JPH11317560A - Optical amplifier and laser oscillator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical waveguide which is easy to manufacture and has high strength.
Provided is an optical amplifier capable of optically amplifying signal light having a wavelength of 570 nm or more. SOLUTION: Excitation light emitted from an excitation light source 11 passes through an optical fiber 13 and a WDM coupler 15, and is transmitted through an EDM.
It is supplied to the amplification optical fiber 10 which is a silica-based optical fiber to which the r element and the P element are added. In addition, the excitation light emitted from the excitation light source 12 is supplied to the amplification optical fiber 10 via the optical fiber 14 and the WDM coupler 16. The signal light input to the input end connector 17 is WD
The light enters the amplification optical fiber 10 via the M coupler 15 and is amplified in the amplification optical fiber 10. The optically amplified signal light is output from the output terminal connector 18 via the WDM coupler 16.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical amplifier and a laser oscillator suitably used in an optical communication system for transmitting signal light having a wavelength of 1570 nm or more.

[0002]

2. Description of the Related Art In an optical communication system capable of transmitting signal light at high speed with a large capacity, a wavelength of 1.55 μm is generally used.
Band light is used as signal light. That is, a light source that outputs signal light and that oscillates laser light in a wavelength of 1.55 μm is used, and an optical amplifier that amplifies the signal light is a light amplifier that has signal light gain in a wavelength of 1.55 μm. Can be In such an optical communication system,
Wider bandwidths are being studied in order to further increase capacity and speed.

[0003] For example, the document "A. Mori, et al.," Broadba
nd Amplification Characteristicsof Tellurite-Based
EDFAs ", IOOC / ECOC'97, Tech.Dig., Vol.3, pp.135-13
8 (1997) "discloses an optical amplifier that amplifies signal light having a wavelength of 1570 nm or more using an optical waveguide (optical fiber) doped with Er (erbium) element using fluoride glass or tellurite glass as a host. Have been. Also, by using such an optical waveguide, a laser oscillator that oscillates laser light having a wavelength of 1570 nm or more can be realized.

[0004]

However, the optical waveguide using the fluoride glass or tellurite glass as the host used in the above-mentioned conventional example is more difficult to manufacture than the generally used silica-based optical waveguide. Difficult, low strength, low reliability. Also, such an optical waveguide is
It is difficult to connect to a generally used quartz optical waveguide.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and has an optical amplifier capable of easily amplifying a signal light having a wavelength of 1570 nm or more with an optical waveguide which is easy to manufacture and has a high intensity. It is another object of the present invention to provide a laser oscillator capable of oscillating laser light having a wavelength of 1570 nm or more and having an optical waveguide that is easy to manufacture and has high strength.

[0006]

An optical amplifier according to the present invention includes a quartz optical waveguide to which Er and P elements are added, and amplifies a signal light having a wavelength of 1570 nm or more input to the optical waveguide. It is characterized by doing. According to this optical amplifier, since the optical waveguide is of a quartz type, it is easy to manufacture, has high strength, and is easily connected to another generally used quartz type optical waveguide. Also, Er
Since the P element is added to the optical waveguide in addition to the element, the wavelength bandwidth of the gain spectrum is wider and the limit wavelength on the longer wavelength side is longer than in the case where the P element is not added.

Further, the optical amplifier according to the present invention is characterized in that an Al element is further added to the optical waveguide.
In this case, the gain flatness is adjusted by adjusting the Al element addition concentration, and an optical amplifier is designed according to the application.

In the optical amplifier according to the present invention, the concentration of the P element added to the optical waveguide is at least 8% by weight. Also, the concentration of the Al element added to the optical waveguide is 0.3% by weight or less. In these cases, the limit wavelength on the long wavelength side of the gain spectrum is almost the same as that when using an Er-doped optical waveguide using tellurite glass as a host.

A laser oscillator according to the present invention includes a quartz-based optical waveguide to which Er and P elements are added, and oscillates laser light having a wavelength of 1570 nm or more, which is induced and emitted from the optical waveguide. I do. According to this laser oscillator, since the optical waveguide is of a quartz type,
It is easy to manufacture, has high strength, and is easily connected to other generally used quartz optical waveguides. Also, E
Since the P element is added to the optical waveguide in addition to the r element, the wavelength band in which laser oscillation can be performed is wider and the limit wavelength on the long wavelength side is longer than when the P element is not added.

Further, the laser oscillator according to the present invention is characterized in that an Al element is further added to the optical waveguide. In this case, the flatness of the laser oscillation intensity with respect to the wavelength is adjusted by adjusting the Al element addition concentration.

Further, in the laser oscillator according to the present invention, the concentration of the P element added to the optical waveguide is at least 8% by weight. Also, the concentration of the Al element added to the optical waveguide is 0.3% by weight or less.
In these cases, the limit wavelength on the longer wavelength side of the wavelength band in which laser oscillation can be performed is Er using the tellurite glass as a host.
It is almost the same as the case where the additional optical waveguide is used.

[0012]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings. In the description of the drawings, the same elements will be denoted by the same reference symbols, without redundant description.

First, an optical waveguide suitably used in each embodiment of the optical amplifier and the laser oscillator according to the present invention will be described. The optical waveguide includes not only an optical fiber but also one formed on a substrate. Hereinafter, an optical fiber will be described as an optical waveguide.

A silica-based optical fiber using quartz glass as a host is easy to manufacture, has high strength, and is therefore widely used. In particular, a quartz optical fiber to which a rare earth element such as an Er (erbium) element is added exhibits an optical amplifying function when excitation light of a predetermined wavelength is supplied, and thus is suitably used in an optical amplifier or a laser oscillator. . In addition, such an Er-doped silica-based optical fiber can be easily connected to another silica-based optical waveguide, and has a small connection loss. In order to adjust gain flatness with respect to wavelength, A
l (aluminum) element is further added.

The limit wavelength on the long wavelength side of the spread of the gain spectrum in such an optical fiber is the signal light amplification gain coefficient of the Er element and the excited state absorption of the Er element (Exciton absorption).
tedState Absorption: Determined by the characteristics of ESA).
That is, in order to generate the signal light gain, the stimulated emission cross-sectional area regarded as the signal light amplification gain coefficient of the Er element is E
It must be larger than the SA cross section. When the stimulated emission cross section is equal to or smaller than the ESA cross section, no matter how strong the pumping light is supplied to the optical fiber, no signal light gain occurs. Further, the stimulated emission cross section and the ESA cross section of the optical fiber each depend on the element and concentration added to the optical fiber and the wavelength.

FIG. 1 is a table summarizing the composition of each of the three types of optical fibers. These three types of optical fibers are all silica-based optical fibers to which Er element is added. In the type a optical fiber, the Er element is added by 1000 ppm by weight and the Al element is added by 7.8% by weight, but the P (phosphorus) element is not added. In the type b optical fiber, Er element is added by 500 ppm by weight,
Al element is added by 2.0% by weight, and P element is added by 5.0% by weight. In the type c optical fiber, the Er element is added at 1000 ppm by weight, the Al element is added at 0.3% by weight, and the P element is added at 8.0% by weight.

FIG. 2 is a graph showing the wavelength dependence of the stimulated emission cross section and the ESA cross section of the type a optical fiber. FIG. 3 is a graph showing the wavelength dependence of the stimulated emission cross section and the ESA cross section of the type b optical fiber. FIG. 4 is a graph showing the wavelength dependence of the stimulated emission cross section and the ESA cross section of the type c optical fiber.

As can be seen from each of FIGS. 2 to 4, in each of the optical fibers of types a to c, 15
In the wavelength band of 80 nm to 1650 nm, as the wavelength becomes longer, the stimulated emission cross section becomes smaller, but the ESA cross section tends to become larger. At a certain wavelength, the stimulated emission cross section and the ESA cross section cross each other. The wavelength at which the two cross is the limit wavelength on the long wavelength side of the spread of the gain spectrum.
That is, at wavelengths below the limit wavelength, the stimulated emission cross section is larger than the ESA cross section, and therefore, signal light gain can occur when pumping light is supplied. However, at wavelengths above the limit wavelength, the stimulated emission cross section is smaller than the ESA cross section,
Therefore, no matter how strong the pumping light is supplied to the optical fiber, no signal light gain occurs.

The limit wavelength on the long wavelength side of the spread of the gain spectrum is 1628 nm in the type a optical fiber,
It is 1632 nm for the type b optical fiber and 1635 nm for the type c optical fiber. That is, E
The limit wavelength of each of the type b and c optical fibers to which the P element is added in addition to the r element is longer than that of the type a optical fiber to which the P element is not added, as described in the section of the prior art. The length is longer than that of an Er-doped optical fiber using fluoride glass as a host. In particular, the limit wavelength of an optical fiber of type c is Er in which tellurite glass is used as a host.
It is about the same as the limit wavelength of the doped optical fiber of 1637 nm. Further, comparing the type b optical fiber with the type c optical fiber, the limiting wavelength of the type c quartz optical fiber having a high P element addition concentration and a low Al element addition concentration is that the P element addition concentration is low and the Al concentration is low. It is longer than a type-b silica optical fiber having a high element addition concentration.

Furthermore, in addition to these three types of silica-based optical fibers, Er-doped silica-based optical fibers having various added concentrations were also examined in the same manner, and the concentration of P element added to the silica-based optical fiber was determined. Is 8% by weight or more, or when the concentration of the Al element added to the quartz-based optical fiber is 0.3% by weight or less, the critical wavelength of the quartz-based optical fiber is based on tellurite glass. Is about the same as the limit wavelength of 1637 nm of the Er-doped optical fiber.

Therefore, an optical amplifier using a silica-based optical fiber to which Er and P elements are added as an amplifying optical fiber can optically amplify a signal light having a wavelength of 1570 nm or more, and a signal having a wavelength of about 1630 nm. Light can also be amplified. A laser oscillator using a silica-based optical fiber doped with an Er element and a P element as an amplification optical fiber in an optical resonator has a wavelength of 1570 nm.
The laser light having the above wavelength can be oscillated,
A laser beam having a wavelength of about nm can be oscillated.

Next, an embodiment of the optical amplifier according to the present invention will be described. FIG. 5 is a configuration diagram of the optical amplifier according to the present embodiment. The optical amplifier according to the present embodiment is configured such that the above-mentioned type b or c optical fiber is
The optical fiber amplifier further includes excitation light sources 11 and 12, WDM couplers 15 and 16, an input terminal connector 17, and an output terminal connector 18. Further, for comparison, an optical amplifier including the above-mentioned type a optical fiber as the amplification optical fiber 10 will be described.

Each of the excitation light sources 11 and 12 outputs excitation light to be supplied to the amplification optical fiber 10, and for example, a laser diode that outputs laser light having a wavelength of 1.48 μm is preferably used. The WDM coupler 15 causes the excitation light emitted from the excitation light source 11 and reached via the optical fiber 13 to enter the amplification optical fiber 10, and also causes the signal light input to the input terminal connector 17 to enter the amplification optical fiber 10. . WDM coupler 16
The pump light emitted from the pumping light source 12 and arriving via the optical fiber 14 is made incident on the amplifying optical fiber 10, and the signal light optically amplified by the amplifying optical fiber 10 is passed toward the output terminal connector 18. Let it.

This optical amplifier operates as follows. The excitation light emitted from the excitation light source 11 is
Then, the light is supplied to the amplification optical fiber 10 via the WDM coupler 15. In addition, the excitation light emitted from the excitation light source 12 is supplied to the amplification optical fiber 10 via the optical fiber 14 and the WDM coupler 16. Input end connector 17
Is input to the amplification optical fiber 10 via the WDM coupler 15 and is optically amplified in the amplification optical fiber 10. The optically amplified signal light is output from the output terminal connector 18 via the WDM coupler 16.

FIG. 6 is a graph showing the gain spectrum of an optical amplifier using three types of silica-based optical fibers. The wavelength of the excitation light emitted from each of the excitation light sources 11 and 12 was 1.48 μm. Also, 1.
The absorption length product of the 53 μm band is 6
90 dB, 1176 dB for type b optical fiber
And 654 dB for the type c optical fiber.

As can be seen from this graph, types a to c
Optical amplifiers using any of the optical fibers
Signal light having a wavelength of m or more can be optically amplified. However, the wavelength bandwidth of the gain spectrum of the optical amplifier using the type b optical fiber doped with the P element in addition to the Er element is 1562 nm to 1628 nm, and the type c optical fiber also doped with the P element is used. The wavelength bandwidth of the gain spectrum of the used optical amplifier is 1558 nm to 1630.
nm or more, which are wider than those of the type a optical fiber to which the P element is not added. In particular, an optical amplifier using an optical fiber of type c has the widest wavelength bandwidth of the gain spectrum and the longest limit wavelength on the long wavelength side, similar to the case of the Er-doped optical fiber using tellurite glass as a host. It has a gain even at a long wavelength of 1630 nm. In addition, the gain flatness of the gain spectrum of the optical amplifier using each of the type a and b optical fibers having a high Al element addition concentration is superior to that of the type c optical fiber having a low Al element addition concentration. .

There are various wavelength division multiplexing optical communication systems for transmitting multi-wavelength signal light. For example, a short-distance transmission system such as an intra-station transmission system or a regional transmission system has a shorter transmission distance than a long-distance transmission system such as a trunk transmission system or a transoceanic transmission system, but generally has a larger capacity, that is, a larger number of wavelengths. . Therefore, in a short-distance transmission system, it is required that the wavelength bandwidth of the gain spectrum of the optical amplifier is wide, but the gain flatness is not important. On the other hand, in a long-distance transmission system, the gain flatness of the optical amplifier is most important. Thus, the requirements for the gain spectrum of the optical amplifier differ depending on the application.

The gain spectrum of the optical amplifier is optimally designed according to the application by appropriately adjusting the elements and the concentration added to the Er-doped silica-based optical fiber. Applications suitable for an optical amplifier using each of the optical fibers of types a to c are as follows. An optical amplifier using an optical fiber of type a has a narrower wavelength bandwidth of a gain spectrum but an excellent gain flatness as compared with the other two types of optical fibers, so that the total loss budget is 300 dB.
It is suitably used for a long distance transmission system having a transmission distance of about 600 km or less. An optical amplifier using an optical fiber of type b has a slightly narrower wavelength bandwidth of the gain spectrum, but has an excellent gain flatness. It is suitable for use in systems. An optical amplifier using an optical fiber of type c is
Compared with the other two types of optical fibers, the wavelength bandwidth of the gain spectrum is wider, but the gain flatness is inferior.
Transmission distance 2 with total loss budget of about 30 dB or less
It is suitably used in a short-distance, large-capacity transmission system in an office or a regional system of about 00 km or less.

Next, an embodiment of a laser oscillator according to the present invention will be described. FIG. 7 is a configuration diagram of the laser oscillator according to the present embodiment. The laser oscillator according to the present embodiment includes the above-mentioned type b or c optical fiber as the amplification optical fiber 20, and further includes an excitation light source 21, an optical isolator 22, an output terminal connector 23, and an optical fiber grating 24. , 25. For comparison, a laser oscillator including the above-mentioned type a optical fiber as the amplification optical fiber 20 will also be described.

The excitation light source 21 is an amplification optical fiber 20.
For example, a laser diode that outputs a laser beam having a wavelength of 1.48 μm is preferably used. The optical isolator 22 allows the light arriving from the amplification optical fiber 20 to pass through to the output end connector 23, but does not allow the light to pass in the opposite direction.

The optical fiber gratings 24 and 25 are
The center wavelength is the wavelength of light to be oscillated. The optical fiber grating 24 includes the excitation light source 21.
And the optical fiber 20 for amplification, the reflectance for the light having the same wavelength as the center wavelength is approximately 100%, and the transmittance for the excitation light emitted from the excitation light source 21 is approximately 100%. 100%. The optical fiber grating 25 is composed of the amplification optical fiber 20 and the optical isolator 22.
And has a reflectance of, for example, 20% for light having the same wavelength as the center wavelength. That is, a resonator is formed between the optical fiber gratings 24 and 25.

This laser oscillator operates as follows. The excitation light emitted from the excitation light source 21 passes through the optical fiber grating 24 and is supplied to the amplification optical fiber 20. In the amplification optical fiber 20, a population inversion occurs with the supply of the excitation light, and spontaneous emission light is generated. Of the spontaneous emission light, light having the same wavelength as the center wavelength of the optical fiber gratings 24 and 25 repeatedly reciprocates between the optical fiber gratings 24 and 25, during which light amplification by stimulated emission in the amplification optical fiber 20 is performed. Occur. Then, part of the optically amplified light passes through the optical fiber grating 25 and the optical isolator 22 and is output from the output end connector 23 as laser light.

The wavelength of the laser light output from the laser oscillator is the same as the center wavelength of the optical fiber gratings 24 and 25, and the center wavelength is a wavelength within the wavelength band of the gain spectrum of the amplification optical fiber 20. is there. For example, assuming that the center wavelength of the optical fiber gratings 24 and 25 is 1625 nm, the center wavelength is within the wavelength band of the gain spectrum of the amplification optical fiber 20, so that the laser light having the same wavelength as the center wavelength 1625 nm is emitted from the laser oscillator. Output from

Therefore, the laser oscillator outputs laser light of any wavelength within the wavelength band of the gain spectrum of the amplification optical fiber 20 by appropriately setting the center wavelength of the optical fiber gratings 24 and 25. be able to. That is, a laser oscillator using any of the optical fibers of types a to c can output laser light having a wavelength of 1570 nm or more. However, the limit wavelength on the longer wavelength side of the laser oscillation wavelength band of the laser oscillator using each of the type b and c optical fibers to which the P element is added in addition to the Er element is the same as that of the type a where the P element is not added. Longer than optical fiber. In particular, a laser oscillator using an optical fiber of type c has the highest limit wavelength on the long wavelength side of the laser oscillation wavelength band, and has a long wavelength of 1630 nm as in the case of the Er-doped optical fiber using tellurite glass as a host. Laser oscillation is possible.

The present invention is not limited to the above embodiment, and various modifications are possible. The configurations of the optical amplifier and the laser oscillator are not limited to those described above. For example, a resonator in a laser oscillator is
The present invention is not limited to the above configuration, and may be a ring resonator. Further, in the above embodiment, the optical fiber is described as the silica-based optical waveguide to which the Er element and the P element are added in each of the optical amplifier and the laser oscillator. However, the same applies to the optical waveguide formed on the substrate. .

[0036]

As described above in detail, according to the optical amplifier according to the present invention, since the optical waveguide is of a quartz type, it is easy to manufacture, has a high strength, and is generally used. Connection with a quartz optical waveguide is easy. Further, since the P element was added to the optical waveguide in addition to the Er element, compared with the case where the P element was not added,
The wavelength bandwidth of the gain spectrum is wide, and the limit wavelength on the long wavelength side is long. Further, when the Al element is further added to the optical waveguide, the gain flatness is adjusted by adjusting the Al element addition concentration, and an optical amplifier is designed according to the application. Further, the concentration of the P element added to the optical waveguide is 8
When the content is not less than 0.3% by weight or the concentration of the Al element added to the optical waveguide is not more than 0.3% by weight, the limit wavelength on the long wavelength side of the gain spectrum is tellurite glass as a host. This is almost the same as the case where the Er-doped optical waveguide is used.

According to the laser oscillator of the present invention, since the optical waveguide is made of quartz, it is easy to manufacture, has high strength, and can be connected to other generally used quartz optical waveguides. Easy. Further, since the P element is added to the optical waveguide in addition to the Er element, as compared with the case where the P element is not added, the wavelength range in which laser oscillation can be performed is wider and the limit wavelength on the longer wavelength side is increased. long. Further, when the Al element is further added to the optical waveguide, the flatness of the laser oscillation intensity with respect to the wavelength is adjusted by adjusting the Al element addition concentration. When the concentration of the P element added to the optical waveguide is 8% by weight or more, or when the concentration of the Al element added to the optical waveguide is 0.3% by weight or less, laser oscillation is possible. The limit wavelength on the long wavelength side of the wavelength band is almost the same as that when an Er-doped optical waveguide using tellurite glass as a host is used.

[Brief description of the drawings]

FIG. 1 is a table summarizing the composition of each of three types of silica-based optical fibers.

FIG. 2 is a graph showing the wavelength dependence of the stimulated emission cross section and the ESA cross section of a type a optical fiber.

FIG. 3 is a graph showing the wavelength dependence of the stimulated emission cross section and ESA cross section of a type b optical fiber.

FIG. 4 is a graph showing the wavelength dependence of the stimulated emission cross section and the ESA cross section of a type c optical fiber.

FIG. 5 is a configuration diagram of an optical amplifier according to the present embodiment.

FIG. 6 is a graph showing a gain spectrum of an optical amplifier using each of three types of silica-based optical fibers.

FIG. 7 is a configuration diagram of a laser oscillator according to the present embodiment.

[Explanation of symbols]

10: amplification optical fiber, 11, 12: excitation light source, 1
3,14 ... optical fiber, 15,16 ... WDM coupler, 1
7 Input terminal connector, 18 Output terminal connector, 20 Amplifying optical fiber, 21 Excitation light source, 22 Optical isolator, 23 Output terminal connector, 24, 25 Optical fiber grating.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI H04B 10/02

Claims (8)

[Claims] 1. A quartz optical waveguide to which Er element and P element are added is provided.
An optical amplifier characterized by optically amplifying signal light having a wavelength of at least nm. 2. The optical amplifier according to claim 1, wherein the concentration of the P element added to the optical waveguide is 8% by weight or more. 3. The optical amplifier according to claim 1, wherein an Al element is further added to said optical waveguide. 4. The method according to claim 3, wherein the concentration of the Al element added to the optical waveguide is 0.3% by weight or less.
An optical amplifier according to any of the preceding claims. 5. A laser oscillator comprising a quartz-based optical waveguide to which Er and P elements are added, and oscillating laser light having a wavelength of 1570 nm or more, which is induced and emitted in the optical waveguide. 6. The laser oscillator according to claim 5, wherein the concentration of the P element added to the optical waveguide is 8% by weight or more. 7. The laser oscillator according to claim 5, wherein an Al element is further added to said optical waveguide. 8. The method according to claim 7, wherein the concentration of the Al element added to the optical waveguide is 0.3% by weight or less.
A laser oscillator as described.