JPWO2019073701A1 - Dual optical frequency comb generation optical system, laser device, measuring device - Google Patents

Abstract

The dual optical frequency comb generation optical system of the present invention is waveguideed along the circumferential direction with an amplification unit that emits laser amplification light in the circumferential direction and the opposite direction along the circumferential direction of the first loop optical fiber. A laser-amplified light return unit that emits the laser-amplified light to the first loop optical fiber only when the phase difference between the laser-amplified light and the laser-amplified light waved along the opposite direction satisfies a predetermined condition. I have.

Description

The present invention relates to a dual optical frequency comb generation optical system that outputs two optical frequency combs, and a laser device and a measuring device including the dual optical frequency comb generation optical system. The present application claims priority based on Japanese Patent Application No. 2017-199843 filed in Japan on October 13, 2017, the contents of which are incorporated herein by reference.

Light whose spectral intensities are precisely arranged in a comb shape on the frequency axis at equal intervals is called an optical frequency comb. For example, in the spectral distribution of a mode-locked laser, which is an ultrashort pulse laser, a large number of light frequency mode sequences arranged at equal intervals appear. That is, the optical frequency comb is emitted from the mode-locked laser. An optical frequency comb having a comb-shaped spectral intensity is widely used as a precise measure of time, space, and frequency. The spacing between the optical frequency mode sequences in the optical frequency domain is called the repetition frequency.

For example, as described in Non-Patent Document 1, information on molecules and atoms in the optical frequency domain can be extracted by performing multi-heterodyne detection of optical frequency combs having different repetition frequencies. Optical frequency combs with different repetition frequencies are called dual optical frequency combs. Wideband, high-precision, high-resolution spectroscopic measurement can be performed using two mode-locked lasers (laser devices) that output dual optical frequency combs.

I. Coddington, N. Newbury and W. Swann, “Dual-comb spectroscopy,” Optica, Vol. 3, No. 4, pp. 414-426 (2016).

However, as disclosed in Non-Patent Document 1 described above, when two laser devices are used, these laser devices are subject to different environmental disturbances and mechanical disturbances. When the two laser devices receive different environmental disturbances and mechanical disturbances, the signal-to-noise ratio (SN ratio) of the interference signal obtained at the time of multi-heterodyne detection becomes low. On the other hand, if the SN ratio of the interference signal is increased, a large-scale optical system for relatively synchronizing the phase of the two laser devices is required, and the laser device becomes large.

The present invention takes into consideration the above circumstances, and is capable of increasing the signal-to-noise ratio of optical frequency combs having different repeating frequencies and reducing the size of the entire optical system or device. A generation optical system, a laser device, and a measuring device are provided.

In the dual optical frequency comb generation optical system of the present invention, the first laser light whose polarization direction is the first direction is waveguideed, and the second laser whose polarization direction is different from the first direction is the second laser. A first loop optical fiber that waveguides light and holds the polarization directions of the first laser beam and the second laser beam, and a first loop optical fiber provided in the first loop optical fiber and provided in the first loop optical fiber. The introduction section for introducing the first laser beam and the second laser beam, and the introduction portion provided in the first loop optical fiber, while maintaining the polarization directions of the first laser beam and the second laser beam, said. The first laser beam and the second laser beam are amplified to generate the first laser amplification light and the second laser amplification light, and the first loop optical fiber is subjected to the circumferential direction and the direction opposite to the circumferential direction. The first laser amplification light and the second laser amplification light provided in the first loop optical fiber and waveguideed along the circumferential direction, and an amplification unit that emits the laser amplification light and the second laser amplification light. The first laser amplification light and the second laser amplification light are provided only when the phase difference between the first laser amplification light and the second laser amplification light waved along the direction opposite to the circumferential direction satisfies a predetermined condition. A laser-amplified light return portion that emits laser-amplified light to the first loop optical fiber along at least one of the circumferential direction and the direction opposite to the circumferential direction, and the first loop optical fiber are provided with the laser amplified light return portion. A first optical frequency comb generated by the first loop optical fiber and having a polarization direction of the first direction and a second optical frequency comb generated by the first loop optical fiber and having a polarization direction of the second direction. It is provided with a derivation unit for deriving the above from the first loop optical fiber.

In the dual optical frequency comb generation optical system of the present invention, even if the first loop optical fiber is composed of a second loop portion and a third loop portion connected to the second loop portion via a connecting portion. Good. The introduction section and the amplification section may be provided in the second loop section, and the lead-out section may be provided in the third loop section. The laser-amplified light return portion may be composed of the connecting portion and the third loop portion. The predetermined condition is that the phase difference is an odd multiple of half the wavelengths of the first laser amplified light and the second laser amplified light. In the connecting portion, the first laser amplification light and the second laser amplification light are obtained only when the first laser amplification light and the second laser amplification light waveguideed from the second loop portion satisfy the predetermined conditions. May go around in the third loop portion and then return to the second loop portion.

In the dual optical frequency comb generation optical system of the present invention, the first loop optical fiber may be composed of a second loop portion and a linear portion connected to the second loop portion via a connecting portion. The introduction section and the amplification section may be provided in the second loop section, the lead-out section may be connected to the connection section, and the laser amplification light return section may be composed of the connection section and the linear section. .. The predetermined condition is that the phase difference is an even multiple of half the wavelengths of the first laser amplified light and the second laser amplified light. In the connecting portion, the first laser amplification light and the second laser amplification light are obtained only when the first laser amplification light and the second laser amplification light guided from the second loop portion satisfy the predetermined conditions. May reciprocate in the linear portion and then return to the second loop portion.

In the dual optical frequency comb generation optical system of the present invention, the third loop portion or the linear portion is provided with a phase modulation section capable of modulating the phases of the first laser amplification light and the second laser amplification light. May be good.

In the dual optical frequency comb generation optical system of the present invention, the first loop optical fiber is provided with a resonator length control element capable of controlling the resonator lengths of the first laser amplification light and the second laser amplification light. You may. When the dual optical frequency comb generation optical system has a second loop portion, it is preferable that the resonator length control element is provided in the second loop portion.

The laser apparatus of the present invention includes a light source that is connected to the introduction portion of the dual optical frequency comb generation optical system and emits the first laser beam and the second laser beam.

The measuring device of the present invention is arranged behind the above-mentioned laser device, the first optical frequency comb and the second optical frequency comb derived from the lead-out unit in the traveling direction, and the first optical frequency comb and the first optical frequency comb. At least one path of the first optical frequency comb and the second optical frequency comb separated from each other by the polarization separating section and the polarization separating portion that separates the second optical frequency comb and advances them in different paths. A polarization that is arranged behind the sample arranged above in the traveling direction of the first optical frequency comb and the second optical frequency comb and interferes with the first optical frequency comb and the second optical frequency comb to be measured. It includes a wave interference unit and a sample information extraction unit that is arranged on the back side in the traveling direction of the interference signal obtained by the polarization interference unit and extracts information on the sample from the interference signal.

According to the dual optical frequency comb generation optical system, the laser device, and the measuring device of the present invention, it is possible to increase the signal-to-noise ratio of optical frequency combs having different repetition frequencies and to reduce the size of the optical system.

It is a top view of the laser apparatus of 1st Embodiment of this invention. It is a top view of the measuring apparatus of 1st Embodiment of this invention. It is a top view of the laser apparatus of 2nd Embodiment of this invention. It is a top view of the laser apparatus of the 3rd Embodiment of this invention. It is a top view of the laser apparatus of 4th Embodiment of this invention. It is a top view of the laser apparatus of 5th Embodiment of this invention. It is a top view of the 1st configuration example of the non-reciprocal phase shift part of the laser apparatus of FIG. It is a top view of the 2nd configuration example of the non-reciprocal phase shift part of the laser apparatus of FIG. It is a top view of the laser apparatus of the 6th Embodiment of this invention. It is a top view of the laser apparatus of 7th Embodiment of this invention. It is a top view of the laser apparatus of 8th Embodiment of this invention. It is a top view of the laser apparatus of the 9th Embodiment of this invention. It is a top view of the laser apparatus of the tenth embodiment of this invention. It is a top view of the laser apparatus of 11th Embodiment of this invention. It is a top view of the laser apparatus of the twelfth embodiment of this invention. It is a top view of the laser apparatus of 13th Embodiment of this invention. It is a top view of the laser apparatus of this invention. It is a top view of another laser apparatus of this invention.

Hereinafter, embodiments of the dual optical frequency comb generation optical system, laser device, and measuring device of the present invention will be described with reference to the drawings.

(First Embodiment)
[Configuration of dual optical frequency comb generation optical system and laser device]
As shown in FIG. 1, in the laser device 60A of the first embodiment of the present invention, a light source 5, a polarization-holding optical fiber 6, a polarization separation element 12, and one end thereof are connected to the polarization separation element 12. It is provided with a polarization-maintaining optical fiber 31 and a dual optical frequency comb generation optical system 10A. The incident-side end (one end) of the polarization-maintaining optical fiber 6 is connected to the light source 5. The exit-side end (the other end) of the polarization-holding optical fiber 6 is connected to the polarization separation element 12. The incident-side end (one end) of the polarization-holding optical fiber 31 is connected to the polarization separation element 12. The exit-side end (the other end) of the polarization-holding optical fiber 31 is connected to the dual optical frequency comb generation optical system 10A.

The light source 5 has at least a laser beam (first laser beam) S1 whose polarization direction is the first direction with respect to the optical axis A and a laser beam (first laser beam) whose polarization direction is the second direction with respect to the optical axis A. 2 Laser light) Laser light S0 including S2 is emitted. The optical axis A indicates the traveling direction of light. Assuming that the optical axis A faces the direction perpendicular to the paper surface of FIG. 1, the first direction is the direction facing the upper side and the lower side of the paper surface, and the second direction is the direction facing the left side and the right side of the paper surface. If the first direction and the second direction are different from each other, they may face in any direction. For example, the laser beam may be guided with the slow axis and the fast axis of the polarization-holding fiber as the first direction and the second direction. The light source 5 of the present embodiment includes laser light S1, S2 and third laser light S3, S4, ... In which the direction of polarization with respect to the optical axis A is an arbitrary direction different from the first direction and the second direction. It is a semiconductor laser that emits light.

The direction of polarization of the laser beam S0 emitted from the light source 5 is maintained in the polarization-maintaining optical fiber 6. The polarization separating element 12 emits only the laser beams S1 and S2 from the laser beam S0 to the polarization-holding optical fiber 31.

The dual optical frequency comb generation optical system 10A includes a first loop optical fiber 30, an introduction unit 21, an amplification unit 40, a laser amplification light return unit 70, and a derivation unit 24 provided in the first loop optical fiber 30. I have.

The first loop optical fiber 30 connects the second loop portion 32 shown on the right side of FIG. 1, the third loop portion 33 shown on the left side of FIG. 1, and the second loop portion 32 and the third loop portion 33. It is provided with a unit 22. The connecting portion 22 is composed of a polarization-holding optical coupler. That is, the first loop optical fiber 30 is configured to draw the number "8" with the connecting portion 22 as a knot. The second loop portion 32 is composed of polarization-holding optical fibers 32A, 32B, and 32C. The third loop portion 33 is composed of polarization-holding optical fibers 33A, 33B, 33C. In the following, the direction in which the light is guided in the order of the polarization-holding optical fibers 32C, 32A, 32B and the direction in which the light is guided in the order of the polarization-holding optical fibers 33A, 33B, 33C are the R1 directions ( Circumferential direction). Further, the direction opposite to the R1 direction is referred to as the R2 direction (reverse direction). The first loop optical fiber 30 is connected to the polarization separating element 12 via the introduction unit 21 and the polarization holding type optical fiber 31.

The introduction section 21 is provided in the second loop section 32 and is composed of a polarization-holding optical coupler. The polarization-holding optical fiber 32C is connected to the front end of the introduction portion 21 in the R1 direction (that is, the end connected to the exit-side end of the polarization-holding optical fiber 31). .. A polarization-retaining optical fiber 32A is connected to the rear end of the introduction portion 21 in the R1 direction. Laser light S1 and S2 and laser amplified light (first laser amplified light, second laser amplified light) L1 and L2 amplified by the amplification unit 40 composed of the rare earth-added optical fiber pass through the introduction unit 21. Therefore, the introduction unit 21 is composed of a wavelength division multiplex type and polarization holding type optical coupler capable of introducing and deriving at least the first wavelength of the laser light S1 and S2 and the second wavelength of the laser amplification light L1 and L2. ing.

The amplification unit 40 is provided between the polarization-holding optical fiber 32A and the polarization-holding optical fiber 32B of the second loop part 32, and is composed of the polarization-holding optical amplification fiber. Examples of the optical amplification fiber include a rare earth-added optical fiber. Examples of the rare earth element added to the rare earth-added optical fiber include erbium (Er), ytterbium (Yb), thulium (Tm) and the like. The rare earth element added to the rare earth-added optical fiber is appropriately selected in consideration of the first wavelength and the second wavelength.

Polarization-holding optical fibers 32B and 32C are connected to the end of the connecting portion 22 on the second loop portion 32 side. Polarized light-holding optical fibers 33A and 33C are connected to the end of the connecting portion 22 on the third loop portion 33 side.

The laser amplification light return unit 70 performs mode-locking of the laser amplification light L1 and L2 amplified by the amplification unit 40. The laser amplification light return unit 70 includes a polarization-holding optical fiber 33A, 33B, 33C provided in a connecting portion 22, a third loop portion 33, and a polarization-holding optical isolator 23. The polarization-holding optical isolator 23 allows only the laser amplification lights L1 and L2 incident from the polarization-holding optical fiber 33B along the R1 direction to pass through the polarization-holding optical fiber 33C, and polarizes along the R2 direction. The laser amplification lights L1 and L2 incident from the holding type optical fiber 33C are removed from the first loop optical fiber 30 by light absorption, branching, or the like.

The lead-out unit 24 is provided in the third loop unit 33 and is composed of a polarization-holding optical coupler.
The polarization-holding optical fiber 33A is connected to the front end of the lead-out portion 24 in the R1 direction (that is, the end on the connecting portion 22 side). In the lead-out unit 24, the incident-side ends (one end) of the polarization-holding optical fibers 33B and 34 are connected to the end on the back side in the R1 direction. The polarization-holding optical fiber 34 takes out optical frequency combs (first optical frequency comb, second optical frequency comb) C1 and C2 having different repetition frequencies from the first loop optical fiber 30 via the lead-out unit 24. Provided for.

As described above, since the first loop optical fiber 30 is composed of the polarization-holding optical fiber and each component provided in the first loop optical fiber 30 can hold the polarization, the first-loop optical fiber 30 can be used. Waveguided and controlled polarization orientation is preserved.

[Operation of dual optical frequency comb generation optical system and laser device]
Next, the operation of the dual optical frequency comb generation optical system 10A and the laser device 60A, and the principle of generating the optical frequency combs C1 and C2 by using the dual optical frequency comb generation optical system 10A and the laser device 60A will be described.

The laser beam S0 emitted from the light source 5 is guided by the polarization-holding optical fiber 6 and incident on the polarization separation element 12. The polarization separation element 12 separates the laser light S1 and S2 from the laser light S0, and only the laser light S1 and S2 are guided to the polarization holding type optical fiber 31.

The laser beams S1 and S2 guided through the polarization-holding optical fiber 31 are guided to the polarization-holding optical fiber 32A via the introduction section 21 and incident on the amplification section 40. Laser light S1 and S2 are amplified by the amplification unit 40, and laser amplification light L1 and L2 are generated. Since the rare earth-added optical fiber is used as the amplification unit 40, the wavelengths of the laser amplification lights L1 and L2 (second wavelengths) are different from the wavelengths of the laser lights S1 and S2 before amplification (first wavelength). The laser amplification lights L1 and L2 having the second wavelength are guided from the amplification unit 40 to the polarization-holding optical fibers 32B and 32A along both the R1 direction and the R2 direction.

The laser amplification lights L1 and L2 pass through the polarization holding type optical fiber 32A and the introduction part 21 in this order from the amplification unit 40 along the R2 direction, and are guided to the polarization holding type optical fiber 32C.

The laser amplification lights L1 and L2 waveguideed to the polarization-retaining optical fiber 32B along the R1 direction and the laser amplification lights L1 and L2 waveguideed to the polarization-retaining optical fiber 32C along the R2 direction are It is incident on the connecting portion 22. The laser amplification lights L1 and L2 that waveguide the polarization-holding optical fiber 32B from the amplification unit 40 along the R1 direction and are incident on the connecting portion 22 have a non-linear phase according to the length of the polarization-holding optical fiber 32B. Receive a shift. The laser amplification lights L1 and L2 incident on the connecting portion 22 by waveguideing the polarization-holding optical fiber 32A, the introduction portion 21, and the polarization-holding optical fiber 32C from the amplification portion 40 along the R2 direction are polarization-holding. It undergoes a non-linear phase shift according to the length of the type optical fibers 32A and 32C.

In the polarization-holding optical coupler constituting the connecting portion 22, the laser amplification lights L1 and L2 incident from the polarization-holding optical fiber 32B along the R1 direction and the polarization-holding optical fiber 32C along the R2 direction The incident laser amplification lights L1 and L2 interfere with each other. In the polarization-holding optical coupler of the connecting portion 22, the phase difference between the laser amplification lights L1 and L2 incident from the polarization-holding optical fiber 32B and the laser amplification lights L1 and L2 incident from the polarization-holding optical fiber 32C. Depending on φ, the light amount ratio of the laser amplification light L1 and L2 waveguideed by the polarization-holding optical fiber 33A and the laser amplification light L1 and L2 waveguideed by the polarization-holding optical fiber 33C changes. The phase difference φ corresponds to the difference in the non-linear phase shift received by the laser amplification lights L1 and L2 incident on the connecting portion 22 from each of the polarization-holding optical fibers 32B and C. When the phase difference φ is an odd multiple of half of the second wavelength (when a predetermined condition is satisfied), the laser amplification lights L1 and L2 enhanced by the interference in the polarization-holding optical coupler of the connecting portion 22 are all in the R1 direction. It is guided to the polarization-maintaining optical fiber 33A along the above.

The laser amplification lights L1 and L2 guided from the connecting portion 22 to the polarization-retaining optical fiber 33A along the R1 direction are incident on the leading portion 24. A part of the laser amplification lights L1 and L2 incident on the lead-out unit 24 is guided by the polarization-holding optical fiber 33B along the R1 direction, passes through the polarization-holding optical isolator 23, and the polarization-holding optical fiber. It is guided by 33C and incident on the connecting portion 22 again. On the other hand, the laser amplification lights L1 and L2 waveguideed from the connecting portion 22 to the polarization-retaining optical fiber 33C along the R2 direction are removed by the polarization-retaining optical isolator 23. That is, the third loop portion 33 circulates only the laser amplification lights L1 and L2 derived from the connecting portion 22 in the R1 direction based on the phase difference φ, and returns them to the connecting portion 22.

A part (about half) of the laser amplification lights L1 and L2 incident on the connecting portion 22 from the polarization-holding optical fiber 33C along the R1 direction is continuously waveguide to the polarization-holding optical fiber 32C along the R1 direction. Then, it passes through the introduction unit 21 and the polarization-retaining optical fiber 32A, and is amplified again by the amplification unit 40. The rest of the laser amplification lights L1 and L2 incident on the connecting portion 22 from the polarization-holding optical fiber 33C along the R1 direction is guided to the polarization-holding optical fiber 32B along the R2 direction, and again the amplification portion 40. Is amplified by. The laser amplification lights L1 and L2 amplified by the amplification unit 40 are guided along both the R1 and R2 directions as described in the previous stage, and are repeatedly amplified.

In the operation of the waveguide and dual optical frequency comb generation optical system 10A of the laser beams S1 and S2 and the laser amplification lights L1 and L2 described above, the second loop portion 32 functions as a gain-free nonlinear amplification optical fiber loop mirror. The second loop portion 32, the connecting portion 22, the polarization-retaining optical isolator 23, and the polarization-retaining optical fibers 33A, 33B, 33C function like a saturable absorber. That is, the connecting portion 22 and the third loop portion 33 function like a saturable absorber. Only the laser amplification lights L1 and L2 strengthened by the interference at the connecting portion 22 circulate around the polarization-maintaining optical fibers 33A, 33B, 33C of the third loop portion 33, return to the second loop portion 32, and return to the amplification portion 32. It is amplified at 40. The weak laser amplification lights L1 and L2 based on the interference at the connecting portion 22 are guided to the polarization-holding optical fiber 33C of the third loop portion 33, but are removed by the polarization-holding optical isolator 23. In this way, the loss in the first loop optical fiber 30 changes according to the light intensity of the laser amplification lights L1 and L2.

The laser amplification lights L1 and L2 guided to the second loop portion 32 along the respective directions from the connecting portion 22 to the R1 and R2 directions perform a non-linear phase shift according to the length of each polarization-holding optical fiber. receive. When the number of circulations in the second loop portion 32 and the third loop portion 33 is less than a predetermined number of times, the power of the laser amplification lights L1 and L2 is low, and the gain in the second loop portion 32 is small. When the gain in the second loop portion 32 is small, the dual optical frequency comb generation optical system 10A and the laser device 60A operate in a state where the laser amplification lights L1 and L2 are continuous light. When the number of circulations of the laser amplification lights L1 and L2 in the second loop portion 32 and the third loop portion 33 becomes a predetermined number or more and the power of the laser amplification lights L1 and L2 becomes higher than the predetermined power, the second The gain in the loop portion 32 becomes very large. When the gain in the second loop portion 32 becomes very large, the dual optical frequency comb generation optical system 10A and the laser device 60A operate in a state where the laser amplification lights L1 and L2 are pulsed lights.

In the dual optical frequency comb generation optical system 10A and the laser device 60A, while the laser amplification lights L1 and L2 oscillate in a state of continuous light or pulsed light, they shift to a mode-locked state, and optical frequency combs C1 and C2 are generated. Will be done. The generated optical frequency combs C1 and C2 are led out from the lead-out unit 24 to the polarization-holding optical fiber 34.

Repetition frequency _{f rep2} of repetition frequency _{f rep1} and optical frequency comb C2 of the optical frequency comb C1 is determined by the resonator length of the dual optical frequency comb generation optical system 10A. The resonator length of the dual optical frequency comb generation optical system 10A is the total length of the polarization-retaining optical fibers 32A, 32B, 32C, 33A, 33B, 33C and the polarization-retaining amplified optical fiber constituting the amplification unit 40. That is, it corresponds to the length of the first loop optical fiber 30. The optical path length of the resonator of the laser amplification light L1 in the dual optical frequency comb generation optical system 10A is determined by the refractive index of the laser amplification light L1 and the resonator length of the dual optical frequency comb generation optical system 10A. The optical path length of the resonator of the laser amplified light L2 in the dual optical frequency comb generation optical system 10A is determined by the refractive index of the laser amplified light L2 and the resonator length of the dual optical frequency comb generation optical system 10A. The resonator length of the dual optical frequency comb generation optical system 10A is common to the laser amplification lights L1 and L2, but the polarization directions of the laser amplification lights L1 and L2 are different between the first direction and the second direction. Therefore, the refractive indexes of the laser amplified lights L1 and L2 are different from each other. Therefore, the optical path length of the resonator of the laser amplified light L1 and the optical path length of the resonator of the laser amplified light L2 are different from each other according to the refractive index difference Δn of the laser amplified light L1 and L2. _Assuming that the optical path length difference between the resonators of the laser amplified lights L1 and L2 is ΔL, the repetition frequency f _rep2 is represented by (f _rep1 + Δf _rep ). The frequency difference Δf _rep depends on the optical path length difference ΔL.

Based on the above-mentioned operating principle, in the dual optical frequency comb generation optical system 10A and the laser device 60A, the laser amplification lights L1 and L2 containing high-intensity pulsed light are polarized light in the R1 direction from the connecting portion 22. Waveguided to fiber 33A. On the other hand, the laser amplification lights L1 and L2 including continuous light having low intensity are also guided to the polarization-holding optical fiber 33C along the R2 direction. However, since the polarization-holding optical isolator 23 is provided, the laser amplification lights L1 and L2 guided by the polarization-holding optical fiber 33A along the R1 direction go around the third loop portion 33. However, the laser amplification lights L1 and L2 guided to the polarization-holding optical fiber 33C along the R2 direction are guided only by the polarization-holding optical fiber 33C and do not go around the third loop portion 33. Therefore, in the dual optical frequency comb generation optical system 10A and the laser device 60A, in the resonator constituting the mode-locked laser of the laser amplification lights L1 and L2, the third loop portion in which the laser amplification lights L1 and L2 circulate only in the R1 direction. The polarization-maintaining optical fibers 33A, 33B, and 33C of 33 are common parts. Based on this, the difference between the length of the polarization-holding optical fiber 32B and the total length of the polarization-holding optical fibers 32A and 32C is set so that the phase difference φ is an odd multiple of half of the second wavelength. Has been done. Then, considering the refractive index and the second wavelength of each of the laser amplification lights L1 and L2, the total length of the polarization-holding optical fibers 33A, 33B, 33C is the resonator length of the laser amplification lights L1 and L2. And the optical path length difference ΔL is set so as to correspond to the desired repetition frequencies _frep1 and _frep2 .

[Effects of dual optical frequency comb generation optical system and laser device]
According to the dual optical frequency comb generation optical system 10A and the laser device 60A, the laser amplification lights L1 and L2 are resonated while shifting to the mode-locked state in the common first loop optical fiber 30. At this time, since the directions of polarization of the laser amplification lights L1 and L2 are different from each other, the refractive indexes of the laser amplification lights L1 and L2 are different. For the laser amplified lights L1 and L2, the optical path lengths of the resonators composed of the first loop optical fiber 30 are different from each other. As a result, from the derivation unit 24, the optical frequency comb C1 in which the polarization direction is the first direction and has the repetition frequency _fp1 and the repetition frequency in which the polarization direction is the second direction and are different from the optical frequency comb C1. An optical frequency comb C2 having f _rep2 can be obtained.

In the dual optical frequency comb generation optical system 10A and the laser device 60A, laser light S1 and S2 and laser amplification light L1 and L2 having different polarization directions are used. In the dual optical frequency comb generation optical system 10A and the laser device 60A, the refractive indexes of the laser amplification lights L1 and L2 are different from each other, and the resonator lengths of the laser amplification lights L1 and L2 are different from each other while sharing the mode-locked laser. be able to. As a result, one mode-locked laser can generate optical frequency combs C1 and C2 (see FIG. 2) having different repetition frequencies. By sharing the dual optical frequency comb generation optical system 10A and the laser device 60A as one mode-locked laser, the laser amplification lights L1 and L2 receive environmental disturbances and machines that the dual optical frequency comb generation optical system 10A and the laser device 60A receive. Disturbance can be shared. As a result, the difference between the environmental disturbances and mechanical disturbances contained in each of the optical frequency combs C1 and C2 can be suppressed, and these environmental disturbances and mechanical disturbances can be easily removed as common noise. The SN ratio of C2 can be increased. Further, when the laser amplification lights L1 and L2 share the dual optical frequency comb generation optical system 10A and the laser device 60A to individually prepare a mode-locked laser that generates optical frequency combs C1 and C2 as in the conventional case. In comparison, the dual optical frequency comb generation optical system 10A and the laser device 60A can be miniaturized.

In the dual optical frequency comb generation optical system 10A and the laser device 60A, the first loop optical fiber 30 is composed of the second loop portion 32 and the third loop portion 33, and the second loop portion 32 and the third loop portion 33 are connected portions. It is connected by 22. In the connecting portion 22, the laser amplification lights L1 and L2 guided along both the R1 and R2 directions interfere with the second loop portion 32. The laser amplification lights L1 and L2, which are strengthened according to the phase difference φ, orbit in the third loop portion 33 only in the R1 direction. Therefore, the connecting portion 22 and the third loop portion 33 function like a simple mirror. In the dual optical frequency comb generation optical system 10A and the laser device 60A, by operating the third loop portion 33 as a simple mirror, laser amplification is performed via the connecting portion 22 without being affected by the phase shift due to the nonlinear optical effect. The optics L1 and L2 can be returned to both the polarization-maintaining optical fibers 32B and 32C. As a result, the laser amplification lights L1 and L2 incident on the connecting portion 22 from the polarization-holding optical fiber 33C are biased along the R1 direction without causing an interference phenomenon due to the phase difference φ of the laser amplification lights L1 and L2. It is made to waveguide to both the wave holding type optical fibers 32B and 32C. That is, the laser-amplified light L1 and L2 circulated in the third loop portion 33 can be guided to both the polarization-holding optical fibers 32B and 32C of the second loop portion 32. Therefore, the operation of the dual optical frequency comb generation optical system 10A can be stabilized, and the mode-locking operation can be satisfactorily generated.

[Measuring device configuration]
The configuration of the measuring device 50 according to the first embodiment of the present invention will be described. As shown in FIG. 2, the measuring device 50 includes a laser device 60A having a dual optical frequency comb generation optical system 10A, a polarization separation unit 52, a polarization interference unit 56, and a sample information extraction unit 58. The exit-side end (the other end) of the polarization-holding optical fiber 34 is connected to the polarization-retaining portion 52. The polarization interference unit 56 interferes with the optical frequency combs C1 and C2 separated by the polarization separation unit 52. The sample information extraction unit 58 extracts sample information from the interference signals of the optical frequency combs C1 and C2 that interfere with each other by the polarization interference unit 56.

The polarization separation unit 52 is arranged behind the optical frequency combs C1 and C2 emitted from the polarization-holding optical fiber 34 in the traveling direction in order to separate the optical frequency combs C1 and C2 having different polarization directions from each other. Has been done. The polarization separation unit 52 is composed of, for example, a polarization separation type optical beam splitter. Of the paths X35 and X36 of the optical frequency combs C1 and C2 separated from each other by the polarization separation unit 52, the sample S is arranged on the path X35 of the optical frequency comb C1. Sample S is the measurement target of the measuring device 50. Polarization-holding type mirrors 57A and 57B are provided along the path X36 of the optical frequency comb C2 to turn back the path X36 toward the polarization interference portion 56.

The polarization interference unit 56 interferes with the optical frequency combs C1 and C2 separated by the polarization separation unit 52. The polarization interference unit 56 interferes with the optical frequency comb C1 (hereinafter referred to as the optical frequency comb C3) including the information of the sample S in the traveling direction of the optical frequency comb C3 from the sample S in order to interfere with the optical frequency comb C2. It is located on the back side. The polarization interference unit 56 is composed of a polarization separation type optical beam splitter and a half mirror.

The sample information extraction unit 58 extracts sample information from the interference signals of the optical frequency combs C1 and C2 that interfere with each other by the polarization interference unit 56. The sample information extraction unit 58 is arranged behind the polarization interference unit 56 in the traveling direction of the multi-heterodyne signal (interference signal) generated by the optical frequency combs C2 and C3 interfering with each other. The sample information extraction unit 58 can acquire information about the sample S from the multi-heterodyne signal, and is composed of a generally known optical system, for example, a device that converts the sample S into an electric signal by a receiver.

[Measurement method using measuring device]
In the measuring device 50, the optical frequency combs C1 and C2 emitted from the polarization-holding optical fiber 34 are separated by the polarization separation unit 52 so as to travel in different paths. The optical frequency comb C1 travels along the path X35 and passes through the sample S. When passing through the sample S, the optical information possessed by the sample S is added to the optical frequency comb C1. The optical frequency comb C2 is folded back by the polarization-holding type mirrors 57A and 57B and travels along the path X35.

The optical frequency comb C3 traveling along the path X35 and the optical frequency comb C2 traveling along the path X36 are reunited at the polarization interference section 56 and interfere with each other. A multi-heterodyne signal is generated by the interference of the optical frequency combs C2 and C3. The multi-heterodyne signal travels along the path X37 and enters the sample information extraction unit 58. As shown in FIG. 2, in the sample information extraction unit 58, the multi-heterodyne signal is converted into a mode-resolved spectrum in a high frequency band by, for example, a Fast Fourier Transform (FFT). The optical information of the sample S is extracted from the waveform (waveform shown by the broken line in FIG. 2) W of the mode decomposition spectrum. In the mode decomposition spectrum, the frequency interval between adjacent spectra on the frequency axis corresponds to the repetition frequency difference Δf _rep .

[Action and effect of measuring device]
In the measuring device 50, the paths of the optical frequency combs C1 and C2 can be separated by the polarization separating unit 52, and the optical information of the sample S can be added to the optical frequency combs C1. By interfering the optical frequency combs C2 and C3 with each other, the polarization interference unit 56 removes environmental disturbances and mechanical disturbances commonly included in the optical frequency combs C2 and C3, and easily observes them in a high frequency band. A possible mode-resolved spectrum can be obtained. The sample information extraction unit 58 can extract the information of the sample S from the waveform W of the spectral distribution of the obtained mode decomposition spectrum. Therefore, according to the measuring device 50 of the present invention, since the optical frequency combs C1 and C2 having a high SN ratio are used, the information of the sample S can be acquired with high accuracy. Since the measuring device 50 has a common configuration for generating the optical frequency combs C1 and C2, it is not necessary to prepare optical systems for generating the optical frequency combs C1 and C2 in separate spaces as in the conventional case, and the measuring device It is possible to reduce the size by 50.

(Second Embodiment)
The dual optical frequency comb generation optical system, the laser device, and the measuring device of the second embodiment of the present invention will be described. In the description and drawings of each embodiment after the second embodiment, the same reference numerals are given to the components common to the dual optical frequency comb generation optical system 10A, the laser device 60A, and the measuring device 50 of the first embodiment. However, the description thereof will be omitted. Each embodiment after the second embodiment basically describes a configuration and an action different from those of the first embodiment, and is common to the first embodiment except for the configuration and the action described.

[Configuration of dual optical frequency comb generation optical system and laser device]
As shown in FIG. 3, the laser device 60B of the second embodiment includes a polarization-holding optical fiber 42 in place of the polarization-holding optical fiber 6 and the polarization-separating element 12 of the laser device 60A, and includes a first polarization-holding optical fiber 42. The dual optical frequency comb generation optical system 10A described in the embodiment is provided.

The polarization-retaining optical fiber 42 is an optical fiber capable of maintaining the polarization directions of the laser beams S1 and S2 guided internally, similarly to the polarization-retaining optical fiber 6. The polarization axis J42 of the clad 77 of the polarization-retaining optical fiber 42 centered on the optical axis A is 45 ° with respect to the polarization axis J31 of the clad 71 of the polarization-retaining optical fiber 31 centered on the optical axis A. The angle is any of 135 °, 225 °, and 315 °. The polarization axes J42 and J31 are determined by the positions of a pair of stress applying portions 80 and 80 provided on each of the claddings 77 and 71 with the core 80 sandwiched in cross-sectional view.

[Operation of dual optical frequency comb generation optical system and laser device]
In the laser device 60B, when the laser light S0 emitted from the light source 5 is waveguideed to the polarization-holding optical fiber 42, the laser light S0 having a plurality of polarization directions is a laser having a polarization direction along the polarization axis J42. Optical SX (not shown) is taken out. When the laser light SX is guided to the polarization-holding optical fiber 31, it is separated into the laser light S1 and S2 by the polarization axis J31. Only the laser beams S1 and S2 are incident on the introduction portion 21 of the dual optical frequency comb generation optical system 10A.

The waveguide of the laser beams S1 and S2 and the generation of the laser amplification lights L1 and L2 introduced into the dual optical frequency comb generation optical system 10A via the introduction unit 21 are the same as those described in the first embodiment. .. From the polarization-retaining optical fiber 34, optical frequency combs C1 and C2 (see FIG. 2) having different repeating frequencies can be obtained.

[Effects of dual optical frequency comb generation optical system and laser device]
Since the laser device 60B has the dual optical frequency comb generation optical system 10A, it has the same effect as the laser device 60A. Further, in the laser device 60B, the polarization axes J42 and J31 of the polarization-holding optical fibers 42 and 31 form 45 ° (or 135 °, 225 °, 315 °) with each other in a cross section orthogonal to the optical axis A. Since it is tilted to, the laser light LX can be divided into lasers S1 and S2 without using the polarization separating element 12. For example, if the polarization-holding optical fiber 42 is directly connected to the emission port of the semiconductor laser constituting the light source 5, the polarization axis J42 is biased with respect to the polarization axis J31 with the optical axis A tilted at the center. The ends of the wave-holding optical fibers 42 and 31 can be connected by fusion or the like. With such a configuration, the configuration of the laser device 60B can be simplified as compared with the configuration of the laser device 60A without using the polarization separating element 12.

[Configuration, operation, and effect of measuring device]
Although not shown, the measuring device of the second embodiment includes the laser device 60B shown in FIG. 3 in place of the laser device 60A of the measuring device 50 shown in FIG. The configuration of the measuring device of the second embodiment other than the laser device is the same as that of the measuring device 50. In the laser device 60B, since the optical frequency combs C1 and C2 can be obtained from the polarization-holding optical fiber 34 as in the laser device 60A, the measuring device of the second embodiment operates in the same manner as the measuring device 50, and the measuring device 50 operates. Has the same effect as.

(Third Embodiment)
Next, the dual optical frequency comb generation optical system, the laser device, and the measuring device according to the third embodiment of the present invention will be described.

[Configuration of dual optical frequency comb generation optical system and laser device]
As shown in FIG. 4, the laser device 60C of the third embodiment replaces one light source 5 of the laser device 60A, the polarization-holding optical fiber 6 and the polarization separation element 12, and two light sources 5A. It includes 5B, two polarization-holding optical fibers 6A and 6B, and a polarization-coupling element 14, and also includes the dual optical frequency comb generation optical system 10A of the first embodiment.

Like the light source 5, the light sources 5A and 5B are composed of a semiconductor laser. The light source 5A emits only the laser light S1, and the light source 5B emits only the laser light S2. The polarization coupling element 14 combines the laser beams S1 and S2 incident from the polarization-holding optical fibers 6A and 6B as different paths, and transfers the combined laser beams S1 and S2 to the common polarization-holding optical fiber 31. Exit. The polarization coupling element 14 is composed of, for example, a polarization beam splitter.

[Operation of dual optical frequency comb generation optical system and laser device]
In the laser device 60C, the laser light S1 emitted from the light source 5A is guided to the polarization-retaining optical fiber 6A, and the laser light S2 emitted from the light source 5B is guided to the polarization-retaining optical fiber 6B. Laser. When the laser beams S1 and S2 are incident on the polarization coupling element 14 from the polarization-holding optical fibers 6A and 6B, they are coupled to each other. The combined laser beams S1 and S2 are incident on the introduction portion 21 of the dual optical frequency comb generation optical system 10A via the polarization-holding optical fiber 31.

The waveguide of the laser beams S1 and S2 introduced into the dual optical frequency comb generation optical system 10A via the introduction unit 21 is the same as the content described in the first embodiment. From the polarization-retaining optical fiber 34, optical frequency combs C1 and C2 (see FIG. 2) having different repeating frequencies can be obtained.

[Effects of dual optical frequency comb generation optical system and laser device]
Since the laser device 60C has the dual optical frequency comb generation optical system 10A, the laser device 60C has the same effect as the laser device 60A. Further, in the laser device 60C, the laser beams S1 and S2 are generated by different light sources, guided by different polarization-holding optical fibers, and coupled by the polarization coupling element 14 to obtain the laser beams L1 and L2. As a result, the laser beams S1 and S2 can be individually controlled, and the characteristics of the optical frequency combs C1 and C2 can be adjusted easily and with high accuracy. For example, and modulating and controlling only the repetition frequency f _rep2 of repetition frequency f _rep1 or optical frequency comb C2 of the optical frequency comb C1, it can control the phase of the optical frequency of only the optical frequency comb C1 or optical frequency comb C2.

[Configuration, operation, and effect of measuring device]
Although not shown, the measuring device of the third embodiment includes the laser device 60C shown in FIG. 4 in place of the laser device 60A of the measuring device 50 shown in FIG. The configuration of the measuring device of the third embodiment other than the laser device is the same as that of the measuring device 50. In the laser device 60C, since the optical frequency combs C1 and C2 can be obtained from the polarization-holding optical fiber 34 as in the laser device 60A, the measuring device of the third embodiment operates in the same manner as the measuring device 50, and the measuring device 50 operates. Has the same effect as.

(Fourth Embodiment)
Next, the dual optical frequency comb generation optical system, the laser device, and the measuring device according to the fourth embodiment of the present invention will be described.

[Configuration of dual optical frequency comb generation optical system and laser device]
As shown in FIG. 5, the configuration from the light source 5 to the introduction unit 21 in the laser device 60D of the fourth embodiment is the same as the configuration from the light source 5 to the introduction unit 21 in the laser device 60A described in the first embodiment. is there. The laser device 60D includes a dual optical frequency comb generation optical system 10B in place of the dual optical frequency comb generation optical system 10A described in the first embodiment.

A phase modulation section 72 is incorporated in the polarization-holding optical fiber 33B of the third loop section 33 of the dual optical frequency comb generation optical system 10B. The phase modulation unit 72 can modulate the phases of the laser amplification lights L1 and L2 guided by the third loop unit 33. The phase modulation unit 72 includes an electro-optical modulator 73A provided on the front side in the R1 direction and an electro-optic modulator 73B provided on the back side in the R1 direction. An emission terminal 81 and a collimator lens 82 are provided between the end of the polarization-holding optical fiber 33B and the electro-optical modulators 73A and 73B, respectively. A high-frequency electric signal of high power is supplied to each of the electro-optical modulators 73A and 73B from the outside of the third loop portion 33 from the high-frequency generator 84 via the amplifier 83. The electro-optical modulator 73A can modulate only the phase of the laser amplification light L1 whose polarization direction is the first direction. The electro-optical modulator 73B can modulate only the phase of the laser amplification light L2 whose polarization direction is the second direction.

[Operation of dual optical frequency comb generation optical system and laser device]
In the dual optical frequency comb generation optical system 10B and the laser device 60D, the polarization-holding optical fiber 34 uses optical frequency combs having different repeating frequencies from each other by the same waveguide and operating principle as those described in the first embodiment. C1 and C2 (see FIG. 2) are obtained.

In the dual optical frequency comb generation optical system 10B and the laser device 60D, of the laser amplification lights L1 and L2 waveguideed in the third loop portion 33 along the R1 and R2 directions, the phase modulation portion 72 is provided along the R1 direction. The optical path length of the incident laser amplified light L1 is changed by the electro-optical modulator 73A. Further, the optical path length of the laser amplification light L2 incident on the phase modulation unit 72 along the R1 direction is changed by the electro-optical modulator 73B. That is, the resonator length and the optical path length difference ΔL of the laser amplified lights L1 and L2 change depending on the amount of change in the optical path length of the laser amplified light L1 by the electro-optical modulators 73A and 73B.

[Effects of dual optical frequency comb generation optical system and laser device]
Since the laser device 60D has the dual optical frequency comb generation optical system 10B, the laser device 60D has the same effect as the laser device 60A. Further, in the dual optical frequency comb generation optical system 10B and the laser device 60C, the amount of change in the optical path length of the laser amplified light L1 by the electrooptical modulator 73A and the amount of change in the optical path length of the laser amplified light L2 by the electrooptical modulator 73B. By adjusting the difference between the laser amplification lights L1 and L2, the resonator length and the optical path length difference ΔL can be controlled with high accuracy. By controlling the resonator length and the optical path length difference ΔL of the laser amplified lights L1 and L2 with high accuracy, only the repetition frequency f _rep1 of the optical frequency comb C1 or the repetition frequency f _{rep2 of the} optical frequency comb C2 can be easily controlled. ..

[Configuration, operation, and effect of measuring device]
Although not shown, the measuring device according to the fourth embodiment of the present invention includes the laser device 60D shown in FIG. 5 in place of the laser device 60A of the measuring device 50 shown in FIG. The configuration of the measuring device of the fourth embodiment other than the laser device is the same as that of the measuring device 50. In the laser device 60D, since the optical frequency combs C1 and C2 can be obtained from the polarization-holding optical fiber 34 as in the laser device 60A, the measuring device of the fourth embodiment operates in the same manner as the measuring device 50, and the measuring device 50 operates. Has the same effect as. According to the laser apparatus 60D, since the repetition frequency difference Delta] f _rep of the optical frequency comb C1, C2 to each other can be easily controlled, thereby easily controlling the frequency interval of the spectrum adjacent on the frequency axis in the mode resolved spectrum, the 4 The measurement resolution of the measuring device of the embodiment can be easily adjusted.

(Fifth Embodiment)
Next, the dual optical frequency comb generation optical system, the laser device, and the measuring device according to the fifth embodiment of the present invention will be described.

[Configuration of dual optical frequency comb generation optical system and laser device]
As shown in FIG. 6, the configuration from the light source 5 to the introduction unit 21 in the laser device 60E of the fifth embodiment is the same as the configuration from the light source 5 to the introduction unit 21 in the laser device 60A described in the first embodiment. is there. The laser device 60E includes a dual optical frequency comb generation optical system 10C instead of the dual optical frequency comb generation optical system 10A described in the first embodiment.

The dual optical frequency comb generation optical system 10C includes at least the configuration of the dual optical frequency comb generation optical system 10B described in the fourth embodiment. In addition, the polarization-holding optical fiber 32C of the second loop portion 32 of the dual optical frequency comb generation optical system 10C incorporates a polarization-multiplexed non-reciprocal phase shift portion 90. Here, "polarization multiplex type" means that it acts on both the laser amplification light L1 in which the direction of polarization is the first direction and the laser amplification light L2 in which the direction of polarization is the second direction. Shown. The above-mentioned "non-reciprocity" means that the laser amplification light L1 and L2 waveguideed in the R1 direction and the laser amplification light L1 and L2 waveguideed in the R2 direction act individually. Shown. That is, the non-reciprocal phase shift unit 90 can shift the phase difference φ between the laser amplification lights L1 and L2 guided in the R1 direction and the laser amplification lights L1 and L2 guided in the R2 direction.

7 and 8 show a first configuration example and a second configuration example of the non-reciprocal phase shift unit 90. As shown in FIG. 7, the non-reciprocal phase shift unit 90A of the first configuration example includes two Faraday rotators 91 and 92 and a quarter-wave plate (QWP) 93. .. In the non-reciprocal phase shift portion 90A, collimators 100A and 100B connected to the polarization-holding optical fiber 32C are provided at the front and back ends of the base 98 in the R1 direction. Faraday rotators 91, QWP93, and Faraday rotators 92 are arranged in this order on the base 98 along the R1 direction between the collimators 100A and 100B at intervals.

The Faraday rotator 91 rotates the direction of polarization of the laser amplification lights L1 and L2 incident along the R1 direction in a predetermined direction. The predetermined direction is, for example, a direction rotated by a predetermined angle θ from the first direction about the optical axis A. The Faraday rotator 91 rotates the direction of polarization of the laser amplification lights L1 and L2 incident along the R2 direction in a predetermined opposite direction. The predetermined reverse direction is, for example, a direction rotated from the first direction about the optical axis A by a predetermined angle θ to the opposite side of the incident from the R1 direction.

The Faraday rotator 92 rotates the direction of polarization of the laser amplification lights L1 and L2 incident along the R2 direction in a predetermined direction. The predetermined direction is, for example, a direction rotated by a predetermined angle θ from the first direction about the optical axis A. The Faraday rotator 92 rotates the direction of polarization of the laser amplification lights L1 and L2 incident along the R1 direction in a predetermined opposite direction. The predetermined reverse direction is, for example, a direction rotated from the first direction about the optical axis A by a predetermined angle θ to the opposite side of the incident from the R1 direction.

In the non-reciprocal phase shift section 90A, the polarization directions of the laser amplification lights L1 and L2 incident on the Faraday rotator 91 from the collimator 100A through the polarization-holding optical fiber 32C along the R1 direction are determined by the Faraday rotator 91. The direction and the second direction are changed to the third direction and the fourth direction. The laser amplified lights L1 and L2 whose polarization directions are in the third and fourth directions are incident on the QWP 93. The directions of polarization of the laser amplified lights L1 and L2 emitted from the QWP 93 along the R1 direction and incident on the Faraday rotator 92 are from the third direction to the first direction and from the fourth direction to the second direction by the Faraday rotator 92. Return to. The laser amplification lights L1 and L2 that have passed through the Faraday rotator 92 are guided from the collimator 100B to the polarization-holding optical fiber 32C.

In the non-reciprocal phase shift portion 90A, the polarization directions of the laser amplification lights L1 and L2 incident on the Faraday rotator 92 from the collimator 100B through the polarization-holding optical fiber 32C along the R2 direction are first determined by the Faraday rotator 92. It rotates in the opposite direction to the R1 direction. At this time, if the crystal axis of the QWP93 is aligned with the direction of polarization in the R1 direction, a phase difference of 90 ° can be given relative to the laser amplification lights L1 and L2 traveling along the R2 direction. Therefore, after passing through QWP93, the direction of polarization is returned by the Faraday rotator 91. The direction of the crystal axis of the QWP93 can be adjusted to, for example, a direction changed from the first direction / second direction to the third direction / fourth direction of the laser amplification lights L1 and L2.

According to the non-reciprocal phase shift unit 90A, both the laser amplification light L1 and L2 incident along the R1 direction and the laser amplification light L1 and L2 incident along the R2 direction from the polarization-holding optical fiber 32C A phase difference offset can be added. The phase difference offset is based on the characteristics of QWP93.

The number of wave plates arranged between the Faraday rotators 91 and 92 is 1 in FIG. 7, but may be changed. A half-wave plate (HWP) and a QWP different from the QWP 93 may be provided on the back side of the QWP 93 in the R1 direction, that is, between the QWP 93 and the Faraday rotator 92.

As shown in FIG. 8, the non-reciprocal phase shift unit 90B of the second configuration example includes four Faraday rotators 91A, 91B, 92A, 92B and two QWP93A, 93B. The Faraday rotators 91A and 91B function in the same manner as the Faraday rotator 91. The Faraday rotators 92A and 92B function in the same manner as the Faraday rotator 92. The QWP93A and 93B function in the same manner as the QWP93.

In the non-reciprocal phase shift unit 90B, a series of configurations of the Faraday rotator 91, the QWP 93, and the Faraday rotator 92 in the non-reciprocal phase shift unit 90A of the first configuration example are provided in parallel. On the base 98, Faraday rotators 91A, QWP93A, and Faraday rotators 92A are arranged in this order as the first series between the collimators 100A and 100B along the R1 direction at intervals. Between the collimators 100A and 100B, Faraday rotators 91B, QWP93B, and Faraday rotators 92B are arranged in this order as the second series at positions different from the first series in the R1 direction. In the first system, a polarization separation coupling element 97A is provided on the front side of the Faraday rotator 91A in the R1 direction. A polarization separation coupling element 97B is provided on the back side of the Faraday rotator 92A in the R1 direction. In the second system, a polarization-maintaining mirror 99A is provided on the front side of the Faraday rotator 91B in the R1 direction. A polarization-maintaining mirror 99B is provided on the back side of the Faraday rotator 92B in the R1 direction.

In the non-reciprocal phase shift unit 90B, the laser amplification lights L1 and L2 incident on the Faraday rotator 91 from the collimator 100A along the R1 direction are separated by the polarization separation coupling element 97A based on the difference in the polarization directions of each other. .. One of the laser amplification lights L1 and L2, the laser amplification light L1, travels from the polarization separation coupling element 97A toward the first system. The laser amplification light L1 passes through the Faraday rotator 91A, the QWP93A, and the Faraday rotator 92A in this order, and undergoes a phase shift based on the characteristics of the QWP93A. The laser amplified light L2 separated by the polarization separation coupling element 97A is folded back by the mirror 99A and travels toward the second system, passes through the Faraday rotator 91B, the QWP93B, and the Faraday rotator 92B in this order, and the characteristics of the QWP93B. Receives a phase shift based on. The laser amplification light L2 emitted from the Faraday rotator 92B is folded back to the polarization separation coupling element 97B by the mirror 99B. The lasers L1 and L2 incident on the polarization separation coupling element 97B are coupled while maintaining the respective polarization directions in the first direction or the second direction, and the polarization holding type light on the back side in the R1 direction from the collimator 100B. It is incident on the fiber 32C.

In the non-reciprocal phase shift portion 90B, the laser amplification lights L1 and L2 incident on the polarization separation coupling element 97B from the collimator 100B along the R2 direction travel along the R1 direction except that the traveling directions are opposite. While undergoing a non-linear phase shift, the laser-amplified light L1 and L2 undergo a non-linear phase shift.

According to the non-reciprocal phase shift unit 90B, both the laser amplification light L1 incident along the R1 direction from the polarization-maintaining optical fiber 32C and the laser amplification light L1 incident along the R2 direction have the characteristics of QWP93A. Based on the phase shift can be given. Further, it is possible to give an offset to the phase difference based on the characteristics of the QWP93B to both the laser amplification light L2 incident along the R1 direction from the polarization-maintaining optical fiber 32C and the laser amplification light L2 incident along the R2 direction. .. In non-reciprocal phase shift unit 90B, since the phase shift can be imparted individually to the laser amplified light L1, L2, optical frequency comb C1 compared to the non-reciprocal phase shift unit 90A, C2 repetition frequency difference Delta] f _rep the precision Can be controlled.

[Operation of dual optical frequency comb generation optical system and laser device]
In the dual optical frequency comb generation optical system 10C and the laser device 60E, optical frequency combs having different repeating frequencies from the polarization-holding optical fiber 34 are used by the same waveguide and operating principle as those described in the fourth embodiment. C1 and C2 (see FIG. 2) are obtained. However, in the dual optical frequency comb generation optical system 10C and the laser apparatus 60E, the laser amplification lights L1 and L2 waveguideed in the second loop portion 32 along the R1 and R2 directions are non-linear phase shifted by the non-reciprocal phase shift portion 90. Receive.

[Effects of dual optical frequency comb generation optical system and laser device]
Since the laser device 60E has the dual optical frequency comb generation optical system 10C, it has the same effect as the laser device 60D. In the dual optical frequency comb generation optical system 10C and the laser device 60E, the resonators of the laser amplification lights L1 and L2 are adjusted by adjusting the amount of the non-linear phase shift to the laser amplification lights L1 and L2 by using the non-reciprocal phase shift unit 90. The length and optical path length difference ΔL can be controlled. Therefore, according to the dual optical frequency comb generation optical system 10C and the laser device 60E, the non-reciprocal phase shift unit 90 is used to control the resonator length and the optical path length difference ΔL of the laser amplification lights L1 and L2, and the optical frequency comb is used. The repetition frequency difference Δf _rep of C1 and C2 can be adjusted. If the resonator length and the optical path length difference ΔL of the laser amplified lights L1 and L2 are individually controlled by using the non-reciprocal phase shift unit 90B as the non-reciprocal phase shift unit 90, the repeating frequency difference Δf _{rep of the} optical frequency combs C1 and C2 Can be finely adjusted.

[Configuration, operation, and effect of measuring device]
Although not shown, the measuring device of the fifth embodiment includes the laser device 60E shown in FIG. 6 in place of the laser device 60A of the measuring device 50 shown in FIG. The configuration of the measuring device of the fifth embodiment other than the laser device is the same as that of the measuring device 50. In the laser device 60E, the optical frequency combs C1 and C2 can be obtained from the polarization-holding optical fiber 34 in the same manner as in the laser device 60A. As a result, the measuring device of the fifth embodiment operates in the same manner as the measuring device 50, and has the same effect as the measuring device 50. According to the laser device 60E, the repeating frequency difference Δf _rep between the optical frequency combs C1 and C2 can be easily controlled. Therefore, in the mode decomposition spectrum, the frequency interval between adjacent spectra on the frequency axis can be easily controlled, and the measurement resolution of the measuring device of the fifth embodiment can be easily and highly accurately adjusted.

(Sixth Embodiment)
Next, the dual optical frequency comb generation optical system, the laser device, and the measuring device according to the sixth embodiment of the present invention will be described.

[Configuration of dual optical frequency comb generation optical system and laser device]
As shown in FIG. 9, the configuration from the light source 5 to the introduction unit 21 in the laser device 60F of the sixth embodiment is the same as the configuration from the light source 5 to the introduction unit 21 in the laser device 60A described in the first embodiment. is there. The laser device 60F includes a dual optical frequency comb generation optical system 10D in place of the dual optical frequency comb generation optical system 10A described in the first embodiment.

The dual optical frequency comb generation optical system 10D includes at least the configuration of the dual optical frequency comb generation optical system 10C described in the fifth embodiment. A resonator length control element 76 is incorporated in the polarization-holding optical fiber 32B of the second loop portion 32 of the dual optical frequency comb generation optical system 10D. The resonator length control element 76 makes it possible to adjust the optical path lengths of the laser amplification lights L1 and L2 in the second loop portion 32. Examples of the resonator length control element 76 include a piezoelectric element, an acoustic optical element, and an electro-optical element.

[Operation and effect of dual optical frequency comb generation optical system and laser device]
In the dual optical frequency comb generation optical system 10D and the laser device 60F, the polarization-holding optical fiber 34 uses optical frequency combs having different repeating frequencies from each other by the same waveguide and operating principle as those described in the fifth embodiment. C1 and C2 (see FIG. 2) are obtained. In the dual optical frequency comb generation optical system 10D and the laser device 60F, the optical path lengths of the laser amplified lights L1 and L2 waveguideed in the second loop portion 32 along the R1 and R2 directions are changed by the resonator length control element 76. it can. The resonator length control element 76 controls the resonator lengths of the laser amplified lights L1 and L2, and the repeating frequency difference Δf _rep between the optical frequency combs C1 and C2 can be easily and finely controlled.

[Configuration, operation, and effect of measuring device]
Although not shown, the measuring device of the sixth embodiment includes the laser device 60F shown in FIG. 6 in place of the laser device 60A of the measuring device 50 shown in FIG. The configuration of the measuring device of the sixth embodiment other than the laser device is the same as that of the measuring device 50. In the laser device 60F, since the optical frequency combs C1 and C2 can be obtained from the polarization-holding optical fiber 34 as in the laser device 60A, the measuring device of the sixth embodiment operates in the same manner as the measuring device 50, and the measuring device 50 operates. Has the same effect as. According to the laser device 60F, the repetition frequency difference Δf _rep between the optical frequency combs C1 and C2 can be controlled with high accuracy. As a result, the frequency interval between adjacent spectra on the frequency axis in the mode decomposition spectrum can be controlled with high accuracy, and the measurement resolution of the measuring device of the sixth embodiment can be adjusted with high accuracy.

(7th Embodiment)
Next, the dual optical frequency comb generation optical system, the laser device, and the measuring device according to the seventh embodiment of the present invention will be described.

[Configuration of dual optical frequency comb generation optical system and laser device]
As shown in FIG. 10, the configuration from the light source 5 to the introduction unit 21 in the laser device 60G according to the seventh embodiment of the present invention is the configuration from the light source 5 to the introduction unit 21 in the laser device 60A described in the first embodiment. Is similar to. The laser device 60G includes a dual optical frequency comb generation optical system 10E instead of the dual optical frequency comb generation optical system 10A of the first embodiment.

The dual optical frequency comb generation optical system 10E includes a first loop optical fiber 30, an introduction unit 21, an amplification unit 40, a connection unit 22, and a spatial resonance unit 102. The first loop optical fiber 30 includes a second loop portion 32 shown on the right side of FIG. 10 and polarization-holding optical fibers 33A, 34, 33C shown on the left side of FIG. Although the polarization-holding optical fibers 33A and 34 are composed of a common polarization-holding optical fiber, they may be composed of different polarization-holding optical fibers connected to each other. The incident-side end (one end) of the polarization-maintaining optical fiber 33A is connected to the side of the connecting portion 22 opposite to the second loop portion 32 side. The exit-side end (the other end) of the polarization-holding optical fiber 33A is connected to the polarization-separating portion 52 of the measuring device 50. The incident-side end (one end) of the polarization-maintaining optical fiber 33C is connected to the side of the connecting portion 22 opposite to the second loop portion 32 side. A spatial resonance portion 102 is connected to an exit-side end (the other end) of the polarization-maintaining optical fiber 33C. Since the light reciprocates along the longitudinal direction in the polarization-maintaining optical fiber 33C, the “incident side” and the “exit side” are the side where the light first enters the polarization-maintaining optical fiber 33C and the light is emitted first. Means the side to do. In the first loop optical fiber 30, an annular loop path is not formed on the left side of FIG. 10 from the connecting portion 22. That is, the first loop optical fiber 30 is configured to draw the number "9" with the connecting portion 22 as a knot.

The laser amplification light return unit 70 includes a connecting unit 22 and a linear unit 38 composed of a polarization-holding optical fiber 33C and a spatial resonance unit 102.

Hereinafter, one of the linear directions separated from the connecting portion 22 from the exit side end portion of the polarization-maintaining optical fiber 33C is referred to as the P1 direction. Further, a linear direction opposite to the P1 direction is referred to as a P2 direction. The spatial resonance unit 102 includes a polarization-holding type emission end 104, a lens 108, and a polarization-holding type mirror 106. The emission end 104 is provided at the end on the emission side of the polarization-maintaining optical fiber 33C. The lens 108 is arranged on the back side in the P1 direction from the emission end 104. The mirror 106 is arranged on the back side in the P1 direction from the lens 108. The transmittance of the laser amplified lights L1 and L2 on the reflecting surface 106r of the mirror 106 is 0%. The lens 108 collimates the laser amplification lights L1 and L2 incident along the P1 direction, and focuses the laser amplification lights L1 and L2 incident along the P2 direction on the emission end 104.

The waveguide of the laser light S1 and S2 and the laser amplification light L1 and L2 from the light source 5 to the connecting portion 22 in the laser device 60G is the laser light from the light source 5 to the connecting portion 22 in the laser device 60A described in the first embodiment. This is the same as the waveguide of S1 and S2 and the laser amplification lights L1 and L2.

In the connecting portion 22, the ratio at which the laser amplification lights L1 and L2 incident on the connecting portion 22 are guided to each of the polarization-holding optical fibers 33A and 33C is determined by the phase difference φ. Since the first loop optical fiber 30 is configured to draw "9", when the phase difference φ is an even multiple of half of the second wavelength (when a predetermined condition is satisfied), the polarization of the connecting portion 22 The laser amplification lights L1 and L2 enhanced by the interference in the holding type optical coupler are all waveguideed to the polarization holding type optical fiber 33A along the R1 direction. A part (about 50%) of the laser amplification lights L1 and L2 incident on the connecting portion 22 is guided to the polarization-maintaining optical fiber 33A. The remaining portion (about 50%) of the laser amplification lights L1 and L2 incident on the connecting portion 22 is guided to the polarization-maintaining optical fiber 33C.

The laser amplification lights L1 and L2 waved from the connecting portion 22 to the polarization-holding optical fiber 33C are incident on the spatial resonance portion 102 from the other end of the polarization-holding optical fiber 33C, and the emission end 104 is provided. It passes through and exits into space, diffuses along the P1 direction, and enters the lens 108. The laser amplified lights L1 and L2 incident on the lens 108 are collimated by the lens 108, propagate in the P1 direction, and reflected by the reflecting surface 106r of the mirror 106. The laser amplified lights L1 and L2 reflected by the reflecting surface 106r propagate along the P2 direction, enter the lens 108, and are focused by the lens 108 on the exit end 104. The laser amplification lights L1 and L2 focused on the emission end 104 pass through the emission end 104 and are guided to the polarization-holding optical fiber 33C along the R1 direction.

The waveguides of the laser amplification lights L1 and L2, which are waveguideed by the polarization-maintaining optical fiber 33C and incident on the connecting portion 22 along the R1 direction, are the dual optical frequency comb generation optical system 10A and the dual optical frequency comb generation optical system 10A described in the first embodiment. This is the same as the waveguide of the laser amplification lights L1 and L2 incident on the connecting portion 22 along the R1 direction in the laser device 60A. Optical frequency combs C1 and C2 having different repetition frequencies are obtained from the connecting portion 22 in the polarization-holding optical fibers 33A and 34.

[Effects of dual optical frequency comb generation optical system and laser device]
The laser device 60G has a dual optical frequency comb generation optical system 10E, and has the same effect as the laser device 60A. Further, since the laser device 60G includes the spatial resonance portion 102, the resonator lengths of the laser amplification lights L1 and L2 can be adjusted by changing the distance between the emission end 104 and the mirror 106, and in addition, the resonator length can be adjusted. A large adjustment range can be secured.

[Configuration, operation, and effect of measuring device]
Although not shown, the measuring device of the seventh embodiment includes the laser device 60G shown in FIG. 10 in place of the laser device 60A of the measuring device 50 shown in FIG. The configuration of the measuring device of the second embodiment other than the laser device is the same as that of the measuring device 50. In the laser device 60G, since the optical frequency combs C1 and C2 can be obtained from the polarization-holding optical fiber 34 as in the laser device 60A, the measuring device of the seventh embodiment operates in the same manner as the measuring device 50, and the measuring device 50 operates. Has the same effect as.

(8th Embodiment)
Next, the dual optical frequency comb generation optical system, the laser device, and the measuring device according to the eighth embodiment of the present invention will be described.

[Configuration of dual optical frequency comb generation optical system and laser device]
As shown in FIG. 11, the laser device 60H of the eighth embodiment includes a polarization-holding optical fiber 42 instead of the polarization-holding optical fiber 6 and the polarization-separating element 12 of the laser device 60G, and has a seventh polarization-holding optical fiber 42. The dual optical frequency comb generation optical system 10E of the embodiment is provided. Similar to the second embodiment, the polarization axis J42 of the clad 77 of the polarization-retaining optical fiber 42 centered on the optical axis A is the polarization of the clad 71 of the polarization-retaining optical fiber 31 centered on the optical axis A. It forms any of 45 °, 135 °, 225 °, and 315 ° with respect to the axis J31.

[Effects of dual optical frequency comb generation optical system and laser device]
The laser device 60H has a dual optical frequency comb generation optical system 10E, and has the same effect as the laser device 60G. Further, according to the laser device 60G, the laser light emitted from the light source 5 can be divided into the lasers S1 and S2 without using the polarization separating element 12 as in the second embodiment.

[Configuration, operation, and effect of measuring device]
Although not shown, the measuring device of the eighth embodiment includes the laser device 60H shown in FIG. 11 in place of the laser device 60A of the measuring device 50 shown in FIG. The configuration of the measuring device of the eighth embodiment other than the laser device is the same as that of the measuring device 50. In the laser device 60H, since the optical frequency combs C1 and C2 can be obtained from the polarization-holding optical fiber 34 as in the laser device 60A, the measuring device of the eighth embodiment operates in the same manner as the measuring device 50, and the measuring device 50 operates. Has the same effect as.

(9th Embodiment)
Next, the dual optical frequency comb generation optical system, the laser device, and the measuring device according to the ninth embodiment of the present invention will be described.

[Configuration of dual optical frequency comb generation optical system and laser device]
As shown in FIG. 12, the laser device 60I of the ninth embodiment replaces one light source 5, the polarization-holding optical fiber 6, and the polarization separation element 12 of the laser device 60G with two light sources 5A. It includes 5B, two polarization-holding optical fibers 6A and 6B, and a polarization-coupling element 14, and also includes a dual optical frequency comb generation optical system 10E described in the seventh embodiment.

[Effects of dual optical frequency comb generation optical system and laser device]
The laser device 60I has a dual optical frequency comb generation optical system 10E, and has the same effect as the laser device 60G. According to the laser device 60I, the laser beams S1 and S2 can be individually controlled and the characteristics of the optical frequency combs C1 and C2 can be adjusted easily and with high accuracy as in the third embodiment.

[Configuration, operation, and effect of measuring device]
Although not shown, the measuring device of the ninth embodiment includes the laser device 60I shown in FIG. 12 instead of the laser device 60A of the measuring device 50 shown in FIG. The configuration of the measuring device of the ninth embodiment other than the laser device is the same as that of the measuring device 50. In the laser device 60I, since the optical frequency combs C1 and C2 can be obtained from the polarization-holding optical fiber 34 as in the laser device 60A, the measuring device of the ninth embodiment operates in the same manner as the measuring device 50, and the measuring device 50 operates. Has the same effect as.

(10th Embodiment)
Next, the dual optical frequency comb generation optical system, the laser device, and the measuring device according to the tenth embodiment of the present invention will be described.

[Configuration of dual optical frequency comb generation optical system and laser device]
As shown in FIG. 13, the configuration from the light source 5 to the introduction unit 21 in the laser device 60J according to the tenth embodiment of the present invention is the configuration from the light source 5 to the introduction unit 21 in the laser device 60A described in the first embodiment. Is similar to. The laser device 60J includes a dual optical frequency comb generation optical system 10F instead of the dual optical frequency comb generation optical system 10A described in the first embodiment.

The dual optical frequency comb generation optical system 10F includes the configuration of the dual optical frequency comb generation optical system 10E of the seventh embodiment and the phase modulation unit 72 described in the fourth embodiment. The electro-optic modulators 73A and 73B of the phase modulation unit 72 are incorporated between the lens 108 of the spatial resonance unit 102 and the mirror 106. The phase modulation unit 72 can modulate the phases of the laser amplification lights L1 and L2 that resonate with the spatial resonance unit 102. A high-power high-frequency signal is supplied from the outside of the spatial resonance portion 102 to each of the electro-optic modulators 73A and 73B from the high-frequency generator 84 via the amplifier 83.

[Effects of dual optical frequency comb generation optical system and laser device]
Since the laser device 60J has the dual optical frequency comb generation optical system 10F, it has the same effect as the laser device 60G. In the laser device 60J, as described in the fourth embodiment, the amount of change in the optical path length of the laser amplified light L1 by the electro-optical modulator 73A and the amount of change in the optical path length of the laser-amplified light L2 by the electro-optical modulator 73B. The difference can be adjusted. As a result, the resonator length and the optical path length difference ΔL of the laser amplification lights L1 and L2 can be controlled with high accuracy. That is, in the laser device 60J, only the repetition frequency f _rep1 of the optical frequency comb C1 or the repetition frequency difference Δf _rep2 of the optical frequency comb C2 can be easily controlled.

[Configuration, operation, and effect of measuring device]
Although not shown, the measuring device of the tenth embodiment includes the laser device 60J shown in FIG. 13 instead of the laser device 60A of the measuring device 50 shown in FIG. The configuration of the measuring device of the tenth embodiment other than the laser device is the same as that of the measuring device 50. In the laser device 60J, since the optical frequency combs C1 and C2 can be obtained from the polarization-holding optical fiber 34 as in the laser device 60A, the measuring device of the tenth embodiment operates in the same manner as the measuring device 50, and the measuring device 50 operates. Has the same effect as.

(11th Embodiment)
Next, the dual optical frequency comb generation optical system, the laser device, and the measuring device of the eleventh embodiment of the present invention will be described.

[Configuration of dual optical frequency comb generation optical system and laser device]
As shown in FIG. 14, the configuration from the light source 5 to the introduction unit 21 in the laser device 60K of the eleventh embodiment is the same as the configuration from the light source 5 to the introduction unit 21 in the laser device 60A described in the first embodiment. is there. The laser device 60K includes a dual optical frequency comb generation optical system 10G instead of the dual optical frequency comb generation optical system 10A described in the first embodiment.

The dual optical frequency comb generation optical system 10G includes at least the configuration of the dual optical frequency comb generation optical system 10F described in the tenth embodiment. In addition, the polarization-holding optical fiber 32C of the second loop portion 32 of the dual optical frequency comb generation optical system 10G incorporates the polarization-multiplexed non-reciprocal phase shift portion 90 described in the fifth embodiment. ..

[Effects of dual optical frequency comb generation optical system and laser device]
Since the laser device 60K has the dual optical frequency comb generation optical system 10G, the laser device 60K has the same effect as the laser device 60J, and the laser amplification light L1 is obtained by using the non-reciprocal phase shift unit 90 as in the fifth embodiment. , L2 resonator length and optical path length difference ΔL can be controlled, and the repeating frequency difference Δf _rep of the optical frequency combs C1 and C2 can be adjusted. In the laser device 60K, the resonator length and the optical path length difference ΔL of the laser amplified lights L1 and L2 can be individually controlled, and the repeating frequency difference Δf _rep of the optical frequency combs C1 and C2 can be finely adjusted.

[Configuration, operation, and effect of measuring device]
Although not shown, the measuring device of the eleventh embodiment includes the laser device 60K shown in FIG. 14 in place of the laser device 60A of the measuring device 50 shown in FIG. The configuration of the measuring device of the eleventh embodiment other than the laser device is the same as that of the measuring device 50. In the laser device 60K, since the optical frequency combs C1 and C2 can be obtained from the polarization-holding optical fiber 34 as in the laser device 60A, the measuring device of the eleventh embodiment operates in the same manner as the measuring device 50, and the measuring device 50 operates. Has the same effect as.

(12th Embodiment)
Next, the dual optical frequency comb generation optical system, the laser device, and the measuring device according to the twelfth embodiment of the present invention will be described.

[Configuration of dual optical frequency comb generation optical system and laser device]
As shown in FIG. 15, the configuration from the light source 5 to the introduction unit 21 in the laser device 60L of the twelfth embodiment is the same as the configuration from the light source 5 to the introduction unit 21 in the laser device 60A described in the first embodiment. is there. The laser device 60L includes a dual optical frequency comb generation optical system 10H in place of the dual optical frequency comb generation optical system 10A described in the first embodiment.

The dual optical frequency comb generation optical system 10H includes at least the configuration of the dual optical frequency comb generation optical system 10G described in the eleventh embodiment. In addition, the resonator length control element 76 is incorporated in the polarization-holding optical fiber 32B of the second loop portion 32 of the dual optical frequency comb generation optical system 10H.

[Effects of dual optical frequency comb generation optical system and laser device]
Since the laser device 60L has the dual optical frequency comb generation optical system 10H, the laser device 60L has the same effect as the laser device 60K, and is guided to the second loop portion 32 along the R1 and R2 directions as in the sixth embodiment. The optical path lengths of the waved laser amplified lights L1 and L2 can be changed by the resonator length control element 76. According to the laser device 60L, the resonator lengths of the laser amplified lights L1 and L2 are controlled, and the repetition frequency f _{rep1 of the} optical frequency comb C1 or only the repetition frequency f _rep2 of the optical frequency comb C2, or the optical frequency combs C1 and C2. The repeating frequency difference Δf _rep between them can be easily and finely controlled.

[Configuration, operation, and effect of measuring device]
Although not shown, the measuring device of the twelfth embodiment includes the laser device 60L shown in FIG. 15 in place of the laser device 60A of the measuring device 50 shown in FIG. The configuration of the measuring device of the twelfth embodiment other than the laser device is the same as that of the measuring device 50. In the laser device 60L, since the optical frequency combs C1 and C2 can be obtained from the polarization-holding optical fiber 34 as in the laser device 60A, the measuring device of the twelfth embodiment operates in the same manner as the measuring device 50, and the measuring device 50 operates. Has the same effect as.

(13th Embodiment)
Next, the dual optical frequency comb generation optical system, the laser device, and the measuring device according to the thirteenth embodiment of the present invention will be described.

[Configuration of dual optical frequency comb generation optical system and laser device]
As shown in FIG. 16, the configuration from the light source 5 to the introduction unit 21 in the laser device 60M of the thirteenth embodiment is the same as the configuration from the light source 5 to the introduction unit 21 in the laser device 60A described in the first embodiment. is there. The laser device 60M includes a saturable absorption reflector 110 instead of the spatial resonance portion 102 of the laser device 60G of the seventh embodiment.

The saturable absorption reflector 110 strengthens each other by interference at the connecting portion 22, and only the laser amplification light L1 and L2 (pulse light) incident on the polarization-retaining optical fiber 33C are transferred to the polarization-retaining optical fiber 33C. reflect. The saturable absorption reflector 110 weakens based on the interference at the connecting portion 22 and absorbs the laser amplification lights L1 and L2 incident through the polarization-retaining optical fiber 33C, and the polarization-retaining optical fiber 33C has Does not emit. That is, the saturable absorption reflector 110 functions in the same manner as the third loop portion 33 described in the first embodiment and the spatial resonance portion 102 described in the seventh embodiment.

[Effects of dual optical frequency comb generation optical system and laser device]
Since the laser device 60M has a dual optical frequency comb generation optical system 10M, it has the same effect as the laser device 60A and the laser device 60G. Since the laser device 60M includes the saturable absorption reflector 110 as a configuration for returning the laser amplification lights L1 and L2 strengthened by the connecting portion 22 to the second loop portion 32, the laser device 60M can be miniaturized. it can.

[Configuration, operation, and effect of measuring device]
Although not shown, the measuring device of the thirteenth embodiment includes the laser device 60M shown in FIG. 16 in place of the laser device 60A of the measuring device 50 shown in FIG. The configuration of the measuring device of the thirteenth embodiment other than the laser device is the same as that of the measuring device 50. In the laser device 60M, since the optical frequency combs C1 and C2 can be obtained from the polarization-holding optical fiber 34 as in the laser device 60A, the measuring device of the thirteenth embodiment operates in the same manner as the measuring device 50, and the measuring device 50 operates. Has the same effect as.

(Other embodiments)
Although the dual optical frequency comb generation optical system of the preferred embodiment has been described above, as another embodiment of the present invention, for example, the dual optical frequency comb generation optical system 10N shown in FIG. 17 and the dual optical frequency shown in FIG. 18 have been described. The comb generation optical system 10P can be mentioned.

As shown in FIG. 17, in the dual optical frequency comb generation optical system 10N, the first loop optical fiber 30 does not have a connecting portion, and is a polarization-holding optical fiber 30A, 30B, 30C, 30D arranged in an annular shape. It is configured. The first loop optical fiber 30 is provided with an introduction unit 21, an amplification unit 40, a derivation unit 24, a saturable absorber 75, and a polarization-holding optical isolator 25 along the R1 direction.

The laser amplification light return unit 70 in the dual optical frequency comb generation optical system 10N is composed of a saturable absorber 75 and a polarization-maintaining optical isolator 25. The saturable absorber 75 has sensitivity in the wavelength band including the second wavelength. Only when the laser-amplified light L1 and L2 having a predetermined power or more are incident on the saturable absorber 75, the loss of the saturable absorber 75 becomes small, and the laser-amplified light L1 and L2 are polarized light-maintaining optical fibers 30C and 30D. It emits to. The polarization-holding optical isolator 25 allows the laser amplification lights L1 and L2 incident from the polarization-holding optical fiber 30E to pass through the polarization-holding optical fiber 30D along the R2 direction. The polarization-holding optical isolator 25 removes the laser-amplified light L1 and L2 incident from the polarization-holding optical fiber 30D along the R1 direction from the first loop optical fiber 30.

In the dual optical frequency comb generation optical system 10N, the process from the extraction of the laser light S1 and S2 from the laser light S0 emitted from the light source 5 to the wavelength conversion of the laser light S1 and S2 by the amplification unit 40 is the first. This is the same as the dual optical frequency comb generation optical system 10A of the embodiment. A part of the laser amplification light L1 and L2 after being amplified by the amplification unit 40 passes through the polarization-holding optical fiber 30B, the extraction unit 24, and the polarization-holding optical fiber 30C along the R1 direction, and is saturable absorption. It is incident on the body 75. The rest of the laser amplified lights L1 and L2 after being amplified by the amplification unit 40 is waveguideed to the polarization-holding optical fiber 30E along the R2 direction, passes through the polarization-holding optical isolator 25, and is polarized. It is waveguideed on the optical fiber 30D and incident on the saturable absorber 75.

In the sataturable absorber 75, only the strong laser amplification lights L1 and L2 incident on the sataturable absorber 75 along the R2 direction are reflected and guided by the first loop optical fiber 30. The strong laser amplification lights L1 and L2 incident on the saturable absorber 75 are high-power pulsed lights. A part of the laser amplification lights L1 and L2 emitted from the saturable absorber 75 along the R2 direction is led out from the lead-out unit 24 to the polarization-holding optical fiber 34. The rest of the laser amplification lights L1 and L2 emitted from the saturable absorber 75 along the R2 direction is guided by the polarization-holding optical fiber 30B, incident on the amplification unit 40, and repeatedly amplified.

According to the above operating principle, in the dual optical frequency comb generation optical system 10N, the laser amplification lights L1 and L2 shift to the mode-locked state, and the optical frequency combs C1 and C2 are generated. Considering the refractive index and the second wavelength of each of the laser amplified lights L1 and L2, the total length of the polarization-holding optical fibers 30A, 33B, and 33C is the resonator length and the optical path of the laser amplified lights L1 and L2. The length difference ΔL is set so as to correspond to the desired repetition frequencies f _rep1 and f _rep2 .

As shown in FIG. 18, in the dual optical frequency comb generation optical system 10P, in the configuration of the dual optical frequency comb generation optical system 10N, the saturable absorber 75 provided between the polarization-holding optical fibers 30C and 30D Instead, the polarization-maintaining optical fiber 30B is provided with the resonator length control element 76. The resonator length control element 76 makes it possible to control the resonator length of the mode-locked laser composed of the first loop optical fiber 30. Examples of the resonator length control element 76 include a piezoelectric element, an acoustic optical element, and an electro-optical element.

In the dual optical frequency comb generation optical system 10P, the process from the extraction of the laser light S1 and S2 from the laser light S0 emitted from the light source 5 and the amplification of the laser light S1 and S2 by the amplification unit 40 is performed in the first embodiment. This is the same as the dual optical frequency comb generation optical system 10A of the embodiment. A part of the laser amplification lights L1 and L2 after being amplified by the amplification unit 40 passes through the polarization-holding optical fiber 30B, the extraction unit 24, and the polarization-holding optical fiber 30C along the R1 direction, and the polarization-holding. It is incident on the type optical isolator 25, but is removed from the first loop optical fiber 30 by the polarization-maintaining optical isolator 25.

The rest of the laser-amplified light L1 and L2 after being amplified by the amplification unit 40 is waveguideed to the polarization-holding optical fiber 30D along the R2 direction, and the polarization-holding optical isolator 25 and the polarization-holding optical fiber It passes through 30C and is incident on the lead-out unit 24. A part of the laser amplification lights L1 and L2 incident on the lead-out unit 24 along the R2 direction is led out from the lead-out unit 24 to the polarization-holding optical fiber 34. The rest of the laser amplification lights L1 and L2 incident on the lead-out unit 24 along the R2 direction is guided by the polarization-holding optical fiber 30B, incident on the amplification unit 40, and repeatedly amplified as described in the previous stage. ..

As described above, in the dual optical frequency comb generation optical systems 10N and 10P, the laser light S1 and S2 and the laser amplification light having different polarization directions are used in the dual optical frequency comb generation optical system 10A of the first embodiment. L1 and L2 are used to make the refractive indexes of the laser amplification lights L1 and L2 different from each other. Therefore, the resonators of the laser beams S1 and S2 and the laser amplification lights L1 and L2 can be made common, but the resonator lengths of the laser amplification lights L1 and L2 can be different from each other. As a result, optical frequency combs C1 and C2 having different repetition frequencies can be generated from the dual optical frequency comb generation optical systems 10N and 10P constituting one mode-locked laser. By sharing the dual optical frequency comb generation optical systems 10N and 10P as one mode-locked laser, the laser amplification lights L1 and L2 share the environmental disturbance and mechanical disturbance contained in each of the optical frequency combs C1 and C2. It can be easily removed. When laser amplification lights L1 and L2 share one dual optical frequency comb generation optical system 10N and 10P to prepare mode-locked lasers that generate optical frequency combs C1 and C2 in separate spaces as in the conventional case. It is possible to reduce the size of the dual optical frequency comb generation optical systems 10N and 10P as compared with the above.

The dual optical frequency comb generation optical system, laser device, and measuring device of the present invention can be widely applied in the field of using optical frequency combs C1 and C2 having different repetition frequencies from each other. According to the dual optical frequency comb generation optical system, the laser device, and the measuring device of the present invention, the optical frequency combs C1 and C2 having a high SN ratio can be obtained. The measuring device can be applied to spectroscopic measurement, signal analysis, and the like, which require high measurement accuracy.

Although the preferred embodiment of the present invention has been described in detail above, the present invention is not limited to the above-mentioned specific embodiment. The present invention can be modified within the scope of the gist of the present invention described in the claims.

For example, the components of the dual optical frequency comb generation optical system described in each of the above-described embodiments are an example, and can be appropriately changed to a known configuration having the same function. For example, the electro-optical modulators 73A and 73B may be changed to a modulator provided with an acoustic optical element.

5 ... Light sources 10A, 10B, 10C, 10D, 10E, 10F, 10G, 10H, 10M, 10N, 10P ... Dual optical frequency comb generation optical system 21 ... Introduction part 22 ... Connecting part 24 ... Derivation part 30 ... First loop light Fiber 32 ... 2nd loop section 33 ... 3rd loop section 40 ... Amplifying section 50 ... Measuring devices 60A, 60B, 60C, 60D, 60E, 60F, 60G, 60H, 60I, 60J, 60K, 60L, 60M, 60N, 60P ... Laser device 70 ... Laser amplification light return unit

0003
Only the laser amplification light return unit that emits the first laser amplification light and the second laser amplification light to the first loop optical fiber along at least one of the circumferential direction and the direction opposite to the circumferential direction. The first optical frequency comb, which is provided in the first loop optical fiber and is generated by the first loop optical fiber and whose polarization direction is the first direction, and the first loop optical fiber are generated and the direction of polarization is The first optical fiber is provided with a lead-out unit for deriving a second optical frequency comb in the second direction and having a repetition frequency different from the repetition frequency of the first optical frequency comb from the first loop optical fiber. The optical path length difference between the optical path length of the first loop optical fiber of the laser amplified light and the optical path length of the first loop optical fiber of the second laser amplified light is the first loop optical fiber of the first laser amplified light. The repetition frequency of the first optical frequency comb and the repetition frequency of the second optical frequency comb are repeated according to the difference in refractive index between the refractive index of the second laser amplification light and the refractive index of the second laser amplified light in the first loop optical fiber. It depends on the frequency difference.
[0008]
In the dual optical frequency comb generation optical system of the present invention, even if the first loop optical fiber is composed of a second loop portion and a third loop portion connected to the second loop portion via a connecting portion. Good. The introduction section and the amplification section may be provided in the second loop section, and the lead-out section may be provided in the third loop section. The laser-amplified light return portion may be composed of the connecting portion and the third loop portion. The predetermined condition is that the phase difference is an odd multiple of half the wavelengths of the first laser amplified light and the second laser amplified light. In the connecting portion, the first laser amplification light and the second laser amplification light are obtained only when the first laser amplification light and the second laser amplification light waveguideed from the second loop portion satisfy the predetermined conditions. Is circulated in the third loop portion and then returned to the second loop portion, and the length of the third loop portion corresponds to the repetition frequency of the first optical frequency comb or the repetition frequency of the second optical frequency comb. However, the optical path length difference may correspond to the repeating frequency difference.
[0009]
In the dual optical frequency comb generation optical system of the present invention, the first loop optical fiber may be composed of a second loop portion and a linear portion connected to the second loop portion via a connecting portion. The introduction section and the amplification section may be provided in the second loop section, the lead-out section may be connected to the connection section, and the laser amplification light return section may be composed of the connection section and the linear section. .. The predetermined condition is that the phase difference is an even multiple of half the wavelengths of the first laser amplified light and the second laser amplified light. In the connecting portion, the first laser amplification light and the second laser amplification light are obtained only when the first laser amplification light and the second laser amplification light guided from the second loop portion satisfy the predetermined conditions. May reciprocate in the linear portion and then return to the second loop portion.

Claims (8)

Along with waveguideing a first laser beam whose polarization direction is the first direction, a second laser beam whose polarization direction is a second direction different from the first direction is waveguideed, and the first laser beam and A first loop optical fiber that holds the direction of polarization of each of the second laser beams,
An introduction unit provided in the first loop optical fiber and introducing the first laser beam and the second laser beam into the first loop optical fiber.
It is provided in the first loop optical fiber, and while maintaining the direction of the polarization of the first laser light and the second laser light, the first laser light and the second laser light are amplified to amplify the first laser. An amplification unit that generates light and a second laser amplification light and emits the first laser amplification light and the second laser amplification light in the circumferential direction of the first loop optical fiber and in a direction opposite to the circumferential direction.
The first laser-amplified light provided on the first loop optical fiber and waveguideed along the circumferential direction and the second laser-amplified light and the second laser amplified light waveguide along the direction opposite to the circumferential direction. Only when the phase difference between the 1 laser amplified light and the 2nd laser amplified light satisfies a predetermined condition, the 1st laser amplified light and the 2nd laser amplified light are at least in the circumferential direction and in the direction opposite to the circumferential direction. A laser-amplified light return unit that emits light from the first loop optical fiber along one direction,
A first optical frequency comb provided in the first loop optical fiber, which is generated by the first loop optical fiber and whose polarization direction is the first direction, and a polarization direction generated by the first loop optical fiber. A derivation unit that derives the second optical frequency comb in the second direction from the first loop optical fiber, and
To prepare
Dual optical frequency comb generation optics. The first loop optical fiber is
The second loop part and
It is composed of a third loop portion connected to the second loop portion via a connecting portion.
The introduction section and the amplification section are provided in the second loop section.
The lead-out unit is provided in the third loop unit, and the lead-out unit is provided.
The laser-amplified light return portion is composed of the connecting portion and the third loop portion.
The predetermined condition is that the phase difference is an odd multiple of half the wavelengths of the first laser amplification light and the second laser amplification light.
In the connecting portion, the first laser amplification light and the second laser amplification light are emitted only when the first laser amplification light and the second laser amplification light waveguideed from the second loop portion satisfy the predetermined conditions. After orbiting in the third loop portion, it is returned to the second loop portion.
The dual optical frequency comb generation optical system according to claim 1. The third loop unit is provided with a phase modulation unit capable of modulating the phases of the first laser amplification light and the second laser amplification light.
The dual optical frequency comb generation optical system according to claim 2. The first loop optical fiber is
The second loop part and
It is composed of a linear portion connected to the second loop portion via a connecting portion.
The introduction section and the amplification section are provided in the second loop section.
The out-licensing part is connected to the connecting part,
The laser-amplified light return portion is composed of the connecting portion and the linear portion.
The predetermined condition is that the phase difference is an even multiple of half the wavelengths of the first laser amplification light and the second laser amplification light.
In the connecting portion, the first laser amplification light and the second laser amplification light are generated only when the first laser amplification light and the second laser amplification light guided from the second loop portion satisfy the predetermined conditions. After reciprocating in the linear portion, it is returned to the second loop portion.
The dual optical frequency comb generation optical system according to claim 1. The linear portion is provided with a phase modulation portion capable of modulating the phases of the first laser amplification light and the second laser amplification light.
The dual optical frequency comb generation optical system according to claim 4. The first loop optical fiber is provided with a resonator length control element capable of controlling the resonator lengths of the first laser amplification light and the second laser amplification light.
The dual optical frequency comb generation optical system according to any one of claims 1 to 5. A light source connected to the introduction portion of the dual optical frequency comb generation optical system according to any one of claims 1 to 6 and emitting the first laser beam and the second laser beam.
Laser device. The laser device according to claim 7 and
The first optical frequency comb and the second optical frequency comb derived from the lead-out unit are arranged on the back side in the traveling direction, and the first optical frequency comb and the second optical frequency comb are separated from each other and have different paths. Polarization separation part to advance to
Advance of the first optical frequency comb and the second optical frequency comb from a sample arranged on at least one path of the first optical frequency comb and the second optical frequency comb separated from each other by the polarization separating portion. A polarization interfering unit that is arranged on the far side in the direction and interferes with the first optical frequency comb and the second optical frequency comb to be measured.
A sample information extraction unit, which is arranged on the back side in the traveling direction of the interference signal obtained by the polarization interference unit and extracts information on the sample from the interference signal,
To prepare
Measuring device.

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