JP2004071889A - Optical fiber for optical amplification and wavelength converter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical fiber for optical amplification suited for being used for a wavelength converter and to provide the wavelength converter containing this optical fiber for optical amplification. <P>SOLUTION: An optical fiber 10 for optical amplification is an optical fiber obtained by applying a rare earth element (e.g., Er, Tm, Pr, Nd, etc.) to an optical guide region, and the rare earth element is stimulated by entering a stimulation light of a predetermined wavelength, and when the stimulated rare earth element is mitigated to a lower level, an emitted light of a predetermined wavelength is generated. The optical fiber 10 for optical amplification has a zero dispersive wavelength λ<SB>0</SB>between a wavelength λ<SB>p</SB>of the excited light which can stimulate the applied rare earth element and a maximum wavelength λ<SB>max</SB>of the emitted light generated when the stimulated rare earth element is mitigated to a lower level. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an optical fiber for optical amplification in which a rare earth element is added to an optical waveguide region, and a wavelength converter including the optical fiber for optical amplification.
[0002]
[Prior art]
2. Description of the Related Art In an optical communication system, an optical amplifier for optically amplifying a signal light is used in order to compensate for a loss incurred by the signal light while propagating through an optical fiber transmission line. As this optical amplifier, a rare earth element-doped optical fiber amplifier using an optical amplification optical fiber in which a rare earth element is added to an optical waveguide region as an optical amplification medium is used. The optical fiber for optical amplification to which the rare earth element is added, the rare earth element is excited by the excitation light of the predetermined wavelength being incident thereon, and the emitted light of the predetermined wavelength is emitted when the excited rare earth element is relaxed to the lower level. The signal light is generated and the signal light can be amplified using the stimulated emission phenomenon.
[0003]
An EDFA (Erbium Doped Fiber Amplifier), which is one type of the optical fiber amplifier, uses an optical amplification optical fiber (EDF: Erbium Doped Fiber) to which an Er element is added as a rare earth element as an optical amplification medium. In this EDFA, by supplying excitation light having a wavelength of 980 nm or 1480 nm to the EDF, signal light having a wavelength included in the C band (1530 nm to 1565 nm) or the L band (1565 nm to 1625 nm) can be optically amplified. .
[0004]
[Problems to be solved by the invention]
The optical fiber for optical amplification to which a rare earth element is added can be used not only as an optical amplification medium of an optical fiber amplifier as described above, but also in a wavelength converter. However, an optical fiber for optical amplification suitably used in an optical fiber amplifier is not suitable for use in a wavelength converter.
[0005]
The present invention has been made in order to solve the above problems, and provides an optical amplification optical fiber suitable for use in a wavelength converter, and a wavelength converter including the optical amplification optical fiber. With the goal.
[0006]
[Means for Solving the Problems]
In the optical fiber for optical amplification according to the present invention, the rare-earth element is added to the optical waveguide region, the wavelength of the excitation light capable of exciting the added rare-earth element, and the excited rare-earth element is in the lower level. It is characterized by having a zero-dispersion wavelength between the longest wavelength of emitted light generated upon relaxation.
[0007]
The wavelength converter according to the present invention includes the optical amplification optical fiber according to the present invention described above, and a pumping light supply unit that supplies pumping light to the optical amplification optical fiber. Light of one wavelength is incident, and light of a second wavelength different from the first wavelength is output from an optical amplification optical fiber.
[0008]
According to the present invention, in the optical fiber for optical amplification in which the rare-earth element is added to the optical waveguide region, the added rare-earth element is excited by the excitation light. When the light of the first wavelength enters the optical fiber for optical amplification, stimulated emission occurs in the optical fiber for optical amplification, and the non-linear optics is generated because the zero wavelength dispersion of the optical fiber for optical amplification is within the above range. One type of phenomenon is four-wave mixing or non-degenerate four-wave mixing. Therefore, light of the second wavelength different from the input light of the first wavelength is generated in the optical amplification optical fiber, and the light of the second wavelength is output from the optical amplification optical fiber.
[0009]
Optical fiber for optical amplification according to the present invention, the ratio of the mode field diameter MFD and cutoff wavelength lambda _c at the wavelength of the emitted light (MFD / lambda _c) it is preferred that it is 6.8 or less. Preferably, the mode field diameter is less than 9 μm at the wavelength of the emitted light. In this case, the optical fiber for optical amplification has good bending characteristics, and has a small bending loss and excellent wavelength conversion efficiency even if it is coiled into a small diameter and modularized.
[0010]
In the optical fiber for optical amplification according to the present invention, it is preferable that the rare earth element is Er, the concentration of Er added is 50 wtppm or more, and the absorption peak at a wavelength of 1.53 μm is 30 dB / m or less. In this case, when the first wavelength and the second wavelength belong to the L band, the concentration quenching is suppressed and the length can be increased.
[0011]
In the optical fiber for optical amplification according to the present invention, it is preferable that the rare earth element is Er, the concentration of Er added is 50 wtppm or more, and the absorption peak at a wavelength of 1.53 μm is 8 dB / m or less. In this case, when the first wavelength and the second wavelength belong to the C band, the concentration quenching is suppressed and the length can be increased.
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described 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.
[0013]
FIG. 1 is a configuration diagram of a wavelength converter 1 according to the present embodiment. The wavelength converter 1 shown in FIG. 1 includes an optical fiber 10 for optical amplification, an optical coupler 20, an excitation light source 30, and an optical filter 40, and is used together with the light source 50. The optical amplification optical fiber 10 is an optical fiber in which a rare-earth element (for example, Er, Tm, Pr, Nd, etc.) is added to the optical waveguide region, and the rare-earth element is excited by exciting light having a predetermined wavelength. Then, when the excited rare earth element is relaxed to a lower level, emitted light of a predetermined wavelength is generated. The optical fiber for optical amplification 10 has a wavelength between the wavelength of the excitation light capable of exciting the added rare earth element and the longest wavelength of the emission light generated when the excited rare earth element relaxes to the lower level. , Zero-dispersion wavelength.
[0014]
Excitation light source 30 is for outputting excitation light of wavelength lambda _p that excites the added rare earth element in the optical amplification optical fiber 10, for example, a semiconductor laser light source is preferably used. Light source 50 outputs the first wavelength lambda ₁ of light. The first wavelength λ ₁ is close to the wavelength of the emitted light generated when the rare earth element added to the optical amplification optical fiber 10 relaxes from the excitation level to the lower level. The optical coupler 20 receives the pumping light output from the pumping light source 30 and the light output from the light source 50, combines them, and outputs the combined light to the optical amplification optical fiber 10. The optical filter 40, the second wavelength lambda ₂ of the light newly generated in the optical amplification optical fiber 10 selectively transmits and outputs.
[0015]
The excitation light output from the excitation light source 30 is supplied to the optical amplification optical fiber 10 via the optical coupler 20. In the optical fiber for optical amplification 10 to which the excitation light is supplied, the added rare earth element is excited. At this time, when the light of the first wavelength λ ₁ output from the light source 50 enters the optical amplification optical fiber 10 via the optical coupler 20, stimulated emission occurs in the optical amplification optical fiber 10, and Since the zero-wavelength dispersion of the optical fiber 10 is within the above range, four-wave mixing or non-degenerate four-wave mixing, which is a kind of nonlinear optical phenomenon, occurs. Accordingly, in the optical fiber 10 for optical amplification, light of the second wavelength λ ₂ different from the light of the first wavelength λ ₁ output from the light source 50 is generated, and the light of the second wavelength λ ₂ is The light is transmitted to the outside through 40. The second wavelength lambda ₂ of the light output from the optical filter 40 is responsible for the same information as the first wavelength lambda ₁ of the light output from the light source 50. That is, the wavelength converter 1 converts the wavelength of the signal light output from the light source 50.
[0016]
In FIG. 1, the pumping light output from the pumping light source 30 is supplied to the optical amplification optical fiber 10 in the forward direction, but the excitation light is supplied to the optical amplification optical fiber 10 in the reverse direction. Alternatively, the pumping light may be supplied to the optical amplification optical fiber 10 in both the forward and reverse directions.
[0017]
FIG. 2 is a diagram illustrating the chromatic dispersion characteristics of the optical fiber for optical amplification 10 according to the present embodiment. As shown in this figure, the optical fiber for optical amplification 10 has a wavelength λ _{p of} excitation light capable of exciting the added rare earth element, and a light beam generated when the excited rare earth element is relaxed to a lower level. _Has a zero dispersion wavelength λ ₀ between the longest wavelength λ _max of the emitted light. If rare earth elements to be added to the optical amplification optical fiber 10 is Er, the pumping light wavelength lambda _p is 1480nm band or 980nm band, emitted light longest wavelength lambda _max is 1615 nm.
[0018]
Further, if the rare earth element doped to the optical amplification optical fiber 10 is Tm, the pumping light wavelength lambda _p is 0.8μm band, 1.05 .mu.m band, a 1.2μm band or 1.4μm band, emitted light The longest wavelength λ _max is 1510 nm. If rare earth elements to be added to the optical amplification optical fiber 10 is Pr, the pump light wavelength lambda _p is 1.04μm band, emitted light longest wavelength lambda _max is 1310 nm. If rare earth elements to be added to the optical amplification optical fiber 10 is Nd, the pumping light wavelength lambda _p is 0.8μm band, emitted light longest wavelength lambda _max is 1310 nm.
[0019]
Further, in the optical fiber 10 for optical amplification according to the present embodiment, it is preferable that the ratio (MFD / λ _c ) between the mode field diameter MFD and the cutoff wavelength λ _{c at} the wavelength of the emitted light is 6.8 or less. It is preferable that the mode field diameter be less than 9 μm at a wavelength of 1550 nm. In this case, the optical amplifying optical fiber 10 has good bending characteristics, and has a small bending loss and excellent wavelength conversion efficiency even if it is coiled into a small diameter and modularized.
[0020]
Further, in the optical fiber for optical amplification 10 according to the present embodiment, it is preferable that the rare earth element to be added is Er, and the concentration of Er added is 50 wtppm or more. Also, Al is co-added in addition to Er, and the Al concentration is preferably 1 wt% or more, and more preferably the Al concentration is 3 wt% or more. By doing so, concentration quenching can be suppressed. Further, if the absorption peak at a wavelength of 1.53 μm is 30 dB / m or less, when the first wavelength λ ₁ and the second wavelength λ ₂ belong to the L band, concentration quenching can be suppressed and the length can be increased. A structure in which four-wave mixing or non-degenerate four-wave mixing is more easily generated can be provided. When the absorption peak at a wavelength of 1.53 μm is 8 dB / m or less, when the first wavelength λ ₁ and the second wavelength λ ₂ belong to the C band, the concentration quenching is suppressed, and the length can be increased. A structure in which four-wave mixing or non-degenerate four-wave mixing is more easily generated can be provided.
[0021]
FIG. 3 is a graph showing the relationship between the effective cutoff wavelength and the bending loss of the optical fiber for optical amplification 10 according to the present embodiment. Here, the optical fiber for optical amplification 10 has a step index type refractive index profile, and Er is added to the core region, and the relative refractive index difference Δn of the core region with respect to the cladding region is 0.5%. Or 0.7%. The bending loss is a value at a wavelength of 1550 nm when the optical fiber amplifier 10 having a length of 67 m is wound with a winding diameter of 35 mmφ. Further, the effective cutoff wavelength is based on ITU-T regulations, and is based on the difference in transmission characteristics when winding is performed once at each of a bending radius of 140 mm and 30 mm. As can be seen from this figure, the bending loss is smaller as the effective cutoff wavelength is longer and the relative refractive index difference Δn is larger. The bending loss is preferably 0.05 dB or less, and for that purpose, the effective cutoff wavelength is preferably 1.03 μm or more, and more preferably 1.10 μm or more.
[0022]
Next, a first embodiment will be described. In the first embodiment, three types of EDF1, EDF2, and EDF3 were prepared as the optical fiber 10 for optical amplification. EDF1 had a zero dispersion wavelength of 1.38 μm, a mode field diameter of 5.74 μm at a wavelength of 1.55 μm, and an Er addition concentration of 912 wt ppm. EDF2 had a zero dispersion wavelength of 1.57 μm, a mode field diameter of 5.46 μm at a wavelength of 1.55 μm, and an Er addition concentration of 1140 wtppm. EDF3 had a zero-dispersion wavelength of 1.65 μm, a mode field diameter of 7.81 μm at a wavelength of 1.55 μm, and an Er addition concentration of 790 wtppm.
[0023]
Light of two wavelengths was simultaneously incident on the optical fiber for amplification 10 from the light source 50, and the wavelengths of the light were 1574.5 nm and 1609.0 nm, and the power of the light of each wavelength was 0 dBm. The excitation light output from the excitation light source 30 has a wavelength of 1480 nm, and was supplied to the optical amplification optical fiber 10 from both the forward direction and the reverse direction. The power of the pump light supplied from the forward direction was 360 mW, and the power of the pump light supplied from the reverse direction was 270 mW.
[0024]
Further, the spectrum of the light output from the optical amplification optical fiber 10 was measured without using the optical filter 40. The ambient temperature was 25 ° C. The power of each of 1574.5 nm and 1609.0 nm output from the optical amplification optical fiber 10 was +22.3 dBm, and the power of all light output from the optical amplification optical fiber 10 was +25.3 dBm.
[0025]
FIG. 4 is a diagram showing a spectrum of light output from the optical amplification optical fiber 10 in the first embodiment. As can be seen from this figure, non-degenerate four-wave mixing occurs in the EDF 2 having a zero dispersion wavelength between the excitation light wavelength (1480 nm) and the emission light wavelength, and the output power peaks around 1583 nm. Was confirmed.
[0026]
Next, a second embodiment will be described. In the second embodiment, two types of EDFs 4 and 5 are prepared as the optical fiber 10 for optical amplification. EDF4 had a zero dispersion wavelength of 1.33 μm, a mode field diameter of 6.01 μm at a wavelength of 1.55 μm, and an Er concentration of 1332 wtppm. The EDF 5 had a zero dispersion wavelength of 1.53 μm, a mode field diameter of 5.40 μm at a wavelength of 1.55 μm, and an Er addition concentration of 1153 wtppm.
[0027]
Light of 10 wavelengths was simultaneously incident on the optical amplification optical fiber 10 from the light source 50, the wavelength of the light was in the range of 1574.5 nm to 1607.6 nm, and the power of the light of each wavelength was +0.3 dBm. . The excitation light output from the excitation light source 30 has a wavelength of 1480 nm, and was supplied to the optical amplification optical fiber 10 from both the forward direction and the reverse direction. The power of the pump light supplied from the forward direction was 400 mW, and the power of the pump light supplied from the reverse direction was 400 mW. Further, the spectrum of the light output from the optical amplification optical fiber 10 was measured without using the optical filter 40. The ambient temperature was 25 ° C. The power of all light output from the optical amplification optical fiber 10 was +26 dBm.
[0028]
FIG. 5 is a diagram showing a spectrum of light output from the optical amplification optical fiber 10 in the second embodiment. FIG. 3A shows an output light spectrum when the EDF 4 is used as the optical fiber 10 for optical amplification. FIG. 2B shows an output light spectrum when the EDF 5 is used as the optical fiber 10 for optical amplification. As can be seen by comparing FIGS. 7A and 7B, four-wave mixing occurs in the EDF 5 having a zero-dispersion wavelength between the excitation light wavelength (1480 nm) and the emission light wavelength. Then, light of a new second wavelength was generated between the wavelengths of the input 10 light beams.
[0029]
【The invention's effect】
As described above in detail, according to the present invention, in the optical fiber for optical amplification in which the rare-earth element is added to the optical waveguide region, the added rare-earth element is excited by the excitation light. When the light of the first wavelength enters the optical fiber for optical amplification, stimulated emission occurs in the optical fiber for optical amplification, and the non-linear optics is generated because the zero wavelength dispersion of the optical fiber for optical amplification is within the above range. One type of phenomenon is four-wave mixing or non-degenerate four-wave mixing. Therefore, light of the second wavelength different from the input light of the first wavelength is generated in the optical amplification optical fiber, and the light of the second wavelength is output from the optical amplification optical fiber. This optical fiber for optical amplification can be suitably used in a wavelength converter.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of a wavelength converter 1 according to the present embodiment.
FIG. 2 is a diagram showing the wavelength dispersion characteristics of the optical fiber for optical amplification 10 according to the present embodiment.
FIG. 3 is a graph showing a relationship between an effective cutoff wavelength and a bending loss of the optical fiber for optical amplification 10 according to the present embodiment.
FIG. 4 is a diagram illustrating a spectrum of light output from the optical amplification optical fiber in the first embodiment.
FIG. 5 is a diagram showing a spectrum of light output from an optical fiber for optical amplification 10 in a second embodiment.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... wavelength converter, 10 ... optical amplification optical fiber, 20 ... optical coupler, 30 ... excitation light source, 40 ... optical filter, 50 ... light source.

Claims (6)

A rare earth element is added to the optical waveguide region,
Having a zero-dispersion wavelength between the wavelength of the excitation light capable of exciting the added rare earth element and the longest wavelength of the emission light generated when the excited rare earth element is relaxed to the lower level;
An optical fiber for optical amplification, characterized in that: 2. The optical fiber according to claim 1, wherein a ratio (MFD / [lambda] _c ) of a mode field diameter MFD to a cutoff wavelength [lambda] _{c at} the wavelength of the emitted light is 6.8 or less. The optical fiber for optical amplification according to claim 1, wherein a mode field diameter is less than 9 µm at a wavelength of the emitted light. The optical fiber for optical amplification according to claim 1, wherein the rare earth element is Er, the concentration of Er added is 50 wtppm or more, and the absorption peak at a wavelength of 1.53 µm is 30 dB / m or less. The optical fiber for optical amplification according to claim 1, wherein the rare earth element is Er, the concentration of Er added is 50 wtppm or more, and the absorption peak at a wavelength of 1.53 µm is 8 dB / m or less. An optical fiber for optical amplification according to claim 1, and an excitation light supply unit for supplying excitation light to the optical fiber for optical amplification,
Light of a first wavelength is incident on the optical fiber for optical amplification, and light of a second wavelength different from the first wavelength is output from the optical fiber for optical amplification;
A wavelength converter characterized in that:

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