JP4752905B2 - Wavelength conversion device and wavelength conversion method - Google Patents

Description

  The present invention relates to a wavelength conversion device and a wavelength conversion method, and more particularly to all-optical wavelength conversion used in an optical communication system.

  A technique for performing signal processing as it is without converting it into an electrical signal, that is, performing all-optical signal processing, is important in an optical communication system.

  A conventional differential phase modulation (DPSK) signal regenerator will be described with reference to FIG. 9 (see, for example, Non-Patent Document 1).

  The DPSK signal input to the DPSK signal regenerator 100 is branched into two and one is sent to the delay interferometer 105 and the other is sent to the clock regenerator 180.

  The delay interferometer 105 converts the DPSK signal into an intensity modulation (OOK: On Off Keying) signal. The OOK signal generated by the delay interferometer 105 is sent to the all-optical wavelength converter 110.

  The all-optical wavelength converter 110 performs wavelength conversion and stabilization of the amplitude of the optical signal. The wavelength-converted OOK signal wavelength-converted by the all-optical wavelength converter 110 is sent to the phase modulator 190.

  On the other hand, the clock regenerator 180 extracts a clock from the DPSK signal and generates an optical clock pulse signal. This optical clock pulse signal is sent to the phase modulator 190.

  The phase modulator 190 includes, for example, a dispersion flat fiber (DFF) as a highly nonlinear fiber, and the wavelength conversion OOK signal and the optical clock pulse signal are input to the dispersion flat fiber. A phase modulation pattern that matches the intensity modulation pattern of the wavelength conversion OOK signal is superimposed on the optical clock pulse signal by cross phase modulation (XPM) that occurs during propagation through the dispersion flat fiber. As a result, the phase modulator 190 outputs a wavelength-converted DPSK signal.

  Here, the all-optical wavelength converter 110 includes an optical amplifier 142, a dispersion flat fiber (DFF) 146 as a highly nonlinear fiber, and an optical bandpass filter 148. The configuration and operation of the all-optical wavelength converter 110 will be described with reference to FIGS.

  FIG. 10 is a schematic diagram showing the configuration of the all-optical wavelength converter. 11 and 12 are diagrams showing wavelength conversion in the all-optical wavelength converter.

  The optical amplifier 142 amplifies the input OOK signal (indicated by an arrow S141 in FIG. 10) to generate an amplified signal (indicated by an arrow S143 in FIG. 10) (FIG. 11A). The dispersion flat fiber 146 widens the wavelength spectrum width of the amplified signal S143 and generates a DFF signal (indicated by an arrow S147 in FIG. 10). The optical bandpass filter 148 has a wavelength band with a center wavelength different from the center wavelength of the input OOK signal S141 (FIG. 11B). Therefore, a converted OOK signal (indicated by an arrow S149 in FIG. 10) that is an output of the optical bandpass filter 148 is converted into an OOK signal having a wavelength different from the input OOK signal S141 by the wavelength shift amount Δλ. (FIG. 11C).

  With reference to FIGS. 12A and 12B, the relationship between the signal intensity of the amplified signal S143 and the wavelength spectrum width of the DFF signal S147 will be described.

  In FIG. 12A, it is assumed that the DFF signal indicated by II in FIG. 12B is obtained by self-phase modulation in the dispersion flat fiber 146 with respect to the amplified signal indicated by II. Here, when the signal intensity of the amplified signal is increased (indicated by I in FIG. 12A), the wavelength spectrum width of the DFF signal becomes wider (indicated by I in FIG. 12B). On the other hand, when the signal intensity of the amplified signal is reduced (indicated by III in FIG. 12A), the wavelength spectrum width of the DFF signal becomes narrow (indicated by III in FIG. 12B).

  Also, with the dispersion flat fiber 146, a flat wavelength spectrum can be obtained as shown in FIG. If this is used, the intensity of the DFF signal becomes substantially constant even if there is fluctuation in the intensity of the input signal, so that the influence of the fluctuation in intensity of the input signal can be suppressed and the noise component can be removed.

  FIG. 12C shows a time waveform of the amplified signal. FIG. 12D shows a time waveform of the wavelength conversion OOK signal S149 that is the output of the wavelength converter. The noise component indicated by IV in FIG. 12C is not included in the time waveform of the wavelength conversion OOK signal S149 (FIG. 12D).

Due to such characteristics, the all-optical wavelength converter acts as an identification circuit in addition to the wavelength converter.
Masayuki Matsumoto "3R regeneration of DPSK signal using nonlinear effect of fiber" 2006 IEICE General Conference, B-10-22

  However, when wavelength conversion is performed using a dispersion flat fiber on a high-speed optical signal having a data rate of 40 Gbps or more, the waveform shaping function tends to be significantly impaired if the wavelength conversion amount is increased.

  For this reason, in the DPSK signal regenerator disclosed in Non-Patent Document 1 described above, wavelength converters are connected in multiple stages, and each wavelength converter adjusts the wavelength conversion amount so that the waveform shaping function does not deteriorate. Yes. Specifically, in order to realize wavelength conversion of 10 nm, five wavelength converters are connected, and the wavelength shift amount in each wavelength converter is set to 2 nm.

  For this reason, it is difficult to reduce the size of the DPSK signal reproducing apparatus, and it is disadvantageous in terms of economy.

  Further, when the data rate increases, it is necessary to narrow the width of the optical pulse in proportion to the transmission rate. In this case, it is necessary to set the dispersion value of the dispersion flat fiber to be small. The appropriate dispersion value required for the dispersion flat fiber is proportional to the square of the pulse width, that is, inversely proportional to the square of the data rate. For this reason, when the data rate is increased from 40 Gbps to 160 Gbps by four times, the dispersion value required for the dispersion flat fiber becomes 1/16. For example, the dispersion value of -0.03 ps / nm / km is extremely small with respect to the dispersion value of -0.5 ps / nm / km of the fiber used in Non-Patent Document 1, for example. This means that it is difficult to manufacture a dispersion flat fiber having a small absolute value of the dispersion value.

  Then, when the inventor who concerns this application did earnestly research, the direction of the wavelength shift in a 1st wavelength converter and the direction of the wavelength shift in a 2nd wavelength converter was used using the wavelength converter of 2 steps | paragraphs. And a wavelength conversion function having a wavelength shaping effect can be realized by making the magnitude of the wavelength shift in the second wavelength converter larger than the wavelength shift in the first wavelength converter. I found it. Further, it has been found that the second wavelength converter can be made free of an optical amplifier by appropriately selecting a nonlinear constant of a dispersion flat fiber used for wavelength conversion.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a wavelength conversion device that achieves a wavelength conversion function having a wavelength shaping effect with a simple configuration and is downsized. In addition, an object of the present invention is to provide a wavelength conversion method executed by this wavelength conversion device.

  In order to achieve the above-described object, a wavelength conversion device according to the present invention is a wavelength conversion device that applies a wavelength shift of a wavelength shift amount Δλ to input light, and includes a first wavelength converter and a second wavelength converter. And is configured.

  The first wavelength converter includes an optical amplifier, a first dispersion flat fiber, and a first wavelength filter, and the first wavelength shift amount Δλ1 is set with respect to the center wavelength of the first wavelength converted light with respect to the center wavelength of the input light. Only change. Here, the optical amplifier amplifies the input light to generate amplified light, the first dispersion flat fiber widens the wavelength spectrum width of the amplified light to generate first fiber output light, and the first wavelength filter Transmits the predetermined wavelength band of the first fiber output light to generate the first wavelength converted light.

  The second wavelength converter is an optical amplifier-free wavelength converter having a second dispersion flat fiber and a second wavelength filter, and changes the center wavelength of the second wavelength converted light to the center wavelength of the first wavelength converted light. On the other hand, it is changed by the second wavelength shift amount Δλ2. Here, the second dispersion flat fiber broadens the wavelength spectrum width of the first wavelength converted light to generate the second fiber output light, and the second wavelength filter has a predetermined wavelength band of the second fiber output light. The second wavelength converted light is generated by transmission.

  The first wavelength shift amount Δλ1 and the second wavelength shift amount Δλ2 are set to satisfy Δλ1 + Δλ2 = Δλ, Δλ1 × Δλ2 <0, and | Δλ1 | <| Δλ2 |.

  According to a preferred embodiment of the wavelength conversion device of the present invention, the second wavelength converter may include a variable optical attenuator. The variable optical attenuator attenuates the light intensity of the first wavelength converted light and then sends it to the second dispersion flat fiber.

  The wavelength conversion device of the present invention preferably further includes wavelength filters on the input side and output side of the optical amplifier.

  In order to achieve the above-described object, the wavelength conversion method of the present invention includes an optical amplifier, a first dispersion flat fiber, and a first wavelength filter, and is first with respect to the center wavelength of input light. The first wavelength converter that generates the first wavelength converted light that is changed by the wavelength shift amount Δλ1, the second dispersion flat fiber, and the second wavelength filter are included, and the center wavelength of the first wavelength converted light is set. On the other hand, in a wavelength converter comprising a second wavelength converter that does not contain an optical amplifier and generates a second wavelength converted light that is changed by a second wavelength shift amount Δλ2, the wavelength shift amount Δλ A wavelength conversion method for giving a wavelength shift, comprising the following steps.

  First, the input light is amplified by an optical amplifier to generate amplified light. Next, with the first dispersion flat fiber, the wavelength spectrum width of the amplified light is widened to generate the first fiber output light. Next, the first wavelength filter transmits the predetermined wavelength band of the first fiber output light to generate the first wavelength converted light. Next, with the second dispersion flat fiber, the wavelength spectrum width of the first wavelength converted light is widened to generate the second fiber output light. Next, the second wavelength filter transmits the predetermined wavelength band of the second fiber output light to generate the second wavelength converted light.

  At this time, the first wavelength shift amount Δλ1 and the second wavelength shift amount Δλ2 are set so as to satisfy Δλ1 + Δλ2 = Δλ, Δλ1 × Δλ2 <0, and | Δλ1 | <| Δλ2 |.

  According to a preferred embodiment of the wavelength conversion method of the present invention, the second wavelength converter includes a variable optical attenuator, and the second dispersion flat fiber is a wavelength spectrum of the first wavelength converted light attenuated in the variable optical attenuator. It is preferable to generate the second fiber output light with a wider width.

  According to the conversion apparatus and the wavelength conversion method of the present invention, the first wavelength shift amount Δλ1 in the first wavelength converter and the second wavelength shift amount Δλ2 in the second wavelength converter are expressed as Δλ1 × Δλ2 <0 and | Δλ1 | < It is set to satisfy | Δλ2 |.

  With this setting, the second fiber output light has a waveform with excellent flatness in a wavelength region opposite to the wavelength shift direction in the first wavelength conversion, and the second wavelength filter has excellent flatness. Since the region is transmitted, wavelength-converted light with excellent quality can be obtained.

  In addition, since the waveform has excellent flatness in a wavelength region opposite to the wavelength shift direction in the first wavelength conversion, the second wavelength shift amount Δλ2 can be increased. As a result, for example, a wavelength shift of 10 nm can be performed by two-stage wavelength conversion as compared with the conventional five-stage wavelength conversion, and the apparatus size can be reduced and power saving can be achieved.

  In addition, since the second wavelength converter is not included in the optical amplifier, two-stage wavelength conversion is performed using one optical amplifier. Here, an erbium-doped fiber amplifier (EDFA), which is a general optical amplifier, includes one or more pump light sources and their drive circuits, one or more isolators, and a gain medium. It is composed of a 10 m erbium-doped optical fiber or the like. For this reason, there is a limit to miniaturization of the optical amplifier. Therefore, further miniaturization and power saving of the wavelength conversion device can be achieved by not including the optical amplifier in the second wavelength converter.

  Also, a variable optical attenuator is provided in the second wavelength converter, and the second dispersion flat fiber generates the second fiber output light by expanding the wavelength spectrum width of the first wavelength converted light attenuated in the variable optical attenuator. According to the configuration, even when the nonlinear constant of the second dispersion flat fiber is not optimal with respect to the light intensity of the first wavelength converted light, the light intensity when being input to the second dispersion flat fiber is reduced. It can be adjusted to the optimum value.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the shape, size, and arrangement relationship of each component are merely schematically shown to the extent that the present invention can be understood. In the following, a preferred configuration example of the present invention will be described. However, the material and numerical conditions of each component are merely preferred examples. Therefore, the present invention is not limited to the following embodiments, and many changes or modifications that can achieve the effects of the present invention can be made without departing from the scope of the configuration of the present invention.

(Principle of two-step wavelength conversion)
The principle of two-stage wavelength conversion will be described with reference to FIG. FIG. 1 is a schematic diagram for explaining the principle of wavelength conversion in two stages.

  Here, the input light (indicated by an arrow S11 in the figure) to the wavelength conversion device 10 is an RZ (Return to Zero) signal having a transmission rate of 160 Gbps and a pulse width of 2.5 ps. And

  The wavelength conversion device 10 that performs two-stage wavelength conversion includes a first wavelength converter 40 and a second wavelength converter 60. In addition, the wavelength conversion device 10 includes a first front wavelength filter (OBF1: Optical Band-pass Filter 1) 20 on the input side of the first wavelength converter 40. This wavelength converter 10 shifts the wavelength of the total wavelength shift amount Δλ with respect to the input light.

  The first wavelength converter 40 includes a first optical amplifier (P1) 42, a second previous-stage wavelength filter (OBF2) 44, a first dispersion flat fiber (DFF1) 46, and a first wavelength filter (OBF3) 48. .

  The second wavelength converter 60 includes a second optical amplifier (P2) 62, a second dispersion flat fiber (DFF2) 66, and a second wavelength filter (OBF4) 68.

  The first pre-stage wavelength filter 20 and the second pre-stage wavelength filter 44 are provided at the input end and the output end of the first optical amplifier 42, respectively, and remove spontaneous emission (ASE) noise contained in the input light S11.

  Here, the first pre-stage wavelength filter 20 is a second-order super Gaussian filter having a transmission bandwidth (BW) of 3 nm. The m-th super Gaussian shape is represented by a function of f (t) = exp {−t ^ (2m)}.

  The second pre-stage wavelength filter 44 is a Gaussian filter having a transmission bandwidth (BW) of 3 nm.

  The first optical amplifier 42 amplifies the input light (indicated by an arrow S21 in the figure) input to the first wavelength converter 40 via the first pre-stage wavelength filter 20 to a desired light intensity and performs first amplification. Light (indicated by arrow S43 in the figure) is generated. The ASE noise added at the time of amplification by the first optical amplifier 42 is removed by the second pre-stage wavelength filter 44.

  The first dispersion flat fiber (DFF1) 46 has a wavelength spectrum width of the first amplified light (indicated by an arrow S45 in the drawing) transmitted through the second pre-stage wavelength filter 44 due to the self-phase modulation (SPM) effect. The first fiber output light (indicated by an arrow S47 in the figure) is generated by spreading.

  The first wavelength filter 48 transmits a predetermined wavelength band of the first fiber output light S47 to generate first wavelength converted light (indicated by an arrow S49 in the figure). Here, the first wavelength filter 48 is a Gaussian filter having a transmission bandwidth (BW) of 3 nm. Further, the center wavelength λ1 of the transmission bandwidth (BW) is changed by the first wavelength shift amount Δλ1 (= λ1-λ0) with respect to the center wavelength λ0 of the input light.

The wavelength spectrum in the first wavelength converter 40 will be described with reference to FIG. FIG. 2 is a diagram illustrating a calculation result of the wavelength spectrum in the first wavelength converter 40. Here, the first dispersion flat fiber is a dispersion flat fiber having a length of 1 km, a dispersion of −0.15 ps / nm / km, and a nonlinear constant of 10 km ⁻¹ W ⁻¹ , and the output power of the first optical amplifier 42 is 23 dBm. Yes. In FIG. 2, the horizontal axis indicates the relative wavelength (nm) based on the center wavelength λ0 of the input light S21 input to the first wavelength converter 40, and the vertical axis indicates the light intensity (dBm). It shows.

  The first fiber output light S47, which is the output of the first dispersion flat fiber 46, has a wider wavelength spectrum width than the input light S21. Note that the center wavelength of the first fiber output light S47 substantially coincides with the input light.

  Here, the first wavelength shift amount Δλ1 is set to 1 nm, and the wavelength is shifted to the long wavelength side with respect to the center wavelength λ0 of the input light S21. That is, the center wavelength λ1 of the first wavelength filter 48 (first wavelength converted light S49) is given by λ1 = λ0 + 1.

  FIG. 3 is a diagram showing eye patterns of the input light S21 and the first wavelength converted light S49. FIG. 3A shows the eye pattern of the input light S21, and FIG. 3B shows the eye pattern of the first wavelength converted light S49.

  Comparing FIG. 3A and FIG. 3B, the first wavelength converted light S49 shown in FIG. 3B has an asymmetric shape as compared to the input light S21 shown in FIG. The pulse width is narrow.

  Due to the narrowing of the pulse width, the second wavelength converter 60 can obtain more efficient and high-quality wavelength-converted light. For example, when the data rate is 160 Gbps, when the pulse width of the input light is 2 to 3 ps, the pulse width of the first wavelength converted light S49 is set to 1 to 1.5 ps.

  The second optical amplifier 62 amplifies the first wavelength converted light S49 input to the second wavelength converter 60 to a desired light intensity to generate second amplified light (indicated by an arrow S63 in FIG. 1). To do. The second dispersion flat fiber 66 generates the second fiber output light (indicated by an arrow S67 in FIG. 1) by expanding the wavelength spectrum width of the second amplified light S63 by the self phase modulation (SPM) effect.

  The second wavelength filter 68 transmits a predetermined wavelength band of the second fiber output light S67 to generate second wavelength converted light (indicated by an arrow S69 in FIG. 1). Here, the second wavelength filter 68 is a Gaussian filter having a transmission bandwidth (BW) of 1.3 nm.

  Further, the center wavelength λ2 of the transmission bandwidth (BW) is changed by the second wavelength shift amount Δλ2 (= λ2-λ1) with respect to the center wavelength λ1 of the first wavelength converted light S49.

  This wavelength conversion device 10 realizes a wavelength shift corresponding to the total wavelength shift amount Δλ by two-stage wavelength conversion of the first wavelength converter 40 and the second wavelength converter 60. That is, Δλ1 + Δλ2 = Δλ.

  Further, one of the first wavelength shift amount Δλ1 and the second wavelength shift amount Δλ2 is set to be positive, and the other is set to be negative so as to satisfy Δλ1 × Δλ2 <0. In this embodiment, the first wavelength shift amount Δλ1 is positive (Δλ1> 0), that is, the wavelength shift toward the long wavelength side. Therefore, the second wavelength shift amount Δλ2 is negative (Δλ2 <0), that is, a wavelength shift toward the short wavelength side. Further, the magnitude (| Δλ2 |) of the wavelength shift in the second wavelength converter 60 is made larger than the magnitude (| Δλ1 |) of the wavelength shift in the first wavelength converter (| Δλ1 | <| Δλ2 |).

  The wavelength spectrum in the second wavelength converter 60 will be described with reference to FIG. FIG. 4 is a diagram illustrating a calculation result of the wavelength spectrum in the second wavelength converter 60. Here, the second dispersion flat fiber 66 has the same configuration as the first dispersion flat fiber 46, and the output power of the second optical amplifier 62 is 26 dBm. In FIG. 4, the horizontal axis indicates the relative wavelength (nm) with reference to the center wavelength λ0 of the input light S21 input to the first wavelength converter 40, and the vertical axis indicates the light intensity (dBm). It shows. Here, the second wavelength filter has a Gaussian shape with a bandwidth of 1.3 nm so that the pulse width of the input 160 Gbps and the pulse width of the second wavelength converted light S69 are substantially equal.

  The second fiber output light S67, which is the output of the second dispersion flat fiber 66, has a wider wavelength spectrum width than the first wavelength converted light S49. Here, the spectral shape of the second fiber output light S67 is asymmetric reflecting the asymmetry of the input first wavelength converted light S49. Looking at the wavelength spectrum of the second fiber output light S67, in the region where the relative wavelength is negative, that is, in the wavelength region (short wavelength side) opposite to the wavelength shift direction (long wavelength side) in the first wavelength converter 40. It can be seen that the waveform is very flat. In the spectrum shown in FIG. 4, the fluctuation of the intensity (dBm) is large on the long wavelength side (region where the relative wavelength is positive). On the other hand, on the short wavelength side (region where the relative wavelength is negative), the fluctuation in intensity is small, and at least up to a relative wavelength of about −10 nm is a flat shape.

  This indicates that the second wavelength converted light S69 having excellent quality can be obtained by setting the center wavelength λ2 of the second wavelength filter 68 to satisfy the condition of Δλ1 × Δλ2 <0. . It can also be seen that the wavelength conversion can be performed efficiently because the second wavelength shift amount Δλ2 can be made larger than the first wavelength shift amount Δλ1.

  That is, the wavelength shift of Δλ = Δλ1 + Δλ2 = −9 nm is possible as a whole by two-step wavelength conversion of Δλ1 = 1 nm and Δλ2 = −10 nm.

  FIG. 5 is a diagram showing eye patterns of the first wavelength converted light and the second wavelength converted light. 5A shows the eye pattern of the first wavelength converted light S49, and FIG. 5B shows the eye pattern of the second wavelength converted light S69.

  No waveform deterioration is observed in the second wavelength converted light S69, and the second wavelength converted light S69 shows a very good eye opening. As a result, when the data rate is 160 Gbps, an excellent waveform shaping effect is exhibited even if the dispersion value of the dispersion flat fiber is about −0.15 ps.

  In general, the degree of the nonlinear optical effect in the dispersion flat fiber (DFF) is determined based on the length L of the DFF, the nonlinear constant γ, and the input optical signal unless the influence of propagation loss and dispersion of the fiber is taken into consideration. Normalized by the product of peak power P.

For example, when the first and second dispersion flat fibers have a length of 1 km, a dispersion of −0.15 ps / nm / km, and a nonlinear constant of 10 km ⁻¹ W ⁻¹ , the wavelength shift Δλ 1 in the first wavelength converter 40. Is set to 1 nm, the light intensity of the input light to the first dispersion flat fiber 46 is set to 23 dBm. Further, in order to set the wavelength shift Δλ2 in the second wavelength converter 60 to −10 nm, the light intensity of the input light to the second dispersion flat fiber 66 is set to 26 dBm.

  In order to set the light intensities of the light input to the first and second dispersion flat fibers 46 and 66 to 23 dBm and 26 dBm, respectively, in the wavelength converter shown in FIG. 1, the first and second dispersion flat fibers 46 and A first optical amplifier 42 and a second optical amplifier 62 are provided in front of 66.

(Embodiment)
With reference to FIG. 6, the wavelength converter of this invention is demonstrated. FIG. 6 is a schematic diagram for explaining an embodiment of the wavelength conversion device of the present invention.

  An erbium-doped optical fiber amplifier (EDFA) generally used as an optical amplifier is composed of one or more pumping light sources and their drive circuits, one or more isolators, a gain medium such as an erbium-doped optical fiber having a length of several tens of meters. Composed. Since there is a limit to downsizing the optical amplifier, it is effective to reduce the number of optical amplifiers provided in the wavelength conversion device in order to reduce the size of the wavelength conversion device.

  Therefore, in the conversion wavelength device of this embodiment, the second wavelength converter is not included in the optical amplifier.

  The wavelength conversion device 12 of this embodiment includes a first wavelength converter 40 and a second wavelength converter 80. Further, the wavelength converter 12 includes a first pre-stage wavelength filter (OBF1) 20 on the input side of the first wavelength converter 40. This wavelength converter 12 shifts the wavelength of the total wavelength shift amount Δλ with respect to the input light.

  Here, it is assumed that the input light (indicated by the arrow S11 in the figure) to the wavelength converter 12 is an RZ signal having a transmission speed of 160 Gbps and a pulse width of 2.5 ps.

  The first wavelength converter 40 includes a first optical amplifier (hereinafter simply referred to as an optical amplifier) 42, a second front-stage wavelength filter (OBF2) 44, a first dispersion flat fiber (DFF1) 46, and a first wavelength filter (OBF3). 48).

  The second wavelength converter 80 includes a variable optical attenuator (VOA) 82, a second dispersion flat fiber (DFF2) 86, and a second wavelength filter (OBF4) 88.

  The first pre-stage wavelength filter 20 and the second pre-stage wavelength filter 44 are provided at the input end and the output end of the optical amplifier 42, respectively, and remove spontaneous emission (ASE) noise contained in the input light S11.

  Here, the first pre-stage wavelength filter 20 is a secondary super Gaussian filter having a transmission bandwidth (BW) of 3 nm. The second pre-stage wavelength filter 44 is a Gaussian filter having a transmission bandwidth (BW) of 3 nm.

  The optical amplifier 42 amplifies the input light (indicated by arrow S21 in the figure) input to the first wavelength converter 40 through the first pre-stage wavelength filter 20 to a desired light intensity, and the first amplified light ( In the figure, it is indicated by an arrow S43). The ASE noise added at the time of amplification by the optical amplifier 42 is removed by the second pre-stage wavelength filter 44.

  The first dispersion flat fiber (DFF1) 46 has a wavelength spectrum width of the first amplified light (indicated by an arrow S45 in the drawing) transmitted through the second pre-stage wavelength filter 44 due to the self-phase modulation (SPM) effect. The first fiber output light (indicated by an arrow S47 in the figure) is generated by spreading.

  The first wavelength filter 48 transmits a predetermined wavelength band of the first fiber output light S47 to generate first wavelength converted light (indicated by an arrow S49 in the figure). Here, the first wavelength filter 48 is a Gaussian filter having a transmission bandwidth (BW) of 3 nm. Further, the center wavelength λ1 of the transmission bandwidth (BW) is changed by the first wavelength shift amount Δλ1 (= λ1-λ0) with respect to the center wavelength λ0 of the input light.

  Here, the first wavelength shift amount Δλ1 is set to 1 nm, and the wavelength is shifted to the long wavelength side with respect to the center wavelength λ0 of the input light S21. That is, the center wavelength λ1 of the first wavelength filter 48 (first wavelength converted light S49) is given by λ1 = λ0 + 1.

  A variable optical attenuator (VOA) 82 attenuates the light intensity of the first wavelength converted light to an intensity suitable for the nonlinear optical effect in the second dispersion flat fiber, thereby changing the variable attenuated light (in FIG. 6). , And is sent to the second dispersion flat fiber 86. If there is no need to attenuate the light intensity of the first wavelength converted light, the attenuation amount in the variable optical attenuator 82 may be zero. Further, the variable optical attenuator 82 may not be provided.

  The second dispersion flat fiber 86 generates the second fiber output light (indicated by an arrow S87 in FIG. 6) by expanding the wavelength spectrum width of the variable attenuation light S83 due to the self-phase modulation (SPM) effect.

  The second wavelength filter 88 transmits a predetermined wavelength band of the second fiber output light S87 to generate second wavelength converted light (indicated by an arrow S89 in FIG. 6). Here, the second wavelength filter 88 is a Gaussian filter having a transmission bandwidth (BW) of 1.3 nm.

  Further, the center wavelength λ2 of the transmission bandwidth (BW) is changed by the second wavelength shift amount Δλ2 (= λ2-λ1) with respect to the center wavelength λ1 of the first wavelength converted light S49.

  This wavelength converter 12 realizes a wavelength shift corresponding to the total wavelength shift amount Δλ by two-stage wavelength conversion of the first wavelength converter 40 and the second wavelength converter 80. That is, Δλ1 + Δλ2 = Δλ.

  Further, one of the first wavelength shift amount Δλ1 and the second wavelength shift amount Δλ2 is set to be positive, and the other is set to be negative so as to satisfy Δλ1 × Δλ2 <0. In this embodiment, the first wavelength shift amount Δλ1 is positive (Δλ1> 0), that is, the wavelength shift toward the long wavelength side. Therefore, the second wavelength shift amount Δλ2 is negative (Δλ2 <0), that is, a wavelength shift toward the short wavelength side. Further, the wavelength shift magnitude (| Δλ2 |) in the second wavelength converter 80 is set larger than the wavelength shift magnitude (| Δλ1 |) in the first wavelength converter 40 (| Δλ1 | <| Δλ2 |).

  That is, as a whole, a wavelength shift of Δλ = Δλ1 + Δλ2 = −9 nm is possible by two-stage wavelength change of Δλ1 = 1 nm and Δλ2 = −10 nm.

  As described above, according to the wavelength conversion device of this embodiment, the first wavelength shift amount Δλ1 in the first wavelength converter and the second wavelength shift amount Δλ2 in the second wavelength converter are expressed as Δλ1 × Δλ2 <0 and It is set so as to satisfy | Δλ1 | <| Δλ2 |.

  With this setting, the second fiber output light has a waveform with excellent flatness in a wavelength region opposite to the wavelength shift direction in the first wavelength conversion, and the second wavelength filter has excellent flatness. Since the region is transmitted, wavelength-converted light with excellent quality can be obtained.

  In addition, since the waveform has excellent flatness in a wavelength region opposite to the wavelength shift direction in the first wavelength conversion, the second wavelength shift amount Δλ2 can be increased. As a result, for example, a wavelength shift of 10 nm can be performed by two-stage wavelength conversion as compared with the conventional five-stage wavelength conversion.

  Furthermore, since the two-stage wavelength conversion is performed using one optical amplifier, the apparatus size can be reduced and the power can be saved.

  The above-described embodiment is merely an example, and the present invention is not limited to this condition. For example, the shape and width of the transmission bands of the first and second pre-stage wavelength filters and the first and second wavelength filters may be arbitrarily set according to the width of the input optical pulse. For the first wavelength shift amount and the second wavelength shift amount, a suitable combination satisfying Δλ1 + Δλ2 <Δλ, Δλ1 × Δλ2 <0 and | Δλ1 | <| Δλ2 | is adopted in accordance with the desired wavelength shift amount Δλ. Just do it.

  The variable optical attenuator 82 has a main body with a length of a rectangular parallelepiped having a longest side length of 5 to 6 cm or less, and a pigtail fiber is attached to the main body as an input / output interface. The The variable optical attenuator is smaller than a general EDFA, and the volume of the variable optical attenuator is considered to be 5% or less of a general EDFA. For this reason, even when the variable optical attenuator is provided in the second wavelength converter, the influence on the device size of the wavelength converter can be ignored.

Example 1
When the first and second dispersion flat fibers 46 and 86 have a length of 1 km, a dispersion of −0.15 ps / nm / km, and a nonlinear constant of 10 km ⁻¹ W ⁻¹ , the wavelength shift in the first wavelength converter 40 In order to set Δλ1 = 1 nm, the optical intensity of the optical signal input to the first dispersion flat fiber 46 may be set to 23 dBm by the optical amplifier 42. On the other hand, in order to set the wavelength shift Δλ2 = −10 nm in the second wavelength converter 80, the light intensity of the input light to the second dispersion flat fiber 86 is required to be 26 dBm. However, when the light intensity of the optical signal input to the first dispersion flat fiber 46 is 23 dBm, the light intensity of the first wavelength converted light S49 is about 17 dBm, which is required as an input to the second dispersion flat fiber. The light intensity is about 9 dB short. That is, the light intensity of the first wavelength converted light S49 is about 1/8 of the required light intensity.

  The degree of the nonlinear optical effect is normalized by the product of the length L, the nonlinear constant γ, and the peak power P0 of the input optical signal.

Therefore, a fiber having a length L of 1 km and a nonlinear constant γ of 80 km ⁻¹ W ⁻¹ that is eight times that of the first dispersion flat fiber 46 is prepared as the second dispersion flat fiber. When light having an intensity of 17 dBm is input to a dispersion flat fiber having a length L of 1 km and a nonlinear constant γ of 80 km ⁻¹ W ⁻¹ , the dispersion flat fiber having a nonlinear constant γ of 10 km ⁻¹ W ⁻¹ is input. The same nonlinear optical effect as when 26 dBm light is input can be obtained.

  FIG. 7A shows an eye pattern of the first wavelength converted light S49, and FIG. 7B shows an eye pattern of the second wavelength converted light S89. At this time, the attenuation amount of the variable optical attenuator 82 is set to zero. As shown in FIG. 7B, no waveform deterioration is observed in the second wavelength converted light S89, and the second wavelength converted light S89 shows a very good eye opening. Thus, when the data rate is 160 Gbps, an excellent waveform shaping effect can be obtained even if the dispersion value of the dispersion flat fiber is about −0.15 ps.

(Example 2)
It may be difficult to optimize the nonlinear constant γ of the second dispersion flat fiber in accordance with the characteristics of the first wavelength converter. In that case, after the optical intensity of the first wavelength converted light is attenuated to a desired intensity by the variable optical attenuator, it is sent to the second dispersion flat fiber.

For example, the second dispersion flat fiber 86 is selected such that the nonlinear constant γ is larger than 80 km ⁻¹ W ⁻¹ , for example, the nonlinear constant γ is 100 km ⁻¹ W ⁻¹ .

  Here, when the configuration of the first wavelength converter 40 is configured in the same manner as in the first embodiment, the light intensity of the first wavelength converted light is about 17 dBm, and a desired nonlinear optical effect can be obtained by the second dispersion flat fiber 86. It becomes about 1 dB larger than the light intensity. Therefore, the variable light attenuator 82 attenuates the light intensity of the first wavelength converted light by about 1 dB and finely adjusts the light intensity to an optimum light intensity.

  As described above, by providing the variable optical attenuator 82 in front of the second dispersion flat fiber 86, even if it is difficult to optimize the nonlinear constant of the second dispersion flat fiber 86, the second dispersion The light intensity input to the flat fiber 86 can be set optimally.

The degree of the nonlinear optical effect in the dispersion flat fiber is determined by the product of the fiber length L, the nonlinear constant γ, and the peak power P of the input optical signal, ignoring the effects of fiber propagation loss and dispersion. Therefore, when the optical intensity of the input optical signal is the same, the degree of the nonlinear optical effect is normalized by the product of the nonlinear constant γ and the fiber length L. Therefore, when it is difficult to obtain a dispersion flat fiber having a desired nonlinear constant γ, here γ = 100 km ⁻¹ W ⁻¹ , the length L may be increased.

For example, a dispersion flat fiber having a length L of 1 km and a nonlinear constant γ of 100 km ⁻¹ W ^{−1 and} a dispersion flat fiber having a length L of 2 km and a nonlinear constant γ of 50 km ⁻¹ W ⁻¹ are the same. The nonlinear optical effect is shown.

When the length L of the dispersion flat fiber is doubled, the chromatic dispersion D needs to be halved in order to keep the dispersion and nonlinear optical effect interaction (SPM-GVD effect) equal. At this time, the length of the second dispersion flat fiber may be L = 2 km, wavelength dispersion D = −0.075 ps / nm / km, and nonlinear constant γ = 50 km ⁻¹ W ⁻¹ .

  Further, by utilizing the fact that the nonlinear optical effect of the dispersion flat fiber is normalized by the product of the nonlinear constant γ, the length L, and the peak power P, by reducing the length L of the first dispersion flat fiber, The light intensity required for the first wavelength conversion can be increased. For example, if the length L of the first dispersion flat fiber is 0.5 km, the light intensity required for the first wavelength conversion is doubled to approximately 26 dBm. As a result, the light intensity of the first wavelength converted light is increased, and for example, a second dispersion flat fiber having a small nonlinear constant γ can be used. When the length of the first dispersion flat fiber is halved, it is necessary to double the chromatic dispersion D in order to keep the SPM-GVD effect equal.

Therefore, for example, a fiber having a nonlinear constant γ1 = 10 km ⁻¹ W ⁻¹ , a length L1 = 0.375 km, and a dispersion D1 = −0.4 ps / nm / km is selected as the first dispersion flat fiber. Further, as the second dispersion flat fiber, a fiber having a nonlinear constant γ2 = 35 km ⁻¹ W ⁻¹ , a length L2 = 1 km, and a dispersion D2 = −0.15 ps / nm / km is selected.

  The intensity of the optical signal amplified by the optical amplifier and input to the first dispersion flat fiber is 27 dBm, and the attenuation at the variable optical attenuator is 1 dB. The eye pattern at this time is shown in FIG.

  FIG. 8A shows the eye pattern of the first wavelength converted light S49, and FIG. 8B shows the eye pattern of the second wavelength converted light S89. As shown in FIG. 8, no waveform deterioration is observed in the second wavelength converted light S89, and the second wavelength converted light S89 shows a very good eye opening.

It is a schematic diagram for demonstrating the principle of wavelength conversion of two steps. It is a figure which shows the calculation result of the wavelength spectrum in a 1st wavelength converter. It is a figure which shows the eye pattern of input light and 1st wavelength conversion light. It is a figure which shows the calculation result of the wavelength spectrum in a 2nd wavelength converter. It is a figure which shows the eye pattern of 1st wavelength conversion light and 2nd wavelength conversion light. It is a schematic diagram for demonstrating a wavelength converter. It is a figure (1) which shows the eye pattern of the 1st and 2nd wavelength conversion light. It is a figure (2) which shows the eye pattern of the 1st and 2nd wavelength conversion light. It is a schematic diagram for demonstrating the conventional DPSK signal regenerator. It is a schematic diagram which shows the structure of an all-optical wavelength converter. It is a figure (1) which shows wavelength conversion in an all-optical wavelength converter. It is a figure (2) which shows wavelength conversion in an all-optical wavelength converter.

Explanation of symbols

10, 12 Wavelength converter 20 First front wavelength filter (OBF1)
40 First wavelength converter 42 First optical amplifier (P1)
44 Second pre-stage wavelength filter (OBF2)
46 First dispersion flat fiber (DFF1)
48 1st wavelength filter (OBF3)
60, 80 Second wavelength converter 62 Second optical amplifier (P2)
66, 86 Second dispersion flat fiber (DFF2)
68, 88 Second wavelength filter (OBF4)
82 Variable Optical Attenuator (VOA)

Claims (5)

A wavelength conversion device that gives a wavelength shift of a wavelength shift amount Δλ to input light,
An optical amplifier that amplifies the input light to generate amplified light, a first dispersion flat fiber that generates a first fiber output light by expanding a wavelength spectrum width of the amplified light, and a predetermined of the first fiber output light A first wavelength filter that transmits a wavelength band and generates first wavelength converted light; and a center wavelength of the first wavelength converted light is set to a first wavelength shift amount Δλ1 with respect to a center wavelength of the input light. A first wavelength converter that changes only,
A second dispersion flat fiber that generates a second fiber output light by expanding a wavelength spectrum width of the first wavelength converted light; and a second wavelength converted light that transmits a predetermined wavelength band of the second fiber output light. A second wavelength filter to be generated, and changing a center wavelength of the second wavelength converted light by a second wavelength shift amount Δλ2 with respect to a center wavelength of the first wavelength converted light; A second wavelength converter,
The wavelength converter according to claim 1, wherein the first wavelength shift amount Δλ1 and the second wavelength shift amount Δλ2 satisfy Δλ1 + Δλ2 = Δλ, Δλ1 × Δλ2 <0, and | Δλ1 | <| Δλ2 |. The second wavelength converter comprises a variable optical attenuator;
2. The wavelength conversion device according to claim 1, wherein the variable optical attenuator attenuates the light intensity of the first wavelength converted light and then sends the attenuated light to the second dispersion flat fiber. The wavelength conversion apparatus according to claim 1, further comprising a wavelength filter on an input side and an output side of the optical amplifier. A first wavelength that has an optical amplifier, a first dispersion flat fiber, and a first wavelength filter, and generates first wavelength converted light that is changed by a first wavelength shift amount Δλ1 with respect to the center wavelength of the input light. A converter,
An optical amplifier having a second dispersion flat fiber and a second wavelength filter, and generating second wavelength converted light that is changed by a second wavelength shift amount Δλ2 with respect to the center wavelength of the first wavelength converted light In a wavelength conversion device comprising a non-containing second wavelength converter, a wavelength conversion method for giving a wavelength shift of a wavelength shift amount Δλ to input light,
A process of amplifying the input light to generate amplified light in the optical amplifier;
Generating a first fiber output light by expanding the wavelength spectrum width of the amplified light with the first dispersion flat fiber;
A step of generating a first wavelength converted light by transmitting a predetermined wavelength band of the first fiber output light with the first wavelength filter;
Generating a second fiber output light by expanding a wavelength spectrum width of the first wavelength converted light in the second dispersion flat fiber;
A step of transmitting a predetermined wavelength band of the second fiber output light by the second wavelength filter to generate second wavelength converted light,
The wavelength conversion method, wherein the first wavelength shift amount Δλ1 and the second wavelength shift amount Δλ2 satisfy Δλ1 + Δλ2 = Δλ, Δλ1 × Δλ2 <0 and | Δλ1 | <| Δλ2 |. The second wavelength converter comprises a variable optical attenuator;
5. The wavelength conversion method according to claim 4, wherein the second dispersion flat fiber generates a second fiber output light by expanding a wavelength spectrum width of the first wavelength converted light attenuated by the variable optical attenuator. .