JP3005074B2 - Fiber amplifier, fiber laser, waveguide device amplifier, and waveguide device laser - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

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

[0003]

However, the optical fiber made of fluoride glass doped with Pr ³⁺ shown in the above report has a problem that the amplification efficiency is extremely low.

[0004]

[0005]

[0006]

Therefore, the present invention has realized an optical functional glass to which Pr ³⁺ is added, which is capable of emitting and amplifying light with high efficiency in a 1.3 μm wavelength band. An object of the present invention is to provide an optical active device including an optical fiber using an optical functional glass and to provide a fiber amplifier and a fiber laser using the optical fiber.

Further, the present invention provides an optical active device having a waveguide element using the above-mentioned optically functional glass, and provides a waveguide element amplifier and a waveguide element laser using the above-mentioned waveguide element. With the goal.

[0009]

The present inventor has conducted intensive studies to solve the above-mentioned problems, and as a result, has found that the wavelength is 1.3.
We have found an optically functional glass that can increase the optical amplification efficiency of Pr ³⁺ in the μm band.

In the optical functional glass used in the present invention,
Praseodymium ion (Pr ³⁺ ) is added as an active substance to the host glass (matrix glass). in this case,
Fluorophosphate glass or phosphate glass is used as the host glass.

According to the above-mentioned optically functional glass, Pr in the host glass is excited by excitation light having a wavelength of about 1.0 μm or less.
As described later, it was found that not only ³⁺ can be excited, but also a glass suitable for light emission in the 1.3 μm band, optical amplification, and the like can be realized.

The present inventor has made the following hypothesis regarding the above-mentioned phenomena.

FIG. 1 is an energy level diagram of Pr ³⁺ .
Excitation light having a wavelength of about 1.0 μm introduced into the optically functional glass to which Pr ³⁺ is added as an active substance excites Pr ³⁺ to cause an electron transition from level ³ H ₄ to level ¹ G ₄ . generate.
As a result, wavelength inversion between the level ¹ G ₄ and level ³ H ₅ is formed, corresponding to the transition ¹ G ₄ → ³ H ₅ ^1.3μ
m-band radiation becomes possible. In this case, since the fluorophosphate glass or the phosphate glass is used as the host glass, the asymmetry of the site where Pr ³⁺ exists is increased as compared with the case where the fluoride glass or the like is used as the host glass. It is thought that there is. Therefore, in the above-mentioned optically functional glass, the asymmetry of the energy level of Pr ³⁺ can be increased, and the originally forbidden transition ¹ G ₄ →
It is considered that the stimulated emission cross section σ corresponding to ³ H ₅ can be increased. Therefore, in the above-mentioned optical functional glass, stimulated emission light can be effectively generated by the presence of light in the 1.3 μm band, and light emission and light emission in this band can be obtained.
It is considered that the efficiency of optical amplification can be increased.

It is unclear whether the above hypothesis is appropriate. In any case, according to the experiments and studies conducted by the present inventors, by adding it to Pr ³⁺ hydrofluoric phosphate glass or phosphate glass as a host glass as active substance, a wavelength 1.3μm band by Pr ³⁺ A promising glass was obtained that would increase the efficiency of light emission and light amplification in the system.

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 made 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 in a wavelength band of 1.3 μm.
That is, the optical functional glass as described above 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 optical functional glass as a core.

As a specific method for manufacturing the above optical fiber, 2
Known production methods such as a crucible method, a built-in casting method, and a rod-in-tube method can be used.

The specific structure of the optical fiber is desirably a single mode fiber, the core diameter is preferably 5 μm or less, and the relative refractive index difference is desirably 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 optical active device used in the present invention comprises an optical fiber, an excitation light source such as a laser for generating an excitation light having a wavelength of about 1.0 μm or less for exciting the active substance Pr ³⁺ , and an excitation light. And an excitation light coupling means such as a coupler for causing the light from the excitation light source to enter the optical fiber.

According to the optical active device described above, Pr ³⁺ is excited by the excitation light having a wavelength of about 1.0 μm or less introduced into the optical fiber by the excitation light coupling means. Part or most of the excited Pr ³⁺ is guided by a signal light in the 1.3 μm band existing in the optical fiber, and a transition ¹ G ₄ →
It emits radiated light corresponding to ³ H ₅ with high efficiency, and facilitates various functions such as an optical amplification function, an optical switch function, and an optical sensor function in this band.

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

According to the above fiber amplifier, the wavelength of about 1.0 μm introduced into the fiber by the pumping light coupling means.
Pr ³⁺ is excited by the following excitation light. Part or most of the excited Pr ³⁺ is simultaneously supplied to the optical fiber by the signal light coupling means at a wavelength of 1.3 μm.
The light is guided by the signal light in the band to generate the emitted light, and the wavelength is 1.3.
Optical amplification in the μm band becomes possible.

A fiber laser according to the present invention comprises the above-mentioned optical active device and a resonator structure for feeding back light in or near the 1.3 μm wavelength band from the inside of the optical fiber to the optical fiber.

According to the above fiber laser, the wavelength of about 1.0 μm introduced into the fiber by the excitation light coupling means.
Pr ³⁺ is excited by the following excitation light. Part or most of the excited Pr ³⁺ is simultaneously guided to a signal light in the 1.3 μm band introduced into the optical fiber to generate radiated light, and emits light in the 1.3 μm band. Laser oscillation becomes possible.

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

[0025]

Embodiments of the present invention will be specifically described below.

First, the composition 16Al (PO ₃ ) ₃ -10 L
Raw materials for fluorophosphate glass corresponding to i ₂ O-42LiF-32BaF ₂ (mol%) were prepared, and a predetermined amount of Pr ₆ O ₁₁ as an active substance was mixed therewith. The mixed raw materials were melted in a platinum crucible under an inert atmosphere, and then glassed by a sudden command.

The composition ZrO ₂ -4SrO-15Na
Raw materials for phosphate glass corresponding to ₂ O-15 Al ₂ O ₃ -65 P ₂ O ₅ (mol%) were prepared, and a predetermined amount of Pr ₆ O ₁₁ as an active substance was mixed therewith. The mixed raw materials were melted in a platinum crucible under an inert atmosphere, and then glassed by a sudden command.

For further comparison, the composition 53.5 ZrF ₄
-20BaF ₂ -3.5LaF ₃ -3.0AlF ₃ -2
Fluoride glass raw materials corresponding to 0NaF (mol%) were prepared, and a predetermined amount of PrF ₃ as an active substance was mixed therewith. The mixed raw materials were melted in a platinum crucible under an inert atmosphere, and then glassed by a sudden command.

Incidentally, the mixing amount of Pr ₆ O ₁₁ and PrF ₃ is such that the concentration of Pr ^{3+ in} the above three types of optical functional glass is 50%.
It has been adjusted to be 0 ppm.

In order to evaluate the optical amplification characteristics of the optically functional glass, a fiber was manufactured as follows. First,
The above three types of optical functional glass are formed into a rod shape to obtain a glass rod for a core. Further, a clad glass pipe having a composition having a lower refractive index than the core glass rod and containing no Pr ³⁺ is prepared. Thereafter, the glass rod and the glass pipe are formed into a preform, and are drawn into an optical fiber. As a result, a single mode fiber having a core diameter of 4 μm, an outer diameter of 125 μm, and a relative refractive index difference of about 0.6% 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 fluorophosphate glass or phosphate glass doped with Pr ³⁺ as an active substance, and a clad 30b having a relatively lower refractive index than the core and not doped with Pr ^3+. Is provided.

FIG. 3 shows a wavelength 1.
1 shows a configuration example of a 3 μm band fiber amplifier. As shown in the figure, the fiber amplifier includes an optical fiber 30 containing Pr ³⁺ for amplifying signal light in a 1.3 μm band and a wavelength of 1.0 μm.
A laser light source 32 for generating excitation light having a wavelength of 07 μm and a wavelength of 1.017 μm, and a coupler 33 serving as excitation light coupling means for causing the excitation light to enter the optical fiber 30 from the excitation light source 32.
And This coupler 33 transmits the signal light to the optical fiber 30.
It also functions as signal light coupling means for guiding the light into the inside. Coupler 33 formed by fusing and stretching two optical fibers 38 and 39
The signal light source 31 having a wavelength band of 1.3 μm is connected to one of the input fibers 38a. The other input fiber 3
The laser light source 32 described above is connected to 9a. Also,
One output fiber 39b of the coupler 33 is immersed in a 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 guides signal light and pump light into the optical fiber 30. 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 measures the intensity, wavelength, and the like of the amplified signal light.

The operation of the fiber amplifier shown in FIG. 3 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 excitation light from the laser
To enter the optical fiber 30. This excitation light excites electrons of Pr ³⁺ , which is an active substance, to a level of ¹ G ₄ . In this state, Pr ³⁺ is induced by the signal light and transitions ¹ G ₄ → ³ H
Emitted light in the 1.3 μm band corresponding to ₅ is effectively generated. Therefore, when the pump light exceeds a predetermined intensity, the signal light is efficiently amplified.

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

(Example 1) As the optical fiber 30, a single mode fiber made of the above fluorophosphate glass was used.
As the laser light source 32, a Ti-sapphire laser was used, the wavelength was 1.007 μm, and the excitation light input was 180 m.
W. Further, a laser diode (LD) was used as the signal light source 31, the wavelength was 1.31 μm, and the signal input was −30 dBm. The gain for signal light having a wavelength of 1.31 μm is 10 dB, and the efficiency is 0.056 dB.
m / mW.

(Example 2) As the optical fiber 30, a single mode fiber made of the above phosphate glass was used. As the laser light source 32, the same Ti-sapphire laser as that in Example 1 was used, and its excitation light input was set to 180 mW. An LD was used as the signal light source 31, the wavelength was 1.31 μm, and the signal input was −30 dBm. The gain for the signal light having a wavelength of 1.31 μm was 8 dB, and the efficiency was 0.045 dBm / mW.

Comparative Example As the optical fiber 30, a single mode fiber made of the above-mentioned fluoride glass was used.
As the laser light source 32, the same Ti-sapphire laser as that in Example 1 was used, and its excitation light input was set to 180 mW. An LD was used as the signal light source 31, the wavelength was 1.31 μm, and the signal input was −30 dBm. The gain for the signal light having a wavelength of 1.31 μm is 6.5 dB.
Its efficiency was 0.036 dBm / mW.

As is clear from the above comparative examples, the optical amplification efficiency of Pr ³⁺ can be increased by using fluorophosphate glass or fluorophosphate glass instead of fluoride glass as the host glass. Understand.

FIG. 4 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. Pr ³⁺ which is an active substance is added to a region of the planar waveguide 130a. 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. The planar waveguide 130c has a wavelength of 1.007 μm.
m excitation light is incident. As the laser light source, the same one as shown in FIG. 3 is used.

The operation of the waveguide element amplifier 100 shown in FIG. 4 will be briefly described. The 1.3 μm wavelength signal light enters the planar waveguide 130a through the planar waveguide 130b,
Ti: wavelength from excitation light source such as sapphire laser
Excitation light of 007 μm also enters the plane waveguide 130a through the plane waveguide 130c. The excitation light excites Pr ³⁺ which is an active substance. The excited Pr ³⁺ is guided by the signal light to effectively generate a 1.3 μm wavelength radiation light corresponding to the transition ¹ G ₄ → ³ H ₅ . When the pump light exceeds a predetermined intensity, the signal light is efficiently amplified.

FIG. 5 is a diagram showing an embodiment of a fiber laser. This fiber laser is an optical fiber 30
And Ti: a laser light source 3 composed of a sapphire laser or the like
2 and an excitation light coupling device 43 composed of a lens.
The laser light source 32 generates excitation light having a wavelength of 1.007 μm. The excitation light coupling device 43 causes the excitation light to enter the optical fiber 30 from the laser light source 32. In this case, the input / output end of the optical fiber 30 is finished to 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, a fiber laser having a ring resonator structure may be used.

In the above-mentioned fiber laser, the excitation light having a wavelength of 1.007 μm from the laser light source 32 is introduced into the optical fiber 30 by the excitation light coupling device 43. This excitation light excites Pr ³⁺ in the optical fiber 30. The excited Pr ³⁺ is guided by spontaneous radiation in the 1.3 μm band, and the 1.3 μm wavelength corresponding to the transition ¹ G ₄ → ³ H _5.
Effectively generates m-band radiation. When the output of the pumping light exceeds a predetermined value, laser oscillation occurs efficiently in the 1.3 μm wavelength band.

[0043]

As described above, according to the optical functional glass used in the present invention, Pr, which is an active substance, is excited by the excitation light having a wavelength of about 1.0 μm or less, and the active substance Pr is excited in the 1.3 μm band. The efficiency of light emission and light amplification can be increased. Furthermore,
By forming this in a waveguide, an optical fiber, or the like, it can be applied to an optical active device such as an optical amplifier or a laser. In particular,
When formed in a fiber, a fiber amplifier with a low threshold and a high gain is obtained.

[Brief description of the drawings]

FIG. 1 is a diagram showing an energy level diagram of Pr.

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

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

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

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

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 30 ... Optical fiber 30a ... Optical fiber core 30b ... Optical fiber clad 32 ... Excitation light source 33 ... Coupler which is excitation light coupling means and signal light coupling means 43 ... Lens which is excitation light coupling means

──────────────────────────────────────────────────続 き Continuing from the front page (72) Koji Nakazato, Inventor Koji Nakazato, 1-chome, Taya-cho, Sakae-ku, Yokohama, Japan Sumitomo Electric Industries, Ltd. Inside the Yokohama Works (72) Inventor Minoru Watanabe 1st Taya-cho, Sakae-ku, Yokohama-shi, Kanagawa Prefecture Sumitomo Electric Industries, Ltd. Inside Yokohama Works (72) Yoshiaki Miyajima 1-1-6 Uchisaiwaicho, Chiyoda-ku, Tokyo Nippon Telegraph and Telephone (56) References JP-A-63-184386 (JP, A) JP-A-1-145881 (JP, A) JP-A-63-21240 (JP, A) JP-A-64-2025 (JP, A A) JP 39-3528 (JP, B1) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01S 3/06 C03C 3/16 C03C 13/04 H01S 3/17 G02B 6/00

Claims (4)

(57) [Claims] 1. An optical fiber having a core made of optically functional glass, wherein Pr is added to a host glass as an active substance and said host glass is a fluorophosphate glass or a phosphate glass, and Pr is excited. An optical active device having an excitation light source for generating excitation light having a wavelength of about 1.0 μm or less, and excitation light coupling means for causing the excitation light to enter the optical fiber from the excitation light source; A signal light coupling unit for guiding signal light into the optical fiber. 2. An optical fiber having a core made of an optically functional glass, wherein Pr is added to a host glass as an active substance and the host glass is a fluorophosphate glass or a phosphate glass, and Pr is excited. An optical active device having an excitation light source that generates excitation light having a wavelength of about 1.0 μm or less, and an excitation light coupling unit that causes the excitation light to enter the optical fiber from the excitation light source; A resonator structure for feeding back light in or near the 1.3 μm wavelength band to the optical fiber. 3. A waveguide element comprising a planar waveguide made of optically functional glass, wherein Pr is added to a host glass as an active substance, and said host glass is a fluorophosphate glass or a phosphate glass; An optically active device comprising: an excitation light source for generating excitation light having a wavelength of about 1.0 μm or less to excite light; and an excitation light coupling means for causing the excitation light to enter the waveguide element from the excitation light source; And a signal light coupling means for guiding signal light in the 3 μm band into the waveguide element. 4. A waveguide element comprising a planar waveguide made of optically functional glass, wherein Pr is added to a host glass as an active substance, and said host glass is a fluorophosphate glass or a phosphate glass; An optically active device comprising: an excitation light source for generating excitation light having a wavelength of about 1.0 μm or less to excite the light; and an excitation light coupling means for causing the excitation light to enter the waveguide element from the excitation light source; A resonator structure for feeding back light in or near the 1.3 μm wavelength band from inside the waveguide element to the waveguide element.