JPS63259844A - Optical head - Google Patents

Abstract

PURPOSE:To detect a reflection light having no false signal with good efficiency by condensing the light from a semiconductor laser on an optical disk via a condensing grating coupler (GC), waveguide path and two piece condensing GC, and distributing the reflection light to an optical detecting element by the two piece GC. CONSTITUTION:The laser light incident through a substrate 11 from a semiconductor laser element 8 is guided to the optical path inside a wave guide path 12 from a condensing GC 13 and condensed on the information recording face 6a of an optical disk 6 through the end face 11a subjected to no reflection coating via the two piece condensing GC 15 and condensing GC 14 whose diffraction efficiencies are adjusted in about 50%. The reflection light light thereof is halved by the two piece condensing GC 15 with its retrograde and made incident on four optical detecting elements 16a-16d. In the case of the focusing being normal, the detection outputs of the elements 16a-16d become equal. A focusing error signal is obtd. by detecting the break of the output ratio. A tracking error signal is obtd. from the ratio of the sum of the elements 16a, 16b and 16c, 16d.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an optical information processing device that optically records and generates information, and specifically relates to an integrated optical information processing device used for reading and writing information. Regarding het.

[Prior Art] An example of a conventional optical head implemented as an IC is shown in FIG. Here, a waveguide 2 is formed on a substrate l, and a crating 3 is used to control the laser light propagating within this waveguide 2.
．． Beam splitter 4. The condensing crepe ink coupler 5 was formed by patterning using an electron beam lithography method or a photolithography method. The optical head 10 formed in this manner guides the laser light emitted from the semiconductor laser element 8 into the waveguide 2 by end-face-coupling the semiconductor laser element 8, converts it into parallel light using the collimator lens formed by the crater 3, and Concentrating grating coupler 5
By this, the laser light is focused on the information recording surface 6a of the optical disk 6 outside the waveguide 2. The reflected light from the information recording surface 6a is again focused by the condensing crater 5, guided into the waveguide 2, and returned to a beam splitter arranged at an angle of 45 degrees with respect to the optical axis. 4
several photodetectors 7 that are separated into two directions by a light beam and one of the reflected lights is coupled to the end face of the waveguide 2 or formed on the substrate 1.
It was configured to perform signal processing by detecting the signal and converting it into an electrical signal.

In such an integrated optical head, the input and output of light to the information recording surface 6a of the optical disk 6 is performed from the waveguide 2 of the substrate 11 to the gap between the waveguide 2 and air by a grating coupler formed in the waveguide. The photodetector 7 is installed on the waveguide end face or the waveguide surface, and the reflected light from the information surface 6a of the optical disk 6 is in the same plane as the guided light from the semiconductor laser element 8. The semiconductor laser device 8. The photodetector 7 was also arranged to exist within the same plane.

[Problems to be solved by the invention] By the way, in such an IC-based optical head 1O, since the semiconductor laser element 8 is bonded to the end face of the optical waveguide 2, the optical coupling efficiency is poor, and , the thickness of the waveguide 2 on the substrate l is approximately lpm, and alignment with the incident laser beam is extremely difficult. In addition, since the semiconductor laser element 8 and the photodetector 7 are on the side surface of the same waveguide 2, the scattered light inside the waveguide 2 is detected by the photodetector 7, which should be detected by the photodetector 7. The S/N ratio of the signal light transmitted becomes small, and in severe cases, false signals are generated, which may cause the optical head device to malfunction. Furthermore, when the photodetector 7 is attached to the end face of the waveguide 2,
When a laser beam is incident on the photodetector 7, the film thickness of the waveguide 2 is about IILm, so the area that the laser beam hits the photodetector 7 becomes small and alignment is also very difficult. However, the conversion efficiency of input light into electrical signals was low.

The present invention has been made in view of the above points, and is an integrated type that is configured to prevent false signals from entering the signal light reflected from the information recording surface of an optical disk as much as possible, and that enables efficient detection. The purpose is to provide an optical head.

[Means for solving the problem] In the present invention, the semiconductor laser element, the photodetector element, and the optical waveguide are arranged three-dimensionally on the substrate, so that the semiconductor laser element, the photodetector element, and the optical waveguide are arranged on the waveguide, respectively. It is formed by patterning a plurality of crater inks designed to guide laser light to predetermined positions, and a focusing grating coupler for focusing the laser light on the information recording surface of the optical disk.

To explain in more detail, a semiconductor laser element and a photodetector element are mounted on the side surface of an optically transparent substrate, an optical waveguide made of a dielectric thin film is formed on the negative side of this substrate, and a laser A grating coupler for coupling light, a converging grating coupler for converging the guided light onto the information recording surface of an optical disk, a semiconductor laser that splits the guided light into two and splits one beam into two. Unlike the optical path from the device, the semiconductor laser device and the waveguide are configured by forming a two-split condensing grating coupler that focuses the laser beam on two sets of photodetecting devices arranged at different positions.

The optical head configured as described above guides the laser light from the semiconductor laser element into the waveguide, and the condensing grating ink coupler focuses the light on the information recording surface of the optical disk outside the waveguide. The reflected light is again taken into the waveguide by the condensing grate ink coupler and guided in the opposite direction, and is distributed to the photodetecting element by the two-split condensing ink coupler. Since the light can be focused on the photodetecting element without being affected by the scattered light from the laser element, the ratio between the signal light and the scattered light can be increased. In addition, the photodetection element is attached to the side of the substrate rather than inside the waveguide, and the signal light in the waveguide passes through the substrate and is focused on the photodetection element, so the signal light enters the photodetection element. The efficiency of conversion into electrical signals is extremely high.

[Embodiments] Hereinafter, embodiments of the present invention will be described based on the drawings. FIG. 1 is a perspective view of this integrated optical head, FIG. 2 is a side view, and FIG. 3 is a plan view. That is, the optical head 20 has a transparent polymethyl methacrylate (hereinafter referred to as PMMA) substrate 11 formed in a two-step ladder shape in cross section, and a rotyl methacrylate film having a refractive index larger than that of PMMA. Polymer thin film waveguide 12 that guides laser light using a photosensitive resin whose main component is a copolymer
form. This waveguide 12'' has a grating coupler 13 made of a curved grating with irregular intervals for introducing the laser light into the waveguide, and a grating coupler 13 for converging and emitting the laser light from the side surface of the substrate 11. A condensing grating coupler 14 made of an equally spaced curved grating, and the condensing grating coupler 14 converge the reflected light from the information recording surface 6a of the optical disk 6 of the laser beam again and direct it to the opposite direction of the waveguide 12. It consists of two unequally spaced curved gratings formed on the waveguide 12 between the condensing grating coupler 14 and the grating coupler 13, and divides the guided light into two and connects the semiconductor laser element 8 and the height A two-split condensing grating coupler 15 arranged so as to focus light on two sets of photodetecting elements 16a, 16b and 16c, 16d divided into two, located on opposite sides of the substrate 11, is shown in -F. It is formed on the waveguide 12 of a polymeric dielectric thin film by photolithography. On the side surface of the substrate 11, a mounting surface 11c formed at an angle of 55 degrees with respect to the waveguide surface 12 of the semiconductor laser element 8, and two sets of photodetecting elements 16a, 16b, 16c,
A mounting surface 11b formed at an angle of 80 degrees with respect to the waveguide surface 12 of 16d, and a laser light input/output surface 11a parallel to the information recording surface 6a of the optical disk 6 at an angle of 60 degrees on the opposite side. It is formed. The semiconductor laser element 8 is mounted at the center of the mounting surface 11c, and the photodetecting elements 16a, 16b and 16c, 16d are divided into two parts and mounted on both sides of the mounting surface 11b.

At this time, the grating coupler 13 has a pattern whose phase is aligned so that the laser light from the semiconductor laser 8 can be input into the waveguide 2 in a collimated state, and the pitch is 14 to 1.5 JL. ing.

In addition, the condensing coupler 14 is also a grating coupler.
13, the phases are aligned so that the collimated light is focused from the input/output surface 11a onto one point on the information recording surface 6a of the optical disk 6, and the pitch is 14 to i, sg.

The two-split condensing grating coupler 15 collimates most of the light that has returned from the information recording surface 6a of the optical disk 6, splits the light propagating into the waveguide 2 into two, and focuses the light on the photodetecting elements 16a to 16b. A pattern whose phases are aligned so that

Therefore, the light takes different optical paths within the substrate 11, and the semiconductor lasers 8. Light Tisph 6. This is done using grating couplers whose patterns are designed to condense light onto the photodetecting elements 16a to 16d, respectively.

Next, the operation of this example will be explained with reference to the side view of FIG. First, the laser light incident from the semiconductor laser element 8 through the substrate 11 passes through the grating coupler 13.
The light beam is cup-linked by the waveguide 12 and guided to the optical path within the waveguide 12. Then, the guided light is guided into the waveguide 12 to the right, or at this time, the diffraction efficiency of the two-split condensing grating coupler 15 in the waveguide 12 is adjusted to about 50%, and the guided light is guided through this grating coupler 15. The light is guided through the condensing grating ink coupler 14. The light is then diffracted so as to be focused by the condensing grating coupler 14, and irradiates the information recording surface 6a of the optical disk 6 in a dotted manner through the end surface 11a of the substrate 11 coated with an anti-reflection coating. The reflected light from the information recording surface 6a passes through the end surface 11a of the substrate 11 again and is returned into the waveguide 2 by the condensing grating coupler 14. At this time, if the focusing or tracking of the optical disc 6 is not normal, the returned light will not be reflected. The light will follow a different optical path from the original guided light. The return light guided to the left inside the waveguide 12 is split into two by the two-split condensing grating coupler 15, and the light in the waveguide 2 and the light from the semiconductor laser element 8 are three-dimensionally separated. The optical path is followed by the center of four photodetecting elements 16a, 16b, 16c, and lad located at different positions, and the light is condensed and incident on each of them. At this time 2
The split condensing grating coupler 15 includes the grating coupler 13 and the condensing grating coupler 14.
It has a shape in which the same unevenly spaced curved grating is cut in half at the center and butted against each other in opposite directions, and the returned light is divided into two parts, and when focusing or normal, four photodetecting elements 16a are detected.
~16d, and the respective intensities I or I (16
a)=I (16b)=1 (16c)=1 (1
6d). When the focusing of the information recording surface 6a of the optical disc 6 is blurred, this ratio is broken and a focusing error signal can be detected using the Foucault method. 1. Tracking is performed using the photodetecting elements 16a and 16.
I(16a)+1(16b), which is the sum of b, and the photodetector element 16c.

It can be detected using the Bushzl method from the ratio of the sum I (16c)+I (16d) of 16d.

For example, the transparent substrate 11 made of PMMA or the mounting surface 1 of the photodetecting elements 16a to 16d as shown in FIG.
1b and the mounting surface 11c of the semiconductor laser element 8 are formed on the opposite side of the emission surface 11a as surfaces with different heights, but the inclination angle of these surfaces is arbitrary between 0 and 90 degrees. , the effective refractive index of the waveguide 12 and the substrate 11
Needless to say, the refractive index is selected from the refractive index of , and the pitch of the crete ink. Further, the substrate 11 may be formed into a flat plane having the same thickness as in the following embodiment.

FIG. 4 is a perspective view showing another embodiment of the present invention;
The substrate 21 of equal thickness made of MA is formed into a planar shape or a hexagonal shape. The surface 21b on the opposite side of the light exit surface 21a is the light exit surface 2.
It is parallel to 1a, and a semiconductor laser element 8 is attached thereto.

Surfaces 21c and 21d on both sides of this surface 21b are equiangularly inclined, and light receiving elements 16a, 16b and 16c, 16
d can be attached. A waveguide 22 formed of a photosensitive resin whose main component is a copolymer of crotyl methacrylate provided on two sides of the substrate 21 includes:
Similar to the first embodiment, the grating coupler 13
The optical head 30 of this example includes a condensing grating coupler 14a and a two-part condensing grating coupler 15a. The optical pickup 30 in this example is the optical pickup 2 in the first embodiment.
Compared to 0, it is thinner and more compact.

Next is the 5th pl! An embodiment of the optical pickup 40 shown in I will be described. In this example, the photodetecting elements 16a, 16b, 16c, 16d shown in FIG. The only difference is that they are arranged at intervals on the mounting surface 31c, and a detailed explanation thereof will be omitted.

Therefore, in this example, the two-split condensing grating coupler 15b formed on the waveguide 32 is
In the example shown in the figure, the grating coupler is formed of a symmetrical unequally spaced curved grating divided in the center; The directions are the same, but the angles are slightly different. Furthermore, in this example, there is one less side surface of the substrate 31, which facilitates its manufacture.

In each of the embodiments described above, the substrate is made of inexpensive PMMA, but it is also possible to use a transparent piezoelectric material such as lithium niobate. Further, an inorganic compound such as glass may be used.

[Effects of the Invention] According to the present invention, light input and output was conventionally performed mainly within the plane of a waveguide, which is a single plane, but it is possible to perform three-dimensional input and output in the thickness direction using a transparent substrate. By this arrangement, scattered light can be greatly reduced, and the possibility of false signals entering reflected signal light from the information recording surface of the optical disk can also be greatly reduced, allowing for efficient detection. Furthermore, the force and linking efficiency of the semiconductor laser element and the light receiving element can be improved, and difficult alignment is not required, making manufacturing extremely easy.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of an optical head showing an embodiment of the present invention, FIG. 2 is a side view of FIG. 1, FIG. 3 is a plan view of FIG. 1, and FIG. 5 is a perspective view of an optical head showing a third embodiment of the present invention. FIG. 6 is a perspective view of a conventional optical head. FIG. 6...Optical disk 6a...Information recording surface 8...Semiconductor laser element 11.21.31...Substrate 11a, 21a, 21b...Input/output surface 12.22.
32...Waveguides 13.13a, 13b...Grating couplers 14.14a, 14b...Concentrating grating couplers 15.15a, 15b---Two-part condensing grating couplers 16a, 16b, 16c, 16d--Photodetection element

Claims (1)

[Claims] An optically transparent dielectric substrate, a dielectric thin film waveguide formed on the substrate for guiding laser light, and curves arranged at unequal intervals on the waveguide. a grating coupler, a two-split condensing grating coupler, and a condensing grating coupler each consisting of a shaped grating; the side surface of the substrate has a light input/output surface, a mounting surface for a semiconductor laser element and a plurality of photodetecting elements; Laser light from a semiconductor laser element is introduced into the waveguide by a grating coupler, and is converged and irradiated from the input/output surface on the side surface of the substrate to the information recording surface of the optical disk by the condensing grating coupler. The beam is converged by a condensing grating coupler through the surface and introduced into the waveguide, and passed through a separate optical path from the laser semiconductor element by a two-split condensing grating coupler, and then divided into two and placed on the side of the substrate. An optical head characterized in that light is focused on two sets of photodetecting elements.