JP3228345B2 - Amplifying waveguide element and optical signal 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 amplifying waveguide device containing two or more rare earth ions and having an optical waveguide structure capable of highly efficient optical amplification, and an optical signal amplifier using the waveguide device.

[0002]

2. Description of the Related Art In recent years, in the field of optical communication, a method of amplifying an optical signal using light emission accompanying optical excitation of ions doped in an optical waveguide has begun to be studied. The principle is
It is based on the fact that when ions in the optical waveguide are photoexcited and in a population inversion state, light emission from the population inversion has an effect of amplifying signal light having the same wavelength as the light emission. Therefore, in order to obtain high amplification characteristics, it is only necessary to efficiently realize the population inversion state. In this sense, it is the same as the design of the waveguide structure or its composition for increasing the laser oscillation efficiency.

[0003]

However, optical signal amplifiers using rare earth ions generally have the following problems. That is, when the rare earth ions involved in the amplification have fluorescence outside the amplification wavelength band, the fluorescence outside the amplification wavelength band may cause laser oscillation. In particular, when the fluorescence in the amplification wavelength band and the other fluorescence emit light from the same energy level, laser oscillation in the fluorescence band other than the amplification wavelength band hinders the optical amplification in the amplification wavelength band that should be performed.

[0004] Here, this problem will be described below by taking as an example an optical fiber in which a core is doped with neodymium, which is expected as an optical fiber amplifier or optical fiber laser in a 1.3 μm band.

[0005]

BACKGROUND OF THE INVENTION The fluorescence intensity of neodymium ions is substantially higher at 1.06 μm than at 1.3 μm band. Therefore, when light in the 1.06 μm band is reflected in the optical amplifier, natural amplification oscillation of 1.06 μm occurs preferentially, and as a result, amplification in the 1.3 μm band is suppressed. To solve this problem, for example, a method is used in which a dielectric mirror having a high transmittance of 1.06 μm light and a high reflectance of 1.3 μm band light is closely attached to both ends of the fiber (W.
J. Miniscaleco et al., Electron. Lett. 1988, 24, 2
8-29, MCBrierley et al., Electron. Lett. 1988,
24, 438-439, F. Hakimi, et al., Optics Lett. 1989,
14, 1060-1061, SG Grubb, Electron. Lett. 1990,
26, 121-122) or a method of using a wavelength-selective fiber coupler to extract only the 1.06-μm-band fluorescence out of the optical amplifier system (Y. Miyajima, et al. Electron. Lett., 1).
990, 26, 1397-1398) have been proposed. Further, a method of directly depositing a wavelength-selective dielectric multilayer film on the end face of the fiber and performing non-reflection coating may be considered.

However, any of the above methods has a complicated configuration of the optical amplifier, and a simpler method has been desired. One solution to this problem is to co-dope ytterbium as an ion that selectively absorbs 1.06 μm fluorescence in a core containing neodymium.

However, ⁴ F of ² F _5/2 and Nejiumu ytterbium as shown in FIG. 1 as in this method, increasing both the concentrations of neodymium and ytterbium
The probability of non-radiative energy transfer with _3/2 increases, the number of neodymium in the excited state decreases, and as a result, 1.3
There is a problem that the fluorescence intensity of μm decreases, and high amplification characteristics cannot be obtained.

SUMMARY OF THE INVENTION The present invention has been made to solve the above technical problems, and an object of the present invention is to provide an optical signal amplifier having a simple structure and exhibiting high amplification characteristics, and an amplifier used in the amplifier. The present invention is to provide a waveguide element for use.

[0009]

In order to achieve the above-mentioned object, in the amplifying waveguide device of the present invention, a single core of the optical waveguide is alternately arranged along the longitudinal direction. It is characterized by comprising a portion containing neodymium and a portion containing ytterbium that absorbs 1.06 μm band fluorescence from the neodymium.

An optical signal amplifier according to the present invention comprises the above-described amplification waveguide element, a signal light source and an excitation light source respectively connected to one end of the amplification waveguide element via an optical coupler, A spectrum analyzer connected to the other end of the waveguide element.

[0011]

In the amplifying waveguide device of the present invention, the portion containing neodymium and the portion containing ytterbium are alternately arranged along the length direction in a single core of the optical waveguide. 1.0 from neodymium
Among the 6 μm fluorescent light, those traveling in the optical waveguide are efficiently absorbed. As a result, the natural amplification oscillation of 1.06 μm is suppressed, so that the fluorescence intensity in the 1.3 μm band increases, and high amplification characteristics are obtained.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in more detail with reference to the drawings.

The inventors studied the amplification characteristics of 1.3 μm band signal light in a zirconium fluoride fiber in which neodymium is dispersed. That is, when the core of the fiber has a double structure as shown in FIG. 1 and neodymium and ytterbium are dispersed in separate portions in the double core,
It has been found that optical signal amplification is greatly improved without using a wavelength-selective fiber coupler for outputting 1.06 μm light outside the amplifier system. In FIG. 1, reference numeral 1 denotes an optical fiber type waveguide device. This device 1 includes a core 2 and a clad 3. The core 2 is a concentric double core and includes an inner core 2a and an outer core 2b. One of neodymium and ytterbium is doped in the inner core 2a, and the other is doped in the outer core 2b.

The base material used for the amplifying waveguide element of the present invention is not limited to the above-mentioned fluoride glass, but may be glass having another composition, for example, silicate glass, phosphate glass, or fluorophosphate glass. Etc. can also be suitably used. Even when the glass having these other compositions is used, although the wavelength region showing the amplification characteristic is slightly different, the amplification characteristic can be greatly improved almost in the same manner as in the case of the above-mentioned fluoride glass.

FIGS. 2 and 3 show the structure of the present invention, which is a further improvement of the initial improvement example shown in FIG. 1, wherein portions containing neodymium and portions containing ytterbium are alternately provided along the length direction. 1 shows a configuration of an optical waveguide device. In FIG. 2, reference numeral 4 denotes a thin-film waveguide element. The element 4 includes a long core 5 having a rectangular cross section and a clad 6 stacked so as to sandwich the core 5. The core 5 includes a portion 5a containing neodymium and a portion 5b containing ytterbium which is divided from the neodymium portion 5a in the length direction of the core 5. FIG. 2 shows a part of the thin-film waveguide element 4. In practice, the portions 5a containing neodymium and the portions 5b containing ytterbium of the core 5 are alternately arranged along the length direction of the core 5. Have been.

In FIG. 3, reference numeral 7 denotes an optical fiber type waveguide device. This element 7 includes a cylindrical core 8 and a cylindrical clad 9. The core 8 includes a portion 8a containing neodymium, and the neodymium portion 8a is divided in the length direction of the core 8 and includes a portion containing ytterbium.
FIG. 3 shows a part of the optical fiber type element 7 similarly to FIG. 2. In practice, the neodymium portions 8a and the ytterbium portions 8b of the core 8 are alternately arranged along the length direction of the core 8. Have been.

As shown in FIGS. 2 and 3, an optical signal amplifier including an optical waveguide element having a configuration in which a portion containing neodymium and a portion containing ytterbium are alternately provided in a single core of the optical waveguide is also provided. As in the case of the amplifier using the element of the initial improvement example shown in FIG. 1, a remarkable improvement in the amplification characteristics is recognized as compared with the amplifier using the amplifying fiber containing neodymium alone. In the embodiment of the present invention,
It is characterized in that portions containing neodymium and portions containing ytterbium are alternately arranged in the length direction of the same core. Therefore, in the configuration of this embodiment, of the 1.06 micron band fluorescence generated by the excitation light, the fluorescence traveling in the core is efficiently absorbed by the portion containing ytterbium. As a result, the alternate arrangement of the present embodiment is more efficient than the case of absorbing the fluorescence that seeps into the portion containing ytterbium in the double core configuration of the above-mentioned initial improvement example.

Hereinafter, the effect of improving the amplification characteristics will be described with reference to a system using fluoride glass as a matrix. In the following effect confirmation test, a conventional technology and an initial improvement example of the present invention were compared in order to confirm the effect of the basic configuration of the present invention.

FIG. 4 shows a loss spectrum of an optical fiber in which only neodymium is dispersed. In FIG. 5, neodymium is used for the outer core 2b of the double core 2 of FIG. 1, ytterbium is used for the inner core 2a of the double core 2, and the concentration ratio of neodymium to ytterbium is 1:10. 7 shows a loss spectrum of an amplifying waveguide element of an initial improvement example. This figure 5
As can be seen, the absorption of ytterbium exists near 1.06 μm, which is the fluorescence wavelength of neodymium. FIGS. 7 and 8 show the results of measuring the fluorescence intensities of these two types of optical fibers using the evaluation system shown in FIG. Here, FIGS. 7 and 8 are normalized by the fluorescence intensity of the 1.06 micron band and the 1.3 micron band, respectively. In FIG. 6, reference numeral 10 denotes an ion-doped optical fiber as an amplification fiber. A signal light LD 12 and a pumping LD 13 are branched from the optical coupler 11 and connected to the incident end (the left side in FIG. 8) of the optical fiber 10 via the optical coupler 11. Further, a spectrum analyzer 15 is connected to the emission end of the optical fiber 10 via another optical coupler 14, and a computer 16 is sequentially connected to the spectrum analyzer 15.

As can be seen from FIGS. 7 and 8, the fluorescence spectrum intensity in the 1.3 μm band indicated by the arrow in the figure is significantly increased by providing the ytterbium-doped portion in addition to the neodymium-doped portion. I have. Comparing the fluorescence intensity of neodymium in the 1.06 μm band and the fluorescence intensity of the 1.3 μm band in such a doped system, 1.3 μm was obtained based on the difference in the absorption intensity of ytterbium in both wavelength regions.
The fluorescence intensity in the m band is relatively higher. FIG. 9 shows a graph of the amplification characteristic with respect to the signal light intensity. As is clear from FIG. 9, an amplification characteristic of 20 dB or more was obtained for a signal light of 20 dBm.

As described above, the features of the present invention are as follows.
The point is that neodymium which is a 1.3 μm phosphor and ytterbium which is an absorber of 1.06 μm light are alternately arranged in the length direction of one core. To explain this in more detail, in a conventional co-doped amplification waveguide element in which neodymium and ytterbium are uniformly dispersed in the same core, as the concentration of each rare earth element increases,
The probability of non-radiative energy transfer between ytterbium ² F _5/2 and neodymium ⁴ F _3/2 in the energy ranking diagram shown in FIG. 10 is increased, indicating a 1.3 μm fluorescence start state.
The number of neodymium in the ⁴ F _3/2 state is reduced,
The phenomenon that the fluorescence intensity of 1.3 micron is reduced becomes remarkable.

Therefore, in the amplification waveguide device of the present invention,
By doping neodymium and ytterbium into separate parts of the core, no such energy transfer occurs.
Ytterbium can be used only as the absorption band of the 06 μm light, and efficient amplification characteristics can be obtained without adding any contrivance to the optical signal amplifier. In addition, although this has a remarkable effect as compared with the prior art even in an optical signal amplifier having an optical waveguide having a double structure, a higher efficiency can be obtained by operating only the light traveling in the core of the optical waveguide. Is obtained, a great effect is produced in an optical signal amplifier in which portions containing neodymium and portions containing ytterbium are alternately arranged along the traveling direction of light. On the other hand, the concentration of the rare earth element may be any concentration as long as energy transfer between ions does not occur, and should be determined in consideration of the loss characteristics of the matrix used. The concentration at which energy transfer occurs was determined by measuring the concentration dependence of the fluorescence intensity or the fluorescence lifetime from the ion. On the other hand, the glass composition is not necessarily limited to fluoride glass. Obviously, any glass composition can be used as long as the ions used can be dispersed and an optical waveguide structure can be formed. However, when a glass having a low glass transition point is used as a matrix, a portion containing neodymium and a portion containing ytterbium form a concentric optical waveguide structure of the initial improvement example as shown in FIG. It is conceivable that an interaction occurs between the two ions due to the diffusion of the two ions at the contact portion. In order to prevent this interaction, it is effective to interpose an insulator layer not containing both ions between the both ion-containing portions in advance, but this causes a problem that the number of manufacturing steps is increased. It goes without saying that the thickness of the insulator layer depends on the conditions for producing the optical waveguide structure or the glass composition used.

[0023]

[0024]

[0025]

[0026]

[0027]

[0028]

As described above, according to the amplifying waveguide device of the present invention, 1.06 μm of neodymium fluorescence can be efficiently absorbed by ytterbium. Thus, an optical signal amplifier which is easier to design than the conventional method and has stable amplification characteristics can be obtained.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a cross-sectional structure of an initial improvement example of an amplification waveguide device of the present invention.

FIG. 2 is a perspective view showing a structure of one embodiment of an amplification waveguide device of the present invention.

FIG. 3 is a perspective view showing the structure of another embodiment of the waveguide device for amplification of the present invention.

FIG. 4 is a characteristic diagram showing loss characteristics of a fluoride fiber doped with neodymium.

FIG. 5 is a characteristic diagram showing a loss characteristic of a fluoride fiber as a specific example of the amplification waveguide element shown in FIG. 1;

FIG. 6 is a configuration diagram of an example of an optical signal amplifier for measuring a loss spectrum or a fluorescence spectrum of an optical fiber sample.

FIG. 7 is a diagram showing a fluorescence spectrum of the optical fiber shown in FIG. 4 when excited at 800 nm.

8 is a diagram showing a fluorescence spectrum when the amplification waveguide device shown in FIG. 5 is excited at 800 nm.

FIG. 9 is a characteristic diagram showing amplification characteristics with respect to signal light intensity in an optical fiber as an example of the amplification waveguide element shown in FIG.

FIG. 10 is an energy order diagram showing the energy order of neodymium and ytterbium.

[Explanation of symbols]

 Reference Signs List 1 optical fiber type waveguide element 2 core 2a inner core 2b outer core 3 clad 4 thin film type waveguide element 5 core 5a neodymium part 5b ytterbium part 6 clad 7 optical fiber type waveguide element 8 core 8a neodymium part 8b ytterbium part 9 clad DESCRIPTION OF SYMBOLS 10 Ion-doped optical fiber 11 Optical coupler 12 Signal light LD 13 LD for excitation 14 Optical coupler 15 Spectrum analyzer 16 Computer

Continuation of the front page (72) Inventor Elia Snitzer, Latgas University, Bread and Bowser Road, Piscataway, NJ, United States (56) References JP-A-3-259125 (JP, A) JP-A-4-31930 (JP A) JP-A-5-37047 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01S 3/07 G02F 1/35-3/02 G02B 6/12-6/14

Claims (2)

(57) [Claims] 1. A waveguide element for optical amplification, wherein a single core of the optical waveguide includes neodymium-containing portions alternately arranged along the length direction and 1.diodes from the neodymium. A portion containing ytterbium that absorbs fluorescence in the 06 μm band. 2. A single core of the optical waveguide, the portion including neodymium alternately arranged along its length and the portion including ytterbium that absorbs 1.06 μm-band fluorescence from the neodymium. An amplification waveguide device comprising: a signal light source and an excitation light source respectively connected to one end of the amplification waveguide device via an optical coupler; and the other end of the amplification waveguide device. An optical signal amplifier, comprising: a connected spectrum analyzer.