JPH06308338A - Waveguide type optical parts - Google Patents

Abstract

PURPOSE:To provide waveguide type optical parts capable of erasing the influence due to minute double refraction in the constitutive material of a waveguide and simultaneously reducing the polarizing fluctuation of coupling efficiency and the polarizing fluctuation of propagation loss. CONSTITUTION:A directional coupler is provided with a coupling part C consisting of plural pieces of waveguides 1, 2 arranged in parallel and close to each other and lead waveguides 3, 3, 4, 4 connected to the waveguides 1, 2 respectively. Then, in the waveguide type optical parts, the path widths of the waveguides 1, 2 in the coupling part C are different from each other, and all path widths of the lead waveguides 3, 3, 4, 4 are the same, and further, tapered waveguides 5, 5 whose path width is changed continuously are held therebetween the waveguide 2 and the lead waveguides 4, 4.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a waveguide type optical component of directional coupler type, and more specifically, even when the material itself constituting the waveguide has a slight natural birefringence. The present invention relates to a waveguide type optical component in which the polarization fluctuation of the coupling efficiency and the polarization fluctuation of the propagation loss are small.

[0002]

2. Description of the Related Art In the field of optical communication, various waveguide type optical components have been highly anticipated.
The directional coupler occupies an important position as a component such as a star coupler or an optical multiplexer / demultiplexer. This directional coupler is usually an optical circuit having a plane pattern as shown in FIG. That is, the waveguides 7 and 8 having a uniform width are arranged in parallel so as to be close to each other so that the evanescent fields of the light propagating therethrough influence each other, thereby realizing the coupling of the propagating light. A coupling portion C is formed. The end portions 7a and 7b of the waveguide 7 and the end portions 8a and 8b of the waveguide 8 respectively have a width equal to that of the waveguides 7 and 8 and form lead patterns 9a, which form a bending pattern. 9b, 9c and 9d are connected.

In the directional coupler having the above structure, even when the number of waveguides in the coupling portion C is three or more, coupling of propagating light is exhibited, so that the number of adjacent waveguides is particularly limited. There is no such thing. The directional coupler having such a plane pattern is usually manufactured as follows.

First, by applying a film forming method such as a flame deposition method, a plasma CVD method, or a vacuum evaporation method on a substrate of Si single crystal or quartz, for example, a lower clad layer made of SiO ₂ and a lower clad layer thereon. First, SiO ₂ is doped with TiO ₂ or the like to form a slab core having a refractive index larger than that of the lower clad layer. Then, a photolithography technique using a reactive ion etching method or the like is applied to this slab core to remove unnecessary portions and form a waveguide core having a plane pattern as shown in FIG. And
In the same manner as the formation of the lower clad layer described above, Si
An upper clad layer made of O ₂ is formed and the waveguide core is buried.

The constituent material is not limited to the above-mentioned SiO ₂ , but may be, for example, various compound semiconductors or multi-component glass.

[0006]

By the way, in the waveguide optical component manufactured by the above-mentioned method, the inside of the waveguide may have an internal stress due to a difference in linear expansion coefficient. Therefore, even if a waveguide is formed of a material that should not have natural birefringence, very small birefringence is observed in the waveguide in many cases. Become.

In the case of a directional coupler composed of a waveguide in which such a minute birefringence occurs, there is a problem in that its coupling efficiency varies depending on the polarization state of propagating light. . In order to eliminate this inconvenience, the conditions at the time of manufacturing the waveguide and the clad may be optimized so that natural birefringence does not occur. However, since the manufacturing process of the waveguide is an integration of many unit processes, even if the individual processes are optimized, problems such as disturbance of the consistency between the processes inevitably occur. Therefore, in the actual manufacturing process, it is very difficult to eliminate natural birefringence by pursuing the appropriateness of the conditions, and it cannot be said that it is a practical measure.

The present invention solves the above problems and provides a waveguide optical component having a novel structure which can alleviate the polarization fluctuation of the coupling efficiency even if a minute birefringence occurs in the manufactured waveguide. For the purpose of provision.

[0009]

As a result of intensive studies to achieve the above object, the present inventor has found that asymmetrical directional couplers having different waveguide path widths at the coupling section have We have found the fact that the polarization fluctuation of the coupling efficiency is mitigated compared to the case of a directional coupler having a coupling part composed of equal waveguides.

At the same time, when the width of one of the waveguides is narrowed, the lead waveguide connected to the waveguide of the coupling portion is shown in FIG.
It was also found that in the case of the curved waveguides 9a, 9b, 9c, 9d as shown in, the polarization fluctuation of the propagation loss of light becomes large. Therefore, the polarization fluctuation of the coupling efficiency can be alleviated by narrowing the width of one of the waveguides in both the coupling portion and the lead waveguide. However, at that time, there arises a problem that the polarization fluctuation of the propagation loss increases in the lead waveguide, and the effect of reducing the polarization fluctuation of the coupling efficiency is actually canceled.

In order to eliminate the contradictory effects described above, the inventors of the present invention make the path widths of the waveguides different from each other only in the coupling portion, make the widths of the lead waveguides all equal, and combine the coupling portions. With the idea that the width of the waveguide can be reduced to the original width at the connection point with the lead waveguide, both the polarization fluctuation of the coupling efficiency and the polarization fluctuation of the propagation loss can be reduced. , Has led to the development of the waveguide type optical component of the present invention.

In other words, the waveguide optical component of the present invention has a direction in which it has a coupling portion composed of a plurality of waveguides arranged in parallel in close proximity to each other, and a lead waveguide connected to each of the waveguides. In the optical coupler, the waveguide widths in the coupling portion are different from each other, and the lead waveguide widths are all the same, and between the waveguide in the coupling portion and the lead waveguide. Provided is a waveguide type optical component in which a tapered waveguide whose path width continuously changes is interposed.

The basic structure of the optical waveguide component of the present invention is shown in FIG. In the figure, in the coupling portion C, a wide waveguide 1 and a narrow waveguide 2 are arranged in parallel in close proximity to each other so as to enable evanescent coupling of propagating light. Bent waveguides 3 having a width equal to the width of the waveguide 1 are connected to both ends 1a and 1b of the wide waveguide 1 as lead waveguides. Also in the narrow waveguide 2, curved waveguides 4 and 4 having the same width as the curved waveguides 3 and 3 are connected as lead waveguides through the tapered waveguides 5 and 5.

Here, the widths of the tapered waveguides 5 and 5 are continuous from the point where they are connected to both ends 2a and 2b of the narrow waveguide 2 to the point where they are connected to the curved waveguides 4 and 4. Has been widened. The above optical component is one in which the width of one of the waveguides in the coupling portion is made narrower than the width of the other waveguide, but any waveguide can be used as long as it operates in a single mode. Since such a configuration is acceptable, the waveguide type optical component of the present invention can be configured, for example, by changing the thickness of the waveguide thick or changing the widths of both the waveguides mutually. .

Further, the basic configuration of the present invention can be applied to a directional coupler in which three or more waveguides are closely arranged in parallel.

[0016]

In the structure shown in FIG. 1, since the whole is an asymmetric directional coupler, the polarization fluctuation of the coupling efficiency is reduced. Then, the one waveguide 2 in the coupling portion C
The phenomenon that the polarization fluctuation of the propagation loss in the curved waveguides 4 and 4 caused by making the width narrower than that of the other increases is due to the fact that the path width is continuous between the waveguide 2 and the waveguides 4 and 4. This is solved by interposing tapered waveguides 5 and 5 which are widened to.

[0017]

Examples of the invention

Example 1 FIG. 2 shows an asymmetric Mach-Zehnder interferometer type wavelength flat coupler that incorporates the basic configuration shown in FIG. In this coupler, a wide waveguide 1 and a narrow waveguide 2 are used.
And the two coupling portion C _1, C ₂ is formed consisting, during the coupling portion C _1, C _2, phase shifting part D is formed by arranging a wide bend waveguides 6. A tapered waveguide 5a is provided between the narrow waveguide 2 and the curved waveguide (lead waveguide) 3.
The narrow waveguide 2 and the curved waveguide 6 in the phase shift portion D are also connected by the tapered waveguide 5b.

This coupler was manufactured by applying the flame deposition method. At this time, the wide waveguide 1 has a path height of 8 μm and a path width of 8 μm.
μm, the height of the narrow waveguide 2 is 8 μm, the width is 6 μm, and the pitch between the waveguides of the coupling portions C ₁ and C ₂ is 1
It was 3 μm. In addition, the curved waveguide 6 in the phase shift portion D
Is 8 μm and the road width is 8 μm, and the curved waveguides 3 and 4 are 8 μm in height, 8 μm in width and 50000 μm in radius of curvature.

The relative refractive index difference of the waveguide is about 0.3%, and the phase shift part D
The path difference between the waveguides at is set to about 0.6 μm. The length of the tapered waveguides 5a and 5b was set to about 500 μm. This coupler has a coupling efficiency of 20 ± 3% when using propagating light having a wavelength of 1.2 to 1.65 μm. The polarization fluctuation of the coupling efficiency is about 0.3 dB, which is a significant improvement over the conventional structure having about 1 dB.

Further, the polarization fluctuation of the propagation loss is as small as about 0.1 dB or less, which is at the same level as that of the conventional structure. Example 2 FIG. 3 shows another coupler. This coupler is a phase shifter D
Is a straight waveguide having a width equal to that of the narrow waveguide 2. Therefore, the phase shift portion D does not include the tapered waveguide.

In the case of this coupler, since the phase-shifting portion D does not include a tapered waveguide, it is possible to shorten the entire element length. When the coupler of FIG. 3 is manufactured, a propagation constant difference occurs between the waveguides in the phase shift part D,
It is possible to reduce the path difference, and for example, in the case of the coupler having the same characteristics as in Example 1, the element length could be shortened by about 1 to 5 mm as compared with Example 1.

The polarization fluctuation of the coupling efficiency and the polarization fluctuation of the propagation loss were substantially the same as those of the coupler of the first embodiment.

[0023]

As is apparent from the above description, in the waveguide type optical component of the present invention, when a directional coupler is manufactured by a usual method, a minute birefringence is generated in the waveguide, so that the coupling efficiency is deviated. The problem of wave fluctuations is solved, and the polarization fluctuation of the coupling efficiency of the directional coupler and the polarization fluctuation of the propagation loss are reduced only by changing the waveguide pattern.

[Brief description of drawings]

FIG. 1 is a plan pattern diagram showing a basic configuration of an optical component of the present invention.

FIG. 2 is a plane pattern diagram showing an asymmetric Mach-Zehnder interferometer type wavelength flat coupler of the present invention.

FIG. 3 is a plan pattern diagram showing another example of the asymmetric Mach-Zehnder interferometer type wavelength flat coupler of the present invention.

FIG. 4 is a plan view showing a conventional directional coupler.

[Explanation of symbols]

1 Wide Waveguide 1a, 1b Wide Waveguide End 2 Narrow Waveguide 2a, 2b Narrow Waveguide End 3,4 Curved Waveguide (Lead Waveguide) 5, 5a, 5b Tapered Conductor Waveguide 6 Bent waveguide C, C ₁ , C ₂ Coupling part D Phase shift part

Claims (3)

[Claims] 1. A directional coupler having a coupling section composed of a plurality of waveguides arranged in parallel with each other in close proximity to each other, and a lead waveguide connected to each of the waveguides, wherein The width of the waveguide is different from each other,
And the widths of the lead waveguides are all the same, and
A waveguide-type optical component, wherein a tapered waveguide whose path width changes continuously is interposed between the waveguide and the lead waveguide in the coupling portion. 2. In a waveguide type optical component having a Mach-Zehnder interferometer type structure in which a phase shift section is arranged between two coupling sections, the waveguide widths in the coupling section are different from each other, In addition, all the lead waveguides have the same path width, and a taper waveguide whose path width changes continuously is interposed between the waveguide in the coupling portion and the lead waveguide. A waveguide type optical component. 3. The one waveguide of the phase shifting portion is a straight waveguide having a width equal to that of the one waveguide of the coupling portion, and the width of the other waveguide of the phase shifting portion is The waveguide type optical component according to claim 2, which is constant.