Optical frequency remote calibration system

Abstract

To provide a calibration system capable of remotely calibrating an optical frequency of the light source to be calibrated by using an optical frequency comb device disposed in a distant place.SOLUTION: A calibration system comprises: a slave calibration unit 103 equipped with one or more light sources to be calibrated; a master calibration unit 102 for measuring and calibrating an optical frequency of the light sources to be calibrated that are provided to the slave calibration unit 103 by using an optical frequency comb device; and an optical transmission unit 106 for connecting the slave calibration unit 103 and the master calibration unit 102 together. The master calibration unit 102 calibrates the optical frequency of output light of the light sources to be calibrated of the slave calibration unit 103 having been transmitted via the optical transmission unit 106 by using the optical frequency comb device, and measures and calibrates an optical frequency with respect to the output light of the optical frequency comb device and electrical output of beam signals of output light of the light sources to be calibrated. The master calibration unit 102 also stabilizes an operating frequency of the optical frequency comb device on the basis of an RF oscillator capable of remote calibration based on a standard pertaining to time and frequency.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a calibration system that calibrates the optical frequency of a light source to be calibrated that is provided in a slave calibration unit, by using an optical frequency comb device that is provided in a master calibration unit. [Background technology]

[0002] As a technique for measuring and calibrating the optical frequency of a laser light source with high accuracy, a method using a beat signal generated by interfering the output light of an optical frequency comb device with the output light of a light source to be calibrated is widely used. A representative example is Patent Document 1. Patent Document 1 provides a means for determining the optical frequency with high accuracy based on the frequency of a beat signal obtained by interfering the output light of a single light source to be measured with the output light of an optical frequency comb device located close to the light source to be measured, the repetition frequency and carrier-envelope offset (CEO) frequency of the optical frequency comb device, and the mode order obtained by measuring the optical frequency of the light source to be measured with a wavemeter. Patent Document 2 provides a method for using the offset laser synchronized with the optical frequency comb and the beat signal of the light source to be measured for calibration without using a wavemeter. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2015-5601 A [Patent Document 2] JP 2014-190759 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, as seen in Patent Documents 1 and 2, operations have been assumed up to now on the premise that the optical frequency of a single light source to be calibrated that is installed in the same room as the optical frequency comb device will be calibrated, and there has been no discussion up to now of a calibration method for remotely calibrating a light source to be calibrated that is installed in a remote location, nor of a distributed calibration method capable of selectively or simultaneously calibrating multiple light sources to be calibrated that are installed in multiple remote locations.

[0005] On the other hand, in recent years, the industrial world, especially in the manufacturing industry, has been facing an increasing importance of improving corporate profitability and international competitiveness through a paradigm shift to "Industry 4.0," which promotes remote command / operation of factory equipment and digitalization of equipment / inspection data to maximize productivity.

[0006] However, in the conventional optical frequency calibration system, the light source to be calibrated must be removed from the equipment in use, transported to a calibration section equipped with an optical frequency comb device for calibration, and then the calibration work must be performed. In addition to the work for calibration, incidental work such as removing, attaching, and transporting the light source to be calibrated is required, and there is a problem that the lead time required for calibration is long. Specifically, the light source to be calibrated is removed from the equipment in use, transported to a calibration section equipped with an optical frequency comb device for calibration, and then installed near the optical frequency comb device, and then the light source is warmed up and calibration is performed. Then, when the calibration is completed, the light source to be calibrated is removed again and transported to the original equipment, and reattached to the equipment, and the light source is warmed up and optically adjusted, and then the equipment is restarted.

[0007] As described above, the conventional optical frequency calibration system had an adverse effect on factory productivity. In addition, when there are multiple light sources to be calibrated, they must be manually removed, transported, installed, and warmed up one by one, which increases labor costs and equipment downtime. Furthermore, the current calibration method using an optical frequency comb requires long measurements to calibrate one light source, and it is necessary to operate the optical frequency comb device for each device to be calibrated.

[0008] Another technical issue is that the optical output of iodine-stabilized helium-neon (HeNe) lasers and axial Zeeman-type HeNe lasers, which are commonly used to calibrate wavelength meters in the 633 nm band, is low, on the order of 0.1 mW, which is an obstacle to scaling up the calibration system.

[0009] To explain step by step, the wavelength of the output light from a HeNe laser is around 633 nm, but the central wavelength of the output light from an optical frequency comb that uses an erbium-doped fiber laser as an oscillator is around 1550 nm, which is far from 633 nm. Even if the bandwidth of this optical frequency comb is expanded to a wavelength of 633 nm by using the nonlinear optical effect of a nonlinear optical fiber, the optical output power of a single longitudinal mode can be low, on the order of a few nW.

[0010] For this reason, when the beat frequency of one of the longitudinal modes of this optical frequency comb and the output light of the calibrated light source is measured by photoelectric conversion using a photodetector, the signal-to-noise ratio (S / N ratio) of the beat signal is low. If the S / N ratio is less than 30 dB, a problem called a slip cycle will occur in the frequency counter, and this, along with the technical background that makes it impossible to measure the frequency correctly, makes frequency measurement difficult.

[0011] Therefore, it is not possible to expand the calibration system by spatially dividing the optical output of the optical frequency comb device and obtaining a beat signal from the output light of each laser to be calibrated. Considering the current situation in which it is technically possible to calibrate a single HeNe laser only by using the full power of the output light from the optical frequency comb device, it is not possible to calibrate a large number of lasers to be calibrated at the same time, and it is not possible to perform calibration of multiple light sources simultaneously.

[0012] The present invention has been made against the above background, and has as one object to provide a calibration system that can remotely calibrate the optical frequency of the output light of a light source to be calibrated using an optical frequency comb device disposed at a location away from the location where the light source to be calibrated is installed, and another object is to provide a distributed calibration system that can selectively or simultaneously calibrate multiple light sources to be calibrated that are installed at multiple remote locations. [Means for solving the problem]

[0013] To solve the above problems, the present invention provides: one or more slave calibration units each having one or more light sources to be calibrated; a master calibration unit including an optical frequency comb device, the master calibration unit using the optical frequency comb device to measure and calibrate the optical frequency of a light source to be calibrated included in the slave calibration unit; an optical transmission unit that connects the slave calibration unit and a master calibration unit; The master calibration unit relates to a remote optical frequency calibration system, in which, when calibrating the optical frequency of the output light of the calibrated light source of the slave calibration unit transmitted via the optical transmission unit using the optical frequency comb device, the master calibration unit is configured to measure and calibrate the optical frequency using an electrical output of a beat signal between the output light of the optical frequency comb device and the output light of the calibrated light source, and has a function of stabilizing the operating frequency of the optical frequency comb device based on an RF oscillator capable of remote calibration based on time and frequency standards.

[0014] According to this remote calibration system, the slave calibration unit and the master calibration unit are connected via an optical transmission unit, so that in order to calibrate the optical frequency of the light source to be calibrated provided in the slave calibration unit, there is no need to transport and install the light source to the vicinity of the optical frequency comb device of the master calibration unit; the light source to be calibrated can be calibrated while remaining installed in the slave calibration unit.

[0015] Therefore, according to the remote calibration system of the present invention, the optical frequency of the light source to be calibrated can be calibrated efficiently in a short time.

[0016] In the remote calibration system of this aspect (first aspect), the optical frequency comb device may include an offset laser to which the frequency stability of the optical frequency comb is transferred by phase synchronization. Also, the optical transmission section may be composed of an optical transmission path such as an optical fiber or an optical waveguide.

[0017] The remote calibration system of the first aspect further includes a management unit having a function of receiving an operating status of the slave calibration unit, a function of transmitting a calibration command for the light source to be calibrated to the master calibration unit, and a function of receiving a calibration result from the master calibration unit; the slave calibration unit has a function of transmitting an operation status to the management unit, a function of receiving an optical path switching signal from the master calibration unit, and a function of coupling the output light of the calibrated light source to an optical transmission path by switching the optical path of the output light, The master calibration unit can adopt an aspect (second aspect) in which the master calibration unit receives a calibration command from the management unit and transmits an optical path switching command to the slave calibration unit, and when calibrating the optical frequency of the output light of the calibrated light source transmitted from the slave calibration unit via the optical transmission path using the optical frequency comb device, the master calibration unit has the function of measuring and calibrating the optical frequency using the electrical output of a beat signal between the output light of the optical frequency comb device and the output light of the calibrated light source, the function of transmitting the calibration results to the management room, and the function of stabilizing the operating frequency of the optical frequency comb device based on an RF oscillator capable of remote calibration based on time and frequency standards via GPS.

[0018] Moreover, the remote calibration system of the second aspect includes: the slave calibration unit further has an encoding function of applying frequency modulation to the optical frequency of the output light of the light source to be calibrated by an optical modulator and of applying a different modulation frequency change to each of the light sources to be calibrated from time to time; A third aspect can be adopted in which the master calibration unit further has a function of selectively measuring and calibrating the optical frequency by mixing and decoding an RF signal used to encode the output light of a specific light source to be calibrated among the multiple light sources to be calibrated, for the electrical output of the beat signal of the output light of the optical frequency comb device and the output light of the light source to be calibrated.

[0019] Moreover, the remote calibration system of the second aspect or the third aspect comprises: The master calibration unit can have a function of calibrating the optical frequency of the output light of the calibrated light source transmitted from the slave calibration unit via the optical transmission path by using the optical frequency comb device including an offset laser to which the frequency stability of an optical frequency comb is transferred by phase synchronization (fourth or fifth aspect).

[0020] Moreover, the remote calibration system of the third aspect includes: A sixth aspect can be adopted in which the master calibration unit has a function of simultaneously executing the decoding in order to calibrate the optical frequencies of a plurality of the light sources to be calibrated.

[0021] Moreover, the remote calibration system of the fifth aspect includes: A seventh aspect can be adopted in which the master calibration unit has a function of simultaneously executing the decoding in order to calibrate the optical frequencies of a plurality of the light sources to be calibrated.

[0022] The present invention also provides a method for calibrating optical frequencies of one or more calibrated light sources provided in one or more slave calibration units, respectively, by using an optical frequency comb device provided in a master calibration unit, the method comprising the steps of: The slave calibration unit and the master calibration unit are connected by an optical transmission unit; transmitting output light of a light source to be calibrated provided in the slave calibration unit to the master calibration unit via the optical transmission unit; The master calibration unit relates to a method for remotely calibrating an optical frequency, in which, when calibrating the optical frequency of the transmitted output light of the calibrated light source using the optical frequency comb device, the optical frequency is measured and calibrated using the electrical output of a beat signal between the output light of the optical frequency comb device and the output light of the calibrated light source, and the operating frequency of the optical frequency comb device is stabilized based on an RF oscillator capable of remote calibration based on time and frequency standards.

[0023] The present invention also provides a calibration system for a calibration target light source, comprising: one or more slave calibration units each having an optical frequency measuring unit for measuring an optical frequency of the calibration target light source; a master calibration unit including an optical frequency comb device and an optical frequency calibration unit for calibrating an optical frequency; an optical transmission unit that connects the slave calibration unit and a master calibration unit; the master calibration unit has a function of stabilizing an operating frequency of the optical frequency comb device based on an RF oscillator capable of remote calibration based on time and frequency standards, and is configured to transmit output light of the optical frequency comb device to the slave calibration unit via the transmission unit; the slave calibration unit is configured to measure an optical frequency of the output light of the light source to be calibrated, based on an electrical output of a beat signal of the output light of the optical frequency comb device transmitted to the slave calibration unit, using the optical frequency measurement unit, and to transmit an RF frequency signal of the obtained beat signal to the master calibration unit via the transmission unit; The master calibration unit further relates to a remote optical frequency calibration system configured to calibrate the frequency of the output light of the calibrated light source by the frequency calibration unit based on the RF frequency signal of the beat signal transmitted from the slave calibration unit via the transmission unit. Effect of the Invention

[0024] According to the remote calibration system of the present invention, the light source to be calibrated can be calibrated without removing the light source to be calibrated from the equipment installed in the slave calibration unit. When calibrating the light source to be calibrated, the equipment can be seamlessly shifted from an operating state to a calibrated state and from the calibrated state to an operating state, eliminating the downtime that has been a problem in the past, such as removing, transporting, installing, and warming up the light source to be calibrated, and maximizing the productivity of the factory. In addition, since the calibration work can be performed by remote operation, the calibration unit, which requires precise measurement, can be made unmanned and its environment can be precisely controlled to an ideal temperature, and a highly stable environment with little vibration caused by human movement can be maintained.

[0025] In addition, the number of slave calibration units can be expanded, and therefore, when production demand increases, the number of light sources that can be calibrated can be increased. In addition, by providing a different modulation / demodulation signal for each light source to be calibrated, multiple light sources to be calibrated can be calibrated simultaneously, and even if the number of light sources to be calibrated increases in the future, this can be accommodated, and a scalable calibration system can be constructed.

[0026] In addition, the offset laser can be considered as a part of the optical frequency comb device because the phase is aligned with the optical frequency comb by the phase-locked loop and the offset laser has high coherence. By utilizing the high optical output of this offset laser, a signal-to-noise ratio of 30 dB or more, which is important for beat frequency measurement, can be achieved. In addition, the optical encoding and electrical decoding mechanisms make it possible to calibrate multiple target lasers simultaneously without splitting the weak output light of the optical frequency comb device.

[0027] In addition, if national standards are applied to the time and frequency standards, and the operating frequency of the optical frequency comb device is determined based on an RF oscillator remotely calibrated by the national standards via GPS satellites, a state that is traceable to the national standard can be established. In addition, by generating the RF frequency used for encoding and decoding by multiplying the RF oscillator by a constant, it is possible to achieve both excellent long-term frequency stability and multiplexing of beat signals. [Brief description of the drawings]

[0028] [Figure 1] 1 is a block diagram showing a schematic configuration of a distributed calibration system according to an embodiment of the present invention. [Diagram 2] FIG. 1 is a block diagram showing a schematic configuration of a slave calibration room according to the present embodiment. [Diagram 3] FIG. 1 is a block diagram showing a schematic configuration of a master calibration room according to an embodiment of the present invention. [Figure 4] FIG. 13 is a block diagram showing a schematic configuration of a master calibration room according to a modified example. [Diagram 5] FIG. 2 is a block diagram showing a schematic configuration of an optical frequency measurement unit according to the present embodiment. [Figure 6] FIG. 13 is a block diagram showing a schematic configuration of an optical frequency measurement unit according to a modified example. [Figure 7] 1 is an explanatory diagram for explaining an optical frequency measurement method according to an embodiment of the present invention; [Figure 8] FIG. 13 is a block diagram showing a schematic configuration of a slave calibration room according to another embodiment of the present invention. [Figure 9] FIG. 13 is a block diagram showing a schematic configuration of an optical frequency measurement unit according to another embodiment of the present invention. [Figure 10] FIG. 4 is a diagram showing a specific example of the configuration of an optical path switching device and multiplexing unit in a slave calibration room according to the present invention. [Figure 11] FIG. 11 is a diagram showing a specific example of the configuration of a photoelectric conversion unit in a master optical path switching device / frequency measurement unit of a master calibration room according to the present invention. [Figure 12] 3A to 3C are schematic diagrams showing two configurations of a frequency measurement unit according to the present invention. [Figure 13] 13 is a configuration example of a master calibration room in the measurement method 2 of FIG. 12. [Figure 14] 13 is a configuration example of a slave calibration room in the measurement method 2 of FIG. 12. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0029] Hereinafter, specific embodiments of the present invention will be described with reference to the drawings.

[0030] 1 is a block diagram showing a schematic configuration of a distributed calibration system (1) according to this embodiment. The distributed calibration system (1) of this embodiment will be described below.

[0031] 1. Configuration of distributed calibration system As shown in Fig. 1, the distributed calibration system (100) of this example comprises a control room (control section) (101), a master calibration room (master calibration section) (102) equipped with an optical frequency comb device, and a group of slave calibration rooms (slave calibration sections) (103) equipped with light sources to be calibrated. The group of slave calibration rooms (103) is made up of N distributed slave calibration rooms 1 (104) to N (105). Each slave calibration room is equipped with one or more light sources to be calibrated. Here, N is a natural number representing the number of slave calibration rooms, and is assumed to include 1.

[0032] In calibration, first, slave calibration room 1 (104) transmits an equipment operation status signal 1, ..., slave calibration room N (105) transmits an equipment operation status signal N to the control room (101), and based on these operation statuses, the control room (101) determines which light source to be calibrated in which slave calibration room can be calibrated (or whether it is necessary to calibrate it), and transmits a calibration command to the master calibration room (102).

[0033] The master calibration room (102) that has received the calibration command sends an optical path switching command to switch the optical paths of the light sources to be calibrated in the group of slave calibration rooms (103) so that the output light of one or more light sources to be calibrated installed in the slave calibration room that is the subject of the calibration command is transmitted to the master calibration room (102). At the same time, it sends an encoding command to modulate and multiplex the optical frequency of the light sources to be calibrated.

[0034] The slave calibration room including the light source to be calibrated that is the subject of the calibration command receives the optical path switching command and the encoded command, switches the optical path of the output light of the light source to be calibrated installed in the slave calibration room, imparts a different modulation pattern to the optical frequency for each light source to be calibrated, propagates the output light of the light source to be calibrated through the corresponding optical transmission path of the optical transmission path group (106), and sends it to the master calibration room (102). Here, examples of the optical transmission path include transmission paths that use optical fiber, optical waveguides, etc., rather than free space propagation.

[0035] After the output light of the light source to be calibrated is sent to the master calibration room (102), the master calibration room (102) uses an installed optical frequency comb device to demodulate and calibrate the optical frequency of the output light of one or more light sources to be calibrated, reports the calibration results to the management room (101), transmits an optical path switching command signal to the group of slave calibration rooms (103), and performs an optical path switching operation in which the optical path of the output light of the calibrated light source for which calibration has been completed is incorporated into the device in the corresponding slave calibration room, thereby completing the calibration of the calibrated light source corresponding to the calibration command.

[0036] The control room (101) receives the calibration results and determines the schedule for the next calibration. When the master calibration room (102) receives a new calibration command from the control room (101) after the calibration is completed, it executes the above series of procedures for the light source to be calibrated in the slave calibration room that corresponds to the new calibration command.

[0037] It is assumed that a plurality of slave calibration rooms can be selected by a calibration command, and that a plurality of light sources to be calibrated can be simultaneously calibrated by a calibration command.

[0038] 2. Configuration of the slave calibration room 2 is a block diagram showing a schematic configuration of the i-th slave calibration room (201) among the group of slave calibration rooms (103), where i is any natural number from 1 to N. The i-th slave calibration room (201) is i The lasers to be calibrated are designated as laser i_1 (202), ..., laser i_N i It is labeled (203). i is a natural number, and when there is only one laser to be calibrated (N i =1).

[0039] When calibration of all the lasers to be calibrated in the i-th slave calibration room (201) is not performed, the lasers to be calibrated are used by the devices (207), but when an optical path switching command signal (208) and an encoded command signal (211) are sent from the master calibration room (102), the optical path switching device (204) switches the optical path of the corresponding laser to be calibrated so as to transmit it to the multiplexer (205) and optical transmission path i (206). Note that Figure 2 also includes cases where each slave calibration room has only one laser to be calibrated or where only one laser is calibrated.

[0040] Furthermore, before the laser to be calibrated is coupled to the optical transmission line i (206), the optical modulator i_1 (209) is i (210) is modulated by an optical modulator placed in the optical path of the laser to be calibrated. Here, M i is the maximum number of calibrated light sources that can be transmitted from the i-th slave calibration room (201), and ranges from 1 to N i The optical modulator performs frequency modulation of the phase or frequency of the output light of the plurality of light sources to be calibrated with different patterns based on the modulation pattern of the encoded command signal (211).

[0041] For example, if an acousto-optic modulator (AOM) is used as an optical modulator that modulates frequency, the RF frequency that is applied to the AOM to diffract the output light of the light source to be calibrated and shift its output frequency can be coded by hopping sequentially during calibration, and the beat signal can be electrically divided in a master calibration room to perform the decoding operation described below, thereby simultaneously calibrating the optical frequencies of multiple light sources to be calibrated (see Figure 8 for a detailed example).

[0042] 3. Master Calibration Room Configuration FIG. 3 is a block diagram showing a schematic configuration of the master calibration room of this example. Solid arrows indicate electrical signals, and dotted arrows indicate optical signals. This master calibration room (300) has a terminal end (301) of an optical transmission path group (106) consisting of N optical transmission paths. When the calibration computer (302) receives a calibration command from the management room (101), it issues a group of optical path switching commands to the corresponding light source to be calibrated in the slave calibration room group (103), and as a result, light from each light source to be calibrated is output from C optical output ports out of the N optical output ports constituting the terminal end (301) of the optical transmission path group (106). Note that the number D of light sources that can be simultaneously calibrated by the optical frequency comb device (303) is C or more than C.

[0043] In order to obtain a beat signal with the optical frequency comb device (303) from the port from which light is actually output among the N optical output ports, the calibration computer (302) switches the optical paths of the master optical path switching device (304), and selects L1, . . . , L C The output light of the light source to be calibrated is distributed to C optical paths (output light of multiple light sources to be calibrated can enter one optical path) consisting of the above, and enters the optical frequency measuring device (305).

[0044] The optical frequency comb device (303) calculates a repetition frequency f based on the optical output of the optical frequency comb (306). rep and CEO frequency f CEO Measure f rep , f CEO A measuring device (307), rep , f CEO The output of the measuring device (307) is f rep , f CEO Feedback is provided to the optical frequency comb (306) to stabilize f rep , f CEO A control device (308), rep , f CEO The signal is output to a calibration computer (302).

[0045] An example of the configuration of the optical frequency comb (306) may include an oscillator such as an Er- or Yb-doped fiber laser or titanium sapphire laser, an amplification mechanism such as an EDFA that branches and amplifies a portion of the optical output, a nonlinear fiber for expanding the wavelength band after amplification, an optical system that measures the CEO frequency by introducing the optical output of the nonlinear fiber into a nonlinear optical crystal such as Periodically Poled Lithium Niobate (PPLN) to generate second harmonics, a detection system, an optical system that measures the repetition frequency, a photodetector, an amplification mechanism such as an EDFA that branches and amplifies the optical output of the oscillator for calibration, a nonlinear fiber that expands the wavelength band for calibration, a mechanism such as a diffraction grating or bandpass filter that cuts off wavelengths other than the calibration wavelength from the output of the nonlinear fiber, and an optical system for pulse dispersion correction.

[0046] The calibration computer (302) issues a command to the optical frequency measurement device (305) to provide a demodulated signal, which will be described later, and the beat frequency f beat and the information of the mode number n, and f rep , f CEO The repetition frequency f from the measuring device (307) rep and the CEO frequency f CEO and determine the optical frequency of the light source under calibration according to Equation 1 below.

[0047] (Formula 1) f = n × f rep ±|f CEO |±|f beat |

[0048] f in Eq. CEO and f beat To determine the sign of each of f rep The method used is to determine the shift direction of the beat frequency and CEO frequency when f is changed. repHowever, since most of the time this is due to warming up, it can be avoided by taking measures such as monitoring information about the installation environment such as temperature, humidity, and air pressure, implementing an alert function to detect abnormalities, and rescheduling the calibration.

[0049] The stability of the optical frequency measurement using the optical frequency comb device (303) is f rep , f CEO A measuring device (307), rep , f CEO It is determined by the frequency stability of the RF oscillator (309) that generates the RF frequency reference signal used for measurement and control by the control device (308) and the optical frequency measurement device (305), and for example, a rubidium oscillator or its GPSDO oscillator is used. In this example, to perform remote calibration of the RF oscillator (309) via the national time and frequency standard device and GPS satellite, a GPS signal and a UTC signal via the Internet are used to stabilize the oscillation frequency of the RF oscillator (309). Remote calibration can be performed by using a service based on the GPS Common View method.

[0050] The above optical frequency measurements are performed for the C light sources under calibration that correspond to the calibration command. As a result, multiple light sources under calibration can be calibrated by the optical frequency comb device without moving them from the slave calibration room.

[0051] 4. Modifications of the Master Calibration Room FIG. 4 is a block diagram showing a schematic configuration of a master calibration room according to a modified example. In the present invention, the master calibration room can adopt the embodiment shown in FIG. 4 instead of the above-mentioned master calibration room (300). In FIG. 4, the solid arrows indicate electrical signals, and the dotted arrows indicate optical signals. This master calibration room (400) has a terminal end (401) of an optical transmission line group (106) consisting of N optical transmission lines. When the calibration computer (402) receives a calibration command from the management room (101), it issues a group of optical path switching commands to the corresponding light source to be calibrated in the slave calibration room group (103), and as a result, light from each light source to be calibrated is output from C optical output ports out of N optical output ports constituting the terminal end (401) of the optical transmission line group (106). Note that the number D of light sources that can be simultaneously calibrated by the optical frequency comb device (403) is C or more than C.

[0052] In order to obtain a beat signal with the optical frequency comb device (403) from the port from which light is actually output among the N optical output ports, the calibration computer (402) switches the optical paths of the master optical path switching device (404), and selects L1, . . . , L C The output light of the light source to be calibrated is distributed to C optical paths (output light of multiple light sources to be calibrated can enter one optical path) consisting of the above, and enters the optical frequency measuring device (405).

[0053] The optical frequency comb device (403) calculates a repetition frequency f based on the optical output of the optical frequency comb (406). rep and CEO frequency f CEO Measure f rep , f CEO A measuring device (407), rep , f CEO The output of the measuring device (407) is f rep , f CEO Feedback is provided to the optical frequency comb (406) to stabilize f rep , f CEO A control device (408), an offset laser (409), and an offset frequency f for the optical frequency comb of the offset laser. offsetand a phase synchronization device (411) for completely phase-synchronizing the offset frequency with respect to the optical frequency comb, rep , f CEO , f offset The signal is output to the calibration computer (402).

[0054] An example of the configuration of the optical frequency comb (406) may include an oscillator such as an Er- or Yb-doped fiber laser or titanium sapphire laser, an amplification mechanism such as an EDFA that branches and amplifies a portion of the optical output, a nonlinear fiber for expanding the wavelength band after amplification, an optical system that measures the CEO frequency by introducing the optical output of the nonlinear fiber into a nonlinear optical crystal such as Periodically Poled Lithium Niobate (PPLN) to generate second harmonics, a detection system, a photodetector that measures the repetition frequency, an amplification mechanism such as an EDFA that branches and amplifies the optical output of the oscillator for calibration, a nonlinear fiber that expands the wavelength band for calibration, and a mechanism such as a diffraction grating or bandpass filter that cuts off wavelengths other than the calibration wavelength from the output of the nonlinear fiber.

[0055] Next, as an example of the configuration of the offset laser (409), a form that realizes single longitudinal mode oscillation by applying feedback to the piezoelectric element that drives the resonator of the external resonator semiconductor laser and the driving current of the laser diode is known. The frequency stability of the offset laser (409) can be achieved by combining slow feedback by a piezoelectric element that adjusts the external resonator as a feedback mechanism with fast feedback by the driving current of the laser diode, and by locking the phase of the offset laser (409) and the optical frequency comb (406) over a wide band of several tens of MHz through a phase locking device (411) (a digital PLL circuit or the like is considered). In other words, since the frequency stability of the optical frequency comb (406) can be transferred to the offset laser (409), the offset laser (409) is included in the optical frequency comb device. In addition, before locking the offset laser (409) to the optical frequency comb (406), the offset laser (409) has a function of controlling the resonator length of the offset laser (409) using a measurement method such as a wavemeter so that the difference between the oscillation frequency of the laser to be calibrated and the oscillation frequency of the offset laser (409) is shorter than the repetition frequency of the optical frequency comb device.

[0056] The calibration computer (402) issues a command to the optical frequency measurement device (405) to provide a demodulated signal, which will be described later, and the offset laser output from the optical frequency measurement device (405) and the beat frequency f beat and the information of the mode number n, and f rep , f CEO The repetition frequency f from the measuring device (407) rep and the CEO frequency f CEO and the beat frequency f of the optical frequency comb (406) and the offset laser (409) from the offset frequency measurement device 410. offset The optical frequency is determined according to the following equation 2.

[0057] (Formula 2) f = n × f rep ±|f CEO |±|f offset |±|f beat |

[0058] f in Eq. CEO and f offset and f beat To determine the sign of each of f rep When changing f offset Or f CEO The shift direction of f offset When changing f beat Depending on the light source, the shift direction of f rep However, since most of the time this is due to warming up, it can be avoided by taking measures such as monitoring the temperature, humidity, air pressure, etc. of the installation environment and implementing an alert function to detect abnormalities and rescheduling the calibration.

[0059] The stability of the optical frequency measurement using the optical frequency comb device (403) is f rep , f CEO A measuring device (407), rep , f CEO It is determined by the frequency stability of the RF oscillator (412) that generates the RF frequency used for measurement and control by the control device (408), offset frequency measurement device (410), phase synchronization device (411), and optical frequency measurement device (405), and may take the form of, for example, a rubidium oscillator or its GPSDO oscillator. In the present invention, the RF oscillator (412) is remotely calibrated via a national time and frequency standard (one example of a standard) and a GPS satellite, so a GPS signal and a UTC signal via the Internet are used to stabilize the RF oscillator (412). Remote calibration can be performed by using a service based on the GPS Common View method.

[0060] The above optical frequency measurements are performed for the C light sources under calibration that correspond to the calibration command. As a result, multiple light sources under calibration can be calibrated by the optical frequency comb device without moving them from the slave calibration room.

[0061] 5. Configuration of optical frequency measurement section Fig. 5 is a block diagram showing a schematic configuration of the optical frequency measurement unit of this example. As shown in Fig. 5, the optical frequency measurement unit (600) calibrates the optical frequency of output light from one of C lasers to be calibrated from the laser to be calibrated L_1 (601) to the laser to be calibrated L_C (602) in the optical frequency measurement device (305) shown in Fig. 3 or the optical frequency measurement device (405) shown in Fig. 4. In Fig. 5, the solid arrows indicate electrical signals, and the dotted arrows indicate optical signals.

[0062] All the corresponding lasers to be calibrated are optical modulators i_1 (209) to i_M (210) in the i-th slave calibration chamber (201) in FIG. i The laser to be calibrated is assumed to be frequency modulated by the corresponding optical modulator among the lasers (210). The output light of the lasers to be calibrated and the output light of the optical frequency comb device (612) are incident on a photoelectric conversion unit (603) consisting of, for example, an optical element and a silicon photodetector, and are optically interfered with to obtain an electrical beat signal. In order to extract the beat signal originating from a specific laser to be calibrated from this beat signal, decoding is performed in the decoding unit (606) based on a decoding command from the calibration computer (604) and an RF oscillator (605).

[0063] In the decoding unit (606), an RF signal generator (607) using an RF oscillator (605) as an external clock generates an RF signal whose frequency changes over time corresponding to the decoding command, and this is multiplied with the beat signal output from the photoelectric conversion unit (603) in an RF mixer (608). As a result, only the original beat frequency of the corresponding laser to be calibrated becomes constant within the frequency stability of the light source regardless of time.

[0064] The beat signals originating from the other lasers to be calibrated are superimposed with a hopping pattern different from the hopping pattern required for decoding in the RF mixer (608), and continue to hop to different frequencies for each hopping time interval. The hopping time interval is set sufficiently shorter than the gate time of the frequency counter (609), so that the signal-to-noise ratio of these lights that are not the subject of calibration can be suppressed, and only the beat frequency originating from the corresponding laser to be calibrated is displayed when measuring with the frequency counter. Furthermore, a portion of the light from the laser to be calibrated L1 (601) is measured with a wavemeter L1 (610), ..., the laser to be calibrated L C A part of the light from (602) is measured by a wavelength meter L C The wavelength information is measured at (611) and output to a calibration computer (604) for use in identifying the mode order of calibration.

[0065] 6. Modification of the optical frequency measurement unit Fig. 6 is a block diagram showing a schematic configuration of an optical frequency measurement unit according to a modified example. In the present invention, the optical frequency measurement unit can adopt the aspect shown in Fig. 6 instead of the optical frequency measurement unit (600) described above. The optical frequency measurement unit (700) shown in Fig. 6 is an example of calibrating the optical frequencies of C lasers out of C lasers to be calibrated from laser to be calibrated L_1 (701) to laser to be calibrated L_C (702) in the optical frequency measurement device (305) in Fig. 3 and the optical frequency measurement device (405) in Fig. 4. In Fig. 6, the solid arrows indicate electrical signals, and the dotted arrows indicate optical signals.

[0066] All the corresponding lasers to be calibrated are optical modulators i_1 (209) to i_M (210) in the i-th slave calibration chamber (201) in FIG. i The output light of the laser to be calibrated and the optical frequency comb device (714) are input to a photoelectric conversion unit (703) consisting of an optical element and a silicon photodetector, for example, to cause optical interference, and an electrical beat signal is obtained.

[0067] In order to extract a beat signal derived from a specific laser to be calibrated from this beat signal, a decoding unit (706) performs decoding based on a decoding command from a calibration computer (704) and an RF oscillator (705). In the decoding unit (706), one or more RF signal generators (707) using an RF oscillator (705) as an external clock generate one or more RF signals whose frequency changes over time corresponding to the decoding command, the beat signal output from the photoelectric conversion unit (703) is divided and multiplied with each of the RF signals by RF mixers L_1 (708) to L_C (710), and the RF frequencies of the corresponding RF mixer outputs are measured by frequency counters 1 (709) to L_c (711).

[0068] As a result, only the original beat frequency of the laser under calibration that corresponds to the decoding pattern applied by each RF mixer remains constant within the frequency stability of the light source regardless of time. The beat signals originating from other lasers under calibration have a hopping pattern different from the hopping pattern required for decoding superimposed on the corresponding RF mixer, and continue to hop to different frequencies for each hopping time interval. By making the hopping time interval sufficiently shorter than the gate time of the corresponding frequency counter, the signal-to-noise ratio of these lights that are not subject to calibration can be suppressed, and only the beat frequency originating from the corresponding laser under calibration is displayed when measuring with the frequency counter.

[0069] Furthermore, a portion of the light from the laser to be calibrated L_1 (701) is measured by a wavemeter L_1 (712), ..., a portion of the light from the laser to be calibrated L_C (702) is measured by a wavemeter L_C (713), and the obtained optical frequencies are output to a calibration computer (704) for use in identifying the mode order of the calibration.

[0070] The above method makes it possible to simultaneously and selectively measure multiple beat frequencies output from one photoelectric conversion unit (703). When combined with the frameworks described in items 2 and 3, this method makes it possible to simultaneously calibrate the optical frequencies of multiple lasers to be calibrated using one optical frequency comb device.

[0071] 7. Operation of distributed calibration system A specific example of the configuration for the optical frequency measurement method described above is shown in Figure 7. The solid arrows indicate electrical signals, and the dotted arrows indicate optical signals. In this example, we will describe the case where the optical frequencies of the output light from two lasers to be calibrated that are installed in the same slave calibration room are selectively measured. The output light from the two lasers to be calibrated is diffracted by AOM1 and AOM2, respectively. The amount of optical frequency shift associated with diffraction is changed over time, and the light is diffracted with different hopping patterns f1(t) and f2(t) for each laser to be calibrated.

[0072] Here, the order of diffraction can be any order except the zeroth order. The output lights of the lasers to be calibrated, encoded with f1(t) and f2(t), are combined and propagated through the same optical fiber, after which the beat signal of the output lights of the two encoded lasers to be calibrated and the output light of an offset laser in an optical frequency comb device, for example, are photoelectrically converted and then electrically mixed with an RF signal having the same frequency hopping pattern f3(t) as f1(t). As a result of the mixing, only the beat frequency of the output light of the laser 1 to be calibrated and the output light of the offset laser always remains constant regardless of time (within the range of the frequency stability of the lasers to be calibrated).

[0073] On the other hand, the beat frequency of the output light of the calibrated laser 2 and the output light of the offset laser is constantly hopping. In order to perform the frequency measurement correctly, if f1(t) and f2(t) are configured to change at intervals sufficiently shorter than the gate time of the frequency counter, the measurement value of the frequency counter will match the beat frequency of the output light of the calibrated laser 1 and the output light of the offset laser, and the beat frequency of the output light of the calibrated laser 2 and the output light of the offset laser will be zero when the time average is taken, so it can be ignored, and selective measurement of the optical frequency, i.e., calibration, will be possible. In addition, by adding the number of decoding electronics as shown in Figure 7, this method will enable simultaneous calibration of the optical frequency of the calibrated laser 1 and the optical frequency of the calibrated laser 2.

[0074] Although specific embodiments of the present invention have been described above, the aspects that the present invention can adopt are not limited to the above-described aspects.

[0075] For example, in the above example, an optical modulator i is provided in the slave calibration room, and when an encoded command signal is transmitted from the master calibration room, the phase or frequency of the output light from the multiple light sources to be calibrated is frequency-modulated with different patterns based on the modulation pattern of the encoded command signal. However, the present invention is not limited to this configuration, and a configuration in which the optical modulator i is omitted may also be used, as shown in FIG. 8.

[0076] In this case, the optical frequency measurement unit can take the form shown in Fig. 9. Fig. 9 is a block diagram showing a schematic configuration of the optical frequency measurement unit of this form. As shown in Fig. 9, the optical frequency measurement unit (500) calibrates the optical frequency of one of C lasers to be calibrated from the laser to be calibrated L_1 (501) to the laser to be calibrated L_C (502) in the optical frequency measurement device (305) shown in Fig. 3 or the optical frequency measurement device (405) shown in Fig. 4. In Fig. 9, the solid arrows indicate electrical signals, and the dotted arrows indicate optical signals.

[0077] All output lights of the relevant lasers to be calibrated are transmitted to the master calibration room via the configuration shown in the example of the i-th slave calibration room (201) in Fig. 8. When output lights of multiple lasers to be calibrated are transmitted to the master calibration room, the output lights of C lasers to be calibrated selected using an optical path switching device in the master calibration room are made to enter C photoelectric conversion units (503) of the optical frequency comb device (512), for example, consisting of an optical element and a silicon photodetector, and are optically interfered to obtain an electrical beat signal.

[0078] The frequency of the beat signal is read out by a frequency counter and used to measure the optical frequency.

[0079] Furthermore, to determine the mode order, a portion of the output light of the calibrated laser L_1 (501) is branched off from the calibrated laser L_C (502), and the optical frequency is determined with a resolution higher than the mode spacing of the optical frequency comb (306) by a wavemeter L_1 (507) to a wavemeter L_C (508).

[0080] 10 shows a specific example of the configuration of the optical path switching device (204) and the multiplexing unit (205) of the slave calibration room (201). In this example, consider the case where four lasers 1-4 to be calibrated are provided in one slave calibration room (201) shown in FIG. 8. When the laser 1 to be calibrated is calibrated, the height of a partial polarizing beam splitter (PPBS) arranged so as not to come into contact with the optical path of the output light of the laser 1 to be calibrated is raised by a driving mechanism such as an actuator, and part of the polarized light of the output light is reflected by the PPBS and coupled to a transmission unit consisting of an optical transmission path such as a polarization-maintaining fiber. Similarly, when multiple lasers are calibrated simultaneously, multiple PPBSs located below the optical paths of multiple lasers to be calibrated are raised, and part of the output light of the multiple lasers to be calibrated is reflected to follow the same optical path, coupled to the transmission unit, and transmitted to the master calibration unit. By changing the deposition conditions to give each PPBS a different polarization-dependent reflectance, it is possible to consider a configuration in which all lasers to be calibrated are coupled to the optical transmission line with equal power, whether they pass through multiple PPBSs or only one. Also, in this example, by adding an optical modulator to the left of the PPBS in Figure 10, it becomes possible to apply different modulation to each laser to be calibrated.

[0081] 11 shows a specific example of the configuration of the master optical path switching device (304) and the optical frequency measurement device (305). In this example, we consider the case where two lasers to be calibrated out of four slave calibration units are calibrated. The output light of the optical frequency comb device is split into four equal powers by the PPBS as described above, and the beat signal generated by combining the output light from slave calibration unit 1 with the half beam splitter (HBS) is photoelectrically converted by a photodetector and used for frequency measurement. Similarly, for slave calibration unit 2, the beat signal with the output light of the optical frequency comb device reflected by another PPBS is photoelectrically converted by another photodetector.

[0082] In addition, in the present invention, not only the method in which the optical frequency measurement device is installed in the master calibration unit as shown in measurement method 1 in FIG. 12, but also the mode in which the optical frequency measurement device is installed in the slave calibration unit as shown in measurement method 2 can be adopted. In that case, the output light of the optical frequency comb device is supplied to each slave calibration unit via the transmission unit, and the measurement frequency data of the wavemeter and the beat frequency data of the frequency counter obtained by the optical frequency measurement device installed in the slave calibration unit are transmitted to the master calibration unit. FIG. 13 is an example of the configuration when the master calibration room (400) in FIG. 4 is changed according to the mode of measurement method 2 in FIG. 12. Unlike FIG. 4, the output light of the offset laser (1309) is selected by the master optical path switching device (1304) to be connected to the terminal end (1301) of the optical transmission path group 106, and is transmitted to the slave calibration unit via the optical transmission path. FIG. 14 is an example of the configuration when the slave calibration room (201) in FIG. 2 is changed according to measurement method 2 shown in FIG. 12. The output light of the offset laser (1309) transmitted from the master calibration room (1300) and the calibrated lasers i_1 to i_N output from the multiplexer (1405) are i The beat signal of the output light of the laser to be calibrated among the above is measured in an optical frequency measuring device (1412) installed in the i-th slave calibration room (1401). The measured beat frequency data is transmitted to the master calibration room (1300), and the oscillation frequency of the laser to be calibrated is calculated in the calibration computer (1302). Here, the output of the RF oscillator (1312) in the master calibration room (1300) is supplied to the group of slave calibration rooms (103), and is used as the clock for the optical frequency measuring device (1412) installed in the i-th slave calibration room (1401) in FIG.

[0083] The above-described embodiment is illustrative in all respects and is not restrictive. Those skilled in the art can make appropriate modifications and changes. The scope of the present invention is indicated by the claims, not by the above-described embodiment. Furthermore, the scope of the present invention includes modifications from the embodiments within the scope of the claims and the scope equivalent thereto. [Explanation of symbols]

[0084] 100 Distributed Calibration System 101 Management room 102 Master Calibration Room 103 Slave Calibration Labs 201 Slave Calibration Lab 204 Optical path switching device 205 Combiner 206 Optical Transmission Line 300 Master Calibration Lab 302 Calibration Computer 303 Optical Frequency Comb Device 305 Optical Frequency Measuring Device 309 RF Oscillator

Claims

1. one or more slave calibration units each having one or more light sources to be calibrated; a master calibration unit including an optical frequency comb device, the master calibration unit using the optical frequency comb device to measure and calibrate the optical frequency of a light source to be calibrated included in the slave calibration unit; an optical transmission unit that connects the slave calibration unit and a master calibration unit; The master calibration unit is configured to measure and calibrate the optical frequency using an electrical output of a beat signal between the output light of the optical frequency comb device and the output light of the light source to be calibrated, when calibrating the optical frequency of the output light of the light source to be calibrated of the slave calibration unit transmitted via the optical transmission unit using the optical frequency comb device, and has a function of stabilizing the operating frequency of the optical frequency comb device based on an RF oscillator capable of remote calibration based on time and frequency standards.

2. one or more slave calibration units each having one or more light sources to be calibrated; a master calibration unit including an optical frequency comb device, the master calibration unit using the optical frequency comb device to measure and calibrate the optical frequency of a light source to be calibrated included in the slave calibration unit; an optical transmission unit that connects the slave calibration unit and a master calibration unit; a management unit having a function of receiving an operating status of the slave calibration unit, a function of transmitting a calibration command for the light source to be calibrated to the master calibration unit, and a function of receiving a calibration result from the master calibration unit; the slave calibration unit has a function of transmitting an operation status to the management unit, a function of receiving an optical path switching signal from the master calibration unit, and a function of coupling the output light of the calibrated light source to an optical transmission path by switching the optical path of the output light, the master calibration unit has the functions of receiving a calibration command from the management unit and sending an optical path switching command to the slave calibration unit, and when calibrating the optical frequency of the output light of the calibrated light source transmitted from the slave calibration unit via the optical transmission path using the optical frequency comb device, measuring and calibrating the optical frequency using an electrical output of a beat signal between the output light of the optical frequency comb device and the output light of the calibrated light source, sending the calibration results to the management unit, and further stabilizing the operating frequency of the optical frequency comb device based on an RF oscillator capable of remote calibration based on time and frequency standards via GPS.

3. one or more slave calibration units each having one or more light sources to be calibrated; a master calibration room including an optical frequency comb device, the master calibration room using the optical frequency comb device to measure and calibrate the optical frequency of a light source to be calibrated included in the slave calibration unit; an optical transmission unit that connects the slave calibration unit and a master calibration unit; a management unit having a function of receiving an operating status of the slave calibration unit, a function of transmitting a calibration command for the light source to be calibrated to the master calibration unit, and a function of receiving a calibration result from the master calibration room; the slave calibration unit has a function of transmitting an operation status to the management room, a function of receiving an optical path switching signal from the master calibration unit, and a function of coupling the output light of the calibrated light source to an optical transmission path by switching the optical path of the output light, the master calibration unit has a function of receiving a calibration command from the management unit and sending an optical path switching command to the slave calibration unit, and when calibrating the optical frequency of the output light of the calibrated light source transmitted from the slave calibration unit via the optical transmission path using the optical frequency comb device including an offset laser to which the frequency stability of the optical frequency comb is transferred by phase synchronization, measuring and calibrating the optical frequency using an electrical output of a beat signal of the output light of the optical frequency comb device and the output light of the calibrated light source, a function of sending the calibration results to the management unit, and further a function of stabilizing the operating frequency of the optical frequency comb device based on an RF oscillator capable of remote calibration based on time and frequency standards via GPS.

4. one or more slave calibration units each having one or more light sources to be calibrated; a master calibration unit including an optical frequency comb device, the master calibration unit using the optical frequency comb device to measure and calibrate the optical frequency of a light source to be calibrated included in the slave calibration unit; an optical transmission unit that connects the slave calibration unit and a master calibration unit; a management unit having a function of receiving an operating status of the slave calibration unit, a function of transmitting a calibration command for the light source to be calibrated to the master calibration unit, and a function of receiving a calibration result from the master calibration unit; the slave calibration unit has a function of transmitting an operating status to the management unit, a function of receiving an optical path switching signal from the master calibration unit, a function of coupling the output light of the calibrated light source to an optical transmission path by switching the optical path of the output light of the calibrated light source, and an encoding function of applying frequency modulation by an optical modulator to the optical frequency of the output light of the calibrated light source and of applying a change in the modulation frequency that differs from moment to moment for each of the calibrated light sources, the master calibration unit has the function of receiving a calibration command from the management unit and sending an optical path switching command to the slave calibration unit, and when calibrating the optical frequency of the output light of the calibrated light source transmitted from the slave calibration unit via the optical transmission path using the optical frequency comb device, selectively measuring and calibrating the optical frequency by mixing and decoding an RF signal used to encode the output light of the calibrated light source using an electrical output of a beat signal of the output light of the optical frequency comb device and the output light of the calibrated light source, a function of sending the calibration results to the management unit, and further a function of stabilizing the operating frequency of the optical frequency comb device based on an RF oscillator capable of remote calibration based on time and frequency standards via GPS.

5. one or more slave calibration units each having one or more light sources to be calibrated; a master calibration unit including an optical frequency comb device, the master calibration unit using the optical frequency comb device to measure and calibrate the optical frequency of a light source to be calibrated included in the slave calibration unit; an optical transmission unit that connects the slave calibration unit and a master calibration unit; a management unit having a function of receiving an operating status of the slave calibration unit, a function of transmitting a calibration command for the light source to be calibrated to the master calibration unit, and a function of receiving a calibration result from the master calibration unit; the slave calibration unit has a function of transmitting an operating status to the management unit, a function of receiving an optical path switching signal from the master calibration unit, a function of coupling the output light of the calibrated light source to an optical transmission path by switching the optical path of the output light of the calibrated light source, and an encoding function of applying frequency modulation by an optical modulator to the optical frequency of the output light of the calibrated light source and of applying a change in the modulation frequency that differs from moment to moment for each of the calibrated light sources, the master calibration unit has a function of receiving a calibration command from the management unit and sending an optical path switching command to the slave calibration unit, and calibrating the optical frequency of the output light of the calibrated light source transmitted from the slave calibration unit via the optical transmission path using the optical frequency comb device including an offset laser to which the frequency stability of the optical frequency comb is transferred by phase synchronization, and during calibration, has a function of selectively measuring and calibrating the optical frequency by mixing and decoding an RF signal used to encode the output light of the calibrated light source using an electrical output of a beat signal of the output light of the optical frequency comb device and the output light of the calibrated light source, a function of sending the calibration result to the management unit, and further a function of stabilizing the operating frequency of the optical frequency comb device based on an RF oscillator capable of remote calibration based on time and frequency standards via GPS.

6. one or more slave calibration units each having one or more light sources to be calibrated; a master calibration unit including an optical frequency comb device, the master calibration unit using the optical frequency comb device to measure and calibrate the optical frequency of a light source to be calibrated included in the slave calibration unit; an optical transmission unit that connects the slave calibration unit and a master calibration unit; a management unit having a function of receiving an operating status of the slave calibration unit, a function of transmitting a calibration command for the light source to be calibrated to the master calibration unit, and a function of receiving a calibration result from the master calibration unit; the slave calibration unit has a function of transmitting an operating status to the management unit, a function of receiving an optical path switching signal from the master calibration unit, a function of coupling the output light of the calibrated light source to an optical transmission path by switching the optical path of the output light of the calibrated light source, and an encoding function of applying frequency modulation by an optical modulator to the optical frequency of the output light of the calibrated light source and of applying a change in the modulation frequency that differs from moment to moment for each of the calibrated light sources, the master calibration unit has the functions of receiving a calibration command from the management unit and transmitting an optical path switching command to the slave calibration unit, and when calibrating the optical frequency of the output light of the calibrated light source transmitted from the slave calibration unit via the optical transmission path using the optical frequency comb device, selectively measuring and calibrating the optical frequency by mixing and decoding an RF signal used to encode the output light of the calibrated light source using an electrical output of a beat signal of the output light of the optical frequency comb device and the output light of the calibrated light source, a function of simultaneously performing the decoding to calibrate the optical frequencies of a plurality of the calibrated light sources, a function of transmitting the calibration results to the management unit, and further a function of stabilizing the operating frequency of the optical frequency comb device based on an RF oscillator capable of remote calibration based on time and frequency standards via GPS.

7. one or more slave calibration units each having one or more light sources to be calibrated; a master calibration unit including an optical frequency comb device, the master calibration unit using the optical frequency comb device to measure and calibrate the optical frequency of a light source to be calibrated included in the slave calibration unit; an optical transmission unit that connects the slave calibration unit and a master calibration unit; a management unit having a function of receiving an operating status of the slave calibration unit, a function of transmitting a calibration command for the light source to be calibrated to the master calibration unit, and a function of receiving a calibration result from the master calibration unit; the slave calibration unit has a function of transmitting an operating status to the management unit, a function of receiving an optical path switching signal from the master calibration unit, a function of coupling the output light of the calibrated light source to an optical transmission path by switching the optical path of the output light of the calibrated light source, and an encoding function of applying frequency modulation by an optical modulator to the optical frequency of the output light of the calibrated light source and of applying a change in the modulation frequency that differs from moment to moment for each of the calibrated light sources, the master calibration unit has a function of receiving a calibration command from the management unit and sending an optical path switching command to the slave calibration unit, and calibrating the optical frequency of the output light of the calibrated light source transmitted from the slave calibration room through the optical transmission path using the optical frequency comb device including an offset laser to which the frequency stability of the optical frequency comb is transferred by phase synchronization, and during calibration, a function of selectively measuring and calibrating the optical frequency by mixing and decoding an RF signal used to encode the output light of the calibrated light source using an electrical output of a beat signal of the output light of the optical frequency comb device and the output light of the calibrated light source, a function of simultaneously executing the decoding to calibrate the optical frequencies of a plurality of the calibrated light sources, a function of transmitting the calibration results to the management unit, and further a function of stabilizing the operating frequency of the optical frequency comb device based on an RF oscillator capable of remote calibration based on time and frequency standards via GPS.

8. 8. The optical frequency remote calibration system according to claim 2, wherein the management unit has a function of managing the calibration results received from the master calibration unit.

9. A method for calibrating optical frequencies of one or more light sources to be calibrated, each of which is provided in one or more slave calibration units, by using an optical frequency comb device provided in a master calibration unit, comprising: The slave calibration unit and the master calibration unit are connected by an optical transmission unit; transmitting output light of a light source to be calibrated provided in the slave calibration unit to the master calibration unit via the optical transmission unit; In the master calibration unit, when calibrating the optical frequency of the transmitted output light of the calibrated light source using the optical frequency comb device, the optical frequency is measured and calibrated using the electrical output of a beat signal between the output light of the optical frequency comb device and the output light of the calibrated light source, and the operating frequency of the optical frequency comb device is stabilized based on an RF oscillator capable of remote calibration based on time and frequency standards.

10. one or more slave calibration units each including one or more light sources to be calibrated and an optical frequency measurement unit for measuring the optical frequency of the light source to be calibrated; a master calibration unit including an optical frequency comb device and an optical frequency calibration unit for calibrating an optical frequency; an optical transmission unit that connects the slave calibration unit and a master calibration unit; the master calibration unit has a function of stabilizing an operating frequency of the optical frequency comb device based on an RF oscillator capable of remote calibration based on time and frequency standards, and is configured to transmit output light of the optical frequency comb device to the slave calibration unit via the transmission unit; the slave calibration unit is configured to measure an optical frequency of the output light of the light source to be calibrated, based on an electrical output of the output light of a light source to be calibrated installed in the slave calibration unit and a beat signal of the output light of the optical frequency comb device transmitted to the slave calibration unit, using the optical frequency measurement unit, and to transmit an RF frequency signal of the obtained beat signal to the master calibration unit via the transmission unit; The master calibration unit is further configured to calibrate the frequency of the output light of the calibrated light source by the frequency calibration unit based on the RF frequency signal of the beat signal transmitted from the slave calibration unit via the transmission unit.

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