JP2003149481A - Optical amplifier-integrated waveguide - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical amplifier-integrated optical waveguide of a small size with no insertion loss. SOLUTION: The waveguide comprises a glass substrate 4 doped with rare earth elements (rare earth ions) and having a step, an amplifying core 3 acting as a waveguide type amplifying part formed by partially increasing the refractive index in the upper part of the step of the glass substrate 4, and a core 1 for signal light acting as the waveguide for the signal light and a core 2 for excitation light acting as the waveguide for excitation both formed on the lower part of the step of the glass substrate 4. The core 1 for the signal light and the core 2 for the excitation light are obtained by forming a film of a quartz-based material having low propagation loss and then patterning the film. The amplifying core 3 is formed by partially increasing the refractive index of the glass substrate 4 doped with rare earth elements along the waveguide pattern.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical amplifier integrated waveguide using a rare earth-doped substrate.

[0002]

2. Description of the ^Related Art Er ³⁺ , Nd ³⁺ , Tm ³⁺ , Yb ³⁺ , Ho
An optical amplifier that amplifies the separately input signal light by doping a base material such as quartz or Si with a rare earth element such as ³⁺ or Pr ³⁺ and irradiating it with excitation light is used for long-distance optical communication. Indispensable for transmission. In particular, the erbium-doped fiber amplifier (EDF) that applies this to the fiber
A) is widely used for submarine cables and the like. If this is applied to an optical waveguide, a smaller and highly functional device can be realized by integrating a modulator, a switch, and a demultiplexer on the same substrate.

An optical amplifier in which a pump light waveguide and a signal light waveguide are integrated is described in "JL Philipsn" et al.
July 000 Optical Amplifire And There Applications International Conference Proceedings "Papers Ot
uD2-1, pages 151-153 (Optical Am
pliers and the Tir Applic
ations '00 Proceedins Otu
D2-1, p. p. 151-153) ”. In this example, an optical waveguide is formed on an Er-doped substrate by ion exchange to form an amplification section, and a signal / excitation waveguide portion is also formed on a glass substrate by ion exchange.
These are joined with an ultraviolet curable resin to obtain a net gain of 3 dB / cm.

However, in this technique, the coupling loss is unavoidable because the amplification section and the ordinary waveguide section are joined together at the time of integration. On the other hand, an example of forming a waveguide type optical amplifier by plasma CVD is 1
September 993 European Conference International Conference on Optical Communication Proceedings, Paper M
oP 2.3, pp. 53-56 (European Con
ference on Optical Commun
ication '93 Proceedings, Vo
l. 2, Paper MoP 2.3, p. p. 53-5
6).

In this technique (film forming method), an Er chelate is added to a raw material gas of an ordinary quartz optical waveguide to form an amplifier. Therefore, the waveguide and the amplifying section are usually formed by processing the film formed by changing the raw material gas, and the coupling loss hardly occurs. However, with this technique, the net gain is as low as 0.3 dB / cm, and sufficient performance as an amplification section cannot be expected unless a long waveguide is formed. S. Musa et al. Reported a waveguide-type optical amplifier using an Er-doped Al ₂ O ₃ thin film formed by sputtering (2000 IEEE JOURNAL OF QUA).
ANTUM ELECTRONICS Vol. 36,
No. 9 p. p. 1089-1097) reported a maximum of 1.0 dB / cm as a thin film waveguide,
This is also 1/3 as low as the ion exchange method, and the lengthening of the waveguide is inevitable.

[0006]

As described above,
First, in the conventional ion exchange method, there is a problem that the formed optical amplifier usually has a large coupling loss with the waveguide even though a high gain is obtained. In addition, in the film formation method,
Although the formed optical amplifier usually has a low loss as a waveguide, it cannot obtain a sufficient gain as an optical amplifier, and thus there is a problem that it is difficult to integrate the optical amplifier and the optical waveguide on one platform. It was The present invention has been made to solve the above problems, and an object of the present invention is to provide an optical amplifier integrated optical waveguide that is small in size and has no insertion loss.

[0007]

According to one embodiment of the present invention, there is provided an optical amplifier integrated waveguide comprising: a glass substrate having a step lower portion and a step upper portion formed therein, to which a rare earth element is added; A signal light core that forms a signal light waveguide having one end formed toward the step between the lower part of the step and the upper part of the step, and the core of the signal light that is disposed in the upper part of the step and on the extension line of the signal light core. An amplifying section core having a higher refractive index than the surroundings by diffusing the additive is provided, and the signal light core and the amplifying section core are arranged so that end faces of one ends thereof face each other. In this optical amplifier integrated waveguide, the signal light guided through the signal light waveguide by the signal light core and introduced into the waveguide type amplification unit by the amplification unit core is incident on the waveguide type amplification unit. It is amplified by the excitation light.

In the above optical amplifier integrated waveguide, the rare earth element added to the glass substrate may be Er, Yb, or a combination thereof. In the above optical amplifier integrated waveguide, crystallized glass may be used for the glass substrate. In the above optical amplifier integrated waveguide, the surface above the step is configured to share substantially the same plane as the upper plane of the signal light core.

Further, in the above optical amplifier integrated waveguide, for the pumping light constituting the pumping waveguide which is directionally coupled to the signal light waveguide having the signal light core at one end on the lower portion of the step of the glass substrate. By providing the core, the pumping light may be introduced into the waveguide type amplifying section by the amplifying section core.

In the above optical amplifier integrated waveguide, the signal light core is a film formed by, for example, any one of a chemical vapor deposition method, a sputtering method, an evaporation method, a flame deposition method and a coating method. Can be formed by processing. In the above optical amplifier integrated waveguide, the amplification section core may be formed by diffusing titanium from the upper surface of the step upper portion of the glass substrate, or may be formed by an ion exchange method.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a perspective view schematically showing a configuration example of an optical amplifier integrated waveguide according to an embodiment of the present invention. This optical amplifier integrated optical waveguide has a stepped glass substrate 4 doped with rare earths (rare earth ions), and a waveguide type amplifier formed by increasing the refractive index of a part of the upper part of the step of the glass substrate 4. And the amplification unit core 3
The glass substrate 4 includes a signal light core 1 serving as a signal light waveguide and a pumping light core 2 serving as a pumping waveguide, which are formed below the step. The signal light core 1 and the excitation light core 2 are made of a silica-based material having a small propagation loss, and can be formed by forming a film of this material and then patterning.

The amplifying section core 3 is formed by increasing the refractive index of a part of the glass substrate 4 doped with rare earth into a waveguide shape. The input signal light emitted from the input signal light source 5 and the excitation light emitted from the excitation light source 6,
They are introduced into a signal light waveguide composed of a signal light core 1 and a pumping waveguide composed of a pumping light core 2, respectively. The introduced pumping light is a directional coupling portion in which the pumping light core 2 is coupled to the signal light core 1, and after being coupled to the input signal light, is guided to the waveguide type amplification section including the amplification section core 3. To do. The signal light guided to the waveguide type amplifying section is amplified by the excitation light that is coupled to the rare earth element of the glass substrate 4 doped with the rare earth element, and is thus amplified.

When light in the 1.55 μm band is used as an input signal, Er is used as a rare earth element to be doped in the glass substrate 4.
And the light of 0.98 μm band is used as the excitation light, it is possible to realize optical amplification. When 1.0 μm band light is used as the input signal, Nd and Er (ions) are used as the rare earth element doped in the glass substrate 4, and 0.8 nm band light is used as the excitation light to perform optical amplification. The action can be obtained.

Here, the addition of rare earth elements will be described. The glass to which the rare earth is added to a certain concentration receives light having an energy higher than the ground level of the rare earth and forms a population inversion inside, which causes optical amplification by stimulated emission. In the case of a glass using erbium as the rare earth to be added, relaxation light in the vicinity of 1.5 μm occurs due to excitation light of 0.98 μm or 1.48 μm.
Stimulated emission occurs when receiving the signal light of optical communication in the μm band,
This signal light is amplified. When a high refractive index region with a waveguide shape is formed in such glass, signal light is confined in the high refractive region, so more efficient optical amplification is realized,
The signal light propagates through the high refraction region and is simultaneously amplified.

The high refractive index can be obtained by ion implantation or ion exchange into a desired portion of the glass substrate to which the rare earth is added. The optical amplifier formed in this way is
Although it is indispensable for appropriately supplementing the attenuated power, noise is generated at the same time as the gain, so that the applicable area within the transmission distance must be limited to the necessary minimum. Therefore, it is desirable that the waveguides other than the amplifying section are made of a silica-based material having a small propagation loss. A material doped with a rare earth element cannot avoid an increase in propagation loss. Therefore, if the high refractive index portion formed on such a substrate is used as an ordinary waveguide, the magnitude of the propagation loss becomes a problem.

For example, in a device in which an optical amplifier and a waveguide are integrated on the same substrate by a method of partially increasing the refractive index of the substrate, it is difficult to obtain sufficient performance in terms of loss. If the waveguide part is made of silica glass that is not doped with rare earths, and the amplification part and the end face are bonded together,
Although the propagation loss in the waveguide portion can be reduced, it is not a fundamental improvement because coupling loss occurs.

In view of the above, chemical vapor deposition (CV)
A high-purity quartz film can be formed by using a film forming method such as the D) method, the flame deposition (FHD) method, the sputtering method, or the vapor deposition method. According to such a method, it is possible to add impurities such as boron and phosphorus to a predetermined concentration in the formed quartz film with good controllability, so that it is easy to provide a refractive index difference between the core and the clad. Therefore, it becomes possible to form an optical waveguide having extremely low propagation loss.

In the film forming method as described above, it is possible to form the optical amplifying portion by adding a rare earth element to the raw material gas, the sputtering target and the vapor deposition source, and two kinds of materials with different additives are used. The waveguide and the amplification section can be integrated by coupling the waveguide according to (1) on the surface of the substrate. However, if the rare earth is added at a certain concentration or more, deterioration such as precipitation occurs in any of the film forming methods. Therefore, the amount of the rare earth added is about 1%. At such a concentration, a sufficient gain cannot be obtained, so that the amplification optical waveguide has to be made long, and it is unavoidable that the amplification optical waveguide becomes large and complicated.

On the other hand, by forming an amplifying portion on a glass substrate doped with rare earth at a high concentration by increasing the refractive index such as ion exchange or ion implantation, and forming the waveguide portion by the above-described film forming method, An optical amplifier having high gain and a waveguide having low propagation loss can be integrated on one substrate on one substrate. By the way, in order to prevent signals from leaking at the boundary between the amplification section and the waveguide section, it is necessary to make the center point of the core formed by film formation coincide with the center point in the depth direction of the amplification section. This is achieved by previously digging the substrate in the waveguide formation region by the required amount. The amount of digging into the board is the height of the core,
This amount corresponds to the height from the bottom of the lower clad to the upper part of the core when the lower clad is used, and the height of the core alone when the lower clad is not used.

Next, a method of manufacturing the waveguide type optical amplifier of FIG. 1 will be described. 2 (a), (b), (c) and FIGS. 3 (a), (b), (c), (d), (e) schematically illustrate a part of the manufacturing process example in the present embodiment. It is a perspective view which shows typically. First, as shown in FIG.
A glass substrate 4 made of crystallized glass doped with ˜4 wt% is prepared, and as shown in FIG. 2B, the surface of the glass substrate 4 is partially etched to form a step.

Next, as shown in FIG. 2 (c), a phosphoborosilicate glass (BPSG) is deposited on the glass substrate 4 having the step formed by the CVD method, and the lower clad layer 1 is formed.
4 is formed. Subsequently, as shown in FIG.
Phosphogermanium glass (GPSG) is deposited on the lower cladding layer 14 by the CVD method to form the core layer 15. At this time, the refractive index of the lower clad layer 14 is
The concentration of added boron, phosphorus, and germanium is adjusted so that it becomes smaller than the refractive index of.

Deposited lower clad layer 14 and core layer 1
After an annealing treatment of 800 to 900 ° C. for 5 and
As shown in FIG. 3B, these are patterned by a known photolithography technique and etching technique (RIE). At this time, the core layer 15 is patterned so that the signal core 1 and the excitation core 2 form a directional coupler.

Next, after a Ti film is formed on the entire surface by a sputtering method, the titanium film is patterned by a well-known photolithography technique and etching technique.
As shown in (c), the titanium pattern 16 is formed on the step of the glass substrate 4. The titanium pattern 16 is arranged on an extension of the signal light core 1. Next, these are heated to 800 to 900 ° C. for several hours to diffuse titanium from the titanium pattern 16 to above the step of the glass substrate 4, and then the titanium pattern 16 is removed. As a result, FIG.
As shown in (d), the amplification section core 3 having a high refractive index due to the diffusion of titanium is formed on the step portion of the glass substrate 4.

The above-mentioned diffusion depth of titanium is determined by the diffusion time and temperature. As an example, in the case of forming a waveguide type amplifying portion having a height of 5.5 μm, the diffusion time at 800 ° C. is required for 5 to 6 hours. The refractive index can be increased to the depth of. Finally, as shown in FIG. 3E, a phosphoborosilicate glass (BPSG) is deposited so as to cover the signal light core 1 and the excitation light core 2, and the upper clad layer 17 is formed to complete the process. . At this time, the concentrations of boron, phosphorus and germanium are adjusted so that the refractive index of the upper cladding layer 17 becomes lower than the refractive index of the core of each waveguide.

In the above description, the respective layers are deposited and formed by the CVD method, but the present invention is not limited to this, and a sputtering method or a flame deposition method may be used, or a liquid material may be applied to form the layers. Good. Further, in the above description, GPSG is used as the core and BPSG is used as the clad, but the present invention is not limited to this combination, and the same applies when SiON is used as the core and SiO ₂ is used as the clad.

In the above-described embodiment, the lower clad layer is formed. However, when the glass substrate 4 has a lower refractive index than the core material and light can be confined, it is not always necessary to use the lower clad. Absent. Further, although the upper clad layer 17 is formed in the above description, the upper clad layer 17 is not necessarily required if the specifications allow multimode propagation. Further, in the above-described embodiment, since the high temperature annealing at 800 ° C. or higher and the Ti diffusion are required, the crystallized glass having high temperature resistance is used, but the crystallized glass is not necessarily used.

For example, photo-CVD which does not require high temperature treatment.
When using the method, soda glass doped with rare earth can be used. In this case, when forming the waveguide type optical amplifying section 3, only the desired shape is used as an opening and the other portions are covered with a SiO ₂ thin film or the like, and the solution is soaked in a potassium solution such as KOH to dissolve sodium in soda glass. By substituting potassium for potassium, it is possible to obtain a high-refractive-index portion that will become the amplification portion core 3. Further, in the above-described embodiment, Er is used as the rare earth element to be doped into the glass substrate 4, but it is not necessarily Er and Yb, Nb.
Alternatively, a combination of these may be used.

Further, in the above-mentioned embodiment, the pumping waveguide is used as an example of the optical amplifier integrated type waveguide, but it is not always necessary to make the waveguide shape. For example, FIG.
As shown in, the signal light guided through the waveguide amplifier may be amplified by irradiating the pumping light from the upper portion of the waveguide amplifier including the amplification unit core 3. Also, FIG.
As shown in (b), the input signal light emitted from the input signal light source 5 and the excitation light emitted from the excitation light source 6 are combined using the 3 dB coupler 31, and the combined input signal is You may make it introduce.

Here, the amplification gain of the optical amplifier integrated optical waveguide in the present embodiment shown in FIG. 1 is 3 dB / c.
m, and the propagation loss of the waveguide was 0.1 dB / cm. An optical waveguide integrated with an arrayed waveguide grating (AW) is applied by applying this optical amplifier integrated optical waveguide.
FIG. 4 shows an example in which a waveguide type amplifier is arranged for each channel as G). In this configuration, the length of the AWG is 5 cm, and the length of the waveguide type amplifier is 2 cm.
A gain that cancels the insertion loss of G can be obtained, and an optical amplifier integrated AWG without insertion loss can be obtained.
As described above, according to the present embodiment, it is possible to obtain a compact optical amplifier integrated optical path with no insertion loss.

[0030]

As described above, according to the present invention,
The excellent effect that an optical amplifier integrated type optical waveguide having a small size and no insertion loss can be provided is obtained.

[Brief description of drawings]

FIG. 1 is a perspective view showing a configuration example of an optical amplifier integrated waveguide according to an embodiment of the present invention.

FIG. 2 is a perspective view schematically showing a part of the manufacturing process example in the present embodiment.

FIG. 3 is a perspective view schematically showing a part of the manufacturing process example in the present embodiment, following FIG. 2;

FIG. 4 is a perspective view showing a configuration example of an optical amplifier integrated waveguide according to another embodiment of the present invention.

FIG. 5 is a perspective view showing a configuration example of an optical amplifier integrated waveguide according to another embodiment of the present invention.

[Explanation of symbols]

1 ... Signal light core, 2 ... Excitation light core, 3 ... Amplifier core, 4 ... Glass substrate, 5 ... Input signal light source, 6 ... Excitation light source.

Claims (10)

[Claims] 1. A glass substrate having a step lower portion and a step upper portion formed therein and a rare earth element added thereto, and one end formed on the step lower portion of the glass substrate toward a step portion between the step lower portion and the step upper portion. And a signal light core forming a signal light waveguide, which is arranged on an extension of the signal light core in the upper part of the step and has a higher refractive index than the surroundings by diffusing the additive from the upper part of the step. An optical amplifier integrated waveguide, comprising: an amplified amplification unit core, wherein the signal light core and the amplification unit core are arranged such that end surfaces of one ends thereof face each other. 2. The optical amplifier integrated waveguide according to claim 1, wherein the rare earth element is Er. 3. The optical amplifier integrated waveguide according to claim 1, wherein the rare earth element is Yb. 4. The optical amplifier integrated waveguide according to claim 1, wherein the rare earth elements are Er and Yb. 5. The optical amplifier integrated waveguide according to claim 1, wherein the glass substrate is made of crystallized glass. 6. The optical amplifier integrated waveguide according to claim 1, wherein the upper surface of the step shares substantially the same plane as the upper plane of the signal light core. Integrated waveguide. 7. The optical amplifier integrated waveguide according to claim 1, wherein one end of the excitation waveguide is directionally coupled to the signal light waveguide having the signal light core on the lower portion of the step of the glass substrate. An optical amplifier integrated waveguide comprising a pumping light core forming a waveguide. 8. The optical amplifier integrated waveguide according to claim 1, wherein the signal light core is formed by a chemical vapor deposition method, a sputtering method,
An optical amplifier integrated waveguide characterized by processing a film formed by any one of a vapor deposition method, a flame deposition method, and a coating method. 9. The optical amplifier integrated waveguide according to claim 1, wherein the amplifier core is formed by diffusing titanium from an upper surface of a step upper portion of the glass substrate. Amplifier integrated waveguide. 10. The optical amplifier integrated waveguide according to claim 1, wherein the amplifier core is formed by an ion exchange method.