JPS63100648A - Magneto-optical information reproducing device - Google Patents

Abstract

PURPOSE:To improve C/N in terms of signal detection by using a polarization beam splitter with an optimum polarization characteristic for a magneto-optical information reproducing device and setting the optical axial orientation of a detection means most suitable. CONSTITUTION:A semiconductor laser 21 emits a P polarization luminous flux, and projects a light spot with an intensity I0 to a recording medium 26 through the polarization beam splitter 12. The reflected luminous is modulated to be polarized, and led to a photodetector 27. Here the mean of the intensity of a polarization component which is not subjected to modulation due to an magnetic optical effect is denoted as IR, the mean of the squared fluctuation of intensity in a magneto-optical signal observation frequency as DELTAI<2>, xsi is shown by equiation 1, the luminous energy of light incident on the recording medium 26, is denoted as I0, amplitude reflectance as R, light usage efficiency from the recording medium to a photodetector 29 except for the splitter 12 and a light detection means as epsilon, amplitude transmissivity as tA, a quenching rate as etaA, photoelectric conversion efficiency as (kappa), the thermal noise of an amplification means as T, the band width of a detection signal as DELTAB, amplitude reflectance with respect to the polarization component in the prescribed direction of the splitter 12 as rP, amplitude reflectance with respect to the polarization components in the prescribed and vertical directions and an angle made by the optical axis of the light detection means and the prescribed direction as thetaA. All of them satisfy equations II-IV.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a magneto-optical information reproducing device that reproduces information magnetically recorded on a recording medium by utilizing the magneto-optical effect.

[Prior art]

In recent years, optical memories that perform recording and reproduction using semiconductor laser light have been actively researched and developed for practical use as high-density recording memories. Among these, in addition to read-only optical disks typified by already commercialized compact disks and DRAW type optical disks, magneto-optical disks that are particularly erasable and rewritable are becoming promising. Magneto-optical disks magnetically record information using the local temperature rise of a magnetic thin film caused by laser spot irradiation, and reproduce the information using the magneto-optic effect (particularly the Kerr effect). The Kerr effect here refers to a phenomenon in which the plane of polarization rotates when light is reflected by a magnetic recording medium.

FIG. 9 shows the basic configuration of a conventional magneto-optical disk device. In FIG. 9, l is a semiconductor laser, 2 is a collimator lens, 11 is a half mirror, 14 is an objective lens, 6 is a magneto-optical recording medium, 7 is an analyzer, 8 is a condensing lens, 9 is a photodetector, P The polarization direction is parallel to the plane of the paper, and the S polarization direction is perpendicular.

Next, the case where magneto-optical information is reproduced in the above device will be explained. The light beam emitted from the semiconductor laser 1 as linearly polarized light in the P polarization direction is converted into a parallel light beam by the collimator lens 2, and passes through the half mirror 11. The amplitude transmittance of the P polarized light component is tl・, and the amplitude transmittance of the S polarized light component is t.
s, in 11, 1tp l"= l ts
I”=0.5.The light beam is transmitted by the objective lens 4,
An image is formed on the magneto-optical recording medium 6 as a minute spot. When magnetic domains (pits) are formed on the medium 6 in advance, the reflected light from the medium 6 is directed in the magnetization direction (upwards or downwards) of the spot irradiation area due to the Kerr effect, as shown in Figure 1O. Accordingly, the plane of polarization is rotated by ±θ, respectively. Here, if the P polarization component of the amplitude reflectance of the recording medium 6 is K and the RSS polarization component is K, the following equation holds true.

The magneto-optically modulated reflected light is again converted into a parallel beam by the objective lens 4, reflected by the half mirror 11, and then passed through the analyzer 7.
is converted into an intensity-modulated luminous flux. That is, the 10th
In the figure, the reflected light flux is analyzed as the orthogonal projection of its amplitude onto the optical axis of the analyzer, so the intensity of the light incident on the magneto-optical medium is Io, and the angle θ^ of the optical axis of the analyzer from the P polarization direction is If the signal light is set at 45° to maximize the signal light, then the intensity of the light flux transmitted through the analyzer I00κ and 1−θ will be calculated as shown in equation (2), depending on the Kerr rotation angle ±θK. make it rain.

Since θ is -10, IRI2)IK12 holds true, so equation (2) can be expressed as -. The second term in the parentheses of equation (3) is the magneto-optical modulation component, and the first term is the ratio modulation property. The light flux converted into intensity modulation in this manner passes through a condenser lens 8 and is detected by a photodetector 9 as a magneto-optical signal.

However, such a conventional optical system using a half mirror 11 without polarization characteristics has the following drawbacks.

l) The Kerr rotation angle θ is approximately 10°, and the resulting magneto-optical modulation component is extremely small, so by passing through a half mirror that does not have polarization characteristics, the amount of light from the magneto-optical modulation component can be halved. C/N of the detection signal is
(ratio of carrier wave to noise) decreases.

2) There are multiple types of noise superimposed on the detection signal.
Since each has a different θ^ dependence, if the analyzer optical axis is set at 45° toward θ where the signal is maximum without taking these into account, the C/N of the detection signal will decrease.

3) Due to the low C/N, conventional devices must use complex detection systems to detect magneto-optical signals, such as photodetectors with motion detection and amplification functions (such as avalanche photodiodes). However, it is disadvantageous in terms of cost and reliability.

[Summary of the invention]

The purpose of the present invention is to improve the above-mentioned drawbacks of the prior art, and to enable reproduction of magneto-optical signals with good C/N with a simple configuration using an inexpensive photodetector that does not have an amplifying effect such as a Vinfort diode. The object of the present invention is to provide a magneto-optical information reproducing device.

The above-mentioned object of the present invention is to provide a magneto-optical information reproducing device with a means for irradiating a light beam polarized in a predetermined direction onto a recording medium on which information is magnetically recorded; a polarizing beam splitter that reflects and transmits the reflected or transmitted light beam from the recording medium modulated by the recording medium at a predetermined ratio according to its polarization component; and an analyzer that analyzes the light beam reflected by the polarization beam splitter. a non-amplifying photodetector for photoelectrically detecting the light beam transmitted through the analyzing means; and an amplifying means for amplifying the detection signal of the photodetector and reproducing the information, and the polarizing beam splitter This is achieved by setting the polarized light reflectance-transmittance characteristics and the optical axis direction of the detection means so as to satisfy the following equation. That is, when the photodetector detects the reflected light of the polarizing beam splitter, , 1 , -: " ) 1r, 1" ~ 1 Also, when the photodetector detects the transmitted light of the polarizing beam splitter, l ts l 1. However, here, the angle between the optical axis of the analyzer and the predetermined direction is θA, and the amplitude reflectance and amplitude transmittance of the polarization beam splitter for the polarized light component in the predetermined direction are rp, ts, respectively, the amplitude reflectance and amplitude transmittance for the polarized light component in the direction perpendicular to the predetermined direction, and rS, t, respectively, the average intensity of the polarized light component that is not modulated by the magneto-optic effect incident on the photodetector. TR1 is the root mean square of this intensity fluctuation at the magneto-optical signal measurement frequency, △I2R9ξ=△I2+< /horse, the light intensity of the incident light beam on the recording medium is I0, and the amplitude reflectance of the recording medium is R1 the polarizing beam splitter. and excluding the light analysis means (the light utilization efficiency of the optical system from the recording medium to the photodetector is ε, the photoelectric conversion efficiency of the photodetector is k, and the thermal noise of the amplification means at the magneto-optical signal observation frequency is T1 detected) The signal bandwidth is ΔB1, the amplitude transmittance of the analyzer is tA, and the extinction ratio of the analyzer is ηA.

〔Example〕

Hereinafter, the present invention will be explained in detail using the drawings.

1 and 2 show a first embodiment of a magneto-optical information reproducing apparatus based on the present invention, respectively. FIG. 1 is a schematic configuration diagram of an optical system, and FIG. 2 is a schematic configuration diagram of a signal processing circuit. be. In FIG. 1, 21 is a semiconductor laser, 22 is a collimator lens, 12 is a polarizing beam splitter, 24 is an objective lens,
26 is a magneto-optical recording medium, 27 is an analyzer, 28 is a condensing lens, and 29 is a non-amplifying photodetector such as a focusing photodiode, in which the P polarization direction is parallel to the plane of the paper and the S polarization direction is perpendicular. Further, reference numeral 13 indicates a luminous flux transmitted through the analyzer 27, and this detected luminous flux 13 is photoelectrically converted by a photodetector 29 as shown in FIG. It is output as a playback signal.

In the above device, the semiconductor laser 21 emits a P-polarized light beam. This emitted light flux becomes parallel light by the collimator lens 22, passes through the polarizing beam splitter, and is irradiated onto the recording medium 26 by the objective lens 24 as a light spot with an intensity I0. The light beam reflected by the recording medium 26 is modulated in its polarization state according to the information magnetically recorded on the recording medium 26, passes through the objective lens 24 again, is reflected by the polarizing beam splitter 12, and is detected. Guided by photon 27. The detection light 13 that has passed through the analyzer 27 is intensity-modulated and is received by a photodetector 29 via a condenser lens 28 . Here, the amplitude transmittance of the P-polarized light and the S-polarized light of the polarizing beam splitter are tp and ts, respectively, and the amplitude reflectance is rp, rSs, and the amplitude transmittance of the analyzer 27 is tA.
(equivalent in the P and S polarization directions), and when the erasure ratio is η^, the intensity of the detection light 13 can be expressed by the following equation (4).

Considering that l Rl”> l K 1*, (4
) formula is called.

In equation (5), the second term in the parentheses is a magneto-optical modulated component, and the first term is a non-modulated component, and the intensities of each are assumed to be 1K and I+t.

Ik~-1o1tAl”lRI IK l l nl
l rSl (1-77A) 5in20^(6)! *
~IoltΔl”lR1”1rpl” (COS2OA
+77A sin”θA)
(7) Incident light ■. The output of the semiconductor laser is adjusted so that a predetermined amount of light is obtained, regardless of the amplitude transmittance tp, t5 of the polarizing beam splitter.

The light beam intensity-modulated in this way is converted into a photocurrent by a photodetector 29 shown in FIG. For the photoelectric conversion efficiency, e is the charge type, h is the blank constant, ρ is the quantum efficiency of the photodetector,
It is given by a linear equation where ν is the frequency of the light flux.

In the present invention, as a result of detailed examination of the noise superimposed on the detection signal through numerous experiments, it was found that there are four types of noise as shown below, each of which has a different dependence on the azimuth angle θΔ of the analyzer. did.

l) Noise caused by the root mean square intensity fluctuation Δ12R of the non-modulated component light IR 2) Noise caused by the root mean square intensity fluctuation ΔI2K of the modulated component light I 3) Shot noise of the photodetector 4) Due to the amplifier Thermal noise 1) △I2R noise and 2) △12K noise are caused by surface roughness and non-uniformity of the recording medium, semiconductor laser
ξ is a constant determined by the noise source such as the medium or semiconductor laser, which is caused by fluctuations in the intensity of the laser.

ζ, the average of the effective values of the non-modulated component and the modulated component are respectively IR,
If T, then the following formula holds true.

Δp, si=ξ notice ΔB (9) ΔI2=ζ & ΔB (10) However, ΔB is the bandwidth of the detection signal.

The noise caused by △I2R, the noise caused by △I2, shot noise, and thermal noise are respectively FR, Fκ, S, and T.
Then, it can be calculated by the following formula.

FR=ξK” To FR8 (H
) Fk=ζ2′PKΔB (1
2) S = 2 e K T R△B
(13) where k is the Boltzmann constant, Te is the equivalent noise temperature, and R+ is the resistance value of the load resistor 16.

From equations (6) and (7), the analyzer optical axis azimuth 0Δ
and extinction ratio η8, the magneto-optical modulation component intensity IK is (
1-ηA) 5in2θΔ, unmodulated component intensity IR is c
Since there is a dependence of o s2θΔ+η8s in2θΔ, the dependence of each noise on θ can be expressed as follows.

FR(X: (COS”θJinshi η to 5in2θA)2(
15) FK” (1-178) sin”θA(1
6) Soccos2 θ A + η A
S in” θ 8
(17) T=const
(18) Using these, C/
If N is expressed in decibels, it will be as follows.

t Since C/N in equation (19) is a function of the amplitude reflectance rP, rS of the polarizing beam splitter and the tilt θΔ of the analyzer optical axis from the P polarization direction, equation (19) can be expressed as Irp, respectively.
It is sufficient to partially differentiate with respect to l, 1rSl, and θA to find the maximum value.

The C/N can be maximized under the following conditions.

0< l rp l"< 1
(21) l rS l”= 1
(22) Third
The figure is a schematic configuration diagram of an optical system showing a second embodiment of the present invention. This embodiment is a modification of the first embodiment described above so as to detect the transmitted light flux of the polarizing beam splitter 2.
In FIG. 3, the same members as in FIG. 1 are given the same reference numerals, and detailed explanations are omitted. Moreover, the signal processing circuit similar to that shown in FIG. 2 can be used.

In the case of this embodiment, the polarization direction of the semiconductor laser 21 is
The S polarization direction may be set perpendicular to the plane of the paper, and the P and S polarization directions used in the explanatory text of FIG. 1 may be replaced. However, in equations (4) to (7), rl・ is ts,
It is necessary to replace rS with tp. That is, 1K ~-
1゜l tΔ121 RI K l ts l tp
l (1-r) 8) 5in2θA (24
)N IR-10l tAI ” l Rl ” l ts
l” (cos”θA+ 77 to 5in2θA
) (25) The C/N in equation (19) is a function of the amplitude transmittance ts, tr+ of the polarizing beam splitter and the tilt θ^ of the analyzer optical axis from the P polarization direction, so (1
9) Each expression l ts l .

It is sufficient to partially differentiate l tpl and θA to find the maximum value. Therefore, 0≦Its・12≦1(27) 1 t p + ! where C/N is the maximum value under the following conditions. = 1 (28) FIG. 4 is a schematic diagram showing a third embodiment of the present invention. In FIG. 4, the same members as in FIG. 1 are designated by the same reference numerals, and detailed explanations will be omitted. In this embodiment as well, the signal processing system after the photodetector 29 is constructed as shown in the second diagram.

In this embodiment, the polarizing beam splitter 12 of the first embodiment is
Instead of κ, a polarizing beam splitter 23 having a beam shaping function is used. As a result, the light beam of the semiconductor laser 21 having an elliptical far-field pattern is transferred to the recording medium 2.
6 can be efficiently imaged as a circular spot. Further, the surface a is inclined at a predetermined angle so that stray light does not enter the photodetector 29.

A focusing groove (not shown) for tracking is formed on the recording medium 26 in a direction perpendicular to the paper surface, and the light beam focused on the recording medium 26 by the objective lens 24 is diffracted by this groove. Ru. A photodetector 25 is fixed to the periphery of the aperture of the objective lens 24 for detecting an imbalance of ±1st-order diffracted light caused by track deviation.

Therefore, even if the objective lens 24 moves in a direction perpendicular to the track groove, there is an advantage that no offset occurs in the tracking error signal.

The photodetector 29 is a photodetector without an amplification effect, such as a Si-bin photodiode, and detects a magneto-optical signal and a focus error signal. A known method is used for focus error detection, but since it has no direct relation to the present invention, detailed explanation will be omitted.

In the explanation of Figure 1, it is assumed that the signal level drop does not occur due to the recording medium and optical system, but in an actual optical system,
In order to accurately predict /N, it is necessary to take this into account. The following two points can be considered as causes of the signal level drop.

l) Light amount loss (decrease in amplitude due to absorption and vignetting) 2) P
−3 l) and 2) contribute to the decrease in the intensity of the magneto-optical modulation component due to the phase difference between polarizations,
Only l) contributes to the reduction of the unmodulated component strength.

In order to evaluate the decrease in the intensity of the magneto-optical non-modulated component (loss of light amount), the light utilization efficiency εr is defined. In the present invention, the light utilization efficiency is defined as the amount of light reaching the tip of the recording medium and the photodetector. Please note that we are focusing on the ratio of εR.In this example, the following points were taken into consideration when determining εR.

l) Tracking groove (pitch 1.6 μm x depth λ/8
, λ = 835 nm) that enters the objective lens entrance pupil, this is called the light utilization efficiency ε. shall be.

2) Consider the product along the optical path of the square of the amplitude transmittance (or reflectance) in the P polarization direction of n optical elements excluding the polarizing beam splitter and analyzer in the optical path from the recording medium to the photodetector. , light utilization efficiency ε1. If the amplitude transmittance of the i-th optical element is tel and the reflectance is γP, ε1 can be expressed by the following equation.

ε+=II ltp+l”
(30) m1 In equation (30), when the luminous flux is reflected by the i-th optical element, Irr'i l instead of l tp+ l''
Note that the polarization characteristic 1rpl of the polarizing beam splitter and the transmittance of the analyzer are treated as the amount of change in the C/N calculation, so they are excluded from εl.

From 1) and 2), the light utilization efficiency εR of the magneto-optical non-modulated component can be calculated by the following equation.

εR: ε0εl (31) Next, consider the decrease in the intensity of the magneto-optical modulation component. For this purpose, it is necessary to consider the phase difference between the p and s polarized lights in addition to the light amount loss. For example, as shown in FIG. 5, the reflected light from the recording medium is not linearly polarized light inside the film as shown in FIG. It is known that long sleeves produce elliptically polarized light tilted only by the Kerr rotation angle θ. That is, the P, s polarization components R, K of the amplitude reflectance of the recording medium are expressed as shown in equation (32).

However, α0. β0 is the phase component of each amplitude reflectance.

In this case, the Kerr rotation angle θ is expressed as follows. If Δo=nπ (n=integer), the reflected light from the recording medium becomes linearly polarized light, but in other cases, θ decreases, which is not preferable.

The same thing can be said about optical elements, and in this example, in order to evaluate the decrease in the intensity of the magneto-optical modulation component, the light utilization efficiency εK was defined, and the following points were taken into consideration when calculating εK.

That is, for the magneto-optical modulation component, the amplitude transmittance (or reflectance) in the P and S polarization directions of n optical elements excluding the polarizing beam splitter and analyzer in the optical path from the recording medium to the photodetector Considering the product along the optical path of , the light utilization efficiency ε2
shall be. The amplitude transmittance in the P and S polarization directions of the optical element on the i-th surface are respectively tp+ and t3B (for reflectance, rr'i,
rSi), the following equation holds true.

Using equation (34), calculate ε2 as shown in the following equation.

1 Era 1 1 Era 1 (35
), when the luminous flux is reflected by the i-th optical element, instead of l tp+ l, l tst l, κ, lr+·+1. Just substitute lrS口. The polarization characteristics of the polarizing beam splitter and the transmittance of the analyzer are C
/N Since it is handled as a change n during calculation, it is excluded from ε2.

From this, the utilization efficiency ε of the magneto-optical modulation component is given by the following equation.

ε=ε0εI (36) Regarding the polarizing beam splitter, let γP and γS be the amplitude 1 opposite gravity in the P and S polarization directions, respectively, where γ and δ are the phase components of each amplitude reflectance.

From the above, the intensities of the magneto-optical modulated component and non-modulated component are respectively Iκ
, IR, then 1K ~-1oε(1' zlrpl 1rSl IR
I IKI (1n A) 5in2θA COS (Σ
Δ, +Δrns) (38) 1 IRN Ioε0εr・1rpl”lR1” (c
os2θA ηA sin”θA)=10e n l
rp l ” l Rl ” (to cos”θ + r
) Asin”θA) (39)

Substituting equations (38) and (39) into equation (19), C/N
The polarization characteristics of the polarizing beam splitter and the angle θA of the optical axis of the analyzer from the P polarization direction that maximize the value are as follows.

0≦l rp l”< 1
(41) l rS l”= 1
(42) The calculation conditions are shown below.

The semiconductor laser 21 has an S wavelength λ=835 nm, and the amount of incident light on the recording medium 26 is κ such that 1o=2xlO−”W.
, the output is adjusted regardless of the polarization beam splitter transmittance l tp l''.

Gd Tb Fe Co is used for the recording medium 26,
lR12=O,12, θ=0.74°p, phase component α0 of amplitude reflectance in s polarization direction. The phase difference △0 of R0 is △
o=20°.

The light utilization efficiency ε0 is the tracking groove (pitch 1.6 μm
, depth λ/8) as N , A , = 0
, 5, εo=0.6. The light utilization efficiency εl is obtained by subtracting the polarizing beam splitter and analyzer in the optical path from the recording medium to the photodetector (considering the product of the transmittance of the optical elements, εr = 0, i9).

The light utilization efficiency ε2 can be determined by considering the product of the P and S amplitude transmittances of optical elements other than the polarizing beam splitter and analyzer in the optical path from the recording medium to the photodetector. In this example, there is no optical element that gives a phase difference to the P-8 polarized light during transmission, so ε2''= cos (X△i) = 1.1 electron 1 Also, 1, since I tp+ l = l tst l. ε2=0.79.

The photodetector 25 has a photoelectric conversion efficiency of =0.54 Si −
It is a pin photodiode. Constants ξ and ζ determined by noise sources such as the recording medium and semiconductor laser are given as follows.

ξ=2X10-” (R,1,N,)ζ=IX10-
” (R, 1, N,) Also, the thermal noise T is Boltzmann constant K = 1.38 x 10-”, equivalent noise temperature T
e=300 [K], load resistance R+=IXIO' [Ω]
, signal detection bandwidth ΔB=3X10' (1/Hz)
, it is given as T = 5 There is no need to follow this.The transmittance of the analyzer l
8l''=0.84, extinction ratio 77Δ=lXIO-3.

Figure 6 shows (40), (41), (42')
The polarization characteristic given by the formula, l rp 12=o, ts,
This figure compares the C/N of this embodiment (shown by the solid line) using a polarizing beam splitter with l rS l''=1 and the conventional device using a half mirror (shown by the dashed-dotted line). The axis is C/N, and the horizontal axis is the angle θA from the P polarization direction of the analyzer optical axis. In this example, θ^ = 79
．． C/N is maximum at 9°, and using a half mirror, θ
Compared to a conventional device that detects signals at an angle of 45°,
The C/N has improved by more than 2 dB. Also, when using a half mirror, θ^ = 83.9° to maximize C/N.
However, in this embodiment, the C/
N has improved. If θA is 75° to 85°,
Sufficiently good C compared to conventional equipment using a half mirror
/N was obtained.

Figure 7 shows the polarization characteristics lrI・I of the polarization beam splitter.
2 is a diagram showing the relationship between C/N and C/N. The vertical axis is C/N, and the horizontal axis is 1rPl 2, both of which are 1rSl""+ θ
= 79.9°. From this, l rP l
When `` is set to 0.08 to 0.4, a sufficiently good C/N can be obtained compared to a conventional device using a half mirror.

In addition, in this example, the phase difference △pns between the P and S polarization directions caused by the polarization beam splitter is △z
+5=160°, and there is a relationship Δ0+Δ=π (44) with the phase difference Δ generated in the recording medium. This prevents a decrease in the intensity of the magneto-optical modulation component. It is easy to manufacture a polarizing beam splitter with such polarization characteristics.

8(A) and 8(B) are schematic diagrams showing a fourth embodiment of the present invention, respectively, and FIG. 8(B) shows a view of FIG. 8(A) viewed from the direction of arrow A. In FIGS. 8(A) and 8(B), the same members as in FIG. 4 are designated by the same reference numerals, and detailed explanations will be omitted. In this embodiment as well, the signal processing system after the photodetector 29 is configured as shown in the second diagram. In this embodiment, a polarizing beam splitter 10 is used instead of the polarizing beam splitter 23 of the third embodiment.
The device is configured to detect transmitted light. The face of the polarizing beam splitter IO is inclined at a predetermined angle so that stray light does not enter the photodetector 29.

In this example, P is used in the explanatory text of FIG.

The S-polarization direction may be replaced with each other. however,(
34), In equations (35), it is necessary to replace rp with tssrS and tp. That is, if the intensities of the magneto-optical modulated component and non-modulated component are Iκ and IR, respectively, then 1
K ~ -1oεoe' 21tsl 1tpl
IRI IKI (1-η8) 5in2θ^・cos (Σ△1+△high)
(45) 1+O IR-1o εOεI l ts l ” l Rl
” (cos”θA+η^sinθA)
(46) It will rain.

Substituting equations (45) and (46) into equation (19), the polarization characteristics of the polarizing beam splitter and the angle from the P polarization direction of the optical axis of the analyzer that maximize t c/N are 0≦l ts l
”< 1 (48)l tp
l''= 1 (49) If the calculation conditions are the same, results similar to those shown in Figures 6 and 7 can be obtained.
” becomes.

Incidentally, it is easy to manufacture such a polarizing beam splitter having polarization characteristics that compensate for the one-disc difference between the P and S polarization directions that occurs in the recording medium.

The present invention can be applied in various ways including the embodiments described above. For example, although the reflected light from the magneto-optical recording medium was detected in the embodiment, it may also be configured to detect the light flux that passes through the magneto-optical recording medium and is modulated by the Faraday effect. [Effects of the Invention] As explained above, the present invention uses a polarizing beam splitter with optimal polarization characteristics in a conventional magneto-optical information reproducing device to optimally set the optical axis direction of the analyzer. This has the effect of improving the C/N of signal detection.Furthermore, since a high C/N can be obtained by the present invention,
A complicated detection system like the conventional device is not required, and the reliability of the device can be improved and the manufacturing cost can be reduced.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing an optical system according to an embodiment of the present invention, and FIG.
The first figure is a schematic diagram showing the signal processing system of the embodiment shown in the third figure.
and FIG. 4 are schematic diagrams showing other embodiments of the present invention, respectively.
FIG. 5 is a diagram showing the polarization state of reflected light from the magneto-optical recording medium, and FIGS. 6 and 7 are the optical axis direction of the analyzer and the polarization characteristics and C/N of the polarizing beam splitter in the present invention, respectively.
FIGS. 8A and 8B are schematic diagrams showing still other embodiments of the present invention, and FIG. 9 is a schematic diagram showing an example of a conventional magneto-optical information reproducing device. FIG. 10 is a diagram showing the principle of general opto-magnetic signal detection. 12... Polarizing beam splitter, 13... Detection light,
21... Semiconductor laser, 22... Collimator lens, 24... Objective lens, 26... Magneto-optical recording medium, 27... Analyzer, 28... Condensing lens, 29... Light Detector.

Claims (2)

[Claims] (1) A means for irradiating a recording medium on which information is magnetically recorded with a light beam polarized in a predetermined direction, and reflection from the recording medium whose polarization state is modulated according to the information by the magneto-optic effect. or a polarizing beam splitter that reflects and transmits the transmitted light beam at a predetermined ratio according to its polarization component, an analysis means that analyzes the light beam reflected by the polarization beam splitter, and a light beam that has passed through the analysis means. a non-amplifying photodetector that photoelectrically detects polarized light that is not modulated by the magneto-optic effect that is incident on the photodetector, and an amplification means that amplifies the detection signal of the photodetector and reproduces the information. The average of the component intensities is @I@_R, and the square mean of this intensity fluctuation at the magneto-optical signal observation frequency is ΔI^2_R, ξ
=ΔI^2_R/@I^2@_R, the light intensity of the incident light beam on the recording medium is I_0, the amplitude reflectance of the recording medium is R, the photodetector is from the recording medium excluding the polarizing beam splitter and the analyzing means. The light utilization efficiency of the optical system leading to ε,
The amplitude transmittance of the analyzing means is t_A, the extinction ratio of the analyzing means is η_A, the photoelectric conversion efficiency of the photodetector is κ, and the thermal noise of the amplifying means at the magneto-optical signal observation frequency is T.
, when the bandwidth of the detection signal is ΔB, the amplitude reflectance r_P of the polarizing beam splitter for the polarized light component in the predetermined direction, the amplitude reflectance r_S of the polarized light component in the direction perpendicular to the predetermined direction, and the optics of the analyzer. The angle θ_A between the axis and the predetermined direction is under the following conditions, |r_P|^2~√{[T/(ξ・ΔB)]・/(k・
ε｜t_A｜＾2｜R｜＾2I_0)}, 0≦｜r_P
A magneto-optical information reproducing device characterized by satisfying |^2≦1|r_S|^2~1 sin θ_A~1/{√[1+√(ηA)]}. (2) A means for irradiating a recording medium on which information is magnetically recorded with a light beam polarized in a predetermined direction, and reflection from the recording medium whose polarization state is modulated according to the information by the magneto-optic effect. Alternatively, a polarizing beam splitter that reflects and transmits the transmitted light beam at a predetermined ratio according to its polarization component, an analysis means that analyzes the light beam that has passed through the polarization beam splitter, and an analysis means that analyzes the light beam that has passed through the analysis means. It consists of a photodetector that performs photoelectric detection without an amplification effect, and an amplification means that amplifies the detection signal of the photodetector and reproduces the information, and the polarized light component that is incident on the photodetector is not modulated by the magneto-optic effect. The average intensity is @I@_R, the square mean of this intensity fluctuation at the magneto-optical signal observation frequency is ΔI^2_R, ξ=
ΔI^2_R /@I^2@_R, the light intensity of the incident light beam on the recording medium is I_0, the amplitude reflectance of the recording medium is R, from the recording medium excluding the polarizing beam splitter and the analyzing means to the photodetector. The light utilization efficiency of the optical system is ε,
The amplitude transmittance of the analyzing means is t_A, the extinction ratio of the analyzing means is η_A, the photoelectric conversion efficiency of the photodetector is κ, and the thermal noise of the amplifying means at the magneto-optical signal observation frequency is T.
, when the bandwidth of the detection signal is ΔB, the amplitude transmittance t_S of the polarizing beam splitter for the polarized light component in the predetermined direction, the amplitude transmittance t_P for the polarized light component in the direction perpendicular to the predetermined direction, and the optics of the analyzer. The angle θA between the axis and the predetermined direction is under the following conditions, |t_S|^2~√{[T/(ξ・ΔB)]・[1/(
k・ε|t_A|＾2｜R｜＾2I_0)]}, 0≦|
A magneto-optical information reproducing device characterized by satisfying t_S|^2≦1|t_S|^2~1 sin θ_A~1/{√[1+√(ηA)]}.