JPH0450135A - Functional multi-component glass, optical fiber and fiber amplifier - Google Patents

Abstract

PURPOSE:To obtain a functional multi-component glass enabling amplification of light in 1.3mum wavelength band by adding a fluoride containing Nd<3+> as an active substance and containing NdF3 having a specific concentration as a main component. CONSTITUTION:Nd<3+> used as an active substance is added to a functional multi- component glass consisting essentially of a fluoride to carry out amplification of light in 1.3mum wavelength band. In the above-mentioned functional multi- component glass, concentration of NdF3 is kept to 100-10000 mol ppm. Thereby the peak wavelength of fluorescent spectrum and ESA spectrum in the vicinity of 1.3mum wavelength band of Nd<3+> is shifted or strength of the peak wavelength is increased or decreased to provide the glass matched in amplification of light in 1.3mum band. The above-mentioned functional multi-component glass is used as a core and clad having refraction index lower than that of the core is provided to afford an optical fiber capable of efficiently enclosing in low loss. Therefore, in the aimed optical fiber, application to light amplifier having high gain is made possible.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a functional multi-component glass containing fluoride as a main component, and is used, for example, for optical amplification in the 1.3 μm band.

[Conventional technology]

Functional multi-component glasses doped with rare earth elements generally contain 1
．． 1,3μm carried out in the range of 310±0.025μm
Applications are being considered for optical fiber amplifiers, optical fiber sensors, etc. used in broadband optical communications.

For example, as such a functional multi-component glass, one in which an oxide-based multi-component glass is used as a host glass and neodymium ions (N d 3+) are added as an active substance is already known. Specifically, New Glass Forum reported that they prepared a glass in which Nd3+ was added to phosphate glass as a host glass, and evaluated the optical amplification characteristics of an optical fiber μ formed from this glass. °Announced in January 1990). In this report, regarding the characteristics of the optical fiber, the fluorescence peak wavelength is 1.323 μm, the ESA
(excited 5tate absorputio
n) Peak wavelength 1.310 μm 1 Amplification peak wavelength 1
．． It is shown that a result of 360 μm was obtained.

Furthermore, a fluoride-based multicomponent glass is used as a host glass, and Nd
Report on the optical amplification characteristics of a fiber doped with 11,000 pp of 3+ as an active substance (OFC90Po5t De
adline Paper”) has also been made. In this report, Z
r-Ba-La-AI-F glass has been reported, and the fluorescence peak wavelength is estimated to be 1.32 μm.

Problem to be solved by invention C] However, in the oxide-based multi-component glass shown in the former report, even though the fluorescence peak is 1.323 μm, the ESA
Since the absorption peak due to the transition exists exactly at 1.310 μm, not only does the amplification peak wavelength shift to the longer wavelength side, but also no gain can be obtained in the 1.3 μm band.

Similarly, in the case of the fluoride-based multi-component glass shown in the latter report, the amplification peak wavelength shifts to the longer wavelength side.
Sufficient gain cannot be obtained in the 1.3 μm band.

Therefore, in view of the above-mentioned circumstances, an object of the present invention is to provide a functional multi-component glass that enables optical amplification in the 1.3 μm band.

Another object of the present invention is to provide an optical fiber using the above functional multi-component glass.

A further object of the present invention is to provide a fiber amplifier using the above optical fiber.

[Means and effects for solving the problem] In order to solve the above problem, the present inventor has conducted extensive research and has developed a functional multi-component glass containing Nd''+ as an active substance and having fluoride as its main component. They discovered a glass that enables optical amplification in the 1.3 μm band.

In this functional multi-component glass containing fluoride as the main component, the concentration of NdF3 is 100 mol ppm to 10 mol ppm.
000 mol ppm. However, Nd”
(7) The addition does not necessarily have to be based on fluoride,
For example, Nd3+ may be added using Nd2O or the like. Various fluorides such as zirconium, barium, and lanthanum can be used as components of the multicomponent glass serving as the host glass (matrix glass). Further, oxides of silicon, aluminum, alkali, etc. may be added as an auxiliary agent.

According to the functional multi-component glass of the present invention, the concentration of NdF3 is 100 mol])I)s to 10000100O
By changing the range of 0 layer, 1.3 of Nd3+
For fluorescence spectra and ESA spectra in the vicinity of μm, the peak wavelength can be shifted or the intensity can be increased or decreased. As a result, it was found that a glass suitable for optical amplification in the 1.3 μm band could be obtained, as described below.

Regarding the above phenomenon, the present inventor formulated and studied the following hypothesis. That is, such changes in the fluorescence spectrum and ESA spectrum near 1.3 μm of Nd3+
"+77) It is possible to think that this is caused by changes in the ligand group, such as the electrostatic field that it receives.

In other words, it is considered that the symmetry of the ligand group, the covalent bonding property with surrounding fluorine, etc. change under the influence of the concentration of Nd3+. As a result, the energy level of the Nd3+ ion changes, or its degenerate body dissolves, and the radiation/absorption transition probability of the Nd3+ ion changes, and furthermore, the peak wavelength of the radiation/absorption shifts. It will be done.

Although the above is a hypothesis, the present inventors utilized or controlled this phenomenon based on the examples described later and studies thereof, and the 1.
The aim was to improve the amplification characteristics in the 3 μm band. Hereinafter, the use of such a phenomenon will be explained based on FIGS. 6 and 7.

Figure 6 shows the amount of N d ” added to a glass sample for comparison.
FIG. 3 is a diagram showing O energy levels.

As a comparative glass sample, Nd''+ doped Z
A fiber of r-Ba-La-A I-Na-F glass was used. The illustrated energy levels were calculated by measuring this fiber using a self-recording spectrophotometer and an optical spectrum analyzer. Typical transitions among these will be explained. The ground level is reached by excitation light of approximately 0.80 μm. Such pumping causes the level
When a population inversion is formed between F3/2 and 1,
It becomes possible to emit light with a peak wavelength of 13/2 and a length of 1.32 μm.

On the other hand, there is a possibility that the electrons existing at level F absorb light with a wavelength of 3/2, 1.31 μm, and be excited to level G7/2. Therefore, in such a glass, even if electrons are pumped to the level F, it is no longer possible to efficiently emit light at a 3/2 wavelength of 1.32 μm. For this reason, laser gain cannot be obtained in the 1.31 μm band either. FIG. 7(a) schematically shows such gain loss in the O 2 comparative glass sample.

Corresponds to the emission spectrum due to the transition to position 1 13/
2 corresponds to the absorption spectrum due to the transition to the G level. The peaks of these spectra each have a wavelength of 1
．． It exists at a wavelength of 32 μm and a wavelength of 1.31 μm. Assuming that these intensities are equal and calculating the average value, the solid line 3a
is given. This solid line 3a is considered to correspond to the wavelength dependence of the optical amplification gain of this glass. Such a model explains why no gain is obtained at 1.3 μm, and explains why a certain amount of gain can be obtained at wavelengths longer than this.

Based on this assumption, the inventor conversely concluded that N d "L7)
By controlling absorption and emission spectra, wavelength 1.
We thought that it might be possible to achieve sufficient gain for optical amplification in the 3 μm band. Here, for example, by changing the concentration of Nd3+, which is an active substance, on the one hand, the ligand group around Nd3+ will be changed, and on the other hand, the energy level of Nd3+ in this ligand group will be changed. It is thought that this results in a relative change in the spectral characteristics of N d ''O absorption and emission.

This idea will be explained with reference to FIGS. m7 (b) to (f).

FIGS. 7(b) and (C) show a method for obtaining a gain in the 1.3 μm band by shifting only the peak wavelength of the absorption/emission spectrum shown in FIG. 7(a). Figure 7 (
In b), only the absorption spectrum 2b is shifted to the long wavelength side, and the peak of the gain characteristic corresponding to the solid line 3b given as the sum of the absorption and emission spectra lb and 2b is shifted to 1.31μ.
The idea is to shift it to m. FIG. 7(C) shows that both the absorption and emission spectra lc and 2c are shifted to the short wavelength side, and the peak of the gain characteristic corresponding to the solid line 3C given as the sum of the absorption and emission spectra 1cs2c is 1.3.
The idea is to shift it to 1 μm.

FIGS. 7(d) to (f) show a method of obtaining a gain in the 1.3 μm band by changing the peak intensity of the absorption/emission spectrum shown in FIG. 7(a). FIG. 7(d) shows absorption and emission spectra ld.

The peak wavelength of 2d itself is not changed, but only the relative intensities of the absorption/emission spectra ld and 2d are changed. As a result, although the peak wavelength of the gain characteristic corresponding to the solid line 3d given as the sum of absorption and emission spectra ld and 2d hardly changes, a gain can be obtained even at a wavelength of 1.31 μm.

In FIG. 7(e), the peak wavelengths of the absorption and emission spectra 1es2e are shifted to the shorter wavelength side, and their relative intensities are changed. As a result, the peak wavelength of the gain characteristic corresponding to the solid line 3e given as the sum of the absorption and emission spectra le and 2e shifts to the shorter wavelength side, and the overall gain increases, resulting in a large gain at 1.31 μm. . 7th
In Figure (f), the peak wavelengths of the absorption and emission spectra 1f and 2f are moved to the longer wavelength side, and their relative intensities are greatly changed. As a result, the peak wavelength of the gain characteristic corresponding to the solid line 3f, which is given as the sum of the absorption and emission spectra If and 2f, shifts to the longer wavelength side, but since the overall gain increases, even at 1.31 μm. gain is obtained.

It is unclear which of the phenomena in FIGS. 7(b) to (f) are occurring by varying the concentration of NdF, and therefore Nd3+, in the multicomponent glass. That is, from the amplification peak characteristics obtained in the following examples, it is considered that the phenomenon shown in FIG. 7(f) is mainly occurring, but there is also a possibility that a complex phenomenon is occurring.

To explain this variation in absorption and emission spectra from considerations within the ligand field, it is thought that the energy level of the electron orbit of the cation (N d 3+) splits or fluctuates under the influence of the host glass. It will be done. At the same time, changes may occur in the arrangement structure of surrounding atoms due to the strong interaction of cations with large radii.

Such structural changes accumulate depending on the amount of Nd3+ added, and the asymmetry of the ligand field formed by the host glass increases or decreases, or the covalent 3+4 nature of the Nd-F bond changes, and Nd itself F level and 3/
2 It is possible that a similar phenomenon is occurring. Therefore, N
The fluctuation phenomenon of the d3''co ligand field is thought to be complex, and the details of the mechanism are unknown.

In any case, according to the inventor's experiments and studies, NdF
3 concentration from 100111 ol ppm to 100001
By setting IO1pp11, the N d 3"O absorption/emission spectrum can be varied, and by selecting the concentration of NdF3 according to the composition of the host glass,
A promising glass that enables optical amplification in the 1.3 μm wavelength band was obtained.

The above-mentioned functional multi-component glass is used as a material for optical transmission paths, and may be formed into, for example, a planar waveguide. In order to obtain a long optical transmission line, it is desirable to produce an optical fiber equipped with a cladding having a low refractive index.

Specifically, the above optical fiber is manufactured as follows. First, a preform having a core of functional multicomponent glass doped with Nd3+ is prepared by a rod-in-tube method or the like. Next, the prepared preform is set in a drawing device as shown in FIG. 3, and drawn into an optical fiber. Third
As shown in the figure, the preform 11 is fixed to a feeding device 12 and gradually lowers. At this time, preform 11
is heated by the heater 13, softens, and starts drawing. The drawn fiber 10 is wound onto a winding drum 15 via a capstan 14.

FIG. 4 shows an enlarged view of the optical fiber 10 thus obtained. The optical fiber 10 includes a core 10a doped with Nd3+ and a cladding layer 10b having a relatively lower refractive index than the core 10a and not doped with Nd3+.

An optical fiber having a core made of functional multi-component glass as described above can be applied to fiber lasers, fiber amplifiers, fiber detectors, etc.

That is, the concentration of NdF3 in the core glass whose main component is fluoride is 100 a+ol ppm to 10000 mo11.
Since it is set to 00O0, an optical amplification gain can be obtained even in the 1.31 μm band. Furthermore, since light is efficiently confined in the core and the loss of the confined light is extremely low, population inversion can be formed with a low threshold value. Therefore, application to high gain optical amplification devices and the like becomes possible.

Furthermore, the optical fiber 10 described above can be used in one application example.
．． It can be used for 3 μm band fiber amplifiers.

As shown in Figure 5, the fiber amplifier has a diameter of 1.3μmμm.
- an optical fiber 30 that serves as a waveguide for the laser, a laser light source 32 that generates excitation light in the 0.8 μm band, and in order to amplify the signal light with the excitation light, the excitation light is input from the laser light source into the optical fiber; Optical means 33. The excitation light from the laser light source 32 is combined with the signal light from the signal light source 31 by an optical means 33 such as a fiber coupler. The combined signal light and excitation light are introduced into the fiber 30 via a connector or the like.

Incidentally, the 0.8μ provided on the output side of the optical fiber 30
The m filter 36 is for filtering and sorting the excitation light, and the optical spectrum analyzer 35 is a device for measuring the amplified signal light. Matching oil 3
7 is for preventing return light from the fiber coupler 33 formed by fusion drawing.

According to a 1.3 .mu.m band fiber amplifier including an optical fiber as described above, a laser light source, and an optical means, Nd3+ is excited by a 0.8 .mu.m laser beam introduced into the fiber by the optical means. This excited Nd
3+ means 1, 3 introduced into the optical fiber at the same time.
It generates laser light by being guided by signal light in the .mu.m band, making it possible to amplify light in the 1.3 .mu.m wavelength band.

〔Example〕

Examples of the present invention will be described below.

First, Z r F s, Ba
F 2 , LaF 5AIF3, and NaF are prepared and mixed in a composition ratio of 53:20:4:3:20. This is combined with Nd, which is a fluoride of the rare earth element Nd.
A predetermined amount of F3 is added, and the atmosphere is controlled to melt it in a platinum crucible. The amount of NdF3 added is such that the concentration of NdF3 is 50.100.100 molar concentration relative to the host glass.
Adjust so that it becomes 0.5000.10000.30000pp■. After sufficient mixing, the molten raw materials are rapidly cooled and vitrified. These vitrified samples are called Samples A and B depending on their concentration.

They were named C, D, and ESF. Its composition is shown in FIG.

In order to evaluate the optical amplification characteristics of this glass sample, a fiber was fabricated as follows. First, glass having the above composition is formed into a rod shape to form a glass rod for a core. Next, glass having approximately the same composition as this glass rod and a slightly lower refractive index is melted and formed into a clad pipe. NdF3 is not added to the glass of the clad pipe. These core rods and clad pipes are formed into preforms using the rod-in-tube method, and drawn using the apparatus shown in Figure 3 to have a core diameter of 6 μm and an outer diameter of 12
A 5M fiber of 5 μm was obtained.

This 5M fiber was cut into 10 m long fiber samples for measurement.

Evaluation of the characteristics of such a fiber sample is based on the fluorescence peak wavelength, ESA peak wavelength, amplification peak wavelength, and 1.310
A fiber amplifier shown in FIG. 5 was used to measure the gain in μm. The results are shown in the table in Figure 2.

The amplification peak and gain are determined by the signal light source 3 of the fiber amplifier.
1 and the laser light source 32 were turned on, and the fluorescence of the fiber sample was measured with the optical spectrum analyzer 35. However, the gain shown in the table of FIG. 2 is 1.
This is at 31 μm. As the laser light source 32, a Ti-sapphire laser (argon excitation) with an excitation wavelength of 0.7'8 um and an excitation output of 10 mW was used. The intensity of the input signal is -30 dBm, and the peak wavelength is 1.
It was set to 310 μm. The ESA peak wavelength was determined by determining the absorption wavelength of the fiber sample using a self-recording spectrophotometer and determining the energy wavelength. The fluorescence peak wavelength was determined by turning off the input of the signal light and measuring it using the optical spectrum analyzer 35 in the same way as the amplification peak.

Focusing on the gain in the 1.3 μm band, it can be seen that a gain greater than a predetermined value can be obtained when the concentration of NdF3 is in the range of 100 mol ppm to 10000 mol pps.

In addition, depending on the concentration of N d Fa, the fluorescence peak, E
The SA peak and the amplification peak gradually move toward longer wavelengths. It should be noted that if it is less than 100 mol ppm, there will be less Nd3+, which becomes active ions, and it is considered that highly efficient optical amplification cannot be performed. On the other hand, at 10,000 mol ppm or more, the amplification peak gradually shifts to the longer wavelength side, and no effective gain can be obtained at 1.31 μm. This is N
It is thought that as the concentration of 4-on increases, the influence on the ion's ligand field becomes too large, resulting in a large wavelength shift.As a result, the influence of the wavelength shift becomes smaller than the influence of the transition probability. It is considered that the amplification becomes larger than the above, and sufficient amplification cannot be obtained.

The optical fiber according to the present invention can also be applied to devices such as fiber lasers, for example.

Specifically, the fiber laser is configured to include the above-mentioned optical fiber, a laser light source, optical means, and an optical resonator. Here, the laser light source generates excitation light with a wavelength band of 0.8 μm. The optical means also causes excitation light to enter the optical fiber from the laser light source. Further, the optical resonator feeds back the 1.3 μm wavelength band emitted light from within the optical fiber to the optical fiber.

According to the above-described fiber laser, Nd3+ is excited by the laser light in the wavelength band of 0.8 μm introduced into the fiber by optical means. This excited N d
”O Part of the light is emitted light in the 1.3 μm wavelength band from within the optical fiber, and the wavelength 1 that is fed back into the optical fiber.
．． It is guided by light in the 3 μm band and generates emitted light in the 1.3 μm wavelength band. By repeating this, laser emission in the wavelength band of 1.3 μm becomes possible.

Examples of fiber lasers will be described below.

The specific configuration is similar to a known Er-doped fiber laser (“Er-doped fiber J, Oplu
s E, January 1990, pp.

See 112-118, etc. ). However, in the case of this embodiment, the Nd-doped optical fiber of the above embodiment is used as the optical fiber. In addition, as an excitation light source, a wavelength of 0.8μ
A laser diode that generates m-band excitation light is used.

The excitation light in the wavelength band of 0.8 μm from the laser diode is
It is introduced into the optical fiber shown in the above embodiments by suitable optical means such as a lens. The Nd''+ in the optical fiber is excited to a predetermined state, making it possible to emit light in the wavelength band of 1.3 μm.Since the output end of the fiber is finished with a mirror finish, this output end and the end face of the laser diode are constitutes a resonator.As a result, when the output of the excitation light exceeds a predetermined value, laser oscillation occurs in the wavelength band of 1.3 μm.

Note that the resonator may be of a type that uses a dielectric mirror or the like.

〔Effect of the invention〕

As explained above, according to the functional multi-component glass of the present invention containing fluoride as the main component, due to the presence of excitation light,
It becomes possible to emit light and amplify light in the μm band. Furthermore, by forming this into waveguides, fibers, etc., optical amplification devices,
Can be applied to lasers, etc. In particular, when formed into a fiber, an optical amplifier with a low threshold and high gain can be obtained.

10.30... Optical fiber having Nd3+ doped glass as its core, 32... Laser light source for excitation, 33
...Cabra is an optical means.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing an example of the functional multi-component glass according to the present invention, Fig. 2 is a diagram showing the absorption/emission characteristics etc. of the glass in Fig. 1, and Fig. 3 is a diagram showing an example of the functional multi-component glass according to the present invention. Figure 4 shows the method of forming the fiber used, Figure 4 shows the fiber sample used for characteristic evaluation, and Figure 5 shows the configuration of the device and optical amplifier for evaluating the characteristics of the fiber sample. , FIG. 6 is a diagram showing an example of the excitation level of Nd3+ ions, and FIG. 7 is a diagram explaining the gain at 1.310 μm.

Claims (1)

[Claims] 1. A functional multi-component glass containing Nd^3^+ as an active substance and containing fluoride as a main component for optical amplification in the wavelength band of 1.3 μm, wherein the concentration of NdF_3 is is 100molppm to 10000
A functional multi-component glass characterized by having mol ppm. 2. An optical fiber comprising a core made of the functional multi-component glass according to claim 1, and a cladding surrounding the core and having a lower refractive index than the core. 3. The optical fiber according to claim 2, which propagates signal light in the wavelength band of 1.3 μm, a laser light source that generates pump light in the wavelength band of 0.8 μm, and for amplifying the signal light with the pump light,
and an optical means for causing the excitation light to enter the optical fiber from the laser light source.