JPH0854511A - Optical amplifier - Google Patents

Abstract

PURPOSE:To prevent multiple reflections and to improve excitation efficiency by an exciting light source by providing an optical amplifier with an optical filter which permits passage of exciting light toward an optical coupler and prohibits the passage of signal light toward the exciting light source. CONSTITUTION:This optical amplifier 10 includes an optical fiber 2 added with, for example, erbium, as an optical amplifying medium, the exciting light source 3 consisting of, for example, a semiconductor laser for exciting the optical fiber 2, the optical coupler 4 for introducing the exciting light from the exciting light source 3 to the optical fiber 2, an optical fiber 8 for guiding the light to the coupler 4 and the optical filter 12 disposed between the exciting light source 3 of the optical fiber 8 and the optical coupler 4. The exciting light of the wavelength different from the wavelength of the light signal which is to be amplified and is emitted from the exciting light source 3 is effectively introduced into the optical fiber 2 having the optical amplifying function from the optical coupler 4 without generating large attenuation at the optical filter 12. On the other hand, the inflow of the signal light of the wavelength different from the wavelength of the exciting light 3 into the exciting light source 3 is prohibited by the optical filter 12.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical amplifier used for optical communication.

[0002]

2. Description of the Related Art Communication using optical signals is used in a wide range of fields. For example, in optical communication using a public network, wavelengths of 0.8 μm band, 1.3 μm band and 1.
A signal in the 55 μm band is used. An erbium-doped optical fiber amplifier is one of so-called optical amplifiers that directly amplify such an optical signal as it is without converting it to an electrical signal.

FIG. 2 shows a block diagram of a conventional erbium-doped optical fiber amplifier. In the erbium-doped optical fiber amplifier 1, as shown in FIG. 2, an erbium-doped optical fiber 2 is used as an optical fiber having an optical amplification function. Further, since the erbium-doped optical fiber 2 into which the optical signal in the 1.55 μm band λ1 is input is excited, it has higher energy than the optical signal.
For example, a wavelength λ2 of 0.98 μm or 1.48 μm
This laser light source is used as the excitation light source 3. When the laser light λ2 from the pumping light source 3 is guided to the optical fiber 2 via the optical coupler 4, the erbium-doped optical fiber 2 is placed in the population inversion state, and the optical signal λ1 causes the stimulated emission of the optical fiber 2. Is amplified and output by.

Isolators 5 and 6 for preventing backflow of the signal light λ1 are provided on the input and output ends of the amplifier 1, respectively. Further, the inflow of the signal light λ1 into the pumping light source 3 causes the reflected wave λ1 * thereof, which causes multiple reflections. Therefore, in order to prevent this, the pumping light source 3 and the optical coupler 4 are combined. In the meantime, conventionally, the isolator 7 for 1.55 μm for preventing the signal light λ1 from flowing into the pumping light source 3 has been used.

[0005]

However, the isolator 7 provided between the pumping light source 3 and the optical coupler 4 is used.
Is emitted from the excitation light source 3 and the erbium-doped optical fiber 2
The excitation light λ2 traveling toward the end is attenuated, causing a large optical loss. Therefore, it has been strongly desired to improve the excitation efficiency by the excitation light source.

[0006]

In order to solve the above-mentioned problems, the present invention provides a pumping light source for an optical fiber having an optical amplification function, and a pumping light from this pumping light source to the optical fiber. An optical filter is provided between the optical coupler and the optical isolator, instead of the conventional isolator, to allow the pumping light to pass toward the optical coupler and to block the signal light from passing toward the pumping light source.

[0007]

In the optical amplifier of the present invention, the pumping light emitted from the pumping light source and having a wavelength different from the wavelength of the optical signal to be amplified is
The optical filter does not cause large attenuation, and is efficiently introduced from the optical coupler to the optical fiber having the optical amplification function. On the other hand, the signal light having a wavelength different from that of the pumping light is blocked from flowing into the pumping light source by the optical filter.

[0008]

The present invention will be described in detail below with reference to the illustrated embodiments. FIG. 1 is a block diagram showing an optical amplifier according to the present invention. As shown in FIG. 1, an optical amplifier 10 according to the present invention includes an optical fiber 2 doped with, for example, erbium as an optical amplification medium, and a pump including a semiconductor laser for pumping the optical fiber 2. Light source 3 and optical coupler 4 for guiding pumping light from the pumping light source to the optical fiber 2.
And an optical fiber 8 for guiding the light from the pumping light source 3 to the optical coupler 4, and an optical filter 12 provided between the pumping light source 3 and the optical coupler 4 of the optical fiber 8.

Since the so-called erbium-doped optical fiber 2 doped with erbium amplifies the optical signal in the 1.55 μm band most efficiently, the 1.55 μm band λ1
Is used as an optical amplifying element for the optical signal. Further, the pumping light source 3 for pumping the erbium-doped optical fiber 2 for amplifying this optical signal has a higher energy than the optical signal, that is, a laser having a short wavelength, for example, a wavelength λ2 of 0.98 μm or 1.48 μm. A light source is used.
When the laser light λ2 from the pumping light source 3 is guided from the optical coupler 4 to the erbium-doped optical fiber 2 via the optical fiber 8, the erbium-doped optical fiber 2 is placed in the inverted distribution state, and the optical signal λ1 is transmitted to the optical fiber. It is amplified and output by the stimulated emission action of 2. Isolators 5 and 6 for preventing backflow of the signal light λ1 are provided on the input and output ends of the amplifier 1, respectively.

Since the inflow of the signal light λ1 into the pumping light source 3 causes the reflected wave λ1 * to cause multiple reflections, in order to prevent this, the pumping light source 3 in the optical fiber 8 and An optical filter 12 that allows the pumping light to pass toward the optical coupler 4 and blocks the signal light λ1 from passing toward the pumping light source 3 is inserted between the optical coupler 4 and the optical coupler 4.

FIG. 3 is a structural diagram of a dual core type optical filter used as the optical filter 12 according to the present invention. In the example shown in FIG. 3, the dual core type optical filter 12 is inserted into the optical fiber 8 so that the left side in the figure is located on the optical coupler 4 side and the right side in the figure is located on the excitation light source 3 side. There is. The optical filter 12 is arranged in alignment with the core 8A of the optical fiber 8 serving as the optical path of the excitation light source.
4 is arranged in parallel with the first core, and the intermediate portion Z is
A second core 16 disposed in proximity to the first core so as to form an evanescent coupling, which is a coupling of light, with the core 14, and a clad 18 surrounding both cores. The diameter of the second core 16 is smaller than that of the first core 14, and both ends face the end surface of the cladding 8A of the optical fiber 8. Further, a reduced diameter portion 20 is formed in an intermediate portion of the clad 18 where the two cores 14 and 16 are close to each other.

In the dual core type optical filter 12, by appropriately selecting the conditions such as the coupling length Z at which the two cores 14 and 16 are coupled, the light incident from one end of the filter 12 is fed to the first core 14 and the other at the other end. Second core 16
In addition, they can be separated according to the wavelength. From this, by selecting the coupling length or the like, as shown by the double arrow in FIG. 3, from the left end side of the optical filter 12 to the first core 1
The optical signal λ1 entering 4 can be guided to the cladding 8B by the second core 16 and removed as a cladding mode as indicated by reference numeral 22. This cladding mode effectively blocks the optical signal λ1 from passing through the filter 12. Also, the excitation light λ2 from the excitation light source side
Are guided to the optical coupler 4 through the first core 14 of the filter 12 without undergoing strong attenuation as in the conventional case.

Therefore, since the pumping light from the pumping light source 3 can be efficiently introduced into the erbium-doped optical fiber 2 without causing a large attenuation, the pumping efficiency of the pumping light source is improved. You can Further, since the signal light is surely blocked from flowing into the pumping light source 3, the signal light is reliably blocked from flowing into the pumping light source without using an expensive isolator between the pumping light source and the optical coupler. Then, multiple reflection due to the reflected wave can be reliably prevented.

An optical fiber doped with a rare earth element other than erbium or another doping material can be used as an optical amplification element as an optical amplification medium. In the illustrated example, the pumping light source is backward pumping, but the present invention is not limited to this, and the present invention can be applied to forward pumping or bidirectional pumping.

[0015]

As described above, in the optical amplifier of the present invention, the optical filter efficiently introduces the pumping light from the pumping light source into the optical fiber without causing large attenuation, while Since the inflow of the light to the pumping light source is surely blocked, the inflow of the signal light to the pumping light source is reliably blocked without using an expensive isolator between the pumping light source and the optical coupler. It is possible to reliably prevent multiple reflection due to reflected waves. In addition, the excitation efficiency of the excitation light source can be improved.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an optical amplifier according to the present invention.

FIG. 2 is a configuration diagram showing a conventional optical amplifier.

FIG. 3 is a structural diagram of a dual core type optical filter according to the present invention.

[Explanation of symbols]

 2 Optical fiber λ1 Optical signal wavelength 3 Pumping light source λ2 Pumping light wavelength 4 Optical coupler 12 Optical filter

Claims (3)

[Claims] 1. An optical fiber having an optical amplification function, a pumping light source for the optical fiber which emits pumping light having a wavelength different from the wavelength of an optical signal to be amplified, and the pumping light from the pumping light source An optical coupler for guiding to a fiber, and light that exists between the optical coupler and the pumping light source and allows passage of the pumping light toward the optical coupler and blocks passage of the signal light toward the pumping light source. An optical amplifier comprising: a filter. 2. The optical amplifier according to claim 1, wherein the optical filter is a dual core type optical filter. 3. The optical filter is inserted in alignment with the optical path of the pumping light source, and is provided with a first core for guiding the pumping light, and arranged in parallel with the first core to separate the optical signal. The optical amplifier according to claim 1, further comprising: a second core coupled to the first core, and a clad surrounding the first and second cores.