JP5210035B2 - Optical frequency synchronous communication device - Google Patents

Description

  The present invention relates to an optical frequency synchronization communication apparatus applied in an optical frequency synchronization photonic network synchronized with an optical absolute phase level in a photonic network or an optical communication network.

  In the prior art, in the wavelength multiplexing transmission system, signal transmission is performed by an optical frequency carrier in which individual wavelengths are phase-synchronized. This signal synchronization relationship remains between the signal lights wavelength-multiplexed in the optical fiber. Since the optical phase is locked between the signal lights, they are correlated with each other. For this reason, equalization compensation can be performed on the optical electric field component even if mutual interference occurs due to a nonlinear phenomenon in optical fiber transmission. However, the correlation can be maintained only within the same optical fiber, and the range in which the group velocity dispersion falls within the coherence length of the light source. As for the coherence length, when the light source line width of the wavelength multiplexed signal is 1 MHz, for example, it is only 100 m. In the current technology, when a delay difference occurs between optical frequency carriers exceeding this coherence length, optical frequency synchronous communication becomes difficult.

  FIG. 1 is a diagram illustrating a configuration example of a conventional optical communication apparatus.

  The configuration example shown in FIG. 1 corresponds to the configuration shown in FIG. 1 of Patent Document 1 and FIG. 1 of Non-Patent Document 2. In FIG. 1, an optical communication device 100 includes an optical phase-synchronized multi-wavelength light source 101 that generates a carrier wave whose phase is synchronized, and M optical modulators 102-1 to 102-1 that modulate the carrier wave with transmission information 106-1 to M-1. M, each wavelength transmission path 103, a wavelength multiplexer 104 that multiplexes the modulated optical signals from each optical modulator, and a multiplex transmission path 105.

  FIG. 2 shows the result of performing equalization compensation for mutual interference caused by nonlinear phenomenon in optical fiber transmission, and FIG. 2A shows the case where the phase of the light source light is not synchronized and there is no interference compensation signal. FIG. 2B shows a case where the optical phase of the light source is synchronized and an interference compensation signal is added. Here, since the interference information is predicted in advance and equalization is performed on the optical electric field, it can be confirmed that the eye diagram is opened even after transmission.

  In this conventional technique, since phase synchronization is established between optical frequency carriers in the same optical fiber, such equalization compensation is possible. However, it is difficult to achieve phase synchronization between optical frequency carriers in an optical fiber that is cross-connected at a node deployed in a photonic network and includes signals with different origins, so equalization compensation is also difficult. It becomes.

Japanese Patent Laying-Open No. 2008-079131 (FIG. 1) E. Yamazaki, et al., “Compensation of Interchannel Crosstalk Induced by Optical Fiber Nonlinearity in Carrier Phase-Locked WDM System,” IEEE Photon Tech. Lett., Vol.19, No.1, pp.9-11, 2007 K. Suzuki et al., “MHz-accuracy, 25 GHz-spaced frequency-stabilised optical comb over S-, C-, L-bands for precise optical frequency measurements,” Electronics Letters, 19th August 2004, Vol.40, No .17, D. J. Jones, et al., “Carrier-envelope phase control of femtosecond laser comb,” Science, 288 (2000) 635-639 T. Kobayashi, et al., “Optical Pulse Compression using High-frequency Eelectrooptic Phase Modulation,” IEEE J-QE, vol.24, No2. Pp.382-387, 1988

  In optical fiber communication, wavelength division multiplexing (WDM) technology has been adopted since the latter half of the 1990s in order to increase capacity. A practical system that employs this technology is realized by mounting multiple semiconductor lasers each having an optical frequency (wavelength) that matches a standardized optical frequency grid. In this case, during the propagation of the optical fiber, the transmission capability is limited as the optical fiber nonlinear phenomenon appears. Due to a phenomenon called four-wave mixing, new light is induced at the optical frequency position of the adjacent grid. This induced light affects the signal of the laser light source arranged on the grid as beat noise, and degrades transmission characteristics. This is to produce beat noise because the induced light is uncorrelated with the light from the individual semiconductor laser sources. This beat noise intensity has a great influence on the signal-to-noise ratio (SNR) of the signal light even if the induced light is weak. When the beat noise intensity exceeds -30 dB compared to the signal light intensity, it affects the error rate characteristics. Appears.

  In order to suppress the influence of beat noise, many methods have been applied so far to reduce the input light intensity to the optical fiber. In addition to this method, a method has been adopted in which the above-described problems are solved by correlating the signal light phase states with each other and controlling the interference state of the electric field. In the latter case, the optical phase synchronization light source is effective. These techniques are effective in optical fiber transmission between two points as described above. However, in the photonic network, that is, the cross-connect node, when optical frequency carriers having different starting points coexist, the signals become uncorrelated with each other, and thus the above-described effect cannot be obtained. This is shown in FIG. 3 below.

  In FIG. 3, a conventional photonics network 300 includes a node # 1 301-1, a node # 2 301-2, a node # 3 301-3, a node # 4 301-4, and a multiplex transmission path 105. Prepare. Here, with respect to the optical frequency carriers 1, 2, and 3 (spectrum 302) starting from the node # 1 301-1, the optical frequency carrier starting from the node # 4 301-4 in the node # 2 301-2. 4 (Spectrum 303) is added in a cross-connected manner and goes to Node # 3 301-3 (Spectrum 304). In the optical fiber multiplex transmission path 105 from the node # 2 301-2 to the node # 3 301-3, the optical frequency carrier 4 and the other optical phase carriers are not synchronized with each other. It is.

  Here, since the optical frequency used in the optical communication is about 200 THz, the optical wavelength is about 1.5 μm. This wavelength is a length that can be changed by a temperature fluctuation of several degrees for an optical fiber length of several tens of meters. Therefore, even if the optical phases are synchronized with each other in the apparatus, phase synchronization becomes difficult between photonic nodes separated by 100 km or more.

In order to solve the above problems, an optical frequency synchronous communication apparatus of the present invention acquires a reference clock in an optical frequency synchronous communication apparatus applied to a photonic network including an optical frequency multiplexing transmission line and an optical cross-connect switch node. A frequency interval between the optical frequency combs based on the reference clock frequency or a multiplied clock frequency thereof, and a frequency interval of the optical frequency combs. Means for determining the absolute value of the frequency of one spectrum, and oscillating the light source for communication in the optical frequency synchronous communication device by synchronizing the phase with one of the optical frequency spectral components of the optical frequency comb, respectively. Or, the optical frequency carrier to be reproduced or optically amplified by the optical frequency synchronous communication device is the optical frequency carrier. By phase-synchronized with one of the optical frequency spectrum components having comb, the optical frequency carrier in a state of phase-synchronized with each other within the photonic network is made is modulation and demodulation, the frequency of each spectrum of the optical frequency comb Is determined by synchronizing the envelope of the short pulse light obtained from the optical frequency comb and the offset phase between optical carriers with the frequency based on the reference clock .

Note that it is difficult to synchronize the optical frequencies of light sources provided independently between nodes only by distributing a reference clock to each node. The technology that makes it possible to synchronize the frequency of light sources that are independently deployed between nodes is the CEOP (Carrier Envelope Offset Phase Rock) technology that narrows the laser line width to the order of 1 Hz. This is because if the line width is reduced, high accuracy is required for the optical frequency accordingly. Furthermore, in order to determine the accuracy as an absolute frequency, it is necessary to stabilize the optical frequency. In order to stabilize the optical frequency of 200 THz in the order of 1 Hz, high stability of 10 ⁻¹² or less is required. The present invention realizes such high accuracy and high stability of the optical frequency, and extends the effect of equivalent compensation by an optical phase-locked multi-wavelength light source that has closed optical fiber transmission between two points to the entire photonics network. The purpose is to do.

In order to solve the above problems, an optical frequency synchronous communication apparatus of the present invention acquires a reference clock in an optical frequency synchronous communication apparatus applied to a photonic network including an optical frequency multiplexing transmission line and an optical cross-connect switch node. A frequency interval between the optical frequency combs based on the reference clock frequency or a multiplied clock frequency thereof, and a frequency interval of the optical frequency combs. Means for determining the absolute value of the frequency of one spectrum, and oscillating the light source for communication in the optical frequency synchronous communication device by synchronizing the phase with one of the optical frequency spectral components of the optical frequency comb, respectively. or, the optical frequency of the optical frequency carrier where the optical frequency synchronization communication apparatus reproduces or optical amplifier By phase-synchronized with one of the optical frequency spectrum components having comb, the optical frequency carrier is characterized in that performed is the modem in a state phase-synchronized with each other within the photonic network.

  In the optical frequency synchronous communication apparatus of the present invention, the means for obtaining the reference clock may receive the reference clock from the outside, or the means for obtaining the reference clock may receive the reference clock by itself. It may be generated.

  In the optical frequency synchronous communication apparatus of the present invention, the reference clock may be distributed by radio waves, and the clock may be extracted from the distributed radio waves, and the reference clock is distributed by an optical fiber and distributed. A clock may be extracted from the signal, and the reference clock may be a clock generated from an optical lattice clock.

  According to the present invention, even when optical frequency carriers are cross-connected in a photonic network and optical frequency carriers having different starting points are mixed in the same optical fiber, equalization compensation for the optical electric field is performed to perform a relay transmission distance without regeneration. Can be expected to expand.

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

  FIG. 4 is a diagram for explaining an implementation concept of the optical frequency synchronous communication apparatus according to an embodiment of the present invention. In FIG. 4, the optical frequency synchronization communication apparatus 400 includes an optical frequency synchronization communication network (photonic network; hereinafter referred to as an optical frequency synchronization PN) 401 and a time / time standard apparatus 402. The optical frequency synchronization PN 401 receives the frequency f0 from the time / time standard device 402 that provides accurate time information. In the optical frequency synchronization PN 401, an optical frequency reference is generated based on the frequency f0, and all the optical frequency carriers in the optical frequency synchronization PN 401 are synchronized with the optical frequency reference. The optical frequency synchronization PN 401 includes a photonic node 403 and a wavelength (optical frequency) multiplex transmission line 410. The photonic node 403 includes an optical cross-connect device 406, a transmission device 405, and an optical frequency reference supply module (OFRSM) 404 for switching the optical frequency carrier to each optical fiber route. Prepare.

The OFRSM 404 receives accurate time information from the time / time standard device 402 and converts it into an optical frequency reference suitable for optical communication. At this time, the signal from the time / time standard device 402 is, for example, a radio wave signal from a GPS satellite in addition to a long wave standard radio wave provided by the Japan Standard Time Group, National Institute of Information and Communications Technology, National Institute of Information and Communications Technology. The former provides frequencies with an uncertainty of ^10-11 , and the latter provides below ^10-12 . Research on more accurate time is being conducted in parallel, and it is expected that more reliable time information will be provided as radio waves or optical fibers in the future. Details of the OFRSM configuration for generating and distributing the optical frequency reference from the received time information will be described later.

  The transmission device 405 includes at least an optical signal termination device 407, an optical signal transmission / reception device 408, and an optical signal amplification device 409. The optical signal terminator 407 means the start / end points of transmission / reception signals, and provides a construction / disassembly function of a transmission signal frame, a termination function of overhead information in a frame, and an optical modulation / demodulation function. The optical signal transmission / reception device 408 provides a signal reproduction function, which includes a signal reproduction function in which the signal-to-noise ratio is degraded by propagation through the wavelength division multiplexing transmission line. The optical signal amplifying device 409 corresponds to a phase sensitive optical amplifier in addition to the optical fiber amplification currently performed. A phase sensitive optical amplifier in which the pumping light source needs to be synchronized with the optical frequency carrier becomes an amplifier suitable for the optical frequency synchronous PN 401 and is effective because it exhibits low noise characteristics.

  As shown in FIG. 5, the individual light sources (synchronized CW light sources # 1 to #M 501-1 to 501-M) included in the optical signal termination device 407 and the optical signal transmission / reception device 408 are optical frequencies supplied from the OFRSM 404. Synchronize the optical frequency and optical phase to the reference. As the synchronization method, injection locking in which the reference from OFRSM 404 is directly injected into the light source, or the optical frequency reference from OFRSM 404 and the light of the light source are received by a photodiode to perform synchronous detection, and the optical phase of the light source is controlled. There is a method using an optical phase lock circuit. As shown in FIG. 5, instead of preparing the light sources individually, as shown in FIG. 6, one light source (synchronized CW light source 601) is synchronized with the optical frequency reference supplied from OFSMM 404 and synchronized CW light source. There is a configuration in which an optical phase-synchronized multi-optical frequency carrier 602 is generated from a modulation sideband from 601 and the light is demultiplexed to be a light modulation / demodulation light source.

  FIG. 7A shows a configuration example 700 for realizing the optical phase synchronization multi-optical frequency carrier 602. The synchronized CW light source 601 is phase-synchronized with an OFR (Optical Frequency Reference) and is stabilized in one of the ITU-T frequency grids. The ITU-T optical frequency grid has n as an integer.

It is. 193.1000 THz is the anchor frequency and 12.5 GHz is the frequency grid spacing. The continuous wave light emitted from the synchronized CW light source 601 is phase-modulated at a frequency of 12.5 GHz which gives a frequency grid interval or its frequency division. When the spectrum is observed for the phase-modulated light, the modulation sideband can be observed at a position multiplied by the modulation frequency fm [Hz]. The relative relationship between the amplitude and the phase between the modulation sidebands by phase modulation is described by the first type Bessel function as the modulation theory teaches. From an intuitive viewpoint, a dense wave is formed with an optical frequency of 200 THz at fm [Hz]. When this dense wave is passed through a dispersion medium 704 having a group velocity dispersion amount B (= ± 1 / (4πfm ² )) [second ² ], the instantaneous optical frequency is constant and converted to light subjected to amplitude modulation. . At this time, the line spectra of the modulation sidebands are in phase with each other. When this light is modulated at a modulation frequency fm [Hz] with a deeper modulation index, a modulation sideband consisting of several tens of spectral intensities is obtained, as shown by a spectrum 710 in FIG. 7B. Can do. When the respective spectra are separated by the optical demultiplexing circuit, an optical frequency carrier in which the optical frequency interval is accurately engraved with fm [Hz] can be obtained.

The most important function of the concept of optical frequency synchronization PN 401 is the synchronization of all optical frequency carriers in the optical frequency synchronization PN 401 to the optical frequency reference.
The optical frequency reference distribution function is realized by an optical frequency reference supply module (OFRSM). The OFRSM 404 has different embodiments depending on the accuracy (uncertainty) of the optical frequency to be provided. For example, an optical frequency reference comb (Comb) can be realized and provided on the order of 10 ⁻⁸ (about 10 MHz) or less based on the absorption line optical frequency of acetylene or cyan gas. Although details are omitted in this embodiment, they are described in detail in Non-Patent Document 2.

FIG. 8A shows a configuration example 800 of the OFRSM having an uncertainty exceeding 10 ⁻⁹ (about MHz). OFRSM 404 generates an optical frequency comb. A configuration example 800 illustrated in FIG. 8A is a configuration in which the carrier envelope offset phase is fixedly controlled. In the configuration example 800, a spectrum spread in an octave band is generated from laser light that has been mode-locked (locked), and the carrier envelope offset phase (CEP) is locked by the f-2f interferometer 804. The apparatus structure which produces | generates a highly accurate optical frequency comb is shown. For this reason, the same accuracy as the time / time standard device 402 can be realized. If the accuracy is Takamare, principle, is capable of providing embodiment the optical frequency reference in the order of Hz ie 10 ^-14. The configuration of the present embodiment is described in detail in Non-Patent Document 3. The CEP controlled optical frequency comb is a pulse train in which the offset phase (CEO) between the optical carrier and envelope of the ultrashort optical pulse emitted by the mode-locked laser 801 is accurately controlled, and is accurate at the frequency f _rep of the reciprocal of the pulse repetition time T. Engrave the optical frequency spectrum. The n-th frequency f (n) is defined by f (n) = n × f _rep + f _CEO . Here, f _CEO is a carrier envelope offset frequency. ΔΦf = 2π (f _CEO / f _rep ), that is, the phase fluctuation of the optical Φ frequency can be suppressed by stably controlling the absolute optical phase.

The short pulse train emitted from the mode-locked laser 801 is increased in intensity by the optical amplifier 802 and then input to the nonlinear medium 803. When conditions are satisfied, light having an octave band is generated. At that time, the 2n-th optical frequency is f (2n) = 2n × f _rep + f _CEO . On the other hand, when the second harmonic is generated for the component of f (n) in the octave light, 2 × f (n) = 2n × f _rep + 2 × f _CEO , so that f (2n) and 2 By offsetting xf (n), it is possible to extract the offset frequency component f _CEO = (ΔΦf / 2π) f _rep . Here, ΔΦ is a carrier envelope offset phase. When the frequency distributed from the time / time standard device 402 is used as a reference and the repetition frequency f _rep and the extracted f _CEO are generated by the PLL circuit, as shown in the spectrum 810 of FIG. A sufficiently suppressed optical frequency comb with small uncertainty can be obtained. This optical frequency comb is referred to as OFRSM 404.

  FIG. 9A shows a configuration example 900 that receives a frequency from a GPS satellite and oscillates a mode-locked laser based on the received frequency. The mode-locked laser can also generate a mode-locked short pulse laser by pulse compression from the embodiment of the optical phase-locked multi-optical frequency carrier light source shown in FIG. A group velocity dispersion medium 906 is provided after the second phase modulator 905. If the spectral bandwidth is about 20 nm as the output of the second modulator 905, in principle, a short pulse 907 of several hundred fsec (see the spectrum 910 in FIG. 9B) can be generated. Non-Patent Document 4 describes in detail the pulse compression by the dispersion medium 906 for the phase-modulated light.

The uncertainty of the frequency being distributed is 10 ⁻¹² (about 100 Hz) or less. With this frequency, the repetition frequency f _rep = (1 / m) f _m [Hz] (m is an integer) is set. The offset frequency f _CEO can be freely set according to the request of the apparatus. For example, here, f _CEO = f _rep is set for simplicity. As already mentioned, domestic national institutions also offer clocks that guarantee the same degree of uncertainty. In the future, higher accuracy may be realized, and research is being conducted around the world aiming at ^10-18 . When the frequency interval in the ITU-T frequency grid is matched with f _m [Hz], f _m = 12.5 GHz, and m = 10, f _rep = 1,250,000,000.000 Hz high-accuracy frequency As a result, mode-locked light is generated. When f _CEO = f _rep = 1,250,000,000.000 Hz, f (154480) = 193.1000,000,000 THz with respect to n = 154480. Therefore, according to this embodiment, the optical frequency comb generated by the optical frequency reference
f (n) = n × f _rep + f _CE
Is

It will be certain in the order of. In the future, when the optical lattice clock under research and development is put into practical use

The repetition frequency can be accurately engraved by a clock having the accuracy of Since these high-accuracy clock sources are supplied by national research institutes, they can be realized even when they are received, and can also be realized by providing a carrier with distribution and supply to its own network. The carrier has a rubidium atomic oscillator with a frequency accuracy of ^10-12 .

  When the optical frequency grid supplied from the OFRSM 404 is distributed within the node 403, in the optical frequency synchronization PN 401, each element of the optical transmission device is optical frequency synchronized to the reference optical peripheral wavelength. The individual elements of the optical transmission device refer to, for example, a light source prepared for multiplex transmission, an optical demodulation circuit, and a pump light source for a phase sensitive optical amplifier.

  In order to bring optical frequency carriers at different nodes into an optical phase synchronization state, it is necessary to synchronize the optical phase in addition to the optical frequency synchronization. Normally, the phase synchronization can be maintained in the node apparatus, but it is difficult to maintain the entire network. Since the frequency used in optical communication is about 200 THz, one wavelength is about 1.5 microns. This is a length that can be changed by several degrees of temperature fluctuation for an optical fiber length of several tens of meters. This is synchronized with each other in the apparatus, but phase synchronization is difficult between photonic nodes separated by 100 km or more.

  Phase synchronization of optical frequency carriers at different nodes is possible by maintaining optical frequency synchronization. In the optical frequency synchronization PN 401, since the frequency synchronization is achieved on the order of the uncertainty of the optical frequency, the optical phase synchronization circuit is provided in the optical demodulation circuit and the pump light source for the phase sensitive optical amplifier, thereby achieving a complete synchronization state. This synchronization enables signal transmission in a single transmission optical fiber with phase synchronization between optical frequency carriers. In addition, the optical demodulation circuit for the phase modulation signal does not require a wide range of frequency pull-in circuits, and the optical demodulation circuit can be configured only by the optical phase detection circuit. For specific phase synchronization, for example, the phase difference between the two lights is adjusted by a phase shifter, an optical delay line, etc. so that the two lights are combined and interfered, and the level of the combined light is always kept constant. Control can be realized.

  When a photonic network is configured by such photonic nodes, an optical frequency synchronization PN 401 in which optical frequency synchronization is applied to the entire photonic network can be realized. In the optical frequency synchronization PN 401, as shown in FIG. 3, even when optical frequency carriers are cross-connected in a photonic node and optical frequency carriers from different routes are mixed, the next node is in a state of being substantially synchronized with each other. The signal can be transmitted through the optical fiber. Therefore, equalization compensation can be performed for mutual interference between optical frequency carriers observed in the optical fiber.

  As can be easily inferred from the above description, in the optical frequency synchronization PN 401, if a frequency with high accuracy is distributed, or if the communication carrier provides the frequency in the photonic node 403, the OFRSM 404 is installed in the photonic network. It can be generated at each node. Even if the optical frequency carrier synchronized with the optical frequency reference generated at each node transmits signals between the nodes, it is synchronized with the accuracy of the microwave transmitter (accuracy below Hz), so optical frequency synchronization is maintained. It will be done.

That is, in general, a laser light source does not have high coherence like a microwave, and the phase changes after a certain distance. As a result, a spread can be seen in the oscillation spectrum. Even in a state-of-the-art communication light source, the oscillation spectrum has a spread of about 100 kHz, so its coherence length is about 300 m. The center frequency, which is the average value of the broad oscillation spectrum, fluctuates on the order of several GHz by simply stabilizing the temperature and injection current. When the fluctuation of the center frequency is synchronized with a microwave transmitter having an accuracy of 10 ⁻¹² , the center frequency can be synchronized with an accuracy of 1 Hz or less. For this reason, the optical frequency carrier is synchronized with the accuracy (accuracy of Hz or less) of the microwave transmitter.

  Even in this case, the phase levels must be synchronized with each other. Thus, the optical frequency synchronization PN 401 can be realized. High-accuracy microwaves may be distributed by mounting clock information of a master clock in an SDH frame as in the current digital synchronous network, or a clock distributed from a satellite such as GPS, or a radio wave provided by NICT. It can also be realized by utilizing the long wave standard radio wave for watches.

It is a figure which shows the structural example of the optical communication apparatus by a prior art. It is a figure which shows the effect of the equalization compensation acquisition obtained by the structure of FIG. It is a figure explaining the subject of the photonics network by a prior art. It is a figure explaining the implementation concept of the optical frequency synchronous communication apparatus by one Embodiment of this invention. It is a figure which shows one structural example of the optical signal transmitter synchronized with the optical frequency reference | standard. It is another example of a structure of the optical signal transmitter synchronized with the optical frequency reference, and is a diagram for configuring an optical phase-synchronized multi-optical frequency carrier light source. (A) is a figure which shows the structural example of an optical phase synchronization multi optical frequency carrier light source. (B) is a figure which shows the spectrum produced | generated from the structural example of (a). (A) is a structural example which carries out fixed control of the carrier envelope offset phase, and is a figure which shows the structural example which gives an absolute optical frequency reference | standard. (B) is a figure which shows the spectrum produced | generated from the structural example of (a). (A) is a figure which shows the structural example of the mode synchronous laser light source shown by Fig.8 (a). (B) is a figure which shows the spectrum produced | generated from the structural example of (a).

Explanation of symbols

401 Optical frequency synchronization PN
402 Time / Time Standard Device 403 Photonic Node 404 OFRSM
405 Transmission device 406 Optical cross-connect device 407 Optical signal termination device 408 Optical signal transmission / reception device 409 Optical signal amplification device 410 Multiplex transmission path 501-1 to 501-M, 601 Synchronized CW light source 502-1 to 502-M, 603 1-603-M optical modulators 503-1 to 503-M, 604-1 to 604-M modulation signals 504, 605 wavelength multiplexer 602 optical phase synchronization multi-optical frequency carrier

Claims (6)

In an optical frequency synchronous communication apparatus applied to a photonic network composed of an optical frequency multiplexing transmission line and an optical cross-connect switch node,
Means for obtaining a reference clock;
Means for generating optical frequency combs whose optical phases are synchronized with each other;
Means for determining a frequency interval of the optical frequency comb based on the reference clock frequency or a multiplied clock frequency thereof, and determining an absolute value of a frequency of any one spectrum of the optical frequency comb;
By oscillating the light source for communication in the optical frequency synchronous communication device in phase-synchronization with any one of the optical frequency spectrum components of the optical frequency comb, or
By phase-synchronizing the optical frequency carrier to be reproduced or optically amplified by the optical frequency synchronization communication device to any optical frequency spectrum component of the optical frequency comb,
The optical frequency carrier is modulated and demodulated in a state of phase synchronization with each other in the photonic network ,
The absolute value of the frequency of each spectrum of the optical frequency comb is determined by synchronizing the envelope of the short pulse light obtained from the optical frequency comb and the offset phase between optical carriers with the frequency based on the reference clock. An optical frequency synchronous communication apparatus.   2. The optical frequency synchronous communication apparatus according to claim 1, wherein the means for obtaining the reference clock receives the reference clock from the outside.   2. The optical frequency synchronous communication apparatus according to claim 1, wherein the means for acquiring the reference clock generates the reference clock by itself.   The optical frequency synchronous communication apparatus according to claim 1, wherein the reference clock is distributed by radio waves, and a clock is extracted from the distributed radio waves.   The optical frequency synchronous communication apparatus according to claim 1, wherein the reference clock is distributed by an optical fiber, and a clock is extracted from the distributed optical signal.   2. The optical frequency synchronous communication apparatus according to claim 1, wherein the reference clock is a clock generated from an optical lattice clock.

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