JP2624783B2 - Optical integrated circuit - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical integrated circuit used for optical communication using a semiconductor laser or an optoelectronic device such as an optical disk recording device, and more particularly, to an optical integrated circuit using a wavelength variation of a semiconductor laser light. The present invention relates to an optical integrated circuit in which various types of generated aberration are corrected.

[Conventional technology]

2. Description of the Related Art Optical components used in fields such as optical communication systems and optical information processing have conventionally been configured by mechanically combining bulk components such as lenses, prisms, and gratings. Therefore, the optical component has a large external dimension and cannot meet the demand for miniaturization, and is expensive.
Alternatively, since they are combined by mechanical coupling, there are various problems that the safety for long-term use is lacking and the reliability is poor. Therefore, in recent years, the concept of an optical integrated circuit (optical IC) in which a plurality of elements are integrated on one substrate has been introduced, and significant miniaturization and cost reduction of optical components have been studied. That is, an optical IC is an optical component in which a light receiving / emitting element, a waveguide type (thin film type) lens, a grating, and the like are integrated on one substrate.

As an example of the optical IC, an optical head for an optical disk has been proposed. (For example, JP-A-61-248244, IEICE Transactions '85 /10vol.J 68-C No.10, IEICE Technical Report '86 / 9vo
l.86, No. 176).

As a constituent element of the optical IC, there is a grating coupler. This is a waveguide-type diffraction grating formed in an optical waveguide, and has the function of guiding light into the optical waveguide and emitting light out of the optical waveguide. It is one of the elements. 4 and 5 show a grating coupler having a function of emitting light out of the optical waveguide as a specific example. The grating coupler 1 is a diffraction grating 4 formed on the optical waveguide 3 of the substrate 2. By optimizing the lattice spacing Δ and the like, the guided light 5 can be emitted into the air as shown in FIG. ,
In addition, the light can be emitted into the substrate as shown in FIG. When the pattern shape of the diffraction grating is a straight line, parallel light can be emitted, and when the pattern shape is a quadratic curve, condensed light can be emitted.

However, the above-mentioned grating coupler has the following problems when a semiconductor laser is used as a light source.
That is, the wavelength of the emitted semiconductor laser light generally changes depending on the operating temperature and variations in the manufacturing process when manufacturing the semiconductor laser. If the emitted wavelength is not a single wavelength, the grating coupler is not used. The problem is that the angle of the light emitted from the light source changes.

That is, the emission angle of light from the grating coupler alpha, the effective refractive index of the optical waveguide of N, lattice spacing of the grating coupler delta, the refractive index of the substrate n _s, and the wavelength of the semiconductor laser beam and λ the following (1 Since α is determined by equation (1), there is a problem that α changes when the wavelength λ changes. Therefore, the light is condensed by the grating coupler or the light emitted from the grating coupler is When the light is condensed by a lens, various aberrations occur due to the wavelength fluctuation, and the spot diameter and the spot position fluctuate.

[Problems to be solved by the invention]

In the above-mentioned prior art, there is a problem that the variation of the semiconductor laser is not considered, and the multi-mode semiconductor laser light cannot be applied practically.

SUMMARY OF THE INVENTION An object of the present invention is to provide an optical integrated circuit in which characteristics do not vary much even when a multi-mode semiconductor laser beam is used.

[Means for solving the problem]

The optical integrated circuit according to the present invention is provided with an optical waveguide comprising a waveguide layer having a higher refractive index than the substrate on the surface of a dielectric or glass substrate, and using an optical recording medium by laser light guided from the semiconductor laser to the optical waveguide. In an optical integrated circuit capable of reading information from a semiconductor laser, a glass block for allowing a semiconductor laser to enter a substrate at a certain angle, a waveguide-type diffraction grating for coupling laser light to an optical waveguide, and an optical waveguide. An optical deflector using surface acoustic waves to deflect light guided into the waveguide, a waveguide-type diffraction grating for emitting guided light into the substrate, and a laser emitted by the waveguide-type diffraction grating A Bragg diffraction type aberration correcting diffraction grating for correcting aberrations due to the wavelength variation of light, a glass block for emitting laser light above the substrate, and a An objective lens that has a mechanism to move in the vertical direction and has a function of condensing light on the optical disk surface, and the return light from the optical disk having the optical recording medium is split into two by the optical waveguide surface, and the split light is converted into a photodiode. An optical integrated circuit used for an optical pickup head for an optical disc having a condensing beam splitter having a function of condensing light on a surface and a photodiode for reading optical information, and a substrate on a dielectric or glass substrate. In an optical integrated circuit using a laser beam guided from a semiconductor laser to an optical waveguide, an optical waveguide formed of a waveguide layer having a high refractive index is provided. A glass block for coupling the laser light into the optical waveguide, and a glass block for coupling the laser light to the optical waveguide. Optical deflector that uses surface acoustic waves to generate light, a waveguide-type diffraction grating that emits guided light into the substrate, and corrects aberrations caused by wavelength fluctuations of the laser light emitted by the waveguide-type diffraction grating This is an optical integrated circuit used for a laser beam printer having a Bragg diffraction type diffraction grating for aberration correction.

[Action]

An example of the operation and effect of the present invention will be described with reference to FIG. The effect of the present invention can be achieved by providing the diffraction grating shown in FIG. That is, as shown in FIG. 1, when the wavelength of the guided light 5 of the semiconductor laser is λ (0) and λ (1) (λ (0)> λ (1), the emission angle of the light emitted from the grating coupler Is α (0) and α (1), respectively, according to the above-mentioned equation (1), so that the light incident on the diffraction grating 6 is incident at different angles, where the grating interval D and the inclination of the diffraction grating. Diffraction grating 6 with optimized δ
Is provided, the emission angles γ from 6 of λ (0) and λ (1) can be made the same or almost the same, and it becomes possible to correct the aberration caused by the wavelength fluctuation of the laser light. Here, D is determined so that the diffraction grating 6 satisfies the Bragg condition for at least one wavelength of the light of λ (0) to λ (1) or diffracts near the Bragg condition. It is important that the shape of No. 6 satisfies the following expression in order to obtain high intensity light, and this is one of the points of the present invention.

T: height of the diffraction grating n ₁ : refractive index change of the diffraction grating θ _B : incidence angle to the grating when the Bragg condition is satisfied in the diffraction grating 6 at the wavelength λ [Example] Next, the model shown in FIG. Will be described in detail, and specific examples of D and δ will be described.

First, at D, the light of wavelength λ (0) is
Diffracted near g or Bragg conditions (3)
Conditions are set so as to satisfy equation (4).

β (0) ≒ γ (0) (4) β (0): incidence angle with respect to the diffraction grating at wavelength λ (0) γ (0): emission angle with respect to the diffraction grating at wavelength λ (0) and wavelength The condition satisfying the expression (5) is set so that the light of λ (1) is diffracted near the Bragg condition.

β (1): incidence angle with respect to the diffraction grating at wavelength λ (1) γ (1): emission angle with respect to the diffraction grating at wavelength λ (1) Further, the following conditions (6) to (11) are satisfied. And D and δ are determined.

α ₀ (0): Exit angle of grating coupler at λ (0) α ₀ (1): Exit angle of grating coupler at λ (1) α ₁ (0): Exit to glass block at λ (0) Incident angle α ₁ (1): Incident angle to glass block at λ (1) Λ: Grating spacing of grating coupler D: Grating spacing of diffraction grating 6 δ: Tilt of diffraction grating 6 m: Diffracted by diffraction grating 6 It is the diffraction order of the light, and is assumed to be -1.

N: effective refractive index of the optical waveguide 5 n _s : refractive index of the substrate 2 n _p : refractive index of a glass block FIG. 2 shows a preferred sectional shape of the diffraction grating 6 used in the present invention, which has high strength. In order to obtain diffracted light, it is desirable to use a diffraction grating having a shape that satisfies the expression (2) described above.

As a specific example of a diffraction grating that satisfies the conditions described above, a semiconductor laser having λ (0) of 0.78 μm and λ (1) of 0.776 μm is used, and a LiNbO ₃ crystal having n _s = 2.2 and N = 2.209 is used. Using the Ti diffused optical waveguide used, a grating coupler of Λ = 10μm is formed on it, and
When a glass block made of BK-7 with n _p = 1.51 is attached and a diffraction grating is attached in parallel with the end face of the substrate, δ is about 80.
D is about 2.5 μm. In this case, the difference between the incident angles of λ (0) and λ (1) with respect to the diffraction grating is as large as about 0.1 °, but the difference between the exit angles from the diffraction grating 6 is as small as 0.01 ° or less. In this case, the efficiency of the diffracted light (light emitted from the diffraction grating 6) becomes 80% or more by setting T to about 10 μm.

As a form of the diffraction grating used in the present invention, there is a reflection type diffraction grating provided with a reflection film 7 as shown in FIG. 3 in addition to the transmission type diffraction grating as shown in FIG. 1 and FIG.

Hereinafter, specific examples of the optical IC using the present invention will be described. FIG. 6 shows an optical IC for condensing a semiconductor laser beam at one point P. The guided light from the semiconductor laser 8 end-coupled to the optical waveguide 3 is converted into parallel light by the waveguide type Fresnel lens 9 and is incident on the grating coupler 1. The incident light is diffracted by the grating coupler 1 and refracted at the boundary between the substrate and the glass prism and enters the diffraction grating 6 of the present invention. The diffraction grating 6 is a transmission type diffraction grating, and is bonded to the block with an adhesive having substantially the same refractive index as the prism. The light incident on 6 is substantially diffracted under the Bragg condition, is reflected on the end face of the prism, is condensed by a lens 10 installed above the substrate 2, and is focused at a point P. The diffraction grating 6 has the function of changing the path of the laser light and diffracting light of different wavelengths in substantially the same direction, whereby the angle of light incident on the lens 10 becomes substantially the same, and light having a small spot diameter is obtained. Is obtained. Here, if the diffraction grating 6 is a simple reflecting mirror, problems such as a change in the point P and an increase in the spot diameter due to a change in the wavelength of the semiconductor laser occur. The optical IC shown in FIG. 6 can be applied to an information reading optical head or the like in an optical disk device. The material constituting the optical IC is quartz, Si
As an O ₂ -based glass substrate, a derivative crystal substrate, an SiO ₂ -based glass optical waveguide, a metal diffused optical waveguide, and an element forming material of 9 and 1, chalcogenide glass and a diffraction grating forming material of TiO ₂ , ZnO, ZnS, and 6 are used. , SiO ₂ -based glass, polymer compounds, and glass block-forming materials of 11 include SiO ₂ -based glass, etc., and all materials generally used for forming optical elements, optical waveguides, and thin-film optical elements are used. An element can be formed by using these materials and making full use of a lithography technique and a vacuum technique used when manufacturing a semiconductor.

FIG. 7 shows an optical IC substantially the same as FIG. The feature is that the diffraction grating 6 is perpendicular to the substrate as compared with the optical IC of FIG. FIG. 6 shows that the laser emission surface of the substrate and the diffraction grating 6 are parallel to each other to facilitate the formation.
Can be arbitrarily set. 8 and 9 are optical ICs substantially the same as FIG. FIG. 8 shows the diffraction grating 6
Is a reflection type diffraction grating provided with a reflection film 7. FIG. 9 is characterized in that light emitted from the diffraction grating 6 is reflected by the lower surface of the glass block and emitted parallel to the substrate. The aberration correction diffraction grating and the glass block as shown in FIG. 9 not only correct the aberration of the light emitted from the grating 1 due to the wavelength variation of the semiconductor laser light, but also connect the semiconductor laser to the end face of the glass block and Considering a grating coupler for input coupling, it can also be used to prevent a decrease in input coupling efficiency due to wavelength fluctuation of a semiconductor laser.

FIG. 10 shows that, instead of the end face coupling of the semiconductor laser of FIG. 6 to the optical waveguide 3, a semiconductor laser is pasted through a prism, the laser light is coupled to the waveguide 3 by a grating coupler, and two more grating couplers are connected. ,
This is an optical IC with a SAW optical deflector formed between 1 '. FIG. 11 shows the grating coupler 1 'and the SAW of the optical IC shown in FIG.
A condensing beam splitter 13 is formed between the optical deflectors 12 and a photodiode 15 is coupled to an end face of the substrate 2.
It is an example of IC. The optical IC shown in FIGS. 10 and 11 is effective as an optical head used in an optical disk device. Hereinafter, the manufacturing method and operation of the optical IC of FIG. 11 will be described.
In the method of manufacturing the optical IC shown in FIG. 11, first, for various waveguide type optical elements, an optically polished LiNbO ₃ crystal is used as the substrate 2, Ti is deposited to a thickness of 24 nm by sputtering, and thermal diffusion is performed to form the optical waveguide 3. Formed. The sputtering conditions were as follows: high frequency power 300 W, argon gas pressure 0.35 Pa,
The sputtering rate is 0.4 nm / sec. The thermal diffusion was performed by using an electric furnace, heating to 1000 ° C., flowing an argon gas atmosphere for 2 hours, and subsequently flowing an oxygen gas for 0.5 hours. Here, the surface refractive index of the waveguide is n _f = 2.22 and the TE of the equivalent refractive index N = 2.209.
It was a single mode director. The optical waveguide may be manufactured by a proton exchange method. The buffer layer formed on the optical waveguide was formed by sputtering Corning # 7059 glass to a thickness of 10 nm. Sputtering condition is high frequency power 10
0 W, argon gas pressure 0.35 Pa, sputtering rate 0.2 nm / sec. On the buffer layer, TiO ₂ was formed to a thickness of 100 nm as a loading layer by reactive sputtering. The sputtering conditions were TiO ₂
Using a target, argon and oxygen as sputtering gas, O ₂ and Ar flow ratio 0.7, sputtering gas pressure 0.42P
a, RF power 500 W, sputtering rate 0.1 nm / sec.
Next, in order to finely process the loading layer and the buffer layer into a shape of a predetermined waveguide type optical element, a resist was formed on the loading layer by a spin coating method. Here, chloromethylated polystyrene (CMS-E) which is an electron beam resist is used as the resist.
XR: manufactured by Toyo Soda) with a thickness of 0.5 μm. After pre-betaning the resist at 130 ° C. for 20 minutes, an electron beam was applied to a predetermined loading layer shape. The irradiation conditions were an electron beam diameter of 0.1 μm and an irradiation amount of 16 μC / cm ² . After the electron beam exposure, development was performed to form a resist mask. Thereafter, the loading layer and the buffer layer were finely processed by ion etching. Conditions of the ion etching, a CF ₄ as an etching gas, and the pressure 3.8Pa, a high-frequency power 200 W, and etching time 15min. After the etching, the resist mask was removed to form various waveguide optical elements. Next, regarding the diffraction grating for aberration correction of 6, the BK-
7 glass, about 10 μm of SiO ₂ , SiCl ₄ and O ₂
It was formed by a CVD method, a vapor deposition method, sputtering, or the like using as a raw material. Next, in order to process SiO ₂ into a predetermined lattice shape by photolithography, a photoresist (OFPR
800) was formed by a 1 μm spin coating method. After pre-baking the resist at 85 ° C. for 30 minutes, the resist was contact-exposed using a UV exposure apparatus using a photomask having a predetermined lattice shape. After the exposure, the film was immersed in chlorbenzene at 40 ° C. for 5 minutes and developed. Cr on resist grid pattern
Was evaporated and subjected to ultrasonic cleaning in acetone to remove the resist, thereby forming a Cr mask. Thereafter, SiO ₂ was finely processed by ion etching using CF ₄ gas, and Cr was removed to form a lattice pattern. This photolithography technique can also be applied to the fine processing of the loading layer and the buffer layer. The substrate 2, the diffraction grating 6, and the glass block 11 made of BK-7, on which the above-described elements are formed, are cut and polished at their respective end faces at various angles, and bonded with an adhesive having a refractive index substantially equal to that of BK-7. Then, the semiconductor laser and the photodiode were end-face-coupled to form an optical IC shown in FIG. Next, the operation of the optical IC in FIG. 11 will be described. Light emitted from the semiconductor laser 8 coupled to the glass block 11 (wavelength 0.77
After being refracted at the interface between the substrate and the prism, it is coupled to the optical waveguide 3 by the grating coupler 1 ′, deflected by the SAW optical deflector 12, and enters the grating coupler 1. The incident light is diffracted into the substrate according to the equations (10) and (11) according to the grating interval of the grating coupler. The light diffracted into the substrate is refracted at the interface between the substrate and the glass block, then diffracted by the diffraction grating 6, reflected at the end face of the glass block, emitted upward, and moved by the lens 10 having a mechanism for moving vertically to the optical disk. The light is focused and focused on pits (information) on the optical disc 14. The light reflected by the optical disk 14 passes through the lens 10, the glass block 11, the diffraction grating 6, and is re-coupled to the waveguide by the grating coupler 1.
The pit information is read out by being split into two by being incident on the photodiode 13 and condensed on the two-division photodiode 15.

Here, when there is no diffraction grating 6, the wavelength of the semiconductor laser is
When changed in the range of 0.776 to 0.78 μm, the angle of incidence on the lens 10 differs by about 0.1 °, and the spot displacement shifts by about 8 μm in the jitter direction. On the other hand, by using the diffraction grating of the present invention having the grating pitch D of about 2.5 μm and the grating height T of about 10 μm, the difference in the incident angle becomes less than 0.01 degree, and the spot position fluctuation in the jitter direction is also less than 0.01 degree. μm or less. With the diffraction grating of the present invention, the wavelength dependence of the spot position fluctuation on the optical disk is greatly reduced, and an optical head from which more accurate information can be read.

FIGS. 12 and 13 show an optical IC substantially the same as FIG.
The optical IC of FIG. 12 has a condensing grating coupler for coupling to a waveguide when the laser light is not parallel light. Thirteenth
In the optical IC shown in the figure, a diffraction grating 6 is provided between a grating coupler 1 'for coupling laser light to a waveguide and a semiconductor laser to prevent a decrease in input coupling efficiency due to wavelength fluctuation.

〔The invention's effect〕

As described above, by providing the diffraction grating of the present invention, it becomes possible to correct various aberrations due to the wavelength fluctuation of light, and therefore, even when a multi-mode semiconductor laser is used as a light source, the characteristic fluctuation is small. An optical integrated circuit can be formed. The present invention is particularly effective for correcting aberrations of an optical disk pickup head.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing an optical element in one embodiment of an optical integrated circuit according to the present invention. FIG. 2 is a sectional view showing a first embodiment of a diffraction grating in the optical integrated circuit according to the present invention. FIGS. 4A and 4B are sectional views showing a second embodiment of the diffraction grating in the optical integrated circuit according to the present invention. FIGS. 4 and 5 are explanatory views for explaining the operation of the grating coupler, and FIGS. 7
8, FIG. 9, FIG. 9, FIG. 10, FIG. 11, FIG. 12, and FIG. 13 respectively show the first, second, third, and third optical integrated circuits according to the present invention.
FIG. 14 is a configuration diagram showing a fourth, fifth, sixth, seventh, and eighth embodiment. 1,1 '... Grating coupler, 2 ... Substrate, 3 ...
... optical waveguide, 4 ... diffraction grating, 5 ... guided light, 6 ... diffraction grating, 7 ... reflection film, 8 ... semiconductor laser, 9 ... waveguide type Fresnel lens, 10 ... lens, 11 ... … Glass block, 12… SAW optical deflector, 13… Condensing beam splitter, 14… Optical disk, 15… Photodiode.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Kazumi Kawamoto 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Prefecture Inside of Hitachi, Ltd. (56) References JP-A-61-265745 (JP, A) JP-A-63-155431 (JP, A) JP-A-60-202553 (JP, A) JP-A-61 −92439 (JP, A)

Claims (2)

(57) [Claims] An optical waveguide comprising a waveguide layer having a higher refractive index than a substrate is provided on the surface of a dielectric or glass substrate, and information of an optical recording medium is transmitted by a laser beam guided from a semiconductor laser to the optical waveguide. In an optical integrated circuit that can be read, a glass block for making a semiconductor laser incident on a substrate at a certain angle, a waveguide type diffraction grating for coupling laser light to an optical waveguide, and An optical deflector using surface acoustic waves to deflect guided light, a waveguide-type diffraction grating for emitting guided light into a substrate, and a wavelength of laser light emitted by the waveguide-type diffraction grating Bragg diffraction type diffraction grating for correcting aberrations due to fluctuation, glass block for emitting laser light above substrate, and moving perpendicular to optical disk surface An objective lens that has a function of condensing light on the optical disk surface, and the return light from the optical disk having the optical recording medium is split into two by the optical waveguide surface, and the split light is condensed on the photodiode surface An optical integrated circuit for use in an optical pickup head for an optical disk having a condensing beam splitter having a function of causing the light to be read and a photodiode for reading optical information. 2. An optical integrated circuit using a laser beam guided from a semiconductor laser to an optical waveguide, wherein an optical waveguide comprising a waveguide layer having a higher refractive index than the substrate is provided on the surface of a dielectric or glass substrate. A glass block for allowing light emitted parallel to the substrate from the laser to enter the substrate at a certain angle, a waveguide-type diffraction grating for coupling the laser light to the optical waveguide, and light guided in the optical waveguide Optical deflector that uses surface acoustic waves to deflect light, a waveguide-type diffraction grating that emits guided light into the substrate, and aberrations associated with wavelength fluctuations of the laser light emitted by the waveguide-type diffraction grating An optical integrated circuit for use in a laser beam printer having a Bragg diffraction type aberration correcting diffraction grating for correcting the aberration.