JP4960198B2 - Optical fiber amplifier - Google Patents

Description

  The present invention relates to an optical fiber amplifier that amplifies an optical signal.

  Er-doped fiber amplifiers (EDFAs) are used as repeaters, pre / post amplifiers, loss compensation devices in high-speed and large-capacity wavelength division multiplexing systems (WDM), or distribution loss compensation devices in optical access systems such as video systems, etc. Widely used in optical communication systems. In particular, in a WDM system using a dispersion-shifted fiber (DSF) as a transmission line, WDM transmission in the C band (1530-1565 nm) is difficult due to nonlinear optical effects such as four-wave mixing (FWM). Since the transmission band is 1625 nm, an L-band EDFA is used as an optical amplifier.

Japanese Patent No. 3288965 H. Ono et al., “1.58-μm band gain-flattened erbium-doped fiber amplifiers for WDM transmission system,” IEEE Journal of Lightwave Technology, vol.17, no.3, pp.490-496, 1999.

However, the L-band EDFA has a larger wavelength difference between the pumping light wavelength and the signal light wavelength than the C-band EDFA. The power conversion efficiency to light is smaller in the L-band EDFA. This is the maximum value of the power conversion efficiency, the excitation light wavelength lambda _p, the signal light wavelength as lambda _s, because given by λ _p / λ _s. If the power conversion efficiency is low, the required pumping light power increases, leading to an increase in device cost, and the power required for driving the pumping light source and adjusting the temperature increases, increasing the power consumption of the entire optical communication system device. Result.

  The present invention has been made in view of such problems, and an object thereof is to provide an efficient optical fiber amplifier.

The present invention, in order to achieve the object, a first aspect of the present invention, an optical fiber amplifier comprising an Er doped fiber L band optical signal is amplified, emitted from the Er-doped fiber The C-band ASE light is returned to the Er-doped fiber, and is provided in a pumping light source for supplying pumping light to the Er-doped fiber. The reflecting means is a reflecting film on the surface of the semiconductor laser chip of the pumping light source. And the reflective film is provided in one of a plurality of semiconductor laser chips of an excitation light source .

According to a second aspect of the present invention, there is provided an optical fiber amplifier including two Er-doped fibers in which L-band signal light is amplified, and C-band ASE light emitted from the two Er-doped fibers. Reflecting means respectively provided in a corresponding pumping light source that returns to the Er-doped fiber and supplies pumping light to the Er-doped fiber, and is a reflecting film on the surface of the semiconductor laser chip of the corresponding pumping light source. And an isolator is further provided between the two Er-doped fibers .

  The excitation of the conventional L-band EDFA has two stages as described in Non-Patent Document 1. First, spontaneous emission amplified light (ASE light) in the C band is generated by the Er-doped fiber by the excitation light in the 980 nm band or 1480 nm band. L-band signal light is amplified using the C-band ASE light as an excitation source. The ASE light is emitted not only from the signal input side to the signal output side of the Er-doped fiber, but also from the signal output side to the signal input side.

  The C-band ASE light is mostly absorbed in the Er-doped fiber, but can be emitted to the signal output side depending on the operating state of the L-band EDFA. By reflecting one or both of the ASE light emitted to the signal input side and the signal output side of the Er-doped fiber and returning them to the Er-doped fiber again, the ASE light generated in the Er-doped fiber is efficiently generated. Absorption by the Er-doped fiber results in an increase in power conversion efficiency and a reduction in the required pump light power.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Throughout the drawings, the same constituent elements will be described with the same reference numerals.

(First embodiment)
FIG. 1 is a block diagram showing an example of an optical fiber amplifier according to the first embodiment of the present invention. The optical fiber amplifier 100 includes an optical isolator 102a that propagates input signal light in one direction, two pumping light sources 104a and 104b that generate pumping light, and pumping light from each pumping light source together with signal light Er. Two multiplexers 106a and 106b for supplying the doped fiber, an Er-doped fiber 108 for amplifying the signal light by the pumping light, and an optical isolator 102b for propagating the amplified signal light in one direction and outputting it. ing.

  In FIG. 1, L-band signal light is input to an optical isolator 102a. This signal light is combined with the excitation light from the excitation light source 104 a in the multiplexer 106 a and input to the Er-doped fiber 108. Similarly, the excitation light from the excitation light source 104b is also input to the Er-doped fiber 108 via the multiplexer 106b. In the Er-doped fiber, Er ions are excited by excitation light, so that spontaneous emission amplified light (ASE light) in C band is generated, and signal light in L band is amplified. The Er-doped fiber 108 can be a fiber whose fiber length is equivalently adjusted, as seen in Patent Document 1, in order to amplify L-band signal light. The amplified input signal light is output from the optical isolator 102b via the multiplexer 106b.

  FIG. 2 shows the transmission spectrum characteristics of the multiplexers 106a and 106b in FIG. 2A shows the transmission spectrum from the signal input side of the multiplexer 106a to the Er-doped fiber side and the opposite direction, and FIG. 2B shows the excitation light input side of the multiplexer 106a. The transmission spectrum in the direction from to the Er-doped fiber side and in the opposite direction is shown. The multiplexer 106b has similar spectral characteristics, and FIG. 2A shows the transmission spectrum in the direction from the Er-doped fiber side to the signal output side of the multiplexer 106b and in the opposite direction. FIG. 2B shows the transmission spectrum in the direction from the pumping light input side to the Er-doped fiber side of the multiplexer 106b and in the opposite direction. As described above, the multiplexers 106a and 106b can multiplex light of approximately 1460-1560 nm, that is, excitation light of 1460-1520 nm, ASE light of C band, and signal light of L band.

  Next, FIG. 3 shows a configuration example of the excitation light source of FIG. The pumping light source 104 includes a semiconductor laser chip 120 that generates laser light, a reflective coating 122 that is adjusted in reflectivity so that laser oscillation occurs in the wavelength band of the pumping light, and pumping light that has passed through the reflective coating. A lens 124 coupled to 126 and a metal case 128 for fixing and protecting each component.

  The semiconductor laser chip 120 can be designed to be suitable for laser oscillation at 1460-1520 nm, for example. The reflective coating 122 has a reflectance in the vicinity of this wavelength of about 8% so that laser oscillation occurs in a wavelength region of about 1465 to 1490 nm. In addition, for one of the excitation light sources 104a and 104b, the reflective coating 122 is further designed to reflect C-band light. In this embodiment, the excitation light source 104a shown in FIG. 1 is an excitation light source coated with a C-band light, and the excitation light source 104b shown in FIG. 1 is coated with a C-band light. A case where an excitation light source not used is used will be described. In this case, for example, the reflectance of light in the C band is set to 10%.

  In such a configuration, ASE light propagating to the signal input side out of the C-band ASE light generated in the Er-doped fiber 108 is transmitted through the multiplexer 106 a to the pumping light source 104 a side and partially reflected by the reflective coating 122. Is reflected, the light returns to the Er-doped fiber 108 via the multiplexer 106a again. Thus, part of the ASE light returns to the Er-doped fiber and contributes to the amplification of the signal light, thereby improving the power conversion efficiency as the optical fiber amplifier.

  The same effect can be obtained by using an excitation light source provided with a coating that reflects C-band light instead of the excitation light source 104a. However, if an excitation light source having such a reflective coating is used for both excitation light sources 104a and 104b, the C-band ASE light may reciprocate between the excitation light sources 104a and 104b and oscillate. Therefore, in the optical fiber amplifier 100 according to the present embodiment, the excitation light source provided with the coating that reflects the C-band light is used only for the front excitation light source 104a.

In the optical fiber amplifier 100 having the above configuration, a silica-based Er-doped fiber having an equivalent fiber length of 6.5 × 10 ⁴ weight ppm · m is used, and signal light having a wavelength of 1590 nm and a signal light power of −19 dBm is input. The pumping light power required when the output signal light power of +8 dBm was obtained was 178.5 mW in total for the pumping light sources 104a and 104b. On the other hand, when a conventional 1480 nm band semiconductor laser (LD) was used as the pumping light source, the pumping light power required under the same operating conditions of the optical fiber amplifier was 190 mW in total for the pumping light sources 104a and 104b. As described above, by effectively using the C-band ASE light generated in the Er-doped fiber 108 for L-band signal amplification, there is an effect that the necessary pumping light power can be reduced as compared with the conventional optical fiber amplifier. I was able to confirm.

  In the present embodiment, the reflectance of the C-band light is set to 10%, but the reflectance is not limited to this. FIG. 4 is a graph plotting the relationship between the required excitation light power and the reflectance. It can be seen that if a conventional 1480 nm band LD is used and the reflectance is approximately 0%, the required excitation light power can be reduced if the reflectance is about 2% or more.

(Second Embodiment)
FIG. 5 is a block diagram showing an example of an optical fiber amplifier according to the second embodiment of the present invention. The optical fiber amplifier 200 includes an optical isolator 102a that propagates input signal light in one direction, two pumping light sources 104a and 104b that generate pumping light, and pumping light from each pumping light source together with signal light Er. Arranged between two multiplexers 106a and 106b for supplying the doped fiber, two Er-doped fibers 108a and 108b in which the signal light is amplified by the pumping light, and the two Er-doped fibers, from the input side An optical isolator 102c that propagates in one direction to the output side and an optical isolator 102b that propagates the amplified signal light in one direction and outputs it are provided.

  This optical fiber amplifier 200 is similar to the optical fiber amplifier 100 according to the first embodiment, but an optical isolator 102c is disposed between two Er-doped fibers 108a and 108b, and any of the pumping light sources 104a and 104b. However, the difference is that the excitation light source provided with the coating for reflecting the C-band light described in connection with FIG. 3 is used.

  In such a configuration, the C-band ASE light reflected by the excitation light source 104b is completely blocked by the optical isolator 102c and cannot be injected into the excitation light source 104a. What provided the coating which reflects the light of C band can be used. In this case, both of the multiplexers 106a and 106b are approximately 1460-1560 nm light, that is, 1460-1520 nm excitation light and C-band ASE light, as shown in FIGS. The band signal light can be multiplexed.

In the optical fiber amplifier 200 configured as described above, the operating conditions of the same optical fiber amplifier as in the first embodiment, that is, the equivalent fiber length of the entire Er-doped fibers 108a and 108b is 6.5 × 10 ⁴ weight ppm · m. Using a silica-based Er-doped fiber, a pumping light power required when a signal with a wavelength of 1590 nm and a signal light power of −19 dBm is input and an output signal light power of +8 dBm is obtained is the sum of the pumping light sources 104 a and 104 b It was 175 mW. Thus, it was confirmed that there is an effect that the necessary pumping light power can be reduced as compared with the conventional optical fiber amplifier described in the first embodiment.

(Third embodiment)
FIG. 6 is a block diagram showing an example of an optical fiber amplifier according to the third embodiment of the present invention. The optical fiber amplifier 300 includes an optical isolator 102a that propagates input signal light in one direction, two pumping light sources 104a and 104b that generate pumping light, and pumping light from each pumping light source together with signal light Er. Two multiplexers 106a and 106b that supply the doped fiber, a filter 110 that reflects C-band light, an Er-doped fiber 108 that amplifies the signal light by the excitation light, and the amplified signal light in one direction And an optical isolator 102b for propagating and outputting.

  This optical fiber amplifier 300 is similar to the optical fiber amplifier 100 of the first embodiment, but a filter 110 that reflects C-band light is disposed between one excitation light source 104a and the multiplexer 106a. A difference is that both of the excitation light sources 104a and 104b use a conventional excitation light source that is not provided with a coating that reflects C-band light. The filter 110 is designed to transmit excitation light in the 1480 nm band and reflect C band light, and is composed of a dielectric multilayer film.

  In such a configuration, ASE light propagating to the signal input side among the C-band ASE light generated in the Er-doped fiber 108 is transmitted through the multiplexer 106a, reflected by the filter 110, and then again the multiplexer. Returning to the Er-doped fiber 108 via 106a. Thus, part of the ASE light returns to the Er-doped fiber and contributes to the amplification of the signal light, thereby improving the power conversion efficiency as the optical fiber amplifier. In the optical fiber amplifier 300 according to the present embodiment, the filter 110 is inserted only between the front excitation light source 104a and the multiplexer 106a in order to prevent oscillation due to reflection of C-band ASE light.

In the optical fiber amplifier 300 having the above-described configuration, the silica-based Er having the same optical fiber amplifier operating condition as that of the first embodiment, that is, an equivalent fiber length of 6.5 × 10 ⁴ weight ppm · m as the Er-doped fiber 108. The pumping light power required when using a doped fiber, inputting a signal with a wavelength of 1590 nm and a signal light power of −19 dBm, and obtaining an output signal light power of +8 dBm is 40 mW for each of the pumping light sources 104a and 104b. The efficiency was 7.9%. On the other hand, when a conventional 1480 nm band LD was used as the pumping light source, the pumping light power required under the same operating conditions of the optical fiber amplifier was 173 mW in total for the two pumping light sources. As described above, by effectively using the C-band ASE light generated in the Er-doped fiber 108 for L-band signal amplification, there is an effect that the necessary pumping light power can be reduced as compared with the conventional optical fiber amplifier. I was able to confirm.

  Further, as shown in FIG. 7, a filter 110 may be inserted between the multiplexer 106 a and the Er-doped fiber 108. In this case, since the filter 110 needs to reflect the C-band ASE light and transmit the excitation light and the L-band signal light, the characteristics of the filter 110 reflect the C-band light as shown in FIG. It is necessary to use a band removal filter.

  While the present invention has been described with respect to several specific embodiments, the embodiments described herein are merely illustrative in view of the many possible embodiments to which the principles of the present invention can be applied. It is not intended to limit the scope of the invention. The configuration and details of the embodiment exemplified here can be changed without departing from the spirit of the present invention. Further, the illustrative components and procedures may be changed, supplemented, or changed in order without departing from the spirit of the invention.

1 is a block diagram illustrating an example of an optical fiber amplifier according to a first embodiment of the present invention. It is a figure which shows an example of the transmission spectrum characteristic of the multiplexer of the optical fiber amplifier by this invention. It is a block diagram which shows the structural example of the excitation light source of the optical fiber amplifier by this invention. It is the graph which plotted the relationship between the excitation light power required in the optical fiber amplifier by the 1st Embodiment of this invention, and a reflectance. It is a block diagram which shows an example of the optical fiber amplifier by the 2nd Embodiment of this invention. It is a block diagram which shows an example of the optical fiber amplifier by the 3rd Embodiment of this invention. It is a block diagram which shows another example of the optical fiber amplifier by the 3rd Embodiment of this invention. It is a figure which shows an example of the reflection spectrum characteristic of the filter of the optical fiber amplifier by this invention.

Explanation of symbols

100, 200, 300, 400 Optical fiber amplifiers 102a, 102b, 102c Optical isolators 108, 108a, 108b Er doped fibers 110 Filters 122 Reflective coatings 124 Lenses 126 Optical fibers 128 Metal cases

Claims (2)

In the optical fiber amplifiers with Er doped fiber L band optical signal is amplified,
A reflection means provided in an excitation light source for returning C-band ASE light emitted from the Er-doped fiber to the Er-doped fiber and supplying the Er-doped fiber to the Er-doped fiber, the semiconductor laser chip of the excitation light source A reflection means that is a reflective film on the surface;
The optical fiber amplifier , wherein the reflection film is provided in one of a plurality of semiconductor laser chips of an excitation light source . In an optical fiber amplifier including two Er-doped fibers in which L-band signal light is amplified,
The C-band ASE light emitted from the two Er-doped fibers is returned to the Er-doped fiber, and is provided in a corresponding excitation light source that supplies the Er-doped fiber with excitation light, respectively. Reflecting means that is a reflecting film on the surface of the semiconductor laser chip of the corresponding excitation light source,
An optical fiber amplifier , further comprising an isolator between the two Er-doped fibers .

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