JP2000137129A - Optical waveguide and manufacture of the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical waveguide optimal to an optical waveguide with a spot size converting part small in deflection dependency and excessive loss, simple in production process, and capable of being mass-produced at a low cost. SOLUTION: This optical waveguide 10 is provided with a core 1 and clads 4 and 5 on a substrate 3, and the width and thickness of a top end part 2 of the core 1 are reduced like a taper in the width direction and thickness direction toward the top end of the core. The top end part of the core is allowed to function as a spot size converting part 2. This method for manufacturing the optical waveguide 10 comprises at least at a process for forming a level in difference by removing one part of the core and a process for forming the level in difference into a smooth oblique face by accumulating a thin film on the level in difference. Thus, the spot size of the connected part with an optical fiber can be enlarged in a simple method, and a compact optical waveguide device with a low loss can be manufactured at a low cost.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical waveguide used for optical communication and the like and a method for manufacturing the same, and more particularly, to an optical waveguide optimal for an optical waveguide having a spot size converter and a method for manufacturing the same. .

[0002]

2. Description of the Related Art With the rapid spread of the Internet, the commercialization of optical communication systems is proceeding at an extremely rapid pace. For example, a 2.5 Gb / s system capable of transmitting 30,000 or more lines using a normal telephone line has been introduced in many regions. In addition, in accordance with the expansion of information transmission capacity, a method of increasing the number of multiplexing times by wavelength multiplexing has been proposed.
It has already been put to practical use. From the initial wavelength multiplexing at several wave levels to the high-density wavelength multiplexing method up to 80 wave levels, commercialization has been started.

In such a wavelength-division multiplexing optical communication system, a multiplexer for introducing a plurality of signal lights having different wavelengths into one optical fiber is provided. A branching filter for signal separation is an important device, and an array waveguide grating (AWG) has attracted attention as an example.

The AWG has an array of optical waveguides having the same optical path length difference between two input and output star couplers. The array waveguide plays the role of a higher-order diffraction grating. Perform the function of multiplexing / demultiplexing. AWGs in which a quartz-based optical waveguide is formed on a Si substrate or a quartz glass substrate have already been commercialized and used in actual optical communication systems. AWGs currently commercially available generally have a size of about 3 cm x 4 cm and require a temperature control function. Therefore, the AWG is attached to a Paltier element and housed in a package. Because it will be about 5cm x 6cm
There is a problem that a considerable amount of space is occupied in the board of the transmission device, and miniaturization of the device is one of the important issues.

[0005] In addition to those used for trunk systems, small-sized optical waveguide devices are also strongly required for access systems requiring two-way communication. The element size of an optical waveguide device having functions such as multiplexing, demultiplexing, and branching is generally limited by the radius of curvature of a curved waveguide portion. In order to form a curved waveguide having a smaller radius of curvature and low loss, the relative refractive index difference Δ between the core layer and the cladding layer may be set to be large. For example, in the case of a waveguide having a relative refractive index difference Δ of about 0.4%, which is usually employed in a silica-based optical waveguide, the radius of curvature is set to 40 mm or more in order to keep the bending loss within 0.1 dB. Although it is necessary, by setting the relative refractive index difference Δ to 1%, the radius of curvature is 10 m.
m or less.

However, when the relative refractive index difference Δ is increased, it is necessary to reduce the core diameter in order to satisfy the single mode condition, and accordingly, the coupling loss due to the difference from the spot size of the optical fiber increases. Even if the size can be reduced, there is a problem that the loss as an optical module is increased. Therefore, in order to manufacture a small and low-loss optical module, it is necessary to reduce the coupling loss with the fiber by making the curved region a high relative refractive index difference Δ and enlarging the spot size of the fiber coupling portion. It is.

Conventionally, as a method of increasing the spot size, there is known a method in which only the waveguide width is tapered. Although this method is a very simple method, it has a problem that the coupling loss has a large dependence on the deflection because the height direction of the waveguide is constant.

A method of changing the thickness of the core in a stepwise manner is disclosed in, for example, Japanese Patent Application Laid-Open No. H8-1710.
No. 20 discloses this. According to this method, it is considered that the dependence of the coupling loss on the deflection is reduced because both the width and the thickness of the core can be reduced. However, the excess loss due to radiation is increased by changing the thickness, which can be up to several μm, in at most several steps. Although the excess loss can be reduced by further increasing the number of steps, the patterning step and the film deposition are repeated, and the number of steps is greatly increased, which is not suitable for mass production.

A method of increasing the spot size by heating the end of the waveguide by laser irradiation and diffusing the dopant in the core into the cladding is disclosed in, for example, JP-A-4-220609. According to this method, the polarization dependence of the coupling loss is small, and the spot size can be greatly increased from 5 μm to 10 μm. However, since the laser is heated one by one, it takes several hours to heat, for example, several tens of arrayed waveguides, so that the throughput is not necessarily high.

[0010]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to solve the problems shown in the prior art, to reduce deflection dependency and excess loss, to simplify the process, and to realize mass production at low cost. An object of the present invention is to provide an optical waveguide optimal for an optical waveguide with a spot size conversion unit and a method for manufacturing the same.

[0011]

In order to achieve the above-mentioned object, an optical waveguide according to the present invention comprises an optical waveguide having a core and a clad on a substrate, wherein both the width and the thickness of the tip of the core are reduced. , Tapered toward the tip of the core. Preferably, the substrate is Si or quartz glass, and the core layer and the cladding layer are quartz glass containing at least one of P, Ge, and B as a dopant. In the present invention, since the core of the optical waveguide has a smooth tapered shape in the width direction and the thickness direction at the front end, the front end of the core functions as a spot size conversion unit having a smaller excess loss than the conventional case.

According to a method of manufacturing an optical waveguide according to the present invention for manufacturing the above-described optical waveguide, a core and a clad are provided on a substrate, and a width and a thickness of a tip portion of the core are reduced in a tapered shape. A step of forming a step by removing a part of the core in a stepped manner, and forming a step on the step by depositing a thin film on the step and forming the step into a smooth slope. And at least steps.

Preferably, the core layer and the clad layer are formed of quartz glass containing at least one of P, Ge, and B as a dopant, and in the slope forming step, the thin film is formed of P and B. It is made of quartz glass containing as a dopant, and the thin film is fluidized by reflow by heat treatment to form a step into a smooth slope. The heat treatment temperature at the time of reflow is 800 ° C. or higher.

Further, the core layer and the cladding layer are formed of quartz glass containing at least one of P, Ge, and B as a dopant, and in the slope forming step, a polymer or a spin-on-glass material is spun on a step. The step may be formed into a smooth slope while forming the thin film by coating.

In the slope forming step, the film thickness is 2 μm or more and 3 μm or more.
A thin film of m or less is formed on the step. In addition to the step of forming the slope, a step of removing the thin film in a region other than the region of the slope on the step is provided.

In a preferred embodiment of the present invention, a lower cladding layer is formed on a substrate by an atmospheric pressure chemical vapor deposition method, and then a tapered shape is formed at a predetermined distance from an upper surface of the lower cladding layer. Having a step of forming a core layer while embedding the stopper film, and then, in a step forming step,
An etching mask is formed on the core layer at a position in contact with the base end of the stopper film, and then, the mask layer is used to etch the core layer up to the stopper film in the stopper film region, and in a region other than the stopper film below the stopper film. Then, the core layer is etched to the position of to form a step in the core layer.

By using the method of the present invention, it is possible to obtain a smooth tapered core tip portion, instead of a shape in which the thickness and width of the core are reduced stepwise as shown in the conventional example. A tip that functions as a spot size converter with a small excess loss can be formed. Further, since the manufacturing method according to the present invention is constituted only by a simple wafer process, it also has a feature that it is excellent in mass productivity and cost reduction.

Hereinafter, embodiments of the present invention will be described specifically and in detail with reference to the accompanying drawings. Embodiment of Optical Waveguide This embodiment is an example of an embodiment in which the optical waveguide according to the present invention is applied to an optical waveguide with a spot size converter, and FIG. FIG. 3 is a perspective view illustrating a configuration of an optical waveguide. The optical waveguide 10 with a spot size converter manufactured by the method of the present embodiment is
As shown in FIG. 1, the optical waveguide has a core 1 and cladding layers 4 and 5 made of a quartz-based material on a substrate 3. A part of the core 1 near the end face 6 of the optical waveguide is machined so as to have a tapered portion 2 whose width and thickness gradually decrease as approaching the end face 6. The core 1 is first processed so as to have a step that becomes thin in a stepwise manner in the thickness direction, and then the stepped step is filled with a second core material to form a tapered portion 2 having a smooth taper shape. It is molded as follows. Thereby, the tapered part 2 functions as the spot size conversion part 2.

The width W1 and the thickness T1 of the core 1 are W
2. By reducing to T2 (W1> W2, T1> T2), the confinement of the guided light propagating in the core 1 is weakened, and the spot size at the optical waveguide end face 6 is enlarged. In addition, since the spot size conversion unit 2 has a smooth tapered shape, the loss due to radiation can be suppressed low.

Embodiment of the Method for Fabricating an Optical Waveguide This embodiment is an example of an embodiment of a method for fabricating an optical waveguide according to the present invention, and will be described below with reference to FIGS.
With reference to FIGS. 3A to 3E, a method of manufacturing the above-described optical waveguide 10 with a spot size converter will be described. FIGS. 2A to 2E show an optical waveguide 10 with a spot size converter according to the method of manufacturing an optical waveguide of the present embodiment.
3 (a) to 3 (e) are top views corresponding to FIGS. 2 (a) to 2 (e).

First, atmospheric pressure chemical vapor deposition (APCVD)
As shown in FIG. 2A, silicon (Si)
A quartz-based film is formed on the substrate 3 as the lower cladding 4 and the core layer 12. The thickness of the lower cladding 4 is about 15 μm, and the thickness of the core layer 12 is 4 μm. As a material for forming the cladding 4 and the core layer 12, a quartz-based film doped with P, Ge, B, or the like is used. The refractive index is controlled by changing the concentration of each dopant. In order to change the thickness of the core layer 12 stepwise in a later step, the metal film 7 is embedded in the core layer 12 here. The metal film 7 is formed 1.5 μm above the interface with the lower cladding 4. Further, as shown in FIG. 3A, the metal film 7 is formed in a tapered shape whose width gradually decreases toward the tip. The core width (W1) is set to 4 μm, and the width (W2) of the tip of the tapered portion is set to 1 μm. As a material of the metal film 7, for example, tungsten silicide (WSi) or the like can be used.

By forming the lower cladding 4 and the core layer 12 in a low-temperature process of 800 ° C. or less using APCVD, a good quartz-based film can be formed, and the metal film 7 is greatly damaged by heat. There is no such thing. Further, a mask 8 for forming a core is formed using a resist or a metal film.

Next, as shown in FIGS. 2B and 3B, the core layer 12 is etched by the RIE method under the metal film 7 and the mask 8 so that the tapered portion 13 is formed at the tip. The step-shaped core 1 is formed. At this time, the metal film 7 serves as an etching stop layer, and a step-like step is formed in a part of the core 1.

Next, as shown in FIGS. 2 (c) and 3 (c), a tapered portion 13 of the core 1 is formed.
Except for the metal film 9 is formed.

Next, as shown in FIGS. 2D and 3D, a quartz film 11 having a thickness of about 2 to 3 μm is formed on the entire surface by APCVD. The core 1 is formed so as to smoothly fill the step. Further, a mask is formed on the quartz-based film 11 so as to include the tapered region of the core 1. The quartz-based film 11
Since BPSG can obtain a good reflow shape by annealing at a temperature of 800 ° C. or more, BPSG is obtained by doping at least P and B (BPSG). In addition, doping of Ge together with P and B (GBPS
G) may be performed. GBPSG can reflow at lower temperatures than BPSG.

Finally, as shown in FIGS. 2 (e) and 3 (e), excess quartz-based film other than the tapered portion 13 of the core 1 is removed by etching. The width,
It is possible to obtain the spot size conversion unit 2 that can smoothly change the thickness on the taper.

The core width (W1) and thickness (T1) are set to 4 μm.
m, core width (W2) and thickness (T
2) is set to 1 μm, the length of the tapered portion 13 in the propagation axis direction is 500 μm, and the relative refractive index difference Δ between the core and the clad is 1
%, And a sample waveguide having the same configuration as the optical waveguide 10 with the spot size conversion unit of the embodiment was prototyped according to the method of the embodiment. Then, when the coupling loss with the fiber was measured, it was 0.3 dB, and an improvement of the coupling loss from 1.5 dB to 1.2 dB when no spot size conversion was performed was observed. For comparison, a sample having a stepped core (a non-smooth tapered shape formed by a reflow layer) was trial-produced and measured, and the coupling loss was 1.0 dB. 0.7d
It can be seen that B was improved. The above dimensions and parameter values are merely examples for understanding the present invention, and needless to say, they are not limited thereto.

As described above, since the method of manufacturing an optical waveguide according to the present invention is constituted by a process which is almost the same as a normal optical waveguide process, there is no problem in mass production. Here, APC is used for forming the quartz-based film.
Although VD is used, it may be plasma CVD or low pressure CVD. The waveguide material may be a polymer material other than the quartz material. In particular, the quartz-based film 11 (reflow layer) can obtain a smooth tapered shape by spin coating using a polymer, SOG (spin on glass), or the like.

Although Si is used for the substrate, there is no problem even if quartz glass or ceramic is used. Further, the metal film 7 may be made of titanium or chromium instead of WSi. In the above embodiment, one step-shaped step is provided in the core 1. However, it is also possible to eliminate this step, that is, to form a taper only with the reflow layer without including the process of forming the metal film 7. is there. Conversely, it is also possible to increase the steps so that the steps are made finer and the taper angle is made shallower.

[0030]

According to the present invention, by forming an optical waveguide having a spot size converter in which the shape of the core is reduced in the width direction and the thickness direction toward the tip, the coupling loss with the optical fiber is reduced. Thus, an optical waveguide with a spot size converter having a small size can be realized. Further, by using the optical waveguide according to the present invention, the size of the optical waveguide device can be reduced. Further, the method of the present invention realizes a manufacturing method capable of mass-producing the optical waveguide according to the present invention by a simple method.

[Brief description of the drawings]

FIG. 1 is a perspective view of an optical waveguide with a spot size converter according to an embodiment.

FIGS. 2A to 2E are side cross-sectional views each showing a cross section of a substrate in each step when an optical waveguide with a spot size converter is manufactured according to the optical waveguide manufacturing method of the embodiment.

FIGS. 3A to 3E respectively show FIGS.
It is a top view corresponding to (e).

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Core 2 Spot size conversion part 3 Substrate 4 Lower clad layer 5 Upper clad layer 6 Core end face 7, 9 Metal mask 8, 10 Mask 11 Reflow layer 12 Core layer 13 Tapered part

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Yutaka Yuno 5-7-1 Shiba, Minato-ku, Tokyo F-term within NEC Corporation 2H047 KA04 KA13 MA05 PA05 PA21 PA24 QA04 QA07 TA01 TA32 TA43

Claims (9)

[Claims] 1. An optical waveguide having a core and a clad on a substrate, wherein both the width and the thickness of the tip of the core are tapered toward the tip of the core. . 2. The method according to claim 1, wherein the substrate is a Si or quartz glass substrate, and the core layer and the cladding layer are formed of quartz glass containing at least one of P, Ge, and B as a dopant. The optical waveguide according to claim 1, wherein: 3. A method of manufacturing an optical waveguide having a core and a clad on a substrate, wherein a width and a thickness of a tip portion of the core are reduced in a tapered shape, wherein a part of the core is stepped. A step of forming a step by removing a step, and a slope forming step of depositing a thin film on the step and forming the step into a smooth slope. 4. The core layer and the cladding layer are formed of quartz glass containing at least one of P, Ge, and B as a dopant. In the slope forming step, quartz glass containing P and B as a dopant is used. 4. The method according to claim 3, wherein the thin film is formed, the thin film is fluidized by reflow by heat treatment, and the step is formed into a smooth slope. 5. The heat treatment temperature at the time of reflow is 80.
The method for producing an optical waveguide according to claim 4, wherein the temperature is 0 ° C. or higher. 6. The core layer and the clad layer are formed of quartz glass containing at least one of P, Ge, and B as a dopant. In the slope forming step, a polymer or a spin-on-glass material is spun on a step. 4. The method according to claim 3, wherein the step is formed into a smooth slope while forming the thin film by coating.
3. The method for producing an optical waveguide according to item 1. 7. In the slope forming step, the film thickness is 2 μm or more.
The method of manufacturing an optical waveguide according to claim 3, wherein a thin film having a thickness of μm or less is formed on the step. 8. The method according to claim 3, further comprising, after the step of forming a slope, a step of removing a thin film in a region other than the region of the slope on the step. A method for manufacturing an optical waveguide. 9. An atmospheric pressure chemical vapor deposition method,
Forming a lower clad layer on the substrate, and then forming a core layer while embedding a tapered stopper film at a predetermined position at a predetermined distance from the upper surface of the lower clad layer; Then, an etching mask is formed on the core layer at a position in contact with the base end of the stopper film, and then, the mask layer is used to etch the core layer up to the stopper film in the stopper film region, and from the stopper film in regions other than the stopper film. The method of manufacturing an optical waveguide according to any one of claims 3 to 8, wherein the core layer is etched to a lower position to form a step in the core layer.