JP3428892B2 - Optical amplifier - Google Patents

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art With the development of the information society, the amount of communication information tends to increase dramatically, and high-speed and large-capacity optical fiber communication has become a necessary and indispensable subject. In recent years, an optical transmission method such as wavelength division multiplexing (WDM) transmission has been studied as an approach to the high speed and large capacity. The wavelength division multiplex transmission is a method of transmitting optical signals (channels) having different wavelengths through one optical fiber. In addition, an optical fiber amplifier is being studied to increase the capacity of the signal light itself.

Of the optical fiber amplifiers, the erbium-doped fiber optical amplifier (EDFA) has been rapidly put into practical use in recent years, and its application range is expanding. EDFA
Is capable of collectively amplifying wavelength-multiplexed optical signals, and is expected as a simpler linear repeater to replace the conventional regenerative repeater in a WDM system. In addition, EDFA is an erbium-doped optical fiber,
By passing excitation light of a certain wavelength, the erbium ion in the erbium-doped optical fiber is excited to create an inverted population state of electrons, and the signal light is passed therethrough. The signal light is amplified by stimulated emission.

By the way, in an EDFA, it is known that a gain difference occurs between channels of wavelength-multiplexed signal light input to the EDFA due to absorption coefficient, stimulated emission coefficient, population inversion state, etc. of the erbium-doped optical fiber. There is.
Further, since the population inversion state changes depending on the intensity of the input signal light, the conventional EDFA has a problem that the gain also changes depending on the change of the intensity of the wavelength division multiplexed signal light. In particular, since the EDFA is used in a multi-stage connection as a linear repeater in a wavelength division multiplexing transmission system, when the gain changes with the input signal light intensity in a single EDFA, the change in the gain is integrated in the entire system. As a result, the change in gain becomes extremely large, which limits the transmission characteristics of wavelength division multiplexing transmission.

Therefore, studies have been made on an optical amplifier which makes the gain constant irrespective of the change in the intensity of the input signal light, for example, reference (1) J, F, Massicott, et al., Ele.
ctron. Lett., 30 (1994), p962.
An optical amplifier having a laser resonator as shown in FIG.

The optical amplifier shown in this document is shown in FIG.
0 is an optical amplifier as shown in FIG.
Reference numeral 20 denotes an input terminal for signal light, and 21 denotes an output terminal for signal light. Isolator 5 on the input terminal 20 side
Is provided, a fiber grating 9a as a light reflector is connected to the isolator 5, and an erbium-doped optical fiber 14 which is a rare earth-doped optical fiber is connected to the fiber grating 9a.
The erbium-doped optical fiber 14 has a wavelength division multiplexer 1
Pumping light source 41 and fiber grating 9b
Are connected to each other, the optical isolator 15 is connected to the fiber grating 9b, and the output terminal 21 is connected to the output side of the optical isolator 15 via the wavelength selective transmission filter 8.

The fiber gratings 9a, 9b,
The erbium-doped optical fiber 14, the excitation light source 41, and the wavelength division multiplexing optical demultiplexer 13 constitute a laser resonator. The erbium-doped optical fiber 14 is an amplifying medium that amplifies both the laser resonant light oscillated by the laser resonator and the signal light, and has a function of amplifying the light by stimulated emission by the pumping light generated from the pumping light source 41. ing. The fiber gratings 9a and 9b selectively reflect light of a predetermined wavelength, for example, 1520 nm, and the wavelength selective transmission filter 8 does not transmit the light of the specific wavelength reflected by the fiber gratings 9a and 9b. Is.

This laser resonator is a Fabry-Perot resonator in which the laser resonant light reciprocates in the laser resonator by the fiber gratings 9a and 9b. When the laser oscillation condition is satisfied by the gain of the erbium-doped optical fiber 14, it is 1520 nm. Laser oscillation occurs at the wavelength of. At this time, the gain in the erbium-doped optical fiber 14 is fixed by the laser oscillation condition, and the input terminal 20
The signal light input by is received by this fixed gain and is amplified. Therefore, in the laser resonator, as long as the laser oscillation condition is satisfied, a stable signal light gain can be obtained regardless of the intensity of the input signal light.
Also, the gain deviation between channels is kept constant.

The laser resonator is not limited to the Fabry-Perot resonator as described above, but is described in, for example, Document (2) H. Okamura "automatic copt.
ical-loss compensation wit
h Er-doped fiber amplifire
r "Electron Letters 23 (199
1) p2155. Alternatively, as disclosed in JP-A-8-116118, JP-A-8-345260, and the like, the same effect can be obtained by using a ring resonator.

[0010]

By the way, in recent years, there has been a demand for an optical amplifier whose output light level is constant irrespective of the intensity of the input signal light. However, the conventional optical amplifier having the laser resonator as described above is required. Since the amplifier keeps the gain constant regardless of the change in signal light intensity, the signal light output level from the optical amplifier changes according to the signal light intensity, regardless of the input signal light intensity. It does not meet the requirement that an optical amplifier is required to keep the signal light output level from the optical amplifier constant.

The present invention has been made in view of the above circumstances, and an object thereof is to provide an optical amplifier capable of outputting a constant level of amplified light regardless of the intensity and wavelength of the input signal light. It is in.

[0012]

In order to achieve the above object, the present invention has the following constitution as means for solving the problem. That is, the first invention has a laser resonator, and the laser resonator includes a first amplification medium for amplifying the laser resonance light, the laser resonance light, and a signal light incident on the laser resonator. Second amplification together
Of the amplifying medium, an optical multiplexer for multiplexing and introducing the signal light and the laser resonant light amplified by the first amplifying medium into the second amplifying medium, and amplified by the second amplifying medium. An optical demultiplexer for demultiplexing and extracting only the amplified signal light of the amplified signal light and the laser resonance light is provided, and the optical demultiplexer of the first amplification medium is provided according to the intensity of the signal light incident on the laser resonator. The problem is solved by having a configuration having a signal light intensity stabilizing means for keeping the amplified signal light intensity constant by changing the gain.

According to the second aspect of the present invention, in addition to the configuration of the first aspect of the present invention, a first pumping light source is connected to the first amplification medium, and the first amplification medium is the first amplification medium. 1. A rare-earth-doped optical fiber for amplifying light by stimulated emission of excitation light generated from one excitation light source, and the signal light intensity stabilizing means changes the intensity of the excitation light from the first excitation light source. Thus, a means for solving the problem is provided by having a configuration in which the gain of the first rare earth-doped optical fiber is changed to keep the amplified signal light intensity constant.

Further, in the third invention, in addition to the configuration of the first invention or the second invention, the second amplifying medium amplifies light by stimulated emission by pumping light generated from a pumping light source. The optical amplifier according to claim 1 or 2, comprising a second rare earth-doped optical fiber having the function of

Further, in the fourth invention, in addition to the configuration of the second invention, a second pumping light source different from the first pumping light source is connected to the second amplification medium, The second
The amplifying medium has a configuration including a second rare earth-doped optical fiber that amplifies light by stimulated emission by the excitation light generated from the second excitation light source, and is a means for solving the problem.

Furthermore, in addition to the configuration of the above-mentioned second invention, the fifth invention is such that a second pumping light source is connected to the second amplifying medium, and the second amplifying medium is the second amplifying medium. A second rare earth-doped optical fiber for amplifying light by stimulated emission by the excitation light generated from the first excitation light source, and pumping between the first pumping light source and the first and second rare earth-doped optical fibers. It has a structure in which a branching coupler for branching the light is provided as a means for solving the problem.

Further, the sixth invention has a structure in which the laser resonator is a Fabry-Perot resonator in addition to the structure of any one of the first invention to the fifth invention. It is a means to solve.

Further, in the seventh invention, in addition to the configuration of the sixth invention, the Fabry-Perot resonator selectively reflects light of a predetermined specific wavelength and selectively reflects light of a wavelength other than the specific wavelength. The structure having a fiber grating that transmits the light is used as means for solving the problem.

Furthermore, in addition to the configuration of any one of the above-mentioned first to fifth inventions, the eighth invention is that the laser resonator emits a laser resonance light amplified by a second amplification medium. A ring resonator formed by providing the first amplification medium on the loop returning to the optical multiplexer is used as means for solving the problem.

Furthermore, in the ninth invention, in addition to the structure of any one of the first to eighth inventions, the laser resonator has an optical isolator, and the optical resonator allows the laser resonance light to be emitted. It has a structure in which the traveling direction is regulated in one direction and is a means for solving the problem.

Further, in addition to the structure of any one of the above first to ninth inventions, the tenth invention is characterized in that the wavelength of the laser resonance light is in a region where the signal light of the laser resonator does not pass. The wavelength selective transmission filter that selectively transmits the light is used as a means for solving the problem.

Further, in the eleventh aspect of the invention, in addition to the configuration of any one of the first to tenth aspects of the invention, an optical attenuator is provided in a region where the signal light of the laser resonator does not pass. The existing structure is used as a means for solving the problems.

Further, the twelfth invention is an optical amplifier which changes in accordance with the intensity of a signal light incident on the laser resonator, in addition to the structure of any one of the first to twelfth inventions. The optical output detecting means for detecting the optical output of the optical disc and the adjusting circuit for adjusting the gain of the first amplifying medium according to the detection level of the optical output detecting means are provided, and the adjusting circuit serves as the signal light intensity stabilizing means. It has a structure and is a means for solving the problems.

In the present invention having the above-mentioned structure, a signal for keeping the intensity of the amplified signal light amplified and taken out by the second amplification medium constant by changing the gain of the first amplification medium according to the intensity of the signal light. Since the light intensity stabilizing means is provided, it is possible to output the amplified signal light having a constant intensity regardless of the signal light intensity input to the optical amplifier. Therefore, it becomes possible to obtain a constant level of output regardless of the wavelength and intensity of the input signal light, and the above problem is solved.

[0025]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. In the description of the example of the present embodiment, the same names as those in the conventional example are denoted by the same reference numerals, and the duplicate description thereof will be omitted. FIG. 1 shows a first embodiment of the optical amplifier according to the present invention. As shown in the figure, the optical amplifier of the present embodiment has a laser resonator 6, and an optical isolator 5 is provided between the laser resonator 6 and an input terminal 20 of the optical amplifier. An optical isolator 15 is provided between the output terminal 6 and the output terminal 21 of the optical amplifier.

The laser resonator 6 has an erbium-doped optical fiber 4 as a first amplification medium for amplifying the laser resonant light, and a second laser light for amplifying both the laser resonant light and the signal light incident on the laser resonator 6. And an erbium-doped optical fiber 14 that functions as an amplifying medium of the. Also,
The laser resonator 6 includes a wavelength-multiplexing optical multiplexer 3 as an optical multiplexer for introducing the signal light and the laser resonant light amplified by the erbium-doped optical fiber 4 into the erbium-doped optical fiber 14, and the erbium-doped optical fiber 3. A wavelength division multiplexing optical demultiplexer 13 is provided as an optical demultiplexer that demultiplexes and extracts only the amplified signal light of the amplified signal light amplified by the optical fiber 14 and the laser resonance light.

Further, the laser resonator 6 is provided with WDM optical multiplexers 2 and 12, and the WDM optical multiplexer 2 is provided.
The first pumping light source 1 is connected to the erbium-doped optical fiber 4 via the, and the second pumping light source 11 is connected to the erbium-doped optical fiber 14 via the wavelength multiplexing optical multiplexer 12. Erbium-doped optical fiber 4,14
Are configured to be forwardly pumped by the first and second pumping light sources 1 and 11, respectively. The wavelength multiplexing optical multiplexers 2, 3 and 12, the wavelength multiplexing optical demultiplexer 13, and the erbium-doped optical fibers 4 and 14 are connected in a ring shape via an optical fiber 23 for connection, The laser resonator 6 is a ring resonator formed by providing the erbium-doped optical fiber 4 on the loop for returning the laser resonant light amplified by the erbium-doped optical fiber 14 to the wavelength division multiplexing optical multiplexer 3.

Further, an optical attenuator 16 is interposed between the optical fiber 23 connecting the wavelength division multiplexing optical demultiplexer 13 and the wavelength division multiplexing optical multiplexer 2, whereby the signal light of the laser resonance light is transmitted. The optical attenuator 16 is provided in a region that does not pass through. An optical fiber 24 is provided on the incident side of the wavelength division multiplexing optical multiplexer 3, and the optical fiber 2
An optical isolator 5 is connected via 4, an optical fiber 25 is connected to the branch side of the wavelength division multiplexing optical demultiplexer 13, and the optical isolator 15 is connected via this optical fiber 25.

Further, in the present embodiment, the signal light intensity stabilizing means 10 is connected to the first pumping light source 1, and the signal light intensity stabilizing means 10 is connected to the signal light transmitting means (not shown). It is connected. Signal light intensity stabilizing means 10
Receives the output of the signal light transmitting means, changes the pumping light intensity of the first pumping light source 1 according to the intensity of the input signal light, and thereby changes the gain of the erbium-doped optical fiber 4. The gain of the erbium-doped optical fiber 14 is also changed to keep the intensity of the amplified signal light amplified by the erbium-doped optical fiber 14 constant.

The principle of stabilizing the amplified signal light intensity in this embodiment will be described below. In the ring resonator as shown in FIG. 1, the laser resonant light of wavelength λ1 circulates,
When laser oscillation is performed, for example, as shown in FIG. 2, the erbium-doped optical fiber 4 has a gain G1 (λ1) and a length L.
1, the gain of the erbium-doped optical fiber 14 is G2 (λ
1), the length is L2, and the total loss of the laser resonator 6 is L (λ
1), then G1 (λ
1) + G2 (λ1) −L (λ1) = 0 holds. At this time, the wavelength λ2 and the light intensity Pin (λ
The signal light of 2) is G from the erbium-doped optical fiber 14
The output light (amplified signal light) having the light intensity Pout (λ2) is emitted by receiving the gain of 2 (λ2), and the amplified signal light intensity Pout (λ2) is expressed by the following equation (1).

[0031]   Pout (λ2) = G2 (λ2) + Pin (λ2) ... (1)

The gains G1 (λ) and G2 (λ) of the erbium-doped optical fibers 4 and 14 when the light having the wavelength λ is incident on the erbium-doped optical fibers 4 and 14 are the erbium-doped optical fibers. Using the average population inversion coefficients n1 and n2, gain coefficients g1 (λ) and g2 (λ), and absorption coefficients α1 (λ) and α2 (λ) of 4 and 14, the following equation (2),
It can be expressed as (3).

[0033]   G1 (λ) = [{g1 (λ) + α1 (λ)} n1-α1 (λ)] L1 ... ・ ・ (2)

[0034]   G2 (λ) = [{g2 (λ) + α2 (λ)} n2-α2 (λ)] L2 ... ・ ・ (3)

Here, the gain coefficients g1 (λ) and g2
(Λ) and absorption coefficients α1 (λ) and α2 (λ) are values unique to the amplification medium such as the erbium-doped optical fibers 4 and 14, and the population inversion coefficients n1 and n2 are, for example, erbium-doped optical fibers 4 and 14. It can be varied from 0 to 1 by changing the intensity of the excitation light introduced into. An optical amplifier equipped with such a laser resonator 6 is a gain-l
ock, that is, as described above, laser resonance occurs at the laser resonance light wavelength λ1, and G1 (λ1) + G2 (λ
The condition that 1) -L (λ1) = 0 is represented by the following expression (4), and the relationship between the population inversion coefficients n1 and n2 is determined from this expression (4).

[0036]   [{G1 (λ1) + α1 (λ1)} n1-α1 (λ1)] L1 + [{g2 (λ 1) + α2 (λ1)} n2-α2 (λ1)] L2-L (λ1) = 0 ... (4)

That is, as in this embodiment, in addition to the erbium-doped optical fiber 14 that amplifies both the laser resonant light and the signal light in the laser resonator 6, the erbium-doped optical fiber 4 that amplifies only the laser resonant light. And the population inversion coefficient n1 of the erbium-doped optical fiber 4 is changed by changing the intensity of the first pumping light source 1 that excites the erbium-doped optical fiber 4, whereby the wavelength λ1 of the erbium-doped optical fiber 4 is changed. The light gain G1 (λ1) of the erbium-doped optical fiber 14 and the population inversion coefficient n2 of the erbium-doped optical fiber 14 are also changed to obtain the light gains G2 (λ1) and G2 (λ2) of the erbium-doped optical fiber 14 at the wavelengths λ1 and λ2. Can be changed.

Specifically, as is clear from the equation (4), when the population inversion coefficient n1 is increased, the population inversion coefficient n is increased.
2 becomes smaller, and conversely, when the population inversion coefficient n1 is made smaller, the population inversion coefficient n2 becomes larger.

Therefore, in this embodiment, as described above,
The signal light intensity stabilizing means 10 increases the intensity of the first pumping light source 1 in response to the input signal light intensity when the input signal light intensity is high, whereby the population inversion coefficient n1 is increased.
To increase the population inversion coefficient n2, and vice versa,
When the intensity of the input signal light is small, the intensity of the first pumping light source 1 is made small, whereby the population inversion coefficient n1 is made small and the population inversion coefficient n2 is made large. And
In this way, by changing the intensity of the first pumping light source 1, the wavelength λ2 by the erbium-doped optical fiber 14 is changed.
By changing the gain G2 (λ2) of the signal light of
The intensity of the amplified signal light determined by is kept constant.

The present embodiment is configured as described above, and each erbium-doped optical fiber 4 of the laser resonator 6 is
Reference numeral 14 amplifies the light by stimulated emission by the pumping light generated from the first and second pumping light sources 1 and 11, respectively, whereby the laser resonant light causes laser resonance, and the laser resonant light is the erbium-doped optical fiber 4. Amplified by 14. When signal light is input to the optical amplifier including the laser resonator 6 from the input terminal 20 side, the signal light is incident on the wavelength multiplexing optical multiplexer 3 via the isolator 5 and the optical fiber 24 and is combined with the laser resonant light. After being waved and introduced into the erbium-doped optical fiber 14, amplified by the erbium-doped optical fiber 14, only the amplified signal light is extracted by the wavelength division multiplexing optical demultiplexer 13 and output through the optical fiber 25 and the optical isolator 15. It is output from the terminal 21.

When the signal light is amplified and output by the erbium-doped optical fiber 14 in this manner, the intensity of the first pumping light source 1 is adjusted by the signal light intensity stabilizing means 10 according to the input signal light intensity. Adjustments are made. That is,
When the input signal light intensity Pin (λ2) increases, the signal light intensity stabilizing means 10 increases the intensity of the first pumping light source 1 to increase the gain G1 (λ of the erbium-doped optical fiber 4
1) is increased and the input signal light intensity Pin (λ2) is decreased, the signal light intensity stabilizing means 10 increases the pump light intensity of the first pump light source 1 to increase the intensity of the erbium-doped optical fiber 4. The gain G1 (λ1) is reduced.

Then, as described above, when the gain of the erbium-doped optical fiber 4 is increased, the gain of the erbium-doped optical fiber 14 is decreased, and conversely, when the gain of the erbium-doped optical fiber 4 is decreased, the erbium-doped optical fiber 4 is decreased. The gain of the optical fiber 14 increases, and the amplified signal light intensity is kept constant by such increase and decrease of the gain of the erbium-doped optical fiber 14.

According to this embodiment, as described above, the laser resonator 6 is provided in the optical amplifier, and the laser resonator 6 is provided.
Is provided with an erbium-doped optical fiber 4 that amplifies the laser resonance light and an erbium-doped optical fiber 14 that amplifies the laser resonance light and the signal light. The signal light intensity stabilizing means is used to respond to the input signal light intensity. By changing the gain of the erbium-doped optical fiber 4 to change the gain of the erbium-doped optical fiber 14 to stabilize the amplified signal light intensity, the amplification of a constant level is achieved regardless of the intensity and wavelength of the input signal light. A signal light can be output.

Further, according to the present embodiment, since the optical attenuator 16 is provided in the region where the signal light of the laser resonator 6 does not pass, the range of the balance between the gain and the loss in the laser resonator 6 is optically attenuated. Since the gain of the erbium-doped optical fiber 4 can be adjusted by the signal light intensity stabilizing means 10 within a desired range by the instrument 16, the erbium-doped optical fiber 4 of the signal light intensity stabilizing means 10 can be adjusted. The gain can be controlled very easily and accurately.

FIG. 3 shows a second embodiment of the optical amplifier according to the present invention. In this embodiment, the same reference numerals are given to the same names as those in the first embodiment. is there.

The optical amplifier of the present embodiment is also configured to have a laser resonator 6 of a ring resonator as in the optical amplifier of the first embodiment, and the embodiment of the present embodiment is the same as the first embodiment. A different characteristic from the first excitation light source 1 is that the erbium-doped optical fiber 4 and the erbium-doped optical fiber 14 are
And a branch coupler 17 for branching the pumping light is provided between the first pumping light source 1 and each of the erbium-doped optical fibers 4 and 14. That is, in the present embodiment example, the pumping light from the first pumping light source 1 is branched by the branching coupler 17, and the branched pumping light is passed through the wavelength multiplexing optical multiplexer 2 and the erbium-doped optical fiber 4
In addition, the light is incident on the erbium-doped optical fiber 14 via the wavelength multiplexing optical multiplexer 12.

Further, in this embodiment, the signal light intensity stabilizing means 10 is connected to the first pumping light source 1 and the input light transmitting means (not shown), and is the same as in the first embodiment. In addition, the intensity of the first pumping light source 1 is adjusted according to the intensity of the input signal light to change the gain of the erbium-doped optical fiber 4 to keep the amplified signal light intensity constant. When the coupler 17 is capable of varying the light branching ratio, the signal light intensity stabilizing means 1
0 is connected to the branching coupler 17 and the branching ratio of the pumping light by the branching coupler 17 is changed according to the input signal light intensity, thereby changing the gain of the erbium-doped optical fiber 4 and keeping the amplified signal intensity constant. You may

The example of the present embodiment is configured as described above. In the example of the present embodiment, the erbium-doped optical fibers 4 and 14 are excited by the excitation light from the first excitation light source 1, and the erbium-doped optical fibers 4 and 14 are excited. Amplification of laser resonance light by the optical fiber 4 and erbium-doped optical fiber 14
Amplification of the laser resonance light and the signal light is performed, and at this time, the signal light intensity stabilizing means 10 adjusts the pump light intensity of the first pump light source 1 according to the intensity of the input signal light. The same effect as the first embodiment can be obtained by the same operation.

FIG. 4 is a block diagram showing a third embodiment of the optical amplifier according to the present invention. In FIG. 4, parts having the same names as those of the first and second embodiments are the same. Is attached.

The example of the present embodiment is constructed almost similarly to the example of the first embodiment, and the characteristic of the example of the present embodiment different from the example of the first embodiment is that the laser resonator 6 is made incident. An optical output detecting means 19 for detecting the optical output of the optical amplifier which changes according to the signal light intensity, and an excitation light adjusting means 18 for adjusting the gain of the erbium-doped optical fiber 4 according to the detection level of the optical output detecting means 19. That is, the adjusting circuit having the pumping light adjusting means 18 and the light output detecting means 19 is provided as the signal light intensity stabilizing means 10. The pumping light adjusting means 18 adjusts the output of the first pumping light source 1, and thereby adjusts the gain of the erbium-doped optical fiber 4.

The present embodiment is configured as described above. In the present embodiment, the pumping light adjusting means 18 pumps the first pumping light source 1 in accordance with the output detected by the light output detecting means 19. By adjusting the light intensity, the gain of the erbium-doped optical fiber 4 is adjusted according to the input signal light intensity, as in the first and second embodiments, and thus the input signal light intensity It is possible to output a constant level of amplified signal light regardless of intensity and wavelength, and it is possible to achieve the same effects as those of the first and second embodiments.

FIG. 5 is a block diagram showing a fourth embodiment of the optical amplifier according to the present invention. This embodiment example also has a laser resonator 6 of a ring resonator as in the first, second, and third embodiment examples, and this embodiment example is different from the first to third embodiment examples. A characteristic is that the optical isolators 5 and 15 are provided in the laser resonator 6. As described above, since the laser resonator 6 is configured to include the optical isolators 5 and 15, the traveling direction of the laser resonant light is reliably restricted to one direction in the present embodiment example.

Further, in the present embodiment, the erbium-doped optical fiber 14 functioning as the second amplification medium is
Divided into two parts, the erbium-doped optical fiber 14 on the left side of the figure
The second excitation light source 11 is provided on the emission side, and the second excitation light source 11 is provided on the incidence side and the emission side of the erbium-doped optical fiber 14 on the right side of the figure. A wavelength division multiplexing optical multiplexer 12 is provided between the erbium-doped optical fiber 14 and the second pumping light source 11. By connecting the second pumping light source 11 to the erbium-doped optical fiber 14 as described above, the erbium-doped optical fiber 14 on the left side of the figure is backward-pumped by the second pumping light source 11a, and the erbium-doped optical fiber 14 on the right side of the figure is shown. The erbium-doped optical fiber 14 is bidirectionally pumped by the second pumping light sources 11b and 11c. In addition, in the present embodiment, the erbium-doped optical fiber 4 is pumped backward by the first pumping light source 1.

The example of the present embodiment is configured as described above, and the same effect can be obtained by the operation of the example of the present embodiment as in the case of the example of the first embodiment.

FIG. 6 shows an experimental result confirming that it is possible to output a constant amplified signal light regardless of the intensity of the input signal light by using the optical amplifier of this embodiment. In addition,
In carrying out this experiment, the erbium-doped optical fiber 4,
In each case, the erbium concentration is 600 ppm, the erbium-doped optical fiber 4 has a length of 10 m, the left erbium-doped optical fiber 14 has a length of 7 m, and the right erbium-doped optical fiber 14 has a length of 12 m. And The wavelength of the laser resonance light is 1530 nm, the wavelength multiplexing optical multiplexer 3 is configured to combine the laser resonance light of the wavelength 1530 nm and the signal light of another wavelength, and the wavelength multiplexing optical demultiplexer 13 is an amplified signal. Only the amplified signal light is extracted from the light and the laser resonance light having a wavelength of 1530 nm. Furthermore, the pumping light intensities of the second pumping light sources 11a, 11b, and 11c were set to 75 mW, 33 mW, and 110 mW, respectively.

In FIG. 6, under the above conditions, the signal light wavelength is 1555 nm, and the signal light intensity is -25 to -15d.
Amplification when the gain of the erbium-doped optical fiber 4 is changed by changing the Bm and changing the pumping light intensity of the first pumping light source 1 by the signal light intensity stabilizing means 10 according to the input signal light intensity. The signal light intensity (output light intensity) is shown. As is apparent from the figure, in the present embodiment, the signal light intensity stabilizing means 10 changes the pump light intensity of the pump light source 1 in accordance with the input signal light intensity, so that the output light intensity is approximately 4. It could be kept constant at 3 dBm.

FIG. 7 is a block diagram showing a fifth embodiment of the optical amplifier according to the present invention. In FIG. 7, parts having the same names as those of the first to fourth embodiments and the conventional example are shown. Are given the same reference numerals. The optical amplifier of the present embodiment is an optical amplifier including a laser resonator 6 of a Fabry-Perot resonator similar to that of the conventional example, and is configured by providing optical reflectors 7 on both ends of the laser resonator 6. . The feature of the present embodiment different from the first embodiment is that the laser resonator 6 is a Fabry-Perot resonator in this way, and the other configurations are the same as those of the first embodiment. Since it is the same, the duplicated description will be omitted.

The present embodiment is configured as described above. In this embodiment, the laser resonator 6 is a Fabry-Perot resonator, but the Fabry-Perot resonator also has a laser as shown in FIG. Resonant light is laser resonator 6
Since it is considered that the light reflector 7 travels back and forth between the light reflectors 7 on both ends, the same effect can be obtained by the same operation as that of the first embodiment.

FIG. 9 is a block diagram showing a sixth embodiment of the optical amplifier according to the present invention. The feature of the present embodiment different from the fifth embodiment is that fiber gratings 9a and 9b are provided in place of the light reflectors 7 on both ends of the laser resonator 6, and other than that. Since the configuration of is similar to that of the fifth embodiment, the duplicated description will be omitted.

The example of the present embodiment is configured as described above, and the example of the present embodiment can also obtain the same effect by the same operation as the example of the fifth embodiment.

It should be noted that the present invention is not limited to the above-mentioned embodiment, and various embodiments can be adopted. For example, in each of the above embodiments, the optical attenuator 16 is provided in the optical fiber 23, and the optical attenuator 16 is provided in a region where the signal light of the laser resonator 6 does not pass. Alternatively, a wavelength selective transmission light filter 8 that selectively transmits light of the wavelength of the laser resonance light may be provided, and the optical attenuator 16 and the wavelength selection transmission light may be provided in a region of the laser resonator 6 where the signal light does not pass. Both filters 8 may be provided. in this way,
When the wavelength selective transmission light filter 8 is provided in the laser resonator 6, it becomes possible to stabilize the oscillation characteristics of the laser resonator 6, whereby the gain stabilization of the erbium-doped optical fiber 4 by the signal light intensity stabilizing means 10 is achieved. Also, the stabilization control can be performed more stably, and the optical amplifier can perform the output light intensity stabilization control more stably.

Further, in each of the above embodiments, the optical attenuator 16 is provided in the laser resonator 6, but the optical attenuator 16 may be omitted. However, it is preferable to provide the optical attenuator 16 in the laser resonator 6 because the provision of the optical attenuator 16 facilitates setting the range of the gain and loss balance of the laser resonator 6 to a desired range.

Further, the method of exciting the erbium-doped optical fibers 4, 14 by the first and second pumping light sources 1, 11 may be backward pumping, forward pumping, or bidirectional pumping.

Further, when the optical amplifier is constructed as in the second, fourth, fifth and sixth embodiments, the light output detecting means 19 and the pumping light adjustment are provided as in the case of the third embodiment. The means 18 may be provided to configure the signal light intensity stabilizing means 10.

Further, in each of the above embodiments, the laser resonator 6 is constructed by providing the erbium-doped optical fibers 4 and 14, but one or both of the erbium-doped optical fibers 4 and 14 is doped with a rare earth element other than erbium. Alternatively, one or both of the erbium-doped optical fibers 4 and 14 may be made of an amplification medium other than the rare-earth-doped optical fiber.

[0066]

According to the present invention, an optical amplifier having a laser resonator provided with first and second amplifying media is provided, and the gain of the first amplifying medium for amplifying only the laser resonant light is set to the intensity of the signal light. Based on the principle that the gain of the second amplification medium that amplifies both the laser resonant light and the signal light can also be changed by changing the gain in accordance with the principle, the amplified signal light intensity amplified and extracted by the second amplification medium is extracted. Since the signal light intensity stabilizing means for keeping constant is provided, it is possible to output the amplified signal light having a constant intensity regardless of the signal light intensity input to the optical amplifier.

Further, a pumping light source is connected to one or both of the first gain medium and the second gain medium, and one or both of the first gain medium and the second gain medium is pumped by the pump light source. According to the second to fifth aspects of the present invention configured by the rare earth-doped optical fiber that amplifies light by stimulated emission of light, the pumping light intensity of the pumping light source is adjusted by the signal light stabilizing means according to the input signal light intensity. By doing so, the amplified signal light intensity can be easily and surely kept constant and output. Further, by using the rare earth-doped optical fiber as the first and second amplification media, the optical amplifier can be downsized.

Further, according to the sixth to eighth inventions in which the laser resonator is composed of a Fabry-Perot resonator or a ring resonator, the laser resonator can be easily formed by using the technique which has been conventionally used. In addition, it is possible to surely configure the optical amplifier that exhibits the above excellent effect.

Further, the laser resonator has an optical isolator, and the traveling direction of the laser resonance light is restricted to one direction by the optical isolator. According to the present invention, by restricting the traveling direction of the laser resonance light, the laser resonance light that can more reliably and stably perform laser resonance is configured, and the optical amplifier including the laser resonator is provided. The output level of the signal light can be made more stable.

Further, a wavelength selective transmission filter for selectively transmitting the light of the wavelength of the laser resonance light is provided in the region where the signal light of the laser resonator does not pass. According to the present invention, the oscillation characteristics of the laser resonator can be stabilized, so that an excellent optical amplifier that can perform signal light amplification at a more stable level can be provided.

Further, an optical attenuator is provided in the region of the laser resonator where the signal light does not pass. According to the present invention, since the range of the balance between the gain and the loss of the laser resonator can be adjusted by the optical attenuator, the gain of the first amplification medium can be easily controlled by the signal light intensity stabilizing means, The amplified signal light intensity can be kept constant more stably.

Further, the optical output detecting means for detecting the optical output of the optical amplifier which changes according to the intensity of the signal light incident on the laser resonator, and the first amplifying medium according to the detection level of the optical output detecting means. According to the present invention, in which an adjusting circuit for adjusting the gain of the optical amplifier is provided, and the adjusting circuit is used as the signal light intensity stabilizing means, the optical output detecting means detects the optical output of the optical amplifier to make it enter the laser resonator. Since the gain of the first amplification medium can be easily and accurately adjusted by the adjusting circuit according to the signal light intensity, the stabilized control of the amplified signal light intensity can be performed very easily and accurately. It can be carried out.

[Brief description of drawings]

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

FIG. 2 is an explanatory diagram of the principle of stabilizing the amplified signal light intensity in the optical amplifier of the above-described embodiment.

FIG. 3 is a main part configuration diagram showing a second embodiment of the optical amplifier according to the present invention by a block diagram.

FIG. 4 is a main part configuration diagram showing a third embodiment of the optical amplifier according to the present invention by a block diagram.

FIG. 5 is a main part configuration diagram showing a fourth embodiment of the optical amplifier according to the present invention by a block diagram.

FIG. 6 is a graph showing the relationship between the input signal light intensity and the output light intensity when the pumping light intensity of the pumping light source 1 is changed according to the input signal light intensity in the optical amplifier of the fourth embodiment. is there.

FIG. 7 is a main part configuration diagram showing a fifth embodiment of the optical amplifier according to the present invention by a block diagram.

FIG. 8 is an explanatory view showing a simplified operation of the laser resonator in the optical amplifier according to the fifth embodiment.

FIG. 9 is a main part configuration diagram showing a sixth embodiment of the optical amplifier according to the present invention by a block diagram.

FIG. 10 is an explanatory diagram showing a block diagram of a configuration of a conventional optical amplifier.

[Explanation of symbols]

1 First excitation light source 4 Erbium-doped optical fiber 6 Laser resonator 8 Wavelength selective transmitted light filter 9,9a, 9b Fiber grating 10 Signal light intensity stabilizing means 11 Second excitation light source 14 Erbium-doped optical fiber 16 Optical attenuator 17 Branch coupler

─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP 10-117031 (JP, A) JP 9-18415 (JP, A) JP 5-206557 (JP, A) JP 10- 4231 (JP, A) JP-A-9-162475 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H01S 3/00-3/30

Claims (12)

(57) [Claims] 1. A laser resonator, wherein the laser resonator has a first amplification medium for amplifying the laser resonance light, and a first amplification medium for amplifying both the laser resonance light and the signal light incident on the laser resonator. A second amplification medium, an optical multiplexer that multiplexes and introduces the signal light and the laser resonant light amplified by the first amplification medium into the second amplification medium, and is amplified by the second amplification medium. And an optical demultiplexer that demultiplexes and extracts only the amplified signal light of the amplified signal light and the laser resonant light, and the first amplifying medium according to the intensity of the signal light incident on the laser resonator. An optical amplifier having a signal light intensity stabilizing means for keeping the amplified signal light intensity constant by changing the gain of the signal light. 2. A first pumping light source is connected to the first amplifying medium, and the first amplifying medium amplifies the light by stimulated emission by the pumping light generated from the first pumping light source. The signal light intensity stabilizing means changes the gain of the first rare earth-doped optical fiber by changing the intensity of the pumping light from the first pumping light source. The optical amplifier according to claim 1, wherein the optical amplifier is configured to be kept constant. 3. The second amplifying medium comprises a second rare earth-doped optical fiber having a function of amplifying light by stimulated emission by excitation light generated from an excitation light source. 2. The optical amplifier according to 2. 4. A second pumping light source different from the first pumping light source is connected to the second amplifying medium, and the second amplifying medium is generated by the pumping light generated from the second pumping light source. The optical amplifier according to claim 2, comprising a second rare earth-doped optical fiber that amplifies light by stimulated emission. 5. A second excitation medium is connected to a first excitation light source, and the second amplification medium amplifies the light by stimulated emission by the excitation light generated from the first excitation light source.
7. A branch coupler for branching pumping light is provided between the first pumping light source and the first and second rare earth-doped optical fibers. 2. The optical amplifier according to 2. 6. The optical amplifier according to claim 1, wherein the laser resonator is a Fabry-Perot resonator. 7. The Fabry-Perot resonator has a fiber grating that selectively reflects light of a predetermined specific wavelength and transmits light of a wavelength other than the specific wavelength. Optical amplifier. 8. The laser resonator is a ring resonator formed by providing the first amplification medium on a loop for returning the laser resonance light amplified by the second amplification medium to the optical multiplexer. The optical amplifier according to any one of claims 1 to 5. 9. The laser resonator has an optical isolator, and the traveling direction of the laser resonance light is restricted to one direction by the optical isolator.
9. The optical amplifier according to claim 8. 10. A wavelength selective transmission filter which selectively transmits light of the wavelength of the laser resonant light is provided in a region of the laser resonator where the signal light does not pass. 9. The optical amplifier according to any one of 9. 11. The optical amplifier according to any one of claims 1 to 10, wherein an optical attenuator is provided in a region of the laser resonator where the signal light does not pass. 12. An optical output detecting means for detecting an optical output of an optical amplifier which changes according to an intensity of a signal light incident on a laser resonator, and a first amplifying medium according to a detection level of the optical output detecting means. An optical amplifier according to any one of claims 1 to 11, wherein an adjusting circuit for adjusting the gain is provided, and the adjusting circuit serves as a signal light intensity stabilizing means.