split by the optical path splitting member; reproducing a magneto-optical signal based on the difference in output of the two photoelectric conversion elements; A reproducing apparatus for a multiple signal recording medium, including a magneto-optical signal reproducing means for reproducing an optical intensity signal based on the output of one of the two photoelectric conversion elements. (2) The apparatus for reproducing a composite signal recording medium according to claim 1, wherein the optical path dividing member divides the light into two optical paths with unequal amounts of light.