JPH0450137A - Functional multi-component glass, optical fiber and fiber amplifier - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

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 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 "") are added as an active substance is already known. Specifically, New Glass Forum, ° (Announced in January 1990). In this report, regarding the characteristics of optical fiber, the fluorescence peak wavelength is 1.323 μm % E
SA (excited 5tate absorption)
It is shown that results were obtained with a peak wavelength of 1.310 μm and an amplification peak wavelength of 1.360 μm.

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 the invention]

However, in the oxide-based multicomponent 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 intensive research and has developed a functional product in which Nd''+ is added as an active substance to a host glass mainly composed of fluoride. We have discovered a multi-component 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 fluoride of lanthanide elements other than Nd is 3 m
The amount is set to be at least 0.1 ol % and to an extent that does not deteriorate the glass shape performance. As such lanthanide elements,
La,,Er,Yb.

HoSPm55m5Eu etc. can be used. Further, a part of the fluoride of these lanthanoid elements may be replaced with an oxide. Various fluorides such as zirconium, barium, and alkali 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, by changing the concentration of fluoride of a lanthanoid element other than Nd within a range of 3 mol% or more and an amount that does not deteriorate the glass form performance, 1 of Nd3+ , the peak wavelength of the fluorescence spectrum and the ESA spectrum near 3 μm 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+
``'' (7) It is possible to consider that this is caused by a change in the ligand field such as the electrostatic field that is received.

In other words, N
d"0':) It is thought that the symmetry of the ligand field, covalent bonding with surrounding fluorine, etc. change.

As a result, the energy level of Nd3-on changes or its degeneracy is resolved, the transition probability of radiation/absorption of Nd3+ ions changes, and furthermore, the peak wavelength of the radiation/absorption shifts. it is conceivable that.

The above is a hypothesis, but based on the examples and studies described later, the present inventors utilized or controlled this phenomenon to create a 1.3 μm band of Nd3+-doped functional multi-component glass. The aim was to improve the amplification characteristics. Hereinafter, the use of such a phenomenon will be explained based on FIGS. 6 and 7.

Figure 6 shows Nd3+O added to a glass sample for comparison.
FIG. 3 is a diagram showing the energy level.

As a comparative glass sample, Nd3+ doped Z
An r-Ba-La-AI-Na-F glass fiber 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. With excitation light of approximately 0.80 μm,
After emitting a phonon, it transitions to the ground level F. When a population inversion is formed between the levels 4F3/2 and 1 due to such pumping, the wave 13/
2 Emission of light with a peak length of 1.32 μm becomes possible.

There is also a possibility that it absorbs light of 1.31 μm and is excited to the G level 7/2. 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. Therefore, laser gain cannot be obtained in the 1.31 μm band. FIG. 7(a) schematically shows such gain loss in the comparison glass sample.

The dotted line 1a above the horizontal line corresponds to the quasi 3/2 level from the level F, and the dotted line 2a below the horizontal line corresponds to the absorption spectrum due to the transition from the level F to the 3/2 level G. 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
or 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 calculated that N d "" (7
) By controlling the 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 fluoride of a lanthanide element other than Nd that constitutes the host glass, the surrounding ligand group of N d 3"+7) can be changed, and the N inside
It is thought that the energy level of d3+ is also relatively changed, and as a result, it becomes possible to change the absorption/emission spectrum characteristics of Nd3+.

This idea will be explained with reference to FIGS. 7(b) to 7(f).

FIGS. 7(b) and 7(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 longer wavelength side, and the peak of the gain characteristic corresponding to the solid line 3b given as the sum of absorption and emission spectra 1b 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 IC12C are shifted to the short wavelength side, and the peak of the gain characteristic corresponding to the real u 3 c given as the sum of the absorption and emission spectra IC%2c is 1.
．． The idea is to shift it to 31 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 the 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 absorption and emission spectra le and 2e 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 absorption and emission spectra 1 es 2 e shifts to the shorter wavelength side, and the overall gain also increases, and a large gain is obtained at 1.31 μm. It will be done. In FIG. 7(f), the peak wavelengths of the absorption and emission spectra if 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 given as the sum of the absorption and emission spectra if and 2f shifts to the long wavelength side, but the overall gain increases by 1.31 μm.
But there are gains.

By changing the concentration of NaF or AlF3 constituting a part of the host glass within a predetermined range,
It is unclear which of the phenomena (f) is occurring. From the amplification peak characteristics obtained in the following examples, mainly Fig. 7 (
It is thought that the phenomenon of C) or (e) is occurring, but there is also a possibility that a combination of phenomena is occurring.

To explain the fluctuation phenomenon of absorption and emission spectra from considerations within the ligand field, by changing the concentration of fluoride of lanthanide elements other than Nd, which constitute a part of the host glass, It can be considered that some of the ions of Nd are replaced by Nd ions, and the ligand group of Nd3+ changes greatly.Also, by changing the concentration of fluoride of lanthanoid elements other than Nd, Nd
"0":) It is also possible that an indirect change occurs in the arrangement structure of surrounding atoms.This change in structure may be caused by accumulation depending on the amount of fluoride of lanthanide elements other than Nd, and the formation of the host glass. The asymmetry of the ligand group formed by Nd is increased or decreased, or the covalentity 3+4 of the Nd-F bond is changed, and the F3/2 level of Nd itself is thought to be complex, and the mechanism is Although the details of
By setting the amount to be 1% or more and not deteriorating the glass form performance, the absorption and emission spectra of Nd3+ can be varied, and the absorption and emission spectra of Nd3+ can be varied to match the concentration of Nd'' and other components constituting the host glass. By selecting the concentration of fluoride of a lanthanoid element other than Nd, wavelength 1.
It was found that a promising glass capable of optical amplification in the 3 μm band could be 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 a final 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, since the concentration of fluoride of lanthanoid elements other than Nd in the core glass mainly composed of fluoride is set to 3 mol% or more, which is an amount that does not deteriorate the glass form performance, optical amplification is possible even in the 1.31 band. gain is obtained. 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. and 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 cutting the excitation light, and the optical spectrum analyzer 35 is a device for measuring the amplified signal light. Matching oil 37
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
”+ 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, as raw materials for host glass, Z r F a, Ba
F, LaF 5ErF 5AIF3 and NaF
are prepared and mixed in various composition ratios. A predetermined amount of NdF3, which is a fluoride of the rare earth element Nd, is added to this, and the atmosphere is controlled to melt it in a platinum crucible. The molten raw materials are vitrified after sufficient mixing is completed. These vitrified samples are classified into samples A1, A2, B1, B2, C1, C2, and Dl according to their composition ratios.
and B2. The compositions of these samples A1 to D2 and the composition of a separately prepared comparative sample are shown in FIG.

In order to evaluate the optical amplification characteristics of this glass sample, a fiber was fabricated as follows. A glass rod having the above composition is formed into a rod shape to form a glass rod for the core. Next, a glass having approximately the same composition as this glass rod and a slightly lower refractive index is melted and molded to form a clad vibe. Cladva 3+ Eve glass does not contain Nd. These core rods and clad vibes are formed into preforms using the rod-in-tube method, and drawn using the apparatus shown in Figure 3 to form 3M wires with a core diameter of 6 μm and an outer diameter of 125 μm.
fiber was obtained. This 3M 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. The laser light source 32 has an excitation wavelength of 0.78. czm, excitation output is 10mW
A Ti-sapphire laser (argon excitation) was used.

The input signal strength 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, the concentration of LaF3 is in the range of 3 to 15 mo1%, or the concentration of ErF3 is in the range of 3 to 15 mo1%.
It can be seen that in the range of 15mo 1%, a gain greater than a predetermined value can be obtained. Also, in this range, the amplification peak is 1
．． It falls within the range of 310±0.015 μm. in this case,
Depending on the concentration of LaF3 or E r F3, the fluorescence peak, ESA peak, and amplification peak gradually move toward shorter wavelengths.

In addition, the concentration of L a F 3 and ErF 3 is 3 m o
If it is less than 1%, no significant effect can be obtained. L a F 3
It is believed that the low concentrations of E r F s and E r F s are unable to cause effective changes in the ligand groups. On the other hand, if the concentration of L a F a exceeds 15 mo1%, the glass will crystallize. Further, even if the concentration of E r Fa exceeds 15 mo1%, the glass will crystallize. However, it is thought that such crystallization can be improved to some extent by improving the glass composition, improving the cooling method, etc.

As already mentioned, it is observed that as the concentration of LaF and E r F 3 increases, the amplification peak gradually shifts to the shorter wavelength side. This is because the amount of La ions or Er ions that are arranged around Nd3+ and have a large radius increases, and these La ions, which affect the ligand groups of Nd3+,
It is thought that the influence of Er ions increases and a large wavelength shift occurs.

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 Nd” (
r) Part of the light is emitted from within the optical fiber in the wavelength band of 1.3 μm 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 with a wavelength of 1° and 3 μm. 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 known Er-doped fiber lasers (rEr-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 0.8 μ
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. Nd3+ in the optical fiber is excited to a predetermined state, and light emission in the 1.3 μm wavelength band becomes possible. Here, since the output end of the fiber is finished with a mirror finish, this output end and the end face of the laser diode constitute 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.

[Brief explanation of drawings]

Figure 1 is a diagram showing an example of the functional multi-component glass containing fluoride as the main component according to the present invention, Figure 2 is a diagram showing the absorption and emission characteristics of the glass in Figure 1, and Figure 3 is a diagram showing the present invention. A diagram illustrating a method of forming a fiber using the functional multicomponent glass according to the invention,
Figure 4 shows the fiber sample used for characteristic evaluation, Figure 5 shows the configuration of the apparatus and optical amplifier for evaluating the characteristics of the fiber sample, and Figure 6 shows the excitation level of Nd3+ ions. FIG. 7 is a diagram showing an example of the gain at 1.310 μm. 10. 0...3+ Optical fiber having Nd-doped glass as its core, 2...Laser light source for excitation, 3...Coupler as optical means.

Claims (1)

[Claims] 1. A functional multi-component glass in which Nd^3^+ is added as an active substance to a host glass mainly composed of fluoride for optical amplification in the 1.3 μm wavelength band, A functional multi-component glass characterized in that the concentration of fluoride of a lanthanide element other than Nd is 3 mol % or more and is in an amount that does not deteriorate glass form performance. 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.