JP3753229B2 - High speed wavelength converter - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a high-speed wavelength converter, and is useful when applied to optical systems such as optical communication, optical switching, and optical information processing using wavelength multiplexing.
[0002]
[Prior art]
Usually, the optical transmission system has a hierarchical structure as shown in FIG. In FIG. 13, 1001 to 1008 are end users, 1009 and 1010 are local networks, and 1011 is an upper network that accommodates a plurality of local networks. Generally, in a local network, the transmission band required by each user is about 10 Gb / s.
[0003]
By the way, the optical transmission system has been developed around the 1.55 micron band with the development of an erbium doped optical fiber amplifier (effective band 1530 to 1560 nm: generically referred to as 1.55 micron band). For example, when wavelength multiplexed signal light is assumed, for example, if wavelength multiplexing is performed at intervals of 1 nm, it means that only about 30 wavelengths can be used. That is, a total throughput of 10 Gb / s × 30 = 300 Gb / s can be expected in the local network.
[0004]
By the way, the upper network accommodates a plurality of, for example, four user networks. Even in the upper network, usable wavelengths are not changed from about 30 wavelengths, and in order to avoid congestion, it is necessary to increase the transmission band to 40 Gb / s in the upper network, for example.
[0005]
FIG. 14 shows a 10 Gb / s NRZ (non-return-to-zero) NRZ signal light converted to RZ (return-to-zero) sig- nal signal light and wavelength-converted. An optical transmission system developed earlier in order to expand the transmission band to 40 Gb / s is shown.
[0006]
In FIG. 14, 2001 to 2004 are 10 Gb / s signal lights having four wavelengths of λ1, λ2, λ3, and λ4, 2005 is an input optical fiber, and 2006 is an absorption as a collective cutting circuit (collective gate circuit), for example. Type optical modulators, 2007-2010 are 10 Gb / s signal light cut out by the batch cut-out circuit 2006 and narrowed in pulse width, 2011 is a wavelength rearrangement circuit, 2012-2015 are λ1, by the wavelength rearrangement circuit 2011, 10 Gb / s signal light shifted so that the pulses of λ2, λ3, and λ4 do not overlap, 2016 is a wavelength converter, 2017 is an output optical fiber, and 2018 is 40 Gb / s signal light.
[0007]
In the figure, signal lights 2001 to 2004 have a pulse width of 100 ps and are wavelength-multiplexed and transmitted. This is cut out by a collective cut-out circuit 2006 to obtain signal lights 2007 to 2010 having a pulse width of 25 ps or less. The signal lights 2007 to 2010 are rearranged in time series (shifted in phase) by the wavelength rearrangement circuit 2011 so that the respective pulses do not overlap with each other to become signal lights 2012 to 2015, and the shifted signal lights 2012 to 2015. Is input to the wavelength converter 2016. At this time, different wavelengths are input to the wavelength converter 2016 every other bit, and the wavelength converter 2016 converts all of them to the same wavelength. This enables wavelength conversion to 40 Gb / s · one wavelength signal light 2018.
[0008]
Although only the absorption type optical modulator has been described as the collective cut-out circuit 2006, a so-called gate circuit that can turn on / off the output of signal light, such as an interference type optical modulator, an optical amplifier, an optical switch, or the like. Anything can be used as long as it is.
[0009]
As the wavelength rearrangement circuit 2011, for example, an optical fiber having chromatic dispersion is used. In general, since an optical fiber has a different propagation speed depending on a wavelength, by setting the optical fiber length to an optimum state, each bit can be shifted so as not to overlap as in the signal light 2012-2015. For example, the signal light 2013 may be shifted by 25 ps, the signal light 2014 by 50 ps, and the signal light 2015 by 75 ps with respect to the signal light 2012.
[0010]
[Problems to be solved by the invention]
In general, a wavelength converter has an upper limit on the speed of wavelength conversion operation, and wavelength conversion cannot be performed for signal light exceeding a predetermined bit rate. This is because the operating speed of wavelength conversion is regulated by the carrier lifetime at the time of wavelength conversion.
For this reason, when the number of wavelength-multiplexed signal light further increases and the bit rate of the signal light input to the wavelength converter increases, a problem that wavelength conversion becomes impossible is expected.
[0011]
An object of the present invention is to provide a high-speed wavelength conversion device that can perform wavelength conversion at high speed when the number of wavelength-multiplexed signal lights increases.
[0012]
[Means for Solving the Problems]
  In the configuration of the present invention that solves the above problems, when a plurality of NRZ signal lights having different wavelengths are input in a wavelength-multiplexed state, the signal lights are cut out and converted into RZ signal lights for output. An optical modulator to
  A chromatic dispersion optical fiber having chromatic dispersion characteristics, which transmits a plurality of RZ-format signal lights output from the optical modulator;
  Depending on the wavelength, a plurality of signal lights whose phases are shifted by transmitting the wavelength dispersion type optical fibern (where n is an integer greater than or equal to 2)A sorting means for sorting and outputting to a plurality of sets;
  A plurality of wavelength converters for outputting the same signal light with the same wavelength by wavelength-converting the distributed signal light for each set;
  There is an optical coupler that wavelength-multiplexes each set of signal light output from each wavelength converter and outputs the wavelength-multiplexed signal light.And
  The distributing means is configured to prevent the signal light in each set from overlapping each other and the bit rate of each set to be equal to the wavelength of the signal light of the wavelength multiplexed signal input to the optical modulator. It is a means of distributing so that the bit rate is 1 / n of the total bit rate.It is characterized by that.
[0013]
In the configuration of the invention, the sorting means is an asymmetric Mach-Zehnder type filter or an arrayed waveguide diffraction grating.
[0014]
Further, according to the configuration of the invention, the distribution unit includes a plurality of subsequent stages that distribute the signal light divided into two sets by the first-stage asymmetric Mach-Zehnder filter and the first-stage asymmetric Mach-Zehnder filter. The asymmetric Mach-Zehnder type filter is used.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below in detail with reference to the drawings.
[0016]
[First Embodiment]
FIG. 1 shows a high-speed wavelength conversion device 100 according to a first embodiment of the present invention. As shown in the figure, an input optical fiber 120 is connected to the input end face of the electroabsorption optical modulator 110, and the output end face of the electroabsorption optical modulator 110 and the input end face of the asymmetric Mach-Zehnder filter 130 are They are connected by a wavelength dispersion type optical fiber 140. The two output end faces of the asymmetric Mach-Zehnder filter 130 and the two wavelength converters 150A and 150B are independently connected by optical fibers 160A and 160B. The output end faces of the wavelength converters 150A and 150B and the two input end faces of the optical coupler 170 are independently connected by optical fibers 180A and 180B. An output optical fiber 190 is connected to the output end face of the optical coupler 170.
[0017]
To the electroabsorption optical modulator 110, eight signal lights S1 to S8 are wavelength-multiplexed through the input optical fiber 120 and transmitted as wavelength division multiplexed signal light (WDM: Wavelength Division Multiplexing signal light). come. The signal lights S1 to S8 are NRZ type signal lights having a pulse width of 100 ps as shown in FIG. 2, the phases of the signal lights S1 to S8 are synchronized, and the bit rates of the signal lights S1 to S8 are 10 Gb. / S. The wavelength of the signal light S1 is 1550 nm, the wavelength of the signal light S2 is 1551 nm, the wavelength of the signal light S3 is 1552 nm, the wavelength of the signal light S4 is 1553 nm, the wavelength of the signal light S5 is 1554 nm, the wavelength of the signal light S6 is 1555 nm, The wavelength of the light S7 is 1556 nm, and the wavelength of the signal light S8 is 1557 nm. In FIG. 2, the signal waveforms of the signal light beams S1 to S8 (arrangement of 1s and 0s) are the same for easy understanding, but in reality, they are often different.
[0018]
A sine wave voltage V having a negative potential of 10 GHz is input to the electroabsorption optical modulator 110. This electroabsorption optical modulator 110 is a period in which the voltage value of the sine wave voltage V is smaller than a preset negative voltage value (the voltage value of the sine wave voltage V is a negative potential and its absolute value is a set negative voltage). And has a characteristic of allowing signal light to pass in a period smaller than the absolute value). Therefore, by adjusting the voltage value and phase of the sine wave voltage V, the electroabsorption optical modulator 110 cuts out the signal light S1 to S8 in the NRZ format and sets the pulse width as shown in FIG. 3 to 25 ps. RZ format signal lights S1 to S8 are wavelength-multiplexed and output.
[0019]
The wavelength dispersion type optical fiber 140 is 1 km in length and has a wavelength dispersion characteristic of 12.5 ps / nm / Km. For this reason, the wavelength-division-multiplexed signal lights S1 to S8 having a pulse width of 25 ps are phase-synchronized as shown in FIG. At the output terminal 140, a phase shift occurs as shown in FIG. That is, the signal light S2 is delayed by 12.5 ps with respect to the signal light S1, the signal light S3 is delayed by 12.5 ps with respect to the signal light S2, the signal light S4 is delayed by 12.5 ps with respect to the signal light S3, and the signal light S4 The signal light S5 is delayed by 12.5 ps, the signal light S6 is delayed by 12.5 ps with respect to the signal light S5, the signal light S7 is delayed by 12.5 ps with respect to the signal light S6, and the signal light with respect to the signal light S7. S8 is delayed by 12.5 ps. The signal lights (wavelength multiplexed signal lights) S <b> 1 to S <b> 8 thus shifted in phase are input to the asymmetric Mach-Zehnder filter 130.
[0020]
The asymmetric Mach-Zehnder filter 130 includes an optical coupler 131, branch waveguides 132 a and 132 b, and an optical coupler 133. At this time, the difference in length between the branch waveguide 132a and the branch waveguide 132b (difference in arm length) is set to 0.2 mm. This is because the wavelength difference 2 nm between the signal light S1 and the signal light S3 corresponds to 250 GHz in the frequency difference Δν, and therefore the refractive index of the branching waveguides 132a and 132b is n (n = 3 when an InP semiconductor waveguide is used). ,
This is because the difference in arm length = light speed / (2 × n × Δν) = 0.2 mm.
[0021]
  Since the arm difference is set in this way, a phase change occurs between the signal lights S1 to S8 that have passed through the branching waveguide 132a and the signal lights S1 to S8 that have passed through the branching waveguide 132b. When the coupler 133 multiplexes the optical interference, the signal light S1, S3, S5, S7 is output from the output terminal of the asymmetric Mach-Zehnder filter 130 to which the optical fiber 160A is connected, and the optical fiber 160B. From the output terminal connected to the signal light S2,S4, S6, S8 are output. That is, the signal lights S1 to S8 are distributed into even-numbered signal lights S1, S3, S5, and S7 and odd-numbered signal lights S2, S4, S6, and S8.
[0022]
The signal lights S1, S3, S5 and S7 output from the asymmetric Mach-Zehnder filter 130 and propagating through the optical fiber 160A do not overlap each other as shown in FIG. Similarly, the signal lights S2, S4, S6, and S8 output from the asymmetric Mach-Zehnder filter 130 and propagating through the optical fiber 160B do not overlap each other as shown in FIG.
[0023]
The wavelength converter 150A receives continuous light CW1 having a wavelength of 1551 nm and signal lights S1, S3, S5, and S7. The wavelength converter 150A converts the wavelengths of the signal light S1 (wavelength is 1550 nm), S3 (wavelength is 1552 nm), S5 (wavelength is 1554 nm), and S7 (wavelength is 1556 nm) into the wavelength 1551 nm of the continuous light CW1. Output. FIG. 6A shows the states of the signal lights S1, S3, S5, and S7 whose wavelengths have been converted to 1551 nm.
[0024]
On the other hand, continuous light CW2 having a wavelength of 1550 nm is input to the wavelength converter 150B, and signal light S2, S4, S6, and S8 are input. The wavelength converter 150B converts the wavelengths of the signal light S2 (wavelength is 1551 nm), S4 (wavelength is 1553 nm), S6 (wavelength is 1555 nm), and S8 (wavelength is 1557 nm) into the wavelength 1550 nm of the continuous light CW2. Output. FIG. 6B shows the state of the signal lights S2, S4, S6, and S8 whose wavelength has been converted to 1550 nm.
[0025]
Various types of wavelength converters 150A and 150B can be employed, and specific examples thereof will be described later.
[0026]
The signal lights S1, S3, S5, and S7 whose wavelengths have been converted to 1551 nm propagate through the optical fiber 180A and are input to the optical coupler 170, and the signal lights S2, S4, S6, and S8 whose wavelengths have been converted to 1550 nm are optical signals. The optical signal propagates through the fiber 180B and is input to the optical coupler 170. The optical coupler 170 wavelength-multiplexes the signal lights S1, S3, S5, and S7 having a wavelength of 1551 nm and the signal lights S2, S4, S6, and S8 having a wavelength of 1550 nm. The
[0027]
The wavelength-multiplexed signal lights S1, S3, S5 and S7 (wavelength is 1551 nm) and signal lights S2, S4, S6 and S8 (wavelength is 1550 nm) are output to the output optical fiber 190 and transmitted. At this time, the bit rate of the signal lights S1, S3, S5 and S7 (wavelength is 1551 nm) is 40 Gb / s, and the bit rate of the signal lights S2, S4, S6 and S8 (wavelength is 1550 nm) is 40 Gb / s.
[0028]
As described above, in the first embodiment, the eight signal lights S1 to S8 are divided into the first set of signal lights S1, S3, S5, and S7 and the second set of signal lights S2, S4, and S6. , S8, wavelength conversion of the first set of signal lights S1, S3, S5, and S7 by the wavelength converter 150A, and the second set of signal lights S2, S4, S6, and S8 as wavelengths. Since the wavelength conversion by the converter 150B is performed simultaneously in parallel, wavelength conversion can be performed at high speed. That is, wavelength conversion can be performed at twice the operating speed as compared with wavelength conversion using one wavelength converter. For this reason, even when the number of wavelength-multiplexed signal lights is further increased and the bit rate of the signal light input to the high-speed wavelength conversion device 100 is increased, the wavelength conversion can be reliably performed.
[0029]
[Second Embodiment]
Next, a high-speed wavelength conversion device 100A according to a second embodiment of the present invention will be described with reference to FIG. The same parts as those in the first embodiment are denoted by the same reference numerals, and the description of the overlapping parts is simplified.
[0030]
In the second embodiment, the electroabsorption optical modulator 110 receives NRZ-format signal lights S1 to S16 having a pulse width of 100 ps. The wavelength-multiplexed signal lights S1 to S16 are synchronized, and the wavelengths are shifted by 1 nm. The signal lights S1 to S16 are cut out by the electroabsorption optical modulator 110 into RZ format signal lights S1 to S16 having a pulse width of 12.5 ps.
[0031]
The wavelength dispersion type optical fiber 140 has a length of 1 km and has a wavelength dispersion characteristic of 6.25 ps / nm / km. For this reason, the RZ-format signal lights S1 to S16 having a pulse width of 12.5 ps have a phase shift at the output end of the wavelength dispersion optical fiber 140, and the signal lights S1 to S16 have a phase difference of 12.5 ps.
[0032]
The phase-shifted signal lights S1 to S16 are transmitted by the asymmetric Mach-Zehnder filter 130 to the signal lights S1, S3, S5, S7, S9, S11, S13, S15 and the signal lights S2, S4, S6, S8, S10. , S12, S14, and S16.
[0033]
In the present embodiment, two asymmetric Mach-Zehnder filters 130A and 130B are arranged after the asymmetric Mach-Zehnder filter 130. The difference in arm length between the asymmetric Mach-Zehnder filters 130A and 130B is set to 0.4 mm. For this reason, the signal lights S1, S3, S5, S7, S9, S11, S13, and S15 are converted into the signal lights S1, S5, S9, and S13 and the signal lights S3, S7, S11, and S15 by the asymmetric Mach-Zehnder filter 130A. Sorted. The signal lights S2, S4, S6, S8, S10, S12, S14, and S16 are distributed to the signal lights S2, S6, S10, and S14 and the signal lights S4, S8, S12, and S16 by the asymmetric Mach-Zehnder filter 130B. .
[0034]
A continuous light CW3 having a wavelength of λ1 and signal lights S1, S5, S9, and S13 are input to the wavelength converter 150C. For this reason, the signal lights S1, S5, S9, and S13 are wavelength-converted into signal lights S1, S5, S9, and S13 having a wavelength of λ1.
[0035]
A continuous light CW4 having a wavelength of λ2 and signal lights S3, S7, S11, and S15 are input to the wavelength converter 150D. For this reason, the signal lights S3, S7, S11, and S15 are wavelength-converted into signal lights S3, S7, S11, and S15 having a wavelength of λ2.
[0036]
The wavelength converter 150E receives continuous light CW5 having a wavelength of λ3 and signal lights S2, S6, S10, and S14. For this reason, the signal lights S2, S6, S10, and S14 are wavelength-converted into signal lights S2, S6, S10, and S14 having a wavelength of λ3.
[0037]
The wavelength converter 150F receives continuous light CW6 having a wavelength of λ4 and signal lights S4, S8, S12, and S16. For this reason, the signal lights S4, S8, S12, and S16 are wavelength-converted into signal lights S4, S8, S12, and S16 having a wavelength of λ4.
[0038]
Signal light S1, S5, S9, S13 with wavelength λ1, signal light S3, S7, S11, S15 with wavelength λ2, signal light S2, S6, S10, S14 with wavelength λ3, and signal with wavelength λ4 The lights S4, S8, S12, and S16 are transmitted through the optical fibers 180C, 180D, 180E, and 180F, wavelength-multiplexed by the optical coupler 170A, and output to the output optical fiber 190.
[0039]
In the second embodiment, wavelength conversion can be performed at high speed because the wavelength conversion is performed simultaneously by the four wavelength converters 150C, 150D, 150E, and 150F. In other words, wavelength conversion can be performed at four times the operating speed compared to wavelength conversion using a single wavelength converter.
[0040]
When the number of signal lights input via the input optical fiber 120 further increases, asymmetric Mach-Zehnder type filters are arranged in more stages to increase the number of combinations for distributing the signal light. If wavelength conversion is performed simultaneously, wavelength conversion can be performed at high speed even if the number of wavelength multiplexed signals increases.
[0041]
The signal light distribution means is not limited to an asymmetric Mach-Zehnder filter, and an arrayed waveguide diffraction grating (AWG) or the like can also be used.
[0042]
[Various examples of wavelength converter]
Here, a specific configuration example of the wavelength converter that can be employed as the wavelength converters 150A to 150F will be described below.
[0043]
A wavelength converter 200 illustrated in FIG. 8 is an example of a wavelength converter that can be employed as the wavelength converters 150A to 150F. The wavelength converter 200 is a cross gain modulation (XGM) type wavelength converter, and includes a semiconductor optical amplifier 201 and a filter 202 as main members. In this wavelength converter 200, the pump light Sp having the wavelength λp is input to the semiconductor optical amplifier 201 to keep the semiconductor optical amplifier 201 in a saturated state. At this time, when the signal light S having the wavelength λs is input, the amplification degree of the pump light Sp at the wavelength λp decreases when the intensity of the signal light S is strong. When the signal light S is cut by the filter 202, the converted signal light Sh having a waveform obtained by inverting the waveform of the signal light S and having a wavelength of λp is obtained as an output.
[0044]
A wavelength converter 300 illustrated in FIG. 9 is an example of a wavelength converter that can be employed as the wavelength converters 150A to 150F. This wavelength converter 300 is a cross phase modulation (XPM) type wavelength converter, and is composed mainly of semiconductor optical amplifiers 301 and 302 and optical couplers 303, 304, 305 and 306.
[0045]
The XPM wavelength converter 300 utilizes the fact that the refractive index changes when the light is input to the semiconductor optical amplifiers 301 and 302, and the optical length thereof changes. That is, the pump light Sp having the wavelength λp is input to the two semiconductor optical amplifiers 301 and 302. On the other hand, the signal light S having a wavelength of λs is input only to the semiconductor optical amplifier 301 from the opposite side. At this time, if the light intensity of the signal light S is strong, the refractive index of the semiconductor optical amplifier 301 changes, and the phase of the pump light Sp changes on the semiconductor optical amplifier 301 side. Since the phases of the semiconductor optical amplifier 301 and the semiconductor optical amplifier 302 are different, when the pump light Sp that has passed through the semiconductor optical amplifier 301 and the pump light Sp that has passed through the semiconductor optical amplifier 302 are coupled by an optical coupler 306 at the output end. A phase change appears as an intensity change. Therefore, the converted signal light Sh having the same waveform as that of the signal light S and the wavelength of λp is output at the output end.
[0046]
A wavelength converter 400 illustrated in FIG. 10 is an example of a wavelength converter that can be employed as the wavelength converters 150A to 150F. This wavelength converter 400 has a loop type interference circuit, and is limited to the speed of the carrier change recovery time by canceling out the region limited to the speed of the carrier change recovery time of the phase change. It performs high-speed wavelength conversion without any problems. That is, the conversion signal light of the wavelength conversion element generally has a rise time as high as several ps, whereas the fall time tends to be as slow as several tens ps. This is because the rate is limited by the carrier lifetime. Therefore, the RZ signal is used and a loop type configuration as shown in FIG. 10 is adopted, and the final converted signal light is combined by interfering with the clockwise converted signal light and the counterclockwise converted signal light. By obtaining this, high-speed wavelength conversion is realized. The clockwise signal light and the counterclockwise signal light arrive at the combined portion with a slight time difference (for example, 10 ps) by changing the optical path length. For example, when the clockwise converted signal light arrives first, since the counterclockwise has not yet arrived, the final converted signal light is equal to the clockwise converted signal light and rises at a high speed (several ps). Further, since the counterclockwise converted signal light arrives at the fall, it is possible to cancel the phase in the clockwise direction and the counterclockwise direction (cancellation effect). By this effect, the fall time, which is originally several tens ps, can be accelerated to several ps.
The wavelength converters 400 and 500 shown in FIGS. 10 and 12 have already been filed by the present applicant (Japanese Patent Application No. 2000-286601) as the name of the invention “light control element”.
[0047]
A wavelength converter 400 shown in FIG. 10 includes a phase modulator with a filter 415 (a block surrounded by a broken line in the drawing), a loop interference circuit 413, and a multimode interference coupler 405 as main members. The attached phase adjuster 415 includes semiconductor optical amplifiers 401 and 402 and multimode interference couplers 403 and 404.
[0048]
In this wavelength converter 400, continuous light 407 having a wavelength λj is incident on the multimode interference coupler 405 at the port 412, divided into two by the multimode interference coupler 405, and guided to the loop interference circuit 413. In the loop type interference circuit 413, the loop is divided into clockwise light 409 and counterclockwise light 408, goes around the loop, passes through the phase modulator with filter 415, and is combined again by the multimode interference coupler 405 and is output to the port 412. . In this state, the signal light 406 having the wavelength λi enters the phase modulator 415 with a filter from the port 417.
[0049]
In this example, as a filter function, a multi-mode interference coupler 403, 404 uses a symmetric Mach-Zehnder circuit in which two waveguides (arms) including semiconductor optical amplifiers 401, 402 are connected. In general, in a symmetric Mach-Zehnder circuit, incident light is demultiplexed in the coupler, passes through two waveguides (arms), is multiplexed again by the coupler, and is output to the exit port at the position of the entrance port and the cross. . The filter function of the present embodiment utilizes the above-described property of the Mach-Zehnder circuit.
[0050]
The signal light 406 having the wavelength λi is incident on the multimode interference coupler 403 from the port 417. The incident signal light 406 is divided into two, passes through the semiconductor optical amplifiers 401 and 402, is combined by the multimode interference coupler 404, and exits to the port 414 at a position crossing the incident port 417. That is, the input signal light 406 does not enter the loop interference circuit 413 due to the filter function of the Mach-Zehnder circuit.
[0051]
The converted light, which is continuous light 407 of wavelength λj propagating counterclockwise in the loop, enters the multimode interference coupler 404 from the port 418, passes through the semiconductor optical amplifiers 401 and 402 in two, and passes through the multimode. The signal is combined by the interference coupler 403, guided to the port 416 at the position crossing the incident port 418, and propagates in the loop again. At this time, since there is no component emitted to the port 417, excess loss does not occur.
[0052]
Similarly, the converted light, which is continuous light 407 of wavelength λj that propagates clockwise, enters the multimode interference coupler 403 from the port 416, passes through the semiconductor optical amplifiers 401 and 402 in two parts, and multimode interference. The signal is combined by the coupler 404 and guided to the port 418 at the position crossing the incident port 416 and propagates in the loop again. At this time, since there is no component emitted to the port 414, no excessive loss occurs. In other words, the converted light, which is the continuous light 407 of wavelength λj propagating in the loop, does not in principle generate excessive loss caused by passing through the couplers 403 and 404 for multiplexing the signal light.
[0053]
When the input signal light 406 passes through the semiconductor optical amplifiers 401 and 402, the refractive index in the semiconductor optical amplifiers 401 and 402 changes. On the other hand, the light having the wavelength λj that is guided in the loop is affected by the refractive index change in the semiconductor optical amplifiers 401 and 402, and causes a phase change as shown in FIG. That is, the clockwise light 409 undergoes a steep phase change, then returns to the original phase at a time corresponding to the speed of the carrier change recovery time of the semiconductor optical amplifier, and enters the multimode interference coupler 405. Although the counterclockwise light 408 undergoes the same phase change, the distance propagating through the loop interference circuit is longer than that of the clockwise light.
[0054]
In the multimode interference coupler 405, the time when the phase change of the clockwise and counterclockwise light occurs is shifted by Δτ. Only during this Δτ, as shown in FIG. 11B, the light of wavelength λj is emitted to the port 411 due to the interference effect. That is, the input signal light having the wavelength λi is transferred to the light having the wavelength λj and is output to the port 411.
[0055]
In the wavelength converter 400 having this loop type interference circuit, the region limited to the speed of the carrier change recovery time of the phase change is canceled out, and high-speed wavelength conversion is possible without being limited by the region.
[0056]
In this example, the input light 406 passes through the port 414 and is not output to the port 411. That is, it is not necessary to install a wavelength filter at the output port in order to separate input light and output light. Therefore, even when the wavelength λi of the signal light and the wavelength λj of the wavelength-converted light are the same, the wavelength conversion can be performed without mixing noise in the output light whose wavelength has been converted to the port 411.
[0057]
Further, the converted light that is the continuous light 407 having the wavelength λj propagating counterclockwise is guided from the port 418 to the port 416, and the converted light propagating clockwise is guided to the port 416 and the port 418, and excessive loss is caused. Does not occur. Therefore, regardless of whether the wavelengths of the signal light and the light to be converted are the same, a filter is not required and high-speed wavelength conversion with low loss is possible.
[0058]
A wavelength converter 500 illustrated in FIG. 12 is an example of a wavelength converter that can be employed as the wavelength converters 150A to 150F. The wavelength converter 500 is a wavelength converter using an asymmetric Mach-Zehnder interference circuit 507 instead of the loop interference circuit 413 employed in the wavelength converter 400 shown in FIG.
[0059]
The wavelength conversion circuit 500 includes a phase modulator 528 with a filter composed of semiconductor optical amplifiers 501 and 502 and multimode interference couplers 503 and 504, multimode interference couplers 505 and 506, and two waveguides having different lengths. An asymmetric Mach-Zehnder interference circuit 507 constituted by:
[0060]
In this wavelength converter 500, continuous light 511 having a wavelength λj is incident on the multimode interference coupler 503 from the port 514, and is split into two by the multimode interference coupler 503, passing through the semiconductor optical amplifiers 501 and 502, and the multimode interference coupler At 504, the signals are combined and output to the port 517, and output to the port 508 via the asymmetric Mach-Zehnder interference circuit 507.
[0061]
In this state, the signal light 510 having the wavelength λi is incident on the multimode interference coupler 503 from the port 515. The incident signal light 510 is divided into two, passes through the semiconductor optical amplifiers 501 and 502, is multiplexed by the multimode interference coupler 504, and exits to the port 516. At this time, the input signal light does not enter the subsequent asymmetric Mach-Zehnder circuit 507 due to the filter function, as in the wavelength converter 400 shown in FIG.
[0062]
When the input signal light 510 passes through the semiconductor optical amplifiers 501 and 502, the refractive index in the semiconductor optical amplifiers 501 and 502 changes. The phase of the light having the wavelength λj that is guided through the phase modulator 528 with filter is modulated by the influence of the refractive index change, and enters the asymmetric Mach-Zehnder interference circuit 507 via the port 517.
[0063]
Phase-modulated light of wavelength λj passes through two waveguides having different lengths, and light passing through a long waveguide is delayed by Δτ compared to light passing through a short waveguide. The light enters the coupler 506 and is multiplexed.
At this time, similarly to FIG. 11A, the interference of the phase-modulated light whose time is shifted by the difference Δτ in the waveguide propagation time occurs, and only when the phase difference occurs, as in FIG. The light 513 having the wavelength λj is emitted to the port 509.
[0064]
In the wavelength converter 500 having the asymmetric Mach-Zehnder interference circuit 507, the region limited to the speed of the carrier change recovery time of the phase change is canceled out, and high-speed wavelength conversion is possible without being limited.
[0065]
In this example, the input light 510 passes through the port 516 and does not enter the asymmetric Mach-Zehnder circuit 507. That is, it is not necessary to install a wavelength filter at the output port in order to separate input light and output light. Therefore, even when the wavelength λi of the signal light and the wavelength λj of the wavelength-converted light are the same, the signal light after giving the refractive index change in the semiconductor optical amplifier does not become noise of the wavelength-converted light, Wavelength conversion is possible.
[0066]
The converted light, which is continuous light 511 of wavelength λj, enters the multimode interference coupler 503 from the port 514, passes through the semiconductor optical amplifiers 501 and 502, and is multiplexed by the multimode interference coupler 504. In this case, since there is no component that is guided to the port 517 that is in a position crossing the incident port 511 and emitted to the port 516, no excess loss occurs. Therefore, regardless of whether the wavelengths of the signal light and the light to be converted are the same, a filter is unnecessary and high-speed wavelength conversion with low loss is possible.
[0067]
【The invention's effect】
As specifically described above with the embodiment, in the present invention, wavelength conversion can be performed at high speed even when the number of signal lights subjected to wavelength conversion increases and the bit rate for wavelength conversion increases.
[Brief description of the drawings]
FIG. 1 is a configuration diagram showing a high-speed wavelength conversion device according to a first embodiment of the present invention.
FIG. 2 is a waveform diagram showing a signal state in the first embodiment.
FIG. 3 is a waveform diagram showing a signal state in the first embodiment.
FIG. 4 is a waveform diagram showing a signal state in the first embodiment.
FIG. 5 is a waveform diagram showing a signal state in the first embodiment.
FIG. 6 is a waveform diagram showing a signal state in the first embodiment.
FIG. 7 is a configuration diagram showing a high-speed wavelength conversion device according to a second embodiment of the present invention.
FIG. 8 is a configuration diagram illustrating an example of a wavelength converter.
FIG. 9 is a configuration diagram illustrating an example of a wavelength converter.
FIG. 10 is a configuration diagram illustrating an example of a wavelength converter.
11 is a characteristic diagram showing the operation of the wavelength converter shown in FIG.
FIG. 12 is a configuration diagram illustrating an example of a wavelength converter.
FIG. 13 is a configuration diagram showing an optical transmission system.
FIG. 14 is a configuration diagram showing a conventional wavelength converter.
[Explanation of symbols]
100, 100A high-speed wavelength converter
  120 optical fiber for input
  130,130A, 130B Asymmetric Mach-Zehnder filter
  140 Wavelength dispersion type optical fiber
  150 A, 150B, 150D, 150E, 150F Wavelength converter
  160A, 160B optical fiber
  170,170A optical coupler
  180A, 180B, 180C, 180D optical fiber
  190 Optical fiber for output
  200,300,400 wavelength converter
S1-S16 Signal light

Claims (3)

When a plurality of NRZ format signal lights having different wavelengths are input in a wavelength-multiplexed state, an optical modulator that cuts out each of the signal lights, converts them into RZ format signal lights, and outputs them,
A chromatic dispersion optical fiber having chromatic dispersion characteristics, which transmits a plurality of RZ-format signal lights output from the optical modulator;
Distribution means for distributing and outputting a plurality of signal lights whose phases are shifted by transmitting the wavelength dispersion type optical fiber into a plurality of sets of n (where n is an integer of 2 or more) according to the wavelength;
A plurality of wavelength converters that output the same set of signal light at the same wavelength by converting the wavelength of the distributed signal light for each set;
The signal light of each set of output from the wavelength converter and a wavelength multiplexing, possess an optical coupler which outputs the signal light wavelength multiplexing,
The allocating means is configured to prevent the signal lights in each set from overlapping each other and the bit rate of each set of the signal lights of each wavelength of the wavelength multiplexed signal light input to the optical modulator. A high-speed wavelength conversion device, characterized in that the high-speed wavelength conversion device is a means for distributing the bit rate so that the bit rate is 1 / n of the total bit rate .   2. The high-speed wavelength conversion apparatus according to claim 1, wherein the sorting means is an asymmetric Mach-Zehnder type filter or an arrayed waveguide diffraction grating.   The distribution means includes a first-stage asymmetric Mach-Zehnder filter and a plurality of subsequent asymmetric Mach-Zehnder filters that further distribute the signal light distributed to the two groups by the first-stage asymmetric Mach-Zehnder filter. The high-speed wavelength converter according to claim 1, wherein

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