JP2788538B2 - Optical amplifier - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to 1.3 μm and 1.5 μm which are important in the optical communication field.
The present invention relates to the structure of an optical amplifier that amplifies signal light in the μm band, and is used, for example, in an optical amplifier applied to an optical communication system using an optical fiber transmission line.

<Prior art> Recently, a 1.5 μm band optical amplification characteristic of an Er clad doped tapered optical fiber having a structure in which Er is doped into a clad portion, melt-drawn and has a tapered shape has been reported (Izumita). History, Izumi Mikawa, Proceedings of the 1990 IEICE Spring Conference, C-345).

FIG. 5 shows the structure and concept of this optical amplifier. As shown in the figure, the core diameter of the Er clad portion-doped optical fiber 15 is reduced by melting and drawing, and a tapered portion 16 and a small-diameter portion 17 that are smoothly connected by a taper shape are provided. As shown in the distribution 18, the density of the signal light and the excitation light is increased in the clad portion of the small-diameter portion 17, and optical amplification is performed by stimulated emission of Er from the clad portion.

The principle of amplification of this signal light is the same as that of the Er-doped optical fiber type optical amplifier. This is to amplify the signal light at the time.
Further, the signal light 21 and the pump light 22 are multiplexed by the interference film filter 19 and are incident on the Er-clad doped optical fiber using the lens 20.

The optical amplifier using such an optical fiber has an optical amplifier using an Er-clad doped optical fiber by providing a tapered portion, and at the same time, has the same core shape as the core diameter and refractive index distribution of the transmission optical fiber, An optical fiber having a refractive index distribution can be formed, and there is an advantage that a transmission optical fiber can be connected with low loss.

<Problems to be Solved by the Invention> However, in an optical amplifier obtained by melting and drawing an optical fiber in which Er is added to the cladding, Er cannot be added only to the tapered portion and the small-diameter portion. In the portion having the above, there is a problem that Er in the clad portion cannot form a population inversion, and the added Er reduces the amplification degree due to absorption loss.

In addition, the mechanical strength at the core small-diameter portion is low, monitoring is required when producing the tapered portion and the core small-diameter portion, and the yield is low. However, there are problems such as difficulty in downsizing due to the use of the above optical components, and the fact that the optical axis is likely to shift due to the effects of impact and temperature change.

The present invention has been made in view of these problems, and has as its object to provide an optical amplifier that can be integrated and reduced in size.

<Means for Solving the Problems> In order to achieve the above object, a configuration of an optical amplifier according to the present invention has a structure in which a clad portion formed on a planar substrate and having a refractive index higher than that of the core portion around the core portion. A glass optical waveguide having a low structure, wherein a light guiding portion having a tapered waveguide structure in which the waveguide width of the glass optical waveguide is slightly short, and a narrow guiding width in which the waveguide width of the optical waveguide connected to the light guiding portion is narrow. An optical amplification unit having a waveguide structure, and a waveguide pattern in which a light extraction unit having a tapered waveguide structure in which a waveguide width of an optical waveguide connected to the optical amplification unit is tentatively connected in a tapered shape sequentially,
Further, the optical amplifier has a glass optical waveguide structure in which a rare earth element is added to at least a part of a clad surrounding the core of the narrow waveguide.

<Operation> According to the optical amplifier having the above configuration, for example, the rare earth element can be added only to the clad portion of the optical amplifier.
It is possible to reduce the absorption loss due to Er in the light introduction part and the light extraction part, and to obtain a high gain as an optical amplifier. In addition, by forming an optical amplifier, which was conventionally configured using a tapered optical fiber, on a flat substrate,
The mechanical strength can be increased and handling becomes easier.

Further, since an optical amplifier can be manufactured by a method substantially similar to that of the LSI process, it is possible to mass-produce optical amplifiers having the same characteristics. In addition, the size can be reduced by integration, and the constituent material quartz has heat resistance,
It has excellent corrosion resistance and can realize stable operation as an optical amplifier.

<Embodiment> A preferred embodiment of the present invention will be described below with reference to the drawings.

Embodiment 1 FIG. 1 shows a waveguide configuration in this embodiment, and FIG. 2 shows a cross-sectional structure of the waveguide.

First, as shown in FIG. 1, a waveguide has a lower cladding having a thickness of 30 μm on a Si substrate 1 and a waveguide width of 8 μm on the lower cladding.
optical waveguides 3 and 3a having a width of 2 μm, a narrow optical waveguide 5 which is an optical amplifier having a waveguide width of 2 μm and a waveguide length of 20 mm, and optical waveguides 3 and 3a.
Waveguide length 10mm connecting the optical waveguide and the narrow optical waveguide 5
A light introducing portion 4 having a tapered waveguide structure with a small waveguide width and light extraction portions 4 and 4a with a tapered waveguide structure with a large waveguide width are formed to constitute a glass optical waveguide. ing.

To form this waveguide type optical amplifier, first, the Si substrate 1
Then, a glass film for a core layer having a thickness of 8 μm and a relative refractive index difference 0.4 of 0.4 is prepared by a fire deposition method. Next, this glass film is
The narrow optical waveguide 5 having the structure shown in FIG. 1 is manufactured by etching using a photolithography process substantially similar to the I process. Next, an Er-doped clad portion 5a containing, for example, an Er concentration of 5000 ppm as a rare earth element is formed around the narrow optical waveguide portion 5.

Next, on the lower clad 6 formed on the Si substrate 1a, only the upper clad 7 surrounding the narrow optical waveguide core 8 is doped with Er, as shown in FIG. As shown in FIG. 1, the signal light and the pumping light pass through the optical waveguide 3 having a normal waveguide width to which Er is not added, and propagate to the narrow optical waveguide 5 via the light introducing portion 4 having a tapered portion. . Here, the signal light and the pumping light seep from the side wall of the core to the upper clad portion 7 doped with Er, and the signal light intensity is amplified by the population inversion and stimulated emission of Er. The amplified light propagates through the light extraction portion 4a of the tapered portion again to the optical waveguide 3a to which the normal waveguide width Er is not added.

In the optical amplifier of FIG. 1, a signal light λ ₁ having a wavelength of 1.535 μm and a wavelength 1.4 having a light intensity of 25 mW are used by using an optical fiber 2.
A 7 μm pump light λ ₂ is incident on each, and the signal light is
When the signal light intensity was measured at a, the signal light intensity could be amplified by 3.0 dB compared to the signal light intensity of the optical fiber 2.

Embodiment 2 In this embodiment, an optical amplifier using a rare-earth clad-doped narrow optical waveguide similar to that of Embodiment 1 is used. However, Nd, which is the same rare earth element, was added instead of Er. The principle of signal light amplification is the same as that of an optical amplifier using an Er clad doped narrow optical waveguide.Nd energy is inverted and distributed by excitation light with a wavelength of 0.80 μm, which is the absorption band of Nd, and stimulated emission is 1.3 μm. It amplifies the signal light in the band.

The structure of this optical amplifier is the same as that of the optical amplifier of the first embodiment shown in FIG.
The excitation light was incident at an intensity of 25 mW, and the signal light intensity at a wavelength of 1.36 μm was measured. As a result, the signal light intensity could be amplified by 2.0 dB.

Embodiment 3 In this embodiment, an optical circuit for multiplexing / demultiplexing signal light and pump light was formed on the same substrate using the optical amplifier of Embodiment 1. This structure is shown in FIG. This optical amplifier has a wavelength of 1.
Optical amplifier with 47μm pumping light source semiconductor LD9, transmission car single mode optical fiber 2b, multiplexing part 10 consisting of directional coupler for multiplexing pumping light and signal light, Er clad doped narrow optical waveguide 11 And a photodetector 12 using a directional coupler for demultiplexing the signal light and the pump light. Er is added only to the clad portion of the waveguide 11 surrounded by the frame in this figure. The operation as an optical amplifier of this optical circuit is performed by the pump light λ of 1.47 μm output from the semiconductor LD9.
The signal light λ ₁ having a wavelength of 1.535 μm propagated through the optical fiber ₂ and the optical fiber ₂ b is incident on the ports A and B of the directional coupler 10. Since the coupling efficiency of the pump light and the signal light in the directional coupler is 100% and 0%, the pump light and the signal light propagate to the port C. Therefore, the excitation light and the signal light propagating history of Er cladding addition narrow optical waveguide 11 after the port C, the signal light lambda ₁ is amplified. The structure of the optical amplifier here is the same as the structure of the optical amplifier shown in Embodiment 1. The optical amplifier has a waveguide width of 2 μm and a waveguide length of 20 mm, and the waveguide length connecting the optical waveguide and the optical amplifier. It is composed of a light introducing section and a light extracting section having a 10 mm taper structure. Further, the excitation light lambda ₂ and the signal light lambda ₁ by the same principle as the case of the directional coupler 10 by the directional coupler 10a is demultiplexed, only the signal light lambda ₁ is
Measured by 12 photodetectors.

By configuring an optical circuit for multiplexing / demultiplexing the signal light λ ₁ and the pump light λ ₂ on the same substrate, the overall size could be reduced to 30 mm × 60 mm.

Further, by using the optical amplifier of FIG. 3, it was measured signal light intensity of the wavelength 1.535Myuemu, the signal light lambda ₁ by operating the semiconductor laser at 25mW can be 2.8dB amplification applications as a compact optical amplifier span It was confirmed that it was wide.

Embodiment 4 In this embodiment, an optical amplifier using a configuration similar to that of Embodiment 3 is described. However, Nd, which is the same rare earth element, was added instead of Er. The configuration is shown in FIG. This optical amplifier has a semiconductor LD13 for a pumping light source having a wavelength of 0.80 μm, a single-mode optical fiber for transmission 2c, a multiplexing section 10b composed of a directional coupler for multiplexing the pumping light and the signal light, a Nd-clad doped narrow optical waveguide. It comprises an optical amplifier by a wave path 14, a demultiplexer 10c using a directional coupler for demultiplexing signal light and pump light, and a photodetector 12a.

The operation as an optical amplifier of this optical circuit is the same as that of the third embodiment. The 0.80 μm pump light output from the semiconductor LD 13 and the 1.36 μm wavelength signal light propagating through the optical fiber 2c are respectively coupled to the directional coupler 10b. , And the two lights are multiplexed and propagate to port C. The pump light and the signal light propagate through the Nd-clad doped narrow optical waveguide 14 after the port C, and the signal light is amplified. The structure of the optical amplifier here is the same as that of the optical amplifier shown in the first embodiment. The optical amplifier has a waveguide width of 2 μm and a waveguide length of 20 mm, and a waveguide length of 10 mm connecting the optical waveguide and the optical amplifier. And a light extraction section having a tapered structure. Further, the excitation light and the signal light are demultiplexed by the directional coupler 10c, and only the signal light is measured by the photodetector 12a.

Using the optical amplifier shown in FIG. 4, the signal light intensity at a wavelength of 1.36 μm could be amplified by 1.8 dB by the operation of the semiconductor laser at 25 mW.

In the first to fourth embodiments, the rare earth element is added only to the upper clad 7, but it is also possible to add the rare earth element to the lower clad 6.

<Effects of the Invention> As described above, since the optical amplifier of the present invention is configured by an integrated optical circuit using a glass optical waveguide on one substrate, a narrow waveguide is used. Since Er can be added only to the optical amplifying section, there is no absorption loss due to Er outside the amplifying section, and a high gain can be obtained.

The mechanical strength of the tapered portion can be increased as compared with the case where an optical fiber is used, handling is easy, and there is no deterioration in amplification characteristics due to impact, temperature change, and the like.

In the fabrication, patterning technology in the LSI process can be applied, and amplifiers having the same characteristics can be mass-produced with a higher yield than in the case where an optical fiber is used.

Since no lens or mirror is used, the amplification characteristics are not degraded by a lens on the optical axis and the size of the optical amplifier can be reduced.

Quartz glass is excellent in heat resistance and corrosion resistance, and can realize an optical amplifier excellent in long-term stability that is not affected by the external environment.

It has such advantages.

[Brief description of the drawings]

1 and 2 are diagrams showing a configuration of an optical amplifier according to a first embodiment of the present invention, FIG. 3 is a diagram showing a configuration of an optical amplifier according to a third embodiment of the present invention, and FIG. FIG. 5 is a diagram showing a configuration of an optical amplifier of Example 4, and FIG. 5 is a diagram showing a structure of a melt-stretched Er clad doped optical fiber and a concept of optical amplification. In the drawing, 1,1a, 1b, 1c is a Si substrate, 2,2a is an optical fiber, 3,3a is an optical waveguide, 4,4a is a tapered optical waveguide, 5 is a narrow optical waveguide, 6 is a lower clad, 7 is an upper clad, 8 is a narrow optical waveguide core, 9 is a semiconductor laser (wavelength 1.47 μm), 10, 10a, 10b, and 10c are directional couplers, 11 is an Er clad doped narrow optical waveguide, and 12 and 12a are light. Detector, 13 is a semiconductor laser (wavelength 0.80 μm), 14 is an Nd-clad doped narrow optical waveguide, 15 is an Er-clad doped optical fiber, 16 is a tapered section, 17 is a small diameter section, 18 is an intensity distribution of propagating light, 19 is an interference film filter, 20 is a lens, 21 is signal light, and 22 is excitation light.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) G02F 1/35 501 H01S 3 / 04,3 / 10

Claims (2)

(57) [Claims] 1. A glass optical waveguide formed on a planar substrate and having a structure in which a cladding part around a core part has a lower refractive index than that of the core part. The light guiding portion having a small tapered waveguide structure, the light amplifying portion having a narrow waveguide structure having a narrow waveguide width leading to the light guiding portion, and the waveguide width of an optical waveguide leading to the eye light amplifying portion being small. It has a waveguide pattern in which the light extraction portion of the tapered waveguide structure is temporarily connected smoothly in a tapered shape, and at least a part of the cladding portion surrounding the core portion of the narrow waveguide of the optical amplification portion. An optical amplifier having a glass optical waveguide structure doped with a rare earth element. 2. An optical amplifier according to claim 1, further comprising an optical circuit for multiplexing or demultiplexing the signal light and the pump light passing through the waveguide.