JP2931694B2 - Optical functional glass - 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 functional glass, an optical fiber, a waveguide element, a fiber amplifier, a waveguide element amplifier, a fiber laser, and a waveguide element laser used for optical amplification in the 1.3 .mu.m band. About.

[0002]

2. Description of the Related Art An optical functional glass to which a rare earth element is added is generally used for a fiber amplifier, a fiber sensor, a fiber laser, and the like used for optical communication in a 1.3 μm band in a wavelength range of 1.310 ± 0.025 μm. Application to optical functional devices is considered. Specifically, a wavelength of 1.3 μm
There is a report on an optical fiber doped with praseodymium ion (Pr ³⁺ ) as an active substance for realizing light amplification near m (OFC'91 Post Deadline Papers (PD 2-
1)).

[0003]

However, in the case of an optical fiber doped with Pr ³⁺ , there is a problem that the amplification efficiency is extremely low, or a simple pumping light source such as a semiconductor laser is used as a pumping light source having a required wavelength around 1.017 μm. There was a problem that a light source could not be obtained.

[0004] In view of the above circumstances, the present invention provides a light having a wavelength of 1.3 μm by using excitation light having a wavelength of 0.7 to 0.9 μm that can be generated using a simple excitation light source such as a semiconductor laser. It is an object of the present invention to provide an optically functional glass that enables amplification or enhances the amplification efficiency.

Another object of the present invention is to provide an optical fiber and a waveguide element using the above-mentioned optically functional glass.

Another object of the present invention is to provide a fiber amplifier and a fiber laser using the above optical fiber.

Another object of the present invention is to provide a waveguide device amplifier and a waveguide device laser using the above waveguide device.

[0008]

The present inventors have made intensive studies to solve the above-mentioned problems, and as a result, have obtained an optically functional glass containing Pr ³⁺ as an active substance, having a wavelength of 1.3.
We have found a glass that enables light amplification in the μm band or that increases the amplification efficiency.

[0009] The optical functional glass according to the present invention comprises Pr ³⁺ as a first rare earth ion, Yb ^{3+ as} a second rare earth ion, and a third rare earth excluding Pr ³⁺ and Yb ^3+. The ion and the active material are co-added to the host glass (matrix glass). Examples of the third rare earth ion include neodymium ion (Nd ³⁺ ), thulium ion (Tm ³⁺ ), holmium ion (Ho ³⁺ ), promethium ion (Pm ³⁺ ), and erbium ion (Er).
³⁺ ) can be used. Further, as the host glass, fluorophosphate glass, phosphate glass, silicate glass,
Chalcogenide glass, fluoride glass, quartz glass and the like can be used.

According to the above optical functional glass, with Pr ³⁺ and ^{Yb 3+, Nd 3+, Tm 3+} , Ho 3+, Pm 3+,
By adding a third rare earth ion, such as Er ^3+, to the host glass, P 3 is excited using excitation light having a wavelength of 0.9 μm or less.
As will be described later, it was found that r ³⁺ can be excited and that a glass suitable for optical amplification in a 1.3 μm band can be obtained as a result.

Regarding the above phenomenon, the present inventors have made the following hypothesis and studied.

FIG. 1 is an energy level diagram for explaining this hypothesis. The excitation light having a wavelength of about 0.9 μm or less introduced into the optically functional glass to which the first to third rare earth ions are co-doped as an active substance is a two-level ² F of Yb ^{3+ as} the second rare earth ion. _7/2, having a slightly larger energy than the energy difference between ² F _5/2. Therefore, Y
b ³⁺ cannot be directly excited. However, if an appropriate rare earth ion X is selected as the third rare earth ion,
The rare earth ion X can be excited to generate an electron transition from the level X ₁ to the level X ₂ . 2 level ² F _7/2 energy difference between these levels is Yb ^3+, since become somewhat larger than the energy difference between the ² F _5/2,
Excitation energy of the rare earth ion X is transmitted to the Yb ³⁺ existing near its excites a Yb ³⁺ to generate electron transition from the level ² F _7/2 to level ² F _5/2. Further, since the energy difference between these levels is similar to the energy difference between the two levels ³ H ₄ and ¹ G _{4 of} Pr ³⁺ which is the first rare earth ion, the excitation energy of Yb ³⁺ is It will be transmitted to Pr ³⁺ existing nearby with a relatively high probability.
In other words, excited electrons transitions from apparently level X ₂ by the energy transmitted fart a level ² F _5/2 to level ¹ G _4.
As a result, radiation in the 1.3 μm wavelength band corresponding to the transition ¹ G ₄ → ³ H ₅ of Pr ³⁺ becomes possible.

In such an optically functional glass, Pr.sup.3 ⁺ is used with an excitation light source having a wavelength of 0.9 μm or less which is relatively easily available.
Can be excited. Furthermore, Yb ³⁺
It is expected that the amplification factor will be improved as compared with the case where Pr ³⁺ is directly excited by the rare-earth ion X without adding the ^compound .
This is because the level X ₂ of the rare earth ion X and the level ¹ G of Pr ³⁺
_This is because the presence of the level _{2F5 /} ² of Yb ³⁺ between ₄ and ₄ is considered to increase the probability of energy transfer.

FIG. 2 is a diagram for explaining the selection of the rare earth ion X.

When an optical functional glass to which Nd ³⁺ is co-doped, for example, is used as the third rare earth ion, the excitation light having a wavelength of about 0.88 μm introduced into the optical functional glass is
^Exciting d ³⁺ causes an electron transition from level ⁴ I _9/2 to level ⁴ F _5/2 . After that, a transition to the ⁴ F _3/2 level occurs due to lattice relaxation. The excited electrons transition from the Nd ³⁺ level ⁴ F _3/2 to the Yb ³⁺ level ² F _5/2 to the Pr ³⁺ level ¹ G ₄ by energy transfer. As a result, radiation in the 1.3 μm wavelength band corresponding to the transition ¹ G ₄ → ³ H ₅ of Pr ³⁺ becomes possible.

As the third rare earth ion, for example, Tm
^In the case of using an optical functional glass to which ³⁺ is co-added, the excitation light having a wavelength of about 0.79 μm introduced into the optical functional glass excites Tm ³⁺ to convert from level ³ H ₆ to level ³ H ^3. Generate an electronic transition to H ₄ . The excited electrons are ^{converted from} the level ³ H ₄ of Tm ^{3+ to} the level ² F _{5/2 of} Yb ³⁺ by energy transfer.
To the Pr ³⁺ level ¹ G ₄ . As a result, Pr
Radiation in the 1.3 μm band corresponding to the ³⁺ transition ¹ G ₄ → ³ H ₅ becomes possible.

Further, as the third rare earth ion, for example, H
In the case of using an optical functional glass to which o ³⁺ is co-doped, the excitation light having a wavelength of about 0.889 μm introduced into the optical functional glass excites Ho ³⁺ and causes a level shift from the level ⁵ I ₈ to the level ⁵ I _8. ⁵ generating an electron transition to I _5. The excited electrons are transferred from the Ho ³⁺ level ⁵ I ₅ to the Yb ³⁺ level ² F by energy transfer.
And fart a _5/2 transition to level ¹ G ₄ of Pr ^3+. As a result,
1.3 μm wavelength corresponding to Pr ³⁺ transition ¹ G ₄ → ³ H ₅
The band can be radiated.

Further, as the third rare earth ion, for example, P
In the case of using an optical functional glass to which m ³⁺ is co-added, the excitation light having a wavelength of 0.7 to 0.8 μm introduced into the optical functional glass excites Pm ³⁺ to generate a level of ⁵ I ₄ From various levels ³
K, ⁵ generating an electron transition to S. This excited electron is
Pm ³⁺ level ³ K, ⁵ S to Y by energy transfer
and fart a level ² F _5/2 of b ³⁺ transition to level ¹ G ₄ of Pr ^3+. As a result, radiation in the 1.3 μm wavelength band corresponding to the transition ¹ G ₄ → ³ H ₅ of Pr ³⁺ becomes possible.

Further, as the third rare earth ion, for example, E
In the case of using an optical functional glass co-doped with r ³⁺ , the excitation light having a wavelength of 0.79 μm introduced into the optical functional glass excites Er ³⁺ to _{generate a} level from level ⁴ I _15/2. An electron transition to position ⁴ I _9/2 occurs. This excited electron is level ² of Yb ³⁺ from the level ⁴ I _9/2 of Er ³⁺ by energy transfer
And fart the F _5/2 transition to level ¹ G ₄ of Pr ^3+. As a result, the wavelength 1.3 corresponding to the Pr ³⁺ transition ¹ G ₄ → ³ H _5.
Radiation in the μm band becomes possible.

It is unclear whether the above hypothesis is appropriate. In any case, according to experiments and studies by the present inventors, Pr ³⁺ and Yb ^{3+ are} contained in host glass,
By co-adding a third rare earth ion such as Nd ³⁺ as an active substance, light emission and light amplification in the 1.3 μm band of Pr ³⁺ can be performed using an excitation light source having a wavelength of 0.7 to 0.9 μm. A promising glass was obtained.

The above-mentioned optically functional glass is used as a material for an optical transmission line. For example, the optically functional glass may be formed in a waveguide element having a planar waveguide formed of this glass. It is desirable to manufacture an optical fiber having a core in order to obtain a long optical transmission line, and also to obtain an optical functional device in a wavelength band of 1.3 μm. That is, the above-mentioned optical functional glass can be applied to optical functional devices such as a fiber laser, a fiber amplifier, and a fiber detector by producing an optical fiber having the optical functional glass as a core.

As a specific method for manufacturing the optical fiber,
Known production methods such as a crucible method, a built-in casting method, and a rod-in-tube method can be used. Further, when the quartz glass is used as a host glass of an active substance such as Pr ³⁺ , a production method such as a VAD method, an MCVD method, and an OVD method can be used.

The specific structure of the optical fiber is preferably a single mode fiber, and the core diameter is preferably 5 μm or less, and the relative refractive index difference is preferably 1% or more. However, even a multimode fiber can be used depending on the application. Further, considering the connection with the existing fiber, it is possible to make the core diameter about 8 μm and the relative refractive index difference about 0.3%.

The fiber amplifier of the present invention has a wavelength of 1.3 μm.
an optical fiber for transmitting m-band signal light, an excitation light source such as a laser for generating excitation light having a wavelength of 0.9 μm or less for exciting a third rare earth ion such as Nd ³⁺ , and an excitation light source for exciting light And an optical means such as a coupler for causing the light to enter the optical fiber.

In the above-described fiber amplifier, the third rare earth ion is excited by the excitation light having a wavelength of 0.9 μm or less introduced into the fiber by the optical means, and further, Yb ³⁺ is excited by energy transfer. In response to this, Pr ^{3+ is} also excited, and a part or most of the excited Pr ³⁺ is simultaneously guided to the 1.3 μm-band signal light or the like introduced into the optical fiber and radiated. Light is generated, and light amplification in the 1.3 μm band becomes possible.

A fiber laser according to the present invention includes the above optical fiber, an excitation light source, and optical means. Here, the excitation light source generates excitation light having a wavelength of 0.9 μm or less, 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.

In the above-described fiber laser, the third rare earth ion is excited by the excitation light having a wavelength of 0.9 μm or less introduced into the fiber by the optical means, and the energy transfer excites Yb ³⁺ . In response to this, Pr ^{3+ is} also excited, and a part or most of the excited Pr ³⁺ is simultaneously guided to the 1.3 μm-band signal light or the like introduced into the optical fiber and radiated. Light is generated, and laser emission in the 1.3 μm wavelength band becomes possible.

If the optical fiber is replaced with a waveguide element, a very small waveguide element amplifier, a waveguide element laser, and the like can be formed.

Further, by combining the above-mentioned optical fiber or waveguide element with an appropriate excitation light source, it becomes possible to realize various optical active devices such as an optical switch.

[0030]

Embodiments of the present invention will be specifically described below.

First, ZrF ₄ -BaF ₂ -LaF ₃ -A
A raw material of a fluoride glass such as 1F ₃ -NaF is prepared, and Pr ³⁺ , Yb ^3+, and a third rare earth ion such as Nd ³⁺ are mixed and dissolved in an appropriate ratio together with the raw material, and the optically functional glass Was prepared.

In order to evaluate the optical amplification characteristics of this optically functional glass, a fiber was produced as follows. First,
The above-mentioned optical functional glass is formed into a rod shape to obtain a glass rod for a core. Further, a cladding glass pipe is prepared which has a composition having a refractive index lower than that of the core glass rod and does not contain not only the third rare earth ions such as Nd ³⁺ but also Pr ³⁺ and Yb ³⁺ . Thereafter, these glass rods and glass pipes were formed into preforms and drawn into optical fibers. As a result, the core diameter was 5 μm and the outer diameter was 125 μm.
Was obtained. This single mode fiber was cut into an appropriate length of optical fiber sample for measurement.

FIG. 3 is an enlarged view of the optical fiber 30 thus obtained. The optical fiber 30 has a core 30a in which rare earth ions such as Nd ³⁺ , Tm ³⁺ , and Ho ³⁺ are co-doped together with Pr ³⁺ and Yb ³⁺ , and a refractive index lower than that of the core Pr ³⁺ A clad 30b to which an active substance such as Yb ³⁺ , Tm ³⁺ , Ho ³⁺ or the like is not added.

FIG. 4 shows a 1.3 μm optical fiber 30.
1 shows a configuration example of an m-band fiber amplifier. As shown in the figure, the fiber amplifier comprises a fiber 30 in which a core for amplifying signal light in the 1.3 μm wavelength band is doped with a rare earth element, and a laser light source 32 for generating excitation light having a wavelength of 0.7 to 0.9 μm.
And a coupler 33 for causing the excitation light to enter the optical fiber 30 from the excitation light source 32. Fibers 38, 39
The signal light source 31 having a wavelength band of 1.3 μm is connected to one input fiber 38a of the coupler 33 formed by the fusion-stretching. The above-mentioned laser light source 32 is connected to the other input fiber 39a. Further, one output fiber 39b of the coupler 33 is immersed in the matching oil 37 to prevent return light. The other output fiber 39a of the coupler 33 is coupled to the optical fiber 30 via a connector or the like, and transmits the signal light and the pump light to the optical fiber 30.
Lead inside. The output light from the optical fiber 30 is guided to an optical spectrum analyzer 35 via a filter 36 that cuts off the excitation light. The optical spectrum analyzer 35
Measure the intensity, wavelength, etc. of the amplified signal light.

The operation of the fiber amplifier shown in FIG. 4 will be briefly described. The 1.3 μm wavelength signal light from the signal light source 31 enters the optical fiber 30 via the coupler 33. At the same time, the wavelength from the excitation light source 32 is 0.7 to 0.9 μm.
The excitation light of m also enters the optical fiber 30 through the coupler 33. This excitation light excites an active substance such as Nd ³⁺ , Tm ³⁺ , Ho ³⁺ , and Yb ³⁺ which receives energy transfer ^therefrom.
Also excites. Furthermore excited Yb ³⁺ is, Pr ³⁺ is also excited by energy transfer. This excited Pr ³⁺
Is guided by the signal light to generate a 1.3 μm wavelength radiation light corresponding to the transition ¹ G ₄ → ³ H ₅ . When the pump light and the signal light exceed predetermined intensities, the signal light is amplified.

The measurement results obtained with the fiber amplifier of FIG. 3 will be described.

(Example 1) As the optical fiber 30, a core 30
500 ppm each of Pr ³⁺ , Yb ³⁺ and Nd ³⁺
A doped single mode fiber was prepared. The relative refractive index difference was 1.0%, and the length was 10 m. As the signal light source 31, an LD having a wavelength of 1.30 μm was used.
The laser light source 32 has a wavelength of 0.8 μm and a power of 50.
An mW LD was used. The gain for signal light having a wavelength of 1.30 μm was 20 dB.

(Example 2) As the optical fiber 30, the core 30
500 ppm each of Pr ³⁺ , Yb ³⁺ and Tm ³⁺
A doped single mode fiber was prepared. The relative refractive index difference was 1.0%, and the length was 10 m. As the signal light source 31, the same one as in (Example 1) was used. The laser light source 32 has a wavelength of 0.79 μm and a power of 50.
An mW LD was used. The gain for signal light having a wavelength of 1.30 μm was 18 dB.

(Example 3) As the optical fiber 30, the core 30
500 ppm each of Pr ³⁺ , Yb ³⁺ and Ho ³⁺
A doped single mode fiber was prepared. The relative refractive index difference was 1.0%, and the length was 10 m. As the signal light source 31, the same one as in (Example 1) was used. The laser light source 32 has a wavelength of 0.89 μm and a power of 50.
An mW LD was used. The gain for signal light having a wavelength of 1.30 μm was 15 dB.

(Example 4) As the optical fiber 30, the core 30
500 ppm each of Pr ³⁺ , Yb ³⁺ and Er ³⁺
A doped single mode fiber was prepared. The relative refractive index difference was 1.0%, and the length was 10 m. As the signal light source 31, the same one as in (Example 1) was used. The laser light source 32 has a wavelength of 0.79 μm and a power of 50.
An mW LD was used. The gain for signal light having a wavelength of 1.30 μm was 15 dB.

As is clear from the above measurement examples, Pr ³⁺
It can be seen that a single-mode fiber co-doped with Yb ³⁺ and a third rare-earth ion such as Nd ³⁺ does not require a short-wavelength, strongly-pumped light source.

FIG. 5 is a diagram showing an embodiment of the waveguide element amplifier. Planar waveguides 130a, 130b, and 130c branched into two are formed on a substrate 120. Planar waveguide 130a is doped with third rare earth ions such as Pr ³⁺ , Yb ^3+, and Nd ³⁺ . At the other end of the planar waveguide 130a, a filter 136 made of a grating is formed. The 1.3 μm wavelength signal light is incident on the planar waveguide 130b. In addition, the planar waveguide 130c includes:
Excitation light having a wavelength of 0.7 to 0.9 μm is incident. As the laser light source for the excitation light, the same one as that of FIG. 3 is used.

The operation of the fiber amplifier 100 shown in FIG. 5 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 0.7 to 0.9 μm from an excitation light source such as D also enters the plane waveguide 130a through the plane waveguide 130c. The excitation light excites a third rare earth ion such as Nd ³⁺ , further excites Yb ³⁺ , and further excites Pr ³⁺ . The excited Pr ³⁺ is guided by the signal light, and the transition ¹ G
Generates radiation in the 1.3 μm wavelength band corresponding to ₄ → ³ H ₅ . When the excitation light exceeds a predetermined intensity, the signal light is amplified.

FIG. 6 is a diagram showing an embodiment of a fiber laser. This fiber laser is an optical fiber 30
, A laser light source 32, and an optical unit 38. As the laser light source 32, an LD that generates excitation light having a wavelength of 0.7 to 0.9 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. Further, a ring laser having a ring-shaped resonator can be formed.

In the above-described fiber laser, the excitation light having a wavelength of 0.7 to 0.9 μm from the laser light source 32 is introduced into the optical fiber 30 by the optical means 38. The excitation light excites third rare earth ions such as Nd ³⁺ in the optical fiber 30, further excites Yb ³⁺ , and further excites Pr ³⁺ . The excited Pr ³⁺ is induced by spontaneous emission light,
The emitted light in the 1.3 μm wavelength band corresponding to the transition ¹ G ₄ → ³ H ₅ is generated. When the output of the pump light exceeds a predetermined value, laser oscillation occurs in the 1.3 μm wavelength band.

[0046]

As described above, according to the optical functional glass of the present invention, Yb and the third glass excluding Pr and Yb can be used.
Can be excited by excitation light having a wavelength of 0.9 μm or less due to the presence of the rare earth element. Therefore, the presence of the excited Pr enables light emission and light amplification in the 1.3 μm band, or increases the amplification efficiency. Further, by forming this into a waveguide, an optical fiber or the like, it can be applied to optical functional devices such as an optical amplifier and a laser. 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 a mechanism for exciting Pr with excitation light in a wavelength band of 0.7 to 0.9 μm.

FIG. 2 is a diagram showing an energy level diagram of a rare earth element such as Pr.

FIG. 3 is a diagram showing an embodiment of an optical fiber.

FIG. 4 is a diagram showing an embodiment of a fiber amplifier.

FIG. 5 is a diagram showing an embodiment of a waveguide element amplifier.

FIG. 6 is a diagram showing an embodiment of a fiber laser.

[Explanation of symbols]

 Reference Signs List 30 ... optical fiber 30a ... core of optical fiber 32 ... excitation light source 33 ... coupler as optical means

────────────────────────────────────────────────── ─── Continued on the front page (51) Int.Cl. ⁶ Identification symbol FI H01S 3/17 G02B 6/00 E (72) Inventor Masashi Onishi 1 Tayacho, Sakae-ku, Yokohama-shi, Kanagawa Prefecture Sumitomo Electric Industries, Ltd. Yokohama Works (72) Inventor Takashi Kogo 1st Tayacho, Sakae-ku, Yokohama-shi, Kanagawa Prefecture Sumitomo Electric Industries, Ltd.Yokohama Mfg. Co., Ltd. 72) Inventor Yoshiaki Miyajima 1-6, Uchisaiwaicho, Chiyoda-ku, Tokyo Nippon Telegraph and Telephone Corporation (58) Field surveyed (Int.Cl. ⁶ , DB name) G02F 1/35 501 C03C 13/04 G02B 1 / 02 G02B 6/00 G02B 6/00 376 H01S 3/17

Claims (10)

(57) [Claims] 1. The method according to claim 1, wherein the host glass contains Pr, Yb, and Pr.
And a third rare earth element other than Yb and an active material. 2. The method according to claim 1, wherein the third rare earth element is Nd, Tm, H
2. The optical functional glass according to claim 1, wherein the optical functional glass is at least one kind of element among o, Pm, and Er. 3. An optical fiber comprising a core made of the optically functional glass according to claim 1. 4. An optical fiber according to claim 3, which propagates signal light in a 1.3 μm band, and an excitation light source which generates excitation light having a wavelength of 0.9 μm or less to excite said third rare earth element. Optical means for causing the excitation light to enter the optical fiber from the excitation light source. 5. The optical fiber according to claim 3, wherein
An excitation light source for generating excitation light having a wavelength of 0.9 μm or less to excite the rare earth element, and optical means for causing the excitation light to enter the optical fiber from the excitation light source. A fiber laser having a resonator structure for feeding back light in or near the 1.3 μm band to the optical fiber. 6. A waveguide device comprising a planar waveguide made of the optically functional glass according to claim 1. 7. The waveguide element according to claim 6, which propagates signal light in a 1.3 μm band, and an excitation light source which generates excitation light having a wavelength of 0.9 μm or less to excite the third rare earth element. Optical means for causing the excitation light to enter the waveguide element from the excitation light source. 8. The waveguide device according to claim 6, wherein
An excitation light source for generating excitation light having a wavelength of 0.9 μm or less to excite the rare earth element, and optical means for causing the excitation light to enter the waveguide element from the excitation light source, from within the waveguide element. A waveguide element laser, wherein a resonator structure for feeding back light in the 1.3 μm band or its vicinity to the waveguide element is formed. 9. An optical fiber according to claim 3, an excitation light source for generating excitation light having a wavelength of 0.9 μm or less for exciting the third rare earth element, and transmitting the excitation light from the excitation light source to the light. Optical means for entering the fiber. 10. The waveguide element according to claim 6, an excitation light source for generating excitation light having a wavelength of 0.9 μm or less for exciting the third rare earth element, and the excitation light is transmitted from the excitation light source to the third rare earth element. Optical means for making the light incident on the waveguide element.