JP3425734B2 - Manufacturing method of optical waveguide - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a waveguide type optical component in the fields of optical communication, optical signal processing and optical measurement. Especially 1.3 μm band and 1.5 μm
A great effect can be expected when used in a waveguide type optical amplifier having a function of amplifying signal light in a band.

[0002]

2. Description of the Related Art Recently, a waveguide type optical amplifier for amplifying a signal light of 1.5 μm band which is important for optical communication has been actively developed.
This waveguide type optical amplifier has a rare earth element of Er 1.5.
Since it uses laser transition in the μm band, it can compensate propagation loss and branch loss by optical amplification.
It is an extremely useful optical component. A waveguide type optical amplifier is manufactured by a process called a convex process, as in the conventional passive optical waveguide circuit manufacturing method.

FIG. 5 shows Er for an optical amplifier by a convex process.
A method for manufacturing the doped optical waveguide will be described. First, the lower clad glass layer 2 is formed on the Si substrate 1 by the flame deposition method (see FIG. 5A). Next, the Er-doped core glass layer 3 co-doped with P is formed, and the Er-doped core glass 4 is processed into a rectangular shape by a photo process and etching (FIG. 5B).
And (c)). Furthermore, by burying the core in the upper clad glass layer 5 (see FIG. 5D), an Er-doped optical waveguide is manufactured.

By using this method, an arbitrary waveguide pattern can be formed. Therefore, an optical circuit such as a directional coupler or a ring resonator used in the conventional waveguide type optical component can be manufactured with high accuracy and reproducibility.

By the way, an optical amplifier using a rare earth-doped optical waveguide has a higher propagation loss than an optical fiber type optical amplifier. Therefore, it is necessary to add a rare earth element in a high concentration and a high excitation light intensity is required. Becomes However, in order to perform optical amplification using a semiconductor laser as an excitation light source, there is a limit to the optical output of the light source, so it is important to improve the gain for unit excitation light intensity and operate with high efficiency. As a means for improving efficiency, in an Er-doped fiber type optical amplifier, a method of using an optical fiber in which Er is added to the core center part has been realized. This is to improve the amplification degree per unit excitation light intensity by adding Er to the core center where the light intensity is high. Similarly, in the optical waveguide, if Er is added to the central portion of the core of the waveguide, improvement in amplification can be expected.

In the conventional convex process, it is practically difficult to add Er to the central portion of the core by a combination of a photo process and etching. As described in Japanese Patent Laid-Open No. 4-271328, Er is first disclosed. After making an optical waveguide consisting of an added core and heating it, the entire core is expanded by heating and diffusing it from the core to the surrounding clad with the substance for refractive index addition. A technique has been proposed in which Er exists only in the central portion.

[0007]

However, the above-mentioned proposed method has a problem that the controllability of the core width and the refractive index distribution of the core is poor because diffusion by heat treatment is utilized. Therefore, an optical circuit utilizing optical interference requires a pattern accuracy of 1 μm or less,
It was difficult to fabricate a directional coupler and a Mach-Zehnder interferometer with good reproducibility.

Further, Japanese Unexamined Patent Publication No. 4-359230 and Japanese Unexamined Patent Publication No. 6-281977 also disclose a technique relating to an optical waveguide having a two-layer core. In each of these, different types of cores are arranged in the vertical direction. There is no proposal that the cores are stacked, and the cores are distributed so that the cores are deposited differently in the horizontal direction.

The present invention has been made in view of these problems, and an object thereof is to provide a method of manufacturing an optical waveguide for an optical amplifier which operates with high efficiency.

[0010]

[0011]

[0012]

[0013]

[0014]

A method of manufacturing an optical waveguide in which an optically active substance of the present invention, which achieves the above-mentioned object, is added only to the central part of a core is a core formed on a flat substrate and the core surrounding the core. In a method of manufacturing an optical waveguide including a clad having a lower refractive index, (1) a lower clad layer forming step of forming a lower clad layer on a planar substrate, and a first groove formation of forming a first groove in the lower clad layer. And (2) a first core layer material having a refractive index higher than that of the lower clad layer, a second core layer material having a refractive index equal to that of the first core layer, and an optically active substance added, a core layer material lamination step of laminating the first core layer material on the lower cladding layer in this order, (3) pre-Symbol first core layer material and the second first core core layer material by sintering Layer and core layer to be the second core layer A sintering step, (4) a core portion molding step of removing a portion other than the first groove portion of the first core layer and the second core layer, (5) the lower clad layer and the first core And an upper clad layer forming step of forming an upper clad layer having a refractive index lower than that of the first core layer on the layer and the second core layer.

In the method of manufacturing the optical waveguide ,
It is characterized in that the core layer raw material laminating step is a flame deposition method.

In the method of manufacturing the optical waveguide ,
The first groove forming process is a photo process and an etching process.

In the method of manufacturing the optical waveguide ,
The optically active substance is a rare earth element.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below with reference to the drawings.

According to the present invention, since the dimensional accuracy of the core is determined by the processed shape of the groove formed in the lower cladding, an optical circuit utilizing interference such as a directional coupler is manufactured without pattern thinning or core deformation. In addition, the rare earth element can be added to the center of the core having a high refractive index.

In this manufacturing method, since the rare earth element is added to the center of the core by the combination of the photo process and the etching, if the flat glass film can be formed, the manufacturing method of the core glass and the core glass composition are limited. There is no.

For example, examples of the glass film manufacturing method to which the present invention is effective include a flame deposition method, a CVD method, and a sputtering method.

Regarding the glass composition, P, Ge,
Ti, B, etc. can be arbitrarily selected.

Examples of the rare earth element include Nd and Er having a laser transition in the 1.3 μm band and the 1.5 μm band used in optical communication, Sm and Ho, and 0 of Er. Another example is Yb, which has a sensitizing effect on absorption in the .98 μm band.

These rare earth elements and elements such as P and Ge which enhance the refractive index can be applied in any combination.

In particular, when the flame deposition method is used, a core glass soot containing no rare earth element is deposited on the lower clad glass grooved into a concave shape, and then a core glass soot containing a rare earth element is further deposited. When a core glass soot containing no rare earth element is deposited and sintered at a high temperature, the rare earth element has a small diffusion amount, so that the core glass soot is embedded in the recess so that it is distributed only in the core central portion. Therefore, if the core glass soot composed of three layers is formed, the rare earth element can be added to the central portion of the core by one-time sintering, and the photo-process and the etching are used only once.

Further, when the flame deposition method is used, the core glass soot composed of three layers can be formed once by continuous deposition. From this, the flame deposition method can simplify the manufacturing process, and is therefore suitable as a manufacturing method for adding a rare earth element to the center of the core.

No matter which method is used, the optical waveguide produced by the method of the present invention has a clear boundary between the core and the clad as compared with the optical waveguide disclosed in Japanese Patent Laid-Open No. 4-271328. It has excellent characteristics, and is disclosed in
Compared with the optical waveguides disclosed in JP-A-359230 and JP-A-6-281977, since the optically active substance is distributed only in the central portion even in the horizontal direction, the effect of the optically active characteristics becomes large.

[0028]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The preferred embodiments of the present invention will be described below with reference to the drawings, but the present invention is not limited thereto.

Reference Example 1 FIG. 1 shows a process of manufacturing an optical waveguide according to the present invention. Here, in this reference example, Er was used as the rare earth element. (1) First, about 30 is deposited on the Si substrate 1 by the flame deposition method.
A lower clad glass layer 2 having a thickness of μm is produced (FIG. 1).
(See (a)). (2) Next, a width of 6 μm and a depth of 6 μm for forming a core
The concave groove 2a is formed by a photo process and reactive ion etching (see FIG. 1B). (3) Next, a core glass soot containing no Er and containing B, P, Ge is deposited by a flame deposition method. (4) In order to make the core glass soot into a transparent glass, it is held in an electric furnace at 1300 ° C. for 2 hours to be sintered. (5) The Er-free core glass layer 6 had a thickness of 12 μm (see FIG. 1C). (6) Next, the Er-free core glass layer 6 is removed by reactive ion etching to fill the groove 2a with the Er-free core glass (see FIG. 1 (d)). (7) Next, the Er-doped core becomes 3 μm in width and 4.5 in depth.
A concave groove 7a having a size of μm is formed by a photo process and reactive ion etching (see FIG. 1E). (8) Next, Er-doped P co-doped core glass soot is deposited by the flame deposition method. (9) In order to make the Er-added P-co-added core glass soot into a transparent vitreous material, hold it in an electric furnace at 1200 ° C. for 2 hours to sinter. (10) The thickness of the Er-doped core glass layer 3 was 12 μm (see FIG. 1 (f)). (11) Next, the Er-doped core glass layer 3 is removed by reactive ion etching (see FIG. 1 (g)). (12) Next, only the upper surface of the Er-doped core glass 4 formed in the groove 7a by the photo process and etching is subjected to 1.5
μm is removed (see FIG. 1 (h)). (13) Next, by the flame deposition method, E with a film thickness of 12 μm
An r-free core glass layer 6 is produced (see FIG. 1 (i)). (13) Next, the Er-free core glass layer 6 is removed by reactive ion etching (see FIG. 1 (j)). (14) Finally, the upper clad glass layer 5 containing B and P having the same refractive index as that of the lower clad glass layer 2 is formed by the flame deposition method by the flame deposition method (see FIG. 1 (k)). ). The waveguide manufactured in this reference example has a core size of 6 μm × 6 μm, a refractive index difference between core clad of 0.75%, an Er-added region of 3 μm × 3 μm, and an Er concentration of 4000 ppm. The Er-doped glass 4 is an Er-free core. It is added to the center of the glass 7.

Next, using the optical waveguide manufacturing method of this reference example, an optical amplifier in which a multiplexing / demultiplexing circuit for pumping light and signal light was integrated was manufactured. FIG. 2 shows a schematic circuit configuration. In FIG. 2, reference numeral 10 is a signal light input optical waveguide, 11 is a pump light input optical waveguide, 12a and 12b are Mach-Zehnder interferometers, 13 is an optical amplification optical waveguide, 14 is a signal light output optical waveguide, and 15
Shows the respective optical waveguides for pumping light output. The entire optical amplifier was constructed by the above-mentioned method by an optical waveguide in which Er was added to the center of the core.

In order to operate this optical amplifier, first, a pumping light having a wavelength of 1.47 μm and a signal light having a wavelength of 1.5 μm are input using a single mode optical fiber to the pumping light inputting waveguide 11 and the signal light inputting. It is incident on the waveguide 10. The Mach-Zehnder interferometer 12a composed of the directional coupler I and the directional coupler II of the pumping light has a light intensity of 99% with respect to the light intensity propagating through the pumping light input optical waveguide 11 To excite Er ions, and the signal light propagates to the optical amplification optical waveguide 13 with a light intensity of 99% with respect to the signal light input optical waveguide 10. Here, the signal light propagating through the optical amplification optical waveguide 13 is amplified by the excited Er ions.

Further, the pumping light propagated through the optical amplification optical waveguide 13 is directed by the Mach-Zehnder interferometer 12b composed of the directional coupler III and the directional coupler IV to the directional coupler I and the directional coupler II. The signal light that is demultiplexed at the coupling rate of 99% by the same operation principle as that of the Mach-Zehnder interferometer 12a and is amplified by the optical waveguide for pumping light 13 to the optical waveguide for optical amplification 13 has a coupling rate of 99%. Respectively propagate to the signal light output optical waveguide 14, and only the signal light is extracted by the single mode optical fiber.

Using this optical amplifier, an optical amplification experiment in the 1.3 μm band was carried out. When the optical intensity of the pumping light at the emission end of the single mode optical fiber was 30 mW, the optical intensity of the signal light was 30 dB. Amplified and gain efficiency is 1dB / m
It became clear that it was W. Since the gain efficiency when the Er is uniformly added to the core is 0.3 dB / mW, it was found that the gain efficiency can be improved three times by using the Er-centered optical waveguide according to the manufacturing method of the present invention.

In the present reference example, the flame deposition method was used for producing the glass film, because this method is suitable for depositing a relatively thick and high-quality glass film. Depending on the case, another glass film synthesizing method, for example, a CVD method or a sputtering method can be partially or entirely used.

Example FIG. 3 shows a process of manufacturing an optical waveguide according to the present invention. Here, Er was used as the rare earth element. (1) First, about 30 is deposited on the Si substrate 1 by the flame deposition method.
A lower clad glass layer 2 having a thickness of μm is produced (FIG. 3).
(See (a)). (2) Next, a width of 6 μm and a depth of 6 μm for forming a core
The concave groove 2a is formed by a photo process and reactive ion etching (see FIG. 3B). (3) Next, by the flame deposition method, the Er-free core glass soot 8 with P added is deposited as the first layer, then the Er-added P co-doped core glass soot 9 is deposited as the second layer, and the third layer is added. An Er-free core glass soot 8 containing P is deposited as a layer (see FIG. 3C). (4) Next, in order to make the core glass soot into a transparent glass, it is held in an electric furnace at 1200 ° C. for 2 hours for sintering. (5) The core glass has a film thickness of 12 μm, and Er of the first layer is
The thickness of the additive-free core glass layer 6 is 4.5 μm, and the second layer E
The film thickness of the r-doped core glass layer 3 was 3 μm, and the film thickness of the third Er-free core glass layer 6 was 4.5 μm (FIG. 3).
(See (d)). (6) Next, the core glass layer having a three-layer structure is removed by reactive ion etching (see FIG. 3 (e)). (7) Next, a glass film containing B and P having the same refractive index as that of the lower clad glass layer 2 is formed by the flame deposition method as the upper clad glass layer 5 of about 30 μm by the flame deposition method (FIG. 3 ( See f)).

The waveguide manufactured in this example has a core size of 6 μm × 6 μm and a refractive index difference of 0.75 between core clads.
%, Er added region 3 μm × 3 μm, Er concentration 4000 p
pm, and the Er-doped glass 4 is added to the center of the Er-undoped core glass 7.

Next, by using the optical waveguide manufacturing method of this embodiment, a ring laser integrated with a multiplexing / demultiplexing circuit using a Mach-Zehnder interferometer was manufactured.

FIG. 4 shows a schematic circuit configuration. In FIG. 4, reference numeral 11 is an excitation light input optical waveguide, 12c is a Mach-Zehnder interferometer, 16 is an oscillation light output optical waveguide, and 17 is a ring optical waveguide. The present ring laser was constructed by using an optical waveguide obtained by the above-mentioned method, in which Er was added to the center of the core.

To operate this ring laser, first,
Excitation light having a wavelength of 1.47 μm is incident on the excitation light input waveguide 11 using a single mode optical fiber. The pumping light is incident on the ring waveguide by the Mach-Zehnder interferometer 12c composed of the directional coupler V and the directional coupler VI so that 99% of the light intensity propagates through the pumping light inputting optical waveguide 11. To excite Er ions. The spontaneous emission light emitted when the excited Er ions are relaxed is because the Mach-Zehnder interferometer 12c composed of the directional coupler V and the directional coupler VI has a high coupling rate of 95% in the 1.5 μm band. It is confined in the ring waveguide and leads to stimulated emission. The oscillated light circulating in the ring waveguide passes through the oscillation output waveguide 16 and is extracted by the single mode optical fiber.

When a laser oscillation experiment in the 1.5 μm band was conducted using this ring laser, the oscillation threshold was 10 m in terms of the light intensity of the excitation light at the exit end of the single mode optical fiber.
W, and the oscillation light intensity is 1 when the excitation light intensity is 50 mW.
It became clear that it was 0 mW. Oscillation threshold excitation light intensity and excitation light intensity when Er is uniformly added to the core 5
The oscillation light intensity at 0 mW is 20 mW and 5 m, respectively.
Since it is W, it was found that the gain efficiency can be improved and the laser oscillation characteristics can be improved by using the Er-center-doped optical waveguide according to the manufacturing method of the present invention.

As described above, in the method for manufacturing the optical waveguide for the optical amplifier of the present invention, Er can be added to the central portion of the core, which is effective in reducing the pumping light intensity required for optical amplification and laser oscillation. Became clear.

In the first embodiment described above, the entire optical circuit was constructed by using the Er-center-doped optical waveguide, but the present invention uses the concave process and connects different types of waveguides with a low loss of 0.1 dB or less. Since it is possible, a circuit unit that requires optical amplification is formed by the Er-centered optical waveguide of the present invention, optical amplification is unnecessary, and a multiplexing / demultiplexing circuit that needs to propagate signal light with low loss. A circuit configuration formed by an optical waveguide in which Er is not added to the circuit portion such as is useful.

[0043]

As described above, according to the method of manufacturing an optical waveguide of the present invention, an optical waveguide in which a rare earth element is added to the central portion of the core can be manufactured, and the core is essentially deformed. It is possible to produce an optical waveguide with less fluctuation. Therefore, for example, when a rare earth element is added to be used for optical amplification, the excitation light intensity of the rare earth addition portion can be increased, and an optical amplifier that operates with a smaller excitation light intensity,
A laser can be manufactured with high accuracy and reproducibility.

[Brief description of drawings]

FIG. 1 is a waveguide cross-sectional view showing a process of manufacturing an optical waveguide according to a reference example .

FIG. 2 is a cross-sectional view showing a circuit configuration of an optical amplifier in which a multiplexing / demultiplexing circuit for pumping light and signal light of a reference example is integrated.

FIG. 3 is a cross-sectional view of a waveguide showing a process for producing an optical waveguide of the present invention.

FIG. 4 is a cross-sectional view showing a circuit configuration of a ring laser in which a multiplexing / demultiplexing circuit using the Mach-Zehnder interferometer according to the embodiment of the present invention is integrated.

FIG. 5 is a diagram showing a process of manufacturing a rare earth-doped optical waveguide by a conventional concave process.

[Explanation of symbols]

1 Si substrate 2 Lower clad glass layer 3 Er-doped core glass layer 4 Er-doped core glass 5 Upper clad glass layer 6 Er-free core glass layer 7 Er-free core glass 8 Er-free core glass soot 9 Er-doped core glass soot 10 Optical waveguide for signal light input 11 Optical waveguide for pumping light input 12a, 12b, 12c Mach-Zehnder interferometer 13 Optical amplification optical waveguide 14 Optical waveguide for signal light output 15 Optical waveguide for pumping light output 16 Optical waveguide for oscillation light output 17 Ring optical waveguide I, II, III, IV, V, VI directional coupler

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Manabu Oguma 1-1-6 Uchisaiwaicho, Chiyoda-ku, Tokyo Inside Nippon Telegraph and Telephone Corporation (56) Reference JP-A-6-331844 (JP, A) JP-A 7-20337 (JP, A) JP 61-83506 (JP, A) JP 4-359230 (JP, A) JP 6-250036 (JP, A) JP 4-60618 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) G02B 6/13 G02B 6/00 G02F 1/35 501

Claims (4)

(57) [Claims] 1. A method of manufacturing an optical waveguide comprising a core formed on a flat substrate formed by sandwiching an active layer and a clad layer with a pair of light reflecting mirrors, and a clad surrounding the core and having a refractive index lower than that of the core. In the step of forming a lower clad layer on a flat substrate, a first groove forming step of forming a first groove in the lower clad layer, and a first clad layer having a refractive index higher than that of the lower clad layer. Core layer, core layer raw material, second core layer raw material having the same refractive index as the first core layer and having an optically active substance added, and the first core layer raw material are laminated in this order on the lower clad layer. a raw material lamination step, a core layer sintering step of the previous SL first core layer material and first core layer by sintering the second core layer material and the second core layer, said first core Layer and the first groove portion of the second core layer A core unit forming step of removing the outer, the lower cladding layer and said first core portion and the second
A step of forming an upper clad layer having a lower refractive index than that of the first core part on the core part of the first core part, and adding an optically active substance only to the core center part.
A method for manufacturing the added optical waveguide. 2. The method of manufacturing an optical waveguide according to claim 1, wherein the core layer raw material laminating step is a flame deposition method. 3. The method of manufacturing an optical waveguide according to claim 1, wherein the first groove forming step includes a photo step and an etching step. 4. The method of manufacturing an optical waveguide according to claim 1, wherein the optically active substance is a rare earth element.