JP4361099B2 - Optical transceiver using wavelength stabilized light source - Google Patents

Description

  The present invention relates to an optical transceiver that uses a wavelength-stabilized light source, and more particularly to an optical transceiver that can easily set the transmission center frequency of a demodulation optical filter used on the receiving side to an optimum value.

  Optical communication systems are becoming relatively easy to increase in capacity by wavelength division multiplexing (WDM) technology, but increasing the bit rate per wavelength is also being actively studied. The reason is that by increasing the bit rate per wavelength, the apparatus cost can be reduced, and the apparatus can be reduced in size and power consumption, thereby reducing the total initial cost and running cost of the system.

  However, the increase in bit rate per wavelength is due to degradation of the fundamental OSNR tolerance, transmission distance limitation by chromatic dispersion (GVD) and polarization mode dispersion (PMD), limitation of the number of passing nodes by multistage optical filtering, Limitation of input power to the fiber due to non-linearity, etc. will be noticeable.

  As countermeasures against these deterioration factors, optical delay detection methods using optical phase modulation (DPSK, DQPSK, etc.) have been studied actively. In the optical phase modulation method, a phase modulation signal is converted into an intensity modulation code using a demodulator such as a Mach-Zehnder interferometer in a receiving apparatus, and then directly detected by a light receiver. At this time, by using a double balanced receiver, differential light reception becomes possible, and the identification sensitivity is improved by 3 dB compared with the case where the intensity modulation signal is directly detected by one light receiver. In general, a receiver is used.

  Now, in order to demodulate the phase modulation signal into the intensity modulation signal using the Mach-Zehnder interferometer, the path difference between the two paths of the Mach-Zehnder interferometer must be controlled at the wavelength level following the fluctuation of the signal light wavelength. Must not. As a method for controlling these, for example, as described in Patent Document 1, a low-frequency signal for control is superimposed on a phase shifter provided on one arm of an interferometer, and a balanced light receiver. There is a method of controlling a phase shifter provided on one arm of the interferometer by utilizing the low frequency signal component for control appearing at the output level.

  As the Mach-Zehnder interferometer, an optical waveguide type produced on a PLC is commercially available. As a path difference control method, the substrate temperature is controlled (passband variation: 1.4 GHz / ° C.) or the heaters attached to both arms are heated (phase variation: 1.33π / W). Can be controlled.

International Patent Application Publication WO / 2005/088886 T.A. Yamamoto, T .; Komukai, S .; Kawanishi, K .; Suzuki, and A.A. Takada, “Optical Frequency Comb Generation Using Phase Modulators and Group Velocity Dispersion Medium,” 2006 Asia-Pacific Pap. 225-227, April 2006.

  However, in the method described in Patent Document 1, “Optical transmission system, optical transmission device and optical reception device of optical transmission system”, since the optimum point of the phase shifter is the maximum value of the detection signal level, A low frequency signal for control is applied to the phase shifter in order to detect a shift in the pass band of the interferometer. This is nothing but superimposing an interference signal on the main signal, and causes signal quality degradation. This is the first problem of the prior art.

  Further, since the 1-bit delay Mach-Zehnder interferometer (MZI) used for demodulation of the optical phase modulation signal has only about half the pass band with respect to the signal band, in order to detect the shift of the transmission center frequency of the MZI, When a modulated signal is used, the detection sensitivity of the shift of the center frequency is lower than when unmodulated continuous light (CW) is used, and the frequency setting accuracy is poor. This is the second problem.

  The present invention has been made in view of such circumstances, and an optical transmission / reception capable of accurately setting an optical filter of an optical reception unit to an optimum operating point that matches an optical frequency of a light source of an optical transmission unit. The purpose is to provide a machine.

  In order to achieve the above object, the present invention provides a light transmission unit comprising a wavelength-stabilized light source, light modulation means for performing light modulation on continuous light output from the wavelength-stabilized light source, and a received light signal as a spectrum. In an optical transceiver constituted by an optical receiver having an optical filtering means for shaping, the transmission center frequency of the optical filtering means is adjusted using unmodulated continuous light.

  As a result, in an optical transceiver using a wavelength-stabilized light source, complicated control is performed by utilizing the temporal stability of the optical frequency of the wavelength-stabilized light source and the optical frequency of the optical filter of the receiver. Without using a mechanism, the frequency characteristic of the optical filter of the optical receiver can be accurately matched with the transmission optical frequency of the opposing optical transceiver.

  The wavelength-stabilized light source may be a multi-wavelength light source that generates a plurality of continuous light beams each having a different wavelength and generates them substantially simultaneously, and the optical receiver may include wavelength-multiplexed signal separation means. Thereby, even if the transmission side is a multi-wavelength light source, the present invention can be applied.

  Further, the plurality of continuous lights output from the multi-wavelength light source may be optical phase-locked wavelength multiplexed light in which an optical phase relationship is established.

  Thereby, even if continuous light having a wavelength different from the wavelength of the main signal is used, the transmission center frequency of the optical filtering means can be adjusted to a desired value, so that the degree of freedom in wavelength selection can be improved.

  Further, the wavelength-stabilized light source has sufficiently high absolute wavelength accuracy with respect to the wavelength shift tolerance of the optical filtering means, and unmodulated continuous light used for adjusting the transmission center frequency of the optical filtering means is It can be continuous light of one wavelength among continuous light of a single wavelength or a plurality of wavelengths of continuous light output from the stabilized light source included in the optical transmitter in the own transceiver.

  As a result, unmodulated continuous light used by the self-light receiver can be obtained using the output of the stabilized light source of the self-light transmitter, so that there is no need to separately provide a non-variable continuous light source, and the configuration is simplified. be able to.

  In addition, the optical transmission unit transmits at least one wavelength of unmodulated continuous light, and the optical signal received from the optical transceiver facing the optical receiver includes at least one wavelength of unmodulated continuous light, and the optical filtering means The non-modulated continuous light used for adjusting the transmission center frequency of the light may be the received non-modulated continuous light.

  As a result, unmodulated continuous light used by the self-light receiver can be obtained using the output of the stabilized light source transmitted from the optical transmission unit of the opposing optical transceiver, so an unmodulated continuous light source must be provided separately. And the configuration can be simplified.

  In addition, the optical receiving unit includes an optical switching unit, the optical switching unit is switched so that the unmodulated continuous light is input to the optical receiving unit when an optical transceiver is installed, and the transmission center frequency of the optical filtering unit is adjusted. And a means for switching the light switching means so as to input an optical modulation signal received after fixing the transmission center frequency to the optical receiver.

  Thereby, since the number of optical signal input ports in the optical filtering means can be reduced, the configuration of the optical filtering means can be simplified. In addition, since control is performed so that unmodulated continuous light is input to the optical receiver only when the optical transceiver is installed, redundant unmodulated continuous light input and adjustment processing can be eliminated.

  The optical filtering means is an optical periodic filter having a periodic transmittance characteristic with respect to an optical frequency, and the optical frequency of unmodulated continuous light used for adjusting the transmission center frequency of the optical filtering means is It is equivalent to the optical carrier frequency of the optical modulation signal to be received, or the optical frequency of the unmodulated continuous light is an integer multiple of the period of the optical periodic filter from the frequency equivalent to the optical carrier frequency of the optical modulation signal to be received It can be a shifted frequency.

  As described above, the optical frequency of the unmodulated continuous light for adjusting the optical filtering means is not limited to one optical frequency, so that the degree of freedom in designing the optical transceiver can be ensured.

  More specifically, the configuration of the optical transmission receiver of the present invention will be described. For example, when the optical signal received by the optical receiver is an optical differential phase shift keying (DPSK) signal, the optical filtering means An optical demodulation circuit including a Mach-Zehnder interferometer capable of demodulating an optical DPSK signal, and adjusting the optical demodulation circuit to a point where the optical output level of a desired output terminal is maximized or minimized.

  Alternatively, when the optical signal received by the optical receiver is an optical differential phase shift keying (DPSK) signal, the optical filtering means includes an Mach-Zehnder interferometer capable of demodulating the optical DPSK signal. A first point at which a light output level of a desired output terminal is minimized and a second point at which a light output level adjacent to the first point at which the light output level is minimized is minimized. Adjust to the middle point.

  Further, for example, when the optical signal received by the optical receiver is an optical differential four-phase phase shift keying (DQPSK) signal, the optical filtering means includes a Mach-Zehnder interferometer that can demodulate the optical DQPSK signal. A demodulating circuit, and adjusting the optical demodulating circuit to a point where the optical output level of a desired output terminal is reduced by about 0.69 dB from the maximum value, or about 8.34 dB.

  Alternatively, when the optical signal received by the optical receiver is an optical differential four-phase phase shift keying (DQPSK) signal, the optical filtering circuit includes a Mach-Zehnder interferometer that can demodulate the optical DQPSK signal. The optical demodulator circuit includes a first point at which a light output level at a desired output terminal is minimized and a second point at which a light output level adjacent to the first point at which the light output level is minimized is minimized. An adjustment is made from a midpoint of the point to a point shifted by an amount equal to 8 between the first point and the second point.

  Further, for example, when the optical signal received by the optical receiver is an optical π / 4 shift differential four-phase shift keying (π / 4-DQPSK) signal, the optical filtering means performs the optical π / 4 An optical demodulating circuit including a Mach-Zehnder interferometer capable of demodulating a DQPSK signal, wherein the optical demodulating circuit is adjusted to a point where the optical output level of a desired output terminal is maximized or minimized, or a point where the optical output level is reduced by about 3 dB from the maximum value. .

  Alternatively, when the optical signal received by the optical receiving unit is an optical π / 4 shift differential four-phase shift keying (π / 4-DQPSK) signal, the optical filtering means performs the optical π / 4-DQPSK signal. An optical demodulator circuit including a Mach-Zehnder interferometer capable of demodulating the optical demodulator circuit. The intermediate point between the adjacent second points where the light output level is minimum or the first point where the light output level is minimum is divided into four equal parts between the first point and the second point. Adjust to the point shifted by the amount you have

  According to the present invention, in an optical transceiver using a wavelength-stabilized light source, utilizing that the optical frequency of the wavelength-stabilized light source and the optical frequency of the optical filter of the receiver are each temporally stable, Without using a complicated control mechanism, the frequency characteristic of the optical filter of the optical receiver can be matched with the transmission optical frequency of the opposing optical transceiver accurately.

(First embodiment)
The optical transceiver according to the first embodiment of the present invention will be described. A configuration example of an optical transceiver according to the first embodiment of the present invention is shown in FIG. In FIG. 1, the optical transceiver includes an optical transmission unit 10-1 and an optical reception unit 20-1. In the optical transmission unit 10-1, continuous light (CW) output from the wavelength stabilized light source 1-1 is input to the optical modulation unit 2-1, and modulation is performed with a data signal. The modulated optical modulation signal is sent to an optical transmission line (not shown).

  In the optical receiver 20-1, the received optical modulation signal is subjected to optical spectrum shaping by the optical filtering means 3-1. The optical signal output from the optical filtering means 3-1 is converted into an electrical signal by the optical detection and identification reproduction circuit 4, identified and reproduced, and output as a data signal. The monitor and control circuit 5 monitors the output light level, and adjusts the transmission center frequency of the optical filtering means 3-1 using unmodulated continuous light based on the monitoring result.

(Second embodiment)
An optical transceiver according to the second embodiment of the present invention will be described. A configuration example of an optical transceiver according to the second embodiment of the present invention is shown in FIG. The present embodiment will be described using differences from the first embodiment shown in FIG.

  The optical transceiver according to the present embodiment is different from the first embodiment in that the stabilized light source can multiplex and generate a plurality of unmodulated continuous lights having different wavelengths and generate them almost simultaneously. 2 is a multi-wavelength optical modulator 2-2 that can simultaneously modulate multi-wavelength continuous light with different data, and demultiplexes the wavelength multiplexed signal received by the optical receiver 20-2. The wavelength multiplexing signal separation means 6-1 is provided on the input side of the optical filtering means 3-1.

  In this embodiment, since the optical filtering means 3-1 is connected to the output side of the wavelength multiplexing signal demultiplexing means 6-1, a plurality of optical filtering means 3-1 are arranged for each wavelength. If it has a function that can be handled, it may be connected to the input side of the wavelength division multiplexing signal separation means 6-1.

  A specific configuration example of the multi-wavelength light modulation means 2-2 in this embodiment is shown in FIG. The wavelength-multiplexed unmodulated continuous light output from the multi-wavelength stabilized light source 1-2 is once demultiplexed for each wavelength by a demultiplexing filter 31 such as an arrayed waveguide grating (AWG). The demodulated continuous light of each wavelength is input to the optical modulators 32-1 to 32-N, and modulated by different data # 1 to #N, respectively. The modulated optical modulation signal of each wavelength is combined again by a multiplexing filter 33 such as AWG and sent out to the optical transmission line as a wavelength multiplexed optical modulation signal.

  In the case of RZ-based optical modulation (RZ, CS-RZ, RZ-DPSK, CSRZ-DPSK, RZ-DQPSK, CSRZ-DQPSK, etc.), as shown in FIG. The optical pulse modulation means 30 may be provided in the previous stage. As a result, optical pulse modulation can be performed simultaneously on optical carriers of all wavelengths, and the load on the optical modulators 32-1 to 32-N of each wavelength can be greatly reduced.

  FIG. 4 shows a specific configuration example of the optical receiver 20-2 in the present embodiment. The wavelength multiplexed optical modulation signal input to the optical receiver 20-2 is separated for each wavelength by a demultiplexing filter 40 such as AWG. The separated signals of each wavelength are subjected to optical spectrum shaping by optical filtering means 41-1 to 41-N, converted into electric signals by optical detection circuits 42-1 to 42-N, and discriminating / reproducing circuits 43-1 to 43-1. The data is reproduced at 43-N and output as data signals # 1 to #N. In this embodiment, as shown in FIG. 4, unmodulated continuous light for adjusting the optical filtering means is required for the number of wavelengths.

(Third embodiment)
An optical transceiver according to a third embodiment of the present invention will be described. FIG. 5 shows a configuration example of the optical transceiver according to the third embodiment of the present invention. This embodiment will be described using differences from the second embodiment shown in FIG.

  The optical transmission system according to this embodiment is different from the second embodiment in that the multi-wavelength stabilized light source is an optical phase-locked multi-wavelength stabilized light source 1-3 in which the optical phases of the respective wavelengths are synchronized. . By synchronizing the optical phase of each wavelength of the multi-wavelength light source, the transmission center frequency of the optical filtering means 3-1 can be adjusted to a desired value even if continuous light having a wavelength different from the wavelength of the main signal is used. It becomes possible. Actually, if the optical frequency is synchronized rather than the optical phase, the optical phase relationship between the wavelengths is determined. Therefore, the respective wavelengths of the optical phase-synchronized multi-wavelength stabilized light source 1-3 are once demultiplexed and the optical phase-synchronized state. Even if the optical filtering means 3-1 cannot be maintained, the optical filtering means 3-1 can be adjusted.

  A specific configuration example of the optical phase-locked multi-wavelength stabilized light source 1-3 is shown in FIG. Single-wavelength continuous light output from the single-wavelength stabilized light source 50 is modulated with an RF (Radio Frequency) signal having a single frequency fm by using an optical phase modulator 51, and a plurality of spectra having an optical frequency interval of fm is obtained. It has light. By passing this light through the wavelength dispersion medium 52, the optical phase relationship of the spectrum of each wavelength can be adjusted. The light whose phase of each wavelength is adjusted by the wavelength dispersion medium 52 is again phase-modulated by the optical phase modulator 53 and output. By adopting such a configuration, it is possible to generate wavelength-division multiplexed continuous light having a very wide band and a flat spectrum. (For example, see Non-Patent Document 1)

(Fourth embodiment)
An optical transceiver according to the fourth embodiment of the present invention will be described. A configuration example of an optical transceiver according to the fourth embodiment of the present invention is shown in FIG. This embodiment will be described using differences from the third embodiment shown in FIG.

  The optical transceiver according to the present embodiment is different from that of the third embodiment in that the wavelength-multiplexed unmodulated continuous light output from the optical phase-locked multi-wavelength stabilized light source 1-3 of the optical transmitter 10-4 is optical branching means. 7 is branched and one of them is used as wavelength-division multiplexed unmodulated continuous light used for adjustment of the optical filtering means 3-2 of the optical receiver 20-4.

  The optical receiver 20-4 receives an optical signal transmitted from the optical transmitter of the opposite optical transceiver, but the optical transmitter 10-4 is an optical phase-locked multi-wavelength stabilized light source with guaranteed absolute wavelength accuracy. By using 1-3, it can be considered that it is the same as the wavelength of the optical signal transmitted from the opposing optical transceiver, and can be used for adjustment of the optical filtering means 3-2 of the optical receiver 20-4.

  A specific configuration example of the optical receiver 20-4 is shown in FIG. The difference from the configuration example of FIG. 4 is that the non-modulated continuous light for adjustment input to the optical filtering means 41-1 to 41-N of each wavelength is supplied from the transmitter 10-4 of the same optical transceiver. The wavelength-division multiplexed non-modulated continuous light is separated into continuous light of each wavelength by a demultiplexing filter 45 such as AWG and input to each of the optical filtering means 41-1 to 41-N.

(Fifth embodiment)
An optical transceiver according to a fifth embodiment of the present invention will be described. FIG. 9 shows a configuration example of an optical transceiver according to the fifth embodiment of the present invention. This embodiment will be described using differences from the third embodiment shown in FIG.

  The optical transceiver according to this embodiment differs from the third embodiment in that the optical transmitter 10-5 outputs at least one wavelength-multiplexed unmodulated continuous light output from the optical phase-locked multi-wavelength stabilized light source 1-3. Is split by the branching unit 8, multiplexed by the multiplexing unit 9 with the wavelength multiplexed optical modulation signal output from the optical modulating unit 2-1, and sent to the optical transmission line, and received by the optical receiving unit 20-5. When the wavelength division multiplexed optical modulation signal is separated by the wavelength division multiplexed signal separating means 6-2, the unmodulated continuous light transmitted from the opposing optical transceiver is used for adjustment of the optical filtering means 3-1.

  The wavelength of the unmodulated continuous light is different from the wavelengths of the other optical modulation signals, but the optical filtering means 3-1 has a periodic transmittance with respect to the optical frequency, such as a Mach-Zehnder interferometer (MZI) type optical filter. In the case of an optical filter having characteristics, it can be realized with almost no change in configuration and adjustment method.

  A specific configuration example of the optical transmission unit 10-5 is shown in FIG. As in the configuration example of FIG. 3, the light output from the optical phase-locked multi-wavelength stabilized light source 60 is demultiplexed for each wavelength by a demultiplexing filter 61 such as AWG, but only one of the wavelengths is modulated. The signals are combined again and sent to the optical transmission line. In FIG. 10, the optical modulators 62-1 to 62- (N-1) are not inserted into the ports of the unmodulated continuous light, but the optical modulators are inserted and the data signals are not input and are not modulated. It may be configured to output as it is.

(Sixth embodiment)
An optical transceiver according to the sixth embodiment of the present invention will be described. FIG. 11 shows a configuration example of the optical transceiver according to the sixth embodiment of the present invention. This embodiment will be described using differences from the fourth embodiment shown in FIG.

  The optical transceiver according to the present embodiment is different from that of the fourth embodiment in that the optical receiving unit 20-6 includes the optical switch 11, and the control circuit 12 switches the optical switch 11 so that the wavelength multiplexed signal separation means 6- The input to 1 is switched to either wavelength-divisionless unmodulated continuous light or wavelength-division multiplexed optical modulation signal.

  When adjusting the transmission center frequency of the optical filtering unit 3-3 of the optical receiving unit 20-6, the wavelength-division-multiplexed unmodulated continuous light is input to the wavelength-multiplexed signal separating unit 6-1 and when the adjustment is completed, The wavelength-division multiplexed optical modulation signal is input to the wavelength-multiplexed signal separating means 6-1 to start operation.

  A specific configuration example of the optical receiver 20-6 is shown in FIG. An optical switch 11 is provided at the input stage and is switched by the control circuit 12 between adjustment and operation. At the time of adjustment, the wavelength-multiplexed unmodulated continuous light supplied from the optical transmitter 10-6 is input to the demultiplexing filter 40 side, and the optical filtering means 41-1 to 41-N are adjusted. When the adjustment is completed, the optical modulation signal is input to the demultiplexing filter 40 side and the operation is started.

  By arranging the optical switch 11 in front of the demultiplexing filter 40, wavelength multiplexed signals can be handled collectively. Further, the optical fiber cord may be manually changed without using the optical switch 11.

(Seventh embodiment)
An optical transceiver according to a seventh embodiment of the present invention will be described. FIG. 13 shows a configuration example of the optical transceiver according to the seventh embodiment of the present invention. This embodiment will be described using differences from the fifth embodiment shown in FIG.

  The optical transceiver according to the present embodiment is different from the fifth embodiment in that the optical receiving unit 20-7 includes the optical switch 11, and the control circuit 12 switches the optical switch 11 to the optical filtering unit 3-3. Is switched to either unmodulated continuous light or an optical modulation signal. When adjusting the transmission center frequency of the optical filtering unit 3-3 of the optical receiver 20-7, the unmodulated continuous light is input to the optical filtering unit 3-3, and when the adjustment is completed, the optical modulation signal is optically filtered. Input to means 3-3 to start operation.

  A specific configuration example of the optical receiving unit 20-7 is shown in FIG. Optical switches 11-1 to 11- (N-1) having the number of signal channels are provided between the demultiplexing filter 40 and the optical filtering means 41-1 to 41- (N-1), and are adjusted and operated. Switching is performed by the control circuit 12. At the time of adjustment, the unmodulated continuous light separated by the demultiplexing filter 40 is input to the optical filtering means 41-1 to 41- (N-1) side, and the optical filtering means 41-1 to 41- (N-1). Make adjustments. When the adjustment is completed, the optical modulation signal is input to the optical filtering means 41-1 to 41- (N-1) side to start operation.

  By branching and using the demultiplexed unmodulated continuous light by the power splitter 13, it is possible to adjust the optical filtering means 41-1 to 41- (N-1) of all channels with one continuous light. is there. Further, the optical fiber cords may be manually switched without using the optical switches 11-1 to 11- (N-1).

  In the fifth and seventh embodiments of the present invention, unmodulated continuous light is wavelength-multiplexed and transmitted by the optical transmitters 10-5 and 10-7, and the unmodulated continuous light is transmitted by the optical receivers 20-5 and 20-7. It takes the form of using light after wavelength separation. Therefore, there is a problem that the carrier frequency of the unmodulated continuous light for adjusting the optical filtering means 3-1 and 3-3 and the optical modulated signal actually used for signal transmission / reception are different.

  However, in the case where the optical filtering means 3-1 and 3-3 are optical filters having periodic transmittance characteristics with respect to the optical frequency, as shown in FIGS. It is possible to similarly adjust the frequency even when the frequency is separated from the carrier frequency of the optical modulation signal by an integral multiple of the period of the optical filtering means 3-1 and 3-3.

  This is because, in the present embodiment, the output light levels of the optical filtering means 3-1 and 3-3 are monitored, so that at optical frequencies separated by an integral multiple of the period of the optical filtering means 3-1 and 3-3. This is because the transmittance exhibits the same characteristics. FIG. 15 shows a case where the carrier frequency of the optical signal and the frequency of the non-modulating continuous light for adjustment coincide with each other. FIG. 16 shows that the frequency of the non-modulating continuous light for adjustment is changed from the optical signal carrier frequency to the optical filtering means 3-1. This is a case of frequencies separated by an integral multiple of the period of 3-3. Such an operating condition is that the optical filtering means 3-1 and 3-3 have only to have a periodic transmittance characteristic with respect to the optical frequency, and are not limited to the fifth and seventh embodiments, but are applicable to all the embodiments. Applicable.

(Eighth embodiment)
An optical transceiver according to an eighth embodiment of the present invention will be described. A configuration example of the optical receiving unit according to the eighth embodiment of the present invention is shown in FIGS. In the present embodiment, the operation will be described with a specific configuration example of the optical filtering means when the optical modulation signal is an optical differential phase shift keying (DPSK) signal.

  The configuration shown in FIG. 17 is a case where the optical modulation signal and the adjustment non-modulated continuous light are incident on the MZI filter 70 in the same direction. The configuration shown in FIG. This is a case where unmodulated continuous light is incident in the opposite direction.

  The received optical DPSK signal is input to the MZI filter 70 delayed by 1 bit by the delay unit 71 for demodulation, and the phase modulation is converted into intensity modulation.

  Two complementary light intensity modulation signals output from the two output ports of the MZI filter 70 are converted into electric signals by the balanced detection circuit 73, reproduced by the identification / reproduction circuit 74, and output as a data signal. When adjusting the transmission center frequency of the MZI filter 70, unmodulated continuous light is used instead of the optical DPSK signal. The light level detection circuit 75 detects the light level of unmodulated continuous light based on the output of the balanced detection circuit 73, and the MZI control circuit 76 adjusts the phase of the phase adjustment terminal 72 so that a desired light level is obtained. .

  In the configuration shown in FIG. 17, the non-modulated continuous light for adjustment is input to the MZI filter 70 from the same input port as the optical DPSK signal. In this case, the optical DPSK signal and unmodulated continuous light are switched before being input to the MZI filter 70. On the other hand, in the configuration shown in FIG. 18, the unmodulated continuous light for adjustment is input to the MZI filter 70 from the output port of the optical DPSK signal via the directional coupler 78. Optical directional couplers 77 and 78 are inserted into the input and output of the MZI filter 70, and the unmodulated continuous light input from the output side of the MZI filter 70 is a directional coupler 77 on the input side of the MZI filter 70. And the light level is detected by the light level detection circuit 75.

  The light level detection circuit 75 detects the light level of unmodulated continuous light based on the output of the directional coupler 77, and the MZI control circuit 76 adjusts the phase of the phase adjustment terminal 72 so that a desired light level is obtained. . In this case, an optical switch function on the input side of the MZI filter 70 or reconnection using an optical fiber cord is not necessary.

  This unmodulated continuous light does not necessarily have to be the same frequency as the carrier frequency of the received optical DPSK signal, and is separated from the carrier frequency of the received signal by an integral multiple of the MZI filter period as shown in FIGS. It may be a frequency.

  The relationship between the optical frequency of unmodulated continuous light for adjusting the MZI filter and the frequency characteristics of the MZI filter 70 is shown in FIGS. FIG. 19 shows a case where the MZI filter 70 is adjusted to a point where the light level output from the MZI filter 70 is maximized, and FIG. 20 shows that the light level output from the MZI filter 70 is minimized. This is a case of adjustment. When one of the two output ports of the MZI filter 70 is adjusted as shown in FIG. 19, the other output port becomes as shown in FIG. 20, and vice versa.

  FIG. 21 shows a case where the transmission center frequency of the MZI filter 70 is adjusted to an intermediate point between the adjacent first and second extinction points at which the light level output from the MZI filter 70 is minimum. When one of the two output ports of the MZI filter 70 is adjusted as shown in FIG. 21, the other output port becomes as shown in FIG.

  As described above, the adjustment can be made to the optimum point regardless of which adjustment method shown in FIGS. 19, 20, and 21 is adopted.

  Since the light source frequency on the transmission side of the opposing optical transceiver is temporally stable, the MZI filter 70 only needs to be temporally stable after adjustment. For example, the driving current (voltage) of the phase adjustment terminal 72 of the MZI filter 70 may be controlled to be constant, and if there is a temperature characteristic, the temperature may be further controlled to be constant. unnecessary.

(Ninth embodiment)
An optical transceiver according to the ninth embodiment of the present invention will be described. FIG. 22 shows a configuration example of the optical receiver according to the ninth embodiment of the present invention. In the present embodiment, the operation will be described with a specific configuration example of the optical filtering means when the optical modulation signal is an optical differential four-phase phase shift keying (DQPSK) signal.

  The received optical DQSK signal is branched by branch 85 and input to two MZI filters 80 and 86 delayed by 1 bit by delay units 81 and 87 for demodulation. The four-value information of the optical DQPSK signal is separated into two-channel binary data by two MZI filters 80 and 86 and converted into intensity modulation. One of the two MZI filters 80 and 86 (MZI80) has an optical phase difference between its two arms of π / 4, and the other (MZI86) has an optical phase difference of −π / 4 between its two arms. is there.

  Two complementary light intensity modulation signals output from the two output ports of the MZI filters 80 and 86, respectively, are converted into electric signals by the balanced detection circuits 83 and 89, and reproduced by the identification and reproduction circuits 84 and 90 to be data. Output as a signal. When adjusting the transmission center frequency of the MZI filters 80 and 86, unmodulated continuous light is used instead of the optical DQPSK signal.

  The optical level detection circuit 91 detects the optical level of the unmodulated continuous light based on the outputs of the balanced detection circuits 83 and 89, and the MZI control circuit 92 includes the phase adjustment terminal 82-1 and the phase adjustment terminal 82-1 so that a desired optical level can be obtained. The phase of 88-1 is adjusted.

  Further, similarly to the eighth embodiment shown in FIGS. 17 and 18, unmodulated continuous light for adjustment may be input from the output ports of the MZI filters 80 and 86.

  This unmodulated continuous light does not necessarily have the same frequency as the carrier frequency of the received optical DQPSK signal, and is separated from the carrier frequency of the received signal by an integral multiple of the period of the MZI filters 80 and 86 as shown in FIG. May be a different frequency.

  The relationship between the optical frequency of unmodulated continuous light for adjusting the MZI filter and the frequency characteristics of the MZI filters 80 and 86 is shown in FIGS. FIG. 23 shows a case where the MZI filters 80 and 86 are adjusted to the point where the light level output from the MZI filters 80 and 86 is reduced by about 0.69 dB from the point where the light level is maximized. This is a case where the MZI filters 80 and 86 are adjusted to a point where the light level is lowered by about 8.34 dB from the point where the light level is maximized.

  When one of the two output ports of the MZI filter 80 is adjusted as shown in FIG. 23, the other output port becomes as shown in FIG. 24, and vice versa.

  The MZI filter 86 has the same light level, but the frequency characteristic of the MZI filter 86 is adjusted to the target position on the optical frequency axis with reference to the non-modulated continuous light for adjustment. If the optical phase relationship between the MZI filter 80 and the MZI filter 86 is stabilized, the other three ports are automatically adjusted by adjusting only one of the four output ports.

  Further, FIG. 25 shows that the MZI filters 80 and 86 are shifted from the adjacent first extinction point and the second extinction point at which the light levels output from the MZI filters 80 and 86 are minimum by 1/8 of the MZI period. This is a case where the transmission center frequency is adjusted. When one of the two output ports of the MZI filters 80 and 86 is adjusted as shown in FIG. 25, the other output port becomes as shown in FIG. As described above, the adjustment can be made to the optimum point regardless of which adjustment method shown in FIGS. 23, 24, and 25 is adopted.

  Since the light source frequency on the transmission side of the opposing optical transceiver is temporally stable, the MZI filters 80 and 86 need only be temporally stable after adjustment. For example, the drive current (voltage) of the phase adjustment terminals 82-1 and 88-1 of the MZI filters 80 and 86 may be controlled to be constant, and if there is a temperature characteristic, the temperature may be further controlled to be constant. A complicated control circuit using a modulation signal is not necessary.

(Tenth embodiment)
An optical transceiver according to the tenth embodiment of the present invention will be described. FIG. 26 shows a configuration example of the optical receiving unit according to the tenth embodiment of the present invention. In the present embodiment, the operation will be described with a specific configuration example of the optical filtering means when the optical modulation signal is an optical π / 4 shift differential four-phase shift keying (π / 4-DQPSK) signal.

  The received optical π / 4-DQSK signal is branched by branch 85 and input to two MZI filters 80 and 86 delayed by 1 bit by delay units 81 and 87 for demodulation. The quaternary information of the optical π / 4-DQPSK signal is separated into binary data of two channels by two MZI filters 80 and 86 and converted into intensity modulation. One of the two MZI filters 80 and 86 (MZI80) has an optical phase difference between its two arms of 0, and the other (MZI86) has an optical phase difference of π / 2 between its two arms.

  Two complementary light intensity modulation signals output from the two output ports of the MZI filters 80 and 86, respectively, are converted into electric signals by the balanced detection circuits 83 and 89, and reproduced by the identification and reproduction circuits 84 and 90 to be data. Output as a signal. When adjusting the transmission center frequency of the MZI filters 80 and 86, unmodulated continuous light is used instead of the optical π / 4-DQPSK signal.

  The optical level detection circuit 91 detects the optical level of the unmodulated continuous light based on the outputs of the balanced detection circuits 83 and 89, and the MZI control circuit 92 includes the phase adjustment terminal 82-1 and the phase adjustment terminal 82-1 so that a desired optical level can be obtained. The phase of 88-1 is adjusted.

  Further, similarly to the eighth embodiment shown in FIGS. 17 and 18, unmodulated continuous light for adjustment may be input from the output ports of the MZI filters 80 and 86.

  The unmodulated continuous light does not necessarily have the same frequency as the carrier frequency of the received optical π / 4-DQPSK signal. As shown in FIG. 16, the period of the MZI filters 80 and 86 is determined from the carrier frequency of the received signal. The frequency may be separated by an integer multiple.

  The relationship between the optical frequency of unmodulated continuous light for adjusting the MZI filter and the frequency characteristics of the MZI filters 80 and 86 is shown in FIGS. FIG. 27 shows the case where the MZI filters 80 and 86 are adjusted to the point where the light levels output from the MZI filters 80 and 86 become maximum, and FIG. 28 shows the case where the light levels output from the MZI filters 80 and 86 become minimum. This is a case where the MZI filters 80 and 86 are adjusted to the points. When either one of the two output ports of the MZI filter 80 is adjusted as shown in FIG. 27, the other output port becomes as shown in FIG. 28, and vice versa.

  FIG. 29 shows a case where the light level output from the MZI filters 80 and 86 is adjusted to a point where the light level is lowered by 3 dB from the maximum value to the higher optical frequency side. FIG. 30 shows a case where the light levels output from the MZI filters 80 and 86 are adjusted to a point where the light level is lowered by 3 dB from the maximum value to the lower light frequency side. When one of the two output ports of the MZI 86 is adjusted as shown in FIG. 29, the other output port becomes as shown in FIG. 30 and vice versa.

  If the optical phase relationship between the MZI filter 80 and the MZI filter 86 is stabilized, the other three ports are automatically adjusted by adjusting any one of the four output ports.

  FIG. 21 shows the case where the transmission center frequency of the MZI filters 80 and 86 is adjusted to the midpoint between the adjacent first and second extinction points at which the light levels output from the MZI filters 80 and 86 are minimum. FIG. 31 shows only a quarter of the period of the MZI filters 80 and 86 from the intermediate point between the adjacent first and second extinction points at which the light levels output from the MZI filters 80 and 86 are minimum. This is a case where the transmission center frequency of the MZI filters 80 and 86 is adjusted to the shifted point. In this embodiment, the MZI filter 80 is adjusted as shown in FIG. 21, and the MZI filter 86 is adjusted as shown in FIG.

  As described above, in this embodiment, the optimum point can be adjusted regardless of which adjustment method shown in FIGS. 21, 27, 28, 29, 30, and 31 is adopted. Since the light source frequency on the transmission side of the opposing optical transceiver is temporally stable, the MZI filters 80 and 86 need only be temporally stable after adjustment. For example, the drive current (voltage) of the phase adjustment terminals 82-2 and 88-2 of the MZI filters 80 and 86 may be controlled to be constant, and if there is a temperature characteristic, the temperature may be further controlled to be constant.

(Eleventh embodiment)
An optical transceiver according to the eleventh embodiment of the present invention will be described. FIG. 32 shows a configuration example of the optical transceiver according to the eleventh embodiment of the present invention. The present embodiment is a configuration example of a ROADM node when the transceiver of the present invention is applied to a ROADM (reconfigurable optical add / drop multiplexer) node. In this configuration example, the ROADM node has two optical transceivers, and one optical transceiver branches and receives a signal from the left side of the drawing, inserts and transmits a transmission signal to the left side of the drawing, and transmits and receives the other optical transceiver. The machine branches and receives the signal from the right side of the drawing, inserts the transmission signal to the right side of the drawing, and sends it out.

  The ROADM node has at least one absolute frequency stabilized light source 100, and the optical transceiver generates multi-wavelength carriers based on the absolute frequency stabilized light source 100. The generated multi-wavelength carrier is branched and one is used as a transmission light source, and the other is used for adjusting a demodulation MZI filter of the reception unit.

  The operations of the optical transmitter and the optical receiver are as described above. In the present embodiment, the most important thing is to prepare at least one absolute frequency stabilized light source 100 at each node. This makes it possible to easily stabilize the optical transceiver of the RAODM system that employs an optical phase modulation system (DPSK, DQPSK, etc.).

  According to the present invention, in an optical transceiver using a wavelength-stabilized light source, utilizing that the optical frequency of the wavelength-stabilized light source and the optical frequency of the optical filter of the receiver are each temporally stable, The frequency characteristics of the optical filter of the optical receiver can be accurately matched to the transmission optical frequency of the opposing optical transceiver without using a complicated control mechanism, so that it can be used to improve communication quality in optical communication. Can do.

The block diagram which shows 1st embodiment of this invention. The block diagram which shows 2nd embodiment of this invention. The block diagram which shows the specific structural example of the multiwavelength light modulation means in 2nd embodiment of this invention. The block diagram which shows the specific structural example of the optical receiver in 2nd embodiment of this invention. The block diagram which shows 3rd embodiment of this invention. The block diagram which shows the specific structural example of the phase-locked multiwavelength stabilization light source in 3rd embodiment of this invention. The block diagram which shows 4th embodiment of this invention. The block diagram which shows the specific structural example of the optical receiver in 4th embodiment of this invention. The block diagram which shows 5th embodiment of this invention. The block diagram which shows the specific structural example of the optical transmission part in 5th embodiment of this invention. The block diagram which shows 6th embodiment of this invention. The block diagram which shows the specific structural example of the optical receiver in 6th embodiment of this invention. The block diagram which shows 7th embodiment of this invention. The block diagram which shows the specific structural example of the optical receiver in 7th embodiment of this invention. The figure which shows the example of optical frequency arrangement | positioning of the unmodulated continuous light for adjustment using the periodicity of an optical filtering means (an optical signal carrier frequency and the continuous optical frequency for adjustment correspond). The figure which shows the optical frequency arrangement | positioning example of the non-modulation continuous light for adjustment using the periodicity of an optical filtering means (The optical signal carrier frequency and the adjustment continuous optical frequency have shifted | deviated by the fixed interval). The block diagram which shows 8th embodiment of this invention (an optical modulation signal and the non-modulation continuous light for adjustment enter from the same direction). The block diagram which shows 8th embodiment of this invention (an optical modulation signal and the unmodulated continuous light for adjustment enter from the opposite direction). The figure which shows the optical frequency arrangement | positioning example of the optical filtering means in the 8th embodiment of this invention, and the unmodulated continuous light for adjustment (adjusted to the point of the maximum MZI output level). The figure which shows the optical frequency arrangement | positioning example of the optical filtering means in the 8th embodiment of this invention, and the unmodulated continuous light for adjustment (adjusted to the point with the minimum MZI output level). The figure which shows the optical frequency arrangement | positioning example of the optical filtering means and the non-modulation continuous light for adjustment in the 8th and 10th embodiment of this invention (adjusted to the middle point of the MZI output level minimum point). The block diagram which shows 9th embodiment of this invention. The figure which shows the optical frequency arrangement | positioning example of the optical filtering means and unmodulated continuous light for adjustment in the ninth embodiment of the present invention (adjusted to the point where the MZI output level is reduced by about 0.69 dB from the maximum value). The figure which shows the optical frequency arrangement | positioning example of the optical filtering means and unmodulated continuous light for adjustment in the ninth embodiment of the present invention (adjusted to the point where the MZI output level is lowered by about 8.34 dB from the maximum value). The figure which shows the optical frequency arrangement | positioning example of the optical filtering means and the non-modulation continuous light for adjustment in 9th embodiment of this invention (Adjustment to the point shifted by 1/8 of the MZI period from the middle point of the MZI output level minimum point) ). The block diagram which shows 10th Embodiment of this invention. The figure which shows the optical frequency arrangement | positioning example of the optical filtering means in the 10th Embodiment of this invention, and the unmodulated continuous light for adjustment (adjusted to the point with the maximum MZI output level). The figure which shows the optical frequency arrangement | positioning example of the optical filtering means and unmodulated continuous light for adjustment in 10th Embodiment of this invention (it adjusts to the point with the minimum MZI output level). The figure which shows the optical frequency arrangement | positioning example of the optical filtering means and unmodulated continuous light for adjustment in the tenth embodiment of the present invention (adjusted to the point where the MZI output level is lowered from the maximum value to the higher side by about 3 dB optical frequency). The figure which shows the optical frequency arrangement | positioning example of the optical filtering means and unmodulated continuous light for adjustment in the tenth embodiment of the present invention (adjusted to the point where the MZI output level is lowered from the maximum value to the lower side by about 3 dB optical frequency). The figure which shows the optical frequency arrangement | positioning example of the optical filtering means and unmodulated continuous light for adjustment in 10th Embodiment of this invention (Adjustment to the point shifted only 1/4 of the MZI period from the middle point of the MZI output level minimum point) ). The block diagram which shows 11th embodiment of this invention.

Explanation of symbols

1-1 Wavelength Stabilized Light Source 1-2 Multiwavelength Stabilized Light Source 1-3 Optical Phase-Locked Multiwavelength Stabilized Light Source 2-1 Light Modulating Unit 2-2 Multiwavelength Light Modulating Unit 3-1, 3-2, 3- 3, 41-1 to 41-N Optical filtering means 4 Optical detection and identification reproduction circuit 5, 44 Monitor and control circuit 6-1, 6-2 Wavelength multiplexed signal separation means 7 Optical branching means 8 Demultiplexing means 9 Multiplexing means 10-1, 10-2, 10-3, 10-4, 10-5, 10-6, 10-7 Optical transmitters 11, 11-1 to 11- (N-1) Optical switch 12 Control circuit 13 Power Splitters 20-1, 20-2, 20-3, 20-4, 20-5, 20-6, 20-7 Optical receiver 30 Optical pulse modulation means 31, 40, 45, 61 Demultiplexing filter 32-1 32-N, 62-1 to 62- (N-1) Optical modulator 33, 63 Multiplexing filter 4 -1 to 42-N Photodetection circuits 43-1 to 43-N Identification and reproduction circuit 50 Single wavelength stabilized light sources 51 and 53 Optical phase modulator 52 Wavelength dispersion medium 60 Optical phase-locked multiwavelength stabilized light sources 70 and 80, 86 MZI filters 71, 81, 87 Delay devices 72, 82-1, 88-1, 82-2, 88-2 Phase adjustment terminals 73, 83, 89 Balanced detection circuits 74, 84, 90 Discrimination and reproduction circuits 75, 91 Optical level detection circuit 76, 92 MZI control circuit 77, 78 Directional coupler 85 Branch 100 Absolute frequency stabilized light source

Claims (15)

An optical transmitter including a wavelength-stabilized light source, and an optical modulator that modulates the continuous light output from the wavelength-stabilized light source; and an optical filtering unit that transmits the received optical signal and demodulates the received signal. In an optical transceiver including an optical receiver,
Using the unmodulated continuous light output from the wavelength-stabilized light source of the optical transmitter, the transmission center frequency of the optical filtering means is adjusted and fixed, and the optical modulation signal received after the transmission center frequency is fixed An optical transceiver characterized by comprising means for inputting to the optical receiver. An optical transmitter including a wavelength-stabilized light source, and an optical modulator that modulates the continuous light output from the wavelength-stabilized light source; and an optical filtering unit that transmits the received optical signal and demodulates the received signal. In an optical transceiver including an optical receiver,
Using unmodulated continuous light extracted from the received optical signal, the transmission center frequency of the optical filtering means is adjusted and fixed, and after the transmission center frequency is fixed, the received optical modulation signal is input to the optical receiver With means to
An optical transceiver characterized by that . An optical transmitter including a wavelength-stabilized light source, and an optical modulator that modulates the continuous light output from the wavelength-stabilized light source; and an optical filtering unit that transmits the received optical signal and demodulates the received signal. In an optical transceiver including an optical receiver,
Using the unmodulated continuous light generated in the optical receiver, the transmission center frequency of the optical filtering means is adjusted and fixed, and the optical modulation signal to be received is input to the optical receiver after the transmission center frequency is fixed With means to
An optical transceiver characterized by that . The wavelength-stabilized light source is a multi-wavelength light source that multiplexes a plurality of continuous lights each having a different wavelength and generates almost simultaneously,
The optical transceiver according to any one of claims 1 to 3, wherein the optical receiver includes a wavelength division multiplexing signal separation unit. The optical transceiver according to claim 4, wherein the plurality of continuous lights output from the multi-wavelength light source are optical phase-locked wavelength-multiplexed lights in which an optical phase relationship is established. The wavelength-stabilized light source is
With sufficiently high absolute wavelength accuracy for the wavelength shift tolerance of the optical filtering means,
Unmodulated continuous light used to adjust the transmission center frequency of the optical filtering means,
The optical transceiver according to claim 1 which is continuous light of any one wavelength of the continuous light of the continuous light or a plurality of wavelengths of the single wavelength output from the previous SL wavelength stabilizing light source. The optical transmitter is
Transmit unmodulated continuous light of at least one wavelength,
The optical transceiver according to claim 2 , wherein the optical signal received from the optical transceiver facing the optical receiver includes at least one wavelength of unmodulated continuous light. The light receiving unit includes light switching means;
And a means for switching light switching means for switching a light switching means so as to input the unmodulated continuous light to the light receiving section and adjusting a transmission center frequency of the light filtering means when an optical transceiver is installed. Item 8. The optical transceiver according to any one of Items 1 to 7 . The optical filtering means comprises:
An optical periodic filter having periodic transmittance characteristics with respect to the optical frequency,
The optical frequency of unmodulated continuous light used to adjust the transmission center frequency of the optical filtering means is
It is equivalent to the optical carrier frequency of the received optical modulation signal,
Or
The optical frequency of the unmodulated continuous light is
From a frequency equivalent to the optical carrier frequency of the received optical modulation signal,
The optical transceiver according to any one of claims 1 to 8, wherein the frequency is shifted by an integral multiple of a period of the optical periodic filter. The optical signal received by the optical receiver is
Optical differential phase shift keying (DPSK) signal,
The optical filtering means comprises:
An optical demodulation circuit including a Mach-Zehnder interferometer capable of demodulating the optical DPSK signal;
The optical demodulation circuit;
Desired optical transceiver according to any one of claims 1 to 3 and 8 light output level is adjusted to the point of maximum or minimum output. The optical signal received by the optical receiver is
Optical differential phase shift keying (DPSK) signal,
The optical filtering means comprises:
An optical demodulation circuit including a Mach-Zehnder interferometer capable of demodulating the optical DPSK signal;
The optical demodulation circuit;
A first point at which the optical output level of the desired output terminal is minimized;
9. The optical transmission / reception according to claim 1 , wherein the optical transmission / reception is adjusted to an intermediate point between the second point where the light output level adjacent to the first point where the light output level is minimum is adjacent to the second point where the light output level is minimum. Machine. The optical signal received by the optical receiver is
Optical differential four-phase phase shift keying (DQPSK) signal,
The optical filtering means comprises:
An optical demodulation circuit including a Mach-Zehnder interferometer capable of demodulating the optical DQPSK signal;
The optical demodulation circuit;
The optical transceiver according to any one of claims 1 to 3 and 8, wherein the optical output level of a desired output terminal is adjusted to a point where the optical output level is reduced by about 0.69 dB from the maximum value, or a point where the optical output level is reduced by about 8.34 dB. The optical signal received by the optical receiver is
Optical differential four-phase phase shift keying (DQPSK) signal,
The optical filtering means comprises:
An optical demodulation circuit including a Mach-Zehnder interferometer capable of demodulating the optical DQPSK signal;
The optical demodulation circuit;
A first point at which the optical output level of the desired output terminal is minimized;
From an intermediate point between the second point where the light output level adjacent to the first point where the light output level is minimum and the minimum light output level,
The optical transceiver according to any one of claims 1 to 3, wherein the first point and the second point are adjusted to a point shifted by an equal amount. The optical signal received by the optical receiver is
An optical π / 4 shift differential four phase shift keying (π / 4-DQPSK) signal,
The optical filtering means comprises:
An optical demodulation circuit including a Mach-Zehnder interferometer capable of demodulating the optical π / 4-DQPSK signal;
The optical demodulation circuit;
The point where the optical output level of the desired output terminal is maximum or minimum,
Alternatively, the optical transceiver according to any one of claims 1 to 3 and 8, wherein the optical transceiver is adjusted to a point about 3 dB lower than the maximum value. The optical signal received by the optical receiver is
An optical π / 4 shift differential four phase shift keying (π / 4-DQPSK) signal,
The optical filtering means comprises:
An optical demodulation circuit including a Mach-Zehnder interferometer capable of demodulating the optical π / 4-DQPSK signal;
The optical demodulation circuit;
A first point at which the optical output level of the desired output terminal is minimized;
An intermediate point between the second point at which the light output level adjacent to the first point at which the light output level is at a minimum,
Or
From the first point where the light output level is minimized,
The optical transceiver according to any one of claims 1 to 3, wherein the first point and the second point are adjusted to a point shifted by an amount equal to four.

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