JPH03130939A - Focus detector - Google Patents

Abstract

PURPOSE:To always detect a focusing state with high accuracy by making reflected light incident from an irradiated object to two light reception parts so as to be mutually reversed and detecting the focusing state based on this output by using light emitting and receiving elements for which a generation part and the two light reception parts are provided on the same semiconductor base. CONSTITUTION:The light emitting surface of a laser diode 51 in light emitting and receiving elements 54 and the light receiving surfaces of photodiodes 52 and 53 on the both sides of the laser diode are arranged between respective two focal points of + or -1st diffracted light and the + or -1st diffracted light is received by the diodes 52 and 53. Thus, when an irradiated object 57 is set at the focal position of an objective lens 56, the beam shape of the diffracted light is made mutually equal and when the object 57 is made close to the lens 56 side rather than the focal position of the lens 56, however, the beam shape is changed. Reversely, when the object 57 is separated from the lens 56, the beam shape is reversely changed and accordingly, by detecting output difference between the diodes 52 and 53, a focus error signal can be obtained to express the focal state of the lens 56 to the object 57.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a recording/reproducing device for recording and/or reproducing information on an optical information recording medium such as an optical disk, an optical card, or a magneto-optical disk. The present invention relates to a focus detection device suitable for use in.

[Conventional technology]

As a conventional focus detection device, one shown in FIG. 14, for example, has been proposed. In FIG. 14, light emitted from a laser diode (LD) 1 passes through a lens 2, a polarizing beam splitter (PBS) 3, a 174 wavelength plate 4, and an objective lens 5, and is projected onto an optical disk 6. The light enters the photodetector 9 through the lens 5, the 1/4 wavelength plate 4, the PBS 3, the hologram element 7, and the lens 8.

As shown in FIG. 15, the photodetector 9 includes a pair of light receiving sections 10 and 11 disposed on the same plane for detecting a focus error (FB) signal, and a pair of light receiving sections 10 and 11 for detecting a tracking error (TB) signal. It has a pair of light receiving sections 12 and 13 for detecting an information reproduction (RF) signal, and a light receiving section 14 for detecting an information reproduction (RF) signal. and 13, and the 0th order light is input to the light receiving section 14,
The ±1st-order diffracted light is made to enter the light receiving sections 10 and 11, respectively.

Note that the light incident on the light receiving sections 12, 13 and 14 is designed to form an image on the light receiving surface of each light receiving section, and the +1st-order diffracted light incident on the light receiving section IO is directed in front of the light receiving section 10. The first-order diffracted light incident on the section 11 is configured to form an image behind the light receiving section 11, respectively.

In addition, the light receiving sections IO and 11 each have three light receiving regions 10A, IOB, IOC, and IIA, IIB.
, IIC.

In this way, the light receiving area 10A of the light receiving section 10.11.

10B, IOC; IIA, IIB, IIC outputs 10a, 10b, 10c; lla.

11b, from llc, [10a-(10b+10C)
)2(lla-(11b+1ie))], the FE signal is detected, the TB times signal is detected from the output difference of the light receiving sections 12 and 13, and the RF signal is detected from the output of the light receiving section 14.

Furthermore, as another conventional focus detection device, one shown in FIG. 16 has been proposed. In FIG. 16, LD21
and the photodetector 22 on the same plane.
1 is projected onto an optical disk 26 via a lens 23, a hologram element 24, and an objective lens 25, and the reflected light is made to enter a photodetector 22 via an objective lens 25, a hologram element 24, and a lens 23. .

As shown in FIG. 17, the photodetector 22 includes a pair of light receiving sections 27 and 2 for detecting FB signals and RF signals.
8 and a pair of light receiving sections 29 and 30 for detecting the TE multiplied signal, a hologram element 24 and a lens 23.
The return light from the optical disk 26 is separated and sent to the light receiving section 2.
At the same time, the +1st-order diffracted light is separated and made to enter the light receiving sections 27 and 28, respectively.

Note that the light incident on the light receiving sections 29 and 30 is designed to form an image on the light receiving surface of each light receiving section, and the +1st-order diffracted light incident on the light receiving sections 27 and 28 is focused in front and behind the light receiving section IO. They are designed to form images. Also,
The light receiving sections 27 and 28 each have three light receiving regions 27A, 27B, 27C and 28A, 28B, 28C as in FIG. 15.

In this way, the light receiving area 27A of the light receiving portion 27.28.

278. Output 27a of 27C, 28A, 28B, 28C
, 27b, 27c; 28a.

From 28b and 28c, [27a −(27b+27
c)) −(28a −(28b+28c)]) The FB signal is determined by
The E times signal is detected respectively.

Furthermore, as other conventional focus detection devices, for example,
There are those disclosed in 6-57013 and 63-10325. In this conventional focus detection device, as shown in FIG. 18, light emitted from an LD 101 is reflected by a semi-transparent surface 103 of a flat plate 102, passes through an objective lens 104, and is converged onto a disk 105. After the reflected light passes through the semi-transparent surface 103 of the flat plate 102 via the objective lens 104, it is reflected by the reflective surface 106 of the flat plate 102, and then it is transmitted through the semi-transparent surface 103 again and is received by the photodetector 107. I have to.

Here, the reflected light from the disk 105 is reflected by the objective lens 1.
Since the light enters the flat plate 102 obliquely through the lens 04 and is transmitted therethrough, astigmatism occurs depending on the thickness of the flat plate 102. In order to detect changes in the beam due to this astigmatism, the photodetector 107 is configured with light receiving areas 108A-1080 divided into four parts, as shown in FIG. 19, and these light receiving areas 108A, 108B, 108C. and outputs 108a, 108b, 108c of 108D
and from 108d, ((108a+108c) −(
108b+108d) ] to convert the PE signal to (10
8a+108c+108b+108d), the RF signals are detected respectively.

[Problem to be solved by the invention]

However, since the focus detection device having the configuration shown in FIG. Since the detector 9 and the detector 9 are provided on different planes, there is a problem in that the entire structure becomes large.

On the other hand, in the focus detection device having the configuration shown in FIG. 16, the LD 21 and the photodetector 22 are provided on the same plane, which has the advantage of making the whole compact. Since we only use folded light,
There are problems in that the efficiency of light utilization is poor and highly sensitive focus detection is not possible.

To solve this problem, as shown in FIG. 20, the LD 31 and two photodiodes (PD) 32 and 33 for obtaining the FE signal are placed on the same plane, and the LD 31 is The light is projected onto the optical disk 36 via the hologram element 34 and the objective lens 35, and the reflected light is made incident on the hologram element 34 via the objective lens 35, and the second order diffracted light is focused on a different imaging position to be transmitted to the PD 32.
．． A conceivable configuration is that the FB signal is made incident on the PD 33 and the FB multiplied signal is obtained based on the difference between the outputs of these PDs 32 and 33.

However, in this way, each independent LD31. P.D.
32.33, in addition to adjusting the position of the PD 32.33 in the optical axis direction (2), the PD 32.33 is adjusted relative to the LD 31 in the diffraction direction (X) in the hologram element 34.
) and in the y direction perpendicular to this, there is a problem that the number of adjustment steps increases and the cost increases.

For example, in FIG. 20, the wavelength λ of the laser light emitted from the LD 31 is 780±10 nm, and the interval between the light emitting point of the LD 31 and the point of incidence of the ±1st-order diffracted light on the PD 32.33 is 0. In the case of 4 mm, in order to keep the focus offset within ±0.2 μm and the focus sensitivity change within 20%, the positioning accuracy shown in FIGS. 21 to 24 is required for the PD32.33 and the hologram element 34. The table below shows the allowable values for each parameter.

In the table, X,; positional deviation Yp of PD in the X direction with respect to tO;
Positional deviation of PD in y direction with respect to LD Zp; Positional deviation of PD in two directions with respect to LD θp; Rotational deviation of PD Xdi Positional deviation in X direction between PDs Ya; Positional deviation in y direction between PDs XH; Positional deviation in the X direction YH; Positional deviation in the y direction of the hologram element ZH; 2 of the hologram element
Directional positional deviation θ8: represents rotational deviation of the hologram element. Note that Z and ZH are not shown in FIGS. 21 to 24. Also, X in Figure 23 is PD32°3
It shows the interval between the incident points of the ±1st-order diffracted light incident on the x-axis 3, and in this case, x=0.8 mm.

From the above table, it can be seen that Yp, Ya and Z have very strict values when adjusting the position of PD32.33.

Now, considering the case where the deviations of Yp, Ya, and Z are adjusted by the parameters of the hologram element 34, in the case of Y, θ□ can be considered as the parameter for adjusting this. However, the movement of the spot on PD32.33 of the ±1st-order diffracted light by adjusting θ□ is the 24th
As shown in the figure, even though it is possible to position the spot on one PD32 or 33, the other PD3
Spot on 3 or 32.

As a result, adjustments cannot be made. Also, in the case of Yd, adjustment using θ□ can be considered, but in this case as well, PD32.
It is not possible to lead the spot to both 33. moreover,
In the case of Z, XH is used as a parameter to adjust it.
is possible. Basically, if you adjust XH, the spot moves in two directions, so it should be possible to adjust Z, but if you adjust Since the movements are different, adjustments cannot be made in the end.

As described above, each independent LD31. PD32
．． 33, PDs 32.33 are arranged symmetrically with respect to the LD 31 to receive the ±1st-order diffracted light of the porogram element 34, and the focus state is detected based on the outputs of these PDs 32.33. .3
Since the positional deviation of 3 cannot be adjusted using other parameters, PD32 and 33 must be aligned with strict accuracy with respect to LD31, which increases the number of adjustment steps and costs as described above. There is a problem with becoming.

Furthermore, in the focus detection device shown in FIG.
Since the photodetector 101 and the photodetector 107 are separate bodies, it is difficult to miniaturize the photodetector 107, and if an error occurs in the thickness of the flat plate 102, the optical axis returning to the photodetector 107 will shift and the spot will move. There is a problem. That is, the photodetector 10
7 is set at a predetermined position, and there is no error in the thickness of the flat plate 102, the center of the return light spot 111 is located at the dividing line that divides the photodetector 107 into four parts, as shown in FIG. 25A. However, if the thickness of the flat plate 102 is thinner than the design value, the center of the spot 111 will shift upward (toward the LD 101 side) from the intersection of the dividing lines, as shown in FIG. If the thickness is thicker than the design value, the 25th
As shown in Figure C, the center of the spot 111 is shifted downward from the intersection of the dividing lines.

In this way, when the optical axis of the returned light is shifted due to an error in the thickness of the flat plate 102, the photodetector 1
07, but this adjustment requires strict precision of 5 μm or less, which poses a problem of increasing the number of adjustment steps and increasing costs.

This invention was made by focusing on the above-mentioned problems of the conventional technology, and has an appropriately configured structure that allows for easy adjustment and therefore low cost, allows for constant detection of the focus state with high precision, and allows miniaturization. An object of the present invention is to provide a focus detection device.

[Means and effects for solving the problem] In order to achieve the above object, the present invention provides a light receiving/emitting element having a light emitting part and two light receiving parts formed on the same semiconductor substrate, and a light receiving/emitting element of this light receiving/emitting element. Converging the light from the light emitting part and guiding it to the irradiated object, and diffracting the reflected light from the irradiated object,
The ±1st-order diffracted light is sent to the two light receiving parts of the light receiving/emitting element,
a hologram element that causes the beam to be incident on the two light-receiving parts so that changes in beam shape are in substantially opposite directions; The device is configured to detect a focus state with respect to an irradiation object.

Furthermore, in this generation, a light emitting/receiving element having a light emitting part and two light receiving parts formed on the same semiconductor substrate, and a convergent light emitting element that converges light from the light emitting part of the light receiving/emitting element and projects it onto an object to be irradiated. The optical system is disposed in an optical path between the light receiving and emitting element and the object to be irradiated, and transmits light from the light emitting part of the light receiving and emitting element, and diffracts reflected light from the object to be irradiated. , a hologram element that makes the ±1st-order diffracted light incident on the two light receiving sections of the light receiving/emitting element so that the beam shapes change in substantially opposite directions on the two light receiving sections; The focusing state of the converging optical system with respect to the object to be irradiated is detected based on the outputs of the two light receiving sections of the light emitting element.

Further, in a preferred embodiment of the present invention, the hologram element has a first surface made of a half-mirror surface and a second surface made of a reflective hologram surface, and the light from the light receiving and emitting element is transmitted to the light emitting element. After being reflected by the first surface, the light is guided to the irradiated object via the converging optical system, and after the reflected light from the irradiating object is transmitted through the first surface via the converging optical system, the light is reflected from the second surface. to generate ±1st-order diffracted light,
The configuration is such that these ±1st-order diffracted lights are transmitted through the first surface and made incident on the two light receiving sections of the light receiving and emitting element.

Furthermore, in a preferred embodiment of the present invention, the hologram element has a first surface made of a reflective hologram surface of a half mirror, and a second surface made of a mirror surface, and the light from the light receiving and emitting element is is refracted and transmitted through the first surface and reflected at the second surface, and then refracted and transmitted through the first surface and guided to the irradiated object via the converging optical system, and the reflected light from the irradiated object is is diffracted and reflected by the first surface through the converging optical system to generate ±1st-order diffracted light, and these ±1st-order diffracted lights are made incident on the two light receiving portions of the light receiving/emitting element.

〔Example〕

FIG. 1 shows a first embodiment of the invention. In this embodiment, the LD 51 is placed on the same semiconductor substrate, and PDPs are placed on both sides of the LD 51 so that the light emitting surface and the light receiving surface are located on the same plane.
Using a light receiving/emitting element 54 integrally formed with a D52.53, the light from the LD 51 is converged and projected onto an irradiated object 57 such as an optical disk via a hologram element 55 and an objective lens 56. The reflected light from the irradiated object 57 is
incident on the hologram element 55 through the objective lens 56,
The ±1st-order diffracted light is received by the PD52.53, and astigmatism is given to the ±1st-order diffracted light by the hologram element 55, so that the beam shapes of the ±1st-order diffracted light are almost opposite to each other on the PD52.53. Make it change in direction. In this way, the focal state of the objective lens 56 with respect to the irradiated object 57 is detected based on the difference between the outputs of the PDs 52 and 53.

As described above, when astigmatism is given to the ±1st-order diffracted light by the hologram element 55, as shown in FIG. 2, the ±1st-order diffracted light has two focal points A I +A, l;
2. A2' will exist. Here, AI+A
For example, 2 is the focus of the meridian plane, AIZA2' is the focus of the spherical plane, and these are in a conjugate relationship, so that AI+AI' and A! +A21 occur on opposite sides of the optical axis (z).

In FIGS. 1 and 2, the focal point AIr AI' +
A2+A,l is located on the xz plane, where xXx is the diffraction direction by the hologram element 55, that is, the arrangement direction of the LD 51 and PD 52.53, and y is the direction perpendicular to the optical axis (z). Here, the hologram element 5
The distances in two directions from 5 to the focal point AI+ AI' + A2+ A, l are respectively Zl+ z, I, Zl,
When the distance between Zz' and the LD 51 and the hologram element 55 is R, the following relationship holds between them.

Therefore, as shown in FIG. 2, if the positions of A1 and A1' are set as Zl>Zl', the positional relationship between the conjugate images A2+ A and l is Zl < Z! ', and the +1st order diffracted light =
The direction of astigmatism is opposite to that of the first-order diffracted light.

From the above, the light emitting surface of the LD51 of the light receiving/emitting element 54 and the light receiving surfaces of the PD52.
2.53, the beam shape of the ±1st-order diffracted light incident on the PD 52.53 will be as shown in FIG. As shown, they are equal to each other and the irradiated object 57
When the object is closer to the objective lens 56 than the focal position of the objective lens 56, it becomes as shown in FIG. Become. That is, the beam shapes of the ±1st-order diffracted lights incident on the PD 52.53 are equal in the focused state, and change in substantially opposite directions depending on the direction of defocus in the out-of-focus state. Therefore, by detecting the difference between the outputs of the PDs 52 and 53, it is possible to obtain a focus error (FB) signal representing the focus state of the objective lens 56 on the irradiated object 57.

FIG. 4 shows the configuration of an example of the light receiving/emitting element 54. As shown in FIG. This light receiving/emitting element 54 has an LD 51 and PDs 52 and 53 formed on a semiconductor substrate 61 made of n-GaAs. LD51 is a striped double hetero (
DH) structure, on one side of the base 61, a cladding layer 62 made of n-type Ga + -z ALx As,
Active layer 63 made of GaAs, p-type Gat-x A
Cladding layer 64 made of Lx As, p-GaAs layer 6
5. An oxide film 66 and an electrode metal 67 are sequentially laminated, and an electrode metal 68 is provided on the other surface. That is, this LD 51 utilizes the interfold planes of the crystals of the cladding layers 62 and 64 to form a Fabry-Perot reflector that is optically parallel to the plane in the direction perpendicular to the pn junction plane, and also clads the active layer 63. By forming a DH structure sandwiched between layers 62 and 64, both effects of carrier confinement and light confinement are obtained. Note that this LD 51 is a typical gain waveguide type that does not have a lateral refractive index distribution in the active layer 63, and the thickness of the active layer 63 is usually 0.1 to 0.5 μm and one cladding layer. The thickness of 62.64 is usually 1-2 μm. Further, the p-GaAs layer 65 on the cladding layer 64 is for making it easier to form an electrode, and the oxide film 66 is for partially passing current to obtain a single fundamental transverse mode, and has a striped structure. It becomes. The forward voltage of the LD51 configured in this way is approximately 2V, and the reverse breakdown voltage is 10V.
~50V.

PD52.53 is formed on the base 61 in the same manner as the LD51, and grooves 69.70 are formed between each of the LD51 and PD52.53 by etching or the like until the base 61 is reached.
form and electrically isolate it. In addition, PD52
．． In LD 53, an oxide film 66 having a stripe structure for partially flowing current as in LD 51 is not provided.

That is, when the wavelength of the laser beam in the LD 51 changes due to temperature changes, etc., the hologram element 5 shown in FIG.
The ±1st-order diffraction light due to the X-ray diffraction angle 5 fluctuates in the X direction. For this reason,
If the active layer 63 of the PD52.53 has a confinement structure similar to that of the LD51, its sensitivity in the X direction will be as shown by the solid line A in FIG. 5, and the detection sensitivity will vary depending on the wavelength variation. . Therefore, PD52
．． In order to prevent the active layer 63 from having a confinement structure, the oxide film 66 having a stripe structure is not provided in the active layer 53. In this way, the sensitivity of the active layer 63 can be made uniform in the X direction as shown by the solid line B in FIG. , it is possible to always obtain a constant detection sensitivity.

The manufacturing process, laser oscillation characteristics, and PD characteristics of the light receiving/emitting element 54 are based on the "monosilicate integrated G
“aALAs Laser/Detector Array” Institute of Electronics and Communication Engineers, QOE86-1-14. PP73-77, 198
6.4, 21.

As shown in FIG. 6, a forward voltage is applied to the LD 51 of the light receiving/emitting element 54 to cause it to emit laser light.
A reverse voltage is applied to D52.53 to make it act as a photodiode, and the output of these PD52.53 is supplied to the differential amplifier 71, thereby generating an FE representing the focus state of the objective lens 56 on the irradiated object 57. Try to get a signal. In addition, when reading the information recorded on the irradiated object 57 from the reflected light from the irradiated object 57, the PD5
The output of 2.53 is supplied to an adder 72 to obtain an RF signal.

Note that, as described above, when the PD52.53 is similarly formed on the same semiconductor substrate 61 as the LD51, the PD52.
The sensitivity characteristics of the PD 53 in the thickness direction, that is, the y direction, are as shown in FIG. 7, and these sensitivity characteristics can be controlled to some extent by the reverse voltage applied to the PD 52.53.

As described above, in this embodiment, since the LD 51 and the PD 52.53 are formed on the same semiconductor substrate, there is no need to adjust the position of the PD 52. It can be done cheaply. In addition, the light receiving sensitivity of the PD52.53 is made almost negative in the direction of diffraction (X direction) by the hologram element 55, so even if the wavelength of the laser light in the LD51 changes due to temperature changes, etc., the detection sensitivity is always constant. Therefore, highly accurate focus detection can be performed at all times.

FIG. 8 shows a second embodiment of the invention. In this embodiment, the hologram element 55 also has the function of an objective lens for converging the laser beam from the LD 51 onto the object to be irradiated, and the other configurations and functions are the same as in the first embodiment.

In this way, by providing the hologram element 55 with an objective lens function, the structure can be made simpler and cheaper, and it can be made extremely lightweight. Furthermore, since the light receiving/emitting element 54 and the hologram element 55 can be made lightweight, they can be driven together when performing focus servo based on the FB signal, which simplifies the driving device and significantly reduces costs. You can try to bring it down.

FIG. 9 shows a third embodiment of the invention. In this embodiment, the light from the light receiving/emitting element 75 is transferred to the hologram element 7.
6 and an objective lens 77 to enter an irradiated object 78, and the reflected light is received by a light receiving/emitting element 75 via an objective lens 77 and a hologram element 76.

As shown in FIG. 1O, the light receiving/emitting element 75 includes an LD 79 on the same semiconductor substrate, and PCO2, 81 on one side of the LD 79, which are electrically isolated by grooves 82, 83 and 84 in the same manner as in FIG. and form it. Further, as shown in FIG. 9, the hologram element 76 is constituted by a parallel plate having a first surface 85 as a half-mirror surface and a second surface 86 as a reflective hologram surface.

In this embodiment, the light from the LD 79 is transmitted to the hologram element 7.
The reflected light is reflected by the first surface 85 of the hologram element 76 and converged onto the irradiated object 78 by the objective lens 77, and the reflected light is transmitted through the objective lens 77 and the first surface 85 of the hologram element 76 to be projected onto the second surface 86. This generates ±1st order diffracted light having astigmatism, and these ±1st order diffracted lights are transmitted through the first surface 85 of the hologram element 76 and received by the PCO2, 81 of the light receiving/emitting element 75.

Note that astigmatism imparted to the ±1st-order diffracted light is such that the beam shapes change in substantially opposite directions on the PCOs 2 and 81, as in the first embodiment.

In this way, by changing the reflective surface of the hologram element 76 on the outbound and return passes, the optical axis can be shifted in the outbound and return passes, so that stray light entering the PCOs 2 and 81 can be extremely reduced. In other words, the stray light incident on the PCO 2, 81 passes through the first surface 85 of the hologram element 76 on the outward path.
, passes through the first surface 85 again after being reflected by the second surface 86 , and on the return trip, the first surface of the hologram element 76
After passing through the surface 85, being reflected by the second surface 86, and sequentially reflected by the first surface 85 and the second surface 86, the first surface 8
However, since this light has a different optical path length from the light actually used for signal detection, PCO2,
The spot on 81 is sufficiently larger than the spot used for signal detection. Furthermore, since the light used for signal detection is reflected twice on the semi-transparent surface, there is a significant loss in the amount of light. Therefore, since the amount of stray light that enters the PCO 2, 81 is extremely reduced, the noise component that enters the focus detection signal can be extremely reduced.

In the third embodiment, if the astigmatism caused by the thickness of the hologram element 76 is large, it will adversely affect the focus detection sensitivity. The thickness is preferably made thin so that it is sufficiently smaller than the aberration.

FIG. 11 shows a fourth embodiment of the invention. In this embodiment, the hologram element 89 uses a parallel plate whose first surface 90 is a half-mirror reflective hologram surface and whose second surface 91 is a mirror surface.The other configuration is similar to that of the third embodiment. It is similar to

That is, in this embodiment, the LD 79 of the light receiving/emitting element 75
The light from the hologram element 89 is refracted and transmitted through the first surface 90 of the hologram element 89, reflected by the second surface 91, and then reflected by the first surface 90 again.
is refracted and transmitted, and the objective lens 77 illuminates the irradiated object 78.
It converges and projects. Further, the reflected light from the irradiated object 78 is diffracted and reflected by the first surface 90 of the hologram element 89 through the objective lens 77, and ±1st-order diffracted light having astigmatism is generated here. The next diffracted light is received by PD80.81 of the light receiving/emitting element 75.

The hologram on the first surface 90 of the hologram element 89 has a pattern such that the diffraction efficiency of transmitted ±1st-order diffracted light is sufficiently smaller than the diffraction efficiency of ±1st-order diffracted light during reflection. In addition, the astigmatism given to the ±1st-order diffracted light incident on PD80.81 is P
The beam shapes are made to change in substantially opposite directions on D80.81.

In this embodiment as well, as in the third embodiment, the reflective surface of the hologram element 89 is changed on the outbound and return passes, and the optical axes on the outbound and return passes are shifted, so that the PD80.
The amount of stray light that enters the lens 81 can be extremely reduced, and therefore a decrease in focus detection sensitivity can be effectively prevented. Note that also in this embodiment, the hologram element 8
If the astigmatism caused by the thickness of the first surface 9 is large, it will have a negative effect on the focus detection sensitivity.
The thickness is preferably made thin so that it is sufficiently smaller than the astigmatism given by the zero reflection hologram surface.

According to the third and fourth embodiments described above, the moving direction of the spot on the PD80.81 due to the error in the thickness of the hologram elements 76 and 89 coincides with the dividing direction of the PD80.81. , there is no adverse effect on focus detection.

Note that this invention is not limited only to the embodiments described above, and numerous modifications and changes are possible. For example, in the above-mentioned embodiment, astigmatism was given to the ±1st-order diffracted light by the hologram element, but the imaging point of the ±1st-order diffracted light by the hologram element was changed, for example, to the focal point AIl A2 in FIG. Alternatively, the focus state may be detected using a beam size method.

In this case, in the focused state, P
The sizes of the ±1st-order diffracted light beams incident on D52゜53 become equal, and when the irradiated object approaches the focal point, one beam becomes smaller and the other beam becomes smaller, as shown in Figure 12A. When it becomes larger and moves away from the focal position, the relationship is reversed as shown in FIG. 12C. Therefore, by detecting the difference between the outputs of the PDs 52 and 53, the focus state can always be detected with high accuracy, as in the above embodiment.

Furthermore, in the first, third, and fourth embodiments, the objective lens was a finite system, and in the second embodiment, the hologram element was made to have the function of a finite system objective lens, but a collimator lens was added to improve these functions. It can also be an infinite system.

Furthermore, in the above-mentioned embodiment, the LD of the light receiving/emitting element is a typical gain waveguide type without a lateral refractive index distribution in the active layer, but a LD with a lateral refractive index difference refractive index waveguide type, which confines the energy, distributed feedback type (DFB), which allows oscillation in a single longitudinal mode without spectrum broadening even when modulated at high frequency, and whose oscillation wavelength does not change depending on the flowing current, or distributed reflection type ( DBR). Also,
The semiconductor substrate constituting the LD and PD is not limited to GaAs, and Si can also be used. In this case, Si
Since peripheral circuits such as a preamplifier can also be integrally formed on the base, the configuration can be made simpler. Furthermore,
The semiconductor substrate is not limited to n-type, but may also be p-type; in this case, the polarity of the applied voltage shown in FIG. 6 may be reversed.

Further, in the third and fourth embodiments, the hologram element is configured with a parallel plate, but it can also be configured with various shapes such as a wedge shape or a curved surface (spheroid, paraboloid, etc.).

Furthermore, in the third and fourth embodiments, as shown in FIG.
D96 and PD97 to 100 on one side of groove 10
1 to 104 are electrically isolated and sequentially provided, the ±1st-order diffracted light is incident on the outermost PDs 97 and 100, and the 0th-order diffracted light is divided into two into the inner PDs 98 and 99. A focus error signal is obtained by the differential output of PD97 and PD100, and the PD
It is also possible to configure the tracking error signal to be obtained by the push-pull method using the outputs of 98 and 99.

〔Effect of the invention〕

As described above, according to the present invention, a light emitting/receiving element in which a light emitting part and two light receiving parts are formed on the same semiconductor substrate is used, and the two light receiving parts are provided with light from an object to be irradiated by a hologram element. The ±1st-order diffracted light of the reflected light is made incident on the two light receiving sections so that the beam shapes change in substantially opposite directions, and the focal state is detected based on the outputs of these two light receiving sections. This eliminates the need to adjust the position of the two light receiving sections with respect to the light emitting section, thereby greatly reducing the number of adjustment steps and making it possible to reduce the cost.Moreover, the focus state can always be detected with high precision.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a first embodiment of the present invention, and FIG. 2 is a diagram showing a first embodiment of the present invention.
Figure 3A, B and C are diagrams for explaining the action of the hologram element shown in Figure 1.
A diagram for explaining changes in the beam incident on D; FIG. 4 is a diagram showing the configuration of an example of the light receiving and emitting element shown in FIG. 1; FIG. 5 is a diagram showing the sensitivity characteristics of the active layer of the PD; FIG. 6 is a diagram showing an example of a drive circuit and a signal processing circuit for a light receiving/emitting element, FIG. 7 is a diagram showing sensitivity characteristics in the thickness direction of a PD, and FIG. 8 is a diagram showing a second embodiment of the present invention. , FIG. 9 is a diagram showing a third embodiment of the invention, FIG. 10 is an enlarged view of the light receiving and emitting element shown in FIG. 9, FIG. 11 is a diagram showing a fourth embodiment of the invention, and FIG. 12 A, B, and C are diagrams for explaining the present invention in detail; FIG. 13 is a diagram showing the configuration of a light receiving/emitting element used in another modification of the present invention; FIGS. 14 to 25 A, B, C is a diagram for explaining a conventional technique. 51-・-[, D 52.53...
-PD54--Receiving/emitting element 55°/'-Hologram element 56...Objective lens 57...
- Irradiated object 61...-semiconductor substrate 62.64
---Clad layer 63---Active layer 6
7, 68--Electrode metal 69.70--Groove
7■...Differential amplifier 75-...Reception/emission element
76, 89 --- Hologram element 77 --- Objective lens 78 --- Irradiated object 79 ---L
D 80.81...PD82, 8
3.84°...Groove 85.90...First surface 86.91-...Second surface 95...Receiving/emitting element 96-...LD 97~1
00-・PDlol-104...-groove Figure 1 Figure 4 Figure 54 Figure 5 Figure 6 Figure 8 Figure 9 Figure 9 θσ @IO diagram σtei σj σZ Figure 1I Figure 13 shows η γγ Figure 14 Figure 15 1C 7A 111:3 Figure 16 Figure 17 Figure 18 Figure 19 Figure 21

Claims (1)

[Claims] 1. A light receiving/emitting element having a light emitting part and two light receiving parts formed on the same semiconductor substrate, converging light from the light emitting part of the light receiving/emitting element and guiding it to an object to be irradiated. , diffracts the reflected light from the irradiated object and sends the ±1st-order diffracted light to the two light receiving sections of the light receiving/emitting element so that the beam shapes change in substantially opposite directions on the two light receiving sections. and a hologram element to make the incident so that
A focus detection device characterized in that the focus detection device is configured to detect a focus state of the hologram element with respect to the irradiated object based on outputs of two light receiving sections of the light receiving and emitting element. 2. A light receiving/emitting element having a light emitting part and two light receiving parts formed on the same semiconductor substrate; a converging optical system for converging light from the light emitting part of the light receiving/emitting element and projecting it onto an irradiated object; It is arranged in the optical path between the light receiving and emitting element and the irradiated object, and transmits the light from the light emitting part of the light receiving and emitting element, and diffracts the reflected light from the irradiated object.
a hologram element that makes the first-order diffracted light incident on the two light receiving sections of the light receiving and emitting element so that changes in beam shape are substantially opposite to each other on the two light receiving sections; A focus detection device characterized in that the focus detection device is configured to detect a focus state of the converging optical system with respect to the irradiated object based on outputs of two light receiving sections. 3. The hologram element has a first surface made of a half-mirror surface and a second surface made of a reflective hologram surface, and the light from the light receiving and emitting element is reflected by the first surface to illuminate the irradiated object. The reflected light from the irradiated object is transmitted through the first surface, and then reflected by the second surface to generate ±1st-order diffracted light, and these ±1st-order diffracted lights are transmitted through the first surface. 3. The focus detection device according to claim 2, wherein the focus detection device is configured to transmit the light and make it incident on the two light receiving sections of the light receiving/emitting element. 4. The hologram element has a first surface made of a reflective hologram surface of a half mirror and a second surface made of a mirror surface, and the light from the light receiving and emitting element is refracted and transmitted by the first surface. The light is reflected by the second surface, and then refracted and transmitted through the first surface to be guided to the irradiated object, and the reflected light from the irradiated object is diffracted and reflected by the first surface.
3. The focus detection device according to claim 2, further comprising a structure in which first-order diffracted light is generated and these ±first-order diffracted lights are made incident on two light receiving sections of the light receiving/emitting element.