JPH0459635A - Optically functional glass and fiber amplifier - Google Patents

Abstract

PURPOSE:To obtain optically functional glass raising light amplification at 1.3/4mum wavelength band, by blending optically functional glass with Nd<3+> as an active substance and Ce<3+>, Tb<3+>, Pr<3+> or Sm<3+>. CONSTITUTION:Optically functional glass which contains Nd<3+> as an active substance is glass which is blended with at least one ion of Ce<3+>, Tb<3+>, Pr<3+> and Sm<3+> together with Nd<3+>. The optically functional glass can emit and amplify light rays at 1.3mum band by existence of an inhibitor such as excited Ce<3+>, etc., or can raise amplification efficiency thereof. The optically functional glass can be applied to optically functional devices such as light amplifier, laser, etc., by forming the optically functional glass into wave-guiding channel, laser, etc. Especially in the case of forming into fiber, a fiber amplifier having high gain at low threshold value is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to optical functional glass and fiber amplifiers used for optical amplification in the 1.3 μm band.

[Conventional technology]

Optical functional glass doped with rare earth elements generally has a
Fiber amplifiers and fiber sensors used for optical communication in the 1 and 3 μm band in the range of 10 ± 0.025 μm,
Application to optical functional devices such as fiber lasers is being considered. For example, there is a report on preparing a phosphate-based multi-component glass with neodymium ions (N d '') added to it, and evaluating the laser oscillation characteristics of an optical fiber formed from this glass (ELECRONIC3LETTER3).
, 1990, Vol. 2B.

No, 2. I) p121-122) etc. have been made.

In this report, regarding the characteristics of optical fiber, the fluorescence peak exists at a wavelength of 1.32 μm, the laser oscillation peak exists at a wavelength of 1.36 μm, and E S A (exceeds
(absorpNon) peak wavelength is 1.31
The results show that it exists in the μm band.

[Invention or problem to be solved]

However, in the multi-component glass shown in the above report, the wavelength 1
．． Only gain was obtained in the 3 μm band.

The reason why no gain is obtained is that N d ””
It is thought that the fluorescence peak at a wavelength of 1.32 μm is relatively weak, and that a relatively large absorption peak due to ESA transition exists exactly in the 1.31 μm band.

Therefore, in view of the above-mentioned circumstances, the present invention has a wavelength of 1.3 μm.
The object of the present invention is to provide an optically functional glass that enables optical amplification in a band or increases the amplification efficiency.

Another object of the present invention is to provide a fiber amplifier including an optical fiber using the optically functional glass described above.

[Means and Effects for Solving the Problems] In order to solve the above problems, the present inventors have conducted intensive research and found that a light functional glass containing Nd3+ as an active substance has a wavelength of 1.
We have discovered a glass that enables optical amplification in the 3 μm band or increases its amplification efficiency.

In the optically functional glass according to the present invention, rare earth element ions such as cerium ion (Ce3+), terbium ion (Tb""), praseodymium ion (Pr), and samarium ion (S m "") are within 30 At least one type of ion is added to the host glass (matrix glass).

In the optically functional glass according to the present invention, 3+
3+ 3+Ce Tb Pr
Alternatively, by co-doping Sm3+ or a combination thereof to the host glass, Nd"Ol, 06μm
It is possible to suppress light emission in the band, and as a result, the wavelength is 1.3μ.
As will be described later, it has been found that it is possible to obtain a glass suitable for optical amplification in the m band.

Regarding the above phenomenon, the present inventor formulated and studied the following hypothesis.

That is, 0, introduced into the Nd3+-doped optical functional glass,
Excitation light in the 8 μm band excites Nd3+, which is an active substance. As a result 1, radiation in the 13/2 1.3 μm band corresponding to the transition from energy level F3/2 to energy level I, and other radiation from energy level F to energy level 3/2 "11 It becomes possible to emit radiation in the 1.06 μm band corresponding to the transition to /2.

Let us consider statistically the above phenomenon regarding Nd ions.

A large number of N d 3''O atoms in the host glass are excited and are in a state in which a transition corresponding to light emission in the 1.06 μm wavelength band, 1.3 μm wavelength band, etc. is possible.

A portion of the excited Nd3+ emits light in the wavelength band of 1.3 μm with a predetermined probability by spontaneous emission or stimulated emission. Further, a part of the excited Nd''+ has a wavelength of 1.3 μm with a predetermined probability due to spontaneous emission or stimulated emission.
It emits light with a wavelength of 1.06 μm instead of m-band light.

In this case, if a certain amount of suppressor for only the radiated light in the 1.06 μm wavelength band is present in the host glass as a substance for suppressing the radiated light in the 1.06 μm wavelength band, these The suppressor is Nd3''Ol, which suppresses radiation at the end of the 06 μm band, and can further suppress stimulated emission caused by light in the 1.06 μm wavelength band.

As a result, it is possible to prevent the efficiency of stimulated emission from decreasing in the wavelength band of 1.3 μm.

The above hypothesis will be explained in more detail with reference to FIGS. 1 and 2.

Figure 2 shows the energy level of N d 3'' (7), an active substance added to a phosphate-based glass sample.The wavelength of the absorption/emission transition shown in the figure is It was calculated by measuring the fabricated fiber using a self-recording spectrophotometer and an optical spectrum analyzer.Explaining the main transitions, the fundamental transition occurs due to excitation light of approximately 0.80 μm.By such pumping, , level 4F, and level 1, 1,
'13/2 9/2 11/2 1
When a population inversion is formed between 3/2 and ■,
15/2 Wavelength 0.88μm, Wavelength 1.06μm, Wavelength 1.33μm
It becomes possible to emit light with a peak of m.

The intensity of these light emissions can be considered to be light emission due to spontaneous emission, assuming that there is no external cause, and is thought to correspond to the height of the fluorescence peak of the Nd"+ doped glass. Wavelength 0.8
The N d ”(r) fluorescence peak height at 8 μm5 wavelength 1.06 μm and wavelength 1.33 μm is 0.8 μm wavelength.
It was determined by injecting only the band excitation light into bulk glass doped with Nd3+, and the ratio was approximately 5:9:
It was 1.

In this way, in response to the fact that the probability of light emission in the 1.06 μm wavelength band is extremely large, the first method was to demonstrate a method for reducing this light emission and the stimulated emission caused by this.
It is a diagram.

Light in the wavelength band of 0.8 μm 6 Excited Nd'' emits light in the wavelength band of 0.88 μm, 1.06 μm, and 1.3 μm by spontaneous emission, for example. Here, an active ion having an energy level about 2000 crn-' above the ground level is in the vicinity of N d "" (7) as a suitable suppressor of light in the 1.06 μm band with a relatively high probability of light emission. If the active ion exists in the
It will be excited to the base 411□/2 of d3+. As a result, the population inversion between 411□/2 selectively disappears, or the degree of the population inversion decreases, and the level 4F
Emission of the 1.06 μm wavelength radiation corresponding to the transition from 3/2 to level 4 1 □/2 is restricted. When signal light in the 1.3 μm band is incident on glass containing Nd in the 3+ state where emission in the 1.06 μm wavelength band is suppressed, stimulated emission in the 1.3 μm wavelength band is 1.06 μm.
This is effectively carried out without being hindered by light emission in the m band.

Therefore, despite the existence of absorption in the 1.3 μm wavelength band caused by ESA, optical amplification and
It is possible to emit light and increase the gain of optical amplification.

The conditions for the above suppressor are approximately 2000 cm of the ground level.
It is necessary not only to have an upper energy level, but also not to absorb emitted light in the 1.3 μm wavelength band and not to absorb excitation light. When using active ions as such suppressors and adding them to the host glass together with Nd3+, it is not suitable to use transition metals with broad absorption bands, but it is preferable to use rare earth elements with sharp absorption bands. Furthermore, it is desirable that the density of states at the energy level approximately 2000 CI11-1 above the ground level of the active ion is high. FIG. 3 shows the selection of rare earth element ions under such conditions.

Note that the energy levels of the rare earth elements shown in FIG. 3 are those in the crystal. Ce3+3+3+Tb Pr or Sm"+ is desirable as a rare earth element candidate that satisfies the above conditions.ce3+7
F6 transition, H5-H4 transition of Pr and 3+3
The 6) I -6H transition of 3 5m3+ is wave 9/
2 5/2 Numerical 2300 cm 1900 cm 210
0 cm-1 and 23008 m-', and these values correspond to the difference between level I and level I of approximately 2000 c.
Corresponds to m-1.

In order to make Ce3+$ ions function as a suppressor for light emission in the 1.06 μm wavelength band, 3+ For example, for Ce, the energy level 2F7/2
An electron must be excited. In order to cause such excitation, excitation light in the 5 μm band is used to excite Nd.
It is desirable to excite

Considering the condition that light in the 5 μm band is not absorbed, it is most desirable to use chalcogenide glass.

Another method to replace the above 5 μm band excitation light is to once excite electrons to another higher energy level, for example ce3+P1g, and then transition the electrons from this other level to level 2F 7/2. It is also possible to transfer energy using other ions.

It is unclear whether the above hypothesis is appropriate.

In any case, according to the experiments and studies of the present inventors, in the glass, together with Nd"+, Ce""Tb"Pr or Sm, or a combination of these 3+3
+ 1.06μm of Nd3+ by adding
Luminescence in the band can be suppressed by Ce etc.
A promising glass that enables optical amplification in the 1.3 μm wavelength band or increases its amplification efficiency was obtained.

The above-mentioned optical functional glass is used as a material for an optical transmission line, and may be formed into a planar waveguide, for example, but it is possible to produce an optical fiber with a core made of the above optical functional glass. This is desirable for obtaining a long optical transmission path, and also for obtaining an optical functional device in the wavelength band of 1.3 μm. In other words, the optically functional glass described above can be used to produce fiber lasers,
Application to optical functional devices such as fiber amplifiers and fiber detectors becomes possible.

Specifically, the above optical fiber is manufactured as follows. When the optically functional glass is made of chalcogenide glass, for example, a preform made of optically functional glass doped with 3+ Nd, Ce''+, etc. is prepared, and then it is placed in a wire drawing device as shown in Figure 4. This preform is set and drawn into an optical fiber.As shown in Fig. 4, the preform 11 is fixed to a feeding device 12 and gradually lowers. It softens and begins to be drawn.

The drawn fiber core 10 is wound onto a winding drum 15 via a capstan 14.

The fiber core 10 thus obtained is coated with a cladding to produce an optical fiber. When the optically functional glass is oxide-based or fluoride-based glass, Nd3+ and C
A preform having a core of optically functional glass doped with e3+1 is prepared by a rod-in-tube method or the like. Next, this preform is set in a drawing device shown in FIG. 4, and drawn into an optical fiber.

An example of the configuration of a 1.3 μm band fiber amplifier using this optical fiber 10 is shown in FIG. As shown in the figure, the fiber amplifier includes a fiber 30 that serves as a waveguide for signal light in the 1.3 μm band, a first pump light source 32 that generates first pump light in the 0.8 μm wavelength band, and a first pump light source 32 in the 5 μm wavelength band. The optical fiber 30 includes a second excitation light source 34 that generates second excitation light, and an optical means 33 that causes these excitation lights to enter the optical fiber 30 from the first excitation light source 32. The excitation light with a wavelength band of 0.8 μm from the first excitation light source 32 and the excitation light with a wavelength band of 5 μm from the second excitation light source 34 are connected to the signal from the signal light source 31 by an optical means 33 such as a fiber coupler. Combined with light. The combined signal light and excitation light are introduced into the fiber 30 via a connector or the like.

Incidentally, the filter 36 provided on the output side of the optical fiber 30 is for cutting off the excitation light, and the optical spectrum analyzer 35 is a device for measuring the amplified signal light. The matching oil 37 is for preventing return light from the fiber coupler formed by fusion drawing.

According to the 1.3 μm band fiber amplifier equipped with the above-mentioned fiber end, first and second pumping light sources, and optical means, the wavelength 0 introduced into the fiber by the optical means
．． N in the core glass is stimulated by N1 excitation light in the 8 μrn band.
d3+ is excited. Furthermore, Ce Tb""Pr or 5m3+ in the core glass 3+ 3+ glass is stimulated by the second excitation light in the 5 μm wavelength band.
or combinations thereof are excited. These 3+ suppressors suppress the emission of Nd in the 1,06 μm band, and most of the excited N d ”0) reacts with the signal light in the 1,3 μm band, etc., introduced into the fiber at the same time. This leads to highly efficient stimulated emission in the wavelength band of 1.3 μm.As a result, it is possible to obtain optical amplification gain even in the wavelength band of 1.3 μm. Further, since light is efficiently confined in the core and the loss of the confined light is extremely low, population inversion can be formed in Nd3+ with a low threshold value.

〔Example〕

Examples of the present invention will be described below.

As an optical functional glass, 3+ as well as Nd3+
3+ 3+Ce Tb
Chalcogenide glass doped with Pr or 5m3+ was prepared. The composition of the host glass is 30Ge-2
It was set as 0As-505.

The concentration of neodymium ions, which is an active substance added to this host glass, is 1000 pp by weight based on the host glass.
It was set as m. CeTb used as inhibitor
The concentration of Pr”+ or Sm”+ is 3+
3+ All were set to 1oooppm. Also, for comparison,
A chalcogenide glass containing no co-added materials such as + was also prepared. These samples were named Samples A to E in the following order: one without Ce3+*, one with Ce3+, one with Tb3+, one with Pr3+, and one with Sm3+. Ta.

In order to evaluate the optical amplification characteristics of this glass, a fiber was fabricated as follows. First, glass having the above composition is formed into a rod shape to form a core preform. after that,
The prepared preform was set in the drawing device shown in FIG. 4, and a fiber core was drawn. This fiber core was covered with a FEP cladding for protection. As a result, an 8M fiber with a core diameter of 8 μm and an outer diameter of 125 μm was obtained. This 8M fiber was cut into 1m long fiber samples for measurement.

The characteristics of the fiber samples A to H were evaluated using a fiber amplifier shown in FIG. 5 or the like.

The first excitation light source 32 has an excitation wavelength of 0.78 μm.
A Ti-sapphire laser with an excitation output of 10 mW was used. The 5 μm band light source 34 consists of a combination of a hot wire heater and a suitable filter. The intensity of the input signal from this light source 34 to the optical fiber 3o was set to 10 mW. A semiconductor laser was used as the signal light source 31. The intensity of the input signal is -30 dBm, and the peak wavelength is 1.310 dBm.
It was set as μm.

In addition, for each sample A-H, the wavelength of Nd3+ is 0.8
Fluorescence in the 8 μm band, 1.06 μm wavelength band, and 1.33 μm wavelength band was also measured.

5. 15.0 mW of 0.8 μm band light δ1100 mW was applied to the bulk glass of each sample A-E. czm band light was incident, and the emitted fluorescence was measured with a spectrum analyzer.

The results of the characteristic evaluation of samples A-E are shown in the table of FIG.

The cane of each sample shown in the table is at 1.310 μm.

3+3+ As is clear from the table, the gain increases by adding Ce TbPr3+ or s m 3"o and using 0 at the wavelength 5 μm band. In other words, without co-doping suppressors such as Ce3+, the gain increases in the 5 μm wavelength band. In a conventional optical fiber (sample A) that does not use pumping light, the gain coefficient is 1 or 2.
dB/mW or when there is a suppressor excited by synchrotron radiation in the wavelength band of 5 μm, the gain coefficient is 1, 5 even for sample E with the lowest gain, Sm""f'+addition.
It is dB/mW. Furthermore, the suppression of luminescence in the N d ""Ol, 06 μm band by using the suppressor is also supported by the intensity ratio of the fluorescence peaks shown in the table. In other words, in fiber samples B-E co-doped with suppressors such as Ce3+, the emission peaks in the 1.06 μm wavelength band are reduced, and the emission peaks in the 0.88 μm band and 1.
．． The fluorescence peak in the 33 μm band has increased.

The optical fiber used in the fiber amplifier of the present invention can also be applied to devices such as fiber lasers.

Specifically, the fiber laser is configured to include the optical fiber, first and second excitation light sources, optical means, and an optical resonator. Here, the first excitation light source has a wavelength of 0.
．． It generates excitation light in the 8 μm band, and the second excitation light source has a wavelength of 5 μm.
Generates excitation light in the μm band. The optical means also causes excitation light to enter the optical fiber from the first and second excitation light sources. Furthermore, the optical resonator has a wavelength of 1.3μ from within the optical fiber.
The m-band radiation is fed back to the optical fiber.

According to the above-described fiber laser, Nd3+ is excited by excitation light in the wavelength band of 0.8 μm introduced into the fiber by optical means. This excited Nd3+o
Some of the light is emitted from the optical fiber with a wavelength of 1.3 μm, and the 1.3 μm wavelength that is fed back into the destination fiber.
m-band light, and generates emitted light with a wavelength of 1.3 μm. By repeating this, wavelengths 1 and 3
Laser emission in the μm band becomes possible.

Examples of fiber lasers will be described below.

The specific configuration is similar to a known Er-doped fiber laser (rEr-doped Phi/<-J, Opl
US E, January 1990, pp.

See 112-118, etc. ). However, in the case of this embodiment, the optical fiber of the above embodiment doped with Nd3+ and thCe3+W is used as the optical fiber. Further, a laser diode that generates excitation light in a 0.8 μm wavelength band is used as the first excitation light source, and a heater that generates excitation light in a 5 μm wavelength band is used as the second excitation light source.

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. At the same time, excitation light with a wavelength band of 5 μm from the heater is also introduced into this optical fiber. As a result, the Nd''+ in the optical fiber is excited to a predetermined state, making it possible to emit light efficiently in the 1.3 μm wavelength band. The 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 optically functional glass according to the present invention, 1.
It becomes possible to emit light and amplify light in the 3 μm band, or increase the amplification efficiency.

Furthermore, by forming this into a waveguide, optical fiber, etc., it can be applied to optical functional devices such as optical amplification devices and lasers. In particular, when formed into a fiber, a low threshold and high gain fiber amplifier can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the energy levels of Nd added to the optically functional glass according to the present invention and the suppressor, FIG. 2 is a diagram showing the energy levels of Nd in the conventional glass, and FIG. The figure shows the energy level of rare earth element ions, Figure 4 shows a fiber forming apparatus using the above-mentioned optical functional glass, and Figure 5 shows the configuration of a fiber amplifier. Figure 6 shows the 1.310μ of the fiber amplifier in Figure 5.
It is a figure showing the gain in m band. 10.30... Optical fiber, 32... First excitation light source, 34... Second excitation light source, 33... Coupler which is optical means.

Claims (1)

[Claims] 1. A photofunctional glass containing Nd^3^+ as an active substance, comprising Ce^3^+, Tb^3^+, Pr^3^+ and Sm^
An optical functional glass characterized in that at least one type of ion among Nd^3^+ is added together with Nd^3^+. 2. An optical fiber comprising the optically functional glass according to claim 1 and propagating signal light in a wavelength band of 1.3 μm;
a first excitation light source that generates excitation light in a wavelength band of 0.8 μm; a second excitation light source that generates excitation light in a wavelength band of 5 μm;
A fiber amplifier comprising: an optical means for causing the excitation light having a wavelength band of 0.8 μm and a wavelength band of 5 μm to enter the optical fiber from the first and second excitation light sources.