JP3001672B2 - Optical amplifier and laser - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical amplifier and a laser using an optically functional glass used for optical amplification in a 1.3 .mu.m band.

[0002]

2. Description of the Related Art Efforts have been made to manufacture optical amplifiers such as fiber amplifiers, fiber sensors, and fiber lasers using glass to which a rare earth element has been added for application to the optical communication field in the 1.3 μm band. I have. For example, a report was prepared that prepared a glass obtained by adding neodymium ion (Nd ³⁺ ) to a phosphate-based multi-component glass and evaluated the laser oscillation characteristics of an optical fiber formed from this glass (ELECRONICS L
ETTERS, 1990, Vol.26, No.2, pp121-122). In this report, Nd ³⁺
At a fluorescence peak wavelength of 1.32 μm, ESA (exci
It is shown that the peak attributable to the ted state absorption) transition had a wavelength of about 1.31 μm and an amplification peak wavelength of 1.36 μm.

[0003]

However, with the multi-component glass disclosed in the above report, a laser oscillation gain was not obtained in a 1.3 μm wavelength band. The reason that the laser oscillation gain cannot be obtained as described above is that N in the 1.32 μm band is
The relatively weak d ³⁺ fluorescence peak and the relatively large absorption peak due to the ESA transition have a wavelength of just 1.3.
It is thought that it exists at 1 μm.

Further, in the case of performing optical amplification using stimulated emission as in the case of the above-mentioned optical fiber, the wavelength is simply 1.31 μm.
The problem is that not only is the fluorescence peak of m small, but also that there are other possible fluorescence peaks due to transitions. That is, in the case of the above optical fiber, the fluorescence peak of the 1.3 μm wavelength band of Nd ³⁺ is relatively weak, and the wavelength 0.8 μm band corresponding to other possible transitions of Nd ³⁺ is obtained. A problem is that light emission in a wavelength band of 1.06 μm or the like is relatively strong. 0.8μ wavelength
The stimulated emission of light in the 1.3 μm wavelength band is hindered by the stimulated emission due to light emission in the m band, the 1.06 μm band, and the like.
It is believed that the efficiency is significantly reduced.

[0005]

[0006]

In view of the above circumstances, the present invention provides an optical waveguide (optical fiber and waveguide) using optically functional glass that enables optical amplification in a 1.3 μm band or enhances the amplification efficiency. It is an object of the present invention to provide an optical amplifier (a fiber amplifier and a waveguide element amplifier) using an element.

Another object of the present invention is to provide a laser (fiber laser and waveguide element laser) using the above optical waveguide (optical fiber and waveguide element).

[0009]

The present inventor has conducted intensive studies to solve the above-mentioned problems. As a result, the present invention relates to an optically functional glass containing Nd ³⁺ as an active substance and having a thickness of 1.3 μm.
We have found a glass that enables light amplification in the band or that increases the amplification efficiency.

In the optical functional glass used in the present invention, a rare earth ion other than Nd ³⁺ having an absorption band near 1 μm is added as an absorber together with Nd ^{3+ as} an active substance, Rare earth ions capable of transferring about 4000 cm ^-1 of energy from Nd ³⁺ are added as promoters. As the multi-component glass serving as the host glass (matrix glass), fluoride-based glass, chalcogenide glass, and the like can be used in addition to oxide-based multi-component glass such as phosphate glass.

According to the optical functional glass used in the present invention, praseodymium ions to be added together with Nd ³⁺ (P
Due to the presence of an absorber such as r ³⁺ ), it is possible to absorb the emission of Nd ³⁺ near a wavelength of 1 μm (for example, a wavelength band of 1.06 μm, a wavelength of 0.88 μm, or the like). Furthermore, Nd
The presence of a promoter of terbium ions (Tb ³⁺⁾ added with ^3+, it is also possible to increase the luminous probability in wavelength 1.3μm band of Nd ^3+. As a result, the wavelength of Nd ³⁺ is 1.3.
It enables light emission and light amplification in the μm band, and its efficiency,
Obtaining glass that can increase gain etc.,
It turned out as described below.

In this case, it is desirable to use Pr ³⁺ , ytterbium ion (Yb ³⁺ ), samarium ion (Sm ³⁺ ), and the like as an absorber for absorbing light in the 1.06 μm band. Further, as an absorbent for absorbing light emission in a wavelength band of 0.88 μm, holmium ion (Ho ³⁺ ) or the like is desirably used.

The concentration of Pr ³⁺ , Yb ³⁺ , Sm ^3+, etc. is changed to Nd ³⁺
If the weight is 50% to 150%, the effect as an absorbent can be further enhanced.

Further, the optical fiber used in the present invention is:
It comprises a core made of the above-mentioned optical functional glass, and a clad surrounding the core and having a lower refractive index than the core.

According to such an optical fiber, since an absorber and / or an accelerator are added to the core glass together with Nd ³⁺ , the wavelength of 1.31 μm propagating in the core glass.
The optical amplification of the m-band light becomes possible, or the optical amplification gain can be increased. The ^{reason is} that the inversion of Nd ³⁺ can be formed at a low threshold value at a low threshold because light is efficiently confined in the core by the fiberization and the loss of the confined light is extremely low.

A fiber amplifier according to the present invention includes the above-described optical fiber, a pump light source, and optical means. Here, the optical fiber propagates signal light in the 1.3 μm band, the excitation light source generates excitation light in the 0.8 μm band, and the optical means causes the excitation light to enter the optical fiber from the excitation light source.

According to the above-described fiber amplifier, Nd ³⁺ is excited by the pumping light having a wavelength of 0.8 μm introduced into the fiber by the optical means. This excited Nd ³⁺
Most of the light is simultaneously guided by a signal light in the 1.3 μm band introduced into the optical fiber to generate radiated light, thereby enabling optical amplification in the 1.3 μm band.

A fiber laser according to the present invention includes the above-described optical fiber, an excitation light source, and optical means. Here, the excitation light source generates excitation light in a wavelength band of 0.8 μm, and the optical means causes the excitation light to enter the optical fiber from the excitation light source. Further, the fiber laser of the present invention has a resonator structure for feeding back light in or around the 1.3 μm wavelength band from the optical fiber to the optical fiber.

According to the above fiber laser, Nd ³⁺ is excited by the excitation light having a wavelength of 0.8 μm introduced into the fiber by the optical means. This excited Nd ³⁺
A part or many of them are simultaneously guided by a 1.3 μm-band signal light or the like introduced into the optical fiber to generate radiated light, thereby enabling optical amplification in the 1.3 μm-band. .

If the above optical fiber is replaced with a waveguide element, an extremely small waveguide element amplifier and waveguide element laser band can be constructed.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The principle of the present invention and the history of its completion will be described below.

With respect to the above phenomenon, the present inventors have made two hypotheses and studied. These hypotheses will be described sequentially.

[Explanation on First Hypothesis] Excitation light in the 0.8 μm band introduced into Nd ^{3+ -doped} optically functional glass excites Nd ³⁺ as an active substance. As a result, the width of 1.3μm band corresponding the energy level ⁴ F _3/2 to transition to an energy level ⁴ I _13/2 morphism becomes possible, as a morphism other width, energy levels ⁴ F _{3 / 2} to energy level
Wavelength 1.06 corresponding to transition to ⁴ I _11/2 or ⁴ I _9/2
It becomes possible to radiate a μm band or a 0.88 μm band.

The above-mentioned phenomenon relating to Nd ions will be considered statistically. Many of the Nd ³⁺ in the host glass are excited and are in a state where transition corresponding to light emission in the 1.3 μm band is possible. In addition, an undesired transition corresponding to light emission in a wavelength band of 0.88 μm, a wavelength of 1.06 μm, or the like is also possible. In this case, a part of the excited Nd ³⁺ emits light having a wavelength of 1.3 μm with a predetermined probability by spontaneous emission or stimulated emission. Also,
A part of the excited Nd ³⁺ emits light having a wavelength of 0.88 μm or 1.06 μm rather than light having a wavelength of 1.3 μm at a predetermined probability due to spontaneous emission or stimulated emission. In this case, a wavelength of 0.88 μm
Band or 1.06 .mu.m band, if there is a certain amount of a substance which is an absorber, that is, an absorber which is not a absorber of the 1.3 .mu.m band synchrotron radiation, these absorbers will emit 0.88 .mu.m Band or 1.06 μm band light. Due to this absorption, a wavelength of 0.88 μm band or 1.
Stimulated emission due to the radiation in the 06 μm band can be suppressed. For example, considering the case where an absorber only for radiation light in a wavelength band of 1.06 μm is used, these absorbers are N 2
Light emission in at least one wavelength band of 1.06 μm of d ³⁺ can be suppressed, and a decrease in efficiency of stimulated emission in a wavelength band of 1.3 μm can be prevented. Further wavelength 0.8
Considering the case of using a light absorber in the 8 μm band, light emission in at least one of the 0.88 μm bands can be suppressed, so that the efficiency of stimulated emission in the 1.3 μm wavelength band is reduced. It is thought that it can be prevented.

Referring to the above hypotheses, FIGS. 1, 2 and 3
This will be described more specifically with reference to FIG.

FIG. 2 is a diagram showing energy levels of Nd ³⁺ added to a phosphate glass sample. The wavelength of the absorption-emission transition shown in the figure was calculated by measuring a fiber made of this glass using a self-recording spectrophotometer and an optical spectrum analyzer. To explain the main transitions, the excitation light of about 0.80 μm causes the electron at the ground level ⁴ I _9/2 to shift to the level ⁴ F _9/2.
Once excited to _5/2 , level ⁴ F due to multiphonon relaxation
Transition to _3/2 . With such pumping, level ⁴
F _3/2 and the levels ⁴ I _9/2 , ⁴ I _11/2 , ⁴ I _13/2 and ⁴ I
_{When the population} inversion is formed between 15/2, the wavelength is 0.88μ.
m, 1.06 μm, wavelength 1.33 μm, wavelength 1.80 μ
Light emission having a peak at m becomes possible. Of these, wavelength 0.88 μm, wavelength 1.06 μm and wavelength 1.33 μm
Were determined from the ratio of the heights of the fluorescence peaks when only the excitation light was incident on this fiber, and were about 5: 9: 1, respectively. Note that the emission intensity at a wavelength of 1.80 μ was not determined because it was relatively weak.

As described above, FIG. 1 shows a method for reducing the stimulated emission due to the fact that the probability of light emission in the wavelength band of 1.06 μm or 0.88 μm is very large. .

Referring to FIG. 1 (a), the excited first
Nd ion 11 has a wavelength of 1.3 due to, for example, spontaneous emission.
Light in the μm band, the 0.8 μm band, or the 1.06 μm band is emitted. In this case, since the light emission probability in the 0.88 μm band and the 1.06 μm band is very large, most of the second Nd ions 12 induced by the spontaneous emission light are in the 0.88 μm band or the 1.0 nm band. It emits light in the 06 μm band. On the other hand, paying attention to FIG. 1B, similarly to FIG. 1A, the excited first Nd ion 11 emits light having a wavelength of 1.3 μm, 0.88 μm, or 1.06 μm. Radiate. For example, here
0.88μm band light or 1.06μm with high emission probability
If there is an absorber 13 which is a suitable absorber of the band light, the radiated light in the wavelength band of 0.88 μm or 1.06 μm is absorbed by the absorber 13 and does not affect the second Nd ions 12.

In the case of the present invention, an absorber (or absorber) having a wavelength of 1.06 μm and an absorber (or absorber) having a wavelength of 0.88 μm are used. In the case of an absorber having a wavelength of 1.06 μm, the probability of light emission is relatively high, so that the probability of stimulated emission in the wavelength of 1.3 μm can be effectively increased. On the other hand, in the case of an absorber having a wavelength of 0.88 μm, the stimulated emission caused by the emitted light of the wavelength 1.06 μm cannot be suppressed, but at least the stimulated emission caused by the emitted light of the wavelength 0.88 μm cannot be suppressed. Since emission can be suppressed, the probability of stimulated emission in the 1.3 μm wavelength band can be increased.

The above wavelength 1.06 μm band or 0.88 μm
The condition of the band absorber is that it absorbs spontaneous emission light or stimulated emission light having a wavelength of about 1.06 μm or 0.88 μm immediately and does not absorb emission light having a wavelength of about 1.3 μm. And so on. When an active ion is used as such an absorber and added to the host glass together with Nd ³⁺ , the use of transition metal ions having a broad absorption band is not suitable, and the use of rare earth ions having a sharp absorption band is desirable. Further, it is necessary that a large number of electrons be present at the energy level to be excited, and that the energy level of the energy level after the transition has a high state density and a low occupancy of the energy level.

FIG. 3 shows the selection of rare earth ions under such conditions. The energy levels of the rare earth ions shown in FIG. 3 are those in the crystal.

As a first candidate of a rare earth ion satisfying the above conditions, the absorption probability at a wavelength of 1.06 μm is high and 1.
Pr ³⁺ , because the absorption probability of 3 μm is negligible
It is understood that Yb ³⁺ and Sm ³⁺ are desirable. Pr ^{3+ 3}
H ₄ → ¹ G ₄ transition about 9700cm ^{- 1} of has become energy, this value wavelength 1.06μm (9400cm
^-1 ) It corresponds to synchrotron radiation. Furthermore, Yb ^3+
6 H _7/2 → ⁶ F of the ² F _7/2 → ² F _5/2 transition and Sm ³⁺ of
_11/2 transition is about 9600cm ^-1 and about 9500c respectively
This is because the energy is m ^-1 and it corresponds to the radiation light having a wavelength of 1.06 μm. It is considered that an inversion distribution cannot be formed in the rare-earth ions such as Pr ³⁺ depending on the absorption to the extent of spontaneous emission.

It is unclear whether the above hypotheses are appropriate. In any case, according to experiments and studies conducted by the present inventor, Pr in glass containing Nd ³⁺ as an active substance was added.
³⁺ is added or its Pr ³⁺ is 50% with respect to Nd ³⁺
By adding Pr ³⁺ in the range of
It can be seen that Pr ³⁺ can absorb the light emission in the 1.06 μm band of d ³⁺ , and a promising glass that enables light amplification in the 1.3 μm band or increases the amplification efficiency can be obtained. Was. Moreover, the Sm ³⁺ was added into glass doped with Nd ³⁺ as an active substance, or also by the Pr ³⁺ adding Sm ³⁺ in the range of 50% to 150% with respect to Nd ³⁺ It has been found that promising glasses are obtained as well. Further, Yb ³⁺ is added to the glass to which Nd ³⁺ is added as an active substance, or the amount of Yb ³⁺ is not less than 50% of Nd ³⁺ and does not deteriorate the glass forming ability. Similarly, a promising glass was obtained by changing.

As a second candidate of a rare earth ion satisfying the above conditions, Ho has a high absorption probability of 0.88 μm and a negligible absorption probability of 1.3 μm.
^It turns out that ³⁺ is desirable. The ⁵ I ₈ → ⁵ I ₅ transition of Ho ³⁺ has a wave number of about 11000 cm ⁻¹ , which is equivalent to a wavelength of 0.
This is because it corresponds to 88 μm (wave number of about 11400 cm ⁻¹ ).

It is unclear whether the above hypothesis is appropriate. In any case, according to experiments and studies made by the present inventors, Ho ³⁺ is added to glass together with Nd ³⁺ so that Ho ³⁺ absorbs the emission of Nd ^{3+ in} the 0.88 μm wavelength band. As a result, a promising glass was obtained which enabled light amplification in the 1.3 μm wavelength band or increased the amplification factor.

[Explanation of Second Hypothesis] Excitation light in the 0.8 μm band introduced into the Nd ^{3+ -doped} optically functional glass excites Nd ³⁺ which is an active substance. As a result, the transition
_Radiation in the 1.3 μm band corresponding to ⁴ F _3/2 → ⁴ I _13/2 becomes possible. Other radiation, the energy level ⁴ F
Radiation in the wavelength band of 1.06 μm or 0.88 μm corresponding to the transition from _3/2 to the energy level ⁴ I _11/2 or ⁴ I _9/2 becomes possible.

The above phenomenon regarding Nd ions will be considered statistically. The majority of Nd ³⁺ in the host glass is 0.8%
Excitation by the excitation light in the μm band, wavelength 1.06 μm
Band, a wavelength of 0.88 μm, and a transition corresponding to light emission of a wavelength of 1.3 μm. A part of the excited Nd ³⁺ emits light having a wavelength of 1.3 μm with a predetermined probability by spontaneous emission. In addition, the excited N
Due to spontaneous emission, a part of d ³⁺ has a higher probability than the wavelength of 1.3 μm radiation and the wavelength of 1.06 μm and 0.88 μm.
Emit light in the μm band. In this case, the wavelength of Nd ³⁺ is 1.3.
As an object for promoting the emission of light in the μm band, a wavelength of 1.
If a luminescence enhancer that emits only light in the 3 μm band, that is, the accelerator is present in a certain amount in the host glass, these accelerators only promote the emission of the 1.3 μm band light of Nd ³⁺ and have a wavelength of 1 μm. It is considered that the efficiency of stimulated emission in the 0.3 μm band can be increased. Further, the wavelength band is 1.06 μm band and the wavelength is 0.1 mm.
Since the light emission probability in the 88 μm band is relatively reduced, it is considered that the possibility that the stimulated emission in the 1.3 μm band is disturbed by, for example, 1.06 μm light.

The above hypothesis will be described more specifically with reference to FIGS.

As described above with reference to FIG.
0.88 μm, wavelength 1.
Light emission with a peak at 06 μm and a wavelength of 1.33 μm becomes possible. These luminescence intensities may be considered to be luminescence intensities due to spontaneous emission if there is no external factor, and are respectively about 5: 9: 1. In other words, it can be seen that the light emission probability in the wavelength band of 1.3 μm is considerably lower than the light emission probability in the wavelength bands of 1.06 μm and 0.88 μm.

FIG. 4 shows a method for increasing the light emission probability in the 1.3 μm wavelength band.
It shows a method of preventing a decrease in the efficiency of stimulated emission in a 1.3 μm wavelength band caused by light emission in a μm band.

Nd excited by light having a wavelength of 0.8 μm band
³⁺ emits light having a wavelength of 0.88 μm, a wavelength of 1.06 μm, and a wavelength of 1.3 μm by spontaneous emission, for example.
Here, as an appropriate promoter for promoting the emission of only the 1.3 μm band light, if an active ion having an excitation level about 4000 cm ⁻¹ above the ground level exists near Nd ³⁺ , Nd ³ The electrons in the excited state existing at the energy level ⁴ I _13/2 of ⁺ can be effectively transitioned to the ground level ⁴ I _9/2 . That is, energy transfer from the excited electrons existing at the energy level ⁴ I _13/2 of Nd ³⁺ gives
Many electrons existing in the ground level of the active ion are excited to the excited level, and the Nd ³⁺ level ⁴ I _13/2
Many of the electrons existing in the above state have the ground level ⁴ I _9/2 transition. In other words, the level of Nd ^{3+ 4} I _13/2
The excited electrons existing in the above are not only relaxed through a radiation process, a phonon emission process and the like, but also effectively relaxed by energy transfer with nearby active ions. As a result, in many Nd ³⁺ , the degree of population inversion between the energy level ⁴ F _3/2 and the level ⁴ I _13/2 is increased, and the emission of light in the 1.3 μm wavelength band is promoted. be able to. Further, with the increase in the emission probability of the 1.3 μm wavelength light, the wavelength of 1.06 μm
The probability of emission of light or the like is relatively reduced. When signal light in the 1.3 μm band is incident on glass containing Nd ^{3+ in} such a state, stimulated emission in the 1.3 μm band may be hindered by light emission in the 1.06 μm band and 0.88 μm band. And light emission is effectively performed. Thus, despite the presence of absorption in the 1.3 μm wavelength band due to ESA,
Optical amplification and light emission in the wavelength band of 1.3 μm are possible, and the gain of optical amplification can be increased.

The conditions of the above accelerator include not only that it has an energy level about 4000 cm ^-1 above the ground level but also that it does not absorb emitted light in the wavelength band of about 1.3 μm, It is also necessary not to absorb the odor.
Using an active ion as such an accelerator, this is converted to Nd
^When adding to the host glass together with ³⁺ , the use of a transition metal having a broad absorption band is not suitable, and the use of a rare earth element having a sharp absorption band is desirable.

Further, about 4% from the ground level of the active ion.
It is desirable that the state density of the energy level above 000 cm ^-1 be high.

As shown in FIG. 3, it can be seen that Tb ³⁺ or Eu ³⁺ is desirable as a rare earth element candidate satisfying the above conditions. ⁷ F ₀ → ⁷ F ₅ transition ⁷ F ₆ → ⁷ F ₄ transition and Eu ³⁺ in Tb ³⁺ is a wave number of about 3200 cm ^-1 and 3800 cm ^-1, respectively, these values are level ⁴ I _This is because the wave number almost corresponds to 4000 cm ⁻¹ which is the energy difference between _11/2 and the level ⁴ I _9/2 .

It is unclear whether the above hypothesis is appropriate. In any case, according to experiments and studies conducted by the present inventors, Tb ³⁺ or Eu ³⁺ together with Nd ^{3+ is contained in} glass.
Alternatively, by adding both, the wavelength of Nd ³⁺ is 1.3 μm.
Light emission in the m band can be promoted by Tb ³⁺ or Eu ³⁺ , and a promising glass that enables light amplification in the 1.3 μm band or increases the amplification efficiency has been obtained.

[Application Examples of Optical Mechanical Glass] (1) Optical Fiber The above-mentioned optical functional glass is used as a material for an optical transmission line, and may be formed in, for example, a planar waveguide. It is desirable to produce an optical fiber including a core made of functional glass and a clad surrounding the core and having a lower refractive index than the core in order to obtain a long optical transmission line.

The above-mentioned optical fiber is produced specifically as follows. First, a preform having a core of Nd ^{3+ -added} optical functional glass is prepared by a rod-in-tube method or the like. Next, the prepared preform is set in a drawing apparatus as shown in FIG. 5 and drawn into an optical fiber.
As shown in FIG. 5, the preform 21 is fixed to the feeding device 22 and gradually descends. At this time, preform 2
1 is heated by the heater 23 and is softened to start drawing. The drawn fiber 20 is wound on a winding drum 25 via a capstan 24. FIG. 6 is an enlarged view of the optical fiber 20 thus obtained. Optical fiber 20, Pr ³⁺ with Nd ^3+, Yb ^3+,
Core 20 added with Sm ³⁺ , Tb ³⁺ , Eu ³⁺ , Ho ^3+, etc.
a and a cladding layer 20b having a relatively lower refractive index than the core 20a and not adding both Nd ³⁺ and Pr ^{3+ and} other rare earth ions.

According to the optical fiber having the above-mentioned optical functional glass as a core, application to a fiber laser, a fiber amplifier, a fiber detector and the like becomes possible. That is, since Pr ^{3+ and} other rare earth ions are added to the core glass together with Nd ³⁺ , not only an optical amplification gain can be obtained even in the 1.31 μm band, but also light emission in the 1.06 μm band. Loss is reduced. Furthermore, since the light is efficiently confined in the core by the fiberization and the loss of the light is extremely low, the population inversion can be formed at a low threshold. Therefore, application to a high gain optical amplifier or the like becomes possible.

(2) Fiber Amplifier The above-mentioned optical fiber 20 has an application example of 1.3 μm.
It can be used for m-band fiber amplifiers.

For example, as shown in FIG. 7, the fiber amplifier comprises an optical fiber 30 doped with rare earth, a laser light source 32 for excitation, and optical means 33, 38a, 38b, 39
a, 39b. The optical fiber 30 is an optical transmission path for 1.3 μm band laser light. In addition, the laser light source 32
Generates excitation light in the wavelength band of 0.8 μm. Further, the optical units 33, 38a, 38b, 39a, and 39b cause the excitation light to enter the optical fiber 30 from the laser light source 32. That is, the excitation light from the laser light source 32 is introduced into the fiber coupler 33 via the optical fiber 39a, and is combined with the signal light introduced from the signal light source 31 into the fiber coupler 33 via the optical fiber 38a. The combined signal light and pump light are introduced into the optical fiber 30 via the optical fiber 38b.

The fiber coupler 30 can be formed, for example, by fusing and stretching two optical fibers 38 and 39. In this case, the end of one optical fiber 39 b extending from the fiber coupler 33 is immersed in the matching oil 37. As a result, return light from the optical fiber 39b to the fiber coupler 33 is prevented.

Incidentally, on the output side of the optical fiber 30, an optical spectrum analyzer 35 is provided, and a filter 36 is interposed between them. The filter 36 cuts the excitation light out of the light output from the optical fiber 30. As a result, the optical spectrum analyzer 35
Can measure only the signal light output from the optical fiber 30, and can further measure the optical amplification gain.

As described above, according to the 1.3 μm wavelength fiber amplifier provided with the optical fiber, the laser light source and the optical means, Nd is emitted by the 0.8 μm laser light introduced into the fiber by the optical means. ³⁺ is excited.
Most of the pumped Nd ³⁺ is simultaneously guided to the 1.3 μm wavelength signal light or the like introduced into the optical fiber to generate radiated light, and optical amplification in the 1.3 μm wavelength band is performed. Becomes possible.

(3) Fiber Laser Further, the above-mentioned optical fiber 20 can be used as a fiber laser having a wavelength of 1.3 μm as another application example.

For example, as shown in FIG. 8, the fiber laser includes an optical fiber 30 doped with a rare earth element, a laser light source 32, and optical means 38. As the laser light source 32, a laser diode that generates excitation light in a wavelength band of 0.8 μm is used. As the optical means 38, a lens or the like for causing the excitation light to enter the optical fiber 30 from the laser light source 32 is used. Also, the output end of the optical fiber is finished to an appropriate mirror surface, and the output end and the end surface of the laser diode form a resonator structure. In this case, the input / output end of the optical fiber on which the excitation light is incident may be finished to an appropriate mirror surface, and the resonator structure may be formed from the input / output end. Further, the resonator structure may be of a normal type using a dielectric mirror or the like.

In the above-mentioned fiber laser, the excitation light of the wavelength 0.8 μm band from the laser light source 32 is
8 is introduced into the optical fiber 30. Nd ³⁺ in the optical fiber 30 is excited to a predetermined state and has a wavelength of 1.3 μm.
m can be emitted. As a result, when the output of the pump light exceeds a predetermined value, laser oscillation occurs in the 1.3 μm wavelength band.

(4) Waveguide Element Amplifier FIG. 9 is a diagram showing an example of application to a waveguide element amplifier. Planar waveguide 130 bifurcated on substrate 120
a, 130b and 130c are formed. Planar waveguide 130
In a, Pr ³⁺ , Yb ³⁺ , Sm ³⁺ , ^Td together with Nd ³⁺
Active substances such as b ³⁺ , Eu ³⁺ , Ho ³⁺ are added.
At the other end of the planar waveguide 130a, a filter 136 made of a grating is formed. Planar waveguide 130b
, A signal light having a wavelength of 1.3 μm is incident. Also,
Excitation light having a wavelength of 0.8 μm is made incident on the planar waveguide 130c. A laser light source similar to that shown in FIG. 3 is used.

The operation of the fiber amplifier 100 shown in FIG. 4 will be briefly described. The 1.3 μm wavelength signal light enters the planar waveguide 130a via the planar waveguide 130b,
Excitation light having a wavelength of 0.8 μm from an excitation light source such as D also enters the plane waveguide 130a through the plane waveguide 130c.
The excited Nb ³⁺ is guided by the signal light, and the transition ⁴ F _3/2
→ _Generates radiation in the 1.3 μm wavelength band corresponding to ⁴ I _13/2 . When the pump light exceeds a predetermined intensity, the signal light is amplified.

[Specific Examples] Hereinafter, specific examples by the present inventors will be described.

(1) When Pr ³⁺ is co-added First, Na ₂ O, Al ₂ O ₃ and phosphorus pentoxide are prepared as host glass raw materials, each having a composition of 15 Na ₂ O.
-15Al ₂ O ₃ -70P ₂ O ₅ formulated to have a glass (mol%). A predetermined amount of Nd ₂ O ₃ , which is an oxide of the rare-earth element Nd, and Pr ₂ O ₃ are added to the mixture and melted in a platinum crucible. The amount of Nd ₂ O ₃
The concentration of ³⁺ is 500 ppm by weight with respect to the host glass.
Adjust so that The amount of Pr ₂ O ₃ added is
The weight concentration of Pr ³⁺ with respect to the host glass is 0, 200,
It adjusted so that it might be set to 500, 700, and 1000 ppm. That is, the concentration of Pr ³⁺ with respect to Nd ³⁺ is 0, 40,
100, 140, and 200%. The molten raw material is quenched after sufficient mixing is completed, and vitrified.

To evaluate the optical amplification characteristics of this glass,
A fiber was produced as described below. First, the glass having the above composition is formed into a rod shape to obtain a glass rod for a core. Next, a glass having a composition substantially equal to that of the glass rod and having a slightly lower refractive index is melted and formed to form a clad pipe. The glass composition of this clad pipe is 2Pb
_{O-15Na 2 O-15Al 2} O 3 -68P 2 O 5 (m
ol%), and Nb ³⁺ and Pr ₂ O ₃ were not added. These core rods and clad pipes are formed into preforms and drawn by the apparatus of FIG. As a result, an SM fiber having a core diameter of 8 μm and an outer diameter of 125 μm was obtained. The SM fiber was cut into a 10 m long fiber sample for measurement.

Evaluation of the characteristics of such a fiber sample is as follows.
This was performed using the fiber amplifier shown in FIG. The result is shown in FIG.
Is shown in the graph.

The gain shown in FIG.
m. As the laser light source 32, Ti
Using a sapphire laser, the excitation wavelength was 0.78 μm, and the excitation light intensity was 100 mW. The intensity of the input signal was −30 dBm, and the peak wavelength was 1.310 μm.

As shown in the figure, the concentration of Pr ³⁺ co-added in the core glass is 50% to 150% with respect to Nd ³⁺ .
It can be seen that a gain equal to or more than a predetermined value can be obtained in the range of.
When the concentration of Pr ³⁺ is 50% or less, the gain obtained is small. However, this is because the concentration of Pr ^{3+ as} an active ion is low and N
This is ^probably because Pr ³⁺ is less likely to be present near d ³⁺ . It is also considered that Pr ³⁺ that does not sufficiently absorb the 1.06 μm band light emitted by Nd ³⁺ is present. Even when the concentration of Pr ³⁺ is 150% or more,
The gain obtained is small, but this is due to Pr
^{It is considered that} the concentration of ³⁺ becomes too high, and a signal light having a wavelength of 1.31 μm is absorbed by the absorption tail near 1.47 μm of Pr ³⁺ .

(2) When Sm ^3T or Yb ^3T is co-added First, Na ₂ O, Al ₂ O ₃ and phosphorus pentoxide are prepared as host glass raw materials, each having a composition of 15 Na ₂ O—
15Al ₂ O ₃ -70 P ₂ O ₅ (mol%) is prepared so as to become a glass. A predetermined amount of Nd ₂ O ₃ , which is an oxide of the rare-earth element Nd, and Sm ₂ O ₃ or Yb ₂ O ₃ are added thereto and melted in a platinum crucible. Nd ₂ O ₃
Is adjusted such that the concentration of Nd ³⁺ is 500 ppm by weight with respect to the host glass. Also, Sm ₂
The amount of O ₃ or Yb ₂ O ₃ added is such that the weight concentration of these Sm ³⁺ or Yb ³⁺ with respect to the host glass is 0, 20 or less.
0, 300, 400, 500, 600, 700, 100
It was adjusted to be 0 ppm. That is, the concentration of Sm ³⁺ or Yb ³⁺ for Nd ³⁺ is 0,40,60,8
0, 100, 120, 140, and 200%.
After thorough mixing is completed, the molten raw material is quenched and vitrified.

In order to evaluate the optical amplification characteristics of this glass,
A fiber was produced as described below. First, the glass having the above composition is formed into a rod shape to obtain a glass rod for a core. Next, a glass having a composition substantially equal to that of the glass rod and having a slightly lower refractive index is melted and formed to form a clad pipe. The glass composition of this clad pipe is 2Pb
_{O-15Na 2 O-15Al 2} O 3 -68P 2 O 5 (m
ol%) without adding Nd ³⁺ , Sm ₂ O ₃ and Yb ₂ O ₃ . These core rods and clad pipes were drawn by the rod-in-tube method using the apparatus shown in FIG. 5 to obtain an SM having a core diameter of 8 μm and an outer diameter of 125 μm.
A fiber was obtained. The SM fiber was cut into a 10 m long fiber sample for measurement.

Evaluation of the characteristics of such a fiber sample is as follows.
This was performed using the fiber amplifier shown in FIG. The result is shown in FIG.
And the graph of FIG.

The gain shown in FIGS. 11 and 12 is 1.3.
It is at 10 μm. The laser light source 32 has an excitation wavelength of 0.78 μm and an excitation output of 100 mW.
Was used. The intensity of the input signal was −30 dBm, and the peak wavelength was 1.310 μm.

It can be seen that when the concentration of Sm ³⁺ co-doped in the core glass is in the range of 50% to 150% with respect to Nd ³⁺ , a gain equal to or higher than a predetermined value can be obtained. Sm ³⁺ concentration of 50
% Scarcely gain is obtained in the following, which has a low concentration of Sm ³⁺ as the active ion, Sm ³⁺ near Nd ³⁺
It is considered that the probability of the existence of becomes low. Also, N
It is also conceivable that Sm ³⁺ that does not sufficiently absorb the 1.06 μm band light emitted by d ³⁺ exists. Sm
Even if the concentration of ³⁺ is 150% or more, almost no gain is obtained. However, this is because the concentration of Sm ³⁺ , which is an active ion, is too high and the weak absorption near 1.3 μm of Sm ³⁺ is 1.3.
It is considered that 1 μm signal light is absorbed.

[0070] On the other hand, the Yb ³⁺ added with Nd ³⁺ in the core glass concentration in the range of amount that does not degrade the glass forming ability was 50% or more of the Nd ^3+, of more than a predetermined value It can be seen that a gain is obtained. The gain is not increased below 50% as in the case of Sm ³⁺ ,
In the case of Yb ³⁺ , since there is no absorption in the 1.06 μm band, Yb ³⁺
Even if the concentration of is increased, the gain does not decrease.

(3) When Ho ³⁺ is co-added First, Na ₂ O, Al ₂ O ₃ and phosphorus pentoxide are prepared as host glass raw materials, and the composition is 15Na ₂ O-15Al.
These are mixed so that another component glass of ₂ O ₃ -70 P ₂ O ₅ (mol%) is formed. The rare earth element N
Predetermined amounts of Nd ₂ O ₃ and Ho ₂ O ₃ , which are oxides of d, are added and melted in a platinum crucible. The amount of Nd ₂ O ₃ added is such that the concentration of Nd ³⁺ is 1 wt.
Adjust to 000 ppm. In addition, Ho ₂ O ₃
The amount of Ho ³⁺ is 0, 100, 200, 300, 400, 500, 6
It was adjusted to be 00, 700, and 1000 ppm.
That is, the concentration of Ho ³⁺ with respect to Nd ³⁺ is 0, 10, 2
0, 30, 40, 50, 60, 70, and 100%. The molten raw material is quenched after sufficient mixing is completed, and vitrifies.

To evaluate the optical amplification characteristics of this glass,
A fiber was produced as described below. First, the other component glass having the above composition is formed into a rod shape to obtain a glass rod for a core. Next, a glass having a composition substantially equal to that of the glass rod and having a slightly lower refractive index is melted and formed to form a clad pipe. As the glass for the clad pipe,
Composition _{2PbO-15Na 2 O-15Al 2} O 3 -68
Another component glass of P ₂ O ₅ (mol%) was used. However, Nd ³⁺ and Ho ³⁺ were not added to the other component glass. These core rods and clad pipes are formed into preforms by a rod-in-tube method, and FIG.
The core diameter is 8 μm and the outer diameter is 1
A 25 μm SM fiber was obtained. The SM fiber was cut into a 10 m long fiber sample for measurement.

Evaluation of the characteristics of such a fiber sample is as follows.
This was performed using the fiber amplifier shown in FIG. The result is FIG.
Is shown in the graph.

The gain shown in FIG. 12 is at 1.310 μm. As the laser light source 32, a Ti-sapphire laser having an excitation wavelength of 0.78 μm and an excitation output of 100 mW was used. The input signal strength is -30dB
m, and the peak wavelength was 1.310 μm.

It can be seen that the gain of the fiber amplifier increases as the concentration of Ho ³⁺ co-doped in the core glass increases. However, when the concentration of Ho ³⁺ with respect to Nd ³⁺ exceeds 100%, the saturation occurs and the gain hardly increases.

It is considered that when the concentration of Ho ^{3+ serving as} an absorber is low, the probability that Ho ³⁺ is present near Nd ³⁺ is reduced, so that the gain is reduced. In addition, H that can sufficiently absorb the 0.88 μm band light emitted by Nd ³⁺ is used.
It is also possible that o ³⁺ does not exist. The concentration of Ho ³⁺ increases the concentration of Ho ³⁺ to be absorbent at least 100%, as it can sufficiently absorb the wavelength 0.88μm band light, the gain be further added Ho ³⁺ is not increased It is considered something.

(4) When Tb ³⁺ or Eu ³⁺ is Added First, a phosphate glass to which Tb ³⁺ or Eu ³⁺ is added together with Nd ³⁺ is prepared as an optical functional glass. In this case, the composition of the host glass, 15Na ₂ O-15Al
_The raw materials were prepared so as to become ₂ O ₃ -70 P ₂ O ₅ (mol%). Further, an oxide of Nd ³⁺ as an active substance is
The concentration of d ³⁺ is 1000 ppm by weight with respect to the host glass.
Was added so that Furthermore, Tb ³⁺
Alternatively, an oxide of Eu ³⁺ is replaced with Tb ³⁺ or Eu.
The concentration of ^{3 +} by weight with respect to Nd ³⁺ 0,20,30,4
0, 50, 60, 70, and 100% were added.

To evaluate the optical amplification characteristics of this glass,
An optical fiber was manufactured as described below. First, the glass having the above composition is formed into a rod shape to obtain a glass rod for a core. Then, the glass is slightly less refractive index than the glass _{rod, 2PbO-15Na 2 O-15Al} 2
_{O 3 -68P 2 O 5 (mol} %) was melt-formation, the clad pipe. Nd ³⁺ for glass of clad pipe
Etc. are not added. These core rods and clad pipes were formed into preforms by the rod-in-tube method, and were drawn by the drawing apparatus of FIG. 5 to obtain SM fibers having a core diameter of 8 μm and an outer diameter of 125 μm. The SM fiber was cut into a 1 m long fiber sample for measurement.

Evaluation of the characteristics of such a fiber sample is as follows.
This was performed using the fiber amplifier shown in FIG.

The excitation light source 32 has an excitation wavelength of 0.78.
A Ti-sapphire laser with a μm and an excitation output of 100 mW was used. As the signal light source 31, a semiconductor laser was used. Here, the intensity of the input signal from the semiconductor laser to the optical fiber is -30 dBm, and the peak wavelength is 1.3.
It was 10 μm.

FIG. 14 is a graph showing the results of the evaluation of the characteristics of the optically functional glass fiber sample. The white square mark is T
This shows the gain of b ³⁺ , and the white circles show the gain of Eu ³⁺ .

As is clear from the graph, the gain is increased by the co-addition of Tb ³⁺ or Eu ³⁺ . That is, T
A conventional optical fiber in which active ions such as b ³⁺ are not co-doped has a gain of 4 dB, but a gain of 7 dB or more is obtained when active ions such as Tb ³⁺ are present in at least 20% or more. You can see that. Further, as the concentration of active ions such as Tb ³⁺ increases, the gain of the fiber amplifier increases. This is because Nd increases as the concentration of Tb ³⁺ etc. increases.
^It is considered that the probability that active ions such as Tb ³⁺ exist near ³⁺ is increased. By increasing the probability of proximity between Nd ³⁺ and active ions such as Tb ³⁺ , the energy level ⁴ I
_This is because the probability of energy transfer from Nd ³⁺ having electrons excited on _13/2 to active ions such as Tb ³⁺ is considered to be increased.

[0083]

As described above, according to the optical functional glass used for the optical amplifier and the laser of the present invention, light emission and optical amplification in a wavelength band of 1.3 μm become possible due to the presence of the excitation light. Alternatively, the amplification efficiency can be increased.
Furthermore, by forming this into a waveguide and a fiber,
Applicable to optical amplifiers and lasers. In particular, when formed in a fiber, a fiber amplifier having a low threshold and a high gain can be obtained.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating the function of rare earth element ions as an absorber added to the optically functional glass according to the present invention.

FIG. 2 is a diagram showing energy levels of Nd.

FIG. 3 is a diagram showing energy levels of ions of various rare earth elements.

FIG. 4 is an explanatory diagram of the function of ions of a rare earth element which is an accelerator added to the optical functional glass according to the present invention.

FIG. 5 is a view showing an apparatus for forming a fiber using optically functional glass.

FIG. 6 is a view showing a fiber sample formed by the apparatus of FIG. 4;

FIG. 7 is a diagram illustrating a configuration of an embodiment of a fiber amplifier.

FIG. 8 is a diagram showing a configuration of an embodiment of a fiber laser.

FIG. 9 shows an embodiment of a waveguide element laser.

FIG. 10 shows a wavelength of 1.310 μm of the fiber amplifier of FIG.
FIG. 9 is a diagram showing a relationship between a gain in the m band and the concentration of Pr ³⁺ .

FIG. 11 shows a wavelength of 1.310 μm of the fiber amplifier of FIG.
FIG. 9 is a diagram illustrating a relationship between a gain in the m band and the density of Sm ³⁺ .

FIG. 12 shows a wavelength of 1.310 μm of the fiber amplifier of FIG.
FIG. 7 is a diagram illustrating a relationship between a gain in the m band and the density of Yb ³⁺ .

FIG. 13 shows a wavelength of 1.310 μm of the fiber amplifier of FIG. 7.
FIG. 6 is a diagram showing a relationship between gain and Ho ³⁺ concentration in the m band.

FIG. 14 shows a wavelength of 1.310 μm of the fiber amplifier of FIG.
FIG. 7 is a diagram showing a relationship between a gain in the m band and the concentration of Eu ³⁺ or Tb ³⁺ .

[Explanation of symbols]

20, 30 optical fiber 32 excitation light source 33, 38, 38a, 38b, 39a, 39b optical means

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI H01S 3/07 H01S 3/07 3/17 3/17 (31) Priority claim number Japanese Patent Application No. 2-220619 (32) Priority date 1990 August 22 (1990.8.22) (33) Priority Country Japan (JP) (72) Inventor Koji Nakazato 1 Tayacho, Sakae-ku, Yokohama-shi, Kanagawa Prefecture Sumitomo Electric Industries, Ltd. Yokohama Works (72) Invention Person Minoru Watanabe 1 Tayacho, Sakae-ku, Yokohama-shi, Kanagawa Prefecture Inside the Yokohama Works, Sumitomo Electric Industries, Ltd. Tomonori 1-6, Uchisaiwaicho, Chiyoda-ku, Tokyo Nippon Telegraph and Telephone Corporation (56) Reference JP-A-56-9250 (JP, A) JP-A-63-182220 (JP, A) JP-A-2- 48431 (JP, A) JP-A-51-107312 (JP, A) JP-A-4-3482 (JP, A) JP-A-4-59635 (JP, A) (58) Fields investigated (Int. ⁷ , DB name) C03C 1/00-13/00 JICST file (JOIS)

Claims (6)

(57) [Claims] 1. An optical waveguide for transmitting signal light in a wavelength band of 1.3 μm, an excitation light source for generating excitation light in a wavelength band of 0.8 μm, and the excitation light is made to enter the optical waveguide from the excitation light source. An optical fiber comprising a core made of optically functional glass and a clad surrounding the core and having a lower refractive index than the core, or a planar waveguide made of optically functional glass. A waveguide element having a waveguide, wherein the optically functional glass contains Nd ³⁺ as an active substance,
At least one of Pr ³⁺ , Yb ³⁺ , Sm ³⁺ and Ho ³⁺ which are rare earth ions other than Nd ³⁺ having an absorption band at a wavelength of about 1 μm is added together with Nd ^3+. Optical amplifier. 2. An optical waveguide for transmitting signal light in a wavelength band of 1.3 μm, an excitation light source for generating excitation light in a wavelength band of 0.8 μm, and the excitation light is made to enter the optical waveguide from the excitation light source. An optical fiber comprising: a core made of optically functional glass; and a clad surrounding the core and having a lower refractive index than the core, or a planar waveguide made of optically functional glass. And the optical functional glass comprises Nd ³⁺ as an active material,
Tb ^3+, which is a rare-earth ion other than Nd ³⁺ that exhibits energy transfer at a level of about 4000 cm ⁻¹ from the ground level, is N
An optical amplifier, which is added together with d ³⁺ . 3. The optical amplifier according to claim 1, wherein the concentration of the rare earth ions other than Nd ³⁺ is 50% to 150% by weight based on Nd ³⁺ . 4. An optical waveguide, comprising: an excitation light source that generates excitation light in a wavelength band of 0.8 μm; and an optical unit that causes the excitation light to enter the optical waveguide from the excitation light source. A resonator structure for feeding back light in the 1.3 μm band or its vicinity to the optical waveguide is formed, and the optical waveguide has a core made of optically functional glass, and has a lower refractive index than the core surrounding the core. An optical fiber comprising a clad having, or a waveguide element comprising a planar waveguide made of optical functional glass, wherein the optical functional glass contains Nd ³⁺ as an active material,
At least one of Pr ³⁺ , Yb ³⁺ , Sm ³⁺ and Ho ³⁺ which are rare earth ions other than Nd ³⁺ having an absorption band at a wavelength of about 1 μm is added together with Nd ^3+. And a laser. 5. An optical waveguide, comprising: an excitation light source for generating excitation light in a wavelength of 0.8 μm band; and optical means for causing the excitation light to enter the optical waveguide from the excitation light source. A resonator structure for feeding back light in the 1.3 μm band or its vicinity to the optical waveguide is formed, and the optical waveguide has a core made of optically functional glass, and has a lower refractive index than the core surrounding the core. An optical fiber comprising a clad having, or a waveguide element comprising a planar waveguide made of optical functional glass, wherein the optical functional glass contains Nd ³⁺ as an active material,
Tb ^3+, which is a rare-earth ion other than Nd ³⁺ that exhibits energy transfer at a level of about 4000 cm ⁻¹ from the ground level, is N
A laser, which is added together with d ³⁺ . 6. The laser according to claim 4, wherein the concentration of the rare earth ion other than Nd ³⁺ is 50% to 150% by weight based on Nd ³⁺ .