JPH03251825A - Optical amplifier - Google Patents

Abstract

PURPOSE:To obtain this optical amplifier which has a high signal amplification gain by constituting an optical coupler so that large loss such as branching loss to signal light is not generated. CONSTITUTION:Exciting light is emitted as shown by an arrow 11 from an SLD module 6b for excitation which is driven by a super-luminescent diode(SLD) for excitation. Then the exciting light is guided by the optical coupler 8b to the core 13c of a rare earth doped double-core optical fiber 13a from the core 12c of an exciting light propagating multi-mode optical fiber 12a. The core 13b of the fiber 13a has a higher refractive index than the core 13c, so the exciting light is guided to the core 13b and absorbed to generate an inverted population inside. When signal light 3 corresponding to resonance wavelength is made incident on the core 13b, light which is equal in wavelength to and in phase with the signal light 3 is emitted. The intensity of the signal light 3 at the projection end of the fiber 13a is larger than that at the incidence end and the signal light 3 is amplified.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical amplifier used in an optical fiber communication system, etc., which amplifies input signal light and then outputs the signal light.

[Conventional technology]

Figure 5 shows 9For example, Oplus E No.
.

113 (1989). FIG. 1 is a partially cutaway perspective view illustrating the configuration of a conventional optical amplifier using a rare earth doped optical fiber as an amplification optical fiber.

In the figure, (1) is an optical amplifier, and (2) is an optical amplifier (1
) housing, +3) is the signal light input to the optical amplifier (1), (4) is the input connector provided on the housing (2) for inputting the signal light (3), and (5) is the amplification Rare earth doped optical fiber α2 is used as a rare earth doped optical fiber (5) for pumping light to enter from one end of the pump light propagation fiber (61 is a pump light propagation fiber for inputting pump light into the pump light propagation fiber). LD module (7
1 is an excitation LD module (LD for driving 61)
The driver (8) is an optical coupler for inputting the signal light (3) and the excitation light to the rare earth doped light 7-eyeper (5).

(9) is an output connector provided in the housing (2) to take out the signal light (3) amplified within the rare earth doped optical fiber (5), αC is an arrow indicating the path of the signal light (3), αυ is an arrow indicating the path of the excitation light. Here, the wavelength of the pumping light is set to be shorter than the wavelength of the signal light (3), and the rare earth-doped optical fiber (5) absorbs the pumping light (9), thereby producing population inversion inside. Rare earth doped optical fiber with population inversion (5)
When signal light (3) having a wavelength corresponding to the resonant wavelength is incident therein, stimulated emission occurs due to this stimulation, and light having the same wavelength and the same phase as the signal light (3) is emitted. Therefore, the intensity of the signal light (3) at the output end of the rare earth-doped optical fiber (5) is greater than that at the input end, and the signal light (
31 is amplified. Note that this optical amplifier is used, for example, as an optical repeater amplifier in an optical fiber communication system.

Furthermore, the optical repeater amplifier is generally used in a single mode optical fiber transmission system that connects long distances, and therefore a single mode optical fiber coupler is often used for the optical coupler (8a). many. In other words, the optical coupler (8
In a), since a single mode optical coupler is used, a branching loss of 3 dB occurs in most cases. Note that the two-branch Higa is designed based on the branching loss between the signal light (31) and the pumping light and the gain of the amplification optical fiber.

In this case, the cutoff wavelength of the pumping light propagation optical fiber α2 needs to be shorter than the wavelength of the pumping light.

[Problem to be solved by the invention]

Since the conventional optical amplifier is configured as described above, a single mode optical fiber coupler or the like must be used as the optical coupler (8a), and signal light (3) such as 1 branching loss must be used.
There were issues such as large losses.

This invention has been made to solve the above-mentioned problems, and aims to provide an optical amplifier with a large optical signal amplification gain in which the signal light is not branched by the optical coupler (8a).

[Means to solve the problem]

The optical amplifier according to the present invention includes a first core that propagates the HE11 mode and contains a rare earth element, and a second core that propagates excitation light having a lower refractive index than the first core outside the first core. and a cladding having a refractive index lower than that of the second core outside the second core.
The excitation light is made to enter the core of the.

[Effect]

In the optical amplifier according to the present invention, the pumping light propagating through the second core is incident on the first core having a high refraction portion to excite the rare earth in the first core, thereby causing population inversion. When signal light with a wavelength corresponding to the resonant wavelength enters the first core of the amplification optical fiber in which population inversion has occurred in this way, stimulated emission occurs due to this stimulation, and light with the same wavelength and the same phase is amplified. released.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings.

In Fig. 1, (6b) is a pumping superluminescent diode module (hereinafter abbreviated as pumping SLD module), (+2b) is a pumping light propagation multimode optical fiber, and (15a) is a rare earth-doped double-core optical fiber ( 8b) is an optical coupler that optically couples the upward pumping light propagation multimode optical fiber (+zb) and the rare earth doped double core optical fiber (15a).

First, a rare earth doped double core optical fiber will be explained.

Figure 2 shows the rare earth doped double core optical fiber (1
3a) is a perspective view of the cross section.

(+5b) is the first core that propagates HE11 mode and contains rare earth elements, (+!Se) is the first core (t
5b) A second core which is a cladding for K and which propagates the excitation light, (+5d) is a second core (+5
cladding for c).

FIG. 3 is a diagram showing the refractive index distribution of the rare-earth doped double-core optical fiber α9, for example, at a wavelength of 1.55 μm.
If it is for amplification, (14a) has a core diameter of about 8μ.
m, mode field diameter of HE11 mode is approximately 10 μm
The refractive index distribution of the first core is designed to be (
+4b) has a relative refractive index of about 0.3 than the refractive index of the first core.
The refractive index of the second core (+aC) is designed to have a core diameter of approximately 50 μm, and the refractive index of the second core (+4
The relative refractive index is about 1% lower than b), and the cladding thickness is about 125μ.
The refractive index distribution of the cladding designed to m is shown. This rare earth doped double core optical fiber has a first core (15b) and a second core (+xc) in the optical fiber base material.
It was manufactured using the rond-in-tube method, in which a part of the cladding (+3d) was prepared using the VAD method, and then placed in a quartz rond and drawn. The amount of eccentricity relative to the diameter can be 1 μm or less.

Next, the optical coupler (8b) will be explained.

FIG. 4 is a cross-sectional structural diagram of the optical fiber portion of the optical coupler (8b), in which the rare earth doped double core optical fiber ([a) is at the optical fiber connection position shown in a9.

Only the cladding (+!Sd) is removed by polishing, and the second core (L5c) is exposed to the surface, and the excitation light propagation multimode optical fiber (+2b) is also removed by polishing the cladding (+2d) at the optical fiber connection position shown in α9. The core (1
2c) is exposed to the surface and bonded with an adhesive having a refractive index of approximately 1.5, thereby forming an optical bonding structure.

Next, the operation will be explained.

The excitation light is emitted in the direction of arrow αυ by the excitation SLD module driven by the SLD driver (7b).

Next, the optical coupler (8b) transfers the excitation light from the core (12C) of the excitation light propagation multimode optical fiber (+2b) to the rare earth doped double core optical fiber (15a) (Dm
2 core (12C).

Since the first core (+5b) of the rare earth-doped double-core optical fiber (15a) has a higher refractive index than the second core (13c), the excitation light is guided to the first core (+5b).

Absorbs excitation light, causing population inversion inside.

When the signal light (3) having a wavelength corresponding to the resonant wavelength enters the first core (+3b) of the rare-earth doped double-core optical fiber (13a) in which population inversion has occurred in this way, this stimulation induces Emission occurs, signal light +3
Light with the same wavelength and the same phase as 1 is emitted. Therefore, the intensity of the signal light (3) at the output end of the rare earth doped double-core optical fiber (15a) is greater than that at the input end, and the signal light (3) is amplified.

Here, the input light 131 is directly inputted into the first core (+5b) of the rare earth doped double core fiber (13a) via the input connector (4), amplified, and then passed through the output connector (9) to the first core (+5b) of the rare earth doped double core fiber (13a). Since it is directly emitted from the core (+sb) of signal light (3), the loss of signal light (3) is due to the input connector (4
) and the output connector (9) are the main cause. However, the above splice loss can be reduced to about 0.2 dB per point by reducing the eccentricity of the first core (+5b) to the cladding (13d) to 1 μm or less, which is common to ordinary single mode fibers. The connection loss is about the same as that of .

Generally, when there are reflection points for the gain wavelength band at both ends of the rare earth doped optical fiber (+5a), the feedback is distorted and laser oscillation occurs, so the end of the rare earth doped optical fiber (13a) is provided with means to suppress reflection. The terminal of the input connector (4) and the terminal of the output connector (91) are processed into a spherical surface with a curvature of about 20 fl. , a non-reflection film for the gain wavelength band may be attached to the terminal of the output connector (9).

In addition, in the above embodiment, an excitation SLD is used as an excitation light source.
Although the one provided with the module (6b) is shown.

Laser diodes and self-pulsation LDs.

It is also possible to use an edge-emitting LED, and the same effect as in the above embodiment can be obtained.

In addition, a multimode optical fiber (+2b) for pumping light propagation,
In order to prevent speckle noise occurring within the rare earth doped double core optical fiber (+5a), a long fiber or mode scrambling may be inserted between the excitation light source and the optical coupler.

Further, in order to stabilize the speckle noise, a means for superimposing a high frequency on the drive current of the excitation light source may be incorporated into the excitation light source driving device.

〔Effect of the invention〕

As described above, according to the present invention, the optical coupler (6b) is configured so that large losses such as branching loss to the signal light (31) do not occur, so that an optical amplifier with high signal amplification gain can be obtained. .

[Brief explanation of drawings]

FIG. 1 is a partially cutaway perspective view of an optical amplifier showing an embodiment of the present invention, FIG. 2 is a perspective view of a cross section of a rare earth-doped double-core optical fiber, which is an important component of the present invention, and FIG. The figure shows the refractive precipitation of the rare earth-doped optical fiber, Figure 4 is a cross-sectional structural diagram of the optical fiber part of the optical coupler, which is an important part of this invention, and Figure 5 shows a part of a conventional optical amplifier. It is a perspective view cut away and shown. (1) is an optical amplifier, (21 is a housing, I31 is a signal light, (
4) is an input connector, (5) is a rare earth doped optical fiber, +61 C is a semiconductor light emitting device module for excitation, (7) is a semiconductor light emitting device driver, (8) is an optical coupler, (9) is an output connector, and αG is an output connector. An arrow indicating the path of the signal light, aυ is an arrow indicating the path of the excitation light, α2 is the excitation light propagation optical fiber, α3 is the rare earth doped double core optical fiber, a4 is the refractive index of the rare earth doped double core optical fiber, and α9 is the optical fiber connection position. Note that in the two figures, the same reference numerals indicate the same or equivalent parts.

Claims (1)

[Claims] In an optical amplifier that amplifies incident signal light using stimulated emission action of an amplification optical fiber, a first core that propagates the HE11 mode and contains a rare earth element;
A second core for amplification that is provided outside the core and has a refractive index lower than that of the first core and that propagates the excitation light, and a crat that is located outside the second core and has a refractive index lower than that of the second core. An excitation semiconductor light emitting element module with a multimode fiber comprising an optical fiber and a superluminescent diode as a light source of excitation light for excitation of the amplification optical fiber;
A semiconductor light emitting element driver for driving the excitation semiconductor light emitting element module, an input connector provided for inputting light into one end of the amplification optical fiber, and an input connector for emitting light from the other end of the amplification optical fiber. an output connector provided on the amplifying optical fiber, and a portion where the second core is exposed except for a part of the cladding of the optical fiber for amplification,
An optical amplifier characterized in that the cores of the multimode optical fibers of the excitation semiconductor light emitting element module are optically coupled.