WO2009104612A1

WO2009104612A1 - Fiber laser

Info

Publication number: WO2009104612A1
Application number: PCT/JP2009/052715
Authority: WO
Inventors: 盛輝大原; 裕己近藤
Original assignee: 旭硝子株式会社
Priority date: 2008-02-18
Filing date: 2009-02-17
Publication date: 2009-08-27
Also published as: JPWO2009104612A1

Abstract

It is possible to provide a small-size fiber laser. The fiber laser includes: an amplification optical fiber having a core containing Er; a light source for optically exciting the Er; an optical coupler which introduces the excitation light to the amplification optical fiber; and an optical coupler for extracting a laser light from the amplification optical fiber. The amplification optical fiber has a length not greater than 0.5 m. The amplification optical fiber has an absorption coefficient not smaller than 100 dB/m in the wavelength range from 1520 to 1540 nm. The product of the length and the absorption coefficient is in the range from 40 to 150 dB.

Description

Fiber laser

The present invention relates to a fiber laser suitable for optical communication, measurement, processing, and the like.

Conventionally, semiconductor lasers, solid state lasers, and gas lasers have been used as laser light sources, but in recent years, fiber lasers have attracted attention due to their high beam quality in addition to ease of maintenance. It is used as a laser.
As a fiber laser amplification medium, a fiber to which rare earth such as erbium (Er), ytterbium (Yb), thulium (Tm) is added is used.

In order to obtain a high output, an amplification optical fiber doped with Yb is generally used, while for communication and measurement, an amplification optical fiber added with Er capable of obtaining a laser beam in a 1.5 μm band is used. It is done.
Also, wavelength division multiplexing (WDM) optical communication requires a light source with a wide wavelength range.
When used as a sensor light source using a fiber Bragg grating (FGB) fiber, the number of observation points can be increased by connecting a broadband laser light source and FGB fibers having different wavelengths in parallel or in series.

As such a fiber laser, a laser using an amplification optical fiber added with Er has been proposed (see Non-Patent Document 1).

As a light source for WDM and a light source for sensors, a small and stable fiber laser is required.
However, the fiber laser disclosed in Non-Patent Document 1 uses a long amplification optical fiber having a length ranging from several meters to several tens of meters, and it is difficult to reduce the size.
An object of the present invention is to provide a fiber laser that can oscillate in a wide wavelength range with a short optical fiber for amplification.

The present invention has the following gist.
(1) An optical fiber for amplification in which Er is added to the core, a light source of excitation light for optically exciting Er, an optical coupler for guiding the excitation light to the optical fiber for amplification, and light for extracting laser light emitted from the optical fiber for amplification A fiber laser having a coupler, wherein the length of the optical fiber for amplification is 0.5 m or less, and the absorption coefficient of the optical fiber for amplification is 100 dB / m at any wavelength in the wavelength range of 1520 to 1540 nm. A fiber laser in which the product of the length and the absorption coefficient is 40 to 150 dB.
(2) The fiber laser according to (1), wherein the resonator is a ring resonator.
(3) The fiber laser according to the above (1) or (2) having a wavelength tunable filter.
(4) The fiber laser according to any one of (1) to (3) above, wherein the wavelength of the excitation light is 900 to 990 nm.
(5) The fiber laser according to any one of (1) to (4) above, wherein the variable wavelength width of the laser light is 100 nm or more.
(6) The fiber laser according to any one of (1) to (5), wherein the core glass of the amplification optical fiber contains 0.1 to 1.0 part by mass of Er with respect to 100 parts by mass of the matrix glass .
(7) The fiber laser according to any one of (1) to (6), wherein the amplification optical fiber has a core diameter of 3 to 8 μm.
(8) The fiber laser according to any one of (1) to (7) above, having an isolator.
(9) A WDM light source comprising the fiber laser of any one of (1) to (8) above.
(10) A sensor light source comprising the fiber laser of any one of (1) to (8) above.

The present inventor has found that the fiber length can be shortened by using an amplification optical fiber having a large absorption coefficient, and has led to the present invention.

According to the present invention, the fiber laser can be miniaturized.
Moreover, it is expected that the fiber laser is less susceptible to environmental changes due to the downsizing of the fiber laser or the shortening of the resonator length.

It is a conceptual diagram for demonstrating an example of the fiber laser of this invention. It is an example of the oscillation spectrum of the fiber laser of the present invention.

Explanation of symbols

1: optical fiber for amplification, 2: pumping light source, 3: optical coupler for guiding pumping light into the resonator, 4: optical coupler for extracting laser light, 5: tunable filter, 6: isolator, 7: output.

FIG. 1 is a conceptual diagram for explaining a fiber laser according to the present invention, in which the resonator is a ring resonator. Note that the present invention is not limited to FIG.
In FIG. 1, reference numeral 1 denotes an amplification optical fiber in which Er is added to the core, 2 denotes a pumping light source for optically exciting Er, that is, a pumping light source, and 3 denotes an optical coupler for guiding the pumping light to the amplification optical fiber 1. That is, an optical coupler for guiding excitation light into the resonator, 4 is an optical coupler for extracting laser light, 5 is a wavelength tunable filter, and 6 is an isolator.

In the optical fiber for amplification 1, the core glass is obtained by adding 0.1 to 1.0 part by mass of Er to 100 parts by mass of the matrix glass. The matrix glass contains 20 to 60 mol of Bi ₂ O _3. %, B ₂ O ₃ and / or SiO ₂ in total 20 to 50 mol%, Al ₂ O ₃ and / or Ga ₂ O ₃ in total 3 to 30 mol%, and the core diameter is 3 to It is preferable that it is 8 micrometers. Total al ₂ O ₃ and _Ga 2 _{O 3} may be 3 to 20 mol%.
If Er is less than 0.1 part by mass, the absorption coefficient may be small. More preferably, it is 0.2 parts by mass or more. If it exceeds 1.0 part by mass, the energy conversion efficiency is lowered, and there is a possibility that sufficient laser oscillation cannot be obtained. More preferably, it is 0.8 mass part or less.
If the core diameter is less than 3 μm, the overlap between the distribution of light in the optical fiber and the core region to which Er is added may be small, and the absorption coefficient may be small. More preferably, it is 3.5 μm or more. If it exceeds 8 μm, the mode field diameter becomes smaller than the core diameter, and Er may not be sufficiently excited. More preferably, it is 7 μm or less.

The difference in refractive index between the core glass and the clad glass of the amplification optical fiber 1 is preferably 0.003 to 0.030. If it is less than 0.003, there is a possibility that the loss when the fiber is bent increases. Preferably it is 0.005 or more. If it exceeds 0.030, connection may be difficult. More preferably, it is 0.020 or less.

If the absorption coefficient (A) of the amplification optical fiber 1 is not 100 dB / m or more at any wavelength in the wavelength range of 1520 to 1540 nm, the absorbance per unit length becomes too small, and the length of the amplification optical fiber 1 It becomes difficult to shorten. Preferably it is 200 dB / m or more, More preferably, it is 300 dB / m or more. In general, it is required that an Er absorption peak exists in the above-mentioned wavelength range, and A related to the absorption peak is 100 dB / m or more.

If the length (L) of the amplification optical fiber 1 exceeds 0.5 m, it is difficult to reduce the size of the fiber laser. In addition, the laser oscillation may become unstable due to the influence of disturbance. Preferably it is 0.35 m or less, More preferably, it is 0.30 m or less. L is preferably 0.05 m or more. If it is less than 0.05 m, handling becomes difficult. More preferably, it is 0.10 m or more, Most preferably, it is 0.15 m or more.

If the product of A and L (A × L) is less than 40 dB, sufficient output may not be obtained, or laser oscillation on the long wavelength side may not be obtained, and the band or variable wavelength width may be narrowed. , Preferably 50 dB or more, more preferably 60 dB or more. If A × L exceeds 150 dB, strong pumping light power is required, and efficiency may deteriorate. (A × L) is preferably 120 dB or less, more preferably 100 dB or less.

The isolator 6 is not essential, but transmits light only in one direction in the resonator. Thus, by oscillating in only one direction, a stable laser with less noise can be obtained.

The wavelength tunable filter 5 is not essential, but is preferably used when it is desired to easily change the oscillation wavelength, or when unnecessary stimulated emission light is to be removed. It is preferable to introduce a tunable filter into the resonator.
When it is desired to remove unnecessary stimulated emission light, the full width at half maximum of the wavelength tunable filter 5 is preferably 5 nm or less, more preferably 2 nm or less.

As the excitation light, laser light having a wavelength of 0.90 to 0.99 μm or 1.46 to 1.49 μm is usually used, but in order to oscillate efficiently, the wavelength of the excitation light is 0.95 to 0. It is preferable to set it to .99 μm.

The width of the oscillation wavelength band of the laser, that is, the variable wavelength width of the laser is preferably 100 nm or more. If it is less than 100 nm, it may be difficult to use the WDM system efficiently, or it may be difficult to increase the number of detection points when used as a light source for a sensor. More preferably, it is 110 nm or more, More preferably, it is 120 nm or more.

As the resonator structure, there is a Fabry-Perot type other than the ring type. When a Fabry-Perot type is used as the resonator structure, a configuration in which optical fiber Bragg gratings are arranged at both ends is typical.

The same configuration as that of FIG. 1 is used as the amplification optical fiber 1 of FIG. 1 having A (absorption coefficient at a wavelength of 1532 nm, unit is dB / m) and L (unit: m) in Examples 1 to 8 in Table 1. A fiber laser was fabricated. The optical coupler 4 can guide 90% of light to the ring resonator and output 10% of light as an output, and the wavelength variable filter 5 has a full width at half maximum of 1 nm. Examples 1 to 7 are examples, and example 8 is a comparative example.

The amplification optical fibers of Example 1 and Example 2 are as follows.
Core glass: mol% display composition is Bi ₂ O ₃ 42.8, SiO ₂ 34.2, CeO ₂ 0.2, Al ₂ O ₃ 3.6, Ga ₂ O ₃ 17.8, La ₂ O ₃ 4, in which 0.32 parts by mass of Er is added to 100 parts by mass of the matrix glass.
Mol% display composition of clad glass: Bi ₂ O ₃ 42.8, SiO ₂ 34.2, CeO ₂ 0.2, Al ₂ O ₃ 7.1, Ga ₂ O ₃ 14.3, La ₂ O ₃ 4.
Core diameter: 5.4 μm.
Cladding diameter: 125 μm.
Difference in refractive index between core and clad: 0.01.

The amplification optical fibers in Examples 3 to 8 are as follows.
Core glass: mol% display composition is Bi ₂ O ₃ 42.8, B ₂ O ₃ 5.0, SiO ₂ 29.2, CeO ₂ 0.2, Al ₂ O ₃ 3.6, Ga ₂ O ₃ 17. 8, which is 0.64 parts by mass of Er to 100 parts by mass of matrix glass which is La ₂ O ₃ 1.4.
Mol% display composition of clad glass: Bi ₂ O ₃ 42.8, B ₂ O ₃ 5.0, SiO ₂ 29.2, CeO ₂ 0.2, Al ₂ O ₃ 7.1, Ga ₂ O ₃ 14. 3, La ₂ O ₃ 1.4.
Core diameter: 3.9 μm.
Cladding diameter: 125 μm.
Difference in refractive index between core and clad: 0.01.

In the fiber lasers of Examples 1 to 8, pumping light having a wavelength (unit: μm) is emitted from the pumping

light sources

2 and 2 in FIG. The variable wavelength width (unit: nm) when excited is shown in the column W1 in Table 1, and the variable wavelength width (unit: nm) when the amplification optical fiber 1 is excited 100 mW in the front and 100 mW in the rear is W2 in Table 1. It shows in each column.

For amplification optical fibers in which A and L are as shown in the corresponding columns of Example 9 and Example 10 in Table 1, W1 and W2 when λe is 0.98 μm were estimated from the value of A Estimated based on gain. The results are shown in the corresponding column of the table. The value of A itself was also estimated by calculating the confinement factor from the refractive index and core diameter of the core and cladding of each amplification optical fiber and using the estimated absorption coefficient of the core glass. Moreover, * mark in a table | surface shows that it is an estimated value. Examples 9 and 10 are comparative examples.

The amplification optical fiber of Example 9 is as follows.
Core glass: mol% display composition is Bi ₂ O ₃ 42.8, B ₂ O ₃ 28.5, SiO ₂ 14.3, CeO ₂ 0.2, Al ₂ O ₃ 7.1, Ga ₂ O ₃ 7. 1 is obtained by adding 0.6 parts by mass of Er to 100 parts by mass of the matrix glass.
_2. Composition in mol% of clad glass: Bi ₂ O ₃ 42.8, B ₂ O ₃ 28.5, SiO ₂ 14.3, CeO ₂ 0.2, Al ₂ O ₃ 10.6, Ga ₂ O ₃ 6.
Core diameter: 2.5 μm.
Cladding diameter: 125 μm.
Difference in refractive index between core and clad: 0.01.

The amplification optical fiber of Example 10 is as follows.
Core glass: mol% display composition is Bi ₂ O ₃ 42.7, B ₂ O ₃ 28.5, SiO ₂ 14.2, CeO ₂ 0.2, Al ₂ O ₃ 7.2, Ga ₂ O ₃ 7. 2, in which 0.06 parts by mass of Er is added to 100 parts by mass of the matrix glass.
Mol% display composition of clad glass: Bi ₂ O ₃ 42.7, B ₂ O ₃ 28.5, SiO ₂ 14.2, CeO ₂ 0.3, Al ₂ O ₃ 14.3.
Core diameter: 7.0 μm.
Cladding diameter: 125 μm.
Difference in refractive index between core and clad: 0.01.

In Examples 1 to 7, even when the pumping light power is small, the variable wavelength width is 100 nm or more (W1). In particular, in Examples 3 to 5 where L is 0.15 to 0.30 m, A × L is 50 to 100 dB, and λe is 0.98 μm, a large W2 can be obtained.

FIG. 2 shows the spectrum of the laser light of Example 4.
The horizontal axis represents the wavelength, and the vertical axis represents the output light intensity. The spectrum of the output light when oscillating at every 10 nm from 1500 nm to 1620 nm and the spectrum of the output light when oscillating at 1491 nm and 1625 nm are shown in one graph. It is shown.
The small peak near 1530 nm is stimulated emission light generated when oscillating at 1491 nm, 1500 nm, and 1625 nm, and it can be seen that the stimulated emission light is suppressed to be small relative to the laser light.

The fiber laser according to the present invention can be widely used in applications that require a small size and excellent stability. For example, it can be suitably used as a WDM light source or a sensor light source.

The entire contents of the specification, claims, drawings and abstract of Japanese Patent Application No. 2008-36585 filed on Feb. 18, 2008 are incorporated herein as the disclosure of the specification of the present invention. Is.

Claims

An optical fiber for amplification in which Er is added to the core, a light source of excitation light for optically exciting Er, an optical coupler for guiding the excitation light to the optical fiber for amplification, and an optical coupler for extracting laser light emitted from the optical fiber for amplification A fiber laser having a length of the amplification optical fiber of 0.5 m or less, and an absorption coefficient of the amplification optical fiber of 100 dB / m or more at any wavelength in a wavelength range of 1520 to 1540 nm. A fiber laser in which the product of the length and the absorption coefficient is 40 to 150 dB.
2. The fiber laser according to claim 1, wherein the resonator is a ring resonator.
3. The fiber laser according to claim 1, further comprising a tunable filter.
The fiber laser according to any one of claims 1 to 3, wherein a wavelength of the excitation light is 900 to 990 nm.
The fiber laser according to any one of claims 1 to 4, wherein a variable wavelength width of the laser light is 100 nm or more.
6. The fiber laser according to claim 1, wherein the core glass of the amplification optical fiber contains 0.1 to 1.0 part by mass of Er with respect to 100 parts by mass of the matrix glass.
The fiber laser according to any one of claims 1 to 6, wherein the amplification optical fiber has a core diameter of 3 to 8 µm.
The fiber laser according to any one of claims 1 to 7, further comprising an isolator.
A WDM light source comprising the fiber laser according to any one of claims 1 to 8.
A light source for a sensor having the fiber laser according to any one of claims 1 to 8.