JPH0450136A - Functional multifunctional 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 Nd<3+> used as an active substance to a host glass consisting essentially of a fluoride and specifying concentration of NaF3, etc., contained in the host glass. CONSTITUTION:Nd<3+> used as an active substance is added to a host glass consisting essentially of a fluoride to carry out amplification of light in 1.3mum wavelength band of functional multi-component glass. In this time, concentration of NaF or AlF3 in the above-mentioned multi-component glass is kept to an amount of >=3mol% and to the extent that the glass performance is not deteriorated. Thereby the functional multi-component glass enabling amplification of light in 1.3mum band is obtained. A core is formed using the above-mentioned glass and clad having refraction index lower than that of the core is provided to afford the optical fiber in which light is enclose, having extremely low light loss. As a result, the optical fiber enables application to light amplifier, etc., having high regain.

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 ion (N d '') is 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 formed from this glass.
°Announced in January 1990). In this report, regarding the characteristics of optical fibers, the fluorescence peak wavelength is 1.323 μm, the ESA
(excited 5tate absorputio
n) Peak wavelength 1.310μm, amplification peak wavelength 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 11000pp of + as an active substance (OFC90Po5t De
In this report, a Zr-Ba-La-Al-F glass having an amplification peak at a wavelength of approximately 1.33 μm has been reported.
The fluorescence peak wavelength is estimated to be 1.32 μm.

[Invention or problem to be solved]

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 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 multi-component in which Nd3+ is added as an active substance to a host glass mainly composed of fluoride. We have discovered a glass that enables optical amplification in the 1.3 μm band.

In this first functional multi-component glass containing fluoride as a main component, the concentration of NaF is 3 mo 1% or more, which is an amount that does not deteriorate the glass form performance. Also,
In the second functional multi-component glass, A I F g
The concentration is set to 3m01% or more, which is an amount that does not deteriorate the glass shape performance. NaF and AlF3 may be partially replaced with oxides. Various fluorides such as zirconium, barium, and lanthanum can be used as components of the multicomponent glass serving as the host glass (matrix glass). In addition, silicon, aluminum,
Oxides such as alkalis may also be added.

According to the first functional multi-component glass of the present invention, N
Regarding the fluorescence spectrum and ESA spectrum of d3+ near 1.3 μm, the peak wavelength can be shifted or the intensity can be increased or decreased. As a result, 1.3μm
It has been found, as described below, that a glass suitable for optical amplification in a strip can be obtained. Further, according to the second functional multi-component glass, by changing the concentration of AlF3 within a range of 3 mol% or more and an amount that does not deteriorate the glass shape performance, it is possible to It was similarly found that it was possible to shift the peak wavelength or increase/decrease the intensity of the fluorescence spectrum and ESA spectrum of , and to obtain a glass suitable for optical amplification in the wavelength band of 1.3 μm.

Regarding the above phenomenon, the present inventor formulated and studied the following hypothesis. In other words, such changes in the fluorescence spectrum and ESA spectrum near 1.3 μm of Nd""(7)
It can be considered that this is caused by a change in the ligand field such as an electrostatic field that is received by d''(r).

In other words, NaF or 30, which forms part of the host glass, is affected by changes in the concentration of A I Fa, and the symmetry of the Nd ligand group, covalent bonding with surrounding fluorine, etc. change. considered to be a thing. As a result, the energy level of the N d "" ion fluctuates, or its degeneracy is resolved, and the N
It is considered that the radiation/absorption transition probability of d''9-on changes, and furthermore, the peak wavelength of the radiation/absorption shifts.

The above is one 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.

FIG. 6 is a diagram showing the energy level of Nd3+ added to a glass sample for comparison.

As a comparative glass sample, Nd3+ doped Z
A fiber of r-Ba-La-A 1-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. Excitation light of approximately 0.80 μm causes electrons in ground level 4 to move to level F.
Dan excited 9/2 5/
2. When a population inversion is formed between the transition to the level F3/2 after emitting a phonon and (1), light emission with a peak wavelength of 13/2 and a length of 1.32 μm becomes possible.

On the other hand, there is a possibility that the electrons existing at the level F absorb light with a wavelength of 3/2, 1.31 μm, and be excited to the level G, 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 comparative glass sample.

The dotted line 1a above the horizontal line corresponds to quasi 3/2 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 F3/2 to the 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
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 present inventor conversely controlled the absorption and emission spectra of Nd3+ to achieve a wavelength of 1.3 μm.
We thought that it might be possible to achieve sufficient gain for optical amplification in the band. Here, for example, by changing the concentration of NaF or AlF3 constituting the host glass, Nd
By changing the ligand group around 3+, the energy level of Nd3+ in this ligand group is also relatively changed, and as a result, the absorption and emission of Nd''+ is It is thought that it becomes possible to change the characteristics of the spectrum.

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

FIGS. 7(b) and 7(C) show a method of 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 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 1c s2c 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 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 1e 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 the absorption and emission spectra le and 2e 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, 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.

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 in (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 this variation in absorption and emission spectra from considerations within the ligand field, by changing the concentration of NaF or AlF3, which constitutes a part of the host glass, N
It can be considered that the ions around d3+ are replaced by Na ions or AI ions, and the N d "" O ligand group changes significantly.

It is also conceivable that by changing the concentration of NaF or AlF3, an indirect change may occur in the arrangement structure of atoms around Nd3+. This kind of structural change causes NaF
Or, depending on the amount of AlF3 added, the asymmetry of the ligand groups formed by the host glass increases or decreases, or the co-3+4 nature of the Nd-F bond changes, and the F level of Nd itself changes. 3/
2. The phenomenon of variation in the ligand group of Nd3+ is thought to be complex, and the details are unknown, but in any case, according to the experiments and studies of the present inventors, NaF or A
By setting the concentration of lF3 to 3m01% or more, which does not deteriorate the glass shape performance, N d "O
The absorption and emission spectra can be varied, and by selecting the concentration of NaF or AlF3 according to the concentration of Nd3+ and other components that make up the host glass, optical amplification in the 1.3 μm wavelength band is possible. It was found that a promising glass can 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 having a cladding having a low refractive index.

Specifically, the above optical fiber is manufactured as follows. First, a preform having a core of functional multi-component glass doped with Nd"+ is prepared by the rod-in-tube method. Next, the prepared preform is set in a drawing device as shown in Figure 3, and an optical fiber is Draw a line to the 3rd
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 Nd''+.

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 NaF or AlF3 in the core glass containing fluoride as a main component is 3 mol % or more, which is an amount that does not deteriorate the glass form performance, optical amplification gain can be obtained even in the 1.31 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 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 the 1.3 μm band fiber amplifier equipped with the above optical fiber, laser light source, and optical means, Nd3+ is excited by the 0.8 am laser light introduced into the fiber by the optical means. This excited Nd3+ was introduced into the optical fiber at the same time.
, a laser beam is generated by being guided by a signal light in the 3 μm band, and optical amplification in the 1.3 μm wavelength band becomes possible.

〔Example〕

Examples of the present invention will be described below.

First, as raw materials for host glass, Z r F a, Ba
F5LaF, AlF3, and NaF are prepared, and each is mixed to have various composition ratios. A predetermined amount of NdF3, which is a fluoride of the rare earth element Nd, is added to this,
The atmosphere is controlled and melted in a platinum crucible. After sufficient mixing, the molten raw materials are rapidly cooled and vitrified. These vitrified samples were named samples A1BSC, D, E, F, and G according to their composition ratios. The compositions of these samples A to G and a separately prepared comparative sample are shown in FIG.

In order to evaluate the optical amplification characteristics of these glass samples, fibers were 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. Nd"+ is not added to the glass of the Clad and Clad pipes. These core rods and Clad Vibes are formed into preforms by the rod-in-tube method, and drawn with the apparatus shown in Figure 3 to have a core diameter of 6 μm and an outer diameter. A 5M fiber of 125 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. The laser light source 32 is a T laser with an excitation wavelength of 0.78 μm and an excitation output of 10 mW.
1-A sapphire laser (argon excitation) was used. The input signal strength is 30 dBm, and the peak wavelength is 1.3
It was set to 10 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 wavelength band of 1.3 μm, the concentration of NaF is in the range of 3 to 40 mo1%, or the concentration of AlF3 is in the range of 3 mo1%.
It can be seen that in the range of ~10mo1%, a gain greater than the predetermined value can be obtained. Also, in this range, the amplification peak is 1
．． It falls within the range of 310±0.015 μm. Furthermore, NaF
If the concentration of AIF3 is less than 3 mol%, no significant effect will be obtained. It is believed that the low concentration of NaF or AlF3 does not allow effective changes in the ligand field. On the other hand, when the concentration of NaF is 30 m
o If it exceeds 1%, the glass tends to crystallize. Also,
Even if the concentration of AlF3 exceeds 10 mo1%, the glass tends to crystallize. However, it is believed that glass crystallization can be improved to some extent by improving the glass composition cooling method.

It is observed that as the concentration of NaF 2 or AlF 3 increases, the fluorescence peak, ESA peak, and amplification peak gradually shift toward shorter wavelengths. This is because the amount of A1 ions or Na ions placed around Nd"+ increases, and the influence of these AI and Na ions on the ligand field of Nd"+ increases, resulting in a large wavelength shift. considered to be a thing.

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. Furthermore, the optical resonator phyto-backs the emitted light in the wavelength band of 1.3 μm from within the optical fiber to the optical fiber.

According to the above-described fiber laser, Nd"+ is excited by a laser beam with a wavelength band of 0.8 μm introduced into the fiber by an optical means. This excited Nd"+
A part of the light is emitted from the optical fiber at a wavelength of 1.3 μm, and a part of the light is emitted from the optical fiber at a wavelength of 1.3 μm and is fed back into the optical fiber at a wavelength of 1.3 μm.
It is guided by light in the 3 μm band and generates emitted light in the 1.3 μm wavelength band. By repeating this, wavelength 1
．． Laser emission in the 3 μm band 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 0.8 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 first and second functional multi-component glasses of the present invention containing fluoride as a main component, the presence of excitation light makes it possible to emit light and amplify light in the 1.3 μm band. .

Furthermore, by forming this into a waveguide, fiber, etc., it can be applied to optical amplification devices, 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 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 the multi-functional multi-component glass according to the present invention. Fig. 4 shows the fiber sample used for characteristic evaluation, and Fig. 5 shows the configuration of the apparatus and optical amplifier for evaluating the characteristics of the fiber sample. Figure 6 is a diagram showing an example of the excited level of N d "!on, and Figure 7 is a diagram explaining the gain at 1.310 μm. 10.30...Glass doped with Nd3+ an optical fiber having a core thereof, 32...a laser light source for excitation, 33
...Cabra is an 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 NaF is 3 mol % or more, which is an amount that does not deteriorate glass shape performance. 2. For optical amplification in the wavelength band of 1.3 μm, this is a functional multi-component glass in which Nd^3^+ is added as an active substance to a host glass whose main component is fluoride, and the concentration of AlF_3 is 3 mol%. A functional multi-component glass characterized in that the amount is above the level that does not deteriorate the glass shape performance. 3. An optical fiber comprising a core made of the functional multi-component glass according to claim 1 or 2, and a cladding surrounding the core and having a lower refractive index than the core. 4. The optical fiber according to claim 3, which propagates signal light with a wavelength of 1.3 μm band, a laser light source that generates pumping light with a wavelength of 0.8 μm band, and a method for amplifying the signal light with the pumping light. and an optical means for causing excitation light to enter the optical fiber from the laser light source.