JPS62145209A - Optical waveguide device - Google Patents

Abstract

PURPOSE:To obtain a high-performance waveguide device which has small crosstalk by providing an area where light is inhibited from being propagated on the surface of an optical waveguide except an optical waveguide. CONSTITUTION:A light absorbing layer 12, a clad layer 13, and an optical waveguide layer 14 are laminated on an InP substrate 11 by a crystal growth method such as LPE. The light absorbing layer 12 uses an InGaAsP mixed crystal material, but band gap wavelength lambdag is only >=1.3mum so as to obtain light absorption characteristics to waveguide light wavelength lambda=1.3mum. The clad layer 13 requires a material which has a lower refractive index than the optical waveguide layer 14 and is transparent to the waveguide light, so an InP material is used; and the optical waveguide layer 14 uses an InGaAsP layer with composition of lambdag=1.1mum. Then, an optical waveguide 14a and a propagation inhibiting area 20 are formed. In this case, the film thickness (t) needs to satisfy cutoff condition to single-mode propagated light so as to obtain the propagation inhibiting area 20.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an optical waveguide device used as a transmission component for optical communication or an optical integrated circuit element.

2. Description of the Related Art In recent years, as optoelectronic technology has progressed, functional elements such as semiconductor lasers, light receiving elements, and optical switches have been actively developed as large-capacity communication devices. Furthermore, research on ultra-wavelength multiplexing transmission as a means of effectively utilizing fibers is progressing steadily in tandem with optical integrated circuit technology. The key points in establishing ultra-wavelength multiplexing transmission technology are optical integration technology and 9-way waveguide control technology. Up until now, both hybrid and monolithic types of optical integration technology have been actively developed by taking advantage of their respective features, but recently, due to improvements in technology and process technology, the latter is becoming more mainstream. . Various functional elements constituting an optical integrated circuit are optically connected to each other by optical waveguides formed on a substrate. In order to effectively confine signal light within the waveguide, the structure of the optical waveguide is modified, and a loaded optical waveguide as shown in FIG. 3 is often used. In the figure, 1 is a substrate, 2 is an optical waveguide layer, 3 is a loading section, and 4 is incident light. The optical waveguide layer directly under the loading section has a slightly higher effective refractive index than other regions. Therefore, the signal light 4 input from the outside into the loading region is three-dimensionally confined in this optical waveguide layer and propagated efficiently.

Problems to be Solved by the Invention However, the above-mentioned method had the following drawbacks. When connecting a waveguide device and an external optical transmission line, such as an optical 7-eyeper, methods are used, such as a method in which a lens or the like is used to optimally narrow down the light beam and image it directly on the end face of the waveguide, or a method using a prism grating. In either case, the coupling efficiency is not 100%, causing scattering loss and unnecessary propagation modes. Broadly speaking, the following two problems arise.

(1) In the case of a loaded waveguide, even if the structure is optimized, at the coupling part with the external optical transmission line during input/output, not only the desired waveguide but also propagation modes near the surface of other waveguide layers Easy to occur.

(2) Furthermore, a radiation mode exists not only on the surface of the waveguide layer but also on the substrate that is transparent to the propagating light, and is affected by reflection from the front and back surfaces.

For the reasons mentioned above, there has been a problem in that the noise becomes a noise component in the photodetector constituting the optical integrated circuit, resulting in a decrease in the S/N ratio. Crosstalk is one of the factors that affects the performance of wavelength division multiplexing communications.

Normally, the lower the crosstalk, the better, but in order to ensure the reliability of the transmission system, a crosstalk of about 2 odB is required.

In conventional examples, it has been difficult to construct an optical waveguide device with good characteristics due to noise components caused by modes propagating in areas other than the desired waveguide within the optical waveguide device or by light transmission due to diffuse reflection within the substrate. . Therefore, an object of the present invention is to provide a high-performance waveguide device that can eliminate the above-mentioned drawbacks, that is, has low crosstalk.

Means for Solving the Problems In order to solve the above problems, according to the present invention, first,
A light absorption layer on a substrate that has the property of being transparent to propagating light,
A cladding layer and an optical waveguide layer are sequentially laminated, and at least one optical waveguide is formed in the uppermost optical waveguide layer, and then a region for blocking light propagation is formed on the surface of the optical waveguide layer other than the optical waveguide. As the propagation blocking region, the thickness of the optical waveguide layer is set to be less than the minimum thickness that allows the fundamental mode to propagate with respect to the propagating light, and as the light absorbing layer, a material with a composition that exhibits absorption characteristics for the propagating light is used. By this, an optical waveguide device with excellent characteristics can be obtained.

As a working waveguide structure, consider a slab waveguide as shown in Figure 2 (,). In the figure, 11 is a substrate, 12 is a light absorption layer, 13 is a cladding layer, 14 is an optical waveguide layer, and 15 is a guided light. A material with a composition having a longer bandgap wavelength than the leading wave light 16 is used as the light absorption layer 12, and the cladding layer is made thick to the extent that it does not affect the waveguide characteristics. If appropriate conditions are set, the guided light 16 will be confined within the optical waveguide layer 14 and propagate. The propagation characteristics at this time are determined by various waveguide conditions, and the characteristics are greatly influenced by the film thickness of the waveguide. Now, InP is used as the substrate 11, waveguide composition: λ
, = 1.1 μm, and the guided light wavelength λ = 1.3 μm, FIG. 2(b) shows how the effective refractive index of the waveguide changes with respect to the waveguide film thickness. The light propagating at this time had a plane of polarization parallel to the waveguide (TE mode) and was in the lowest order mode.

When the waveguide film thickness is 0.75 μm or less, the waveguide is in a cut-off state, and no mode of light can propagate through the waveguide, but becomes a radiation mode toward the substrate. In addition, stray light components that are generated when coupling light from an external transmission system to a waveguide to a region other than the desired waveguide, and radiation and scattering components from the waveguide into the inside of the substrate are guided through the cladding layer 3. All of the light is absorbed and removed by the light absorption layer 2 placed below the wave path 4.

From the above, it is possible to thin the waveguide layer area other than the desired waveguide tread using appropriate means, set the film thickness to a cutoff condition with respect to the predetermined conditions, and By arranging the light absorption layer through the cladding layer, unnecessary propagation modes that occur when signal light is input, and scattering and scattering within the waveguide can be avoided.
This means that all stray light components can be cut out.

Example Next, the present invention will be described in detail with reference to the drawings.

In the figure, 11 is a substrate, 12 is a light absorption layer, 13 is a cladding layer,
14 is an optical waveguide layer, 14a is an optical waveguide, and 21 is a propagation blocking region. First, in the creation process, the InP substrate 11
A light absorption layer 12 on top. The cladding layer 13 and the optical waveguide layer 14 are sequentially laminated by a crystal growth method such as LPE. Light absorption layer 1
2, an InGaAs P mixed crystal material is used, but in order to have absorption characteristics for the guided light wavelength λ=1.3 μm, it is sufficient if the band gap wavelength λ9 is 1.3 μm or more, and here, 1 A composition of .6 μm was used. As the cladding layer 13, an InP material was used because a material that has a lower refractive index than the optical waveguide layer 14 and is transparent to the guided light is required. As the optical waveguide layer 14, an InGaAs P layer having a composition of λg=1.1 μm was used. Also, the film thicknesses are as follows: light absorption layer 12, cladding layer 13. Each optical waveguide layer 14 is 1μ"
+ 5 Jim, 1 prn.

Next, an optical waveguide 14a and a propagation blocking region 2o are created.

This is achieved by a normal photolithography process with W=2~3μ.
After forming a pattern with a width of m, the propagation blocking region 20 is etched to make it thinner. In order to act as the propagation blocking region 20, the film thickness: t must satisfy a cutoff condition for single mode propagation light.

Here, t was set to 0.571 m from the viewpoint of process stability. Finally, by removing the etching mask, the present device can be constructed.

In this configuration, the input light 2o coupled from one end surface of the optical waveguide 14a is effectively confined and propagated in the optical waveguide 14a. Optical direct imaging methods such as lenses are often used for optical coupling with the outside, but in this case, in conventional methods, propagation modes are generated in areas other than the desired waveguide, which mix with the regular signal light and reduce the S/N. There was a problem that this resulted in a decrease in the ratio.

According to the method of this embodiment, such unnecessary propagation modes can be completely cut off in the propagation blocking region, so that the influence of noise can be significantly reduced. In addition, the substrate mode during input/output and scattered light from the waveguide were also a cause of noise, but since these stray light components can be completely absorbed and removed by the light absorption layer installed under the optical waveguide, they can be removed at ultra-high wavelengths. This means that a sufficiently good S/N ratio can be achieved even for multiplex transmission.

In this example, InGaAsP on the InP substrate
Although we used a combination of layers, it can be realized by combining a material with low loss for the transparent waveguide as the substrate and a material with excellent absorption characteristics as the light absorption layer. Needless to say, this can also be achieved by combining the above.

Effects of the Invention As described above, according to the present invention, an optical waveguide device, which is a basic component in an optical integrated circuit, can be realized with extremely low crosstalk characteristics, and can be used satisfactorily as a device for ultra-wavelength multiplexing transmission. Its practical effect is a dog because it can provide what it can.

[Brief explanation of drawings]

11...Substrate, 12...Light absorption layer, 1
3... Cladding layer, 14... Optical waveguide layer, 14a... Optical waveguide, 20... Propagation blocking region. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 2 (cL) Guideway depth, hand [μm

Claims (3)

[Claims] (1) A light absorption layer, a cladding layer, and an optical waveguide layer are sequentially laminated on a substrate made of a material transparent to propagating light, and at least one optical waveguide is formed on the optical waveguide layer,
An optical waveguide device characterized in that a region for blocking propagation of light is provided on the surface of the optical waveguide layer other than the optical waveguide. (2) The optical waveguide device according to claim 1, wherein the thickness of the optical waveguide layer as the propagation blocking region is set to be less than a cutoff for propagating light. (3) The optical waveguide device according to claim 1, wherein a material having a composition with a bandgap wavelength larger than that of propagating light is used as the light absorption layer.