JPH0450134A - Functional multi-component glass, optical fiber and fiber amplifier - Google Patents

Abstract

PURPOSE:To improve light amplification in 1.3mum band by adding an oxide of element of Lanthanoids other than Nd to an oxide-based functional multi- component glass obtained by adding Nd<3+> used as an active substance to a host glass at a specific amount. CONSTITUTION:Nd<3+> used as an active substance is added to a host glass to provide the oxide based functional multi-component capable of amplifying light in 1.3mum wavelength band. An oxide of element belonging to Lanthanoids other than Nd is added as a component of the host glass to the above-mentioned multi-component glass at an amount of >=5mol% and to the extent that the glass forming function is not deteriorated, preferably at an amount of about 5-50mol%. Thereby a glass suitable in light amplification in 1.3mum band is obtained. The aimed optical fiber applicable to optical fiber amplifier having low light loss and high regain is obtained from a core consisting of the functional multicomponent glass obtained therefrom and clad having refraction index lower than that of the core.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an oxide-based functional multi-component glass, which is used, for example, for light 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 (Nd3+) are added thereto as an active substance is already known. Specifically, N d ” is added to the phosphate glass that is the host glass.
It has been reported that glass doped with `` was prepared and the laser oscillation characteristics of an optical fiber formed from this glass glass were evaluated (Electronics Letter
rs vol, 2B, No, 2. PL21) o In this report, regarding the characteristics of optical fiber, the fluorescence peak wavelength 1
, 323μm, ESA (excited 5tat
peak wavelength 1.310μ
It is shown that a result of rn, laser oscillation peak wavelength of 1.360 μm was obtained.

[Problem to be solved by the invention]

However, in the functional multi-component glass shown in the above report, even though the fluorescence peak is 1.323 μm, the absorption peak due to ESA transition exists at exactly 1.310 μm, so the oscillation peak wavelength shifts to the longer wavelength side. Not only this, but also no gain can 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 an oxide-based 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 Problems] In order to solve the above problems, the present inventors have conducted intensive research and have developed an oxide-based functional multi-component glass containing Nd3+ as an active substance.1. We have discovered a glass that enables optical amplification in the 3 μm band.

In the functional multi-component glass according to the present invention, the concentration of oxides of elements belonging to the lanthanoid series other than Nd in the host glass is 5 mo 1% or more, which is an amount that does not deteriorate the glass forming ability. . For example, preferably
It is desirable that the concentration of oxides of elements belonging to the lanthanide series other than Nd in the host glass is 5 to 50 mo1%.

As the oxide-based functional multi-component glass serving as the host glass (matrix glass), in addition to phosphate glass, borate glass, aluminosilicate glass, etc. can be used.

According to the above-mentioned functional multi-component glass, the concentration of oxides of elements belonging to the lanthanide series other than Nd in the host glass is changed within a range of 5 mol% or more and within an amount that does not deteriorate the glass forming ability. Accordingly, it is possible to shift the wavelength or increase/decrease the intensity of the fluorescence spectrum and ESA spectrum of Nd3+ near 1.3 μm. 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 Nd''+
(1) It can be considered that this is caused by changes in the ligand group, such as the electrostatic field that it receives.

In other words, under the influence of changes in the concentration of oxides of elements belonging to the lanthanide series other than Nd in the host glass, N
d'' (7) It is thought that the symmetry of the ligand group, covalent bonding with surrounding oxygen, etc. change.

As a result, the energy level of Nd3+ ions fluctuates,
Alternatively, it is considered that the degeneracy is resolved, the transition probability of radiation/absorption of Nd3+ ions changes, and furthermore, the peak wavelength of the radiation/absorption shifts.

The above is a hypothesis, but based on the examples and studies described later, the present inventors utilized or controlled this phenomenon to increase the thickness of Nd3+-doped glass to 1.3 μm.
The aim was to improve the amplification characteristics in the band. 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.

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,
Base level. By such pumping, the level 4F3
When a population inversion is formed between /2 and I, 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. For this reason, laser gain could not 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
, 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 gain of the second glass optical amplification. Such a model explains why no gain can be obtained at 1.31 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 spectrum of the intraocular emission of Nd''+ 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 oxides of elements belonging to the lanthanoid series other than Nd that constitute the host glass, the ligand field around Nd3'' will be changed, and this ligand field will change. Nd inside
3''17) The energy level is also relatively changed, and as a result, it is thought that it becomes possible to change the spectral characteristics of Nd3+l171+ absorption/emission.

This idea will be explained with reference to FIGS. 7(b) to 7(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 longer wavelength side, and the solid line 3 is the sum of the absorption and emission spectra lb and 2b.
The purpose is to shift the peak of the gain characteristic corresponding to b to 1.31 μm. FIG. 7(C) shows that both the absorption and emission spectra IC and 2C are shifted to the short wavelength side.
The purpose is to shift the peak of the gain characteristic corresponding to the solid line 3C, which is the sum of the absorption and emission spectra IC12C, to 1.31 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, which is 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. FIG. 7(e) shows the absorption/emission spectrum l e 1
The peak wavelength of 2e is 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, which is the sum of the absorption and emission spectra le and 2e, shifts to the shorter wavelength side, and the overall gain also increases, resulting in a large gain at 1.31 μm.

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 absorption/emission spectrum If.

Although the peak wavelength of the gain characteristic corresponding to the solid line 3f, which is the sum of 2f, shifts to the longer wavelength side, the overall gain increases, so a gain can be obtained even at 1.31 μm.

It is unclear which of the phenomena shown in FIGS. 7(b) to 7(f) is caused by changing the concentration of oxides of elements belonging to the lanthanoid series other than Nd in the host glass within a predetermined range. That is, from the amplification peak characteristics obtained in the following examples, it is thought that the phenomenon shown in FIG. Considering these factors, it is possible that a complex phenomenon is occurring.

To explain this variation in absorption and emission spectra from considerations within the ligand field, by changing the concentration of oxides of elements belonging to the lanthanide series other than Nd in the host glass, the ions surrounding Nd3+ Substituted with ions of elements belonging to the lanthanide series other than Nd, N
d"" (7) It can be considered that the ligand group changes greatly. In addition, by changing the concentration of oxides of elements belonging to the lanthanoid series other than Nd, Nd
It is also conceivable that indirect changes may occur in the arrangement structure of atoms around the +.Such structural changes accumulate depending on the amount of oxides of elements belonging to the lanthanoid series other than Nd, and the host It is thought that the asymmetry of the ligand group formed by the glass increases or decreases, or the covalent nature of the Nd-0 bond changes, and the F3/2 of Nd itself changes.Therefore, the coordination of Nd3+ The phenomenon of variation in child groups is thought to be complex, and the details of the mechanism are unknown, but in any case, according to the experiments and studies of the present inventors, oxides of elements belonging to the lanthanoid series other than Nd By setting the concentration of N to an amount of 5 mol% or more that does not deteriorate the glass forming ability,
(7) The absorption and emission spectra can be varied, and N d 3 can be combined with other components constituting the host glass.
By selecting the concentration of the oxide of an element belonging to the lanthanoid series other than Nd in accordance with the concentration of (!), a promising glass capable of optical amplification in the wavelength band of 1.3 μm was obtained.

The above oxide-based functional multi-component glass is used as a material for optical transmission lines, and may be formed into, for example, a planar waveguide. In order to obtain a long optical transmission path, it is desirable to produce an optical fiber that includes a cladding that surrounds a core and has a refractive index lower than that of the core.

Specifically, the above optical fiber is manufactured as follows. First, a preform having a core of oxide-based functional multi-component 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. As shown in FIG. 3, the preform 11 is fixed to a feeding device 12 and gradually lowers. At this time, the preform 11 is heated by the heater 13, softened, and wire drawing is started. The drawn fiber 10 is wound onto a winding drum 15 via a capstan 14. The fourth image shows an enlarged view of the optical fiber 10 obtained in this way.
It is a diagram. The optical fiber 10 includes a core 10a doped with Nd3+ and a core 10a doped with Nd3+, which has a relatively lower refractive index than the core 10a.
and a cladding layer 10b to which 3+ is not added.

An optical fiber having a core made of oxide-based functional multicomponent glass as described above can be applied to fiber lasers, fiber amplifiers, fiber detectors, and the like. That is, since the concentration of oxides of elements belonging to the lanthanoid series other than Nd in the core glass is set to 5 mol% or more, an amount that does not deteriorate the glass forming ability1, and the wavelength is 1.3.
Optical amplification gain can be obtained even in the 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, it becomes possible to apply it to high-gain optical amplification devices and the like.

Furthermore, the optical fiber 10 described above can be used in one application example.
．． It can be used for 3 μm band optical fiber amplifiers. As shown in FIG.
It includes a laser light source 32 that generates a band of excitation light, and an optical means 33 that causes the excitation light to enter the optical fiber from the laser light source in order to amplify the signal light with the excitation light. 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 pumping light are transmitted through the fiber 30.
The device is introduced into the device 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 μm band fiber amplifier equipped with an optical fiber as described above, a laser light source, and an optical means, Nd''+ is excited by a 0.8 μm 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.
Guided by signal light in the μm band, it generates light in the 1.3 μm band, making it possible to amplify light in the 1.3 μm wavelength band.

〔Example〕

Examples of the present invention will be described below.

First, as a host glass raw material, LaO or Er, which is an oxide of an element belonging to the lanthanide series other than Nd, is used.
2O3 and other components Na O, AI O,5
In2 is prepared and mixed to have various composition ratios. This is combined with N, which is an oxide of the rare earth element Nd.
A predetermined amount of d 20 g is added and melted in a platinum crucible.

The amount of Nd 2 O added is adjusted so that the concentration of Nd 3+ is 1% by weight based on the host glass. After sufficient mixing, the molten raw materials are rapidly cooled and vitrified. These vitrified samples were classified into Samples A, B, and C depending on their composition ratios.

They were named D, E and F, and their compositions are shown in FIG. Samples B-E are samples with varying concentrations of La2O3,
Sample F is a sample in which the concentration of E r 203 was changed instead of La2O3. Oxides of elements belonging to the lanthanide series other than Nd include not only I, a, and Er, but also Yb5Ho and Pm.

Oxides such as Eu may also be used.

In order to evaluate the optical amplification characteristics of these glasses, optical 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, 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. Nd3+ is not added to the glass of the clad pipe. 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 have a core diameter of 6 μm and an outer diameter of 1.
A 25 μm 8M fiber was obtained.

This 8M fiber was cut into 10m long fiber samples for measurement.

Evaluation of the characteristics of such a fiber sample was performed using the fluorescence peak wavelength, ESA peak wavelength, amplification peak wavelength, and 1.3 μm
A fiber amplifier such as that shown in Fig. 4 was used to measure the gain in the band. 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 Figure 1 is 1.31
This is at 0 μm. As the laser light source 32,
Ti with excitation wavelength of 0.78 μm and excitation power of 10 mW
- A sapphire laser (argon excitation) was used. The input signal strength is -30 dBm, and the peak wavelength is 1.31
It was set to 0 μm. The ESA peak wavelength was determined by determining the absorption wavelength of the fiber sample using a self-recording spectrophotometer and calculating the energy. 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.

Paying attention to the gain at 1.310 μm, it can be seen that a gain greater than a predetermined value can be obtained when the concentration of La2O3 is in the range of 5 to 50 mo1%.

If the concentration of La2O3 is less than 5 mol%, no significant effect can be obtained. It is believed that due to the low concentration of La2O3, it is not possible to cause effective changes in the coordination field. On the other hand, if the concentration of La2O3 exceeds 55 mol%, the glass will crystallize. However, it is thought that these problems caused by an increase in the concentration of oxides of lanthanide elements such as La can be improved to some extent by changing the cooling temperature during glass formation, improving the composition, etc.

Depending on the increasing concentration of La2O3, the fluorescence peak, ESA
It is observed that the peak and the amplification peak gradually move to the shorter wavelength side. This is considered to be because the amount of La ions arranged around N d ''(1) increases, and the influence of these La ions on the ligand field of Nd 3+ increases, resulting in a large wavelength shift.

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
3"O part is guided by the 1.3 μm wavelength band emitted light from within the optical fiber and the 1.3 μm wavelength light fed back into the optical fiber, and the 1.3 μm wavelength band
Generates a band of emitted light. 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 oxide-based functional multi-component glass according to the present invention, 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.

FIG. 2 is a diagram showing the absorption/emission characteristics of the glass in FIG. 1, and FIG. 3 is a method for forming a fiber using the oxide-based functional multi-component glass according to the present invention. Figure 4 is a diagram showing the fiber sample used for characteristic evaluation, Figure 5 is a diagram showing the configuration of the apparatus and optical amplifier for evaluating the characteristics of the fiber sample, and Figure 6 is Nd3+. A diagram showing an example of the excited level of an ion, Figure 7 is 1.310
FIG. 2 is a diagram illustrating gain in μm.

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

Representative Patent Attorney Yoshi Itsuki Hase

[Brief explanation of the drawing]

Figure 1 shows the composition of the host glass used in each sample of the oxide-based functional multicomponent according to the present invention. Gain N (lJt ion's N7L fertilization)

Claims (1)

[Claims] 1. An oxide-based functional multi-component glass in which Nd^3^+ is added as an active substance to a host glass for optical amplification in the 1.3 μm wavelength band, the host glass comprising: is a functional multi-component glass characterized by containing as a constituent component an oxide of an element belonging to the lanthanoid series other than Nd in an amount of 5 mol % or more, which is an amount that does not deteriorate the glass forming ability. 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,
A fiber amplifier comprising: optical means for causing the excitation light to enter the optical fiber from the laser light source.