JPH0558674A - Optically functional glass - Google Patents

Abstract

PURPOSE:To provide an optically functional glass capable of amplifying light having a wavelength band of 1.3mum, and to provide a fiber amplifier using the same, etc. CONSTITUTION:Optically functional glass used for an optical fiber 30 contains Pr, Cr and Yb as active substances. The Cr is excited by the presence of white exciting light from a Xe lamp 32, the Yb received the transmission of energy from the Cr is also excited. Further, the Pr received the transmission of energy from the Yb is also excited. The excited Pr is induced into signal light to generate radiation light having a wavelength band of 1.3mum corresponding to a transition from <1>G4 to <3>HS. When the excited light exceeds a prescribed strength, 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 element, an optical active device, a fiber amplifier, a waveguide element amplifier, a fiber laser and a waveguide element laser used for 1.3 .mu.m band optical amplification and the like.

[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 ion (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 excitation light source becomes large. there were.

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 and optical 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, found that the wavelength of 1.3 μm
We have found an optical functional glass that enables light emission and light amplification in the m band, or that can enhance its amplification efficiency.

In the optical functional glass according to the present invention, ytterbium ions (Yb ³⁺ ) and chromium ions (Cr ³⁺ ) are used.
Is added to the host glass (matrix glass) together with Pr which is an active substance, or neodymium ions (Nd ³⁺ ) and Cr ³⁺ are added to the host glass together with Pr which is an active substance. 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, Yb ³⁺ and C
The combination of r ^3+, or a combination of Nd ³⁺ and Cr ³⁺ by adding to the host glass together with Pr ^3+, with a Xe lamp other simple excitation light source Pr ³⁺
It has been found that not only can be excited, but as a result, a glass suitable for optical amplification in the wavelength band of 1.3 μm can be obtained as described later.

Regarding the above phenomenon, the present inventor made two hypotheses and studied it.

FIG. 1 is an energy level diagram for explaining the first hypothesis. As the active substance, for example, Pr ³⁺ , Yb
The excitation light having a wavelength of about 0.7 μm or less introduced into the optical functional glass co-doped with ³⁺ and Cr ³⁺ excites Cr ³⁺ having a relatively broad absorption band to ^generate a level ⁴ A ₂ Level ⁴ T
Generates electronic transitions to _two or more levels.
As a result, an inversion distribution is formed between the level ⁴ T ₂ etc. and the level ⁴ A ₂ . Since the energy difference between these levels ⁴ T ₂ etc. and ⁴ A ₂ substantially corresponds to the energy difference between the two levels ² F _5/2 and ² F _{7/2 of} Yb ³⁺ , Cr ³⁺ The excitation energy of is transferred to Yb ³⁺ existing near it. As a result, an inversion distribution is formed between the levels ² F _5/2 and ² F _7/2 . Furthermore, these levels ² F _5/2
And the energy difference between ² F _7/2 and Pr ³⁺ is two levels ¹ G ₄
And the energy difference between ³ H ₄ approximately correspond to Y
The excitation energy of b ³⁺ is transferred to Pr ³⁺ existing near it. That is, the excited electrons make a transition from the apparent level ⁴ T ₂ etc. to the level ¹ G ₄ via the level ² F _5/2 by apparent energy transfer. As a result, the transition of Pr ^{3+ 1} G
Radiation in the 1.3 μm wavelength band corresponding to ₄ → ³ H ₅ becomes possible.

FIG. 2 is a diagram showing the fluorescence intensity of Cr ³⁺ and the absorption coefficient of Yb ³⁺ . The overlapping portion of the light emission characteristic of Cr ³⁺ and the absorption characteristic of Yb ³⁺ corresponds to the occurrence probability of energy transfer. That is, since the energy corresponding to the emission wavelength of Cr ³⁺ is transmitted as the energy corresponding to the absorption wavelength of Yb ³⁺ , the more overlapping portions the absorption / emission characteristics have, the more Cr ³⁺ and Yb ^3+. It can be said that the closer the are, the higher the probability of energy transfer. As is clear from the illustrated absorption / emission characteristics, it is considered that energy transfer between Cr ³⁺ and Yb ³⁺ occurs with a sufficient probability. Similarly, energy transfer between Yb ³⁺ and Pr ³⁺ can be expected to occur with a sufficient probability.

FIG. 3 is an energy level diagram for explaining the second hypothesis. As the active substance, for example, Pr ³⁺ , Nd
The excitation light having a wavelength of about 0.7 μm or less introduced into the optical functional glass co-doped with ³⁺ and Cr ³⁺ excites Cr ³⁺ to excite the level ⁴ A ₂ to the level ⁴ T ₂ or higher. Causes an electronic transition to the level of. As a result, level ⁴ T ₂ etc. and level ⁴
A population inversion is formed between A ₂ and A ₂ . Level ⁴ F _3/2, etc. of the energy difference between these levels is Nd ³⁺ and level ⁴ I _9/2
Since it substantially corresponds to the energy difference between and, the excitation energy of Cr ³⁺ is transferred to Nd ³⁺ existing in the vicinity. As a result, level ⁴ F _3/2 and level ⁴ I _11/2
An inversion distribution is formed between and. Furthermore, since the energy difference between these levels are substantially corresponds to the energy difference between the two levels ¹ G ₄ and ³ H ₄ of Pr ^3+, excitation energy of Nd ³⁺ is present near the Pr It will be transmitted to ³⁺ . That is, the excited electrons move from the apparent level ⁴ T ₂ etc. to the level ⁴ F _3/2 and the level ¹ G ₄ by energy transfer.
Transition to. As a result, radiation in the 1.3 μm wavelength band corresponding to the Pr ³⁺ transition ¹ G ₄ → ³ H ₅ becomes possible.

It is unclear whether the above hypothesis is appropriate. In any case, according to the experiment and examination by the present inventor, Yb ³⁺ or Nd ³⁺ and Cr together with Pr ³⁺
Addition of ³⁺ and host glass enables light emission / amplification in the 1.3 μm wavelength band by Pr ³⁺ .
Alternatively, it has been found that a promising glass that enhances its amplification efficiency and the like can be obtained.

The above-mentioned optical functional glass is used as a material for an optical transmission line, and may be formed, for example, 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 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. Further, when quartz glass is used as a host glass of Pr ³⁺ which is an active material, manufacturing methods such as VAD method, MCVD method and OVD method 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%.

The optical active device of the present invention comprises the above optical fiber and C having a wide range of absorption in the range of 400 nm to 500 nm.
An excitation light source that generates excitation light for exciting r ³⁺ and an excitation light coupling means such as a coupler that causes the excitation light to enter the optical fiber from the excitation light source are provided. In this case, if a white light source such as a Xe lamp is used as the excitation light source,
The excitation energy can be effectively used.

According to the above-mentioned photoactive device, Cr is generated by the excitation light introduced into the optical fiber by the excitation light coupling means.
^3d was excited and received energy transfer from it Nd ³⁺
Was also excited, and P that received energy transfer from this
r ^{3+ is} also excited. A 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, and the emitted light corresponding to the transition ¹ G ₄ → ³ H ₅ is emitted with high efficiency. And facilitates exhibiting various functions such as optical amplification function, optical switch function, and optical sensor function in this band.

A fiber amplifier according to 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, P is generated by the pumping light introduced into the fiber by the pumping light coupling means.
r ³⁺ is indirectly excited. A part or most of this excited Pr ³⁺ is simultaneously induced by the signal light coupling means into the signal light of wavelength 1.3 μm band introduced into the optical fiber to generate radiated light, and wavelength 1 Optical amplification in the 3 μm band 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, P is generated by the pumping light introduced into the fiber by the pumping light coupling means.
r ³⁺ is indirectly excited. A part or most of the excited Pr ³⁺ is induced by spontaneous emission light or the like in the 1.3 μm wavelength band to generate radiated light, which enables laser oscillation in the 1.3 μm wavelength band.

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.

[0027]

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 CrF ₃ were mixed together in predetermined amounts. The mixed raw materials were melted in a platinum crucible under an inert atmosphere and then vitrified by quenching.

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. In addition, a glass pipe for a clad having a composition having a refractive index lower than that of the glass rod for a core and not containing not only Cr ³⁺ but also Pr ³⁺ is prepared. Then, these glass rods and glass pipes were formed into preforms and drawn into optical fibers. As a result, the core diameter was 5 μm, the outer diameter was 125 μm, and the relative refractive index difference was 1.
0% of single mode fiber was obtained. This single mode fiber was cut into an optical fiber sample having a length of 8 m for measurement.

FIG. 4 is an enlarged view of the optical fiber 30 thus obtained. The optical fiber 30 includes a core 30a made of optical functional glass in which Cr ³⁺ , Yb ^3+, etc. are added together with Pr ³⁺ , and a refractive index P is relatively lower than that of the core 30a.
and a cladding 30b to which rare earth ions such as r ³⁺ , Cr ³⁺ and Yb ³⁺ are not added.

FIG. 5 shows a case where the wavelength 1.
1 shows an example of the configuration of a 3 μm band fiber amplifier. The illustrated fiber amplifier includes a fiber 30 containing a rare earth ion such as Pr ³⁺ that amplifies a signal light in a wavelength band of 1.3 μm, and a white Xe lamp or a halogen lamp that generates a pump light having a wavelength of 0.7 μm or less. The light source 32 and the white light source 3
And a coupler 33 for making the light incident on the optical fiber 30 from 2.

The optical fiber 38a provided on the coupler 33 formed by fusion-drawing the optical fibers 38 and 39 has
A signal light source 31 having a wavelength band of 1.3 μm is connected. The input side of the optical fiber 30 is coupled to the optical fiber 38b facing this via a connector or the like, and the signal light is made incident into the optical fiber 30. An optical fiber 39a provided in the coupler 33 is connected to a white light source 32 such as a Xe lamp or a halogen lamp that generates excitation light having a wavelength of 0.7 μm or less. Therefore, pumping light having a wavelength of 0.7 μm band or less is also introduced into the optical fiber 30 together with the signal light. The amplified signal light from the output side of the optical fiber 30 is guided to the optical spectrum analyzer 35 via the filter 36 that cuts the excitation light. Optical spectrum analyzer 35
Measures the intensity, wavelength, etc. of the amplified signal light. The remaining optical fiber 39b provided in the coupler 33
Is dipped in matching oil 37 to prevent returning light.

The operation of the fiber amplifier shown in FIG. 5 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 excitation light with a wavelength of 0.7 μm or less from the white light source 32 also enters the optical fiber 30 via the coupler 33. This excitation light excites Cr ³⁺ having a broad absorption in the range of 400 to 500 nm, excites Yb ³⁺ or Nd ³⁺ to which energy is transferred, and further activates the active substance Pr ^{3+ to} which energy is transferred. Also excites. The excited Pr ³⁺ is induced by the signal light, and the transition ¹ G ₄ → ³ H
_It emits radiation in the 1.3 μm wavelength band corresponding to ₅ . 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 the optical fiber 30, the core 30a has Pr ³⁺ of 1000 ppm and Yb ³⁺ of 1000 p.
A single mode fiber containing 2000 ppm of pm and Cr ³⁺ was prepared. The signal light source 31 has a wavelength of 1.
A 30 μm LD was used and the signal light input was set to −30 dB. A continuous emission Xe lamp was used as the white light source 32, and the input intensity of the excitation light was 500 mW. Wavelength 1.
The gain for the signal light of 30 μm was 18 dB.

(Example 2) As the optical fiber 30, the core 30a has Pr ³⁺ of 1000 ppm and Nd ³⁺ of 1000 p.
A single mode fiber containing 2000 ppm of pm and Cr ³⁺ was prepared. As the signal light source 31, the same one as the LD of (Example 1) was used. A continuous emission Xe lamp was used as the white light source 132, and the input intensity of the excitation light was 500 mW. The gain for the signal light of wavelength 1.30 μm was 17.5 dB.

FIG. 6 is a diagram showing an embodiment of the waveguide element amplifier. Planar waveguides 130a, 130b, and 130c that are bifurcated are formed on the substrate 120. Cr ³⁺ with the active substance Pr ³⁺ in the region of the planar waveguide 130a,
Rare earth ions such as Yb ³⁺ and Nd ³⁺ are added. A filter 136 formed of a grating is formed on the other end of the planar waveguide 130a. Signal light having a wavelength band of 1.3 μm is incident on the planar waveguide 130b. In addition, excitation light having a wavelength of 0.7 μm or less is incident on the planar waveguide 130c. As a white light source such as a Xe lamp for generating excitation light, the same one as shown in FIG. 5 is used.

The operation of the waveguide element amplifier 100 shown in FIG. 6 will be briefly described. The signal light having a wavelength of 1.3 μm enters the plane waveguide 130a through the plane waveguide 130b,
Excitation light with a wavelength of 0.7 μm or less from a white light source also enters the planar waveguide 130a through the planar waveguide 130c. Excitation light excites the Cr ^3+, further via the Yb ³⁺ Pr ³⁺
Excite. The excited Pr ³⁺ is induced by the signal light,
It emits radiation in the 1.3 μm wavelength band corresponding to the transition ¹ G ₄ → ³ H ₅ . When the excitation light exceeds a predetermined intensity, the signal light will be amplified.

FIG. 7 is a diagram showing an embodiment of a fiber laser. This fiber laser uses an optical fiber 30
And a white light source 32 such as a Xe lamp, and an excitation light coupling device 43 including a lens and the like. The white light source 32 generates excitation light having a wavelength of 0.7 μm or less. Excitation light coupling device 4
3 causes excitation light to enter the optical fiber 30 from the white light source 32. In this case, the input and output ends of the optical fiber 30 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 racer having a ring-shaped resonator.

In the above fiber laser, the excitation light from the white light source 32 is introduced into the optical fiber 30 by the excitation light coupling device 38. The excitation light is the optical fiber 30.
Cr ³⁺ inside is excited, and further Pr ³⁺ is excited via Yb ³⁺ . The excited Pr ³⁺ is guided by spontaneous emission light of 1.3 μm and has a wavelength of 1.3 corresponding to the transition ¹ G ₄ → ³ H _5.
Generates synchrotron radiation in the μm band. When the output of the excitation light exceeds a predetermined value, laser oscillation occurs in the 1.3 μm wavelength band.

[0041]

As described above, according to the optical functional glass of the present invention, the presence of Cr and Yb or Nd efficiently excites Pr indirectly while using a simple light source. You can Due to the presence of the excited Pr, light emission / optical amplification in the wavelength band of 1.3 μm becomes possible, or its amplification efficiency can be improved. 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.

[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 another diagram showing an energy level diagram of a rare earth element such as Pr.

FIG. 3 is a diagram showing light emission of Cr and absorption of Yb.

FIG. 4 is a diagram showing an example of an optical fiber.

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

FIG. 6 is a diagram showing an example of a waveguide element amplifier.

FIG. 7 is a diagram showing an example of a fiber laser.

[Explanation of symbols]

 30 ... Optical fiber 30a ... Optical fiber core 32 ... Excitation light source 33, 43 ... Coupler as excitation coupling means

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification number Reference number within the agency FI Technical indication location H01S 3/07 8934-4M 3/0915 3/17 8934-4M (72) Inventor Koji Nakazato Kanagawa Yokohama City, Sakae-ku, No. 1 Sumitomo Electric Industries Co., Ltd. Yokohama Works (72) Inventor Hiroo Kanamori Kanagawa, Sakae-ku, No. 1 Taya-cho, Yokohama City Sumitomo Electric Co., Ltd. (72) Inventor Minoru Watanabe Kanagawa 1 Taya-cho, Sakae-ku, Yokohama-shi Sumitomo Electric Industries, Ltd. Yokohama Works (72) Inventor Yoshiaki Miyajima 1-1-6, Uchi-cho, Chiyoda-ku, Tokyo Nihon Telegraph and Telephone Corporation

Claims (12)

[Claims] 1. An optical functional glass, wherein Yb and Cr are added to a host glass together with Pr which is an active substance. 2. An optical functional glass, wherein Nd and Cr are added to a host glass together with Pr which is an active substance. 3. An optical fiber provided with a core made of the optical functional glass according to claim 1. Description: 4. The optical fiber according to claim 3, an excitation light source for generating excitation light for exciting Cr, and an excitation light coupling means for causing the excitation light to enter the optical fiber from the excitation light source. , An optically active device comprising :. 5. The photoactive device according to claim 4, wherein the excitation light source is a Xe lamp or a halogen lamp. 6. A fiber amplifier comprising: the optical active device according to claim 4; and a signal light coupling means for guiding a signal light in a 1.3 μm wavelength band into the optical fiber. 7. A fiber laser comprising the optical active device according to claim 4, 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. 8. A waveguide device comprising a planar waveguide made of the optical functional glass according to claim 1. Description: 9. The waveguide element according to claim 8, an excitation light source for generating excitation light for exciting Cr, and excitation light coupling for causing the excitation light to enter the waveguide element from the excitation light source. An optically active device comprising :. 10. The photoactive device according to claim 9, wherein the excitation light source is a Xe lamp or a halogen lamp. 11. A waveguide device amplifier comprising: the optical active device according to claim 9; and a signal light coupling means for guiding signal light in a 1.3 μm wavelength band into the optical waveguide device. 12. A waveguide element comprising: the optical active device according to claim 9; 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 waveguide element to the waveguide element. laser.