Optical fiber communication system using distribution amplifying fiber raman amplifier

Description: TECHNICAL FIELD [Detailed description of the invention]

【0001】

[Technical field to which the invention belongs]

The present invention relates to an optical fiber communication system using a distributed amplification type fiber Raman amplifier.

【0002】

[Conventional technology]

Figure 16 shows the basic configuration of an optical fiber communication system using a conventional distributed amplification type fiber Raman amplifier (hereinafter referred to as "Raman amplifier" for simplicity) used in a wavelength division multiplexing (WDM) system (Reference: H. Masuda, S. Kawai, K.-I. Suzuki, and K. Aida, 75-nm 3-dB gain-band optical ampllfication with erbium-doped fluoride fibre ampllfiers and distributed Raman amplifiers in9 x 2.5 Gb / s WDM transmission experiment, Proc. Of European Conferenceon Optical Communications, 1997, Vol. 3, pp. 73-76). The Raman amplifier 100 uses the transmission fiber 101 as a gain medium and is excited backward using the excitation light source 102 and the combiner 103. The excitation light wavelength is generally a single wavelength or multiple wavelengths, but FIG. 16 shows the case of two wavelengths for the sake of simplicity.

【0003】

A centralized optical amplifier 200 is installed behind the Raman amplifier 100, and these two amplifiers amplify the signal light. The centralized optical amplifier 200 is a rare earth-added fiber amplifier such as an erbium-added fiber amplifier (EDFA), a semiconductor laser amplifier (SLA), a centralized Raman amplifier, or the like, and generally has a gain equalizer inside. The signal light emitted from the centralized optical amplifier is incident on the second transmission fiber 300, and the second transmission fiber 300 is a second Raman amplifier having the same configuration as the Raman amplifier 100 (for simplicity, the figure). It is a part of (omitted in 16). The configuration of FIG. 16 is an example of using a hybrid optical amplifier consisting of a Raman amplifier 100 and a centralized optical amplifier 200 as a linear relay optical amplifier, but it is clear if the second transmission fiber 300 is replaced with an optical receiver. In addition, the hybrid optical amplifier can be used as the pre-optical amplifier.

【0004】

The signal light gain spectral characteristics in the prior art of FIG. 16 are shown in FIG. The internal gain of Raman, the external gain of the centralized optical amplifier, and the total gain, which is the sum of them, are shown. Here, when the total gain balances the transmission line loss, the gain in one relay section is zero. The total gain value is G₀It is flattened to. The wavelengths on the short wave side and the long wave side of the flat gain wavelength range are λ, respectively._s1And λ_s2And. In addition, the wavelengths on the long wave side and the short wave side of the two excitation light wavelengths are set to λ, respectively._p1And λ_p2And. At this time, λ_p1And λ_s2The wavelength interval of is about 100 nm in the vicinity of 1.5 μm.

【0005】

The optical signal-to-noise ratio (SNR) spectral characteristics of the prior art of FIG. 16 are shown in FIG. Signal light wavelength λ_s2The value of optical SNR in R₀And. Since the Raman gain exists in the transmission fiber, the larger the distributed Raman gain, the larger the optical SNR, and the longer the relay transmission distance. Since the distributed Raman gain is wavelength-dependent, the optical SNR shows a wavelength-dependent spectrum. Therefore, there is a problem that the relay transmission distance differs depending on the wavelength, that is, the channel. For example, the value of optical SNR is the wavelength λ at the short wave end._s1Is the smallest, and generally the relay transmission distance of channels close to this wavelength is the shortest.

【0006】

[Problems to be Solved by the Invention]

An object of the present invention is to provide an optical fiber communication system using a distributed amplification type fiber Raman amplifier, which solves the drawback that the optical SNR has wavelength dependence in the above-mentioned conventional optical fiber communication system.

【0007】

[Means for solving problems]

In order to solve the above problems, the invention according to claim 1 is an optical fiber communication system using a distributed amplification type fiber Raman amplifier and a centralized amplifier, wherein the distribution amplification type fiber Raman amplifier is a transmission fiber and the transmission fiber. A combiner and an excitation light source for inputting excitation light to the combiner are provided on the incident side and the exit side of the signal light, respectively, and the excitation light wavelength of the excitation light source on the incident side is set to the excitation light source on the exit side. The excitation light from the excitation light source is input to the transmission fiber by using the combiner, and the signal light incident on the transmission fiber is Raman in the transmission fiber. It is characterized in that it is configured to be amplified by using the centralized amplifier after amplification.

【0008】

Further, the invention according to claim 2 is an optical fiber communication system using a distributed amplification type fiber Raman amplifier and a centralized amplifier, wherein the distribution amplification type fiber Raman amplifier is a transmission fiber and a signal light incident side of the transmission fiber. Alternatively, a combiner and an excitation light source for inputting excitation light to the combiner are provided on the exit side, the excitation light wavelengths of the excitation light source are set to a plurality, and a short wavelength among the plurality of excitation light wavelengths is set. The excitation light power of the excitation light wavelength on the side is made larger than the excitation light power of the excitation light wavelength on the long wavelength side, and the excitation light from the excitation light source is input to the transmission fiber using the combiner. It is characterized in that the signal light incident on the transmission fiber is Raman-amplified in the transmission fiber and then amplified by using the centralized amplifier.

【0009】

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of the present invention will be described with reference to the drawings. Figure 1 shows the basic configuration of the optical fiber communication system according to the present invention in the case of bidirectional excitation. In FIG. 1, the same configurations as those shown in FIG. 16 are designated by the same reference numerals and the description thereof will be omitted. The optical fiber communication system shown in FIG. 1 is significantly different from the conventional technique shown in FIG. 16 in that one excitation light source for Raman amplification is added to the Raman amplifier 100a. The excitation light wavelength of the excitation light source 104 is generally a single wavelength or multiple wavelengths, but FIG. 1 shows the case of two wavelengths for the sake of simplicity. The wavelength of the excitation light source 104 is λ_p3And λ_p4And. The excitation light from the excitation light source 104 is incident on the transmission fiber 101 from the front by the combiner 105.

【0010】

In the above configuration, the excitation light wavelength λ generated by the excitation light source 104 on the incident side_p3,λ_p4However, the excitation light wavelength λ of the excitation light source 102 on the exit side_p1,λ_p2It is located on the shorter wavelength side. Further, the power of each excitation light from the excitation light source 104 is set to be smaller than the light power of each excitation from the excitation light source 102. The centralized optical amplifier 200a in FIG. 1 has the same configuration as the centralized optical amplifier 200 in FIG. 16, but the gain setting value is different from that in FIG. 16 as described later. .. Further, the second transmission fiber 300a has the same configuration as the centralized optical amplifier 300 of FIG. 16 as a part of the Raman amplifier having the same configuration as the Raman amplifier 100a according to the present invention, or has the same configuration as the Raman amplifier 100. It is configured as part of a Raman amplifier.

【0011】

The signal light gain spectral characteristics of the present invention in FIG. 1 are shown in FIG. The internal Raman gain, the external gain of the centralized optical amplifier, and their sum, the total gain, are shown. The total gain value is G₀It is flattened to. The two wavelengths of the additional excitation light, the long wave side and the short wave side, are λ, respectively._p3And λ_p4And. Signal optical band (λ) due to additional excitation light_s1From λ_s2The Raman gain in the short wavelength region within) is increasing. The gain of the centralized optical amplifier 200a is reduced by the increase in its Raman gain.

【0012】

The optical SNR spectral characteristics of the present invention in FIG. 1 are shown in FIG. Optical SNR, signal light wavelength λ_s2Peak value R in wavelength range other than₀Has improved. The Raman gain spectrum in Fig. 2 is not flat, but the optical SNR spectrum in Fig. 3 is flat. This is because the forward excitation and the backward excitation have the same gain, and the forward excitation has a larger improvement in optical SNR. As described above, the wavelength dependence of the optical SNR is flattened, and the above-mentioned drawbacks in the prior art are solved.

【0013】

FIG. 4 shows the excitation light power spectrum in the prior art of FIG. Wavelength λ_p1And λ_p2Power in P₀And. At this time, the excitation light power spectrum of the present invention in FIG. 1 is as shown in FIG. Due to the bidirectional excitation arrangement, the Raman amplification effect between the anterior excitation light and the posterior excitation light is small, and the excitation light power in the anterior and posterior directions is the Raman gain value (in dB) in the anterior and posterior directions. Almost proportional. Therefore, the Raman gain spectrum of FIG. 2 is realized by the excitation light power spectrum of FIG.

【0014】

FIG. 6 shows the basic configuration of the optical fiber communication system according to the present invention in the case of unidirectional excitation (or backward excitation). Compared with the conventional technique of FIG. 16, the difference is that the number of excitation light wavelengths of the excitation light source 102b is increased from 2 to 4. In the following, the case of backward excitation is described, but the same can be said for the case of forward excitation.

【0015】

As described above, the Raman amplifier 100b shown in FIG. 6 has the number of excitation light wavelengths of the excitation light source increased from 2 to 4 as compared with the Raman amplifier 100 of FIG. And the wavelength on the short wave side is λ, respectively._p3And λ_p4Is. Here, each excitation light wavelength of the excitation light source 012b is λ._p1, λ_p2, λ_p3, λ_p4It is set from the long wavelength side to the short wavelength side in the order of. In addition, each excitation light has an excitation light wavelength λ on the short wavelength side._p3, λ_p4The excitation light power of is the excitation light wavelength λ on the long wavelength side._p1, λ_p2It is set to be larger than the excitation light power of. The centralized optical amplifier 200b and the transmission fiber 300b in FIG. 6 are configured in the same manner as the centralized optical amplifier 200 and the transmission fiber 300 in FIG. 16, respectively.

【0016】

The signal light gain spectral characteristics of the present invention in FIG. 6 are shown in FIG. The internal gain of Raman, the external gain of the centralized optical amplifier, and the total gain, which is the sum of them, are shown. The total gain value is G₀It is flattened to. The Raman gain spectrum is in the signal optical band (λ) due to the four excitation lights._s1From λ_s2) Is flattened. The gain of the centralized optical amplifier 200b is reduced by the increase in its Raman gain.

【0017】

The optical SNR spectral characteristics of FIG. 6 in the present invention are the same as those of FIG. Since the Raman gain spectrum is flat, the optical SNR spectrum is also flat.

【0018】

FIG. 8 shows the excitation light power spectrum of FIG. 6 in the present invention. Due to the unidirectional excitation arrangement, there is Raman amplification / absorption action between excitation lights with different wavelength intervals, and energy is transferred from short-wavelength excitation light to long-wavelength excitation light. Therefore, as shown in FIG. 8, the input excitation light power is set to be large for short-wavelength excitation light and small for long-wavelength excitation light.

【0019】

As described above, the optical fiber communication system in which the optical SNR spectrum is flattened can be obtained by the bidirectional excitation or unidirectional excitation configuration of the present invention.

【0020】

[Example]

Next, examples of each embodiment of the optical fiber communication system according to the present invention described above will be described as a first embodiment in the case of bidirectional excitation and a second embodiment in the case of unidirectional excitation.

【0021】

[First Example] FIG. 9 shows the configuration of the first embodiment of the present invention. In the case of bidirectional excitation, 80 km of dispersion shift fiber (DSF) is used as the transmission fiber 101,300a, and EDFA is used as the centralized optical amplifier 200a. The excitation light sources 102 and 104 of the Raman amplifier 100a are a plurality of semiconductor laser diodes (LDs), and the excitation light wavelengths are 1.51, 1.49 μm for the backward excitation light source 102 and 1.45, 1.43 μm for the forward excitation light source 104.

【0022】

The gain spectrum obtained using this example is shown in FIG. As a flat gain value of the total gain, 20 dB is obtained in the signal light wavelength band of 1.53-1.61 μm. The peak value of Raman gain is about 12 dB, and the peak value of EDFA gain is about 15 dB. The optical SNR spectrum obtained using this example is shown in FIG. As a flat value of optical SNR, 30 dB is obtained in the signal light wavelength band of 1.53-1.61 μm. The excitation light power spectrum in this example is shown in FIG. The excitation light power at 1.51, 1.49 μm is about 100 mW, and the excitation light power at 1.45, 1.43 μm is about 30 mW. As described above, according to this example, a flat optical SNR spectrum is obtained in the signal light wavelength band of 1.53-1.61 μm.

【0023】

[Second Example] FIG. 13 shows the configuration of the second embodiment of the present invention. In the case of unidirectional (posterior) excitation, 80 km dispersion shift fiber (DSF) is used as the transmission fiber 101,300b, and EDFA is used as the centralized optical amplifier 200b. The excitation light source 102b of the Raman amplifier 100b is a plurality of semiconductor laser diodes (LDs), and the excitation light wavelengths are 1.51, 1.49, 1.45, 1.43 μm.

【0024】

The gain spectrum obtained using this example is shown in FIG. As a flat gain value of the total gain, 20 dB is obtained in the signal light wavelength band of 1.53-1.61 μm. The peak value of Raman gain is about 12 dB, and the peak value of EDFA gain is about 8 dB. The optical SNR spectrum obtained using this example is the same as in FIG. As a flat value of optical SNR, 30 dB is obtained in the signal light wavelength band of 1.53-1.61 μm. The excitation light power spectrum in this example is shown in FIG. The excitation light power at 1.51, 1.49 μm is about 20 mW, and the excitation light power at 1.45, 1.43 μm is about 200 mW. As described above, according to this example, a flat optical SNR spectrum is obtained in the signal light wavelength band of 1.53-1.61 μm.

【0025】

As described above, as described in Examples 1 and 2, according to the present invention, there is an effect that a flat optical SNR spectrum can be obtained.

【0026】

[Effect of the invention]

As described above, according to the present invention, the optical SNR has the effect of reducing the wavelength dependence and obtaining a flat optical SNR spectrum.

[Simple explanation of drawings]

[Figure 1]

The figure which shows the basic structure (in the case of bidirectional excitation) of this invention. [Figure 2]

The figure which shows the gain spectrum characteristic (in the case of bidirectional excitation) of this invention. [Fig. 3]

The figure which shows the optical SNR spectral characteristic (in the case of bidirectional excitation) of this invention. [Fig. 4]

The figure which shows the excitation light power spectrum of the prior art [Fig. 5]

The figure which shows the excitation light power spectrum (in the case of bidirectional excitation) of this invention. [Fig. 6]

The figure which shows the basic structure (in the case of unidirectional excitation) of this invention. [Fig. 7]

The figure which shows the gain spectrum characteristic (in the case of unidirectional excitation) of this invention. [Fig. 8]

The figure which shows the excitation light power spectrum (in the case of one-way excitation) of this invention. [Fig. 9]

The figure which shows the structure of 1st Example of this invention [Fig. 10]

The figure which shows the gain spectrum of 1st Example of this invention [Fig. 11]

The figure which shows the optical SNR spectrum of 1st Example of this invention [Fig. 12]

The figure which shows the excitation light power spectrum of the 1st Example of this invention [Fig. 13]

The figure which shows the structure of the 2nd Example of this invention [Fig. 14]

The figure which shows the gain spectrum of the 2nd Example of this invention [Fig. 15]

The figure which shows the excitation light power spectrum of the 2nd Example of this invention [Fig. 16]

Diagram showing the basic configuration of the prior art [Fig. 17]

The figure which shows the gain spectrum characteristic of the prior art [Fig. 18]

The figure which shows the optical SNR spectrum characteristic of the prior art [Explanation of symbols]

100,100a, 100b Raman amplifier 101,300,300a, 300b transmission fiber 102,102b,104 Excitation light source 103,105 combiner 200,200a, 200b Centralized optical amplifier