JP2003149488A - Fiber-type optical component, optical module using the same, optical fiber amplifier, and ASE light source - Google Patents

Abstract

(57) [Problem] To provide a low-loss, easy-to-handle fiber type optical component having a function of removing unnecessary light and flattening output light. SOLUTION: A plurality of optical fibers are closely adhered in parallel, and a fusion-stretched portion is formed by locally heating and stretching to multiplex / demultiplex propagating light. Fiber-type optical components are configured as input / output fibers.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to optical communication,
The present invention relates to a fiber type optical component that removes and takes out a part of signal light.

[0002]

2. Description of the Related Art In optical fiber amplifiers and ASE light sources, when the wavelength of the pumping light source and the wavelength of the signal light are close to each other, for example, in the amplifier using an erbium-doped fiber amplified by a semiconductor laser pumping 1.48 μm, the signal light, AS
When a part of the E light returns into the semiconductor laser that emits the excitation light,
Interference and resonance occur inside the semiconductor laser, causing noise, which deteriorates the S / N of the signal light.

Therefore, an optical isolator is installed in front of the pumping semiconductor laser to remove the returning light. Usually, this type of optical isolator is configured by installing polarizers on both sides of a Faraday rotator, the transmission polarization directions of which are rotated by 45 °.

However, although this type of optical isolator removes the return light in the vicinity of the wavelength of the semiconductor laser of the light source, it has a wide band wavelength because the isolation is lowered for wide band light of different wavelengths. It cannot be removed sufficiently for the returning light. In order to remove such unnecessary light, it is necessary to install an in-line type optical isolator having a wider band characteristic in front of the semiconductor laser.

Further, in the optical isolator having such a spatial optical system, when light passes through the inside of the element, reflection occurs at the end face of the element. When it returns to the semiconductor laser, it causes unstable operation. Also, when the wavelength spectrum of the output light of the semiconductor laser for excitation is wide, the light of the spectrum component outside the absorption region of the rare earth-doped fiber is also emitted, so the spectrum component of the light outside the absorption region becomes return light and returns to the semiconductor laser. , Makes the oscillation unstable and becomes noise.
Therefore, there is a need for a means for easily removing unnecessary light that causes such a phenomenon.

The present applicant has already devised a fiber type optical isolator in order to solve such a problem (utility model registration No. 2585272). According to it, a fiber with the two protective coatings peeled off is heated, fused, and stretched to form a tapered Y-branch. One of the other ends of the fiber is used as an open end, and the other end of the fiber is used as an open end. We proposed a structure that eliminates. With this structure, a coupling portion having characteristics such as branching or demultiplexing is formed, and it is possible to sufficiently remove unnecessary light such as return light having a wavelength different from that of the light source.

[0007]

However, in this fiber type optical filter, the input / output terminals of the optical fiber are two on each side,
The other one is a 2 × 1 type fiber type optical component, and it is necessary to predetermine the mounting direction when fixedly mounting, and bidirectional arbitrary usage cannot be performed. There is also a problem with the integrated mounting method.

[0008]

According to the present invention, in order to solve the above-mentioned problems, a plurality of optical fibers consisting of a core and a clad are installed in parallel and partially heated and stretched to form a fusion stretched portion. Thus, the distributed coupling portion is formed, one of the plurality of optical fibers at both ends is used as an input / output fiber, and the unnecessary light output port portion of the optical fiber is incorporated as a radiation end.

The formed coupling portion length has wavelength dependence, and by adjusting the coupling portion length (stretching length), arbitrary multiplexing / demultiplexing characteristics can be realized. The relationship between the strength P2 of the output port due to the coupling due to such propagation is approximated by the following equation.

P2 (L) = (e1−e2) cos ² (kL) e1: strength when the joint length is L k: coupling coefficient
L: length of coupling part e2: strength of opposite end at coupling part length L This relationship is shown in FIG. 3 and is a function of the square of the sine wave with respect to wavelength. The coupling coefficient k is a unique coefficient determined by the core diameter of the coupling portion of the two fibers, the refractive index, and the wavelength of the propagating light.

By adopting such a configuration, the input / output port can be provided on either side of the fiber type optical component, and the structure can be easily handled. Further, when there are a plurality of coupling portions, a plurality of them may be mounted on a single board, and they may be integrated into a single component. Further, a plurality of coupling portions may be fixed on different substrates and separately mounted for use.

[0012]

FIG. 1 is an external view of a fiber type optical component according to the present invention, in which an input / output fiber 1 is projected from both ends of a mounting case 5. In this case, the input / output ports P1 and P
Either side of 2 may be used. For example, when light of wavelength λ1 and wavelength λ2 is input from port P1, it acts so that only wavelength λ1 is output from port P2, and conversely, port P1 is output.
Even if light is incident from 2 in the same manner, the same operation as described above is performed.

FIG. 2 is a view showing the internal structure of a fiber type optical component according to the present invention. This fiber-type optical component can be obtained by installing a plurality of optical fibers 1 and 7 from which the protective coating has been peeled off in parallel, and locally heating and stretching the fibers to form the fusion-stretched portion 6. The fusion-bonded extending portions 6 serving as the connecting portions are fixed to the mounting substrate 2 at both ends with fixing members 4 such as an adhesive. The fusion-bonding extension portion 6 is adjusted and formed in the coupling portion length so as to demultiplex the wavelength of λ1 and the wavelength of λ2, whereby the above-described operation can be performed.

Therefore, by adjusting the conditions for the fusion-stretching, that is, the length L of the joint, it is possible to obtain the fusion-stretching portion 6 having the characteristic of demultiplexing the desired wavelength.

There are the following two configurations. Figure 2
In (a), one optical fiber 1 is used as a through port, and both ends of the optical fiber 7 on the coupling portion side are used as radiating ends 3. The radiating end 3 is provided with a translucent adhesive in a spherical shape so that the light emitted from the fiber is radiated. Thereby, the branched light from the fiber end is radiated to the outside and does not return to the inside of the fiber due to reflection. In this embodiment, the radiation end 3 is installed on the mounting board 2, but the mounting board 2,
It may be outside the mounting case 5.

In FIG. 2B, the end faces of the two fibers arranged side by side are the radiation ends 3, and the fibers are fusion-spread. In the case of the same coupling length as in FIG. 2A, light of wavelength λ2 is emitted and only light of wavelength λ1 passes.

FIG. 2 (c) shows two fusion-bonded extending portions 6a and 6a.
b is formed in series and mounted on one mounting substrate 2, and in this case, the fusion extending portion 6 which is an optical branching portion of the wavelength λ1.
Since there are two a and 6b, for the separation of light of wavelength λ1,
It can be configured as a fiber type optical component with high isolation. Here, each fusion-stretching part 6 by fusion-stretching
When the multiplexing / demultiplexing characteristics of a and 6b are slightly shifted (Δλ),
It has the characteristics shown in. That is, when the value of Δλ is close to zero, the total characteristics of the fusion stretched portions 6a and 6b are
It functions as a high-isolation filter, and as the value of Δλ increases, it functions as a filter having a wide band characteristic, and can be adjusted as a filter having necessary characteristics by the value of Δλ.

Reference numeral 6b in FIG. 3 shows the propagation characteristics of the transmitted light through the port P2 having the configuration shown in FIG. 2 (b), in which the transmitted light level is minimum at the wavelength λ2 and maximum at the wavelength λ1. Therefore, it can be used to remove light of wavelength λ2.
In this case, the degree of separation D of the light having the wavelength λ1 is represented by the ratio of (P1 → P2) and (P1 → P3) as follows.

D = -10Log (e2 / e1) where e1: maximum level of transmitted light e2: minimum level of transmitted light Normally, there is a separation of about 20 dB per coupling part, and two points are formed in series. As a result, a degree of separation of 35 dB or more can be realized.

The fiber type optical component of the present invention may be constructed by fusion-drawing not only two fibers but also three or more fibers. Further, as the above-mentioned optical fiber, a polarization-maintaining fiber or a rare earth-doped fiber can be used in addition to a normal single mode fiber.

Further, in the example of FIG. 2, the mounting substrate 2 and the mounting case 5 are mounted, but the fusion extending portions 6a, 6 are formed.
It is also possible to mount b on a plurality of mounting boards 2 and a plurality of mounting cases 5.

FIG. 4 is a structural example of an optical amplifier using the fiber type optical component of the present invention. Here, assuming that the wavelength λ1 is the signal light and the wavelength λ2 is the pump light, both of them are WDM13.
Are combined, and pass through the rare earth-doped fiber 14 to be emitted as amplified light. By providing the fiber type optical component 10a of the present invention on the output side of the pump module 11, the fiber type optical component 10a serves as a filter that transmits the pumping light (wavelength λ2) and blocks the signal light (wavelength λ1). Operate.

In fact, in the rare-earth-doped fiber 14, when the energy level of the excited rare-earth element rises due to the excitation light and the energy level lowers in an attempt to return to a stable state, spontaneous emission light (ASE light) Are generated in both ends of the rare earth-doped fiber 14. Such spontaneous emission light
Incoherent broadband light including the band of the signal light enters the pump module 11 via the WDM 13 for combining the pumping light. Further, since the light has a wide band, it cannot be completely removed even by the optical isolator mounted on the pump module 11. In particular, in the case of a fiber type WDM that uses a fiber fusion / stretch type WDM 13, since the wavelength characteristic of the combined / demultiplexed output changes in a sine wave shape, a part of the ASE light is directly incident on the pump module 11, The semiconductor laser element in the pump module resonates and interferes with each other, destabilizes the oscillation, and causes discontinuous ripples in the output of the amplifier, resulting in unstable output.

Therefore, by installing the fiber type optical component 10a of the present invention on the output side of the pump module 11, the wavelength λ2 of the pumping light component passes and the signal light component of the wavelength λ1 is removed. Are almost removed, and the semiconductor laser in the module can be stably operated without returning to the pump module 11. A polarization-maintaining fiber may be used as the output optical fiber from the pump module 11, but in this case, the fiber-type optical component by fusion drawing may be configured and used on the polarization-maintaining fiber side and used as a filter. It can also be configured as an optical module with a function.

When the polarization maintaining fiber is used to form the fiber type optical component 10a according to the present invention, the polarization axes of the cross sections of the respective fibers are precisely aligned and arranged in parallel.
It is produced by fusion drawing.

The fiber type optical component 10b installed on the output side of the amplifier is used for flattening the wavelength characteristic of the output light. In this case, the wavelength branching ratio characteristic must be determined in consideration of the gain characteristic of the amplifier. In this case, the fiber-type optical component 10b of the present invention is used as the rare earth-doped fiber 1
4 may be configured as the output side fiber or may be configured within the rare earth-doped fiber 14. As a result, it is possible to integrate and combine optical circuits using the rare earth-doped fiber 14.

FIG. 5 shows another embodiment of the optical amplifier according to the present invention, in which the fiber type optical component 10 according to the present invention is used.
c is installed in the rare earth-doped fiber 14. Its function is to obtain broadband spontaneous emission light (A) generated separately from the amplified signal light generated in the rare earth-doped fiber.
It is used to remove the (SE light) component and improve the amplification characteristics. The ASE light is a factor that deteriorates the noise characteristic of the amplifier, and is a component to be removed.

Similarly, the signal light is transmitted to the rare earth-doped fiber 1
It can also be used for an ASE light source that uses the spontaneous emission light in a wide band by the excitation light without putting it in the No. 4 output.

FIG. 6 shows an ASE light source by a reflection type optical circuit using a total reflection mirror 16. Bidirectional excitation excites the rare earth element in the rare-earth-doped fiber 14 in the front and rear stages to obtain a wide band natural light. The emitted light is output. Of the excitation light λ2 emitted from each pump module 11,
Light of a spectrum component that cannot be completely absorbed by the rare earth-doped fiber 14 is incident on the semiconductor laser element in each pump module 11 and makes oscillation unstable. In order to prevent this, the filter type optical component 10c according to the present invention is installed in the rare earth-doped fiber 14, the excitation light component λ2 is removed here, and the spontaneous emission light component λ1 is passed. Its function is used to remove unwanted pumping light components that remain unabsorbed in the rare earth doped fiber. This embodiment can be similarly applied to the case of a bidirectional pumping optical amplifier.

FIG. 8 shows a spectrum waveform of the pumping light, and shows that a component which is not absorbed remains in the rare earth-doped fiber 14. Generally, the pumping light source wavelength band is wider than the absorption wavelength band of the rare earth-doped fiber 14.
That is, an unnecessary excitation light component that is not absorbed remains. It is used to remove the component of the excitation light λ2. Otherwise, the component will enter the semiconductor laser in the pump module 11 and make its oscillation operation unstable.
In this case, the filter type optical component 10c may be configured by fusion splicing using the rare earth-doped fiber 14 and installed in the rare earth-doped fiber 14.

FIG. 7 shows a fiber type optical component 10a of the present invention.
Is formed in the output optical fiber of the pump module 11 to pass the excitation light source wavelength λ2 and demultiplex and remove unnecessary light such as the amplified light wavelength λ1 and is used for stable operation of the pump module. . For pump modules,
A fiber Bragg grating (FBG) 17 is formed in the output optical fiber, a part of the pumping light source wavelength λ2 is reflected, returned to the semiconductor laser in the pump module, and resonated between them for stable operation. With this configuration, the output of the pump module and the wavelength spectrum characteristic can be stabilized.

The FBG 17 periodically changes the refractive index of the material inside the core so as to reflect light of a specific wavelength by irradiating it with ultraviolet light, so that the excitation light component wavelength is Bragg-reflected. It is the one.

Further, the fiber type optical component 10a may be used for removing an unnecessary output light component from the spectrum component of the pumping light and shaping the wavelength spectrum of the pumping light λ2.

[0034]

EXAMPLE FIG. 9 is an actual measurement example of an ASE light source waveform obtained by using the ASE light source shown in FIG. 6 without the filter type optical component 10a by an optical spectrum analyzer. By returning to the pump module 11, the pumping light output from the pump module oscillates at a constant cycle and becomes unstable, resulting in an ASE light source output including a periodic noise component.

On the other hand, FIG. 10 shows a filter type optical component 10a before the pump module 11 of the ASE light source of FIG.
In the actual measurement example in the case of the embodiment of the present invention, the unnecessary excitation light component is removed, so that the noise waveform due to oscillation is almost completely eliminated, and the stable ASE light source output waveform is obtained.

[0036]

As described in detail above, the fiber type optical component according to the present invention has the following excellent effects. 1. It is possible to provide an optical component with high isolation and low loss with a simple structure of a joint portion formed by fusion drawing. 2. By connecting a plurality of fusion splicing portions having different multiplexing / demultiplexing characteristics, the required isolation can be easily adjusted and configured. 3. The wavelength loss characteristic can be adjusted with a simple structure such as fusion drawing, and it can be configured as a wavelength flattening filter or an output spectrum shaping filter for an amplifier output. 4. Both sides of the fiber type optical component can be used as input / output ports for easy handling. 5. Due to the distributed coupling method by fusion and stretching, there is almost no end face reflection, and unnecessary return light components do not occur.

[Brief description of drawings]

FIG. 1 is an external view of a fiber type optical component according to the present invention.

2 (a) to 2 (c) are views showing various embodiments of a fiber type optical component according to the present invention.

FIG. 3 is a graph showing the propagation characteristics of the fiber type optical component according to the present invention.

FIG. 4 is a diagram showing an optical fiber amplifier using a fiber type optical component according to the present invention.

FIG. 5 is a diagram showing an optical fiber amplifier using a fiber type optical component according to the present invention.

FIG. 6 is an AS using a fiber type optical component according to the present invention.
It is a figure which shows an E light source.

FIG. 7 is a diagram showing a module using a fiber type optical component according to the present invention.

FIG. 8 is a wavelength spectrum of excitation light λ2 from the pump module.

FIG. 9 is a graph showing a waveform of an ASE light source according to a comparative example.

FIG. 10 is a graph showing a waveform of an ASE light source according to an embodiment of the present invention.

[Explanation of symbols]

1,7: Optical fiber 2: Mounting board 3: Radiant end 4: Fixed member 5: Mounting case 6: Fused stretched part

Claims (9)

[Claims] Claim: What is claimed is: 1. A plurality of optical fibers are closely adhered in parallel and locally heated and drawn to form a fusion splicing portion for multiplexing and demultiplexing propagating light, and one of the plurality of optical fibers at both ends is formed. Fiber-type optical components characterized in that each is used as an input / output fiber. 2. The fiber type optical component according to claim 1, wherein an end of an optical fiber other than the input / output fiber is a radiating end. 3. The fiber according to claim 1, comprising a plurality of the fusion splicing portions, which are fixed on one substrate or a plurality of substrates and are mounted in one or a plurality of cases. Mold optical parts. 4. The fiber type optical component according to claim 1, wherein a polarization maintaining fiber is used as the optical fiber. 5. The fiber Bragg grating is formed on the input / output fiber.
4. The fiber type optical component according to any one of 4 above. 6. At least one rare earth-doped fiber is used as the optical fiber.
5. The fiber type optical component according to any one of 5 above. 7. An optical module using the fiber type optical component according to claim 1 as an output optical fiber or an input optical fiber. 8. The fiber-type optical component or optical module according to claim 1 in at least one of the optical circuit on the output side of the pumping light source, the output side of the amplified light, and the rare earth-doped fiber. An optical fiber amplifier characterized by being provided. 9. The fiber-type optical component or optical module according to claim 1 in at least one position in an optical circuit on the output side of a pumping light source, an output side of amplified light, or a rare earth-doped fiber. An ASE light source characterized by being provided.