KR100333639B1 - Multi-wavelength fiber Raman laser scheme - Google Patents

Abstract

The present invention relates to the composition of a multi-wavelength optical fiber Raman laser, which is a nonlinear optical medium having a Raman scattering with respect to a pump light source, and having a selective reflection characteristic for different wavelengths within the Raman gain wavelength range of the optical fiber. It consists of a resonator using multiple optical fiber diffraction grating pairs. By individually adjusting the reflection characteristics according to the wavelength of the diffraction grating pair constituting the resonator, the oscillating wavelength and its intensity can be controlled independently. An embodiment of the present invention provides a cascade optical fiber Raman laser that oscillates two wavelengths of secondary stock frequency shift. In this embodiment, using a 1313 nm Nd: YLF laser as the pump light source, a Raman laser oscillating at 1480 nm and 1500 nm was implemented. When used as a pump light source of an optical amplifier, such a laser has the advantage of extending the gain wavelength range of the amplifier and simultaneously implementing the gain flattening.

Description

Multi-wavelength fiber Raman laser scheme

FIELD OF THE INVENTION The present invention relates to optical fiber Raman laser compositions, and more particularly, to optical fiber Raman laser compositions having multiple short-period diffraction grating pairs for multiwavelength output.

Recently, many researches on ultra-wideband optical amplification technology over a wavelength range of 1.4 μm to 1.6 μm have been conducted in order to maximize the low loss wavelength of an optical fiber to obtain tens of terabits of optical communication speed. The optical fiber Raman amplifier, which is expected to contribute to the development of long-distance optical communication, has an advantage of easily expanding the amplification band when using multi-wavelength pump light because the amplification wavelength band is determined by the pump light.

Hereinafter, with reference to the accompanying Figure 1 will be described a conventional optical fiber Raman laser composition. As shown in FIG. 1, the conventional optical fiber Raman laser using the selective reflection characteristic of the optical fiber diffraction grating includes an optical fiber 13 causing Raman scattering and a plurality of optical fiber diffraction gratings 11, 12, 14, 15 and 16) to output the wavelength light I2S on which the secondary stock is transitioned.

That is, the first optical fiber diffraction grating 11 receiving the pump light Ip from the pump light source 100 has a high transmittance with respect to the pump light wavelength, has a maximum reflectance at the output wavelength of the Raman laser, and is adjacent to both ends of the optical fiber 13. Each of the second and third optical fiber diffraction gratings 12, 14 has a maximum reflectance with respect to the first stock frequency shifted wavelength and acts as an internal resonator for the first stock frequency shifted wavelength. On the other hand, the fourth optical fiber diffraction grating 15 has a slightly lower reflectance at the output wavelength of the Raman laser corresponding to the second stock frequency shift. Accordingly, each of the first and fourth optical fiber diffraction gratings 11 and 15 functions as a resonator mirror and an output mirror for the second stock frequency conversion wave, and the fifth optical fiber diffraction grating 16 connected to the output terminal is a Raman laser. The transmittance is high with respect to the output wavelength, and has the maximum reflectance characteristic at the pump light wavelength.

Conventional multi-wavelength pump light sources are implemented by combining the output of laser diodes or fiber lasers oscillating at different wavelengths. Since the conventional optical fiber Raman laser composition only outputs light of a single wavelength, the system is complicated because a wavelength multiplexing device combining multiple pump light sources and wavelengths of each pump light is required to construct a multi-wavelength laser. The price is rising.

2 shows a conventional composition for implementing a four wavelength fiber laser. In the conventional composition, four pump light sources 21A, 22A, 23A, and 24A are required for the four wavelengths to come together. Generally, the pump light source uses a semiconductor laser or a fiber laser that operates at different wavelengths. In order to combine the four wavelengths, an optical waveguide 20 in the form of a Mach-Zender, as shown in FIG. 2, is used. Because this structure uses the interference phenomenon of light, incident light with a stable wavelength having a narrow line width is required. To this end, the wavelength of the light incident from each pump light source is stabilized through the optical fiber diffraction gratings 21B, 22B, 23B, and 24B, and then is incident on the optical waveguide 20 of the Mach gender type. The Mach-Zehnder optical waveguide 20 coupler having such a structure generates an insertion loss for injecting light, and because the interferometer structure is used, the coupling loss of the pump light source is large when the wavelength is variable. In addition, an additional pump light source is required every time the number of operating wavelengths is increased, and manufacturing costs are greatly increased due to the complexity of the waveguide structure.

The present invention for solving the above problems does not require the addition of a pump light source according to the increase in the number of operating wavelengths, it is possible to solve problems such as insertion loss, coupling loss of the pump light by not using the Mach-Zehnder optical waveguide coupler, The purpose of the present invention is to provide a multi-wavelength optical fiber cascade Raman laser composition with relatively simple composition, which is economical and has excellent operating characteristics.

1 is a schematic view showing a short wavelength optical fiber Raman laser composition according to the prior art,

2 is a schematic diagram showing a laser composition operating at four wavelengths according to the prior art;

3 is a schematic diagram showing an optical fiber cascade Raman laser composition for simultaneously outputting two wavelengths of secondary stock frequency transition in accordance with an embodiment of the present invention;

4A and 4B are characteristic diagrams of a wavelength division multiple optical fiber coupler and an optical fiber diffraction grating according to an embodiment of the present invention;

5 is an output spectrum of a dual wavelength Raman laser according to an embodiment of the present invention,

6 is an output spectrum showing the variable wavelength operation of the dual wavelength Raman laser according to an embodiment of the present invention,

7 is an output spectrum showing the results of the relative power intensity control operation of each wavelength in a dual wavelength Raman laser according to an embodiment of the present invention,

8 is a schematic diagram showing a four wavelength Raman fiber laser composition implemented in accordance with an embodiment of the invention.

* Description of reference numerals for the main parts of the drawings *

31: wavelength division multiple optical fiber coupler 32: optical fiber

33: optical fiber diffraction grating

34A, 35A, 34B, 35B: Short Cycle Fiber Diffraction Grating

The present invention for achieving the above object is an optical fiber causing Raman scattering for the pump light source; Internal resonating means connected to the optical fiber to resonate light of a first wavelength generated by the optical fiber; A first optical fiber diffraction grating comprising at least two optical fiber diffraction gratings for reflecting light of different wavelengths, the first optical fiber being connected to a pump light input terminal of the internal resonating means and transmitting the pump light source and reflecting at least two output light generated by the optical fiber Group of short period optical fiber diffraction gratings; A second group of stages positioned in the internal resonating means of the optical fiber to transmit light of the pump light source and the first wavelength and reflect light of the same wavelength as at least one of the optical fiber diffraction gratings of the first group Periodic optical fiber diffraction gratings; And a pump light source reflecting means connected to an output end of the internal resonating means and reflecting a pump light source to re-incident into the optical fiber.

In addition, the present invention for achieving the above object is an optical fiber causing Raman scattering for the pump light source; Wavelength division multiple optical fiber coupling means connected in parallel to the optical fiber and configured to internally resonate light of a first wavelength generated by the optical fiber; It is composed of at least two optical fiber diffraction gratings reflecting light of different wavelengths and is connected to a pump light input terminal of the wavelength division multiple optical fiber coupling means, and transmits a pump light source and reflects at least two output light generated by scattering of the optical fiber. A first group of short period optical fiber diffraction gratings; Located in an internal resonator made of the wavelength division multiple optical fiber coupling means to transmit the pump light source and the light of the first wavelength and reflect light of the same wavelength as at least one of the optical fiber diffraction gratings of the first group of optical fiber diffraction gratings. A second group of short period optical fiber diffraction gratings; And a pump light source reflecting means connected to the wavelength division multiple optical fiber coupling means to reflect a pump light source and re-incident into the optical fiber.

The present invention is a non-linear optical medium and a plurality of optical fiber diffraction gratings that can cause the Raman scattering for the pump light source, and the resonant light according to the wavelength and resonate the light of the wavelength shifted by the stock by the Raman scattering of the optical fiber It is a feature to provide a multiwavelength Raman laser composition comprising a pair. Accordingly, by independently adjusting the reflection characteristics according to the wavelength of the diffraction grating pair within the Raman gain range, the oscillation wavelength and its intensity can be controlled independently.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

Figure 3 is a schematic diagram showing the composition of an optical fiber cascade Raman laser that simultaneously outputs two wavelengths of secondary stock frequency transition in accordance with an embodiment of the present invention. As shown in FIG. 3, an optical fiber cascade Raman laser for selecting two wavelengths of secondary stock frequency transition as output light includes an optical fiber 32 which causes Raman scattering for a pump light source as a nonlinear optical medium, A wavelength division multiplexing (WDM) optical fiber combiner 31, which constitutes an internal resonator for light of wavelengths shifted to the primary stock frequency by Raman scattering of the optical fiber 32, and the WDM optical fiber combiner 31 Two pairs of short-period optical diffraction gratings 34A, 34B / 35A, which select and reflect a second stock frequency shifted wavelength corresponding to an output wavelength in an internal resonator composed of an input terminal and the WDM optical fiber combiner 31; 35B) and an optical fiber diffraction grating 33 having a maximum reflectance at the wavelength of the pump light.

The internal resonating means may comprise at least one WDM optical fiber coupler 31, and constitutes an internal resonator for wavelength light having a primary stock frequency shifted by adding a pair of optical fiber diffraction gratings instead of the WDM optical fiber coupler 31. You may.

The operating principle of the optical fiber Raman cascade Raman laser of the present invention having the configuration as described above is as follows. The pump light (IP) from the pump source (100) passes through the optical fiber diffraction gratings (34A, 35A) and enters the first port (a) of the WDM optical fiber combiner (31). Since the wavelength of the pump light IP shows a high coupling ratio close to 100% due to the coupling characteristic of the WDM coupler 31 as shown in FIG. 4A, the wavelength of the pump light IP is incident to the first port a. Most of the pump light IP passes through the fourth port d to the optical fiber 32 used as a Raman active medium. The light passing through the optical fiber 32 among the input pump light IP passes through the short-period optical fiber diffraction gratings 34B and 35B, so that the third port C and the second port B of the WDM optical fiber combiner 31 are provided. The total reflection is caused by the fifth optical fiber diffraction grating 33 having the maximum reflectance at the pump light source wavelength, and then reenters the optical fiber 32.

In the course of the pump light Ip passing through the optical fiber 32 in a reciprocating manner, the light beam having the primary stock frequency shifted by the nonlinear Raman effect is oscillated. As shown in FIG. 4A, since the coupling ratio of the WDM optical fiber coupler 31 to the primary stock frequency shifted wavelength I1S is very low, the light of this wavelength is transferred to the third port c of the WDM optical fiber coupler 31. And the fourth port (d) is unable to exit the ring, and as a result it is re-incident to the Raman optical fiber 32 again. Through this process, the internal resonator for the wavelength shifted by the primary stock frequency is formed by the WDM optical fiber coupler 31. The internal resonator thus formed helps to efficiently generate light of the next order stock frequency shifted wavelength.

Most of the light is WDM fiber coupler because the coupling ratio of the WDM fiber coupler 31 is high for the light of the second stock frequency shifted wavelength (34 ', 35' in FIG. 4A) generated by the first stock frequency shifted wavelength. You will exit 31. Among them, the light emitted from the first port (a) of the WDM optical fiber coupler 11 is selected and reflected by the first and second optical fiber diffraction gratings 34A and 35A, and is again used as the first port of the multiplexer. Passes through the optical fiber 32 through the fourth port (ad) port and is reflected back and resonated by the short-period optical fiber diffraction gratings 34B and 35B.

In the resonance process of the wavelength light shifted to the second stock frequency, the wavelength is selected by the optical diffraction grating of the narrow line width of the reflected wavelength band, and the coupling ratio of the WDM optical fiber coupler 31 to the selected wavelengths is greater than 0% and 100. When adjusted to be less than%, some of these wavelengths exit the second port (b) of the WDM optical fiber coupler 31 and pass through the fifth optical fiber diffraction grating 33 to become the output light source I2S of the Raman laser.

The optical fiber cascade Raman laser according to the present invention constructed as described above can greatly reduce the number of optical components used by using the periodic characteristics of the wavelength division multiplexing optical coupler.

FIG. 4B is a wavelength division multiplexing that was actually manufactured and used to obtain an output of 1480 nm and 1500 nm using a 1313 nm Nd: YLF laser as a pump light source using the Raman laser composition shown in FIG. 3. WDM) shows the coupling characteristics according to the wavelength of the optical fiber coupler. In other words, FIG. 4B shows a linear resonator and a linear resonator made of a pair of first and fourth optical fiber diffraction gratings 34A and 34B, in which the optical fiber diffraction grating 33 reflects pump light having a wavelength of 1313 nm in a Raman laser composition as shown in FIG. A linear resonator composed of pairs of second and third optical fiber diffraction gratings 35A and 35B reflects light of secondary stock frequency shifted wavelengths 34 'and 35', i.e. 1480 nm and 1500 nm, respectively, as shown in FIG. In addition, two output wavelengths of 1480 nm and 1500 nm are obtained from the Raman laser.

As described above, since the third to fourth ports (cd port) of the WDM optical fiber combiner 31 show a low coupling ratio with respect to the first stock frequency shifted wavelength, the internal resonator for the first stock frequency shifted wavelength is reduced. Can be formed. In addition, the WDM optical fiber coupler 31 shows a coupling ratio of about 80% to 90% on two secondary stock frequency shifted wavelengths, which are laser output wavelengths.

5 is a graph showing the characteristics of the output spectrum of the Raman laser manufactured according to an embodiment of the present invention. It can be seen that the primary stock frequency shifted wavelength occurred near 1400 nm and the laser output wavelength secondary stock wave occurred at 1480 nm and 1500 nm selected by the optical fiber diffraction grating.

On the other hand, by simultaneously stretching or compressing a pair of diffraction grating constituting the linear resonator by applying a mechanical deformation, the output wavelength can be varied by varying the reflection characteristics according to the wavelength of the diffraction grating. have. However, if only one of the pair of diffraction gratings implementing the linear resonator is selected and the wavelength is varied, the oscillation conditions of the laser are not established because the reflection characteristics of the two diffraction gratings for the resonator do not match. As a result, the output light intensity of the wavelength is reduced. In this case, since the intensity of the output light is reduced according to the degree of deviation of reflection characteristics according to the wavelength, the intensity of the oscillated wavelength can be controlled by adjusting the degree of change of the wavelength. When the wavelength is varied by applying mechanical strain to the optical fiber diffraction grating, the transmission characteristics of the wavelength band other than the reflected wavelength do not change, and thus the oscillation of another wavelength is not affected. Therefore, the intensity of each wavelength can be controlled independently.

In FIG. 6, as an experimental result of varying a wavelength of 1480 nm, which is one of output wavelengths, the wavelength variable characteristic of the Raman laser from 1480 nm to 1485 nm is shown. After fixing the optical fiber diffraction grating, a pair of optical fiber diffraction gratings constituting a 1480 nm wavelength resonator was simultaneously stretched using a mechanical translator. Using this method, a variable of about 5 nm could be obtained. In the same manner, the wavelength can be varied in the 1500 nm wavelength range, and the width of the wavelength can be further widened by compressing the optical fiber length.

FIG. 7 shows experimental results of controlling the relative intensities of the oscillating wavelengths by individually adjusting the optical fiber diffraction gratings constituting each resonator. As shown in FIG. 7, intensity control for wavelengths oscillating at wavelengths of 1480 nm and 1500 nm may be independently performed. FIG. 7 (a) shows the output of two wavelength lights, and FIG. 7 (b) shows the case where the reflection characteristics of the diffraction grating pairs in the 1480 nm wavelength range are intentionally shifted to decrease the intensity of the output light. FIG. 7C shows a result of intentionally shifting the reflection characteristics of the diffraction grating pair in the 1500 nm wavelength band to reduce the intensity of the output light.

Thus, a Raman laser having two wavelengths and whose relative intensity is controlled can be usefully used to control gain characteristics in an optical amplifier using the same as a pump light source.

To achieve more than one multi-wavelength Raman laser operation, this can be achieved by simply adding a diffraction grating pair of the desired wavelength to the previously described Raman laser. In this case, the operating region of the multi-wavelength laser is possible only within the region of the Raman gain.

FIG. 8 illustrates a Raman laser composition according to another embodiment of the present invention, which improves the problem of the conventional four-wavelength laser (see FIG. 2). As shown in FIG. 8, a four-wavelength Raman laser may be realized by adding two pairs of diffraction gratings to a Raman laser composition (see FIG. 3) according to an embodiment of the present invention. As described above, when the optical fiber diffraction grating reflection wavelength is changed, there is no change in the transmission characteristics of other wavelength bands, so that the intensity of each wavelength can be controlled independently. However, the operating range of a multiwavelength laser is only possible within the range of Raman gain.

The present invention described above is not limited to the above-described embodiments and the accompanying drawings, and various substitutions, modifications, and changes can be made in the art without departing from the technical spirit of the present invention. It will be apparent to those of ordinary knowledge.

That is, although the embodiment of the present invention implements a Raman laser using the second stock frequency conversion, the Raman laser with the first stock frequency shift, an optical fiber diffraction grating, or a wavelength division combiner is further used to sequentially perform the third order or more. It can also be applied to the Raman laser with the stock frequency conversion. In addition to the Raman gain, the present invention can be applied to a multi-wavelength laser using a gain-added optical fiber having a wide range of wavelength selection, and other applications besides the application fields disclosed herein are possible within the scope and spirit of the present invention.

The optical fiber cascade Raman laser of the present invention made as described above has an advantage that the number of optical components is small and the output wavelength and intensity can be easily adjusted as compared with the conventional composition.

In addition, according to the selection of the pump light, it is possible to obtain the light output of various wavelength bands, there is an advantage that the economical and stable laser operation can be obtained. The optical fiber cascade Raman laser of the present invention can lead to the development of ultra-wideband large-capacity long-range optical communication technology.

Claims (6)

In a multi-wavelength fiber laser, Optical fibers causing Raman scattering for pump light sources; Internal resonating means connected to the optical fiber to resonate light of a first wavelength generated by the optical fiber; A first group consisting of at least two optical fiber diffraction gratings reflecting light of different wavelengths and connected to a pump light input terminal of the internal resonating means, transmitting the pump light source and reflecting at least two output light generated by the optical fiber Short period optical fiber diffraction grating; A second group of stages positioned in the internal resonating means of the optical fiber to transmit light of the pump light source and the first wavelength and to reflect light having the same wavelength as at least one of the optical fiber diffraction gratings of the first group of optical fiber diffraction gratings Periodic optical fiber diffraction gratings; And Pump light source reflecting means connected to the output terminal of the internal resonating means to reflect the pump light source and re-incident into the optical fiber Multi-wavelength fiber laser comprising a. The method of claim 1, The internal resonance means A multi-wavelength optical fiber laser, characterized in that at least a pair of optical fiber diffraction grating. The method of claim 1, The internal resonance means A multi-wavelength optical fiber laser, characterized in that at least one wavelength division multiple optical fiber combiner. In a multi-wavelength fiber laser, Optical fibers causing Raman scattering for pump light sources; Wavelength division multiple optical fiber coupling means connected in parallel to the optical fiber and configured to internally resonate light of a first wavelength generated by the optical fiber; It is composed of at least two optical fiber diffraction gratings reflecting light of different wavelengths and is connected to a pump light input terminal of the wavelength division multiple optical fiber coupling means, and transmits a pump light source and reflects at least two output light generated by scattering of the optical fiber. A first group of short period optical fiber diffraction gratings; Located in an internal resonator made of the wavelength division multiple optical fiber coupling means to transmit the pump light source and the light of the first wavelength and reflect light of the same wavelength as at least one of the optical fiber diffraction gratings of the first group of optical fiber diffraction gratings. A second group of short period optical fiber diffraction gratings; And Pump light source reflecting means connected to the wavelength division multiple optical fiber coupling means for reflecting a pump light source and re-incident into the optical fiber Multi-wavelength fiber laser comprising a. The method of claim 4, wherein And a coupling ratio of the wavelength division optical fiber coupling means to the output light is greater than 0% and less than 100%. The method according to any one of claims 1 to 5, The pump light source reflecting means, A multi-wavelength optical fiber laser, characterized in that the optical fiber diffraction grating.