JPS62293528A - Optical information reproducing device - Google Patents

Abstract

PURPOSE:To improve the accuracy and to attain mass-production by providing a reflection type diffraction grating lens between a semiconductor laser and an objective lens and separating the reflected light so as to specify the angle of optical axes made incident in the laser and a four-split photodetector. CONSTITUTION:The 0th order refracted light of an emitted light 2 of the semiconductor laser 1 is collected by a reflection diffractive grating lens 16 onto an information recording face 10 via an objective lens 18. The 0th order diffracted light among the reflected lights from the face 10 is reflected on the lens 16 and collected by the laser 1 while going backward to the emitted light 2. Further, the 1st order diffracted light subject to split is luminous flux 10 and made incident to a four-split photodetector 14. Thus, only the reflected light having bit information is led to the detector 14. Further, the optical axis angle 0 between the emitted light 2 and the luminous flux 19 is selected within equation I, even if the emitted wavelength of the laser 1 is changed, the automatic focus error signal is stabilized. Thus, the accuracy is improved and mass- production are attained.

Description

[Detailed Description of the Invention] [Field of Industrial Application] This invention is for example used for reproducing information on an optical information recording medium (hereinafter referred to as a disk) in an optical disk device such as an optical disk memory or a digital audio disk. The present invention relates to an optical information reproducing device.

[Conventional technology]

FIG. 8 is a diagram showing an example of the configuration of a conventional optical information reproducing apparatus disclosed in Japanese Patent Publication No. 60-28044. In the above, (1) is a semiconductor laser, (2) is an emitted light, and (3) is a semiconductor laser.
is the first glass substrate, X4) is the collimating ophaxis gelating lens, (5) is the parallel light beam, (6) is the second glass substrate, (7) is the converging ophaxis gelating lens, 1st-order diffracted light, (91 is the disk, the back is the information recording surface, [Iυ is the optical axis, aa is the zero-order transmitted light, (I3 is the grating lens for astigmatism.

The α-ray is a four-quadrant photodetector.

Next, the operation will be explained. The emitted light (2) from the semiconductor laser fi+ is collected by a collimating off-axis gelating lens (4) formed in a part of the first glass substrate (3), and The light beam becomes a parallel light beam forming an angle of several tens of degrees with respect to the normal to the surface, and enters a converging ophaxis gelating lens (7) formed in a part of the second glass substrate (6).

The first-order diffracted light (8) of this parallel light beam (5) by the ophaxis gelating lens (7) is focused on the information recording surface aa of the disk (91A).

In this case, the opacity η' rating lens (7) is formed so that the optical axis of the first-order diffracted light (8) is perpendicular to the information recording iqa.

First-order diffracted light (8) containing information about the focused pit
The reflected light (y) again goes to the converging off-axis gelating lens (7), but the zero-order transmitted light a2 of this reflected light simply travels backwards as transmitted light and passes through the converging off-axis gelating lens (7). ) has an optical axis αυ different from the optical axis of the parallel light beam (5) which is the incident light on the parallel light beam (5).

Therefore, the emitted light +2) or parallel light (5) from the semiconductor laser fi+ and the zero-order transmitted light a containing bit information from the information recording surface 0G are 5r'AI! can do.

A grating lens (3) for astigmatic optics, for example, is formed on a part of the first glass substrate (3) from the reflected light consisting of the zero-order transmitted light α2 thus obtained.

For example, a recording information signal, a focus error signal, and a tracking error signal are detected by a light receiving optical system consisting of a four-quadrant photodetector.

[Problem that the invention seeks to solve]

The conventional optical pickup of this type described above has the following problems.

First, there is a problem that the light utilization efficiency is extremely low because two transmissive opaxis gelating lenses and a transmissive inline grating lens are used. For example, the diffraction efficiency of the +41(1) first-order diffraction source of the ophaxis gelating lens for collimator is relatively high since the numerical aperture is about 01 (although it is still only 30% at most).

A for off-axis grating lens for convergence (+7)
ppl ied 0ptics Vol 24 Nα2
4 As shown in P4307-4311, the diffraction efficiency of the first-order diffracted light is only 21%. In addition, the diffraction efficiency of the first-order diffraction source of the grating lens 0 for astigmatism optics is as described in the above Applied Optics Vol 24.
N (only 30% as shown in 124P4307-4311. Therefore.

The diffraction efficiency of the zero-order diffracted light of the convergent ophaxis gelating lens is set to 50%, and the reflectance of the disc is set to 10%.
Even if it is 0%, the efficiency from the collimator ophaxis gelating lens (3) to the astigmatism optics grating lens 0) is only 0.9596.

Second, the converging ophaxis gelating lens (7
), in order to read the pit information recorded on the information recording surface of the disk (91+1 Since the parallel light beam (51) is inclined at about 30° with respect to the exit side optical axis αυ of the converging ophaxis gelating lens, the maximum value of the equivalent diffraction angle reaches 57°, and the wavelength is λ The minimum grating spacing for a semiconductor laser beam of =780 mm is about 082 .mu.m, and the grating width when a rectangular diffraction grating is about 0.41 .mu.m, which requires submicron processing precision. In order to further increase the diffraction efficiency, the grating shape must be blazed, but the grating spacing is 082
There is a problem in that it is not easy to make the lattice shape triangular in μm.

Third, the semiconductor laser (1), the first glass substrate +S+
.

Second glass substrate (6) O and 4'1f-side photodetector α
4 is built into one housing α9, but in the configuration shown in the eighth part, the dimensions are thick (and in order to realize autofocus and autotracking, the housing O
Although not shown in FIG. 8, the entire actuator must be driven integrally, which poses a problem in that the driving weight of the actuator becomes large.

Fourthly, in order to obtain a diffraction-limited condensed spot for reading bit information on the information recording surface, the first-order diffraction source of the above-mentioned convergent ophaxis gelating lens (7) is used, and the numerical aperture of this lens is As mentioned above, NA=0.45~
0.5, and its minimum lattice spacing is 0.82
It is about μm.

Such a high numerical aperture grating lens is sensitive to changes in the wavelength of the semiconductor laser, which is the light beam, and the focal length and diffraction angle of the lens are large (there is a problem that aberrations increase as the lens changes). .

Finally, the fifth problem is that there are many components, and there is also an assembly problem in that the relative positions of each other must be precisely aligned.

The present invention eliminates the above-mentioned problems and has a simple structure with a reduced number of parts, allowing for thinning, easy manufacture and adjustment, and is therefore suitable for mass production, inexpensive, and has good characteristics. The purpose is to obtain δ.

[Means for solving problems]

The optical information reproducing device according to the present invention provides a single objective lens with the functions of the off-axis collimator lens +141 and the off-axis gelating lens for convergence (7), and the off-axis lens for convergence (7) A single reflective diffraction grating lens has the functions of separating light and reflected light and the function of a grating lens α3 for astigmatic optics, and the reflective diffraction grating lens also has the function of a 21 reflecting mirror by bending the optical path. This improves the first and second drawbacks of the conventional device, such as low light collection efficiency and a large aspect ratio of the 9-diffraction grating (not easy to manufacture).

Furthermore, the third and fifth drawbacks of the conventional device are improved, such as having a large number of parts, making it difficult to reduce the price, and making the device large.

Historically, the above-mentioned division of functions makes it possible to separate the diffraction angle changing element for the irradiation optical path from the same changing element for the reflected optical path, thereby limiting the driven object to a single objective lens, which eliminates the third drawback of conventional devices. Improve.

Furthermore, the light irradiated onto the disk (91) is made to be the 0th order diffracted light in the reflective diffraction grating lens.

This device is characterized in that it improves the fourth drawback of the conventional device due to the wavelength fluctuation of the semiconductor laser (1).

[For production]

In this invention, by using a single objective lens, the functions of the collimating ophaxis gelating lens (4) and the converging ophaxis gelating lens (7), which were necessary in conventional devices, can be achieved by using a single objective lens. This is done by an objective lens, and by using a 0-reflection type concave grating lens, it is possible to separate the human fA4 light of the converging ophaxis gelating lens (7) and the reflected light by 5 degrees. At the same time, the function of the inline type grating lens αj for astigmatism, which was necessary in the conventional device, is performed by one reflection type diffraction grating lens, and it also serves as the function of one reflection lens to bend the optical path. The size of the information reproducing device can be reduced to make it thinner.

Moreover, the minimum grating spacing of the reflective diffraction grating lens used here is approximately 2 μm, as described below.9
It can be easily obtained through a process that applies microfabrication technology used in the manufacture of products such as I.

High viscosity products can be manufactured manually and at low cost.
It is suitable for mass production.

Further, by using an aspherical 1 m lens made of plastic or the like as the objective lens, it can be made into a single lens, and this lens can also be produced at a large loss by injection molding or the like.

[Real cat example]

An embodiment of the present invention, an example of a lid, will be described below with reference to the drawings.

FIG. 1 is a perspective view showing an example of the present invention, and FIG.
The figures are a plan view and a side view showing one embodiment of the invention shown in FIG. 1. As shown in the figure (a reflective diffraction grating lens α is placed in the optical path between the milk semiconductor laser (1) and the objective lens.
Place e.

Since the optical information reproducing device according to the present invention has the above configuration, the divergent emitted light (2) from the semiconductor laser tl) is directly incident on the reflection type diffraction grating lens αe, and the reflection carved on the surface thereof is reflected. The 0th order diffracted light that is not diffracted by the shaped diffraction grating enters the objective lens αe.

The objective lens Ql is designed so that the light emitting point of the semiconductor laser fi+ is the object point, and the point on the disk surface is the image point. : The light is focused on the upper information recording surface 1III at an approximately diffraction-limited focusing spot.The reflected light having the bit information from the information recording surface αa enters the objective lens again, and the objective lens The light is converted into convergent light with the light emitting point of the semiconductor laser (1) as the condensing point, and is incident on the reflective grating lens (Ii19). Among the convergent light that has entered the reflective grating lens +l[9, the The zero-order diffracted light generated by the reflective diffraction grating lens 4 has its optical path bent and is focused onto the semiconductor laser (1) in the form of reversing the divergent light (2).
The first-order diffracted light of the reflective diffraction grating lens is converted into a light beam 0 that is focused on the center a of the four-split photodetector. Figure 2 (b
As shown in 1, the light beam (2) does not overlap the optical path of the diverging light (2), and forms a non-zero angle θ with the optical axis from the semiconductor laser (1) to the reflective diffraction grating lens αe. Therefore, only the reflected light having the bit information of the information recording surface σG can be guided to the 4-split light detection 1t14).

The grating pattern engraved on the surface of the reflective diffraction grating lens indicates the arrangement positional relationship of the semiconductor laser (1), the 4-split photodetector α0, and the reflective diffraction grating lens αG, and the wavelength of the emitted light from the semiconductor laser fi+. It is determined by the aberration added to the convergent light a9, and is expressed as an equiphase curve in which the phase difference defined by the first equation is an even or odd multiple of π.

In the first equation, ΦLD is the phase on the αe plane of the reflection grating lens when the semiconductor laser il+ is used as the wave source, and ΦPD is the phase of the reflection type diffraction grating with the 4-split light detection aa center as the wave source. Phase on the αQ plane of the lattice lens.

(x, y) is the reflective diffraction grating lens 0 shown in FIG.
These are the coordinates taken on the 5th plane. Various aberrations can be generated by selecting the value of the coefficient Cij of the third term and the orders i and j in the first equation. For example, Co2=-2X
10, C, , = -2X10, and the other coefficients are set to zero, a lattice pattern as shown in FIG. 3 is obtained. In Figure 3, for illustration purposes, the grid pattern is 66.
Book S only depicts kimono. In this way, when light enters the reflective diffraction grating lens a4 having the grating pattern shown in FIG. 3 with the configuration shown in FIG. , a second focal line, and an astigmatic beam having a circle of least confusion Qυ.In FIG. Once installed, an autofocus error signal can be obtained.

FIG. 4 shows an example of a spot diagram on the 4-split photodetector surface when the distance between the objective lens haze and the disk (91) changes.

Since the pattern changes on one surface of the two 4-division source detectors in this way, an autofocus error signal is generated as the output of the differential amplification HQa connected to the output terminal of the 4-division source detector 3aa as shown in FIG. can be obtained. Further, the tracking error signal can be easily obtained by a so-called push-pull method, and the information signal can be obtained by adding the outputs of each of the four-divided photodetector α center.

Now, in FIG. 2, if the angle θ is arbitrarily selected, the oscillation wavelength of the semiconductor laser (1) changes due to ambient temperature liquefaction, etc., so the light spot on the 4-split light detection gi'a4 surface is almost aligned with the coordinate axis X. Since the autofocus error signal moves along the same direction, the autofocus error signal deteriorates, and in the worst case, a problem may occur in which the signal cannot be obtained. In the present invention, in order to eliminate this problem, the angle θ is limited. This will be explained below. FIG. 6 is a diagram for explanation.

The reflective diffraction grating lens aQ is considered to be a transmission hologram. In the figure, the distance between the semiconductor laser fi+ and the reflective grating lens ae is t1 The distance between the reflective grating lens αe and the second focal line @ is R9 The astigmatic difference is △
Z is the angle between the optical axis +21 and the second optical axis NA number
O, the numerical aperture of the objective lens α on the output side is NA, the numerical aperture of the 4-split light detection 2IC side of the reflective diffraction grating lens αG is NAG, the diameter of the circle of least confusion is Dspot, the radius of the circle of least confusion is Rspot, If the amount of movement of the disk (9) that gives the maximum or minimum autofocus error signal is ΔZd, then the following equations 2 to 3 hold true.

D=24NAOt2+ Δ21 Rspot =-g X-7-X NAO+・”On the other hand,
If the magnification of the optical system consisting of the reflective diffraction grating lens αe and the objective lens u19 is ml, the relationship between the astigmatism difference ΔZ and the disk movement amount ΔZd is expressed by the fourth equation.

△Z=4Xm XΔzd t4
1Here, 2 magnification m1 is the magnification of objective lens Q&.

m = NA/NAO I can tell. Therefore, Equation 6 holds true.

Rspot -2X ml'x-X NAQ X△Z
d (61) Next, when the oscillation wavelength of the semiconductor laser (1) changes, the light spot moves almost along the X axis shown in Figure 2, but if this moving type △X exceeds the minimum confusion radius R5pot. Unable to obtain autofocus error signal.

Namely.

△! <RspotXA (0<A<0.8)
t71 (must not be. On the other hand, the amount of wavelength change △λ of the oscillation wavelength λ of the semiconductor laser fi+ and the amount of movement △
The relationship with X can be determined as △λ △x=R field θ□ (9) λ by differentiating the equation (%) (8) for a single diffraction grating. Substituting Equation 6 and Equation (91) into Equation (7).

, NAOλ request θ(2X, X −X−X△Z(IXA, (1
The inequality 1t Δλ is obtained. This equation 01 is the limiting condition for the angle θ in the present invention. By establishing this limiting condition, it is possible to stably obtain an autofocus error signal even if the oscillation wavelength of the semiconductor laser (1) changes. In FIG. 7 - for example m=5, NAO=
0.09. t=16yll, λ/Δλ=78°A=0
．． 7. The relationship between the angle θ and the disk movement amount ΔZd in the nth equation is shown below. The area surrounded by diagonal lines in the figure is the feasible area.

The reflective diffraction grating lens Q61 used in the optical information reproducing device according to the present invention is made by drawing a grating pattern directly with an electron beam on a glass plate coated with an electron beam resist exclusively for PMMA, and then undergoing post-processing. It can be manufactured by plating or vapor depositing a metal such as At on the surface of. For mass production, it is preferable to create a mold from the reflective diffraction grating lens by electroforming or the like, and use this as a master to create a replica by injection molding or the like to manufacture the required reflective diffraction grating lens.

Furthermore, since the optical fit information/main reproducing device according to the present invention has only two optical elements, the reflective diffraction grating lens and the objective lens, the light utilization efficiency is higher than that of the conventional device shown in FIG. It has the advantage of being expensive. For example, even when the cross-sectional shape of the grating of the above-mentioned square-shaped diffraction grating lens is rectangular, the efficiency of the zero-order diffracted light is 50%, and the diffraction efficiency of the first-order diffraction source is 20.3%. Therefore, when the reflectance of the disk (91) is 100% and the transmittance of the objective lens is 95%, the reflective diffraction grating lens αe passes from the objective lens uen, and the disk (9) returns from the objective lens The efficiency up to the anti-tooth I-shaped diffraction grating is 92%, which is about 10 times as efficient as the conventional device.

Furthermore, for autofocus and autotracking, it is preferable to drive only the objective lens, and although not shown in FIG. 1, there is an advantage that the driving weight of the actuator is light.

〔Effect of the invention〕

As explained above, in this invention, a reflective diffraction grating lens is disposed between the semiconductor laser and the objective lens, and this reflective diffraction grating lens has the effect of separating the 0-person output light and the condensed spot to constantly improve information recording. By simultaneously providing the function of the sensor optical system to generate an error signal for irradiating the light beam and the function of bending the optical path necessary to make the device thinner, it is possible to reduce the number of parts and also to reduce the number of parts. Lenses can be produced in large quantities with high precision by injection molding, vapor deposition of metal films, etc., and are effective in providing inexpensive optical information reproducing devices.

[Brief explanation of the drawing]

Fig. 71 is a perspective view showing one practical example of the present invention, Fig. 2 is a plan view showing an example of the foam structure of the invention shown in Fig. 1, Fig. 3 is a view showing an example of a grid pattern, Figure 4 shows the change in spot diagram on the 4-split photodetector surface, Figure 5 shows how to obtain the focus error signal, and Figure 6 shows the relationship between the amount of wavelength change and the focus error signal. FIG. 7 is a diagram showing the relationship between the angle θ and the disk movement angle ΔZd, and FIG. 8 is a diagram showing a conventional optical information reproducing apparatus. In Figure 3, (1) is a semiconductor laser, (21 is an emitted light beam, (3) is a first glass substrate, (4) is an ophaxis gelating lens for collimating, t5) is a parallel light beam, (
61 is the second glass plate, (7) is the focusing ophaxis gelating lens, (8J is the first-order diffracted light, +91 is the disk, [11] is the information recording surface, aυ is the optical axis, and Q2 is the zero-order transmitted light. Q31 i! Grating lens for astigmatism, (1
41 is a 4-split photodetector, Q9 is a housing, ■ is a reflective diffraction grating lens, αD is a diverging beam, Kake is an objective lens, and Q9 is a convergent beam. ■ is the first focal line, Qυ is the circle of least confusion, is the focal line of Kaya 2,
Circle is the optical axis, 04) is the differential amplifier, and ■ is the second optical axis. Note that the same reference numerals in Figure 0 indicate the same or equivalent parts.

Claims (3)

[Claims] (1) A semiconductor laser, an objective lens for condensing the emitted light from the semiconductor laser onto an optical information recording medium, and an optical path from the semiconductor laser to the objective lens that includes the emitted light from the semiconductor laser. to make the reflected light incident on the objective lens, guide the reflected light containing information from the optical information recording medium to a position different from the installation position of the semiconductor laser, and convert the reflected light into an astigmatic beam. comprising a reflective diffraction grating lens and a 4-split photodetector for detecting the reflected light separated by the reflective diffraction grating lens, and a line segment connecting the semiconductor laser and the center of the reflective diffraction grating lens; The angle formed by the line segment connecting the center of the 4-split photodetector and the center of the reflective diffraction grating lens is tanθ<2×m^2×(NA0/l)×(λ/Δλ)
×Δ_d×A (0<A≦0.8) (where m is the magnification of the objective lens, l is the distance between the semiconductor laser and the reflection grating lens, and λ is the oscillation wavelength of the semiconductor laser △λ is the variation width of the oscillation wavelength, NA0 is the numerical aperture of the objective lens on the semiconductor laser side, ΔZ_d is the disk movement amount at which the autofocus error signal output by the astigmatism method is maximized or minimized, and A is a coefficient. ) An optical information reproducing device characterized by being within the range of (2) The optical information reproducing device according to claim (1), wherein the light condensed onto the optical information recording medium is 0th order diffracted light in the reflective diffraction grating lens. . (3) The light reflected by the optical information recording medium, diffracted by the reflective diffraction grating lens, and incident on the 4-split photodetector is first-order diffracted light in the reflective diffraction grating lens. An optical information reproducing device according to claim (1).