JPH04190334A - Light integrated circuit - Google Patents

Abstract

PURPOSE:To increase the use efficiency of light and to enable reduction of size by including a converging grating coupler provided in a dielectric thin film waveguide path continuously formed by the same constituent material as that of the second high frequency generating portion. CONSTITUTION:Laser light generated by a semiconductor laser 4 and laser light of a wavelength half that of the laser light are propagated from the second high frequency generating portion 13 to a dielectric thin film waveguide path 3 formed in such a manner so as to be connected to the second high frequency generating portion 13 by the same constituent material as that of the second high frequency generating portion 13. Laser light of two wavelengths propagated to the dielectric thin film waveguide path 3 is separated by a converging grating coupler 6 to converge laser light of half wavelength on one point in a space. Thus, the use efficiency of light is increased and assembling is easy without any increase in adjusting portions. Furthermore, as the light wave is divided by a converging grating coupler, it is not necessary to use a special wave divider for separating the light of two wavelengths so as to enable reduction of size.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to optical integrated circuits.

[Conventional technology]

As an optical integrated circuit, it is constructed by integrating a light source, an optical waveguide containing various functional elements, a photodetector, etc. Conventionally, three configurations have been proposed: a monolithic optical integrated circuit, a hybrid optical integrated circuit, and a quasi-hybrid optical integrated circuit. FIG. 5 is a perspective view of a conventional example in which an optical integrated circuit is configured as an optical head for reading signals from an optical disk. In this figure, 1 is a substrate, 2 is a buffer layer, 3 is an optical waveguide, 4 is a semiconductor laser, and 5 is a beam splitter, 6 is a condensing grating coupler, 7.11.12 is a laser beam, 8,
Reference numeral 9 denotes a light receiving element, 10 a condensing spot, and D an optical disk.
The light is focused on the optical disc D along the path from the coupler 6 to the optical disc D, producing a focused spot 10 on the disc surface. Then, the optical disc D by the above-mentioned condensed spot 10
The reflected light from the optical disk D → the condensing grating
The light is applied to the light receiving elements 8 and 9 through the path of coupler 6 → beam splitter 5 → light receiving elements 8 and 9, and the light that is incident on the light receiving elements 8 and 9 is photoelectrically converted and converted into a signal (not shown). The signal is supplied to a processing circuit, and the signal processing circuit generates a reproduction signal, a tracking control signal, and a focus control signal, so that each of the above-mentioned signals is supplied to a required circuit portion. (Problem A to be Solved by the Invention) By the way, an optical integrated circuit that generates a condensing spot with a minute diameter is equipped with, for example, a condensing grating in addition to the optical head for reading the signal of the optical disc D.・
A laser printer head with a surface acoustic wave deflector installed on a Ti/LiNb○1 waveguide to deflect a small diameter focused spot focused in space by a coupler, high frequency spectrum・Although it can be used as an analyzer and other devices, the performance of the various devices described above improves as the diameter of the minute focused spot formed by these devices becomes smaller.7 For example, optical disc D
The limit of information recording density is determined by the focused spot diameter on the optical disk, and the aforementioned focused spot diameter is determined by the limit of beam focusing based on the phenomenon of light diffraction, that is, the diffraction limit, so it is proportional to the wavelength of the light. Therefore, when the wavelength of the light becomes 1/2, the diameter of the converging groove becomes 1/2, and the area of the condensing spot becomes 1/4. In other words, if the diameter of the condensed spot on the optical disc D can be halved, the information recording density can be quadrupled. Furthermore, in devices such as laser printer heads and high frequency spectrum analyzers, for example, if the diameter of the focused spot can be reduced to 1/2, the resolution can be doubled. Therefore, in order to improve the performance of various devices that use a focused spot, it is necessary to reduce the diameter of the focused spot. When the numerical aperture of the optical lens is NA, λ/N
Since it is proportional to the value of A, in order to reduce the diameter of the focused spot, it is necessary to shorten the wavelength λ of the light or increase the numerical aperture NA of the focusing lens. However, condensing lenses with large numerical apertures inevitably have a shallow depth of focus, it is difficult to make ones with good characteristics, and there are many other problems, so focusing lenses with a large numerical aperture It is not possible to adopt a solution that relies on the size of several NAs to obtain a focused spot with a necessary diameter. Therefore, in order to reduce the diameter of a focused spot in order to improve the performance of various devices that use a focused spot, it is necessary to generate light with a short wavelength λ. However, semiconductor lasers that can generate laser light with a shorter wavelength than the laser light that can be generated using semiconductor lasers currently in practical use are not currently in practical use due to reasons such as the lack of materials that can be used. For this purpose, in order to generate laser light with a shorter wavelength than the laser light generated using the semiconductor lasers currently in use, the laser light generated using the semiconductor lasers currently in use is generated using nonlinear optical effects. Attempts have been made to use the generated harmonic light, but for example, it has been attempted to use a second harmonic generation element that uses laser light emitted from a semiconductor laser to generate the second harmonic using a nonlinear optical effect. It is possible to obtain a laser beam with a wavelength of 1/2 of the wavelength of the laser beam emitted from the semiconductor laser as the output of the second high shoulder wave generation element and make it incident on the substrate of the optical integrated circuit. However, with such a configuration, the number of end face joints is large, resulting in low light utilization efficiency, and the increase in the number of parts causes problems such as a shape that is difficult to assemble. [1 [Means for Solving the Problem] The present invention provides a channel type in which laser light emitted from a semiconductor laser end face-coupled to one end of a dielectric thin film waveguide layer formed on the surface of a substrate is injected. The second waveguide consists of a waveguide.
A harmonic generation section and a light condensing device provided in a dielectric thin film waveguide that is made of the same material as the second harmonic generation section and is continuous with the second harmonic generation section. An optical integrated circuit including a brating coupler is provided. [Operation] A laser beam emitted from a semiconductor laser which is face-coupled to one end of a dielectric thin film waveguide layer formed on the surface of the substrate is injected into a second harmonic generation section consisting of a channel type waveguide. , a second harmonic generation section generates a laser beam with a wavelength half the wavelength of the laser beam generated by the semiconductor laser5, and from the second harmonic generation section, the laser beam generated by the semiconductor laser and the semiconductor laser beam are generated. A state in which the laser beam of 172 wavelengths of the laser beam generated by the laser is made of the same constituent material as the second harmonic wave generating section described above and is continuous with the second harmonic wave generating section described above. The signal is propagated through a dielectric thin film waveguide made up of. The two wavelengths of laser light propagating into the dielectric thin film waveguide are separated by a condensing grating coupler.
Laser light with a wavelength of 172, which is longer than that generated by the semiconductor laser described above, is focused on one point in space. As mentioned above, 1/2 of the laser light generated by the semiconductor laser
The diameter of the condensed spot obtained by concentrating a laser beam with a wavelength of 1/2 of the diameter of the focused spot obtained by focusing the light using a grating coupler
becomes. Since the second harmonic generation section and the components of the condensing grating coupler are provided in a continuous dielectric thin film waveguide, there is little loss of light, and therefore the light It has a high utilization rate, and is easy to assemble without increasing the number of adjustment points.Furthermore, since it is demultiplexed by a condensing grating coupler, a special demultiplexer is used to separate the two wavelengths of light. Since it is not necessary, miniaturization is also possible. Embodiments Hereinafter, specific contents of the optical integrated circuit of the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a perspective view showing an example of the configuration of an optical integrated circuit according to the present invention configured as an optical head for reading signals from an optical disc D. FIG. FIG. 3 is a propagation vector diagram, and FIG. 4 is a side sectional view showing an example of the configuration of a light receiving element. In FIG. 1, which shows a perspective view of an example configuration in which the optical integrated circuit of the present invention is configured as an optical head for reading signals of an optical disk D, 1 is a substrate, and in the description of the following embodiments, the substrate is 1 is said to be a LiTa○3 substrate, and 3 is a dielectric thin film waveguide layer (an optical waveguide layer made of a dielectric thin film) 3 formed on the surface of the LiTa○3 substrate 1 described above. In the description of the following examples, this dielectric thin film waveguide layer 3 is a LiNbO3 single crystal thin film whose refractive index has been controlled by doping with another substance (for example, magnesium oxide). has been done. L i T a 03 L formed on the surface of the substrate 1
A dielectric thin film waveguide layer 3 made of an L i N b O3 single crystal thin film is injected with laser light emitted from a semiconductor laser 4 that is facet-coupled to the dielectric thin film waveguide layer 3 made of an i N b O3 single crystal thin film. The portion 13 constitutes a second high shoulder wave generating section 13 (see FIG. 2 showing a cross section of the optical integrated circuit) made of a channel type waveguide. That is, the laser beam emitted from the semiconductor laser 4 described above is transmitted to the LiNb constituting the second harmonic generation section 13.
○3 When the laser beam is injected into the channel type waveguide portion of the dielectric thin film waveguide layer 3 made of single crystal Kambara, the second harmonic generation section 13 generates the second harmonic wave of the laser beam injected therein. However, the second harmonic laser beam and the fundamental wave laser beam are well phase-matched, and the second harmonic laser beam and fundamental wave laser beam are
After propagating through the harmonic generation section 13, the same as the channel type waveguide section 13 of the dielectric thin film waveguide layer 3 made of the L i N b O3 single crystal thin film that constitutes the second harmonic generation section 13 described above. The waveguide continues to advance through a slab-type waveguide that is continuously constructed of constituent materials. That is, the channel type waveguide portion 13 of the dielectric thin film waveguide layer 3 made of the LiNbO3 single crystal thin film constituting the second harmonic generation section 13 described above is formed as a slab type waveguide on the entire surface of the LiTaO3 substrate 1. L i N
Since it is constructed by providing a notch 20.21 in a part of the dielectric thin film waveguide layer 3 made of a b○3 single crystal thin film, the LiNbO3 which constitutes the second harmonic generation section 13 described above is Dielectric thin film waveguide layer 3 made of single crystal thin film
The channel-type waveguide portion 13 and the slab-type waveguide formed continuously therewith are made of the same constituent material, and the L i N forming the second false wave generation section 13 is made of the same material.
b There is no interface between the channel waveguide portion 13 of the dielectric thin film waveguide layer 3 made of O3 single crystal thin source and the slab waveguide continuous thereto, and the second harmonic wave is generated in the second harmonic generation section 13. The laser light of the second high harmonic wave propagates into the slab waveguide without loss and can be used efficiently. As described above, L constituting the second harmonic generation section 13
The fundamental wave laser light and the second harmonic continue to travel from the channel waveguide portion 13 of the dielectric thin film waveguide layer 3 made of the iNbO3 single crystal thin film through the slab waveguide that is constructed continuously thereto. The laser beam is given to the condensing grating coupler 6 through the beam splitter 5, and the second harmonic laser beam is condensed onto the optical disc D by the condensing grating coupler 6, and is condensed onto the disc surface. The spot 10 is generated, but due to the wavelength selectivity of the condensing grating coupler 6, the fundamental wave laser beam is different from the direction in which the second harmonic laser beam is emitted from the condensing grating coupler 6. The light is emitted in a completely different direction, and this is clear from the propagation vector diagrams illustrated in FIGS. 3(a) and 3(b). 3(a) is a propagation vector diagram of the fundamental laser beam, that is, the laser beam with a wavelength of λ, and FIG. 3(b) is the propagation vector diagram of the laser beam of the second harmonic, that is,
This is a propagation vector diagram of a laser beam with a wavelength of λ/2, in which O9°θS' is the emission angle on the substrate side, θ
C2θC' is the emission angle on the air side, N is the effective refractive index of the dielectric thin film waveguide layer 3 made of LiNbO3 single crystal thin film, and K (=
2π/Δ) is the grating period of the condensing grating coupler 6, nc is the refractive index on the output side (air), ns is the refractive index of the substrate, and nf is the refractive index of the dielectric thin film waveguide layer 3 made of LiNbO3 single crystal thin film. , βl is the propagation vector, is 2π/λ, and k″ is 2. In this way, in the optical integrated circuit of the present invention, the fundamental wave laser light and the second harmonic laser light are separated using different filters. This is done automatically without using any means due to the wavelength selectivity of the condensing grating coupler 6, and the second
A condensed spot 1o with a minute diameter can be generated on the optical disc D by the harmonic laser beam. The light reflected from the optical disc D by the above-mentioned focused spot 1o is given to the light receiving elements 8, 9 through the path of the optical disc D → the condensing grating coupler 6 → the beam splinter 5 → the light receiving elements 8, 9. 8
, 9 photoelectrically convert the light incident thereon. The signals outputted from the light receiving elements 8 and 9 described above are supplied to a signal processing circuit (not shown), and the signal processing circuit generates a reproduction signal, a tracking control signal, and a focus control signal. Supplies the required circuit parts. FIG. 4 is a side sectional view showing a configuration example of a light receiving element, and the light receiving elements 8 and 9 illustrated in FIG. 4 are made of LiTaO
3 A lower electrode 14, a photoconductor layer 15, and a transparent electrode 16 are sequentially laminated on a dielectric thin film waveguide layer (optical waveguide layer made of a dielectric thin film) 3 formed on the surface of a substrate 1. has been done. 17 is a power supply, 18 is a resistor, and 19 is an output terminal. (Effects of the Invention) As is clear from the above detailed explanation, the present invention provides a laser beam emitted from a semiconductor laser that is facet-coupled to one end of a dielectric thin film waveguide layer formed on the surface of a substrate. A second harmonic generation section consisting of a channel type waveguide into which light is injected, and a second harmonic generation section made of the same constituent material as the second harmonic generation section described above and configured in a state continuous to the second harmonic generation section described above. An optical integrated circuit comprising a condensing grating and a coupler provided on a dielectric thin film waveguide, which is edge-coupled to one end of the dielectric thin film waveguide layer formed on the surface of the substrate. Laser light emitted from a semiconductor laser is injected into a second harmonic generation section made of a channel type waveguide, and the laser beam generated by the semiconductor laser in the second harmonic generation section has a wavelength of 172. The second harmonic generating section generates the laser beam generated by the semiconductor laser and the laser beam having a wavelength that is 1/2 of the laser beam generated by the semiconductor laser. The above-described wave propagates through a dielectric thin film waveguide which is made of the same material as the second harmonic generation section and is continuous with the second harmonic generation section. The two wavelengths of laser light are separated by a condensing grating coupler, and compared to the laser light generated by the semiconductor laser described above, the laser light with a wavelength of 172 is focused on one point in space. The diameter of the condensed spot obtained by condensing the laser beam having a wavelength of 172 generated by the semiconductor laser with the condensing grating coupler is the diameter of the condensed spot obtained by condensing the laser beam generated by the semiconductor laser with the condensing grating coupler. For example, the diameter of the focused spot obtained by condensing the light using a condensing grating coupler with the same numerical aperture is 1/2. In addition, the resolution can be doubled in devices such as laser printer heads and high-frequency spectrum analyzers. However, since it is provided in a continuous dielectric thin film waveguide, there is little loss of light, so the light utilization rate is high, and assembly is easy without increasing the number of adjustment parts. moreover,
Since the light is split by the condensing grating coupler, there is no need to use a special splitter to separate the two wavelengths of light, and miniaturization is also possible.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing an example of the configuration of an optical integrated circuit according to the present invention configured as an optical head for reading signals from an optical disc D. FIG. 2 is a sectional view taken along line X--X in FIG. 3 is a propagation vector diagram, FIG. 4 is a side sectional view showing an example of the configuration of a light receiving element, and FIG. 5 is a perspective view of a conventional example in which an optical integrated circuit is configured as an optical head for reading signals from an optical disk. 1--Substrate, 2--buffer layer, 3--optical waveguide, 4
... Semiconductor laser, 5... Beam splinter, 6...
・Concentrating grating coupler, 7,11°12...
Laser light, 8, 9... Light receiving element, 10... Focusing spot, D... Optical disk, 13... Second harmonic generation section, 14... Lower electrode, 15... Photoconductor layer , 16...
・Transparent electrode, 17... Power supply, 18... Resistor, 19.
...output terminal, patent applicant: Japan Victor Co., Ltd., agent: patent attorney, Zero Go-7-Heiji. ~ Nee

Claims (1)

[Claims] a second harmonic generation section comprising a channel type waveguide into which laser light emitted from a semiconductor laser end-coupled to one end of a dielectric thin film waveguide layer formed on the substrate surface is injected; The structure includes a condensing grating coupler provided in a dielectric thin film waveguide that is made of the same material as the second harmonic generation section and is continuous with the second harmonic generation section. optical integrated circuits