JP2003188444A - Optical amplifier - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical amplifier which can eliminate connecting optical fiber between components for forming the optical amplifier and can further reduce the size thereof in comparison with existing fiber. <P>SOLUTION: The optical amplifier is formed by respectively connecting fiber collimeters 4 to 7 to one-side ends of input optical fiber 1 and output optical fiber 2 and both ends of amplifying fiber 3, and by fixing, on the common substrate 10, the amplifying fiber 3, the fiber collimeters 4 to 7, a laser diode 12 for supplying the excited light beam, and an optical multiplexing/ branching filter 11 which is composed of a dielectric material multilayer film filter for multiplexing the signal beam and excited light beam. In this optical amplifier, it is further preferable to provide a micro lens 13, mirrors 14 to 16 or a prism on the substrate. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to wavelength division multiplexing (WD).
M) An optical amplifier used in optical communication technology such as transmission, and more particularly to a miniaturized optical amplifier.

[0002]

2. Description of the Related Art With the progress of optical communication technology, optical communication systems using optical fibers have become an important social infrastructure.
In order to extend the distance and increase the capacity of optical communication, an optical amplifier is indispensable for amplifying an optical signal propagating in an optical fiber. Conventionally, optical amplifiers have been widely used in long-distance optical communication systems such as undersea communication systems and backbone systems for terrestrial communication, but due to the spread of the Internet in recent years, the demand for large-capacity optical communication systems is increasing, Even in an optical communication system of a relatively short distance, an optical amplifier has come to be used in order to extend the communication distance and improve the reliability.

For this type of optical amplifier, a rare earth-doped optical fiber whose core is doped with ions of a rare earth element such as erbium (Er), neodymium (Nd), thulium (Tm) and praseodymium (Pr) is generally used. The old optical amplifier is used.

FIG. 3 is a schematic configuration diagram showing an example of a conventional optical amplifier. In FIG. 3, reference numeral 103 is an amplification optical fiber. An optical multiplexer / demultiplexer 111 is connected to the incident end of the amplification optical fiber 103. This optical multiplexer / demultiplexer 11
1 has two incident ends, one of which has the signal light propagating through the optical transmission line 101, and the other of which has an incident end.
The excitation light oscillated from the excitation light source 112 is made to enter, respectively. The signal light and the pumping light are combined by the optical multiplexer / demultiplexer 111 and are incident on the amplification optical fiber 103. The signal light receives the energy of the pumping light inside the amplification optical fiber 103, is amplified, and is emitted to the optical transmission line 102 again.

The optical amplifier further includes an optical isolator 120 at the front stage of the optical multiplexer / demultiplexer 111 and at the rear stage of the amplification optical fiber 103 in order to block the return light and stabilize the operation of the pumping light source 112. It is provided.
Further, in order to measure the optical power before and after amplification of the signal light, a total of two monitor means 121 are provided on the input side and the output side. The monitor means 121 includes a branch coupler 122.
And a photodetector 123. A part of the signal light is branched and taken out by the branch coupler 122, and the power of this branched light can be measured and monitored by the photodetector 123.

In the conventional optical amplifier, the optical multiplexer / demultiplexer 1
Optical components such as 11, the pumping light source 112, the optical isolator 120, and the branching coupler 122 are usually connected via a connecting optical fiber.

[0007]

In recent years, there is an increasing demand for high speed and large capacity optical communication. In order to improve the degree of integration of the optical communication system, it is necessary to further downsize the optical amplifier. Therefore, various proposals have been made for reducing the size of the optical amplifier. For example, in order to reduce the number of parts and the occupied area, two or more types such as the optical multiplexer / demultiplexer 111 and the optical isolator 120 are used. The functions of the optical components are combined to manufacture an optical composite component housed in a single housing.

However, even if this kind of optical composite component is used, the connecting optical fiber is arranged between the optical composite component and the amplifying optical fiber or between the optical composite component and another optical component. Therefore, a space corresponding to the bending radius (20 to 30 mm) of the connecting optical fiber is required around the optical component. As described above, the size of the optical amplifier is restricted by the bending radius of the connecting optical fiber, so that further miniaturization becomes extremely difficult.

The present invention has been made in view of the above circumstances, does not require an optical fiber for connection between parts constituting an optical amplifier, and can be further miniaturized as compared with the conventional optical fiber. It is an object to provide an amplifier.

[0010]

Means for Solving the Problems The problems are as follows: an input optical fiber for inputting the signal light, an output optical fiber for outputting the signal light, an amplifying optical fiber for amplifying the signal light, and the amplifying optical fiber. A laser diode that supplies pumping light to an optical fiber, and an optical multiplexing / demultiplexing filter that combines the pumping light with the signal light to enter the amplification optical fiber, the input optical fiber and the output light A fiber collimator is connected to one end of the fiber and both ends of the amplification optical fiber, and the amplification optical fiber, the fiber collimator, the laser diode, and the optical multiplexing / demultiplexing filter are provided on a common substrate. The signal light is fixed on the upper side, and the signal light is emitted from one end of the input optical fiber until it enters the amplification optical fiber, and for the amplification. Is emitted from the fiber, during the period until is incident on one end of the output optical fiber,
It is adapted to propagate through a space without passing through a waveguide, the excitation light is emitted from the laser diode, until it enters the amplification optical fiber through the optical multiplexing and demultiplexing filter, It is solved by an optical amplifier characterized in that it is adapted to propagate in space without passing through a waveguide.

With such a structure, a connecting optical fiber for connecting the components of the optical amplifier is not required, and the size can be remarkably reduced as compared with the conventional one.

In the optical amplifier of the present invention, one or a plurality of microlenses are further provided on the substrate, and the microlenses focus either one or both of the signal light and the excitation light. It is preferable. As a result, it is possible to suppress an increase in loss due to divergence of light and generation of noise.

Further, one or a plurality of mirrors or prisms may be provided on the substrate so that either one or both of the signal light and the excitation light are reflected to change the direction. As a result, the degree of freedom in arranging the components can be improved, the components can be arranged in a smaller area, and the optical amplifier can be further downsized.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail based on the embodiments. FIG. 1 is a schematic configuration diagram showing a first embodiment of an optical amplifier of the present invention. In FIG. 1, reference numeral 10 is a substrate. The substrate 10 is made of plastic or metal and has a length of 70 to 110 mm and a width of 40 to 5
It is a plate-shaped material having a thickness of 0 mm and a thickness of 0.5 to 1.0 mm.
The shape of the substrate 10 can be a desired shape such as a rectangle, a circle, and an ellipse. Further, in order to prevent irregular reflection of light, the surface may be painted black or the like.

This optical amplifier comprises an input optical fiber 1, an output optical fiber 2 and an amplification optical fiber 3,
The signal light input from the input optical fiber 1 is amplified by the amplification optical fiber 3 and output from the output optical fiber 2. As the input optical fiber 1 and the output optical fiber 2, ordinary silica optical fibers are used.

A first fiber collimator 4 is connected to one end of the input optical fiber 1, and a second fiber collimator 5 is connected to one end of the output optical fiber 2. The other ends of the input optical fiber 1 and the output optical fiber 2 can be connected to an external optical transmission line. The first fiber collimator 4 and the second fiber collimator 5 are provided on the substrate 10
It is fixed on the top by means such as adhesion.

The connection type for connecting the input optical fiber 1 and the output optical fiber 2 to an external optical transmission line may be a pigtail type, or a connector may be provided at the tip and connected via this connector. You can also choose to do so. The lengths of the input optical fiber 1 and the output optical fiber 2 are not particularly limited as long as they can be connected to an external optical transmission line. For example, in the case of a pigtail, it can be projected outside the substrate 10. Further, when the receptacle is provided on the peripheral portion of the substrate 10, the distance between the fiber collimator and the receptacle may be very short.

The amplification optical fiber 3 has a rare-earth element such as erbium added to the core or to the clad portion close to the core at about 500 to 1500 ppm (doped), and has an element diameter of 123 to 127 μm and a long length. 10
A single mode optical fiber of ~ 30 m, for example,
It is wound around a bobbin or the like (not shown) and is fixed on the substrate 10 via the bobbin or the like. The diameter of the bobbin is determined by the allowable bending radius of the amplification optical fiber 3,
Generally, it is 40 to 50 mm.

A third fiber collimator 6 and a fourth fiber collimator 7 are provided at both ends of the amplification optical fiber 3 in order to suppress loss of signal light and pumping light. The third fiber collimator 6 and the fourth fiber collimator 7 are fixed on the substrate 10 by means such as adhesion. In the present embodiment, the first fiber collimator 4 and the third fiber collimator 6 are opposed to each other with a predetermined gap, and
The second fiber collimator 5 and the fourth fiber collimator 7 face each other with a predetermined gap. The distance between the first fiber collimator 4 and the third fiber collimator 6 and the distance between the second fiber collimator 5 and the fourth fiber collimator 7 are generally 2
It is set to 0 to 40 mm.

The first to fourth fiber collimators 4 to
A known fiber collimator having a collimating lens such as a GRIN lens, a spherical lens or an aspherical lens can be used as 7. The dimensions of the fiber collimators 4 to 7 used in this embodiment are 2-3 m in diameter.
m, the length is about 5 to 10 mm.

Then, the signal light is emitted from the first fiber collimator 4 and is incident on the amplification optical fiber 3 via the third fiber collimator 6 and during the amplification optical fiber. From the third to the fourth fiber collimator 7, the space is propagated through the space without passing through the waveguide between the time when the light is emitted through the fourth fiber collimator 7 and the time when the light is incident on the second fiber collimator 5.

In front of the third fiber collimator 6,
An optical multiplexing / demultiplexing filter 11 is installed. A laser diode 12 is installed near the optical multiplexing / demultiplexing filter 11 (outside the path of the signal light). The laser diode 12 is directed toward the optical multiplexing / demultiplexing filter 11,
The substrate 1 is separated from the optical multiplexing / demultiplexing filter 11 via a predetermined space.
It is fixed on the surface by means such as adhesion. The distance between the laser diode 12 and the optical multiplexing / demultiplexing filter 11 is
It is 5 to 12 mm.

The optical multiplexing / demultiplexing filter 11 is, for example, appropriate at a position and an angle where the signal light emitted from the first fiber collimator 4 and the excitation light emitted from the laser diode 12 are incident. It is fixed on the substrate 10 through such a support member.

Between the optical multiplexing / demultiplexing filter 11 and the laser diode 12, a microlens 13 for collecting the excitation light is provided. The microlens 13 is fixed on the substrate 10 via, for example, an appropriate supporting member. As a result, the excitation light emitted from the laser diode 12 propagates in the space without passing through the waveguide until it enters the amplification optical fiber 3 through the microlens 13 and the optical multiplexing / demultiplexing filter 11. It is like this.

As the optical multiplexing / demultiplexing filter 11, generally,
A dielectric multilayer filter is used that allows light of a certain wavelength to pass therethrough and reflects light of another wavelength. For example, in the arrangement shown in FIG. 1, a dielectric multilayer filter that transmits signal light and reflects excitation light is used. However, by changing the arrangement of the optical multiplexing / demultiplexing filter 11 and the laser diode 12, conversely, a dielectric multilayer filter having a characteristic of reflecting signal light and passing excitation light can be used. Optical multiplexing / demultiplexing filter 11 used in the present embodiment
The dimensions are generally 1-3 mm wide and 0.5 mm thick
Is.

The laser diode 12 is a diode including a laser element that oscillates a laser having a predetermined wavelength.
It is already widely used as a pumping light source for optical amplifiers. The laser diode 12 used in the present embodiment generally has a diameter of 5 to 6 mm and a length of 3 to 4 mm. The oscillation wavelength band of the laser diode 12 is determined by the type of the amplification optical fiber 3, but for example, when the amplification optical fiber 3 is an erbium-doped optical fiber,
Generally, 970 to 985 nm band, or 1450 to
The 1495 nm band is used.

The microlens 13 may be installed arbitrarily, but by disposing it at a predetermined position between the laser diode 12 and the optical multiplexing / demultiplexing filter 11, the divergence of the excitation light is suppressed and the amplification efficiency is improved. At the same time, it is possible to suppress an increase in noise due to the scattered pumping light being scattered in the optical amplifier. As the microlens 13, a known one made of optical glass or the like can be used. The microlens 13 generally has a diameter of 1 to 3 mm and a length of 2 to 5 mm, and a focal length of 1 to 6
mm.

Further, in order to prevent the oscillation of the amplification optical fiber 3, the optical isolator 20 can be installed so that the propagation direction of the signal light is the forward direction, if necessary. When the optical isolator 20 is installed, it may be installed on either the input side or the output side. However, in order to improve the stability of the optical amplifier, as shown in FIG. It is preferable to install them in both.

The optical isolator 20 can be realized, for example, by combining a Faraday rotator and a birefringent crystal. The dimensions of the optical isolator 20 used in this embodiment are generally 3 to 5 mm in diameter and 1 in length.
It is 0 to 15 mm.

Further, monitor means 21 may be provided to monitor the signal light. Such monitor means 21
As a configuration of, for example, a configuration including an optical branching filter 22 for extracting a part of the signal light and a photodiode 23 for detecting the extracted branching signal light can be considered. FIG. 1 illustrates a mode in which two monitor means 21 are provided in order to monitor both the input signal light and the output signal light. According to such an embodiment, for example, the gain of the optical amplifier can be acquired and controlled. However, only one of the input signal light and the output signal light may be monitored. In this case, for example, control that makes the power of the output signal light constant can be considered. It is also possible to monitor the reflected light returning from the outside via the output optical fiber 2.

As the optical branching filter 22, a filter formed so that the transmitted light and the reflected light are branched at a predetermined branching ratio in the wavelength band of the signal light is used. The optical branching filter 22 having such characteristics can be manufactured as a dielectric multilayer filter. The size of the optical branching filter 22 used in the present embodiment has a width of 1 to 3 mm,
The thickness is about 0.5 mm.

As the photodiode 23, for example,
It is possible to use a device having a characteristic of outputting a current substantially proportional to the power of the incident light. The dimensions of the photodiode 23 are generally 4-5 mm in diameter and 2-3 in length.
mm. The distance between the photodiode 23 and the light branching filter 22 is generally 5 to 20 mm.

The operation principle of the optical amplifier of the present embodiment is similar to that of the conventional optical amplifier, in which the signal light and the pumping light are made incident on the amplification optical fiber and the rare earth element contained in the amplification optical fiber 3 is added. By the action of ions, the energy of the excitation light is given to the signal light to amplify it.

The optical amplifier of this embodiment is different from the conventional one in that the signal light inputted from the outside and the pumping light oscillated from the laser diode 12 are amplified by the optical fiber 3 for amplification.
Conventionally, a component having an optical fiber for connection was used as a component constituting an optical system for making the signal light incident on or output to the outside, whereas in the present embodiment, That is, the unnecessary parts of the connecting optical fiber are used and they are arranged on the common substrate 10. Therefore, it becomes possible to manufacture an optical amplifier which is significantly smaller than the conventional one.

Next, a second embodiment of the optical amplifier according to the present invention will be described. FIG. 2 is a diagram showing an example of the optical amplifier according to the second embodiment. In FIG. 2, the same reference numerals as those used in FIG. 1 mean that they have the same configurations as those in FIG. In the present embodiment, the amplification optical fiber 3 is arranged on the back side of the substrate 10. The amplification optical fiber 3 has a radius whose lower limit is the allowable bending radius,
It is wound around a bobbin (not shown). The diameter of this bobbin or the like is generally 40 to 50 mm.

The substrate 10 is made of plastic or metal and has a length of 40 to 50 mm, a width of 40 to 50 mm and a thickness of 0.
It is a plate-shaped material of about 1 to 1.0 mm. The length and width of the substrate 10 are at least larger than the diameter of the bobbin or the like so that the amplification optical fiber 3 does not protrude outside the substrate 10.

A through hole 30 is provided on the substrate 10, and the tip of the amplification optical fiber 3 is inserted into the through hole 30 and faces the front side of the substrate 10. A third fiber collimator 6 and a fourth fiber collimator 7 are connected to both ends of the amplification optical fiber 3. This third
The fiber collimator 6 and the fourth fiber collimator 7 are installed on the substrate 10.

In a region between the third fiber collimator 6 and the fourth fiber collimator 7, a first fiber collimator 4 to which the input optical fiber 1 is connected and an output optical fiber 2 to which the output optical fiber 2 is connected. Two fiber collimators 5 are installed and fixed on the substrate 10. The end face of the first fiber collimator 4 and the end face of the third fiber collimator 6 are in the same direction (right side in FIG. 2).
Looking at Similarly, the end surface of the second fiber collimator 5 and the end surface of the fourth fiber collimator 7 face the same direction (rightward in FIG. 2).

On the front surface of the first fiber collimator 4,
The mirror 14 is installed via the monitor means 21 and the optical isolator 20. The mirror 14 is fixed on the substrate 10 at an angle such that the signal light emitted from the first fiber collimator 4 is reflected upward in FIG. The monitor means 21 and the optical isolator 20 are fixed to predetermined positions on the substrate 10, respectively.

The optical multiplexing / demultiplexing filter 11 is installed at a position where the signal light reflected by the mirror 14 is incident. Moreover, the position of the optical multiplexing / demultiplexing filter 11 is set so that the signal light incident on the optical multiplexing / demultiplexing filter 11 is reflected toward the third fiber collimator 6. Therefore, the signal light emitted from the output optical fiber 1 via the first fiber collimator 4 enters the amplification optical fiber 3.

Further, the third fiber collimator 6
A laser diode 12 is installed via a microlens 13 on an extension line connecting the optical multiplexer / demultiplexer filter 11 and the optical multiplexer / demultiplexer filter 11. Optical multiplexing / demultiplexing filter 11 and microlens 13
Is 5 to 10 mm, and the distance between the microlens 13 and the laser diode 12 is 0.2 to 2.0 mm.

As a result, the excitation light emitted from the laser diode 12 enters the amplification optical fiber 3 via the microlens 13 and the optical multiplexing / demultiplexing filter 11. Here, it goes without saying that the characteristics of the optical multiplexing / demultiplexing filter 11 are such that the signal light is reflected and the excitation light is transmitted as described above.

A mirror 15 is installed in front of the fourth fiber collimator 7 connected to the amplification optical fiber 3, and in front of the second fiber collimator 5 connected to the output optical fiber 2. Means monitor means 21,
The mirror 16 is installed via the optical isolator 20. As a result, the signal light emitted from the amplification optical fiber 3 via the fiber collimator 7 is reflected by the mirror 15
After being reflected by the mirror 16 and then by the mirror 16, the light is reflected by the optical isolator 20 and the monitor means 21.
The light enters the output optical fiber 2.

As the mirrors 14 to 16, for example,
A dielectric multilayer mirror having a total reflection characteristic in a predetermined wavelength band can be preferably used. The dimensions of the mirrors 14-16 used in this embodiment generally range from 1 to 3 widths.
mm and the thickness is about 0.5 mm.

According to the second embodiment, the substrate 10
The optical system in which the spatial light propagates is arranged on the front side of, and the amplification optical fiber 3 is arranged on the back side. And mirror 1
4 to 16 are used to change the propagation direction of the signal light.
By doing so, the size of the optical amplifier can be further reduced.

In the second embodiment, the amplification optical fiber 3 is arranged on the back side of the substrate 10, but instead of this, an appropriate supporting member is used to move the amplification optical fiber 3 to the optical system. You may make it support above.

Although the present invention has been described with reference to the preferred embodiments, the present invention is not limited to the above embodiments, and various modifications can be made without departing from the gist of the present invention. It goes without saying that is possible. For example, the substrate 10 may be housed inside the housing to prevent damage to the components. In this case, the connecting means such as the pigtail or the connector is exposed to the outside of the housing. Examples of the material of the housing include plastic and metal. The shape of the housing is not particularly limited and can be a desired shape.

Although not shown in FIGS. 1 and 2, a gain equalizer may be provided. In the present embodiment, it is preferable to use a small gain equalizer composed of a dielectric multilayer filter, an etalon filter, or the like. The dimensions of such a gain equalizer are generally about 1 to 3 mm in width and about 0.5 mm in thickness.

As a pumping method for the width optical fiber 3, in the above-mentioned embodiment, the forward pumping in which the pumping light is made incident by being incident in the same direction as the traveling direction of the signal light is shown, but it is not limited to this. There is nothing to be done, and the backward pumping may be performed by pumping the pumping light in a direction opposite to the traveling direction of the signal light, or by providing two laser diodes 12 as pumping light sources, Bidirectional pumping may be performed in which pumping light is incident and excited in both directions, that is, the same direction as the signal light traveling direction and the opposite direction.

[0050]

As described above, according to the present invention,
An optical fiber for connection between the components that make up the optical amplifier is not required, and it is possible to manufacture an optical amplifier that can be made more compact than in the past. Further, since the number of connecting points of the connecting optical fiber is reduced and the connection loss due to the fusion splicing is reduced, the reliability of the optical amplifier is improved.

Particularly, when an optical system for propagating spatial light on the front side of the substrate 10 and an amplification optical fiber 3 on the back side are arranged, the allowable bending radius of the amplification optical fiber 3 is 20 m.
If m, the length and width of the optical amplifier are (allowable bending radius of the amplification optical fiber 3 20 mm) × 2 + (clearance 1 mm) × 2 + (plate thickness of the casing 1 mm) × 2 = 44 mm, and the thickness Can be about 9 to 12 mm.

[Brief description of drawings]

FIG. 1 is a diagram showing a first embodiment of an optical amplifier according to the present invention.

FIG. 2 is a diagram showing a second embodiment of an optical amplifier according to the present invention.

FIG. 3 is a schematic configuration diagram showing an example of a conventional optical amplifier.

[Explanation of symbols]

1 ... Input optical fiber, 2 ... Output optical fiber, 3 ... Amplifying optical fiber, 4-7 ... Fiber collimator, 10 ...
Substrate, 11 ... Optical multiplexing / demultiplexing filter, 12 ... Laser diode, 13 ... Microlens, 14-16 ... Mirror.

   ─────────────────────────────────────────────────── ─── Continued front page    F term (reference) 5F072 AB09 AK06 JJ01 KK05 KK30                       PP07 YY17                 5K002 AA06 CA13 DA02 FA01 FA03

Claims (3)

[Claims] 1. An input optical fiber for inputting signal light,
An output optical fiber that outputs a signal light, an amplification optical fiber that amplifies the signal light, a laser diode that supplies pumping light to the amplification optical fiber, and the pumping light that is multiplexed with the signal light An optical multiplexing / demultiplexing filter that is incident on an amplification optical fiber is provided, and a fiber collimator is connected to one ends of the input optical fiber and the output optical fiber and both ends of the amplification optical fiber, and the amplification light is used. A fiber, the fiber collimator,
The laser diode and the optical multiplexing / demultiplexing filter,
It is fixed on a common substrate, the signal light is emitted from one end of the input optical fiber, until entering the amplification optical fiber, and emitted from the amplification optical fiber, Until it is incident on one end of the output optical fiber, it is adapted to propagate in space without passing through a waveguide, the excitation light is emitted from the laser diode, the optical multiplexing and demultiplexing filter. An optical amplifier, characterized in that it propagates in a space without passing through a waveguide until it is incident on the amplification optical fiber via the optical fiber. 2. The optical amplifier according to claim 1, further comprising one or a plurality of microlenses provided on the substrate, the microlenses focusing either one or both of signal light and pump light. An optical amplifier characterized in that 3. The optical amplifier according to claim 1, further comprising one or a plurality of mirrors or prisms provided on the substrate, and either or both of the signal light and the excitation light are the mirrors. Alternatively, the optical amplifier is characterized in that it is reflected by a prism to be changed in direction.