JPH04127130A - Optical fiber amplifier - Google Patents

Abstract

PURPOSE:To decrease the number of optical components and to reduce the cost by constituting a polarized wave coupler and a multiplexer integrally as a prism unit. CONSTITUTION:A total reflecting film 34 is formed on one surface of a 1st prism 33 which has a 45 deg. included angle and a multiplexing film 35 is formed on the other surface. On the latter surface of the 1st prism 33, a quadrangular prism 36 which has a 2nd included angle of 45 deg. opposite a 1st included angle is stuck so that the 1st included angle is enough to multiplex signal light and pumping light sufficiently and adjoins to the included angle of the 1st prism 33. A polarized wave multiplexing film 38 is formed on the surface of the quadrangular prism 36 facing the surface where a multiplexing film 35 is formed and a triangular prism 40 is stuck on the surface of the quadrangular prism 36 where the polarized wave multiplexing film 38 is formed to constitute the prism 32, thus constituting the polarized wave coupler and multiplexer in one body. Consequently, the constitution of the optical coupler can be simplified.

Description

[Detailed Description of the Invention] Table of Contents Overview Industrial Application Fields Prior Art Problems to be Solved by the Invention Means for Solving the Problems Implementation Examples Summary of Effects of the Invention Doped Optical Fiber Doped with Rare Earth Elements Regarding optical fiber amplifiers that directly amplify signal light by inputting signal light and pumping light (pumping light) into the optical fiber amplifier, there is a multiplexer that can input signal light and pumping light with a small wavelength difference at right angles or in parallel to each other. The purpose of the present invention is to provide an optical fiber amplifier in which a first pumping light and a second pumping light whose polarization directions are orthogonal to each other are combined by a polarization coupler so that they are connected to the same optical axis. The first and/or second pumping light from the polarization coupler and the signal light are combined by a multiplexer and input into an Er-doped optical fiber, and the signal light is directly emitted. In an optical fiber amplifier for amplification, a total reflection film is formed on one surface of a first prism that defines the included angle of 45°, and a multiplexing film is formed on the other surface, and the multiplexing film is formed on the other surface. A first prism is formed on the other surface of the first prism on which a film is formed.
The included angle is an angle that can sufficiently combine the signal light and the pumping light, and the second included angle opposite to the first included angle is 45
゜A quadrilateral prism is attached such that the first included angle is adjacent to the included angle of the first prism, and a polarization synthesis film is placed on the surface of the quadrilateral prism that faces the surface on which the multiplexing film is formed. The polarization coupler and the multiplexer are integrally configured by a prism unit configured by pasting a triangular prism on the surface of the quadrilateral prism on which the polarization synthesis film is formed, The first and/or second pumping light is totally reflected by the total reflection film, then enters the multiplexing film, where it is multiplexed with the signal light, and the combined signal light and the first as well as/
Alternatively, the second pumping light is configured to enter the Er-doped optical fiber.

INDUSTRIAL APPLICATION FIELD The present invention relates to an optical fiber amplifier that directly amplifies signal light by inputting signal light and pumping light (excitation light) into a doped fiber doped with a rare earth element.

In optical fiber communication systems currently in practical use, repeaters are inserted at fixed distances to compensate for optical signal attenuation due to optical fiber loss. The repeater is configured to convert an optical signal into an electrical signal using a photodiode, amplify the signal using an electronic amplifier, convert it into an optical signal using a semiconductor laser, etc., and send it out again to the optical fiber transmission line. If this optical signal can be directly amplified as an optical signal with low noise, the optical repeater can be made smaller and more economical.

Therefore, research into optical amplifiers that can directly amplify optical signals is actively underway, and the optical amplifiers that are the subject of research can be roughly divided into: ■ Rare earth elements (Er).

There are three types of amplifiers: one that combines an optical fiber doped with Nd, Yb, etc.) and pumping light, one that uses a semiconductor laser doped with rare earth elements, and one that uses the nonlinear effect in the optical fiber to stimulate Raman amplifiers and stimulated Prillouin amplifiers. .

Among these, the optical amplifier that combines rare earth element-doped optical fiber and pumping light has excellent characteristics such as no polarization dependence, low noise, and low coupling loss with the transmission line. It is expected that this technology will dramatically increase the transmission relay distance in optical fiber transmission systems and enable the distribution of optical signals to a large number of users.

Er-doped optical fibers doped with Er as a rare earth element are generally used for amplification in the 1.55 μm band used in optical fiber communications.

BACKGROUND OF THE INVENTION FIG. 6 shows the principle of optical amplification using a rare earth element-doped optical fiber. 2 is an optical fiber composed of a core 4 and a cladding 6, and the core 4 is doped with Er (erbium). When pumping light (excitation light) with a wavelength of, for example, 1.48 μm is incident on such an Er-doped optical fiber 2, Er atoms are excited to a high energy level. For example, when signal light with a wavelength of 1.55 μm enters the Er atoms in the optical fiber 2 excited to a high energy level, the Er atoms transition to a lower energy level, but at this time, the optical guidance Emission occurs, the power of the signal light gradually increases along the optical fiber, and the signal light is amplified.

FIG. 7 shows a schematic configuration of a conventional Er-doped optical fiber amplifier based on the amplification principle described above. 10 is a polarization coupler, and this polarization coupler 10 includes an optical fiber 11.
．． A first pumping light having a horizontally polarized wave plane and a second pumping light having a vertically polarized wave plane are respectively incident through the polarization coupler 12, and these pumping lights are combined by the polarization coupler 10 and output. The wavelength of both the first pumping light and the second pumping light is, for example, 1.48 μm. The polarization coupler 10 includes two triangular prisms 13 and 14 and a polarization coupling film 15.
It has a polarization coupling prism unit 16 having a structure sandwiching the polarization coupling prism unit 16.

A first beam having a horizontal polarization plane incident from the optical fiber 11
The pumping light is collimated by the collimating lens 17, enters the polarization coupling prism unit 16, and passes through the polarization coupling film 15 as it is. On the other hand, optical fiber 1
The second pumping light having a vertically polarized plane incident from 2 is collimated by the collimating lens 18 and then incident on the polarization coupling prism unit 16, and then the polarization coupling film 15 causes the second pumping light to enter the polarization coupling film 15 on the same optical path as the transmission optical path of the first pumping light. reflected. Therefore, the light emitted from the polarization coupling prism unit 16 is a combination of the first pumping light and the second pumping light, and this combined pumping light is focused by the lens 19 and input to the optical fiber 20. . The optical fiber 21 is connected to the optical fiber 20 by a connection adapter 22, and the first and second pumping lights transmitted through the optical fiber 20 and 21 are input to a multiplexer 23 and transmitted through the optical fiber 28. The received signal light is combined with, for example, a 1.55 μm band signal light.

The multiplexer 23 includes a multiplexing prism 26 in which a multiplexing film 25 made of a dielectric multilayer film or the like is formed on the inclined surface of a triangular prism 24, and the first and second optical fibers from the optical fiber 21 are
The pumping light is collimated by the collimating lens 27, enters the multiplexing prism 26, passes through the multiplexing film 25, and is emitted. On the other hand, the signal light having a wavelength of 1.55 μm, for example, transmitted through the optical fiber 28 is collimated by the collimating lens 29, then enters the multiplexing prism 26, is reflected by the multiplexing film 25, and becomes the transmission optical path of the pumping light. The light is emitted onto the same optical path. The signal light and pumping light thus combined are focused by the lens 30 and input into the Er-doped optical fiber 31, where the signal light is amplified based on the above-described principle.

In the configuration of the second conventional example, the first pumping light and the second pumping light are combined by the polarization coupler 10 because the single conductor laser (
The purpose is to use two semiconductor lasers to increase the output of the pumping light when the output of the laser diode (LD) is not sufficient, and when the output of the semiconductor laser is sufficient, only one of the pumping lights is used. A redundant configuration is possible.

Problems to be Solved by the Invention In the Er-doped optical fiber amplifier, as described above, a laser beam with a wavelength of 1.55 μm is used as the signal light, and a laser beam with a wavelength of 1.48 μm is used as the pumping light. In this case, when the wavelength difference between the signal light and the pumping light is small, the angle of incidence of the signal light on the multiplexing film must be less than 45° to achieve sufficient multiplexing of the signal light and the pumping light. There is a problem in that the signal light cannot be made perpendicular or parallel to the optical path of the bomb pink light to be incident on the multiplexing prism, making the arrangement of optical components such as the multiplexing prism complicated.

In addition, in the conventional configuration, the polarization coupler and the multiplexer were formed separately from each other, so the structure of the optical coupler that couples the signal light and pumping light into the Er-doped optical fiber is complicated. There was a problem with getting bigger.

The present invention has been made in view of these points, and its purpose is to provide a multiplexer that can input signal light and pumping light with a small wavelength difference at right angles or in parallel to each other by polarization coupling. An object of the present invention is to provide an optical fiber amplifier that is integrated with a device.

Means for Solving the Problem A first pumping light and a second pumping light whose polarization directions are orthogonal to each other are combined by a polarization coupler and emitted on the same optical axis, and the first and second pumping lights from the polarization coupler are /Or in an optical fiber amplifier that directly amplifies the signal light by combining the second pumping light and the signal light by a multiplexer and inputting the combined signal into an Er-doped optical fiber, the polarization coupler and the multiplexer A wave device is integrally formed from one prism unit.

This prism unit has a total reflection film formed on one surface of the first prism that defines the included angle, and a multiplexing film formed on the other surface, and the multiplexing film is formed on the other surface. The other surface of the first prism formed has a first included angle that is an angle that can sufficiently achieve multiplexing of the signal light and the pumping light, and a second included angle that is opposite to the first included angle is 45° on each side. A shaped prism is attached such that the first included angle is adjacent to the included angle of the first prism, and a polarized wave synthesis film is formed on the surface of the quadrilateral prism that faces the surface on which the multiplexed film is formed. ,
It is constructed by pasting a triangular prism on the surface of the quadrilateral prism on which the polarization synthesis film is formed.

Then, the first and/or second pumping light is totally reflected by the total reflection film of the prism unit, and then enters the multiplexing film, where it is multiplexed with the signal light and is multiplexed. The signal light and the first and/or second pumping light are transmitted to the Er
The beam is configured to be incident on a doped optical fiber.

As another configuration of the prism unit that integrates the polarization coupler and the multiplexer, a total reflection film is formed on one surface of the first prism that defines the included angle of 45°. At the same time, a multiplexing film is formed on the other surface of the first prism, and a first included angle between the first slope and the bottom surface is formed on the other surface of the first prism on which the multiplexing film is formed. A triangular prism having a second included angle of 45° between the second slope and the bottom surface, which is an angle that can sufficiently achieve wave combining, is attached such that the first included angle is adjacent to the included angle of the first prism, A polarization synthesis film may be formed on the second slope of the triangular prism, and a parallelogram prism may be attached on the second slope of the triangular prism on which the polarization synthesis film is formed.

Preferably, the signal light component is reflected at the interface between the first prism and the quadrilateral prism or the interface between the first prism and the triangular prism, through which the first and/or second pumping light passes. /Or a filter film that transmits the second pumping light is arranged.

Operation: By integrating a polarization coupler and a multiplexer as one prism unit, the configuration of an optical coupler that multiplexes and inputs signal light and pumping light into an Er-doped optical fiber is simplified. Furthermore, the optical path of the pumping light and the optical path of the signal light incident on the prism unit can be made perpendicular or parallel to each other.

Furthermore, in a configuration in which a filter film is provided that reflects the signal light wavelength component and transmits the first and/or second pumping light, the signal light wavelength component of the pumping light can be blocked with a high attenuation amount, and the S/N ratio of the signal light can be reduced. can be improved.

Embodiments Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram of an embodiment of the present invention. 32 is a prism unit that integrates a polarization coupler and a multiplexer, and includes a prism 33 having an included angle of 45° and a quadrilateral prism 36.
and a right-angled isosceles triangular prism 40 are pasted together. A total reflection film 34 formed of a dielectric multilayer film is formed on one surface of the prism 33 defining an included angle of 45°.
is formed, and on the other surface, a multiplexing film 35 also made of a dielectric multilayer film is formed by means such as vapor deposition. The transmission characteristics of the multiplexing film 35 are as shown in FIG. 3, and signal light in the wavelength band of 1.55 μm is transmitted.
The first and second pumping lights having a wavelength of 1.48 μm have a characteristic of being reflected. Further, at the interface between the prism 33 and the quadrilateral prism 36 through which the pumping light passes, there is provided a filter film 37 having transmission characteristics as shown in FIG. 4 that reflects the signal light wavelength component and transmits the pumping light. There is.

The quadrilateral prism 36 has a first included angle of 22.5° and a second included angle of 45° opposite the first included angle, and has a second included angle of 22.5°.
2. The quadrilateral prism 36 is attached to the prism 33 such that the first included angle is adjacent to the 45° included angle of the prism 33.
affixed to.

On the surface of the quadrilateral prism 360 defining the second included angle of 45°, a polarization synthesis film 38 made of a dielectric multilayer film is formed by vapor deposition or the like. The transmission characteristics of the polarization synthesis film 38 are as shown in FIG.
The second pumping light P2, which is S-polarized light with a wavelength of 1.48 μm and has a vertical polarization plane, is reflected.

Furthermore, a right-angled isosceles triangular prism 40 is attached on the surface of the quadrilateral prism 36 on which the polarization synthesis film 38 is formed. Then, on the surface of the triangular prism 40,
On the surface of the quadrilateral prism 36, filter films 41 and 42 having the same characteristics as the filter film 37 are provided, which reflect the signal light wavelength component and transmit the pumping light.

43° and 44 are antireflection films.

However, the signal light S in the wavelength band of 1.55 μm is transmitted through the ferrule 4.
The light is emitted from the single mode optical fiber 45 inserted into the optical fiber 6, is collimated by the lens 47, enters the prism unit 32, passes through the multiplexing film 35, is emitted from the prism unit 32, and is focused by the lens 54. The first pumping light PI having a wavelength of 1.48 μm and having a horizontal polarization plane is inputted to the Er-doped optical fiber 55 inserted into the ferrule 56, and is emitted from the polarization maintaining optical fiber 48 inserted into the ferrule 49. 50 and the signal light wavelength component is removed by a filter film 41, the light enters the prism unit 32, passes through the polarization synthesis film 38, and continues straight. Second pumping light P1 with a wavelength of 1.48 μm and a vertical polarization plane
is emitted from the polarization-maintaining optical fiber 51 inserted into the ferrule 52, collimated by the lens 53, the signal light wavelength component is removed by the filter film 42, and then input to the prism unit 32, where it enters the polarization synthesis film 38.
It is reflected by and emitted onto the same optical path as the transmission optical path of the first pumping light P, and the first pumping light P1 and the second pumping light P2 are combined.

The reason why the first pumping light and the second pumping light are combined by the polarization combining film 38 is that when the output of the semiconductor laser (LD) that emits the pumping light is not sufficient, the two This is to combine pumping light and increase its output. When the output of the pumping light source is sufficient, only one pumping light source can be driven to provide redundant pumping light.

The first and/or second pumping light combined by the polarization combining film 38 passes through the filter film 37 to further attenuate the signal light wavelength component of the pumping light.
It is totally reflected by the total reflection film 34 and the incident angle is smaller than 45°,
For example, it enters the multiplexing film 35 at an incident angle of about 20'', is reflected by the multiplexing film 35, and is emitted on the same optical path as the transmission optical path of the signal light, and the signal light and the first and/or second pumping light. are combined.

The signal light multiplexed by the multiplexing film 35 in this way and the first and/or
Alternatively, the second pumping light is focused by the lens 54 and input to the Er-doped optical fiber 55 inserted into the ferrule 56, and the signal light is amplified based on the above-described principle and sent out to the transmission path.

In this embodiment, a prism 33 having an included angle of 45°,
Quadrilateral prism 36 and right isosceles triangular prism 40
are bonded together to form a prism unit 32 that integrates a polarization coupler and a gold wave device, so when combining signal light with a small wavelength difference and pumping light, the pumping light is completely reflected by the total reflection film 34. Since the light can be reflected and made incident on the multiplexing film 35, the optical path of the pumping light and the optical path of the signal light can be set to be perpendicular or parallel to each other with respect to the prism unit 32.

Next, referring to FIG. 5, a block diagram of a prism unit according to another embodiment of the present invention is shown.

In this figure, components that are substantially the same as those of the embodiment shown in FIG. 1 are designated by the same reference numerals.

The prism unit 62 of this embodiment is constructed by attaching a prism 33 having an included angle of 45 degrees, a triangular prism 64, and a parallelogram prism 65 as shown.

The triangular prism 64 has an included angle of 22.5° between the first slope 64a and the bottom surface 64c, and the angle between the second slope 64b and the bottom surface 64 is 22.5°.
The included angle with 4C is 45°. Inclination angle 4
A wave combining film 35 and a filter film 37 are arranged between the prism 33 having an angle of 5° and a triangular prism 64, and a polarization combining film 38 is arranged at the interface between the triangular prism 64 and the parallelogram prism 65. There is. By employing the prism unit 62 having such a configuration, the first and second pumping lights PP2 and the signal light S can be made to enter the prism unit 62 from the same direction.

Effects of the Invention As detailed above, the optical fiber amplifier of the present invention has an integrated configuration of a polarization coupler and a multiplexer as a prism unit, which has the effect of reducing the number of optical components and reducing costs. play.

Further, since the first pumping light and the second pumping light are combined to increase the output of the pumping light, it is possible to suppress the output of the pumping light source and extend its life.

Furthermore, the signal light wavelength component contained in the pumping light can be blocked with a high attenuation amount depending on the number of filter films inserted, and the S/N ratio of the signal light can be improved.

[Brief explanation of the drawing]

Fig. 1 is a schematic configuration diagram of an embodiment of the present invention, Fig. 2 is a transmission characteristic diagram of a polarization combining film, Fig. 3 is a transmission characteristic diagram of a combining film, Fig. 4 is a transmission characteristic diagram of a filter film, Fig. 5 is a schematic diagram of a prism unit according to another embodiment of the present invention, Fig. 6 is a schematic diagram showing the principle of optical amplification using a doped optical fiber doped with a rare maxillary element, and Fig. 7 is a schematic diagram of a conventional example. FIG. 32.62... Prism unit, 33... Prism having an included angle of 45°, 34...
Total reflection film, 35... Combined film, 36... Quadrilateral prism, 37.41.42... Filter film, 38... Polarization synthesis film, 40... Right-angled isosceles triangular prism, 43.44...
-Anti-reflection film, 55...Er-doped optical fiber, 64...triangular prism, 65...parallelogram prism.

Claims (1)

[Claims] 1. First pumping lights (P_
1) and the second pumping light (P_2) are combined by a polarization coupler and emitted on the same optical axis, and the first and/or second pumping light (P_1, P_2) and the signal from the polarization coupler are combined. In an optical fiber amplifier that directly amplifies signal light by multiplexing light (S) with a multiplexer and inputting the signal light into an Er-doped optical fiber (55), the first prism has an included angle of 45°. A total reflection film (34) is formed on one surface defining the included angle of (33), and a multiplexing film (35) is formed on the other surface, and the multiplexing film (35) is formed on the aforementioned The other surface of the first prism (33) has a first included angle that is an angle that can sufficiently combine the signal light and the pumping light, and a second included angle that is opposite to the first included angle of 45 degrees. A quadrilateral prism (36) is attached such that the first included angle is adjacent to the included angle of the first prism (33), and the quadrilateral prism faces the surface on which the multiplexing film (35) is formed. A polarization synthesis film (38) is formed on the surface of (36), and the quadrilateral prism (3) on which the polarization synthesis film (38) is formed is formed.
6) The polarization coupler and the multiplexer are integrally configured by a prism unit (32) configured by pasting a triangular prism (40) on the surface of the first and/or second pumping light. (P_1, P_2) are totally reflected by the total reflection film (34) and then incident on the multiplexing film (35), where they are combined with the signal light and are multiplexed. An optical fiber amplifier, characterized in that the signal light and the first and/or second pumping light are input into the Er-doped optical fiber (55). 2. The signal light component is reflected on the bonded surface of the first prism (33) and the quadrilateral prism (36) through which the first and/or second pumping light passes, and the first and/or second pumping light is transmitted. 2. The optical fiber amplifier according to claim 1, further comprising a filter membrane (37) that transmits the light. 3. First pumping light (P_
1) and the second pumping light (P_2) are combined by a polarization coupler and emitted on the same optical axis, and the first and/or second pumping light (P_1, P_2) and the signal from the polarization coupler are combined. A first prism (33) having an included angle of 45° in an optical fiber amplifier that directly amplifies the signal light by multiplexing the signal light with a multiplexer and inputting the signal light into an Er-doped optical fiber (55). A total reflection film (34) is formed on one surface defining the included angle, and a multiplexing film (35) is formed on the other surface, the first prism having the multiplexing film (35) formed thereon. (33) on the other surface of the first slope (6
The first included angle between 4a) and the bottom surface (64c) is the angle that can sufficiently combine the signal light and the pumping light, and the second
The second included angle between the slope (64b) and the bottom surface (64c) is 45°, and the first included angle is 45° between the triangular prism (64).
A polarization synthesis film (38) is attached so as to be adjacent to the included angle of the prism (33), and a polarization synthesis film (38) is formed on the second slope (64b) of the triangular prism (64). A prism unit (
62), the polarization coupler and the multiplexer are integrally configured, and the first and/or second pumping light (P_1,
P_2) is totally reflected by the total reflection film (34) and then enters the multiplexing film (35), where it is multiplexed with the signal light and the multiplexed signal light and the first and/or second pumping light into the Er-doped optical fiber (55).
An optical fiber amplifier characterized in that the optical fiber is made incident on the optical fiber. 4. The signal light component is reflected on the bonded surface of the first prism (33) and the triangular prism (64) through which the first and/or second pumping light passes, and the first and/or second pumping light is transmitted. 4. The optical fiber amplifier according to claim 3, further comprising a filter membrane (37). 5. A filter film (41, 42) that reflects the signal light component and transmits the first and/or second pumping light on the end surface of the prism unit (32, 62) on which the first and/or second pumping light is incident. 5. The optical fiber amplifier according to claim 2, further comprising: an optical fiber amplifier.