JP2014179916A - Frequency transmission system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical fiber frequency transmission system performing comparison of clocks between two different points, and including an optical amplifier that can amplify optical signals arriving from the two-way, respectively, without branching an optical path even when amplification of the optical signal is required in a fiber transmission path.SOLUTION: An optical fiber frequency transmission system includes a first atomic clock, a first optical frequency COM, a first secondary harmonic generator, a laser light source existing at some points, and a second atomic clock, a second optical frequency COM, a second secondary harmonic generator, optical amplification means of bidirectional amplification type capable of amplifying an optical signal existing at points different from the some points. In the optical amplification means of bidirectional amplification type, parametric amplification is used.

Description

  The present invention relates to a frequency transmission system. Specifically, the present invention relates to a transmission system that transmits a frequency standard to a remote location.

Frequency standards have long been studied as providing standards for frequency, time interval, and time. In the old days, it was maintained by a quartz clock based on the rotation of the earth. However, in order to obtain a more accurate time and frequency standard, after 1967, two ultrafine interlevel microwaves in the ground state of 133 Cs atoms were used. The transition frequency was replaced by the cesium atomic frequency standard with 9,192,631,770 Hz. At present, the maximum accuracy is about 10 ¹⁵ .

  In order to provide an atomic clock that emits accurate radio waves to indicate the correct position of GPS satellites, it is a type of quartz clock that receives standard radio waves based on accurate time information from atomic clocks and receives time errors In order to provide a radio timepiece that corrects the time and to accurately measure the length using a laser, it is important to develop an accurate timepiece.

  In order to increase the accuracy of the frequency standard, it is necessary not only to stabilize the transmitter but also to increase the frequency. Increasing the accuracy of frequency standards using microwave transitions has reached its limit, and in order to obtain higher accuracy, it is necessary to use optical transitions instead of microwave transitions. If the oscillation frequency of about 9.2 GHz can be raised to 100 THz to 1 PHz, which is the frequency range of light, the standard accuracy of time and frequency can be improved by 4 to 5 digits. Yes.

  In order to realize an atomic clock using optical transition, it can be broadly classified as follows: (1) Means by a method using a single ion (mercury, ytterbium, aluminum, etc.) in an ion trap (so-called single ion clock) And (2) a method using a method using a neutral atomic group such as laser-cooled calcium (so-called neutral atomic group clock) has been studied, and in recent years has exceeded the accuracy of a cesium clock. Performance has been demonstrated.

  (1) The method using a single ion in an ion trap can use the Lamb-Dicke effect by confining a single ion in a region narrower than the wavelength of its own radiation (absorption). It is possible to remove the effects of Doppler shift and photon recoil caused by. In addition, since a single particle is used, there is an advantage that there is no frequency shift due to interaction with other atoms, but since one particle must be observed, the signal-to-noise ratio (SN ratio) is small, This is a fatal drawback for frequency stability.

  On the other hand, (2) a neutral atomic group clock using a laser-cooled neutral atom group is advantageous in terms of frequency stability because there are a large number of atoms (about 1 million), but is completely constrained. Therefore, it is extremely difficult to maintain the atomic group in an unperturbed state due to the frequency shift caused by the Doppler effect due to the movement of the atoms, the frequency shift due to the photon view, and the frequency shift due to the collision between atoms. There is a problem that the uncertainty of the clock frequency is caused by the elements, and the improvement of the accuracy of the clock is hindered.

  Both of the above-mentioned two methods have advantages and disadvantages, but a method having both advantages of these methods has been devised (see Non-Patent Document 1). The optical lattice clock described in Non-Patent Document 1 uses about 1 million low-temperature neutral atoms (strontium and ytterbium) by the Lamb-Dicke effect in the three-dimensional optical lattice potential created by the interference standing wave of laser light. It can be realized by a method of strong binding. The influence of Doppler shift and lattice recoil shift can be eliminated by the Lamb-Dicke effect, so that a high Q value can be realized and a high S / N ratio can be obtained by measuring about 1 million atoms simultaneously. . Furthermore, by appropriately selecting the wavelength of the laser constituting the optical grating, it is possible to eliminate the spectral perturbation due to the trap potential of the optical grating using the wavelength dependence of the optical grating potential. Such a wavelength is called a magic wavelength, and by realizing an optical grating at the magic wavelength, it is possible to constitute an optical clock that is extremely less affected by light shift.

  This optical lattice clock has the advantages of the conventional atomic clock, but in order to confirm its effectiveness, it must be evaluated by comparing it with a clock having equivalent or better performance. In addition, in order to use the frequency obtained from the timepiece as a frequency standard, it is necessary to confirm that the frequencies of a plurality of independent timepieces that exist physically apart from each other match. However, research on optical lattice clocks has progressed remarkably, and there was no means to measure the frequency difference of a clock at a long distance with high accuracy to match its performance, so the reliability of the clock was guaranteed only to 15 digits. Was not. In recent years, frequency comparison experiments of two optical lattice clocks separated by 24 km were performed, and it was confirmed that they matched with an accuracy of 16 digits, which is one digit higher than before (see Non-Patent Document 2).

  FIG. 1 is a configuration diagram of an optical fiber frequency transmission system shown in Non-Patent Document 2, and is a system for transmitting frequency standards obtained from two optical lattice clocks separated from each other. In order to transmit the frequency standard at two points with high accuracy, it is necessary to grasp the noise caused by vibration or temperature change superimposed on the optical signal when it passes through the optical fiber, and cancel the noise. It is essential to add modulation to the transmission side. For this purpose, it is necessary to return the received optical signal from the receiving side to the transmitting side, instead of sending the optical signal unilaterally from the transmitting side to the receiving side. It should be noted in that case that in order to ensure the accuracy of the optical lattice clock, it is important to match the optical paths of the forward path and the backward path, and therefore, it is necessary to use the same optical fiber in the round trip.

  By the way, in order to apply this optical lattice clock to gravity detection or the like, it is important to compare the optical lattice clocks 101 and 105 between two different points at an arbitrary distance. However, since the optical fiber 109 has a loss of 0.2 dB / km in the 1.55 μm band, for example, the optical signal is attenuated to 1 / 10,000 at a point away from 200 km. In order to compare the optical lattice clock between two different points, as shown in FIG. 1, a bidirectionally amplifiable optical amplifier 108 is provided to compensate for the attenuation of the optical signal in the middle of the optical fiber transmission line. There must be.

T. Ido, H. Katori, “Recoil-Free Spectroscopy of Neutral Sr Atoms in the Lamb-Dicke Regime”, Phys. Rev. Lett. 91, 053001 (2003). A. Yamaguchi1, M. Fujieda, M. Kumagai1, H. Hachisu1, S. Nagano, Y. Li, T. Ido, T. Takano, M. Takamoto, and H. Katori, “Direct Comparison of Distant Optical Lattice Clocks at the 10-16 Uncertainty ”Applied Physics Express Vol. 4 (2011) 082203 Tomoyuki Kato, Hideyuki Kimura, Yasuhiro Murakami, Ikuo Yamashita, Tamotsu Takenaka, Keiyuki Aomi “Development of a one-core bidirectional optical multi-drop system using a bidirectional optical amplifier” Furukawa Electric Time Report, No. 103 (January 1999) T. Umeki, H. Takenouchi, and M. Asobe, “First Demonstration of In-Line Phase Sensitive Amplifier based on PPLN Waveguide”, Proc. Of European Conf. On Optical Communication, Tu.3.E.1 (2012)

  However, a laser optical amplifier represented by an erbium-doped optical fiber amplifier (EDFA) (see Fig. 2), which has been used as an optical amplifier, has been amplified by stimulated emission from an inverted distributed medium. The optical amplifier to be used) has a problem of causing a laser oscillation by forming a resonator in the erbium-doped optical fiber due to slight reflection at the fusion splice point between the erbium-doped optical fiber and the other optical fiber. . In order to solve this problem, it is necessary to insert an optical isolator 204 in the EDFA as shown in FIG. 2. Therefore, simply inserting one optical amplifier amplifies the optical signal in both directions. It is impossible to do.

  For this reason, when an EDFA is inserted in the middle of the transmission system shown in Non-Patent Document 2, the optical transmission path is divided into the forward path and the backward path only at the insertion position of the optical amplifier, and two optical amplifiers are used for the forward path and the backward path. It will be necessary to use it separately for each purpose. The difference in the fluctuation of the optical fiber length at the portion where the optical path is branched limits the accuracy of the optical lattice clock.

As an EDFA capable of amplifying a bidirectional optical signal, a configuration as shown in Non-Patent Document 3 has been proposed. FIG. 3 is a diagram showing a configuration of a bidirectional amplifier using an EDFA disclosed in Non-Patent Document 3. However, as is clear from FIG. 3, the bidirectional amplifier shown in FIG. 3 does not avoid the limitation that the optical isolator must be arranged in the optical path when using the laser amplifier. The wavelength of the optical signal is changed in the return path (λ ₁ and λ _{2 in} FIG. 3), the optical signal for the forward path and the return path is branched by the WDM coupler, amplified by the amplifier in the same direction, and multiplexed again by the WDM coupler Therefore, the problem that the optical path has been branched and the difference in fluctuation of the optical fiber length of the branched optical path portion limits the accuracy of the optical lattice clock has not been solved.

  In order to realize an optical lattice clock with an accuracy higher than 16 digits, it is necessary to realize an optical amplifier capable of amplifying a bidirectional signal in the same optical path. It was discovered for the first time that an optical amplifier capable of amplifying a bidirectional optical signal can be constructed by amplifying the optical signal using parametric amplification instead.

  The present invention has been made in view of the above problems. An object of the present invention is an optical fiber frequency transmission system that compares clocks between two different points, and even when amplification of an optical signal is necessary in a fiber transmission line, it can be performed from both directions without branching the optical path. An object of the present invention is to provide an optical fiber frequency transmission system including an optical amplifier capable of amplifying each optical signal that arrives. Thereby, it is possible to provide a highly accurate optical lattice clock.

  The invention according to claim 1 of the present invention includes a first atomic clock, a first optical frequency comb, a first second harmonic generator, a laser light source, and the laser light source that are present at a certain point. A second atomic clock, a second optical frequency comb, a second second harmonic generator, and a bidirectional amplification type optical amplifying means capable of amplifying an optical signal, which are present at a point different from the point In the optical fiber frequency transmission system, parametric amplification is used in the bidirectional amplification type optical amplification means.

  According to the present invention, in an optical fiber frequency transmission system for comparing clocks between two different points, an optical lattice clock can be used even when optical signal amplification is required for loss compensation of the fiber transmission line. Therefore, it is possible to amplify the optical signal without reducing the accuracy of the optical clock, so that it is possible to construct an extremely accurate optical lattice clock.

It is a figure which shows the structural example of an optical fiber frequency transmission system. It is a figure which shows the structural example of an erbium doped optical fiber amplifier (EDFA). It is a figure which shows the structure of the bidirectional | two-way amplifier using the conventional EDFA. It is a figure which shows the basic composition of the conventional one-way amplification type phase sensitive optical amplifier. It is a figure which shows the basic structural example of the bidirectional | two-way amplification type phase sensitive optical amplifier which concerns on embodiment of this invention. It is a figure which shows the specific structure of a one-way amplification type phase sensitive optical amplifier using a periodically poled lithium niobate waveguide. It is a figure which shows the specific structural example which concerns on embodiment of this invention.

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

[Basic configuration of phase sensitive optical amplifier (PSA)]
First, before describing the optical fiber frequency transmission system, a phase sensitive optical amplifier (PSA) capable of bidirectional amplification, which is a component thereof, will be described.

  FIG. 4 shows a basic configuration of the phase sensitive optical amplifier. This optical amplifier includes a phase sensitive light amplification unit 401, a pumping light source 402, a pumping light phase control unit 403, and three light branching units 404-1, 404-2, 404-3. In this optical amplifier, the input signal light 410 is amplified when the phase of the signal light and the pumping light in the phase sensitive light amplification unit 401 coincides, and when the phase of both is shifted by 90 degrees, the input signal light 410 is It has a characteristic to attenuate. If the phase between the pumping light and the signal light is matched so that the amplification gain is maximized by utilizing this characteristic, the spontaneous emission light having the quadrature phase with the signal light is not generated, that is, the SN ratio is not deteriorated. Signal light can be amplified.

  In order to achieve phase synchronization between the signal light and the pump light, the phase of the pump light 411 is controlled so as to be synchronized with the phase of the input signal light 410 branched by the optical branching unit 404-1. The pumping light phase control unit 403 detects a part of the output signal light 412 branched by the light branching unit 404-3 with a narrow-band detector and controls the phase of the pumping light 411 so that the output signal becomes maximum. To do. As a result, the phase sensitive light amplification unit 401 is controlled so that the phase of the signal light and the phase of the pumping light are synchronized, and light amplification without degradation of the SN ratio can be realized. The pumping light phase control unit 403 may be configured to directly control the phase of the pumping light source 402 in addition to the configuration of controlling the phase of the pumping light on the output side of the pumping light source 402 as shown in FIG.

  The phase-sensitive optical amplifier whose basic configuration is shown in FIG. 4 is based on parametric amplification and does not require an isolator in the optical path of the optical signal, and thus can be amplified in both directions. Hereinafter, the configuration of a phase sensitive optical amplifier for performing bidirectional amplification will be described with reference to FIG.

  As shown in FIG. 5, this optical amplifier has a phase sensitive light amplification unit 501, a pumping light source 502, a pumping light phase control unit 503, and three light branching units 504-1, as in the configuration shown in FIG. , 504-2, 504-3. The optical amplifier further includes a pumping light source 505, a pumping light phase control unit 506, and three light branching units 507-1, 507-2, and 507-3.

  The phase sensitive optical amplifier shown in FIG. 5 has a configuration in which the phase sensitive optical amplifier 501 is shared for the forward path and the backward path. By using such a configuration, it is possible to realize phase-sensitive amplification independently in the forward path and the backward path while keeping the optical path completely the same in bidirectional signals.

[Specific configuration of phase sensitive optical amplifier (PSA)]
Before describing a specific configuration of a phase-sensitive optical amplifier capable of amplifying a bidirectional signal according to the present embodiment, binary phase modulation (BPSK) or binary differential phase modulation (non-patent document 4) FIG. 6 shows a specific configuration for realizing unidirectional phase sensitive amplification from a DPSK) transmission signal.

  In the configuration shown in FIG. 6, a part of the signal light is amplified using a fiber laser amplifier (EDFA) in order to obtain sufficient power from the weak laser light used for optical communication to obtain the nonlinear optical effect. . In the configuration shown in FIG. 6, the signal light and the first excitation light are combined and amplified, and then incident on the second-order nonlinear optical element. A second harmonic of the signal light is generated inside the second-order nonlinear optical element, and a carrier wave is extracted by generating a difference frequency between the generated second harmonic and the first excitation light. The difference frequency light is injection-locked to the second pumping light oscillated at the same wavelength, and then combined with the first pumping light, and is then used as the first and second pumping light by using a fiber laser amplifier (EDFA). The constructed excitation fundamental wave light is amplified. The amplified fundamental wave light is incident on the second-order nonlinear optical element in the subsequent stage to generate sum frequency light. Then, the signal light and the sum frequency light are incident on the second-order nonlinear optical element in the subsequent stage to perform degenerate parametric amplification, thereby performing phase sensitive amplification.

  Hereinafter, the configuration of a phase sensitive amplification device including a carrier extraction unit that extracts a carrier for amplifying 1.54 μm signal light subjected to BPSK or DPSK will be described with reference to FIG. A part of the input signal light 601 is adjusted in polarization by using the polarization controller 602, branched by the optical branching unit 603, and combined with the first pumping light, and then an erbium-doped fiber laser amplifier (EDFA). ) Is amplified at 606. The amplified signal light and the first excitation light are input to the second-order nonlinear optical element 607-1. The second-order nonlinear optical element 607 according to this embodiment includes an optical waveguide 651 made of lithium niobate (PPLN) that is periodically poled. The optical waveguide 651 has a periodically poled structure that satisfies the quasi-phase matching condition that enables the second harmonic generation of the signal light and the difference frequency generation between the generated second harmonic and the first excitation light. Is formed.

  A second harmonic having a wavelength half that of the signal light is generated by the second-order nonlinear optical element 607-1 to which the signal light and the first excitation light are input. Further, the second-order nonlinear optical element 607-1 generates difference frequency light between the second harmonic generated inside and the first excitation light. Since there is a relationship of 2φs−φp1−φp2 = 0 between the phase φs of the signal light, the phase φp1 of the first excitation light, and the phase φp2 of the difference frequency light, the phase φp2 of the difference frequency light is Using the phase φs of the signal light and the phase φp1 of the first excitation light, φp2 = 2φs−φp1. That is, it is difficult to extract the phase of the carrier wave because the normal data signal is modulated. However, by using the second harmonic generation, the signal light phase φs is doubled to obtain a binary value. Phase modulation can be removed. Further, by using the difference frequency generation, the difference frequency light including the phase information of the carrier wave can be extracted in the 1.55 μm band which is the same wavelength band as the signal light.

  If the transmitted signal light is a complete binary phase modulation state, the difference frequency light has no modulation effect. However, since the phase noise is superimposed on the optical signal that has propagated through the transmission line such as a fiber, a complete binary phase modulation state is not obtained. The effect due to non-uniformity remains. Further, since the originally weak signal light is further demultiplexed and input to the second-order nonlinear optical element 607-1, the light intensity of the obtained difference frequency light is weak. In order to solve these problems, light injection locking is performed using difference frequency light.

  As shown in FIG. 6, the signal light, the first excitation light, and the difference frequency light output from the second-order nonlinear optical element 607-1 pass through the optical circulator 608 and are then demultiplexed into the respective lights. . An arrayed waveguide grating (AWG) type wavelength multiplexer / demultiplexer 609 is used for demultiplexing. The signal light output from the duplexer 609 is emitted to the space system. The first excitation light output from the duplexer 609 is quenched using the isolator 610. A semiconductor laser 611 that oscillates at substantially the same wavelength as the difference frequency light is connected to the duplexer output port having a wavelength that matches the difference frequency light. After adjusting the light intensity of the difference frequency light to be 10 μW to 100 μW, light injection synchronization is performed by inputting to the semiconductor laser 611. The second excitation light having the same phase as the difference frequency light can be generated by the light injection locking.

  The second excitation light has the same phase as the difference frequency light phase φp2. Since the light intensity of the second excitation light is determined by the output of the semiconductor laser 611, it is possible to obtain excitation light of several tens of mW or more using weak difference frequency light of about several tens of μW. The influence due to the non-uniformity of the modulation of the signal light superimposed on the frequency light can be mitigated. The first excitation light is incident from the multiplexing side of the AWG type multiplexer / demultiplexer 609, combined with the second excitation light, and then extracted using the circulator 608. The first excitation light and the second excitation light obtained by extracting the signal light carrier phase by the nonlinear element and the light injection synchronization are used as the excitation fundamental wave light.

  The sum frequency light and the excitation light emitted from the PPLN waveguide 651-2 are separated using a dichroic mirror 653. The sum frequency light having a wavelength of 0.77 μm reflected by the dichroic mirror 653 is guided to the second-order nonlinear optical element 607-3 via the polarization maintaining fiber 616 having a single mode propagation characteristic at the wavelength of 0.77 μm. It is. At this time, excitation light and ASE light in the vicinity of a wavelength of 1.54 μm that could not be completely removed by the dichroic mirror 653 are also incident on the polarization maintaining fiber 616, but this fiber that is single mode at 0.77 μm Since light confinement is weak with respect to light having a wavelength of 1.54 μm, it is possible to effectively attenuate such unnecessary light by propagating a length of about 1 m. The sum frequency light guided by the polarization maintaining fiber 616 is combined with the signal light 601 having a wavelength of 1.54 μm using the dichroic mirror 654. In order to reflect only the sum frequency light, the dichroic mirror 654 is emitted from the PPLN waveguide 651-2, is reflected by the dichroic mirror 653, and passes through the polarization maintaining fiber 616. And ASE light can be effectively removed. The signal light 601 and the sum frequency light are combined and enter the PPLN waveguide 651-3. The PPLN waveguide 651-3 has the same performance and phase matching wavelength as the PPLN waveguide 651-2, and can perform phase-sensitive amplification of signal light by degenerate parametric amplification. In the present embodiment, the two PPLN waveguides 651-2 and 651-3 are each controlled to have a constant temperature by individual temperature controllers. It is conceivable that the phase matching wavelengths do not match at the same temperature due to manufacturing errors of the two PPLN waveguides, but even in such a case, the phase matching wavelengths of both must be matched by individually controlling the temperatures. Can do. The light emitted from the PPLN waveguide 651-3 is separated by the dichroic mirror 656 into sum frequency light that is excitation light and amplified signal light. Also at this time, since the wavelength of the sum frequency light and the amplified signal light are completely different, the unnecessary second harmonic component in the output can be effectively removed.

  In the phase sensitive amplification, it is necessary to synchronize the phases of the excitation light and the signal light. However, in the configuration shown in FIG. 6, a part of the output amplified signal light is branched by the optical branching unit 618 and is detected by the photodetector 619. After receiving the light, phase synchronization was performed by a phase locked loop circuit (PLL) 620. Using the phase modulator 621 disposed in front of the AWG type multiplexer, weak phase modulation is applied to the first excitation light by the sin wave. The optical detector 619 and the PLL circuit 620 detect the phase shift of the phase modulation, and the driving voltage of the extender of the optical fiber 622 and the bias of the phase modulator 621 by PZT arranged in front of the AWG type multiplexer. By feeding back to the voltage, the fluctuation of the optical phase due to the vibration of the optical fiber component and the temperature fluctuation is absorbed, so that the phase sensitive amplification can be stably performed.

  FIG. 7 shows a specific configuration of a phase sensitive optical amplifier capable of bidirectional amplification. As shown in FIG. 7, the phase sensitive optical amplifier has the same configuration as the configuration shown in FIG. Further, this optical amplifier has a configuration similar to the configuration shown in FIG. 6 (a configuration in the 700s order) for amplifying signal light in which the forward path in the configuration shown in FIG. Element). The phase sensitive optical amplifier shown in FIG. 7 is configured to share the second-order nonlinear optical element 607-3 for bidirectional signal light. With the configuration as shown in FIG. 7, it is possible to independently amplify the phase of the signal light from both directions.

In addition, the bidirectional amplifier in this embodiment uses lithium niobate (LiNbO ₃ ) doped with Zn as a second-order nonlinear optical material whose polarization is periodically inverted, but the present invention is limited to lithium niobate. Lithium tantalate (LiTaO ₃ ), mixed crystal of lithium niobate and lithium tantalate (LiNb _(x) Ta _(1-x) O ₃ (0 ≦ x ≦ 1)), potassium niobate (KNbO ₃₎ ), A second-order nonlinear optical material typified by potassium titanyl phosphate (KTiOPO ₄ ) and the like, the same effect can be obtained. Further, the additive of the second-order nonlinear optical material is not limited to Zn, and Mg, Zn, Sc, In, Fe may be used instead of Zn, or no additive may be added. Good.

  Actually, in the optical fiber frequency transmission system shown in FIG. 1, an optical fiber frequency transmission experiment was performed using the configuration of FIG. 7 as a bidirectional amplification type optical amplifier. An optical frequency comb that uses a signal of wavelength 1538nm for transmission, converts it to a 769nm signal by taking the second harmonic of the optical signal of 1538nm at both points, and locks it at the frequency of the strontium atomic clock of wavelength 698nm. The frequency of both atomic clocks was compared by detecting the beat signal. In the experiment, the influence of the general relativistic gravity shift due to the elevation difference between the two points is corrected.

When time accuracy was evaluated by the Allan deviation (uncertainty of frequency difference) of the atomic clocks at both points, it was 5 × 10 ^-18 in 1000 seconds. As a result, it was confirmed experimentally that both watches matched with an 18-digit accuracy far exceeding the 16-digit accuracy that was the limit of the prior art.

101, 105 Optical lattice clocks 102, 106 Optical frequency combs 103, 107 Second harmonic generator 104 Laser light source 108 Optical amplifier 109 Optical fiber 201 WDM coupler 202 Excitation laser 203, 204 Optical isolator 205 Erbium-doped optical fiber 300 Bidirectional Amplifiers 301 to 304 WDM coupler 305 EDFA
401 Phase sensitive light amplification unit 402 Excitation light source 403 Excitation light phase control units 404-1, 404-2, 404-3 Optical branching unit 410 Input signal light 411 Excitation light 412 Output signal light 501 Phase sensitive light amplification units 502, 505 Excitation Light source 503, 506 Excitation light phase controller 504-1, 504-2, 504-3, 507-1, 507-2, 507-3 Optical branching unit 510 Input signal light (outward path)
511 Excitation light (outward)
512 Output signal light (outward)
513 Input signal light (return)
514 Excitation light (return path)
515 Output signal light (return path)
601 Input signal light 602 Polarization controllers 603, 605, 612, 618 Optical branching unit 604 ECL
606, 613 EDFA
607 Second-order nonlinear optical element 608 Optical circulator 609 AWG type multiplexer / demultiplexer 610 Isolator 611 Semiconductor laser 614 Band pass filter 616 Polarization maintaining fiber 619 Photo detector 620 Phase locked loop circuit (PLL)
621 Phase modulator 622 PZT optical fiber 623 PM optical attenuator 651 PPLN waveguides 653, 654, 656 Dichroic mirror 701 Input signal light 702 Polarization controllers 703, 705, 712, 718 Optical branching unit 704 ECL
706, 713 EDFA
707 Second-order nonlinear optical element 708 Optical circulator 709 AWG type multiplexer / demultiplexer 710 Isolator 711 Semiconductor laser 714 Bandpass filter 716 Polarization maintaining fiber 719 Photodetector 720 Phase-locked loop circuit (PLL)
721 Phase modulator 722 Optical fiber 723 by PZT PM optical attenuator 751 PPLN waveguide 753 Dichroic mirror

Claims (5)

Exists at a certain point,
A first atomic clock;
A first optical frequency comb;
A first second harmonic generator;
A laser light source;
Exists at a point different from the certain point,
A second atomic clock;
A second optical frequency comb;
A second second harmonic generator;
An optical fiber frequency transmission system comprising a bidirectional amplification type optical amplification means capable of amplifying an optical signal, wherein the bidirectional amplification type optical amplification means uses parametric amplification. Fiber frequency transmission system.   2. The optical fiber frequency transmission system according to claim 1, wherein the bidirectional optical amplification means is a phase sensitive optical amplifier using a parametric amplification effect.   3. The optical fiber frequency transmission system according to claim 1, wherein both the first atomic clock and the second atomic clock are optical lattice clocks.   The optical fiber frequency transmission system according to any one of claims 1 to 3, wherein the parametric amplification is performed using an optical waveguide made of a second-order nonlinear optical material that is periodically poled. Optical fiber frequency transmission system. The optical fiber frequency transmission system according to claim 4, wherein the second-order nonlinear optical material is LiNbO ₃ , KNbO ₃ , LiTaO ₃ , LiNb _x Ta _1-x O ₃ (0 ≦ x ≦ 1), KTiOPO ₄ , or An optical fiber frequency transmission system characterized in that at least one selected from the group consisting of Mg, Zn, Fe, Sc, and In is added thereto.

Images