JP2016161603A - Optical relay transmission system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve an inexpensive optical relay transmission system with a simple configurations and low power consumption capable of performing low-noise relay amplification.SOLUTION: An optical relay transmission system 1000 employs EDFAs (Erbium-Doped Fiber Amplifier) 1021, 1022, and 1023 serving as a phase insensitive optical amplifier, and non-degenerate phase sensitive optical amplifiers 1031, 1032, and 1033 for an optical relay amplifier provided on multiple places of an optical fiber 1010. Additionally, using the EDFA 1021 as the optical relay amplifier at a first stage, the EDFAs 1021, 1022, and 1023 and the non-degenerate phase sensitive optical amplifiers 1031, 1032, and 1033 are alternately disposed as the optical relay amplifiers from the first stage to a final stage.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an optical repeater transmission system provided with optical amplifiers at a plurality of locations of an optical fiber that is an optical transmission line.

In a conventional optical repeater transmission system, an identification reproduction optical repeater is used to regenerate an optical signal attenuated by propagating through an optical fiber. This discriminating / reproducing optical repeater converts an optical signal into an electric signal and discriminates a digital signal (electric signal), and then reproduces the optical signal.
However, with this identification and reproduction optical repeater, there are problems such as a limited response speed of electronic components that convert an optical signal into an electrical signal and an increase in power consumption as the speed of the transmitted optical signal increases. was there.

As optical amplification means for solving this problem, there are fiber laser amplifiers and semiconductor laser amplifiers that amplify optical signals by making excitation light incident on optical fibers doped with rare earth elements such as erbium and praseodymium.
Such fiber laser amplifiers and semiconductor laser amplifiers can amplify an optical signal as it is, so that there is no limitation on the electrical processing speed that has been a problem in the identification reproduction optical repeater. In addition, the device configuration has the advantage of being relatively simple.

  However, these laser amplifiers do not have a function of shaping a deteriorated optical signal waveform. Further, in these laser amplifiers, unavoidably and randomly generated spontaneous emission light is mixed regardless of the signal component, so that the S / N of the optical signal is reduced by at least 3 dB before and after amplification. These lead to an increase in transmission code error rate at the time of digital signal transmission, which is a factor of reducing transmission quality.

  As means for overcoming the limitations of the conventional laser amplifier, a phase sensitive amplifier (PSA) has been studied. This PSA has a function of shaping an optical signal waveform and a phase signal which are deteriorated due to the influence of dispersion of the transmission fiber. In addition, since spontaneous emission light having a quadrature phase irrelevant to the signal can be suppressed and in-phase spontaneous emission light can be minimized, S / N of the optical signal can be kept the same before and after amplification. It is possible in principle.

FIG. 4 shows a basic configuration of a conventional PSA. As shown in FIG. 4, the PSA 100 includes a phase-sensitive optical amplification unit 101 using optical parametric amplification, a pumping light source 102, a pumping light phase control unit 103, a first optical branching unit 104-1, and a second optical branching unit 104-1. Optical branching unit 104-2.
As shown in FIG. 4, the optical signal 110 input to the PSA 100 is branched into two by the optical branching unit 104-1, one incident on the phase sensitive light amplification unit 101, and the other incident on the excitation light source 102. . The phase of the excitation light 111 emitted from the excitation light source 102 is adjusted via the excitation light phase control unit 103 and enters the phase sensitive light amplification unit 101. The phase sensitive amplification unit 101 outputs an output optical signal 112 based on the input optical signal 110 and pumping light 111.

  The phase-sensitive optical amplifying unit 101 amplifies the optical signal 110 when the phase of the incident optical signal 110 and the phase of the excitation light 111 coincide with each other. It has a characteristic to attenuate. If the phase between the pumping light 111 and the optical signal 110 is matched so that the amplification gain is maximized using this characteristic, the spontaneous emission light having the quadrature phase with the optical signal 110 is not generated, and the in-phase component is not generated. Also, since no spontaneous emission light exceeding the noise of the optical signal 110 is generated, the optical signal 110 can be amplified without degrading the S / N ratio.

  In order to achieve such phase synchronization between the optical signal 110 and the pumping light 111, the pumping light phase control unit 103 includes the phase of the optical signal 110 branched by the first optical branching unit 104-1 and the pumping light 111. The phase of the excitation light 111 is controlled so that the phases are synchronized. In addition, the pumping light phase control unit 103 detects a part of the output optical signal 112 branched by the second optical branching unit 104-2 with a narrow-band photodetector, and the amplification gain of the output optical signal 112 is maximized. The phase of the excitation light 111 is controlled so that As a result, the phase sensitive light amplifying unit 101 realizes optical amplification without degradation of the S / N ratio based on the above principle.

  The pumping light phase control unit 103 may be configured to directly control the phase of the pumping light source 102 in addition to the configuration of controlling the phase of the pumping light 111 on the output side of the pumping light source 102. When the light source that generates the optical signal 110 is disposed near the phase-sensitive light amplification unit 101, a part of the optical signal light source can be branched and used as excitation light.

JP 2013-182140 A International Publication No. 2012/098911

T. Umeki, O. Tadanaga, A. Takada and M. Asobe, "Phase sensitive degenerate parametric amplification using directly-bonded PPLN ridge waveguides," Optics Express, 2011, Vol. 19, No. 7, p.6326-6332 M. Asobe, T. Umeki, H. Takenouchi, and Y. Miyamoto, "In-line phase-sensitive amplifier for QPSK signal using multiple QPM LiNbO3 waveguide," In Proceedings of the OptoElectronics and Communications Conference, OECC, 2013, PDP paper PD2-3 T. Umeki, O. Tadanaga, M. Asobe, Y. Miyamoto and H. Takenouchi., "First demonstration of high-order QAM signal amplification in PPLN-based phase sensitive amplifier," Optics Express, February 2014, Vol. 22, No.3, p.2473-2482 Takeshi Umeki, Masaki Asobe, and Hirokazu Takenouchi, "In-line phase sensitive amplifier based on PPLN waveguides," Optics Express, May 2013, Vol. 21, No. 10, p.12077-12084 R. Slavik et al., "All-optical phase and amplitude regenerator for next-generation telecommunications systems," Nature Photonics., Vol. 4, pp. 690-695 (2010).

However, the above-described prior art has the following problems. As the nonlinear optical medium for performing the above optical parametric amplification, a method using a second-order nonlinear optical material typified by a periodically poled LiNbO ₃ (PPLN) waveguide and a third-order nonlinear optical material typified by a quartz glass fiber are used. There is a way.

  FIG. 5 illustrates a configuration of a conventional PSA using a PPLN waveguide disclosed in Non-Patent Document 1 and the like. A PSA 200 shown in FIG. 5 includes an erbium-doped fiber laser amplifier (EDFA) 201, a first second-order nonlinear optical element 202, a second second-order nonlinear optical element 204, a first optical branching unit 203-1, and Second optical branching unit 203-2, phase modulator 205, optical fiber stretcher 206 made of PZT (lead zirconate titanate), polarization maintaining fiber 207, photodetector 208, phase locked loop ( PLL) circuit 209.

  The first second-order nonlinear optical element 202 includes a first spatial optical system 211, a first PPLN waveguide 212, a second spatial optical system 213, and a first dichroic mirror 214. The second second-order nonlinear optical element 204 includes a third spatial optical system 215, a second PPLN waveguide 216, a fourth spatial optical system 217, a second dichroic mirror 218, and a third dichroic. And a mirror 219.

The first spatial optical system 211 couples light input from the input port of the first second-order nonlinear element 202 to the first PPLN waveguide 212. The second spatial optical system 213 couples the light output from the first PPLN waveguide 212 to the output port of the first second-order nonlinear optical element 202 via the first dichroic mirror 214.
The third spatial optical system 215 couples light input from the input port of the second second-order nonlinear optical element 204 to the second PPLN waveguide 216 via the second dichroic mirror 218. The fourth spatial optical system 217 couples the light output from the second PPLN waveguide 216 to the output port of the second second-order nonlinear optical element 204 via the third dichroic mirror 219.

  In the example shown in FIG. 5, the optical signal 250 incident on the PSA 200 is branched by the first optical branching unit 203-1, one is incident on the second second-order nonlinear optical element 204, and the other is the excitation base. The phase of the wave light 251 is controlled via the phase modulator 205 and the optical fiber expander 206 and enters the EDFA 201. In order to obtain sufficient power to obtain a nonlinear optical effect from a weak laser beam used for optical communication, the EDFA 201 amplifies the incident excitation fundamental light 251 and enters the first secondary nonlinear optical element 202. In the first second-order nonlinear optical element 202, a second harmonic (hereinafter referred to as “SH light”) 252 is generated from the incident excitation fundamental light 251, and the generated SH light 252 passes through the polarization maintaining fiber 207. Through the second second-order nonlinear optical element 204. The second second-order nonlinear optical element 204 performs phase-sensitive amplification by performing degenerate parametric amplification with the incident optical signal 250 and the SH light 252 and outputs an output optical signal 253.

In PSA, in order to amplify only light in phase with a signal, the phases of the optical signal and pumping light must match or be shifted by π radians as described above. That is, when the second-order nonlinear optical effect is used, it is necessary that the phase φ _2ωs of the excitation light, which has a wavelength corresponding to the SH light, and the phase φ _{ωs of the} optical signal satisfy the following relationship (Equation 1). Become. Here, n is an integer.
_{Δφ = 1/2 (φ 2ωs} -φ ωs) = nπ ( Equation 1)
FIG. 6 is a graph showing the relationship between the phase difference Δφ between the input optical signal and the pumping light and the gain (dB) in the conventional PSA using the second-order nonlinear optical effect. It can be seen that the gain is maximum when Δφ is −π, 0, or π.

  In the configuration shown in FIG. 5, in order to phase-synchronize the optical signal 250 and the excitation fundamental wave light 251, the phase modulation unit 205 is used to perform phase modulation on the excitation fundamental wave light 251 using a weak pilot signal, and then output. A part of the optical signal 253 is branched and detected by the photodetector 208. Since this pilot signal component is minimized when the phase difference Δφ shown in FIG. 6 is minimized, the PLL circuit 209 is used so that the pilot signal is minimized, that is, the amplified output signal is maximized. Feedback to the optical fiber stretcher 206. The phase of the excitation fundamental light 251 can be controlled to achieve phase synchronization between the optical signal 250 and the excitation fundamental light 251.

  In the configuration in which the PPLN waveguide is used as a nonlinear medium and the optical signal 250 and the SH light 252 are incident on the second second-order nonlinear optical element 204 and degenerate parametric amplification is performed, the SH light 252 is generated once. When performing parametric amplification, for example, the components of the excitation fundamental wave light 251 are removed by using the characteristics of the dichroic mirror 214 and the dichroic mirror 218, so that only the SH light 252 and the optical signal 250 are converted into the second secondary nonlinear optical element 204. It can enter into such a parametric amplification medium. Therefore, noise due to mixing of spontaneously emitted light generated by the EDFA 201 can be prevented, so that low-noise optical amplification is possible.

  As described above, the PPLN waveguide is used as a nonlinear optical medium, and the nonlinear medium is excited using the SH light 252 to perform low-noise phase-sensitive amplification without being affected by noise generated by the EDFA 201. In addition, the phase noise can be reduced by utilizing the characteristic of attenuating the quadrature component.

As shown in FIG. 6, the conventional configuration method described above has a characteristic of attenuating orthogonal phase components, so that an ordinary intensity modulation signal or a binary phase modulation such as IMDD, BPSK, or DPSK is used. It can be used to amplify the modulation signal. However, signals such as QPSK (four values), 8PSK, and QAM, which are multilevel modulation formats, cannot be amplified.
On the other hand, by using a configuration based on non-degenerate parametric amplification as disclosed in Non-Patent Document 2 and Non-Patent Document 3, etc., phase-sensitive amplification of multi-level phase modulation signals such as QPSK and QAM is performed. It is known that a configuration capable of regenerative amplification can be taken.

  Consider an optical repeater transmission system using an optical amplifier as an optical repeater amplifier. FIG. 7 shows a configuration example of an optical repeater transmission system using an EDFA which is a general phase insensitive laser amplifier.

The optical repeater transmission system 300 shown in FIG. 7 includes a plurality (six in this example) of EDFAs 320 (321 to 326) as optical repeater amplifiers at a plurality of locations of optical fibers 310 (311 to 317) that are optical transmission lines. It is prepared for.
More specifically, the output end of the optical transmitter TX and the input end of the first stage EDFA 321 are connected by an optical fiber 311, and the output end of the first stage EDFA 321 and the input end of the second stage EDFA 322 are connected by an optical fiber 312. The output terminal of the second stage EDFA 322 and the input terminal of the third stage EDFA 323 are connected by an optical fiber 313, and the output terminal of the third stage EDFA 323 and the input terminal of the fourth stage EDFA 324 are connected by an optical fiber 314. The output terminal of the fourth stage EDFA 324 and the input terminal of the fifth stage EDFA 325 are connected by an optical fiber 315, and the output terminal of the fifth stage EDFA 325 and the input terminal of the sixth stage EDFA 326 are connected by an optical fiber 316. The output terminal of the final stage EDFA 326 and the input terminal of the optical receiver RX are connected by an optical fiber 317. That.
Incidentally, “first stage” is used to indicate an optical repeater amplifier (EDFA) connected to the optical transmitter TX, and “last stage” is an optical repeater amplifier (EDFA) connected to the optical receiver RX. Used to indicate.

The optical repeater transmission system 300 transmits an optical signal output from the optical transmitter TX through the optical fiber 310 and sends it to the optical receiver RX, and also includes EDFAs 320 (321 to 326) provided at a plurality of locations in the middle of the optical fiber 310. ) To amplify the optical signal.
That is, since the optical intensity of the optical signal transmitted from the optical transmitter TX is attenuated by the propagation loss in the optical fiber 310, the EDFAs 320 (321 to 326) as optical repeater amplifiers are arranged at fixed intervals and attenuated. The optical signal is transmitted to the optical receiver RX while being recovered by the EDFA 320 (321 to 326).

  In this relay amplification, as described above, in the laser amplifier, spontaneously emitted light inevitably and randomly generated is mixed regardless of the signal component, so that the S / N ratio of the optical signal is increased every time amplification is performed. Decreases at least 3 dB before and after amplification, so that the transmission code error rate increases and the transmission quality decreases. For example, if the regenerative repeater that converts the optical signal into the electric signal is not performed once, and the linear repeater is performed six times using only the optical amplifier, the S / N ratio of the optical signal deteriorates by at least 3 dB × 6 = 18 dB. .

  By replacing the optical repeater amplifier (EDFA) in FIG. 7 with a non-degenerate type phase sensitive amplifier, in principle, optical repeater transmission without degradation of the S / N ratio is possible. However, the phase sensitive amplifier has an excitation light control mechanism. Since it is necessary to provide the amplifier, the configuration of the amplifier is complicated and expensive compared to the EDFA. Furthermore, it is difficult to reduce the power consumption of the optical repeater amplifier because an EDFA is required for the pump light generation itself for realizing parametric amplification. For this reason, it is not practical in terms of price and power consumption to configure all of the optical repeater amplifiers of the optical repeater transmission system using many optical amplifiers as non-degenerate phase sensitive amplifiers.

  An object of the present invention is to provide an inexpensive optical repeater transmission system that can perform relay amplification with low noise, has a simple configuration, and can reduce power consumption in view of the above-described problems of the prior art. It is.

The present invention for solving the above problems
In an optical repeater transmission system equipped with optical repeater amplifiers at multiple locations of an optical fiber that is an optical transmission line,
In a state where the first stage optical repeater amplifier is a phase insensitive optical amplifier, the phase insensitive optical amplifier and the phase sensitive optical amplifier are alternately arranged as the optical repeater amplifier from the first stage to the last stage.

The present invention also provides
The number of arrangements of the phase insensitive optical amplifier and the phase sensitive optical amplifier is an even number.

The present invention also provides
Providing another phase sensitive optical amplifier in front of the phase insensitive optical amplifier in the first stage;
Or
Further, another phase insensitive optical amplifier is provided after the phase sensitive optical amplifier in the final stage.

The present invention also provides
The phase sensitive optical amplifier is a non-degenerate type phase sensitive optical amplifier.

The present invention also provides
The optical parametric amplification medium in the phase sensitive optical amplifier or the non-degenerate phase sensitive optical amplifier is LiNbO ₃ , KNbO ₃ , LiTaO ₃ , LiNb _x Ta _1-x O ₃ (0 ≦ x ≦ 1) having a periodically poled structure. ) Or KTiOPO ₄ , or an optical waveguide made of a material containing at least one selected from the group consisting of Mg, Zn, Sc, and In as an additive.

The present invention also provides
The phase insensitive optical amplifier is one of an EDFA, a Raman amplifier, and a semiconductor optical amplifier.

The present invention configures an optical repeater transmission system by alternately arranging phase insensitive optical amplifiers (laser amplifiers) and phase sensitive amplifiers, so that even if the number of repeater stages is increased, the principle of the S / N ratio of the optical signal is increased. It is possible to relay an optical signal with high quality without causing deterioration.
In addition, an optical repeater transmission system in which all of the optical repeater amplifiers are phase sensitive amplifiers has the same transmission characteristics, the structure is simplified, the power consumption can be reduced, and the price is low.

1 is a configuration diagram illustrating an optical repeater transmission system according to a first embodiment of the present invention. It is a characteristic view which shows an example of the constellation before and behind amplification which amplified 16QAM signal with the nondegenerate type phase sensitive optical amplifier. The S / N ratio of the optical repeater system in FIG. 7, the S / N ratio of the optical repeater transmission system in which all EDFAs are replaced with phase sensitive amplifiers in the optical repeater system of FIG. 7, and the ideal in the optical repeater transmission system in this embodiment It is a characteristic view which shows the change of a favorable S / N ratio. It is a block diagram which shows the conventional phase sensitive optical amplifier. It is a block diagram which shows the phase sensitive optical amplifier using the conventional secondary nonlinear optical effect. It is a graph which shows the relationship between phase difference (DELTA) (phi) between an input optical signal and pump light, and a gain in the phase sensitive optical amplifier using the conventional secondary nonlinear optical effect. It is a block diagram showing an optical repeater transmission system using an EDFA as a repeater amplifier.

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

Example 1
FIG. 1 shows an optical repeater transmission system 1000 according to Embodiment 1 of the present invention. This optical repeater transmission system 1000 uses a configuration based on EDFAs 1021, 1022, and 1023 that are phase-insensitive optical amplifiers and non-degenerate parametric amplification as optical repeater amplifiers provided at a plurality of locations of an optical fiber 1010 that is an optical transmission line. Non-degenerate phase sensitive optical amplifiers 1031, 1032, and 1033, which are conventional phase sensitive optical amplifiers, are used. The number of optical repeater amplifiers including the EDFAs 1021, 1022, and 1023 and the non-degenerate phase-sensitive optical amplifiers 1031, 1032, and 1033 is an even number (six in this example).
In addition, the first-stage optical repeater amplifier is the EDFA 1021, and the EDFAs 1021, 1022, and 1023 and the non-degenerate phase-sensitive optical amplifiers 1031, 1032, and 1033 are alternately arranged as the first to last-stage optical repeater amplifiers. For this reason, the first-stage optical repeater amplifier is the EDFA 1021, and the last-stage optical repeater amplifier is the non-degenerate phase-sensitive optical amplifier 1033.

More specifically, the output end of the optical transmitter TX and the input end of the first stage EDFA 1021 are connected by an optical fiber 1011, and the output end of the first stage EDFA 1021 and the input end of the second stage non-degenerate phase-sensitive optical amplifier 1031. Are connected by an optical fiber 1012, and the output terminal of the second-stage non-degenerate phase-sensitive optical amplifier 1031 and the input terminal of the third-stage EDFA 1022 are connected by an optical fiber 1013, and the output terminal of the third-stage EDFA 1022 is 4 The input end of the non-degenerate phase sensitive optical amplifier 1032 at the stage is connected by an optical fiber 1014, and the output end of the non-degenerate phase sensitive optical amplifier 1032 at the fourth stage and the input end of the fifth stage EDFA 1023 are the optical fiber 1015. The output terminal of the fifth stage EDFA 1023 and the input terminal of the sixth stage non-degenerate phase-sensitive optical amplifier 1033 are connected to each other. Are connected by bus 1016, non-degenerate type output terminal of the phase sensitive optical amplifier 1033 and the input end of the optical receiver RX of the last stage is connected by an optical fiber 1017.
Incidentally, “first stage” is used to indicate an optical repeater amplifier connected to the optical transmitter TX, and “final stage” is used to indicate an optical repeater amplifier connected to the optical receiver RX.

  In this embodiment, as the non-degenerate type phase sensitive optical amplifiers 1031, 1032, and 1033, the phase sensitive optical amplifier using the PPLN shown in FIG. 5 as a parametric amplification medium is configured, but a second-order nonlinear medium other than LN is used. Alternatively, it may be used as a parametric amplification medium using a third-order nonlinear medium such as a highly nonlinear fiber.

Here, a method for manufacturing a PPLN waveguide used in the non-degenerate phase-sensitive optical amplifier in this embodiment will be exemplified below. First, a periodic electrode having a period of about 17 μm was formed on LiNbO ₃ to which Zn was added. Next, a polarization inversion grating corresponding to the above electrode pattern was formed in Zn: LiNbO ₃ by an electric field application method. Next, the Zn: LiNbO ₃ substrate having this periodic domain-inverted structure was directly bonded onto the LiTaO _{3 serving} as the cladding, and heat treatment was performed at 500 ° C. to firmly bond both substrates. Next, the core layer was thinned to about 5 μm by polishing, and a ridge type optical waveguide was formed using a dry etching process. This waveguide can be temperature-controlled by a Peltier element, and the length of the waveguide is 50 mm. The second-order nonlinear optical element having the PPLN waveguide formed as described above is a module capable of inputting / outputting light with a polarization maintaining fiber in a 1.5 μm band.

Here, LiNbO ₃ doped with Zn was used in this example, but other nonlinear materials such as KNbO ₃ , LiTaO ₃ , LiNb _x Ta _1-x O ₃ (0 ≦ x ≦ 1) or KTiOPO are used. ₄ or a material containing at least one selected from the group consisting of Mg, Zn, Sc, and In as an additive.

  By the way, if optical amplification is performed by non-degenerate phase-sensitive optical amplification, as disclosed in Patent Document 1 (Japanese Patent Laid-Open No. 2013-182140) or Patent Document 2 (International Publication No. 2012/009911), random The gain of an ASE light having a correct phase (including an in-phase component and a quadrature phase component equivalent to the pump light) is half of the gain of an optical signal having a phase correlation, and as a result, the S / N of the signal It is known that the ratio can be improved by 3 dB. However, since the ASE light once amplified by the phase sensitive optical amplifier has a phase correlation with the pumping light like the optical signal, the non-degenerate type phase sensitive optical amplifier is continuously connected as an optical repeater amplifier. However, the improvement effect of the S / N ratio due to the difference between the gain of the ASE light and the gain of the optical signal can be expected only with the first-stage optical amplifier of the continuous relay span.

  However, as shown in FIG. 1, phase-insensitive optical amplifiers (EDFAs) 1021, 1022, and 1023 and non-degenerate type phase-sensitive optical amplifiers 1031, 1032, and 1033 are alternately arranged to be excited by the non-degenerate type phase-sensitive optical amplifier. Since the ASE light that has phase correlation with the light is amplified by the phase insensitive optical amplifier in the next stage to become an ASE having a random phase again, the ASE is again performed by the non-degenerate phase sensitive optical amplifier in the next stage. An SN improvement effect due to the difference between the optical gain and the optical signal gain can be expected.

  FIG. 2 shows a constellation before and after a 16QAM signal is amplified by a non-degenerate phase-sensitive optical amplifier. That is, FIG. 2A shows the constellation of the input optical signal, and FIG. 2B shows the constellation of the output light in the phase sensitive optical amplifier. As can be seen from FIG. 2, the S / N ratio of the optical signal is improved by the non-degenerate phase sensitive optical amplifier.

In FIG.
(1) Transition of ideal S / N ratio in the optical repeater transmission system of FIG.
(2) Transition of ideal S / N ratio in the optical repeater transmission system in which all EDFAs are replaced by non-degenerate phase sensitive optical amplifiers in the optical repeater transmission system of FIG.
(3) The transition of the ideal S / N ratio in the optical repeater transmission system in this embodiment is compared.
As can be seen from FIG. 3, by using the optical amplifier arrangement of the present invention, the S / N ratio once deteriorated by the EDFA can be transmitted while being recovered by the non-degenerate type phase-sensitive optical amplifier, resulting in optical reception. The ideal S / N ratio when reaching the optical device is the same as the S / N ratio of an optical repeater transmission system composed of only non-degenerate phase-sensitive optical amplifiers.

  Actually, an optical repeater transmission system in which six NF5 dB non-degenerate phase-insensitive optical amplifiers are connected, three phase-insensitive optical amplifiers with NF5 dB, and three non-degenerate phase-sensitive optical amplifiers with NF2 dB are alternately used. As a result of comparing the difference in the S / N ratio at the optical receiver of the connected optical repeater transmission system, it was 18 dB, confirming the effectiveness of the present invention.

  As shown in the present embodiment, by alternately arranging the phase insensitive optical amplifier and the non-degenerate type phase sensitive optical amplifier, ideally, all of the optical repeater amplifiers are not degraded without degrading the S / N ratio. Compared with an optical repeater transmission system composed of degenerate phase sensitive amplifiers, multistage repeater amplification can be realized at low cost and low power consumption.

(Other examples)
In the first embodiment, an optical repeater transmission system including three EDFAs and three non-degenerate phase-sensitive optical amplifiers is taken as an example, but the number of installed units is not limited to three. In other words, if the number of installed EDFAs is the same as the number of installed non-degenerate phase-sensitive optical amplifiers, and the system is one in which EDFAs are alternately connected as a first stage amplifier, the number of installed EDFAs is not limited to three, and the same effect is obtained. I can expect.

The same effect can be obtained even when the number of non-degenerate phase-sensitive optical amplifiers is increased by one more than the number of EDFAs and the first-stage amplifier is a non-degenerate phase-sensitive optical amplifier.
Conversely, if the number of EDFAs is one more than the number of non-degenerate phase-sensitive amplifiers, the first stage optical amplifier is used as an EDFA, and the last stage optical amplifier becomes an EDFA when alternately connected. Although the ideal S / N ratio is degraded to 3 dB compared to the above two forms, when the number of relay stages N is 3 or more, the S / N ratio in the optical receiver is (3N ) dB, the overall system can be expected to have a gain improvement effect of 3 (N−1) dB.

In the above embodiment, the non-degenerate type phase sensitive optical amplifier is adopted. However, when transmitting a normal intensity modulated signal or a modulated signal such as IMDD, BPSK or DPSK using binary phase modulation, the phase sensitive optical amplifier is used. May be adopted.
As the phase insensitive optical amplifier, not only an EDFA but also a Raman amplifier or a semiconductor optical amplifier can be adopted.

  The present invention can be used in an optical repeater transmission system.

1000 optical repeater transmission system 1010, 1011-1017 optical fiber 1021, 1022, 1023 EDFA (phase insensitive optical amplifier)
1031, 1032, 1033 Non-degenerate phase-sensitive optical amplifier

Claims (7)

In an optical repeater transmission system equipped with optical repeater amplifiers at multiple locations of an optical fiber that is an optical transmission line,
A light characterized by alternately arranging a phase insensitive optical amplifier and a phase sensitive optical amplifier as the optical repeater amplifier from the first stage to the last stage in a state where the optical repeater amplifier in the first stage is a phase insensitive optical amplifier. Relay transmission system. In claim 1,
The optical repeater transmission system according to claim 1, wherein the number of arrangement of the phase insensitive optical amplifier and the phase sensitive optical amplifier is an even number. In claim 1,
An optical repeater transmission system further comprising another phase sensitive optical amplifier before the phase insensitive optical amplifier in the first stage. In claim 1,
An optical repeater transmission system further comprising another phase insensitive optical amplifier after the phase sensitive optical amplifier in the final stage. In any one of Claims 1 thru | or 4,
An optical repeater transmission system, wherein the phase sensitive optical amplifier is a non-degenerate phase sensitive optical amplifier. In any one of Claims 1 thru | or 5,
The optical parametric amplification medium in the phase sensitive optical amplifier or the non-degenerate phase sensitive optical amplifier is LiNbO ₃ , KNbO ₃ , LiTaO ₃ , LiNb _x Ta _1-x O ₃ (0 ≦ x ≦ 1) having a periodically poled structure. ) Or KTiOPO ₄ , or an optical waveguide made of a material containing at least one selected from the group consisting of Mg, Zn, Sc, and In as an additive. . In any one of Claims 1 thru | or 6,
An optical repeater transmission system, wherein the phase insensitive optical amplifier is one of an EDFA, a Raman amplifier, and a semiconductor optical amplifier.

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