JPH0537047A - Optical active element - Google Patents

Abstract

PURPOSE:To provide an optical active element capable of photo-amplifying at a wavelength 1.3mum band, a photo-amplifier using it, and the like. CONSTITUTION:An Nd is added to a central core 2a as an active matter for amplifying a signal beam in a wavelength 1.3mum band. A Yb is added to a core 2b arranged in parallel, as a matter absorbing an unnecessary beam (a wavelength 1.05 to 1.06mum) that the Nd generates. From a left end of the core 2a, the signal beam in a wavelength 1.3mum band and an excited beam in a wavelength 0.8mum come in. While the excited beam reciprocates between the cores 2a, 2b, it excites the Nd inside the core 2a. On the other hand, while the signal beam in a wavelength 1.3mum band also reciprocates between the cores 2a, 2b, it induces the Nd to produce an induced emission beam in a wavelength 1.3mum band. Thus, a photo-amplification at a wavelength 1.3mum band can be made. In this embodiment, as the unnecessary beam that the Nd generates is absorbed in the core 2b, a photo-amplification gain can be elevated.

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 Optical functional glass doped with a rare earth element is generally used for optical communication in the 1.3 .mu.m wavelength band in the range of 1.310. +-. 0.025 .mu.m, such as fiber amplifier, fiber sensor, fiber laser, etc. Is considered to be applied to photoactive devices.

For example, a multi-component glass prepared by adding neodymium ion (Nd ³⁺ ) to a phosphate-based multi-component glass,
Report on evaluation of laser oscillation characteristics of optical fiber formed from this glass (ELECRONICS LETTERS, 1990,
Vol. 26, No. 2, pp121-122), etc. More recently, an optical fiber doped with praseodymium ion (Pr ³⁺ ) as an active substance that realizes optical amplification around a wavelength of 1.3 μm has also been reported (OFC '90 Post Deadl
inePapers (PD2-1)).

[0004]

However, in the multi-component glass containing Nd ³⁺ shown in the above report, the fluorescence peak of Nd ^{3+ at} a wavelength of 1.32 μm is relatively weak. As a result, even if the input intensity of the pumping light is increased, a sufficient gain cannot be obtained in the 1.3 μm wavelength band region. FIG. 1 shows the amplification degree of light of 1.3 μm wavelength band when the input intensity of pumping light is increased. With a certain input intensity as a boundary, a wavelength of 1.05 rather than an electronic transition ⁴ F _9/2 → ⁴ I _13/2 corresponding to amplification of light of wavelength 1.3 μm band
Electronic transition ⁴ F corresponding to stimulated emission in the ~ 1.06 μm band
_9/2 → ⁴ It turns out that I _11/2 becomes dominant. As a result,
Amplification of light having a wavelength of 1.3 μm will be limited.

FIG. 2 is a proposal for solving the above problem, in which light having a wavelength of 1.05 to 1.06 μm is cut off at both ends of the Nd ³⁺ -doped fiber 302 or in the middle thereof.
The couplers 304a and 304b for demultiplexing are arranged, and the filter 306 for cutting 0.8 μm band light is arranged on the output side thereof. In the device as shown, the couplers 304a, 30
Wavelength of 1.3 μm due to insertion of 4b into the optical path
There was a problem that loss of signal light in the band was unavoidable. Furthermore, since the removal of light in the wavelength band of 1.05 to 1.06 μm is only partially performed, when the excitation light input is increased, stimulated emission in the wavelength band of 1.05 to 1.06 μm also occurs. There was a problem that it would increase.

Therefore, the present invention enables optical amplification in the 1.3 μm band and other bands by removing unnecessary light that interferes with light emission and optical amplification in the 1.3 μm band and other bands. It is an object of the present invention to provide a photoactive device that can increase or increase its amplification factor.

Another object of the present invention is to provide an optical active device including the above-mentioned optical active element.

It is another object of the present invention to provide a fiber amplifier, a waveguide element amplifier, a fiber laser, a waveguide element laser and the like which are composed of the above optical active device.

[0009]

In order to solve the above problems, the photoactive element according to the present invention comprises: (a) a photofunctional glass formed by adding a rare earth element as an active substance to a host glass. 1) and (b) a second optical transmission line formed of optical functional glass that absorbs only unnecessary light of a specific wavelength. Where the first and second
The optical transmission lines of are arranged substantially parallel to each other in a predetermined coupling region.

This optically active element can be implemented, for example, as an optical fiber, a waveguide element or the like. Further, as the rare earth element which becomes the active substance, in addition to Nd, Yb, Dy,
It is possible to use Sm, Pm, Er and the like.

In the above-mentioned optically active element, necessary light such as pumping light and signal light that have entered the first or second optical transmission line reciprocates between the first and second optical transmission lines in the coupling region. . The rare earth element excited by the pumping light propagating through the first optical transmission line may generate unnecessary light of a specific wavelength together with necessary emitted light equal to the wavelength of the signal light or the like.
Is absorbed by the optical transmission line. Therefore, it is possible to prevent the generation of necessary stimulated emission light equal to the wavelength of the signal light or the like due to the generation of unnecessary light. Such an optical active element can be applied to various devices such as an optical amplifier, a laser, and an optical switch.

An optical active device according to the present invention comprises (a) the above-mentioned optical active element formed in an optical fiber, (b) an excitation light source for generating excitation light for exciting a rare earth element, and (c) excitation light for excitation. Excitation light coupling means for making the first fiber core of the optically active element incident from the light source.

In the above-mentioned photoactive device, the rare earth element in the first optical transmission line is excited by the pumping light introduced into the photoactive element by the pumping light coupling means. Unwanted light of a specific wavelength from the excited rare earth element is absorbed by the second optical transmission line. As a result, it is possible to prevent unnecessary light from interfering with the generation of necessary emitted light. That is, it is possible to suppress the generation of the emitted light of the specific wavelength induced by the unnecessary light of the specific wavelength, and it is possible to prevent the generation probability of the necessary emitted light from decreasing. The necessary emission light generated by the excited rare earth element or the signal light incident on the first optical transmission line is
Further, it induces a rare earth element to generate stimulated emission light with high efficiency, and facilitates exhibiting various functions such as an optical amplification function, an optical switch function, and an optical sensor function in this band.

The fiber amplifier of the present invention comprises: (a) a first fiber core formed of an optical functional glass obtained by adding Nd as an active substance to a host glass, and an optical functional element that absorbs only unnecessary light of a specific wavelength. An optical active element having a second fiber core formed of glass, wherein the first and second fiber cores are arranged substantially parallel to each other in a predetermined coupling region; and (b) a wavelength of 0 for exciting Nd. An excitation light source for generating excitation light of 0.8 μm, and (c) excitation light coupling means for guiding the excitation light from the excitation light source to the first and second fiber cores,
(D) Signal light coupling means for guiding the signal light in the 1.3 μm wavelength band to the first and second fiber cores. As an optical functional glass that absorbs only unwanted light of a specific wavelength,
Wavelength 1.05 to 1.0 without absorbing excitation light and signal light
As a material that absorbs unnecessary light in the 6 μm band or the like, for example, glass to which Yb, Dy, Sm, Pm, Er or the like is added can be used.

In the above fiber amplifier, Nd in the first fiber core is pumped by the pumping light having a wavelength of 0.8 μm introduced into the photoactive element by the pumping light coupling means. Wavelength from excited Nd 1.05 to 1.06 μm
Unnecessary light is absorbed by the second fiber core. Therefore,
It is possible to prevent the unnecessary light from interfering with the generation of the emitted light in the required wavelength band of 1.3 μm. In this state, the signal light incident on the first fiber core induces Nd to generate stimulated emission light with high efficiency, which enables optical amplification in the wavelength band of 1.3 μm.

The fiber laser of the present invention comprises: (a) a first fiber core formed of an optical functional glass obtained by adding Nd as an active substance to a host glass, and an optical functional element that absorbs only unnecessary light of a specific wavelength. An optical active element having a second fiber core formed of glass, wherein the first and second fiber cores are arranged substantially parallel to each other in a predetermined coupling region; and (b) a wavelength of 0 for exciting Nd. An excitation light source for generating excitation light of 0.8 μm, and (c) excitation light coupling means for guiding the excitation light from the excitation light source to the first and second fiber cores,
(D) 1.3 wavelengths from within the first and second fiber cores
and a resonator structure for feeding back light in or near the μm band to the first and second fiber cores.

In the above fiber laser, Nd in the first fiber core is excited by the excitation light having the wavelength of 0.8 μm introduced into the first and second fiber cores by the excitation light coupling means. Wavelength from excited Nd 1.
Unwanted light of 05 to 1.06 μm is absorbed by the second fiber core. Therefore, the required wavelength of 1.3μ due to unnecessary light
Not only can the hindrance of the emission of m-band emission be prevented, but the wavelength of 1.3 μm generated in the first fiber core can be prevented.
The emission light in the m band induces Nd to generate the stimulated emission light with high efficiency, and laser oscillation in the 1.3 μm wavelength band becomes 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.

As a concrete manufacturing method of the optical fiber, known manufacturing methods such as a built-in casting method and a rod-in-tube method can be used.

As a concrete structure of the optical fiber, it is desirable that each fiber core satisfies the condition of single mode.

[0021]

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

FIG. 3 shows an optical fiber which is an embodiment of an optical active element for optical amplification. FIG. 3 (a) is its longitudinal sectional view and FIG. 3 (b) is its lateral direction. FIG. The illustrated optical fiber 2 includes two cores. Nd ³⁺ is added to the first core 2a arranged at the center of the optical fiber 2 as an active substance for amplifying the signal light in the 1.3 μm wavelength band. Yb ³⁺ is added to the second core 2b provided along the first core 2a as a substance that absorbs unnecessary light (wavelength 1.05 to 1.06 μm) generated by Nd ^3+. There is. The length L of the optical fiber 2,
The distance D and the like between the first and second cores 2a and 2b will be described in detail below. However, the distance D and the like are appropriately set according to the wavelengths of the signal light and the unnecessary light propagating through the first and second cores 2a and 2b. Is being adjusted.

The operation of the optical fiber 2 shown in FIG. 3 will be described. From the left end of the first core 2a, the signal light in the 1.3 μm wavelength band and the excitation light in the 0.8 μm wavelength are incident. The excitation light in the wavelength band of 0.8 μm is generated by the second
Evanescently couples to the core 2b. As a result, the excitation light alternately reciprocates between the first and second cores 2a and 2b for each length L ₁ according to the propagation constant β ₁ . This pumping light is transmitted through the first core 2a while the N
^Excite d ³⁺ . On the other hand, the signal light of 1.3 μm wavelength band,
Evanescent coupling is performed on the second cores 2b that are closely arranged at the distance D. That is, the signal light alternately reciprocates between the first and second cores 2a and 2b for each length L ₂ according to the propagation constant β ₂ . This signal light induces Nd ³⁺ that is excited during the transmission through the first core 2a and has a wavelength of 1.3 μm.
Generates stimulated emission light of the band. This gives a wavelength of 1.3
Optical amplification in the μm band becomes possible. However, the excited N
Unwanted spontaneous emission light and stimulated emission light having a wavelength of 1.05 to 1.06 μm generated by d ³⁺ are absorbed by the second core 2b. Since the spontaneous emission light component that is a seed of stimulated emission with a wavelength of 1.05 to 1.06 μm is suppressed to a low level over the entire length of the optical fiber 12, the optical amplification degree in the 1.3 μm wavelength band is the input intensity of the excitation light. There is no limit even if you increase.

The total length L of the optical fiber 2 is an odd multiple of the length L _{1 and} an even multiple of the length L ₂ . As a result, the signal light in the 1.3 μm wavelength band is emitted from the first core 2a, and the excitation light in the 0.8 μm wavelength band is emitted from the second core 2b. Thus, if the wavelength dependence of the propagation constant is used, the pumping light in the wavelength 0.8 μm band can be removed from the first core 2a at the end of the optical fiber 2. That is, unlike the conventional example, a filter for cutting the pumping light is not required, and the loss of signal light due to such a filter can be reduced. As specific parameters of the optical fiber 2, for example, the non-refractive index difference between the cores 2a and 2b is about 1%, the core diameter is 3 μm, and the distance D is 5
The total length L can be about 1 m. In addition,
The coupling length of the 0.8 μm wavelength light and the 1.3 μm wavelength light, that is, the total length L was adjusted by actually injecting the light and cutting the end portion of the optical fiber 2. Nd ³⁺ added to the first core 2a was 5000 ppm, and Yb ³⁺ added to the second core 2b was 5 wt%.

FIG. 4 shows an example of the configuration of a fiber amplifier of the wavelength 1.3 μm band using the optical fiber 2 of FIG. The illustrated fiber amplifier comprises an optical fiber 2 having a pair of cores doped with Nd ³⁺ and Yb ³⁺ , respectively, and a wavelength of 0.8 μm.
A laser light source 4 such as a laser diode that generates m-band excitation light, and a multiplexing coupler 6 that causes the excitation light to enter the optical fiber 2 from the laser light source 4.

A signal light source 10 having a wavelength of 1.30 μm is connected to the optical fiber 16a provided in the coupler 6 formed by fusion-spreading the optical fibers 16 and 26. The input side of the optical fiber 2 is coupled to the optical fiber 16b facing this, and the signal light is made incident on the inside of the optical fiber 2. The optical fiber 26a provided in the coupler 6 has a wavelength of 0.8 μm.
A laser light source 4 that generates m excitation light is connected. Therefore, the excitation light with a wavelength of 0.8 μm from the laser light source 4 is also introduced into the optical fiber 2 together with the signal light. In addition,
The remaining optical fiber 26b provided in the coupler 6 is dipped in matching oil 12 to prevent returning light. The amplified signal light from the output side of the optical fiber 2 is guided to the photodetector 18 via the optical fiber 14. The photo detector 18 detects the intensity of the amplified light of wavelength 1.30 μm and the like.

FIG. 5 is a diagram showing a main part of the fiber amplifier shown in FIG. The end of the core 116a of the optical fiber 16a is aligned with the input end of the first core 2a of the optical fiber 2. Therefore, both the pumping light and the signal light are incident on the input end of the first core 2a. In addition, the first of the optical fiber 2
The output end of the core 2a is aligned with the end of the core 114a of the optical fiber 14. Therefore, the first core 2a
Only the signal light output from the output end of is coupled to the core 114a of the optical fiber 14. The pumping light output from the output end of the second core 2b leaks to the outside without being coupled to the core 114a of the optical fiber 14.

The operation of the fiber amplifier shown in FIG. 4 will be briefly described. The signal light having a wavelength of 1.30 μm from the signal light source 10 goes through the coupler 6 to the first core 2 a of the optical fiber 2.
Incident on the inside. At the same time, the wavelength of 0.
The excitation light of 8 μm is also transmitted through the coupler 6 to the first optical fiber 2.
Nd ³⁺ , which is an active substance, is excited by being incident on the core 2a. Excited Nd ³⁺ is induced by this signal light, and transition
The radiant light having a wavelength of 1.30 m corresponding to ⁴ F _3/2 → ⁴ I _13/2 is generated. When the excitation light exceeds a predetermined intensity, the signal light will be amplified. In this case, since unnecessary spontaneous emission light and stimulated emission light with a wavelength of 1.05 to 1.06 μm generated by the excited Nd ³⁺ are absorbed by the second core 2b,
The stimulated emission of wavelengths 1.05 to 1.06 μm can be suppressed to a low level, and the optical amplification of wavelengths of 1.30 m can be increased.

FIG. 6 shows a waveguide element which is an embodiment of an optical active element for optical amplification. FIG. 6 (a) is its plan view and FIG. 6 (b) is its sectional view. is there. The illustrated waveguide element 202 comprises two parallel planar waveguides. First
Nd ³⁺ is added to the planar waveguide 202a as an active substance for amplifying the signal light of wavelength 1.30 μm. Second provided along the first planar waveguide 202a
Yb ³⁺ is added to the planar waveguide 202b as a substance that absorbs unnecessary light (wavelength 1.05 to 1.06 μm) generated by Nd ³⁺ .

The operation of the optical fiber 2 shown in FIG. 6 will be described. From the left end of the first planar waveguide 202a, wavelengths of 1.
Signal light of 30 m and excitation light of wavelength 0.8 μm are incident. The excitation light with a wavelength of 0.8 μm is generated by the second
Evanescently couples to the planar waveguide 202b of. As a result, the excitation light is transmitted to the first and second planar waveguides 20.
It alternately reciprocates between 2a and 202b, during which Nd ³⁺ inside the first planar waveguide 202a is excited. On the other hand, the signal light with a wavelength of 1.30 μm is also used for the first and second planar waveguides 2.
02a and 202b are alternately reciprocated to guide the excited Nd ³⁺ inside the first planar waveguide 202a to generate a wavelength of 1.3
A stimulated emission light of 0 μm is generated. This enables optical amplification at a wavelength of 1.30 μm. Excited Nd ³⁺
Unnecessary emitted light having a wavelength of 1.05 to 1.06 μm is absorbed by the second planar waveguide 202b. Therefore, the optical amplification factor of the wavelength of 1.30 μm is limited even if the input intensity of the excitation light is increased. Never be done.

The total length of the waveguide element is the same as that of the optical fiber 2 of FIG.
Is adjusted as well. As a result, the wavelength is 1.30 μm
Signal light is emitted from the first planar waveguide 202a, and the excitation light having a wavelength of 0.8 μm is emitted from the second planar waveguide 202b. For example, if the width of each planar waveguide 2a, 2b is 2 μm
The distance can be 3 μm, and the total length can be about 5 cm. Nd added to the first planar waveguide 202a
³⁺ was 2 wt%, and Yb ³⁺ added to the second planar waveguide 202b was 20 wt%.

The waveguide element shown in FIG. 6 can be applied to a waveguide element amplifier. The specific configuration is such that the optical fiber 12 of the fiber amplifier of FIG. 4 is replaced with the waveguide element of FIG. The operation is basically the same as that of the fiber amplifier shown in FIG.

FIG. 7 is a diagram showing a main part of the waveguide element amplifier. The end of the core 116a of the optical fiber 16a is aligned with the input end of the first planar waveguide 202a of the waveguide element 202. Both the pumping light and the signal light are incident on the input end of the first planar waveguide 202a. The output end of the first planar waveguide 202a is the core 114 of the optical fiber 14.
Aligned to the end a. Therefore, only the signal light output from the output end of the first planar waveguide 202a is coupled to the core 114a of the optical fiber 14.

The present invention is not limited to the above embodiment. A fiber laser can also be constructed using the optical fiber 2 of FIG. Specifically, both end surfaces of the optical fiber 2 are mirror-finished, and excitation light is introduced into the first core of the optical fiber 2 by using a light source similar to the laser light source 4 shown in FIG.

[0035]

As described above, in the photoactive device according to the present invention, unnecessary light of a specific wavelength from the rare earth element excited by the pumping light propagating through the first optical transmission line is transmitted by the second optical transmission. Absorbed on the road. Therefore, it is possible to prevent generation of necessary stimulated emission light equal to the wavelength of signal light or the like due to unnecessary light, and to enable optical amplification in the wavelength band of 1.3 μm or other bands, or gain thereof. Can be increased.

[Brief description of drawings]

FIG. 1 is a diagram showing a relationship between a pumping light input intensity and an amplification degree of a conventional fiber amplifier.

FIG. 2 is a diagram showing an example of a conventional fiber amplifier.

FIG. 3 is a diagram showing an embodiment of an optical fiber which is an optically active element of the present invention.

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

5 is a diagram showing a main part of the fiber amplifier of FIG.

FIG. 6 is a diagram showing an example of a waveguide element which is an optically active element of the present invention.

7 is a diagram showing a main part of an embodiment of a waveguide element amplifier using the waveguide element of FIG.

[Explanation of symbols]

2, 202 ... Optical active element 2a, 202a ... First optical transmission line 2b, 202b ... second optical transmission line 4 ... Excitation light source 33, 133 ... Coupler as excitation light coupling means

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification number Reference number within the agency FI Technical display location G02F 1/35 501 7246-2K H01S 3/094 (72) Inventor Takashi Mugo Sakaekuda, Yokohama City, Kanagawa Prefecture Tanimachi No. 1 Sumitomo Electric Industries, Ltd. Yokohama Works (72) Inventor Yoshiaki Miyajima 1-1-6, Uchisaiwaicho, Chiyoda-ku, Tokyo Nihon Telegraph and Telephone Corporation

Claims (11)

[Claims] 1. A first optical transmission line formed of an optical functional glass in which a rare earth element is added as an active substance to a host glass, and a first optical transmission line formed of an optical functional glass that absorbs only unnecessary light of a specific wavelength. 2 optical transmission lines, wherein the first and second optical transmission lines are arranged substantially parallel to each other in a predetermined coupling region. 2. The first and second optical transmission lines are formed in parallel in a fiber cladding, respectively.
The optical active element according to claim 1, which is a fiber core of 3. The photoactive element according to claim 2, an excitation light source for generating excitation light for exciting a rare earth element, and the excitation light from the excitation light source to the first and second optical active elements.
And a pumping light coupling means for guiding the fiber to the fiber core. 4. The photoactive device according to claim 3, wherein Nd is used as the active substance, and 0.8 μm wavelength band light is used as the excitation light. 5. A fiber amplifier comprising the optical active device according to claim 4, and a signal light coupling means for guiding signal light in a 1.3 μm wavelength band to the first and second fiber cores. 6. The optical active device according to claim 4, and the light in the 1.3 μm wavelength band or its vicinity from the inside of the first and second fiber cores is fed back to the first and second fiber cores. Laser structure having a resonator structure. 7. The optical active device according to claim 1, wherein the first and second optical transmission lines are first and second planar waveguides formed in parallel on a substrate, respectively. . 8. The photoactive element according to claim 7, an excitation light source for generating excitation light for exciting a rare earth element, and the excitation light from the excitation light source to the first and second optical active elements.
And a pumping light coupling means for guiding the light into the planar waveguide. 9. The photoactive device according to claim 8, wherein Nd is used as the active substance, and 0.8 μm wavelength band light is used as the excitation light. 10. 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 to the first and second planar waveguides. 11. The optical active device according to claim 9, and a resonator structure for feeding back light in the 1.3 μm wavelength band or in the vicinity thereof from inside the planar waveguide to the first and second planar waveguides. A waveguide element laser comprising: