JPH0926379A - Monitoring structure of optical amplifier - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a monitoring structure of a rare earth-doped optical fiber amplifier which has a high detection capacity for gain and high reliability of detection in the monitoring structure of the rare earth-doped optical fiber amplifier. SOLUTION: In a rare earth-doped optical fiber amplifier, a rare earth-doped optical fiber 1, which is wound in the from of a coil, filled with a transparent bonding agent of a refraction factor, which is equal or substantially equal to the refraction factor of the protection layer of the optical fiber, in wound gaps and a light detector 20 fixed on a base mounting the rare earth-doped optical fiber 1 so that a light receiving face may be adjacent to and be opposed to the side of the coil of the rare earth-doped optical fiber 1 are equipped.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a monitor structure for a rare earth-doped optical fiber amplifier. In recent years, a rare-earth-doped optical fiber amplifier has been provided as an optical amplifier used for amplifying an input optical signal as it is to obtain an optical signal with a large output.

A rare earth-doped optical fiber amplifier transmits a signal light having a wavelength near 1.55 μm to a rare earth-doped optical fiber (for example, erbium-doped optical fiber) having a length of several meters to several hundred meters, and 1.48 from a pumping light source. A pumping light having a wavelength of about μm is injected and stimulated to be emitted into the rare earth-doped optical fiber. The direction of the stimulated emission light in this rare earth-doped optical fiber is exactly the same as the direction of the signal light, so 1.55
Signal light having a wavelength in the vicinity of μm is amplified.

An example of such an optical amplifier is shown in FIG. 4, and a sectional view of a rare earth-doped optical fiber is shown in FIG. In the figure, reference numeral 1 denotes an erbium-doped rare earth-doped optical fiber, the core 1-1 has an outer diameter of several μm (for example, 6 μm), and the cladding 1-2 has an outer diameter of about 125 μm.

The refractive index around the outer circumference of the clad 1-2 is clad 1-
A protective layer of plastics slightly larger than the refractive index of 2
It is covered with 1-3. The outer diameter of the protective layer 1-3 is about 250.
μm.

Such a rare earth-doped optical fiber 1 is wound around a bobbin 10, and an incident side fiber / lens assembly 1A is attached to the emitting side end thereof. 3A is an excitation light source side fiber / lens assembly for introducing the excitation light of the excitation light source 3 into the rare earth-doped optical fiber 1, and 2A is an emission side fiber / lens assembly attached to the incident end of the output optical fiber 2.

Reference numeral 4 is a rectangular casing having side walls 4A, 4B and 4D and a side wall 4C opposed to the side wall 4A. Reference numeral 5 is a wavelength separation film that transmits the excitation light (wavelength is around 1.48 μm) of the light emitted from the excitation light source 3 and reflects the light emitted from the rare earth-doped optical fiber 1 (wavelength is 1.55 μm).

Reference numeral 6 is an optical isolator inserted and mounted between the wavelength separation film 5 and the output side fiber / lens assembly 2A. The incident side fiber / lens assembly 1A penetrates the selected side wall 4A of the case 4 and is attached to the case 4, and the excitation light source side fiber / lens assembly 3A has an optical axis of the light of the incident side fiber / lens assembly 1A. It is attached to the housing 4 through the side wall 4C facing the side wall 4A so as to match the axis.

The wavelength separation film 5 has a desired angle (for example, 45 degrees) with respect to the optical axis of the incident side fiber lens assembly 1A.
Incident fiber lens assembly 1A, tilted
And the excitation light source side fiber / lens assembly 3A.

On the other hand, the output optical fiber 2 is mounted on the housing 4 so as to penetrate the other side wall 4D so that the reflected light of the wavelength separation film 5 enters through the optical isolator 6. With the configuration as described above, the pumping light of the pumping light source 3 enters the rare earth-doped optical fiber 1 and amplifies the signal light transmitted to the rare earth-doped optical fiber 1.

The amplified signal light is emitted from the incident side fiber / lens assembly 1A, projected onto the wavelength separation film 5, reflected by the wavelength separation film 5, passed through the optical isolator 6, and emitted onto the emission side fiber / lens assembly 2A. And is transmitted to the output optical fiber 2.

[0011]

Excited state ions of rare earth-doped optical fibers include not only stimulated emission but also spontaneous emission after a certain excitation lifetime.

This spontaneous emission light P is not in a specific direction,
Since the light is emitted in all directions, it is not confined in the rare earth-doped optical fiber and a part thereof is emitted to the outside from the side surface of the rare earth-doped optical fiber.

"A method of controlling the gain of an EDFA by detecting spontaneous emission light from the side surface of the fiber" in which the intensity of the spontaneous emission light P emitted outside the rare earth-doped optical fiber is measured to monitor the gain of the optical amplifier. Are described in 91-32 of IEICE Optical Communication System Research Group.

FIG. 4 is a sectional view showing the structure of a conventional monitor of an optical amplifier devised based on the above document. In FIG. 4, reference numeral 10 is a desired long rare-earth-doped optical fiber 1
Body part 11 and a pair of flanges
It is a bobbin consisting of 12. The material of the bobbin 10 is plastics or metal such as aluminum.

A rare earth-doped optical fiber 1 is attached to the bobbin 10.
After winding, the bobbin 10 is placed on a base (not shown). Reference numeral 20 is a prismatic photodetector with one side of the light receiving surface of about 5 mm.

A photodetector 20 is fixed to the base so that the light receiving surface faces and approaches the side surface of the coil of the rare earth-doped optical fiber 1 wound around the bobbin 10. Therefore, the spontaneous emission light P emitted from the side surface of the coil of the rare earth-doped optical fiber 1 facing the photodetector 20 is incident on the photodetector 20 and is photo-electrically converted and detected as the output of the photodetector 20. To be done. Therefore, the gain of the optical amplifier can be monitored.

[0017]

However, since there is a gap filled with air between the rare earth-doped optical fibers (hereinafter referred to as optical fibers) wound on the bobbin, the optical fibers wound on the inner layer are provided. The spontaneous emission light emitted by is scattered and refracted by the optical fiber located outside the coil portion due to the presence of this air gap.

Therefore, the spontaneous emission light emitted from the side surface of the optical fiber wound on the inner layer is hardly emitted to the outside of the coil. The conventional monitor structure has the following reasons.
The spontaneous emission light emitted by the coil portions of the optical fibers located in the outermost layer and the layer close to the outermost layer only enters the photodetector. Therefore, the received light power is small.

Since the coil portion of the optical fiber located in the outermost layer and the layer close to the outermost layer is either the winding start portion or the winding end portion of the coil, the excited state of the entire optical fiber is Not reflected correctly.

Due to the above-mentioned two points, the conventional monitor structure has a problem that the gain detection capability is low. Moreover, since the optical fiber is only wound around the bobbin, the coil portion of the outermost layer is not sufficiently fixed and sways. Therefore, the spontaneous emission light incident on the photodetector is unstable, and the reliability of detection may be reduced.

The present invention has been made in view of the above points, and an object thereof is to provide a monitor structure of an optical amplifier having a high gain detection capability and a high detection reliability.

[0022]

In order to achieve the above object, the present invention provides a rare earth-doped optical fiber amplifier, which has a refractive index equal to or substantially equal to that of a protective layer of an optical fiber, as illustrated in FIG. A rare earth-doped optical fiber 1 in which a transparent adhesive 25 having a refractive index is filled and adhered in a space between optical fibers and wound in a multilayer coil shape, and a base on which the rare earth-doped optical fiber 1 is placed. The photodetector 20 is fixed on the table 30 so as to be close to the side surface of the coil of the rare-earth-doped optical fiber 1 having a light-receiving surface wound around and fixed to face it.

Further, as illustrated in FIG. 2, the rare earth-doped optical fiber 1 has a structure wound around a bobbin 10.
Alternatively, the photodetector 20 is closely adhered to the transparent adhesive 25 so that the photodetector 20 is wound around the rare earth-doped optical fiber 1 or the rare earth-doped optical fiber 1 wound around the bobbin 10. It has a fixed configuration.

Furthermore, the reflecting film 15 is formed on the outer peripheral surface of the body portion 11 of the bobbin 10 and the inner surface of the flange 12. Alternatively, the outer peripheral surface of the body portion 11 of the bobbin 10 and the inner surface of the flange 12 are mirror-finished.

As illustrated in FIG. 3, the window 40 provided on the flange 12 of the bobbin 10 around which the rare earth-doped optical fiber 1 is wound.
The photodetector 20 is inserted into the photodetector 20, and the light receiving surface of the photodetector 20 is filled with a transparent adhesive filled in the gap between the rare earth-doped optical fibers.
In addition to closely adhering to 25, a film 45 having a reflective film or a metal foil is attached to the outer peripheral surface of the coil around which the rare earth-doped optical fiber 1 is wound.

[0026]

According to the present invention, the gap between the rare earth-doped optical fibers is filled with a transparent adhesive having a refractive index equal to or substantially equal to the refractive index of the protective layer of the optical fiber, and the rare earth-doped optical fiber is It is fixed in the state of being wound in a multilayer coil shape.

Therefore, the spontaneous emission light emitted not only by the outer layer portion but also by the coil portion of the rare earth-doped optical fiber wound on the inner layer is generated by the transparent adhesive and the protective layer of the rare earth-doped optical fiber of the outer layer. The light passes through the clad and enters the photodetector. Further, the spontaneous emission light emitted to the coil end face side is reflected to the coil side at the boundary surface between the transparent adhesive and air, and a part thereof enters the photodetector.

Therefore, the optical power of the spontaneous emission light received by the photodetector is large. Further, as described above, since the spontaneous emission light emitted by the rare earth-doped optical fiber inside the coil is received almost evenly, the excitation state of the entire optical fiber is correctly reflected, and the gain detection capability is improved. .

Further, the rare earth-doped optical fiber is securely fixed by the transparent adhesive while maintaining the coil state. Therefore, the spontaneous emission light entering the photodetector is stable and constant, and the reliability of detection is high.

On the other hand, since the light receiving surface is closely adhered to the transparent adhesive and the photodetector is fixed to the bobbin, the spontaneous emission light is reflected by the light receiving surface of the photodetector and is guided to the inside of the coil. Will be prevented from returning. Therefore, most of the spontaneous emission light projected on the light receiving surface side of the photodetector is incident on the photodetector, and the optical power received by the photodetector is increased.

Further, as in claim 6, the photodetector is inserted into the window provided on the flange of the bobbin, and the light-receiving surface of the photodetector is transparently filled in the gap between the rare earth-doped optical fibers. The optical amplifier monitor structure in which a film having a reflective film or a metal foil is attached to the outer surface of the coil around which the rare-earth-doped optical fiber is wound while closely adhering to the agent is arranged in the circumferential direction of the coil. The emitted spontaneous emission light is reflected by the film or metal foil and returns to the inside of the coil.

Therefore, the optical power received by the photodetector becomes larger.

[0033]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. The same reference numerals indicate the same objects throughout the drawings.

FIG. 1 is a sectional view of an embodiment of the present invention, FIG. 2 is a sectional view of another embodiment of the present invention, and FIG. 3 is a sectional view of yet another embodiment of the present invention. In the figure, 1 is a rare earth-doped optical fiber having a length of several tens to several hundreds meters doped with erbium, for example, the outer diameter of its core is about 6 μm, and the outer diameter of its cladding is 125 μm. Further, the outer periphery of the clad is covered with a plastic protective layer having a refractive index slightly higher than that of the clad.

When an optical signal having a predetermined wavelength is transmitted to the rare earth-doped optical fiber 1 and pumping light is introduced from the pumping light source into the rare earth-doped optical fiber 1, signal light is induced and emitted into the rare earth-doped optical fiber. Is amplified. Further, the spontaneous emission light P is emitted in all directions of the rare earth-doped optical fiber 1.

Numeral 20 is a prism whose one side of the light receiving surface is about 5 mm,
It is a photodetector having a photoelectric conversion function. 25 is the refractive index equal to or nearly equal to the refractive index of the protective layer of the optical fiber,
For example, it is a transparent adhesive made of epoxy resin.

As shown in FIG. 1, the rare earth-doped optical fiber 1 is wound around a tube 35 in multiple layers, and a transparent adhesive 25 is filled and bonded in the gap between the optical fibers. The wound rare-earth-doped optical fiber 1 has one end face side inserted into the concave portion of the base 30, and the base is formed by using, for example, an adhesive.
Fixed to 30.

The photodetector 20 is fixed on the base 30 in close proximity to the side surface of the coil of the rare earth-doped optical fiber 1 having the light receiving surface wound. Since it is configured as described above, the spontaneous emission light P emitted by not only the outer layer portion of the rare earth-doped optical fiber 1 wound in a coil shape but also the coil portion wound in the inner layer is transparently bonded. After passing through the agent 25, the protective layer of the rare earth-doped optical fiber 1 in the outer layer, and the clad, it is emitted to the outside of the coil and is incident on the photodetector 20.

A part of the spontaneous emission light emitted to the coil end surface side is reflected to the coil side at the boundary surface between the transparent adhesive 25 and the air, and a part thereof enters the photodetector 20. Therefore, the optical power of the spontaneous emission light P received by the photodetector 20 is relatively large.

Further, since the spontaneous emission light emitted from the rare earth-doped optical fiber 1 in the inner layer of the coil is received almost evenly, the excitation state of the entire rare earth-doped optical fiber is correctly reflected, and the gain is detected. Ability is improved.

To fill the gap between the optical fibers with the transparent adhesive 25 and bond and fix the rare earth-doped optical fiber 1 in a coil shape, after winding the rare earth-doped optical fiber 1 around the tube body 35, The transparent adhesive may be vacuum-impregnated.

In order to hold the rare earth-doped optical fiber 1 in the form of a multilayer coil, the rare earth-doped optical fiber 1 wound around the tube 35 and then removed from the tube 35 and wound into a coil is essential. After tightening the required places with a band, etc., clear adhesive 25
May be vacuum impregnated.

The thus constructed tube body 35 shown in FIG.
It is fixed to the base 30 in the absence of any. The end face of the wound rare earth-doped optical fiber may be directly fixed to the surface of the base 30 with an adhesive without providing the base 30 with a recess.

In FIG. 2, reference numeral 10 denotes a bobbin which is composed of a body portion 11 and a pair of flanges 12 and which winds the rare earth-doped optical fiber 1 in a multilayer coil shape. It is a metal such as plastics or aluminum.

When the bobbin 10 is made of metal such as aluminum, the outer peripheral surface of the body portion 11 of the bobbin 10 and the inner surface of the flange 12 are mirror-finished. When the bobbin 10 is made of plastic, the reflection film 15 is provided on the entire outer peripheral surface of the body portion 11 of the bobbin 10 and the inner surface of the flange 12.

A transparent adhesive 25 is filled in the gap between the body portion 11 and the flange 12 of the bobbin 10 and the rare-earth-doped optical fiber 1, and the gap between the rare-earth-doped optical fibers 1 is filled with the rare-earth-doped optical fiber 1. Is wound around and fixed to the bobbin 10 in the form of a multilayer coil.

On the other hand, the photodetector 20 faces the coil side surface of the rare earth-doped optical fiber 1 whose light receiving surface is wound, and is closely adhered to the transparent adhesive 25. Therefore, the rare earth-doped optical fiber 1 is securely fixed to the bobbin 10 while maintaining the coil state by the transparent adhesive 25, and the rare earth-doped optical fiber itself moves or the photodetector 20.
The side never moves.

Therefore, the spontaneous emission light incident on the photodetector 20 is stable and constant, and the detection reliability is high. Since the light receiving surface is in close contact with the transparent adhesive 25, the spontaneous emission light is hardly reflected by the light receiving surface of the photodetector 20 without forming an antireflection film on the light receiving surface.

Therefore, the spontaneous emission light is prevented from returning to the inside of the coil, and most of the spontaneous emission light projected on the light receiving surface is incident on the photodetector 20, and the light received by the photodetector 20 is received. The power increases.

Furthermore, by providing the reflection film 15 on the outer peripheral surface of the body of the bobbin 10 and the inner surface of the flange, or by mirror-finishing, the spontaneous emission light emitted toward the body or the flange can be prevented. The light is reflected by the outer peripheral surface or the inner surface of the flange, returns to the inside of the coil, and emits in the direction of the photodetector.
It is incident on 20. Therefore, the optical power received by the photodetector becomes larger.

As shown in FIG. 3, a window 40 is provided on the flange 12 of the bobbin 10 around which the rare earth-doped optical fiber 1 is wound, and the photodetector 20 is inserted into the window 40 so that the photodetector 20 receives light. The surface is adhered to the transparent adhesive 25.

A reflecting film 15 is provided on the entire outer peripheral surface of the body 11 of the bobbin 10 and the inner surface of the flange 12. Further, a film 45 having a reflection film or a metal foil is attached to the outer peripheral surface of the coil around which the rare earth-doped optical fiber 1 is wound.

Since the spontaneous emission light emitted in the circumferential direction of the coil is reflected by the film 45 or the metal foil and returns to the inside of the coil, the optical power received by the photodetector 20 becomes larger.

[0054]

As described above, according to the present invention, the refractive index of the protective layer of the optical fiber is the refractive index of the gap between the rare earth-doped optical fibers and the outer peripheral surface of the coil wound in a multilayer coil shape. Which is filled with and bonded with a transparent adhesive equal to or almost equal to, has a practically excellent effect that the gain detection capability of the rare earth-doped optical fiber amplifier is high and the detection reliability is high.

[Brief description of drawings]

FIG. 1 is a sectional view of an embodiment of the present invention.

FIG. 2 is a sectional view of another embodiment of the present invention.

FIG. 3 is a diagram of yet another embodiment of the present invention.

FIG. 4 is a configuration diagram of an optical amplifier.

FIG. 5 is a cross-sectional view of a rare earth-doped optical fiber.

FIG. 6 is a sectional view of a conventional example.

[Explanation of symbols]

 1 Rare earth doped optical fiber 1-1 Core 1-2 Clad 1-3 Protective layer 2 Output optical fiber 3 Excitation light source 4 Housing 5 Wavelength separation film 6 Optical isolator 10 Bobbin 11 Body 12 Flange 15 Reflective film 20 Photodetector 25 Transparent adhesive 40 Window 45 Film P Spontaneous emission light

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Kenji Tagawa Kenji Tagawa 1015 Kamiodanaka, Nakahara-ku, Kawasaki-shi, Kanagawa Within Fujitsu Limited (72) Inventor Yoshiaki Sato 1-6, Uchisaiwaicho, Chiyoda-ku, Tokyo Nihon Telegraph Telephone Within the corporation

Claims (7)

[Claims] 1. In a rare earth-doped optical fiber amplifier, a multi-layered coil is wound, and the wound gap is filled with a transparent adhesive having a refractive index equal to or substantially equal to the refractive index of the protective layer of the optical fiber. A monitor structure for an optical amplifier, comprising: a rare earth-doped optical fiber, and a photodetector having a light-receiving surface that closely faces a coil side surface of the rare earth-doped optical fiber. 2. The monitor structure of the optical amplifier according to claim 1, wherein the photodetector is fixed on a base on which the rare earth-doped optical fiber is mounted. 3. The monitor structure for an optical amplifier according to claim 1, wherein the rare earth-doped optical fiber is wound around a bobbin. 4. The photodetector is fixed to the outer peripheral portion of the coil-shaped rare earth-doped optical fiber by adhering the light-receiving surface to the transparent adhesive. Optical amplifier monitor structure. 5. The monitor structure for an optical amplifier according to claim 3, wherein a reflecting film is formed on the outer peripheral surface of the body of the bobbin and the inner surface of the flange. 6. The monitor structure for an optical amplifier according to claim 3, wherein the outer peripheral surface of the body of the bobbin and the inner surface of the flange are mirror-finished. 7. A rare earth-doped optical fiber is inserted into a window provided in a flange of a bobbin wound around the light receiving surface, and a light-receiving surface is adhered to a transparent adhesive filled in a gap between the rare earth-doped optical fibers. A monitor structure for an optical amplifier, comprising: a photodetector; and a film or metal foil having a reflective film, which is attached to the outer peripheral surface of the rare earth-doped optical fiber wound in a coil shape.