JP3088790B2 - 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 fiber using an optical functional glass used for optical amplification in a 1.3 .mu.m band,
The present invention relates to a waveguide element, an optical active device, a fiber amplifier, a waveguide element amplifier, a fiber laser, and a waveguide element laser.

[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. Is considered to be applied to optical active devices.

For example, a multi-component glass obtained by adding neodymium ions (Nd ³⁺ ) to a phosphate-based multi-component glass is prepared.
Report on evaluation of laser oscillation characteristics of optical fiber formed from this glass (ELECRONICS LETTERS, 1990,
Vol. 26, No. 2, pp. 121-122). More recently, an optical fiber doped with praseodymium ion (Pr ³⁺ ) as an active substance for realizing light amplification near a wavelength of 1.3 μm has been reported (OFC '90 Post Deadl).
inePapers (PD2-1)).

[0004]

[SUMMARY OF THE INVENTION However, in the multi-component glass Nd ³⁺ added as indicated in the above report, and the fluorescence peak at the wavelength of Nd ³⁺ 1.32 .mu.m is relatively weak, ESA transition , A gain could not be obtained in the 1.3 μm wavelength region.

[0005] In an optical fiber doped with Pr ³⁺ ,
There are problems such as extremely low amplification efficiency and a problem that a simple excitation light source such as a semiconductor laser cannot be obtained as an excitation light source having a required wavelength of around 1.017 μm.

Accordingly, the present invention makes it possible to amplify light in the 1.3 μm wavelength band or to increase the amplification efficiency thereof by using excitation light having a wavelength of 0.5 μm or in the vicinity thereof, which can be generated using a simple excitation light source. An object is to provide an optical fiber using optically functional glass.

[0007]

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

[0011]

The present inventor has conducted intensive studies to solve the above-mentioned problems, and as a result, has found that the wavelength is 0.5.
The present inventors have found an optically functional glass that enables amplification of light in the 1.3 μm band by using excitation light having a wavelength of about μm or in the vicinity thereof, or enhances the amplification efficiency.

The optical fiber according to the present invention has a core made of an optically functional glass obtained by adding samarium ions (Sm ³⁺ ) as an active substance to a host glass (matrix glass). As the host glass, fluorophosphate glass, phosphate glass, silicate glass, chalcogenide glass, fluoride glass, quartz glass, or the like can be used.

According to the above-mentioned optical functional glass forming the core, by adding Sm ³⁺ to the host glass, it is possible to excite Sm ³⁺ by using excitation light having a wavelength of 0.5 μm or near the wavelength. As a result, it was found that glass suitable for optical amplification in the 1.3 μm wavelength band could be obtained as described later.

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 wavelength 0.49 μm and the wavelength 0.5 introduced into the optical functional glass to which Sm ³⁺ is added as an active substance.
Excitation light having a wavelength of 0 μm, a wavelength of 0.53 μm, or the like excites Sm ³⁺ to level ⁶ H _5/2 to levels ⁴ G _7/2 , ⁴ G _3/2 and ⁴ G.
Generate an electron transition to _5/2 . In this case, the level ⁴ G
Many electrons excited to _7/2 and ⁴ G _3/2 becomes possible transition to level ⁴ G _5/2 by lattice relaxation like. As a result, an inversion distribution is formed between the level ⁴ G _5/2 and the level ⁶ F _11/2, and the wavelength 1.3 corresponding to the transition ⁴ G _5/2 → ⁶ F _11/2.
Radiation in the μm band becomes possible. It is considered that Sm ^{3+ in} this state generates stimulated emission light due to the presence of light in the 1.3 μm band, and enables light amplification and the like in this band.

It is unclear whether the above hypothesis is appropriate. In any case, according to the experiments and studies conducted by the present inventors, the addition of Sm ³⁺ in the glass as active substance, a wavelength 1 by Sm ³⁺ using an excitation light source of wavelength 0.5μm or near. Promising glass capable of emitting and amplifying light in the 3 μm band 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 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 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. Further, when the quartz glass is used as the host glass of Sm ³⁺ which is an active substance, 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 optical active device according to the present invention comprises the above optical fiber and a wavelength of 0.5 μm for exciting the active material Sm ^3+.
Or a pumping light source such as a laser that generates pumping light in the vicinity thereof, and pumping light coupling means such as a coupler that causes the pumping light to enter the optical fiber from the pumping light source.

According to the above-mentioned optical active device, Sm ³⁺ is excited by the excitation light having a wavelength of 0.5 μm or its vicinity introduced into the optical fiber by the excitation light coupling means. Part or most of the excited Sm ³⁺ is guided by a 1.3 μm-band signal light or the like existing in the optical fiber, and the transition ⁴
Generates radiation corresponding to G _5/2 → ⁶ F _11/2 and enables 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, Sm ³⁺ is excited by the excitation light having a wavelength of 0.5 μm or its vicinity introduced into the fiber by the excitation light coupling means. Some or many of the excited Sm ³⁺ may be simultaneously emitted into the optical fiber by the signal light coupling means.
Radiation light is generated by being guided by signal light or the like in the 3 μm band, and optical amplification in the 1.3 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-described fiber laser, Sm ³⁺ is excited by the excitation light having a wavelength of 0.5 μm or its vicinity introduced into the fiber by the excitation light coupling means. A part or a large part of the excited Sm ³⁺ is simultaneously guided to a signal light in a 1.3 μm band introduced into the optical fiber to generate a radiated light, and a light in the 1.3 μm band is generated. Laser oscillation becomes possible.

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

[0027]

Embodiments of the present invention will be specifically described below.

First, the composition 53.5ZrF ₄ -20BaF
Prepare ₂ -3.5LaF ₃ -3.0AlF ₃ of fluoride glass corresponding to -20NaF starting materials, and the SmF ₃ is these together with the active substance is mixed predetermined amounts. The mixed raw materials were melted in a platinum crucible under an inert atmosphere, and subsequently vitrified by a rapid reaction. Note that the amount of SmF ₃ mixed was such that the concentration of Sm ^{3+ in} the obtained optically functional glass was 10%.
It has been adjusted to be 00 ppm.

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. In addition, a clad glass pipe having a composition having a lower refractive index than the core glass rod and containing no Sm 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 5 μm, an outer diameter of 125 μm, and a relative refractive index difference of about 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 doped with Sm ³⁺ as an active substance, and a clad 30 having a relatively lower refractive index than the core and not doped with Sm ^3+.
b.

FIG. 3 shows an example of a configuration of a 1.3 μm wavelength fiber amplifier using the optical fiber 30 of FIG. As shown in the figure, the fiber amplifier includes an optical fiber 30 containing a rare earth element for amplifying signal light in a wavelength band of 1.3 μm,
A laser light source 32 for generating 0.5 μm band excitation light and a coupler 33 as excitation light coupling means for causing the excitation light to enter the optical fiber 30 from the laser light source 32. The coupler 33 also functions as signal light coupling means for guiding the signal light into the optical fiber 30. Two optical fibers 3
A 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 fusion-stretching of the components 8 and 39. 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. Coupler 3
The other output fiber 39a is coupled to the optical fiber 30 via a connector or the like, and guides the signal light and the pump light into the optical fiber 30. The output light from the optical fiber 30 is
The light 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 ^converts the electrons of the active substance Sm ³⁺ to levels ⁴ G _7/2 , ⁴ G _3/2 and
⁴ is excited to G _5/2. Then, level ⁴ G _7/2 and ⁴ G
Many of the _3/2 excited electrons are also relaxed and transition to the level ⁴ G _5/2 . In this state, Sm ³⁺ is induced by the signal light, and transition ⁴
G _5/2 → Generates radiation in the 1.3 μm band corresponding to ⁶ F _11/2 . Therefore, when the pump light exceeds a predetermined intensity, 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, the above-mentioned single mode fiber was used. An Ar laser was used as the laser light source 32, the excitation wavelength was 0.488 μm, and the excitation light input was 100 mW. In addition, the signal light source 3
For 1, a laser diode (LD) was used, the wavelength was 1.31 μm, and the signal input was -30 dBm. The gain for signal light with a wavelength of 1.31 μm is 4.5 dB,
Its efficiency was 0.045 dBm / mW.

(Example 2) As the optical fiber 30, the above-mentioned single mode fiber was used. An Ar laser was used as the laser light source 32, the excitation wavelength was 0.5145 μm, and the excitation light input was 100 mW. In addition, the signal light source 3
As 1, an LD was used, the wavelength was 1.31 μm, and the signal input was −30 dBm. The gain for a signal light having a wavelength of 1.31 μm is 4.8 dB, and the efficiency is 0.048.
It was dBm / mW.

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. Sm ³⁺ which is an active substance is added to the planar waveguide 130a. At the other end of the planar waveguide 130a, a filter 136 made of a grating is formed. Planar waveguide 13
A signal light having a wavelength of 1.3 μm is incident on 0b. Further, excitation light having a wavelength of 0.5 μm is incident on the planar waveguide 130c. 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,
Excitation light having a wavelength of 0.49 μm and a wavelength of 0.50 μm from an excitation light source such as an Ar laser also enters the planar waveguide 130a via the planar waveguide 130c. The excitation light excites Sm ³⁺ which is an active substance. The excited Sm ³⁺ is guided by the signal light, and has a wavelength 1. corresponding to the transition ⁴ G _5/2 → ⁶ F _11/2 .
Generates radiation in the 3 μm band. When the excitation light exceeds a predetermined intensity, the signal light is amplified.

FIG. 5 is a diagram showing an embodiment of a fiber laser. This fiber laser is an optical fiber 30
, A laser light source 32 composed of an Ar laser or the like, and an excitation light coupling device 43 composed of a lens. Laser light source 32
Generates excitation light having a wavelength of 0.49 μm and a wavelength of 0.50 μm. The excitation light coupling device 43 supplies the excitation light to the laser light source 32.
From the optical fiber 30. 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-described fiber laser, the excitation light having a wavelength of 0.49 μm and a wavelength of 0.50 μm from the laser light source 32 is supplied to the optical fiber 30 by the excitation light coupling device 43.
Introduced within. This excitation light is transmitted to the S
^Excite m ³⁺ . The excited Sm ³⁺ has a wavelength of 1.3 μm
Induced by the natural radiation of the band, the transition ⁴ G _5/2 → ⁶ F _11/2
, And emits radiation in a 1.3 μm band. When the output of the pump light exceeds a predetermined value, laser oscillation occurs in the 1.3 μm wavelength band.

[0040]

As described above, according to the optical fiber of the present invention, the active material Sm added to the host glass is excited by the excitation light having a wavelength of 0.5 μm or near. Light emission and light amplification in the 1.3 μm band can be achieved, or the amplification efficiency can be increased. Further, this optical fiber can be applied to an optical amplifier, an optical active device such as a laser, and a fiber amplifier. Also, the same effect can be obtained by using optical functional glass for the waveguide.

[Brief description of the drawings]

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

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]

 Reference Signs List 30 optical fiber 30a optical fiber core 32 excitation light source 33 coupler serving as excitation light coupling means and signal light coupling means 43 lens serving as excitation light coupling means

────────────────────────────────────────────────── ─── Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI H01S 3/0915 G02B 6/12 H 3/16 H01S 3/091 J (72) Inventor Koji Nakazato 1 Tayacho, Sakae-ku, Yokohama-shi, Kanagawa-ken Address: Sumitomo Electric Industries, Ltd., Yokohama Works (72) Inventor Hiroo Kanamori 1st, Taya-cho, Sakae-ku, Yokohama, Kanagawa Prefecture (72) Inventor Yoshiaki Miyajima 1-1-6 Uchisaiwaicho, Chiyoda-ku, Tokyo Nippon Telegraph and Telephone Corporation (56) References JP-A-4-50137 (JP, A) 4-265249 (JP, A) JP-A-4-59635 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C03C 13/04 G02B 6/00 376 G02B 6/12 G02F 1 / 35 501 H01S 3/07 H01S 3/0915 H01S 3/16

Claims (7)

(57) [Claims] 1. An optical fiber comprising a core made of an optically functional glass obtained by adding Sm as an active substance to a host glass. 2. An optical fiber according to claim 1, a pump light source for generating a pump light having a wavelength of 0.5 μm or in the vicinity thereof for pumping Sm, and transmitting the pump light from the pump light source into the optical fiber. An optically active device comprising: an excitation light coupling means for making the light enter. 3. A fiber amplifier comprising: the optical active device according to claim 2; and signal light coupling means for guiding signal light in a 1.3 μm band into the optical fiber. 4. A fiber laser comprising: the optical active device according to claim 2; and a resonator structure for feeding back light in or near a 1.3 μm wavelength band from inside the optical fiber to the optical fiber. 5. A waveguide element having a planar waveguide made of an optically functional glass in which Sm is added as an active substance to a host glass, and an excitation light having a wavelength of 0.5 μm or near to excite Sm. An optical active device comprising: an excitation light source; and excitation light coupling means for causing the excitation light to enter the waveguide device from the excitation light source. 6. A waveguide element amplifier comprising: the optical active device according to claim 5; and signal light coupling means for guiding signal light in a 1.3 μm band into the optical waveguide element. 7. A waveguide device comprising: the optical active device according to claim 5; and a resonator structure for feeding back light in or near a wavelength of 1.3 μm from inside the optical fiber to the waveguide device. laser.