JPH10270785A - Amplifying optical waveguide and optical amplifier using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical waveguide for configuring a wideband optical amplifier having a small gain power dependency and a small signal transmission amount dependency of a gain, and an optical amplifier using the same. SOLUTION: The clad part is made of at least one kind of glass selected from oxide glass, halide oxide glass, halide glass and chalcogenide glass, and the clad part is made of Er, Fe, Ni, Co, Cu, Cr. An amplifying optical waveguide containing at least one element selected from the group consisting of at least one kind of glass selected from halide oxide glass, halide glass and chalcogenide glass; Including an element, an optical isolator, and an optical waveguide for amplification,
And 1.5 using the optical waveguide as an amplification optical waveguide.
μm band optical amplifier.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical waveguide used in optical communication and the like, and an optical amplifier using the same.

[0002]

2. Description of the Related Art Quartz glass fibers doped with Er as active ions have been used in optical amplifiers for amplifying optical signals in the 1.5 μm band, and have played a major role in speeding up optical communication. However, since a silica-based glass fiber can obtain a flat gain characteristic only in a narrow wavelength range, an amplification medium having a wider band is required. Against this background, broadening the bandwidth of Er-doped quartz glass fibers,
Research on Er-doped halide glass, chalcogenide glass, etc. has been actively conducted.

[0003]

SUMMARY OF THE INVENTION Halide glass, chalcogenide glass and halide oxide glass to which Er is added have a flat gain band wider than that of quartz glass and 1.5 μm.
It is expected as an amplification medium for m-band wavelength multiplexing communication.
However, in these media, the slope of the gain flat portion changes due to the change in pump power (hereinafter, this slope is referred to as the gain slope).
However, it is necessary to use a narrow pump power range or correct the gain slope. To correct the gain slope, the signal light intensity is compared before and after amplification, the pump power is adjusted to make the gain constant, or the attenuation is adjusted by a variable filter. Both are problems that lead to the enlargement of the system. A method of connecting a plurality of fibers having different gain inclinations has also been proposed, but has the same problem in that the system becomes complicated. Further, when performing wavelength division multiplexing communication, the gain is small at a wavelength where the signal transmission amount is large, and the gain is large at a wavelength where the signal transmission amount is small, so that the signal strength is likely to vary.

[0004]

The present inventors have conducted intensive studies to solve the above-mentioned problems, and as a result, have found that the cladding portion of the optical waveguide has at least one selected from Er, Fe, Ni, Co, Cu, and Cr. The inventors have found that the addition of one kind of element can alleviate the dependence of the gain gradient on the excitation power and the difference in signal intensity, and have reached the present invention.

That is, according to the present invention, there is provided an oxide waveguide, a halide oxide glass, a halide glass, in which a clad portion of an optical waveguide contains at least one element selected from Er, Fe, Ni, Co, Cu and Cr. An optical waveguide made of at least one kind of glass selected from chalcogenide glass, and at least an excitation light source, an optical multiplexer / demultiplexer, an optical isolator, and an amplification optical waveguide,
The present invention also provides a 1.5 μm band optical amplifier using the optical waveguide as an optical waveguide for amplification.

Hereinafter, the present invention will be described in detail. The present invention
The cladding of the optical waveguide is made of at least one selected from Er, Fe, Ni, Co, Cu, and Cr in order to reduce the pump power dependence of the gain slope of the broadband optical amplifier and the gain difference due to the difference in signal transmission amount. It is characterized by comprising at least one kind of glass selected from oxide glass, halide oxide glass, halide glass and chalcogenide glass containing an element.

In order to realize an amplifying action in the 1.5 μm band, it is common to add Er to the core portion of the optical waveguide. Amplifying action of 1.5μm band, from ⁴ I _13/2 of Er ⁴
We are using the transition to the I _15/2. FIG. 1 shows an example of the absorption cross section in the 1.5 μm band of Er, and FIG. 2 shows an example of the stimulated emission cross section. The following relationship exists between the stimulated emission cross section, absorption cross section, and gain coefficient.

G = N _u * σ _e −N _l * σ _a (1) G: gain coefficient N _u : number of upper level atoms N _l : number of lower level atoms σ _e : Stimulated emission cross section σ _a : absorption cross section When the excitation power is increased, N _l decreases and _Nu increases.
Therefore, the gain increases, but the gain spectrum also changes. The calculation results of the gain coefficient change in the case of changing the ratio of N _u and N _l in fluoride glass in FIG. 3. The vertical axis is normalized with the maximum gain coefficient being 0 dB. In this example, when the pumping power is increased, the gain near 1.53 μm is selectively increased, and the gain gradient is reduced to the right. Also, increasing than other wavelengths the signal transmission amount of a particular wavelength in the wavelength division multiplexing, the N _u corresponding to the specific wavelength decreases selectively. As a result, the gain spectrum changes according to the amount of signal transmission, and a constant amplification factor cannot be obtained.

As a method of alleviating or suppressing such a phenomenon, the present inventors have proposed a wavelength band in which the gain becomes larger than other wavelength ranges when the pumping power is increased (1.
In the 53 μm band), a method was found in which the absorption was increased or the absorption was selectively increased at a wavelength where the signal light intensity was large, and the gain could be flattened. Specifically, Er,
Adding at least one element selected from the group consisting of Fe, Ni, Co, Cu, and Cr (hereinafter, referred to as an absorption factor element);
This is a method of wavelength-selectively giving a loss to signal light that slightly penetrates and propagates into the cladding, thereby improving the pump power dependence and signal transmission amount dependence of the gain gradient as a whole.

Hereinafter, the principle will be described. In optical communication such as wavelength division multiplexing communication, when the pump power of an optical amplifier is increased, the signal light intensity of a specific wavelength (in the example of FIG. 3, the 1.53 μm band) is selectively increased. In addition, when the signal transmission amount of a specific wavelength is small, a relatively large gain is obtained, and a difference occurs in the intensity of the output signal light. The light intensity at the core / cladding interface is proportional to the light intensity of the signal light propagating in the core,
The light intensity distribution in the cladding decreases exponentially with distance from the core / cladding interface. For this reason, when the signal light intensity of a specific wavelength increases due to a change in gain slope,
The amount of light seeping into the clad will also increase. This state is schematically shown in FIG. As a result, the more strongly amplified signal light is absorbed and attenuated.
By this operation, a signal light that is uniformly amplified is finally obtained. For example, when Er is added as an absorption factor element, a selective gain limitation in the 1.53 μm band can be performed, so that the phenomenon illustrated in FIG. 3 can be suppressed. F
When e is added, signal light having a large amplification factor can be selectively attenuated in a wide wavelength range of 1.52 to 1.57 μm. When Cu is added, an effect similar to that when Er is added is obtained. The addition of the absorption factor element may be used alone or in combination depending on the purpose.

The amount of the absorption factor element to be added varies depending on the combination of the elements to be added, the waveguide design such as the length of the optical waveguide and the amount of Er added to the core, the applicable excitation power range, and the allowable range of the signal light intensity. Depends on various factors.
A range from 00 ppb to 5000 ppm is preferred. Below this range, a sufficient effect cannot be obtained, and above this range, the loss becomes too large and the amplification efficiency decreases.

When an optical amplifier is constructed using the optical waveguide of the present invention, any pumping source may be used as long as it is a laser in the 0.98 μm band, but it is small in size and high in efficiency and easily coupled to the optical waveguide. Preferred is a semiconductor laser (pigtailed semiconductor laser) that is coupled to the fiber using a lens system. As an excitation method, any method can be used as long as the excitation is efficiently performed, such as forward excitation, backward excitation, and bidirectional excitation. In addition, one laser may be used for excitation, or a plurality of lasers may be collectively used. Further, Er
It is also effective to use a laser having a wide oscillation wavelength band in order to enhance the pumping efficiency by making full use of the absorption band. Such a laser can be realized by combining a plurality of lasers having slightly different oscillation wavelengths or by using stimulated Raman scattering.

In order to combine the pump light and the signal light into one optical waveguide, an optical multiplexing / demultiplexing device is required. As the optical multiplexing / demultiplexing device, any method can be used as long as the insertion loss is small and multiplexing / demultiplexing can be performed efficiently. As such a multiplexing / demultiplexing element, a wavelength division multiplexing element (WDM) is suitable. From the viewpoint of reducing insertion loss, the optical multiplexing / demultiplexing device is preferably composed of a fiber or a planar waveguide optical component. When an optical isolator is built in the optical multiplexing / demultiplexing device, the size of the amplifier can be reduced and the insertion loss can be reduced.

The optical isolator may be any optical isolator that sufficiently suppresses return light and has a small insertion loss. As described above, it is preferable to integrate the optical element with another optical component because the amplifier can be reduced in size.

It is preferable that the gain monitoring function is built in or attached to the amplifier because the reliability of the optical communication system is improved. For monitoring the gain, any method may be used as long as the method can substantially compare the incident signal light intensity and the output signal light intensity. In the case of performing wavelength division multiplexing communication, a method capable of detecting and monitoring each signal assigned to each wavelength is desirable. Preferably, these functions are automatically adjustable by a remotely programmable microprocessor or the like.

As described above, by including at least one element selected from Er, Fe, Ni, Co, Cu, and Cr in the cladding of the amplification optical waveguide, the pump power dependence of the gain gradient can be reduced. By relaxing and reducing the difference in signal light intensity, an optical amplifier having a wide band and a constant gain can be provided.

[0017]

EXAMPLES The present invention will be further described below with reference to examples, but the present invention is not limited to these examples.

Example 1 Er was 0.1 wt% in the core and Cu was 1 ppm in the clad.
The added fluoride glass fiber was used. The basic glass compositions of the core and the clad are shown below. Er is replacing La. The numbers are mol%. Core: 51ZrF ₄ -19BaF ₂ -4.5LaF ₃ -2YF ₃ -2AlF ₃ -13.5LiF-8Pb
F ₂ clad: 40HfF ₄ -10ZrF ₄ -19BaF ₂ -3LaF ₃ -2YF ₃ -4AlF ₃ -22
NaF This fiber had a relative refractive index difference of 3.3% and a cutoff wavelength of 1.4 μm.

Next, the configuration of the optical amplifier used for the measurement is shown in FIG.
Shown in The fiber used for the measurement is 10 m in length. A semiconductor laser 3 with a fiber pigtail is used for excitation, and the optical multiplexing / demultiplexing device 2 and the high N.P. A. And the fluoride fiber 4 for optical amplification via the quartz fiber 5 of the first embodiment. The quartz fiber 5 and the fluoride fiber 4 were bonded using a V-groove block, and the bonded end face was optically polished obliquely to reduce reflection loss and fixed with an optical adhesive. The 1.55 μm band signal light was input from the optical multiplexing / demultiplexing element 2, the amplified outgoing light was passed through the optical isolator 6, and the measurement device 7 measured the pump power dependency of the gain.

FIG. 6 shows the pump power dependence of the gain. A gain flat width defined in a wavelength range of -1 dB from the maximum gain is used for evaluation. If the slope of the gain changes significantly, the flat gain width also changes greatly. As can be seen from FIG. 6, the change in the gain flat width is 1 nm when the pump power is from 80 mW to 120 mW.

Comparative Example 1 A fluoride glass fiber having Er added to the core in an amount of 0.1 wt% was used. No absorption factor element was added to the cladding. The glass composition is the same as in Example 1. Er replaced La.

The relative refractive index difference of this fiber is 3.3%,
The cutoff wavelength was 1.4 μm. The length of the fiber used for the measurement is 10 m. The dependence of the gain on the pump power at this time was measured in the same manner as in Example 1.
FIG. 7 shows the pump power dependence of the gain. Excitation power of 8
The change in the gain flat width when changing from 0 mW to 120 mW is 5.7 nm, and the change in the 1.53 μm band is large.

Example 2 1 wt% of Er was added to the core with the glass composition described in Example 1.
%, A fluoride glass planar optical waveguide in which Co was added to the cladding at 1 ppm was used. Er replaced La. The relative refractive index difference of this waveguide is 3.3%, and the cutoff wavelength is 1.
45 μm and the waveguide length is 20 cm. A measurement system was configured in the same manner as in Example 1. The positioning of the fiber and the waveguide was performed using a stage with fine movement adjustment so that the signal light transmittance was maximized. Pump power from 80mW to 1
When changed to 20 mW, the change in gain flat width is 2n
m.

Example 3 With the glass composition described in Example 1, 1 wt% of Er was added to the core.
%, And a fluoride glass planar optical waveguide in which 1 ppm of Ni was added to the cladding was used. Er replaced La. The relative refractive index difference of this waveguide is 3.3%, and the cutoff wavelength is 1.
45 μm and the waveguide length is 20 cm. A measurement system was configured in the same manner as in Example 1. The positioning of the fiber and the waveguide was performed using a stage with fine movement adjustment so that the signal light transmittance was maximized. Pump power from 80mW to 1
When changed to 20 mW, the change in gain flat width is 2n
m.

COMPARATIVE EXAMPLE 2 1 wt% of Er was added to the core in the glass composition described in Example 1.
An added fluoride glass planar optical waveguide was used. No absorption factor element was added to the cladding. Er is replacing La. This waveguide has a relative refractive index difference of 3.3%, a cutoff wavelength of 1.45 μm, and a waveguide length of 20 cm. A measurement system was configured in the same manner as in Example 1. The positioning of the fiber and the waveguide was performed using a stage with fine movement adjustment so that the signal light transmittance was maximized. When the pump power was changed from 80 mW to 120 mW, the change of the gain flat width was 6 nm.

Example 4 Er was 0.1 wt% in the core and 10 pp Er was in the clad.
Fluoride / fluorophosphate glass fiber added with m was used. The basic glass compositions of the core and the clad are shown below. E
r replaced La. The numbers are mol%. Core: 53ZrF ₄ -20BaF ₂ -4LaF ₃ -3AlF ₃ -20NaF Clad: 9.7AlF ₃ -9.5Al (PO ₃ ) ₃ -53.8RF-27.1MF ₂ (R: L
i, Na, M: Mg, Ca, Sr, Ba)

The relative refractive index difference of this fiber is 2.0%,
The cutoff wavelength was 1.35 μm. The fiber used for the measurement is 10 m in length. A measurement system was configured in the same manner as in Example 1, and the pump power dependence of the gain was measured. As a result, when the pump power was changed from 80 mW to 120 mW, the change of the gain flat width was 0.9 nm.

COMPARATIVE EXAMPLE 3 The same basic glass composition as in Example 4, except that Er was 0.1
Fluoride / fluorophosphate glass fiber with wt% added was used. No absorption factor element was added to the cladding. The relative refractive index difference of this fiber was 2.0%, and the cutoff wavelength was 1.35 μm. The fiber used for the measurement is 10 m in length. A measurement system was configured in the same manner as in Example 1, and the pump power dependence of the gain was measured. as a result,
When the pump power was changed from 80 mW to 120 mW, the change of the gain flat width was 5.8 nm.

Example 5 Er was 0.1 wt% for the core and 10 pp for Er for the clad.
Fluoride / fluorophosphate glass fiber added with m was used. The basic glass compositions of the core and the clad are shown below. The numbers are mol%. Core: 18InF ₃ -12GaF ₃ -20ZnF ₂ -30BaF ₂ -10GdF ₃ -10LuF ₃ Cladding: 12Al (PO ₃ ) ₃ -11.1AlF ₃ -36.6RF-40.3MF ₂ (R: L
(i, Na, M: Mg, Ca, Sr, Ba)

The relative refractive index difference of this fiber is 1.9%,
The cutoff wavelength was 1.35 μm. The fiber used for the measurement is 10 m in length. A measurement system was configured in the same manner as in Example 1, and the pump power dependence of the gain was measured. As a result, when the pump power was changed from 80 mW to 120 mW, the change of the gain flat width was 0.9 nm.

Example 6 Er was 0.1 wt% in the core and Fe was 100 p in the clad.
Fluoride / fluorophosphate glass fibers added with pb were used. The basic glass compositions of the core and the clad are the same as in Example 4.

The relative refractive index difference of this fiber is 1.9%,
The cutoff wavelength was 1.35 μm. The fiber used for the measurement is 10 m in length. A measurement system was configured in the same manner as in Example 1, and the pump power dependence of the gain was measured. As a result, when the pump power was changed from 80 mW to 120 mW, the change of the gain flat width was 0.9 nm.

COMPARATIVE EXAMPLE 4 The same basic glass composition as in Example 5, except that the core contained
Fluoride / fluorophosphate glass fiber with wt% added was used. No absorption factor element was added to the cladding. The relative refractive index difference of this fiber was 1.9%, and the cutoff wavelength was 1.35 μm. The fiber used for the measurement is 10 m in length. A measurement system was configured in the same manner as in Example 1, and the pump power dependence of the gain was measured. as a result,
When the pump power was changed from 80 mW to 120 mW, the change of the gain flat width was 5.6 nm.

Example 7 Er was 1 wt% in the core, and 500 ppm of Er was in the clad.
An added chalcogenide / fluorophosphate glass planar waveguide was used. The basic glass compositions of the core and the clad are shown below. The numbers are mol%. Core: 30In ₂ S ₃ -40Ga ₂ S ₃ -30La ₂ S ₃ Cladding: 12Al (PO ₃ ) ₃ -11AlF ₃ -30.5RF ₂ -46.5MF ₂ (R: Mg,
(Ca, M: Sr, Ba)

The waveguide had a relative refractive index difference of 3% and a cutoff wavelength of 1.45 μm. The waveguide used for the measurement is 20 cm in length. A measurement system was configured in the same manner as in Example 2, and the pump power dependence of the gain was measured. As a result, when the pumping power was changed from 80 mW to 120 mW, the change in the gain flat width was 1.1 nm.

Comparative Example 5 The same basic glass composition as in Example 7 was used, and 1 wt% of Er was added to the core.
% Planar chalcogenide / fluorophosphate glass waveguide was used. No absorption factor element was added to the cladding. The relative refractive index difference of this waveguide was 3%, and the cutoff wavelength was 1.45 μm. The waveguide used for the measurement is length 2
0 cm. A measurement system was configured in the same manner as in Example 2, and the pump power dependence of the gain was measured. As a result, when the pump power was changed from 80 mW to 120 mW, the change of the gain flat width was 6.2 nm.

[0037]

By using the optical waveguide of the present invention,
A wide-band optical amplifier having a small dependence of the gain on the pump power and the signal transmission amount can be constructed, whereby a large-capacity high-speed optical communication network with high reliability can be constructed.

[Brief description of the drawings]

FIG. 1 is a diagram showing a 1.5 μm band absorption cross section of Er.

FIG. 2 is a diagram showing a 1.5 μm band stimulated emission cross section of Er.

3 is a graph showing changes in gain factor in the case of changing the ratio of N _u and N _l.

FIG. 4 is a diagram schematically showing a relationship between signal light intensity and an amount of signal light entering a clad.

FIG. 5 is a configuration diagram of an optical amplifier of the present invention.

FIG. 6 is a diagram illustrating the pump power dependence of the gain of the fiber amplifier according to the first embodiment.

FIG. 7 is a diagram illustrating pump power dependence of the gain of the fiber amplifier of Comparative Example 1.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Incident part of signal light 2 Optical multiplexing / demultiplexing element 3 Semiconductor laser 4 Optical amplification fiber 5 High N.P. A. Quartz fiber 6 Optical isolator 7 Measuring instrument

Claims (6)

[Claims] 1. An optical waveguide having an amplifying effect substantially in a 1.5 μm band, wherein Er, Fe,
An amplification optical waveguide comprising at least one element selected from the group consisting of Ni, Co, Cu, and Cr. 2. The amplification optical waveguide according to claim 1, wherein the clad portion is made of at least one kind of glass selected from oxide glass, halide oxide glass, halide glass, and chalcogenide glass. 3. The core part is made of at least one kind of glass selected from halide oxide glass, halide glass and chalcogenide glass.
An optical waveguide for amplification as described in the above. 4. A 1.5 μm band comprising at least an excitation light source, an optical multiplexing / demultiplexing element, an optical isolator, and an optical waveguide for amplification, and using the optical waveguide according to claim 1 as an optical waveguide for amplification. Optical amplifier. 5. The 1.5 μm band optical amplifier according to claim 4, wherein the amplification optical waveguide is made of a fiber. 6. The 1.5 μm band optical amplifier according to claim 4, wherein the amplifying optical waveguide comprises a planar optical waveguide.