JPH0529699A - Optical functional glass - Google Patents

Abstract

PURPOSE:To provide an optical functional glass and a fiber amplifier, etc., using the same for optically amplifying in a 1.3mum wavelength band. CONSTITUTION:At least one type of Sm and Dy is added as second rare earth element together with Pr of a first rare earth element to optical functional glass to be used for an optical fiber 30. The second rare earth element is excited due to presence of an exciting light having 1.07, 0.98mum, etc., wavelengths from a laser light source 32. The first rare earth element which receives energy from the second rare earth element is also excited in response to it. The excited first rare earth element is guided to a signal light to generate an emitting light having 1.3mum a wavelength band corresponding to a transition <1>D2 <1>G4. If the exciting light exceeds a predetermined intensity, the signal light is amplified.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical active device, an optical active device, a fiber amplifier, a waveguide device amplifier, a fiber laser and a waveguide device laser used for optical amplification in the 1.3 .mu.m band and other wavelength bands. Regarding

[0002]

2. Description of the Related Art An optical functional glass to which a rare earth element is added as an active substance is a fiber amplifier, a fiber sensor used for optical communication in a wavelength band of 1.3 μm, which is generally performed within a range of 1.310 ± 0.025 μm, Applications to fiber lasers and other optically active devices are being considered. For example, an optical fiber made of fluoride glass doped with praseodymium ions (Pr ³⁺ ) as an active substance has a wavelength of 1.3 μm.
It has been reported that optical amplification in the m band can be realized (OFC '90 Post Deadline Papers (PD2-1)).

[0003]

However, in the optical fiber made of Pr ³⁺ -doped fluoride glass shown in the above report, there is a problem that the absorption intensity of light having a wavelength of 1 μm is small and the amplification efficiency is extremely poor. . Also, the wavelength for excitation is 1μ
Since there is no LD of m, there was a big problem in practical application of the amplifier.

Therefore, an object of the present invention is to provide an optical functional glass containing Pr ³⁺ and having a high efficiency of light emission / amplification in the wavelength band of 1.3 μm. .

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

Another object of the present invention is to provide an optical active device including the above optical fiber and waveguide element.

It is another object of the present invention 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.

[0009]

[Means and Actions for Solving the Problems] The inventors of the present invention have conducted extensive studies to solve the above problems, and as a result, have a wavelength of about 1.0.
The inventors have found an optical functional glass that can emit light and amplify light in the 1.3 μm wavelength band by using excitation light of μm, or can enhance its amplification efficiency.

The optical functional glass according to the present invention comprises a samarium ion (Sm ³⁺ ) and a dysprosium ion (Dy).
^At least one kind of ions of ³⁺ ) is added as a second rare earth ion to the host glass (matrix glass) together with Pr ³⁺ which is the first rare earth ion. As the host glass, it is possible to use fluorophosphate glass, phosphate glass, silicate glass, chalcogenide glass, fluoride glass, quartz glass and the like.

According to the optical functional glass, Sm ³⁺ or Dy ³⁺ or by a combination thereof is added to the host glass together with Pr ^3+, Pr ³⁺ using an excitation light having a wavelength of approximately 1.0μm It has been found that not only can be excited, but as a result, glass suitable for optical amplification in the wavelength band of 1.3 μm can be obtained as described later.

With respect to the above phenomenon, the present inventor made a study by making the following hypothesis.

FIG. 1 is an energy level diagram for explaining this hypothesis. Examples of active substances include Pr ³⁺ and Sm
Wavelength introduced into optical functional glass co-doped with ³⁺ about 1.
The excitation light of 07 μm excites Sm ³⁺ by the two-photon process, and electronic transition from the level ⁶ H _5/2 to the level ⁶ F _9/2 and the level
An electronic transition from ⁶ F _9/2 to level ⁴ G _5/2 is generated. Since the energy difference between the two levels ⁴ G _5/2 and ⁶ H _5/2 substantially corresponds to the energy difference between the two levels ¹ D ₂ and ³ H _{4 of} Pr ³⁺ , Sm ³⁺ The excitation energy of is transferred to Pr ³⁺ existing near it. That is, the excited electrons are apparently at a level ⁴ G _5/2 due to energy transfer.
To the level ¹ D ₂ . As a result, the transition ^{1 of} Pr ³⁺
Radiation in the 1.3 μm wavelength band corresponding to D ₂ → ¹ G ₄ becomes possible.

Further, the excitation light having a wavelength of about 0.98 μm introduced into the optical functional glass co-doped with Pr ³⁺ and Dy ³⁺ excites Dy ³⁺ by the two-photon process and the level ⁶ H _{15 / 2}
To the level ⁴ F _9/2 via the level ⁶ H _5/2 . As a result, energy transfer causes Dy ³⁺
An electron transition occurs from the level ⁴ F _9/2 of Pr ^{3+ to} the level ¹ D _{2 of} Pr ³⁺ , and radiation in the 1.3 μm wavelength band corresponding to the transition ¹ D ₂ → ¹ G ₄ of Pr ³⁺ is possible. become.

It is unclear whether the above hypothesis is appropriate. In any case, according to the experiments and studies by the present inventors, by adding Sm ³⁺ or Dy ³⁺ or a combination thereof to the host glass together with Pr ³⁺ ,
It has been found that a promising glass that enables light emission and light amplification in the wavelength band of 1.3 μm by Pr ³⁺ , or that enhances the amplification efficiency and the like can be obtained.

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

As a concrete manufacturing method of the above optical fiber, 2
Known manufacturing methods such as a melting crucible method, a built-in casting method, and a rod-in-tube method can be used. Furthermore, when quartz glass is used as a host glass of Pr ³⁺ which is an active material, VAD method, MCVD method, OVD method and the like can be used.

As a concrete structure of the optical fiber, it is desirable to use a single mode fiber, and it is desirable that the core diameter is 5 μm or less and the relative refractive index difference is 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 set the core diameter to about 8 μm and the relative refractive index difference to about 0.3%.

An optical active device of the present invention comprises the above optical fiber and second rare earth ions Sm ³⁺ and / or Dy ^3+.
For generating excitation light with a wavelength of about 1 μm to excite the laser
Other pumping light sources such as lasers, and pumping light coupling means such as a coupler that causes the pumping light to enter the optical fiber from the pumping light source are provided.

According to the above optical active device, the second rare earth ion such as Sm ³⁺ is excited by the excitation light having the wavelength of about 1 μm introduced into the optical fiber by the excitation light coupling means,
Pr ³⁺ that has received energy transfer from this is also excited.
Part or most of this excited Pr ³⁺ is guided to the signal light in the 1.3 μm wavelength band existing in the optical fiber,
It emits radiated light corresponding to transition ¹ D ₂ → ¹ G ₄ with high efficiency, and facilitates various functions such as optical amplification function, optical switch function, and optical sensor function in this band.

The fiber amplifier of the present invention comprises the above-mentioned optical active device and a signal light coupling means such as a coupler for guiding the signal light in the 1.3 μm wavelength band into the above optical fiber.

According to the above fiber amplifier, Pr ³⁺ is pumped by the pumping light having a wavelength of about 1 μm introduced into the fiber by the pumping light coupling means. This excited Pr
At the same time, a part or most of ³⁺ is induced by the signal light of the wavelength 1.3 μm band introduced into the optical fiber by the signal light coupling means to generate radiated light, and the ³⁺ Optical amplification becomes possible.

The fiber laser of the present invention comprises the above-mentioned photoactive device and a resonator structure for feeding back the light in the 1.3 μm wavelength band or in the vicinity thereof from the inside of the optical fiber to the optical fiber.

According to the above fiber laser, Pr ³⁺ is excited by the excitation light having a wavelength of about 1 μm introduced into the fiber by the excitation light coupling means. This excited Pr
Part or most of ³⁺ is induced by spontaneous emission light in the 1.3 μm wavelength band to generate radiated light, and laser oscillation in the 1.3 μm wavelength band is possible.

If the above optical fiber is replaced with a waveguide element, an extremely small waveguide element amplifier, waveguide element laser or other optically active device can be constructed.

[0026]

EXAMPLES Examples of the present invention will be specifically described below.

First, the composition 53.5ZrF ₄ -20BaF
₂ -3.5LaF ₃ -3.0AlF ₃ -20NaF (m
(ol%) fluoride glass raw materials were prepared, and PrF ₃ and a fluoride such as SmF ₃ were mixed in a predetermined amount together with them. The mixed raw materials were melted in a platinum crucible under an inert atmosphere and then vitrified by quenching. Further, a fluoride glass containing only PrF ₃ was prepared for comparison.

In order to evaluate the optical amplification characteristics of this optical functional glass, a fiber was produced as follows. First,
The above-mentioned optical functional glass is molded into a rod shape to obtain a glass rod for a core. Further, a glass pipe for cladding is prepared which has a composition having a refractive index lower than that of the glass rod for core and does not contain not only second rare earth ions such as Sm ³⁺ but also Pr ³⁺ . Then, these glass rods and glass pipes were formed into a preform and drawn into an optical fiber.
As a result, the core diameter is 5 μm, the outer diameter is 125 μm,
A single mode fiber having a relative refractive index difference of 1.0% was obtained. This single mode fiber was cut into an optical fiber sample having a length of 8 m for measurement.

FIG. 2 is an enlarged view of the optical fiber 30 thus obtained. The optical fiber 30 includes a core 30a made of an optical functional glass in which Sm ³⁺ , Dy ^3+, etc. are added together with Pr ³⁺ , and P has a relatively lower refractive index than the core.
and a clad 30b to which an active substance such as r ³⁺ , Sm ³⁺ , Dy ³⁺ is not added.

FIG. 3 shows a case where the wavelength 1.
An example of the configuration of a 3 μm band fiber amplifier is shown. The illustrated fiber amplifier has a bidirectional two-wavelength pumping type configuration, and includes a fiber 30 containing a rare earth element that amplifies signal light in the wavelength band of 1.3 μm, and a first pumping light in the wavelength band of 1.07 μm. Generating a first laser light source 32 and a wavelength of 0.98
Second laser light source 13 for generating second excitation light in the μm band
2 and each of the first and second excitation lights, the respective excitation light source 3
The first and second couplers 33 and 133 that enter the optical fiber 30 from the second and second 132 are provided.

An optical fiber 38a provided on the first coupler 33 formed by fusion-spreading the optical fibers 38 and 39.
A signal light source 31 having a wavelength band of 1.3 μm is connected to.
The input side of the optical fiber 30 is coupled to the optical fiber 38b facing this through a connector or the like, and the signal light is made incident into the optical fiber 30. A first laser light source 32 that generates excitation light in a wavelength band of 1.07 μm is connected to the optical fiber 39a provided in the first coupler 33. Therefore, the excitation light of the wavelength 1.07 μm band from the laser light source 32 is also introduced into the optical fiber 30 together with the signal light.

On the other hand, the fiber 139a provided in the second coupler 133 is connected to the second laser light source 132 which generates the excitation light in the wavelength band of 0.98 μm. further,
The fiber 138 a provided in the second coupler 133 is coupled to the output side of the optical fiber 30. Therefore, the excitation light in the wavelength band of 0.98 μm from the laser light source 132 is also second
Is introduced into the optical fiber 30 via the coupler 133.

The amplified signal light from the output side of the optical fiber 30 is guided to the optical spectrum analyzer 35 via the fiber 138a, the second coupler 133 and the fiber 138b, and the filter 36 for cutting the pumping light. The optical spectrum analyzer 35 measures the intensity, wavelength, etc. of the amplified signal light. The first and second couplers 3
3, the remaining optical fibers 39b and 13 provided in
9b is a matching oil 37 to prevent returning light.
Is soaked in.

The operation of the fiber amplifier shown in FIG. 3 will be briefly described. The signal light in the 1.3 μm wavelength band from the signal light source 31 enters the optical fiber 30 via the coupler 33. At the same time, the pumping lights of the wavelengths 1.07 μm band and 0.98 μm band from the first and second pumping light sources 32 and 132 also enter the optical fiber 30 through the first and second couplers 33. These excitation light, Sm ^3+, excites the active substance Dy ³⁺ etc., excites also Pr ³⁺ that received therefrom energy transfer. The excited Pr ³⁺ is induced by the signal light to generate radiation light having a wavelength band of 1.3 μm corresponding to the transition ¹ D ₂ → ¹ G ₄ . When the excitation light exceeds a predetermined intensity, the signal light will be amplified.

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

Example 1 As an optical fiber 30, Pr ³⁺ is 1000 ppm and Sm ³⁺ is 2000 p in the core 30a.
A single mode fiber doped with pm was prepared. An LD having a wavelength of 1.32 μm was used as the signal light source 31, and the signal light input was set to −30 dB. An LD-excited Nd-YAG laser was used as the first excitation light source 32, the wavelength was 1.06 μm, and the excitation light input was 100 mW. No excitation light was generated from the second excitation light source 132.
The gain for signal light having a wavelength of 1.32 μm was 7 dB and the efficiency was 0.07 dB / mW.

(Example 2) As the optical fiber 30, Pr ³⁺ is 1000 ppm and Dy ³⁺ is 2000 p in the core 30a.
A single mode fiber doped with pm was prepared. As the signal light source 31, the same one as the LD of (Example 1) was used. A Ti-sapphire laser was used as the second pumping light source 132, the wavelength was 0.98 μm, and the pumping light input was 100 mW. No excitation light was generated from the first excitation light source 32. The gain for signal light of wavelength 1.32 μm is 6.4 dB, and its efficiency is 0.064 dB / mW.
Met.

Example 3 As the optical fiber 30, the core 30a has Pr ³⁺ of 1000 ppm and Sm ³⁺ of 1000 p.
A single mode fiber containing 1000 ppm of pm and Dy ³⁺ was prepared. As the signal light source 31, the same one as the LD of (Example 1) was used. First and third excitation light sources 3
The LDs 2 and 132 are the LDs described in (Example 1) and (Example 2).
A pumping Nd-YAG laser and a Ti-sapphire laser are used, and the wavelengths are 1.06 μm and 0.98 μm, respectively.
And the excitation light input was equally set to 100 mW. Wavelength 1.
The gain for the signal light of 32 μm was 13 dB, and the efficiency was 0.065 dB / mW.

(Comparative Example) As the optical fiber 30, a single mode fiber in which only 1000 ppm of Pr ³⁺ was added to the core 30a was prepared. As the signal light source 31, the same one as the LD of (Example 1) was used. A Ti-sapphire laser was used as the second pumping light source 132, the wavelength was 1.007 μm, and the pumping light input was 100 mW. No excitation light was generated from the first excitation light source 32. Gain for signal light of wavelength 1.32 μm is 4.1d
In B, the efficiency was 0.041 dB / mW.

As is clear from the above comparative examples and the like, Pr
Sm is better than single mode fiber doped with ³⁺ only
It can be seen that the single-mode fiber co-doped with the second rare earth ion such as ³⁺ has higher optical amplification efficiency.

FIG. 4 is a diagram showing an embodiment of the waveguide element amplifier. Planar waveguides 130 a, 130 b, and 130 c that branch into two are formed on the substrate 120. A second rare earth ion such as Sm ³⁺ is added to the region of the planar waveguide 130a together with Pr ³⁺ . A filter 136 made of a grating is formed at the other end of the planar waveguide 130a. The planar waveguide 130b has a wavelength of 1.3 μm.
The band signal light is made incident. Further, excitation light having a wavelength of 1.07 μm, a wavelength of 0.98 μm, or the like is incident on the planar waveguide 130c. As a laser light source for generating excitation light,
The same one as in FIG. 3 is used.

The operation of the waveguide element amplifier 100 shown in FIG. 4 will be briefly described. The signal light having a wavelength of 1.3 μm enters the flat waveguide 130a through the flat waveguide 130b,
Excitation light with a wavelength of 1.07 μm or the like from an excitation light source such as an LD-excited Nd-YAG laser also enters the planar waveguide 130a through the planar waveguide 130c. The excitation light excites a second rare earth ion such as Sm ³⁺ and further excites Pr ³⁺ . The excited Pr ³⁺ is induced by the signal light, and the transition ¹ D
₂ → Generates synchrotron radiation of 1.3 μm wavelength band corresponding to ¹ G ₄ . When the excitation light exceeds a predetermined intensity, the signal light will be amplified.

FIG. 5 is a diagram showing an embodiment of the fiber laser. This fiber laser uses an optical fiber 30
A laser light source 32 made of an LD-excited Nd-YAG laser or the like, and an excitation light coupling device 43 made of a lens or the like. The laser light source 32 has a wavelength of 1.07 μm and a wavelength of 0.9
Excitation light of 8 μm or the like is generated. The excitation light coupling device 43 causes excitation light to enter the optical fiber 30 from the laser light source 32. In this case, the input and output ends of the optical fiber are finished into an appropriate mirror surface to form a resonator structure. The resonator structure may be of a normal type using a dielectric mirror or the like. Further, it is possible to form a ring laser having a ring-shaped resonator.

In the above fiber laser, the pumping light with a wavelength of 1.07 μm from the laser light source 32 is introduced into the optical fiber 30 by the pumping light coupling device 38. The excitation light excites second rare earth ions such as Sm ³⁺ in the optical fiber 30 and further excites Pr ³⁺ . Excited P
r ³⁺ is induced by 1.3 μm spontaneous emission light, and the transition ¹ D
₂ → Generates synchrotron radiation of 1.3 μm wavelength band corresponding to ¹ G ₄ . Wavelength 1.3 μm when pump light output exceeds a specified value
Laser oscillation occurs in the band.

[0045]

As described above, according to the optical functional glass of the present invention, Pr is efficiently excited by the excitation light having a wavelength of about 1 μm due to the presence of at least one element of Sm and Dy. be able to. Existence of excited Pr enables emission / amplification in 1.3 μm band,
Alternatively, its amplification efficiency can be increased. Further, by forming this in a waveguide, an optical fiber or the like, it can be applied to an optical amplifier, an optical functional device such as a laser. In particular, when formed into a fiber, a low threshold and high gain fiber amplifier can be obtained. Further, it becomes possible to excite with LD.

[Brief description of drawings]

FIG. 1 is a diagram showing an energy level diagram of a rare earth element such as Pr.

FIG. 2 is a diagram showing an example of an optical fiber.

FIG. 3 is a diagram showing an example of a fiber amplifier.

FIG. 4 is a diagram showing an example of a waveguide element amplifier.

FIG. 5 is a diagram showing an example of a fiber laser.

[Explanation of symbols]

30 ... Optical fiber 30a ... Core of optical fiber 32, 132 ... Excitation light source 33, 133 ... Couplers as optical means

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁵ Identification number Internal reference number FI Technical indication location H01S 3/094 (72) Inventor Koji Nakazato 1 Taya-cho, Sakae-ku, Yokohama-shi, Kanagawa Sumitomo Electric Industries Co., Ltd. Company Yokohama Works (72) Inventor Hiroo Kanamori 1 Taya-cho, Sakae-ku, Yokohama-shi, Kanagawa Sumitomo Electric Industries, Ltd. Yokohama Works (72) Minoru Watanabe 1 Taya-cho, Sakae-ku, Yokohama, Kanagawa Sumitomo Electric Industries Co., Ltd. Company Yokohama Works (72) Inventor Yoshiaki Miyajima 1-1-6 Uchisaiwaicho, Chiyoda-ku, Tokyo Nihon Telegraph and Telephone Corporation

Claims (9)

[Claims] 1. An optical functional glass, wherein the host glass contains Pr and at least one element selected from Sm and Dy as a second rare earth element. 2. An optical fiber having a core made of the optical functional glass according to claim 1. 3. The optical fiber according to claim 2, an excitation light source for generating excitation light having a wavelength of about 1 μm for exciting the second rare earth element, and the excitation light from the excitation light source into the optical fiber. A pumping light coupling means for making incident light, and a photoactive device. 4. A fiber amplifier comprising: the optical active device according to claim 3; and a signal light coupling means for guiding a signal light in the 1.3 μm wavelength band into the optical fiber. 5. A fiber laser comprising the optical active device according to claim 3 and a resonator structure for feeding back light in the 1.3 μm wavelength band or in the vicinity thereof from inside the optical fiber to the optical fiber. 6. A waveguide device comprising a planar waveguide made of the optical functional glass according to claim 1. 7. The waveguide element according to claim 6, an excitation light source for generating excitation light having a wavelength of about 1 μm for exciting the second rare earth element, and the excitation light from the excitation light source to the waveguide element. And an excitation light coupling means to be incident on the inside of the optically active device. 8. A waveguide device amplifier comprising: the optical active device according to claim 7; and a signal light coupling means for guiding a signal light of a wavelength band of 1.3 μm into the optical waveguide device. 9. A waveguide element comprising: the optical active device according to claim 7; and a resonator structure for feeding back light in the 1.3 μm wavelength band or in the vicinity thereof from inside the waveguide element to the waveguide element. laser.