Optical amplifier

Abstract

To suppress the deterioration of amplification efficiency without using FBG.SOLUTION: An optical amplifier includes: means for outputting third multiplexed light by optically parametrically amplifying signal light included in first multiplexed light; means for outputting fourth multiplexed light by optically parametrically amplifying the signal light included in second multiplexed light; a second coupler for outputting pump light on the basis of the third and fourth multiplexed lights and outputting fifth multiplexed light; and an additional amplification unit. The additional amplification unit includes: control means for controlling the phase of the pump light outputted by the second coupler; a third coupler for outputting sixth and seventh multiplexed lights on the basis of the pump light after the phase control by the control means and the fifth multiplexed light; means for outputting eighth multiplexed light by optically parametrically amplifying the signal light included in the sixth multiplexed light; and fourth amplification means for outputting ninth multiplexed light by optically parametrically amplifying the signal light included in the seventh multiplexed light.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present disclosure relates to optical amplifiers. [Background technology]

[0002] Optical amplifiers that use second-order, third-order, and other nonlinear optical effects are called optical parametric amplifiers. Compared to optical amplifiers that use ion-doped optical fibers such as EDFAs, optical parametric amplifiers are capable of amplifying signals over an extremely wide bandwidth.

[0003] In an optical parametric amplifier, a combined light obtained by combining signal light and pump light is input into a nonlinear medium. As the combined light propagates through the nonlinear medium, the signal light contained in the combined light is amplified by the pump light contained in the combined light. The pump light is usually unmodulated continuous light. In the process of amplification by the pump light, the pump light is attenuated and idler light is generated. The idler light is generated on the frequency axis at a position opposite to the signal light, centered around the pump light, and its bandwidth corresponds to the bandwidth of the signal light.

[0004] For efficient optical parametric amplification, it is important to maintain the phase relationship between the pump light at the start of amplification by a nonlinear medium and the idler light generated at the start. However, the phase of the pump light changes during propagation through the nonlinear medium due to factors such as the Kerr effect. The change in the phase of the pump light during propagation through the nonlinear medium deteriorates the amplification efficiency of optical parametric amplification. For this reason, Non-Patent Document 1 discloses a configuration in which multiple nonlinear media are connected in series and the phase of the pump light contained in the combined light that has passed through one nonlinear medium is adjusted before it is input to the next nonlinear medium, thereby suppressing the deterioration of amplification efficiency. [Prior art documents] [Non-patent literature]

[0005] [Non-Patent Document 1] S. Takasaka, et al., "Flat and broad amplification by quasi-phase-matched fiber optical parametric amplifier", OFC / NFOEC, Los Angeles, CA, USA, 2012, pp. 1-3. Summary of the Invention [Problem to be solved by the invention]

[0006] In the configuration of Non-Patent Document 1, a fiber Bragg grating (FBG) is used to adjust the phase of the pump light contained in the combined light. However, the FBG causes a loss in the power of the combined light. In addition, it is necessary to use an FBG that is appropriate for the wavelength of the pump light used for optical parametric amplification.

[0007] The present disclosure provides a technique for suppressing degradation of amplification efficiency without using an FBG. [Means for solving the problem]

[0008] According to one aspect of the present disclosure, an optical amplifier includes: a first coupler that outputs first multiplexed light including the pump light and the signal light based on pump light and signal light, and outputs second multiplexed light including the pump light and the signal light; a first amplifying means that outputs third multiplexed light by optically parametrically amplifying the signal light included in the first multiplexed light using the pump light included in the first multiplexed light; a second amplifying means that outputs fourth multiplexed light by optically parametrically amplifying the signal light included in the second multiplexed light using the pump light included in the second multiplexed light; a second coupler that outputs the pump light based on the third multiplexed light and the fourth multiplexed light, and outputs fifth multiplexed light including the signal light and idler light generated by the optical parametric amplification; and an additional amplifying unit, wherein the additional amplifying unit amplifies the pump light output by the second coupler. a third coupler that outputs a sixth multiplexed light including the pump light, the signal light, and the idler light based on the pump light after phase adjustment by the adjustment means and the fifth multiplexed light output by the second coupler, and outputs a seventh multiplexed light including the pump light, the signal light, and the idler light; a third amplifying means that outputs an eighth multiplexed light by optically parametrically amplifying the signal light included in the 6th multiplexed light with the pump light included in the sixth multiplexed light; a fourth amplifying means that outputs a ninth multiplexed light by optically parametrically amplifying the signal light included in the seventh multiplexed light with the pump light included in the seventh multiplexed light; and a fourth coupler that outputs the pump light based on the eighth multiplexed light and the ninth multiplexed light, and outputs a tenth multiplexed light including the signal light and the idler light. [Effects of the Invention]

[0009] According to the present disclosure, it is possible to suppress deterioration of amplification efficiency without using an FBG. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a diagram showing an example of the configuration of an optical amplifier. [Figure 2] FIG. 2 is a diagram showing an example of each light inside an optical amplifier. [Figure 3] FIG. 1 is a diagram showing an example of the configuration of an optical amplifier. [Figure 4] FIG. 1 is a diagram showing an example of the configuration of an optical amplifier. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, the embodiments will be described in detail with reference to the accompanying drawings. Note that the following embodiments do not limit the scope of the invention as claimed, and not all combinations of features described in the embodiments are necessarily essential to the invention. Two or more features among the multiple features described in the embodiments may be arbitrarily combined. Furthermore, the same reference numerals are used for the same or similar components, and redundant explanations will be omitted.

[0012] First Embodiment FIG. 1 is a schematic diagram of an optical amplifier according to this embodiment. Pump light #1 generated by a light source (not shown) is input to port #1 of a coupler 31 via an optical circulator 21. Wavelength-multiplexed signal light to be amplified is input to port #2 of the coupler 31 via an optical circulator 22. The coupler 31 is, for example, a 2×2 coupler, which outputs multiplexed light #1 obtained by multiplexing the pump light #1 and the wavelength-multiplexed signal light from port #3, and outputs multiplexed light #2 obtained by multiplexing the pump light #1 and the wavelength-multiplexed signal light from port #4. The multiplexed light #1 and the multiplexed light #2 are each output to a nonlinear medium 41. As shown in FIG. 1, in the nonlinear medium 41, the multiplexed light #1 and the multiplexed light #2 propagate in different directions.

[0013] Fig. 2(A) shows wavelength-multiplexed signal light used to explain this embodiment. In the example of Fig. 2(A), the wavelength-multiplexed signal light includes three signal lights S1 to S3 whose center frequencies are equally spaced on the frequency axis. In this example, the signal lights S1 to S3 have the same bandwidth. Fig. 2(B) shows multiplexed light #1 and multiplexed light #2. The arrow on the high-frequency side of signal light S3 in Fig. 2(B) indicates pump light #1.

[0014] The wavelength-multiplexed signal light contained in the multiplexed light #1 is amplified by the pump light #1 contained in the multiplexed light #1 during propagation through the nonlinear medium 41. During this process, idler light is generated and the pump light #1 is attenuated. Furthermore, the phase of the pump light #1 contained in the multiplexed light #1 changes during propagation through the nonlinear medium 41. In the following description, the multiplexed light #1 after amplification by the nonlinear medium 41 will be referred to as multiplexed light #3. Similarly, the wavelength-multiplexed signal light contained in the multiplexed light #2 is amplified by the pump light #1 contained in the multiplexed light #2 during propagation through the nonlinear medium 41. During this process, idler light is generated and the pump light #1 is attenuated. Furthermore, the phase of the pump light #1 contained in the multiplexed light #2 changes during propagation through the nonlinear medium 41. In the following description, the multiplexed light #2 after amplification by the nonlinear medium 41 will be referred to as multiplexed light #4. The nonlinear medium 41 functions as an amplification medium that amplifies the wavelength-multiplexed signal light using pump light.

[0015] 2(C) shows multiplexed light #3 and multiplexed light #4. In the figure, the idler light of the signal light Sn (n is an integer from 1 to 3) is represented as Sn * As shown in FIG. 2(C), the idler light of the signal light Sn is generated so as to be symmetrical with the signal light Sn with respect to the pump light on the frequency axis.

[0016] The combined light #3 is input to port #4 of the coupler 31, and the combined light #3 is input to port #3 of the coupler 31. The coupler 31, which is a 2×2 coupler, outputs combined light C of light A and light B from port #3 and outputs combined light D of light A and light B from port #4 based on light A input to port #1 and light B input to port #2. When combined light C is input to port #4 and combined light D is input to port #3, the coupler has the characteristic that light A is output from port #1 and light B is output from port #2.

[0017] Therefore, the pump light #1 contained in the multiplexed light #3 and the multiplexed light #4 is output from port #1 of the coupler 31. Furthermore, the wavelength-multiplexed signal light contained in the multiplexed light #3 and the multiplexed light #4 is output from port #2 of the coupler 31. Furthermore, since the idler light and wavelength-multiplexed signal light contained in the multiplexed light #3 are in phase and the idler light and wavelength-multiplexed signal light contained in the multiplexed light #4 are in phase, the idler light contained in the multiplexed light #3 and the multiplexed light #4 is output from port #2 of the coupler 31, the same as the wavelength-multiplexed signal light.

[0018] Therefore, the coupler 31 outputs pump light #2 from port #1 and outputs combined light #5, which is the combination of the wavelength-multiplexed signal light and the idler light, from port #2. Figure 2(D) shows combined light #5. Pump light #2 is generated from pump light #1 contained in combined light #3 and pump light #1 contained in combined light #4, and its phase is shifted from the phase of pump light #1 generated by the light source due to the Kerr effect in the nonlinear medium 41.

[0019] The pump light #2 is input to the phase shifter 51 via the optical circulator 21. The phase shifter 51 adjusts (shifts) the phase of the pump light #2 and inputs the phase-adjusted pump light #2 as pump light #3 to port #1 of the coupler 32. The combined light #5 is input to port #2 of the coupler 32 via the optical circulator 22.

[0020] Coupler 32 is similar to coupler 31, and outputs multiplexed light #6 and multiplexed light #7, which are obtained by multiplexing pump light #3 and multiplexed light #5, from ports #3 and #4. Multiplexed light #6 and multiplexed light #7 propagate in opposite directions through nonlinear medium 42, and during this propagation process, the wavelength-multiplexed signal light contained in multiplexed light #6 and multiplexed light #7 is amplified by pump light #3. Multiplexed light #6 and multiplexed light #7 after amplification by nonlinear medium 42 are input to ports #4 and #3 of coupler 32 as multiplexed light #8 and multiplexed light #9, respectively.

[0021] Similar to the description of the coupler 31, the coupler 32 outputs pump light #4 from port #1 and outputs combined light 10, which is obtained by combining wavelength-multiplexed signal light and idler light, from port #2. The pump light #4 is output from the port of the optical circulator 21 to which the pump light #1 is input. The combined light 10 is output from the port of the optical circulator 22 to which the wavelength-multiplexed signal light is input. Thereafter, the idler light of the combined light #10 is removed by a filter or the like, and the amplified wavelength-multiplexed signal light is output from the optical amplifier.

[0022] The amount of phase shift imparted to pump light #2 by the phase shifter 51 can be experimentally determined so as to increase the efficiency of optical parametric amplification by pump light #3 in the nonlinear medium 42. Alternatively, the amount of phase shift imparted to pump light #2 by the phase shifter 51 is set so as to bring the phase of pump light #3 closer to the phase of pump light #1.

[0023] As described above, in this embodiment, it is possible to adjust the phase of the pump light used for amplification in the nonlinear medium 42 without using an FBG. Therefore, it is possible to suppress deterioration in amplification efficiency without using an FBG.

[0024] In this embodiment, the pump light is arranged on the higher frequency side than the wavelength-multiplexed signal light, but the pump light can also be arranged on the lower frequency side than the wavelength-multiplexed signal light. Furthermore, the pump light can also be arranged on the higher frequency side than some of the signal lights in the wavelength-multiplexed signal light and on the lower frequency side than the remaining signal lights. In this embodiment, the bandwidths of the signal lights are the same, and the center frequencies of the signal lights are equally spaced on the frequency axis. However, the bandwidths of the signal lights may be different, and the center frequencies of the signal lights do not need to be equally spaced on the frequency axis. Furthermore, in this embodiment, wavelength-multiplexed signal light is optically parametrically amplified, but the target to be amplified may be a single signal light that is not wavelength-multiplexed.

[0025] 1, an amplifier 52 for amplifying pump light #3 can be provided downstream of the phase shifter 51 and upstream of the coupler 32. The amplifier 52 is, for example, an ion-doped optical fiber such as an EDFA, and the pump light #3 is amplified by another pump light. By amplifying the power of the pump light, which has been reduced by amplification in the nonlinear medium 41, with the amplifier 52, the amplification gain in the nonlinear medium 42 can be increased.

[0026] Second Embodiment Next, the second embodiment will be described, focusing on the differences from the first embodiment. Figure 3 is a configuration diagram of an optical amplifier according to this embodiment. Note that components similar to those in the first embodiment are given the same reference numerals and their description will be omitted. In this embodiment, a wavelength multiplexer 6 is used instead of the coupler 32. The wavelength multiplexer 6 outputs multiplexed light #11, which is obtained by wavelength-multiplexing multiplexed light #5 and pump light #3. The wavelength-multiplexed signal light contained in the multiplexed light #11 is amplified by a nonlinear medium 42 and output as multiplexed light #12. Thereafter, the pump light and idler light of the multiplexed light #12 are removed by a filter or the like, and the amplified wavelength-multiplexed signal light is output from the optical amplifier.

[0027] Third Embodiment Next, a third embodiment will be described, focusing on the differences from the first embodiment. Fig. 4 is a configuration diagram of an optical amplifier according to this embodiment. In Fig. 4, "P" indicates pump light, "S" indicates wavelength-multiplexed signal light, "I" indicates idler light, "P+S" indicates combined light obtained by combining pump light and wavelength-multiplexed signal light, "P+S+I" indicates combined light obtained by combining pump light, wavelength-multiplexed signal light, and idler light, and "S+I" indicates combined light obtained by combining wavelength-multiplexed signal light and idler light.

[0028] The pump light and the wavelength-multiplexed signal light are each input to coupler 33, which is a 2×2 coupler. Coupler 33 outputs combined light obtained by combining the pump light and the wavelength-multiplexed signal light to nonlinear media 43 and 44. Nonlinear media 43 and 44 each amplify the wavelength-multiplexed signal light included in the combined light with the pump light included in the combined light, and output combined light including the pump light, wavelength-multiplexed signal light, and idler light. The combined light output by nonlinear media 43 and 44 is input to coupler 34, which is a 2×2 coupler. Similar to coupler 31 of the first embodiment, coupler 34 outputs pump light and combined light including wavelength-multiplexed signal light and idler light.

[0029] The optical amplifier according to this embodiment has N additional amplification units 7-1 to 7-N. N is an integer equal to or greater than 1, and when N is equal to or greater than 2, the additional amplification units 7-1 to 7-N are connected in series. The additional amplification units 7-1 to 7-N have the same configuration, and Fig. 4 shows the internal configuration of only the additional amplification unit 7-1. The configuration of the additional amplification unit 7-1 will be described below.

[0030] The phase shifter 51 adjusts the phase of the pump light. The coupler 35 is a 2×2 coupler that combines the combined light output by the coupler 34 with the pump light after phase adjustment by the phase shifter 51, and outputs combined light including the pump light, wavelength-multiplexed signal light, and idler light to the nonlinear media 45 and 46. The nonlinear media 45 and 46 each amplify the wavelength-multiplexed signal light included in the combined light with the pump light included in the combined light, and output combined light including the pump light, wavelength-multiplexed signal light, and idler light. The amount of phase shift applied to the pump light by the phase shifter 51 can be determined experimentally so as to increase the efficiency of optical parametric amplification in the nonlinear media 44 and 45. The combined light output by the nonlinear media 45 and 46 is input to the coupler 36, which is a 2×2 coupler. Similar to the coupler 31 of the first embodiment, the coupler 36 outputs combined light including the pump light, wavelength-multiplexed signal light, and idler light.

[0031] The pump light output from an additional amplification unit 7-m (m is 1 to N-1) is input to the phase shifter 51 of the next additional amplification unit 7-(m+1). Also, the multiplexed light output from an additional amplification unit 7-m (m is 1 to N-1) is input to the coupler 35 of the next additional amplification unit 7-(m+1). The optical amplifier removes idler light from the multiplexed light output from the most downstream additional amplification unit 7-N and outputs wavelength-multiplexed signal light.

[0032] In this embodiment, similarly to the first embodiment, the pump light after phase adjustment by the phase shifter 51 can be amplified by the amplifier 52, and the amplified pump light can be output to the coupler .

[0033] Note that the first embodiment corresponds to a configuration in which the number N of additional amplification units in the third embodiment is 1, and several components in the third embodiment are combined into one component. Specifically, couplers 33 and 34 in the third embodiment correspond to coupler 31 in the first embodiment. Furthermore, nonlinear media 43 and 44 in the third embodiment correspond to nonlinear media 41 in the first embodiment. Furthermore, couplers 35 and 36 of additional amplification unit 7-1 in the third embodiment correspond to coupler 32 in the first embodiment. Furthermore, nonlinear media 45 and 46 of additional amplification unit 7-1 in the third embodiment correspond to nonlinear media 42 in the first embodiment.

[0034] Therefore, the configuration of the second embodiment can also be configured like the third embodiment. That is, the most downstream additional amplification unit 7-N can be configured to have a wavelength multiplexer 6 instead of the coupler 35, amplify the wavelength-multiplexed signal light included in the multiplexed light output by the wavelength multiplexer 6 with a nonlinear medium 45, and extract and output the wavelength-multiplexed signal light from the multiplexed light amplified by the nonlinear medium 45.

[0035] The above configuration makes it possible to suppress degradation in amplification efficiency without using FBGs, thereby contributing to Goal 9 of the United Nations' Sustainable Development Goals (SDGs), which is to "Build resilient infrastructure, promote sustainable industrialization and foster innovation."

[0036] The invention is not limited to the above-described embodiment, and various modifications and variations are possible within the scope of the gist of the invention. [Explanation of symbols]

[0037] 33, 34, 35, 36: couplers, 43, 44, 45, 46: nonlinear media, 51: phase shifter, 7-1 to 7-N: additional amplification units

Claims

1. a first coupler that outputs a first multiplexed light including the pump light and the signal light based on the pump light and the signal light, and outputs a second multiplexed light including the pump light and the signal light; a first amplifying means for optically parametrically amplifying the signal light included in the first multiplexed light using the pump light included in the first multiplexed light, thereby outputting a third multiplexed light; a second amplifying means for optically parametrically amplifying the signal light included in the second multiplexed light using the pump light included in the second multiplexed light, thereby outputting a fourth multiplexed light; a second coupler that outputs the pump light based on the third multiplexed light and the fourth multiplexed light, and outputs a fifth multiplexed light that includes the signal light and idler light generated by the optical parametric amplification; an additional amplification unit; Equipped with The additional amplification unit is an adjusting means for adjusting the phase of the pump light output from the second coupler; a third coupler that outputs a sixth multiplexed light including the pump light, the signal light, and the idler light, based on the pump light after phase adjustment by the adjustment means and the fifth multiplexed light output from the second coupler, and outputs a seventh multiplexed light including the pump light, the signal light, and the idler light; a third amplifying means for optically parametrically amplifying the signal light included in the sixth multiplexed light using the pump light included in the sixth multiplexed light, thereby outputting eighth multiplexed light; a fourth amplifying means for optically parametrically amplifying the signal light included in the seventh multiplexed light using the pump light included in the seventh multiplexed light, thereby outputting a ninth multiplexed light; a fourth coupler that outputs the pump light based on the eighth multiplexed light and the ninth multiplexed light, and outputs a tenth multiplexed light including the signal light and the idler light; An optical amplifier comprising:

2. 2. The optical amplifier of claim 1, wherein the first coupler and the second coupler are the same device.

3. 2. The optical amplifier of claim 1, wherein the third coupler and the fourth coupler are the same device.

4. 2. The optical amplifier of claim 1, wherein said first amplifying means and said second amplifying means are the same nonlinear medium.

5. 2. The optical amplifier of claim 1, wherein said third amplifying means and said fourth amplifying means are the same nonlinear medium.

6. one or more further additional amplification units downstream of the additional amplification unit; the adjusting means of the one or more further additional amplifying units adjusts the phase of the pump light output from the fourth coupler of the additional amplifying unit on the upstream side; 2. The optical amplifier of claim 1, wherein the third coupler of one or more of the further additional amplification units receives the pump light output by the adjustment means of the same additional amplification unit and the tenth combined light output by the fourth coupler of the upstream additional amplification unit.

7. a first coupler that outputs a first multiplexed light including the pump light and the signal light based on the pump light and the signal light, and outputs a second multiplexed light including the pump light and the signal light; a first amplifying means for optically parametrically amplifying the signal light included in the first multiplexed light using the pump light included in the first multiplexed light, thereby outputting a third multiplexed light; a second amplifying means for optically parametrically amplifying the signal light included in the second multiplexed light using the pump light included in the second multiplexed light, thereby outputting a fourth multiplexed light; a second coupler that outputs the pump light based on the third multiplexed light and the fourth multiplexed light, and outputs a fifth multiplexed light that includes the signal light and idler light generated by the optical parametric amplification; an adjusting means for adjusting the phase of the pump light output from the second coupler; a multiplexing means for wavelength-multiplexing the pump light after the phase adjustment by the adjusting means and the fifth multiplexed light output from the second coupler, and outputting a sixth multiplexed light; a third amplifying means for optically parametrically amplifying the signal light included in the sixth multiplexed light using the pump light included in the sixth multiplexed light, thereby outputting a seventh multiplexed light; An optical amplifier comprising:

8. 8. The optical amplifier of claim 7, wherein the first coupler and the second coupler are the same device.

9. 8. The optical amplifier of claim 7, wherein said first amplifying means and said second amplifying means are the same nonlinear medium.

10. 10. The optical amplifier according to claim 1, further comprising an amplifier for amplifying the pump light after the phase adjustment by the adjustment means.

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