WO2019073701A1

WO2019073701A1 - Dual optical frequency comb generating optical system, laser device and measurement device

Info

Publication number: WO2019073701A1
Application number: PCT/JP2018/031150
Authority: WO
Inventors: 薫美濃島; 善晶中嶋
Original assignee: 国立大学法人電気通信大学
Priority date: 2017-10-13
Filing date: 2018-08-23
Publication date: 2019-04-18
Also published as: JP7181613B2; JPWO2019073701A1

Abstract

This dual optical frequency comb generating optical system comprises: an amplification unit for emitting laser amplification light in the circumferential direction of a first optical fiber loop and in the reverse-oriented direction along the circumferential direction; and a laser amplification light returning unit for emitting the laser amplification light to the first optical fiber loop only when a predetermined condition is satisfied by the phase difference between the laser amplification light that has been wave-guided along the circumferential direction and the laser amplification light that has been wave-guided along the reverse-oriented direction.

Description

Dual optical frequency comb generation optical system, laser device, measurement device

The present invention relates to a dual optical frequency comb generation optical system that outputs two optical frequency combs, and a laser apparatus and a measurement apparatus that include the dual optical frequency comb generation optical system. Priority is claimed on Japanese Patent Application No. 2017-199843, filed Oct. 13, 2017, the content of which is incorporated herein by reference.

The light whose spectral intensity is precisely and equally spaced in a comb shape on the frequency axis 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 optical frequency mode trains arranged at equal intervals appear. That is, the optical frequency comb is emitted from the mode-locked laser. Optical frequency combs having a comb-like spectral intensity are widely used as precise measures of time, space, and frequency. The spacing of the optical frequency mode sequence in the optical frequency domain is called the repetition frequency.

For example, as described in Non-Patent Document 1, by performing multi-heterodyne detection of optical frequency combs having different repetition frequencies, it is possible to take out information of molecules and atoms in the optical frequency domain. Optical frequency combs having different repetition frequencies are called dual optical frequency combs. Broadband, high-precision, high-resolution spectroscopy can be performed using two mode-locked lasers (laser devices) that output dual optical frequency combs.

However, as disclosed in the above-mentioned Non-Patent Document 1, when using two laser devices, these laser devices are subject to different environmental disturbances and mechanical disturbances. The two laser devices are subjected to different environmental disturbances and mechanical disturbances, thereby reducing the signal-to-noise ratio (SN ratio) of the interference signal obtained at the time of multiheterodyne detection. On the other hand, if the SN ratio of the interference signal is increased, a large optical system for relatively phase-synchronizing the two laser devices is required, and the laser device becomes large.

The present invention takes the above-mentioned circumstances into consideration, and is a dual optical frequency comb capable of enhancing the signal-to-noise ratio of optical frequency combs having different repetition frequencies and miniaturizing the optical system and the entire apparatus. Provided are a generation optical system, a laser device, and a measurement device.

The dual optical frequency comb generation optical system according to the present invention guides the first laser light whose polarization direction is the first direction, and the second laser whose polarization direction is the second direction different from the first direction. A first loop optical fiber for guiding light and maintaining the polarization direction of each of the first laser light and the second laser light; and a first loop optical fiber provided in the first loop optical fiber An introducing unit for introducing the first laser beam and the second laser beam, and the first loop optical fiber, and the polarization direction of the first laser beam and the second laser beam is maintained while the direction of the polarization is maintained. The first laser light and the second laser light are amplified to generate a first laser amplification light and a second laser amplification light, and the first direction of the first loop optical fiber in the circumferential direction and the direction opposite to the circumferential direction are generated. laser An amplification unit for emitting the width light and the second laser amplification light; and the first laser amplification light and the second laser amplification light provided in the first loop optical fiber and guided along the circumferential direction The first laser amplified light and the second laser only when the phase difference between the first laser amplified light and the second laser amplified light guided along the direction opposite to the circumferential direction satisfies a predetermined condition. A laser amplification light return unit that emits amplification light to the first loop optical fiber along at least one of the circumferential direction and a direction opposite to the circumferential direction; and the first loop optical fiber, A first optical frequency comb generated in the one-loop optical fiber and having a polarization direction of the first direction and a second optical frequency code generated in the first loop optical fiber and having a polarization direction of the second direction And a, a deriving unit that derives from the first loop optical fiber and.

In the dual optical frequency comb generation optical system according to the present invention, the first loop optical fiber may be configured of a second loop portion and a third loop portion connected to the second loop portion via a coupling portion. Good. The introduction unit and the amplification unit may be provided in the second loop unit, and the lead-out unit may be provided in the third loop unit. The laser amplification light return unit may be configured by the connection unit and the third loop unit. The predetermined condition is that the phase difference is an odd multiple of half of the wavelengths of the first laser amplified light and the second laser amplified light. In the connection 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 condition. May be returned to the second loop portion after being circulated in the third loop portion.

In the dual optical frequency comb generation optical system of the present invention, the first loop optical fiber may be configured of a second loop portion and a linear portion connected to the second loop portion via a coupling portion. The introduction unit and the amplification unit may be provided in the second loop unit, the lead-out unit may be connected to the connection unit, and the laser amplification light return unit may be configured by the connection unit and the linear unit. . 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 connection 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 condition. May be returned to the second loop portion after reciprocation in the linear 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 portion capable of modulating the phases of the first laser amplification light and the second laser amplification light. It is also 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 length of the first laser amplification light and the second laser amplification light. May be When the dual optical frequency comb generation optical system includes a second loop unit, the resonator length control element is preferably provided in the second loop unit.

The laser device of the present invention is connected to the introduction portion of the above-described dual optical frequency comb generation optical system, and includes a light source that emits the first laser light and the second laser light.

The measurement apparatus according to the present invention includes the above-described laser device, and is disposed on the far side of the traveling direction of the first optical frequency comb and the second optical frequency comb derived from the derivation unit, and the first optical frequency comb and A polarization separation unit that separates the second optical frequency comb and travels on different paths, and a path of at least one of the first optical frequency comb and the second optical frequency comb separated from each other by the polarization separation unit A polarization which is disposed on the far side of the traveling direction of the first optical frequency comb and the second optical frequency comb from the sample disposed on the upper side, and causes the first optical frequency comb and the second optical frequency comb to be measured to interfere A wave interference unit, and a sample information extraction unit disposed on the back side in the traveling direction of the interference signal obtained by the polarization interference unit and extracting information of the sample from the interference signal.

According to the dual optical frequency comb generating optical system, the laser device, and the measuring device of the present invention, the signal-to-noise ratio of optical frequency combs having different repetition frequencies can be increased, and the optical system can be miniaturized.

It is a top view of a laser device of a 1st embodiment of the present invention. It is a top view of a measuring device of a 1st embodiment of the present 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 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 structural example of the non-reciprocal phase shift part of the laser apparatus of FIG. It is a top view of the 2nd structural example of the non-reciprocal phase shift part of the laser apparatus of FIG. It is a top view of the laser equipment of a 6th embodiment of the present 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 9th Embodiment of this invention. It is a top view of the laser apparatus of 10th 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 12th 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 a laser device of the present invention. FIG. 7 is a plan view of another laser apparatus of the present invention.

Hereinafter, embodiments of a dual optical frequency comb generation optical system, a laser device, and a measurement apparatus according to 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 apparatus 60A according to the first embodiment of the present invention, the light source 5, the polarization maintaining optical fiber 6, the polarization separation element 12, one end is connected to the polarization separation element 12. The polarization maintaining optical fiber 31 and the dual optical frequency comb generating optical system 10A are provided. The incident end (one end) of the polarization maintaining optical fiber 6 is connected to the light source 5. The end (the other end) of the output side of the polarization maintaining optical fiber 6 is connected to the polarization separation element 12. The end (one end) of the incident side of the polarization maintaining optical fiber 31 is connected to the polarization separation element 12. The end (other end) of the output side of the polarization maintaining optical fiber 31 is connected to the dual optical frequency comb generation optical system 10A.

The light source 5 is 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 whose polarization direction is the second direction with respect to the optical axis A 2) Laser beam S2 is emitted. The optical axis A indicates the traveling direction of light. Assuming that the optical axis A is in a direction perpendicular to the paper surface of FIG. 1, the first direction is a direction toward the upper side and the lower side of the paper surface, and the second direction is a direction toward the left side and the right side of the paper surface. The first direction and the second direction may be respectively directed in any directions as long as they are different from each other. For example, laser light may be guided with the slow axis and the fast axis of the polarization maintaining fiber as the first direction and the second direction. The light source 5 according to the present embodiment includes the laser beams S1 and S2, and third laser beams S3 and S4 in any direction different from the first direction and the second direction with respect to the optical axis A. Is a semiconductor laser that emits

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

The dual optical frequency comb generation optical system 10 A includes a first loop optical fiber 30, an introducing unit 21 provided in the first loop optical fiber 30, an amplifying unit 40, a laser amplification light returning unit 70, and an extracting unit 24. 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. And a unit 22. The connection unit 22 is configured of a polarization maintaining optical coupler. That is, the first loop optical fiber 30 is configured to draw the numeral “8” with the connecting portion 22 as a knot. The second loop portion 32 is composed of polarization maintaining

optical fibers

32A, 32B, 32C. The third loop portion 33 is composed of polarization maintaining

optical fibers

33A, 33B and 33C. In the following, the direction in which light is guided in the order of polarization maintaining

optical fibers

32C, 32A, and 32B, and the direction in which light is guided in the order of polarization maintaining

optical fibers

33A, 33B, and 33C in the direction R1 ( Circumferential direction). Also, a direction opposite to the direction R1 is referred to as an R2 direction (reverse direction). The first loop optical fiber 30 is connected to the polarization separation element 12 via the introduction unit 21 and the polarization maintaining optical fiber 31.

The introducing unit 21 is provided in the second loop unit 32, and is configured of a polarization maintaining optical coupler. The polarization maintaining optical fiber 32C is connected to the near end of the introduction portion 21 in the R1 direction (that is, the end connected to the end on the exit side of the polarization maintaining optical fiber 31). . The polarization maintaining optical fiber 32 </ b> A is connected to the end on the back side in the R <b> 1 direction in the introducing unit 21. Laser light S1 and S2 and laser amplification light (first laser amplification light and second laser amplification light) L1 and L2 amplified by the amplification section 40 formed of a rare earth-doped optical fiber pass through the introduction portion 21. Therefore, the introducing unit 21 is composed of a wavelength division multiplexing type and polarization maintaining type optical coupler capable of introducing and deriving at least a first wavelength of the laser beams S1 and S2 and a second wavelength of the laser amplified beams L1 and L2. ing.

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

The polarization maintaining

optical fibers

32B and 32C are connected to the end of the connecting portion 22 on the second loop 32 side. The polarization maintaining

optical fibers

33A and 33C are connected to the end of the connecting portion 22 on the third loop 33 side.

The laser amplification light return unit 70 performs mode synchronization of the laser amplification lights L1 and L2 amplified by the amplification unit 40. The laser amplification light return unit 70 includes a coupling unit 22, polarization maintaining

optical fibers

33 A, 33 B, and 33 C provided in the third loop unit 33, and a polarization maintaining optical isolator 23. The polarization maintaining optical isolator 23 passes only the laser amplification lights L1 and L2 incident from the polarization maintaining optical fiber 33B along the R1 direction to the polarization maintaining optical fiber 33C, and polarizes the light along the R2 direction. The laser amplification lights L1 and L2 incident from the holding optical fiber 33C are removed from the first loop optical fiber 30 by light absorption, branching, and the like.

The lead-out unit 24 is provided in the third loop unit 33, and is configured of a polarization maintaining optical coupler.
The polarization maintaining optical fiber 33A is connected to the near end of the lead-out portion 24 in the R1 direction (that is, the end on the connection portion 22 side). The end (one end) on the incident side of each of the polarization-maintaining

optical fibers

33B and 34 is connected to the end on the back side in the R1 direction in the lead-out portion 24. The polarization maintaining 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 through the lead-out unit 24. Provided for

As described above, since the first loop optical fiber 30 is composed of the polarization maintaining optical fiber and each component provided in the first loop optical fiber 30 can hold the polarization, the first loop optical fiber 30 The orientation of the guided and controlled polarization is maintained.

[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 using the dual optical frequency comb generation optical system 10A and the laser device 60A will be described.

The laser beam S 0 emitted from the light source 5 is guided to the polarization maintaining optical fiber 6 and enters the polarization separation element 12. The polarization separation element 12 separates the laser beams S1 and S2 from the laser beam S0, and only the laser beams S1 and S2 are guided to the polarization maintaining optical fiber 31.

The laser beams S1 and S2 guided through the polarization maintaining optical fiber 31 are guided to the polarization maintaining optical fiber 32A through the introduction unit 21 and enter the amplification unit 40. The laser beams S1 and S2 are amplified by the amplification unit 40, and the laser amplification lights L1 and L2 are generated. Since a rare earth-doped optical fiber is used as the amplification unit 40, the wavelengths (second wavelengths) of the laser amplification lights L1 and L2 are different from the wavelengths (first wavelengths) of the laser lights S1 and S2 before amplification. The laser amplification lights L1 and L2 having the second wavelength are guided from the amplification unit 40 to the polarization maintaining

optical fibers

32B and 32A along both the R1 direction and the R2 direction.

The laser amplification lights L1 and L2 are guided from the amplification unit 40 along the R2 direction in this order through the polarization maintaining optical fiber 32A and the introducing unit 21 to the polarization maintaining optical fiber 32C.

The laser amplified lights L1 and L2 guided to the polarization maintaining optical fiber 32B along the R1 direction and the laser amplified lights L1 and L2 guided to the polarization maintaining optical fiber 32C along the R2 direction are The light is incident on the connecting portion 22. The laser amplified lights L1 and L2 which propagate the polarization maintaining optical fiber 32B from the amplifying unit 40 along the R1 direction and enter the connection unit 22 have nonlinear phases according to the length of the polarization maintaining optical fiber 32B. Get a shift. The laser amplified lights L1 and L2 that are guided from the amplifying unit 40 to the polarization maintaining optical fiber 32A, the introducing unit 21 and the polarization maintaining optical fiber 32C along the R2 direction and enter the connection unit 22 are polarization maintaining Nonlinear phase shift according to the length of the

optical fibers

32A, 32C.

In the polarization maintaining optical coupler constituting the connecting portion 22, the laser amplified lights L1 and L2 incident from the polarization maintaining optical fiber 32B along the R1 direction and the polarization maintaining optical fiber 32C along the R2 direction The incident laser amplified lights L1 and L2 interfere with each other. In the polarization maintaining optical coupler of the connecting portion 22, the phase difference between the laser amplification lights L1 and L2 incident from the polarization maintaining optical fiber 32B and the laser amplification lights L1 and L2 incident from the polarization maintaining optical fiber 32C. The light quantity ratio of the laser amplification lights L1 and L2 guided to the polarization maintaining optical fiber 33A and the laser amplification lights L1 and L2 guided to the polarization maintaining optical fiber 33C changes according to φ. The phase difference φ corresponds to the difference between the non-linear phase shifts received by the laser amplified lights L1 and L2 incident on the coupling portion 22 from the polarization maintaining

optical fibers

32B and 32C. In the case where the phase difference φ is an odd multiple of half of the second wavelength (when the predetermined condition is satisfied), all the laser amplified lights L1 and L2 intensified by the interference in the polarization maintaining optical coupler of the connecting portion 22 are in the R1 direction. , And guided to the polarization maintaining optical fiber 33A.

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

A portion (about half) of the laser amplified lights L1 and L2 incident on the coupling portion 22 along the R1 direction from the polarization maintaining optical fiber 33C continues to be guided to the polarization maintaining optical fiber 32C along the R1 direction. The light passes through the introduction unit 21 and the polarization maintaining optical fiber 32A, and is amplified again by the amplification unit 40. The remaining portions of the laser amplified lights L1 and L2 incident on the coupling portion 22 along the R1 direction from the polarization maintaining optical fiber 33C are guided to the polarization maintaining optical fiber 32B along the R2 direction, and the amplification unit 40 is performed again. It 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 guiding the laser beams S1 and S2 and the laser amplification beams L1 and L2 and the dual optical frequency comb generation optical system 10A, the second loop unit 32 functions as a nonlinear amplification optical fiber loop mirror having a gain. The second loop portion 32, the connection portion 22, the polarization maintaining optical isolator 23, and the polarization maintaining

optical fibers

33A, 33B, and 33C function as a saturable absorber. That is, the connection portion 22 and the third loop portion 33 function as a saturable absorber. Only the laser amplified lights L1 and L2 reinforced by the interference at the connecting part 22 circulate the polarization maintaining

optical fibers

33A, 33B and 33C of the third loop part 33, and return to the second loop part 32, and the amplifying part It is amplified at 40. The weak laser amplification lights L1 and L2 based on the interference at the coupling portion 22 are guided to the polarization maintaining optical fiber 33C of the third loop portion 33, but are removed by the polarization maintaining optical isolator 23. Thus, the loss in the first loop optical fiber 30 changes in accordance with the light intensity of the laser amplification lights L1 and L2.

The laser amplified lights L1 and L2 guided from the connecting part 22 to the second loop part 32 along each direction of R1 and R2 have nonlinear phase shift according to the length of each polarization maintaining optical fiber. receive. When the number of circulations in the second loop portion 32 and the third loop portion 33 is smaller than a predetermined number, the powers of the laser amplified lights L1 and L2 are low, and the gain in the second loop portion 32 is small. In a state where the gain in the second loop unit 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 lights. When the number of times of circulation of the laser amplified light L1 and L2 in the second loop unit 32 and the third loop unit 33 becomes equal to or greater than a predetermined number, and the power of the laser amplified light L1 and L2 becomes higher than the predetermined power The gain in the loop section 32 becomes very large. When the gain in the second loop unit 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 pulse lights.

In the dual optical frequency comb generation optical system 10A and the laser device 60A, while the laser amplified lights L1 and L2 oscillate respectively in the state of continuous light or pulsed light, transition to the mode synchronization state is performed, and the optical frequency combs C1 and C2 are generated. Be done. The generated optical frequency combs C1 and C2 are led from the lead-out unit 24 to the polarization maintaining 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 maintaining

optical fibers

32A, 32B, 32C, 33A, 33B, 33C and the polarization maintaining amplifying optical fiber constituting the amplifying unit 40. , That is, 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 amplification light L2 in the dual optical frequency comb generation optical system 10A is determined by the refractive index of the laser amplification 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 in the first direction and the second direction. Therefore, the refractive indexes of the laser amplification 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 differ 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 of 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 operation principle, in the dual optical frequency comb generation optical system 10A and the laser device 60A, the laser amplification lights L1 and L2 including pulse light with high intensity are held along the R1 direction from the coupling unit 22 It is guided to the fiber 33A. On the other hand, the laser amplified lights L1 and L2 including continuous light with small intensity are also guided to the polarization maintaining optical fiber 33C along the R2 direction. However, since the polarization maintaining optical isolator 23 is provided, the laser amplification lights L1 and L2 guided to the polarization maintaining optical fiber 33A along the R1 direction circulate the third loop portion 33. However, the laser amplified lights L1 and L2 guided to the polarization maintaining optical fiber 33C along the R2 direction are guided only by the polarization maintaining 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, the third loop portion in which the laser amplified lights L1 and L2 circulate only in the R1 direction in the resonator constituting the mode-locked laser of the laser amplified lights L1 and L2. The 33 polarization maintaining

optical fibers

33A, 33B and 33C are common parts. Based on this, the difference between the length of the polarization maintaining optical fiber 32B and the total length of the polarization maintaining

optical fibers

32A and 32C is set so that the phase difference φ is an odd multiple of half of the second wavelength It is done. In addition, the total length of the polarization maintaining

optical fibers

33A, 33B and 33C is the resonator length of the laser amplified lights L1 and L2 in consideration of the refractive index and the second wavelength of each of the laser amplified lights L1 and L2. And the optical path difference ΔL is set to correspond to the desired repetition frequencies f _rep1 and f _rep2 .

[Operation effect 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 being shifted to the mode synchronization state in the common first loop optical fiber 30. At this time, since the directions of polarization of the laser amplified lights L1 and L2 are different from each other, the refractive indexes of the laser amplified lights L1 and L2 are different. The optical path lengths of the resonators configured by the first loop optical fiber 30 differ from each other for the laser amplification lights L1 and L2. By this, from the lead-out portion 24, the optical frequency comb C1 whose polarization direction is the first direction and has the repetition frequency f _rep1 , and the repetition frequency _whose polarization direction is the second direction and which is different from the optical frequency comb C1 An optical frequency comb C2 having f _rep2 can be obtained.

The dual light frequency comb generation optical system 10A and the laser device 60A use laser lights S1 and S2 and laser amplified lights L1 and L2 whose polarization directions are different from each other. In the dual optical frequency comb generation optical system 10A and the laser device 60A, while making mode-locked lasers common, the refractive indices of the laser amplification lights L1 and L2 are made different from each other, and the resonator lengths of the laser amplification lights L1 and L2 are made different from each other. be able to. By this, it is possible to generate optical frequency combs C1 and C2 (see FIG. 2) having different repetition frequencies with one mode-locked laser. The environmental disturbance or mechanical disturbances received by the dual optical frequency comb generation optical system 10A and the laser device 60A by sharing the dual optical frequency comb generation optical system 10A and the laser device 60A as one mode-locked laser as the laser amplification lights L1 and L2 Common disturbances. By this, the difference between the environmental disturbance and the mechanical disturbance included in each of the optical frequency combs C1 and C2 is suppressed, and the environmental disturbance and the mechanical disturbance are easily removed as common noise, and the optical frequency comb C1 and C2 are eliminated. The SN ratio of C2 can be increased. Furthermore, when the laser amplified lights L1 and L2 share the dual optical frequency comb generation optical system 10A and the laser device 60A, when separately preparing mode-locked lasers that generate the optical frequency combs C1 and C2 as in the prior art. 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 constituted by the second loop portion 32 and the third loop portion 33, and the second loop portion 32 and the third loop portion 33 are connection portions 22 are linked. In the connecting portion 22, the laser amplified lights L1 and L2 which are guided along the second loop portion 32 in both the R1 and R2 directions interfere with each other. The laser amplification lights L1 and L2, which are intensified with each other according to the phase difference φ, circulates in the third loop section 33 only along the R1 direction. Therefore, the connection part 22 and the 3rd loop part 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 unit 33 as a simple mirror, the laser amplification is performed via the connecting unit 22 without being affected by the phase shift due to the nonlinear optical effect. The lights L1 and L2 can be returned to both of the polarization maintaining

optical fibers

32B and 32C. By this, without causing the interference phenomenon by the phase difference φ of the laser amplification lights L1 and L2, the laser amplification lights L1 and L2 incident on the coupling portion 22 from the polarization maintaining optical fiber 33C along the R1 direction are polarized. The light is guided to both of the wave holding

optical fibers

32B and 32C. That is, the laser amplified lights L1 and L2 circulated in the third loop portion 33 can be guided to both of the polarization maintaining

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 synchronization operation can be favorably generated.

[Configuration of measuring device]
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 apparatus 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 end (the other end) of the output side of the polarization maintaining optical fiber 34 is connected to the polarization separation unit 52. The polarization interference unit 56 causes the optical frequency combs C1 and C2 separated by the polarization separation unit 52 to interfere with each other. The sample information extraction unit 58 extracts information of the sample from the interference signal of the optical frequency combs C1 and C2 interfered by the polarization interference unit 56.

The polarization separation unit 52 is disposed at the far side in the traveling direction of the optical frequency combs C1 and C2 emitted from the polarization maintaining optical fiber 34 in order to separate the optical frequency combs C1 and C2 whose polarization directions are different from each other. It is done. The polarization separation unit 52 is configured of, for example, a polarization separation type light beam splitter. The sample S is disposed on the path X35 of the optical frequency comb C1 among 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 a measurement target of the measuring device 50. Polarization maintaining mirrors 57A and 57B are provided along the path X36 of the optical frequency comb C2 for turning the path X36 toward the polarization interference unit 56.

The polarization interference unit 56 causes the optical frequency combs C1 and C2 separated by the polarization separation unit 52 to interfere with each other. The polarization interference unit 56 performs an optical frequency comb C3 traveling direction from the sample S in order to cause the optical frequency comb C1 (hereinafter referred to as the optical frequency comb C3) including the information of the sample S to interfere with the optical frequency comb C2. It is arranged on the back side. The polarization interference unit 56 is configured of a polarization separation type light beam splitter or a half mirror.

The sample information extraction unit 58 extracts information of the sample from the interference signal of the optical frequency combs C1 and C2 interfered by the polarization interference unit 56. The sample information extraction unit 58 is disposed on the far side in the traveling direction of the multiheterodyne signal (interference signal) generated by the optical frequency combs C2 and C3 interfering with each other in the polarization interference unit 56. The sample information extraction unit 58 is capable of acquiring information on the sample S from the multiheterodyne signal, and is configured of a generally known optical system, for example, a device that converts it into an electric signal by a light receiver.

[Measuring method using a measuring device]
In the measuring device 50, the optical frequency combs C1 and C2 emitted from the polarization maintaining optical fiber 34 are separated by the polarization separating unit 52 so as to travel on different paths. The optical frequency comb C1 travels along the path X35 and passes through the sample S. When passing through the sample S, 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 maintaining 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 combined again in the polarization interference unit 56 and interfere with each other. The interference of the optical frequency combs C2, C3 generates a multiheterodyne signal. The multiheterodyne signal travels along the path X 37 and enters the sample information extraction unit 58. As shown in FIG. 2, in the sample information extraction unit 58, the multiheterodyne signal is converted into a mode decomposition spectrum of a high frequency band by, for example, Fast Fourier Transform (FFT). Optical information of the sample S is extracted from the waveform W (waveform indicated by a broken line in FIG. 2) of the mode decomposition spectrum. The frequency interval between adjacent spectra on the frequency axis in the mode decomposition spectrum corresponds to the repetition frequency difference Δf _rep .

[Operation effect of measuring device]
In the measuring device 50, the polarization separation unit 52 separates the paths of the optical frequency combs C1 and C2, and can add optical information of the sample S to the optical frequency comb C1. The polarization interference unit 56 interferes with the optical frequency combs C2 and C3 to remove environmental disturbances and mechanical disturbances commonly included in the optical frequency combs C2 and C3, and allows easy observation in a high frequency band. Possible mode resolved spectra can be obtained. The sample information extraction unit 58 can extract the information of the sample S from the waveform W of the spectrum distribution of the obtained mode decomposition spectrum. Therefore, according to the measuring apparatus 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 configuration relating to the generation of the optical frequency combs C1 and C2 is made common in the measuring device 50, it is not necessary to prepare optical systems for generating the optical frequency combs C1 and C2 in the respective spaces as in the prior art. 50 can be miniaturized.

Second Embodiment
A dual optical frequency comb generation optical system, a laser device and a measurement apparatus according to a second embodiment of the present invention will be described. In the description and drawings of the second and subsequent embodiments, 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 are designated by the same reference numerals. And I omit the explanation. The second and subsequent embodiments basically describe configurations and operations different from those of the first embodiment, and are common to the first embodiment except for the configurations and operations 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 maintaining optical fiber 42 in place of the polarization maintaining optical fiber 6 and the polarization separation element 12 of the laser device 60A, and The dual optical frequency comb generation optical system 10A described in the embodiment is provided.

Like the polarization maintaining optical fiber 6, the polarization maintaining optical fiber 42 is an optical fiber capable of maintaining the direction of polarization of the laser beams S1 and S2 guided internally. The polarization axis J42 of the cladding 77 of the polarization maintaining optical fiber 42 centered on the optical axis A is 45 ° to the polarization axis J31 of the cladding 71 of the polarization maintaining optical fiber 31 centered on the optical axis A, Any one of 135 °, 225 °, and 315 ° is formed. The polarization axes J42 and J31 are determined by the positions of the pair of

stress applying portions

80 and 80 provided in each of the

clads

77 and 71 with the core 80 interposed in a cross sectional view.

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

The guiding of the laser beams S1 and S2 introduced into the dual optical frequency comb generation optical system 10A through the introducing unit 21 and the generation of the laser amplified beams L1 and L2 are the same as the contents described in the first embodiment. . From the polarization maintaining optical fiber 34, optical frequency combs C1 and C2 (see FIG. 2) having mutually different repetition frequencies are obtained.

[Operation effect of dual optical frequency comb generation optical system and laser device]
The laser device 60B has the dual optical frequency comb generation optical system 10A, and therefore exhibits the same effect as the laser device 60A. In the laser device 60B, the polarization axes J42 and J31 of the polarization maintaining

optical fibers

42 and 31 are mutually 45 ° (or 135 °, 225 °, 315 °) in a cross section orthogonal to the optical axis A The laser beam LX can be divided into the lasers S1 and S2 without using the polarization separation element 12. For example, if the polarization maintaining optical fiber 42 is directly connected to the emission port of the semiconductor laser constituting the light source 5, the polarization axis J42 is polarized with the polarization axis J31 being inclined with respect to the optical axis A. 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 separation element 12.

[Configuration, Operation, and Effect of Measurement Device]
Although not shown, the measurement device of the second embodiment includes a laser device 60B shown in FIG. 3 instead of the laser device 60A of the measurement device 50 shown in FIG. The configuration of the measurement device of the second embodiment other than the laser device is the same as that of the measurement device 50. In the laser device 60B, the optical frequency combs C1 and C2 are obtained from the polarization maintaining optical fiber 34 as in the laser device 60A. Therefore, the measuring device of the second embodiment operates in the same manner as the measuring device 50. It produces the same effect as

Third Embodiment
Next, a dual optical frequency comb generation optical system, a laser apparatus and a measurement apparatus according to a 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 is replaced by one light source 5, a polarization maintaining optical fiber 6, and a polarization separation element 12 of the laser device 60A, and two

light sources

5A, 5B, two polarization maintaining

optical fibers

6A and 6B, and a polarization coupling element 14 are provided, and the dual optical frequency comb generation optical system 10A of the first embodiment is provided.

Similar to the light source 5, the

light sources

5A and 5B are composed of semiconductor lasers. The light source 5A emits only the laser beam S1, and the light source 5B emits only the laser beam S2. The polarization coupling element 14 couples the laser beams S1 and S2 incident from the polarization maintaining

optical fibers

6A and 6B as different paths, and combines the coupled laser beams S1 and S2 into a common polarization maintaining optical fiber 31. I will emit. The polarization coupling element 14 is configured 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 maintaining optical fiber 6A, and the laser light S2 emitted from the light source 5B is guided to the polarization maintaining optical fiber 6B. Ru. When the laser beams S1 and S2 enter the polarization coupling element 14 from the polarization maintaining

optical fibers

6A and 6B, they are mutually coupled. The coupled laser beams S1 and S2 are incident on the introduction portion 21 of the dual optical frequency comb generation optical system 10A through the polarization maintaining optical fiber 31.

The guiding of the laser beams S1 and S2 introduced into the dual optical frequency comb generation optical system 10A through the introduction unit 21 is the same as the contents described in the first embodiment. From the polarization maintaining optical fiber 34, optical frequency combs C1 and C2 (see FIG. 2) having mutually different repetition frequencies are obtained.

[Operation effect of dual optical frequency comb generation optical system and laser device]
The laser device 60C has the dual optical frequency comb generation optical system 10A, and therefore exhibits the same effect as the laser device 60A. In the laser device 60C, the laser beams S1 and S2 are generated by different light sources, guided by different polarization maintaining optical fibers, and coupled by the polarization coupling element 14 to obtain laser beams L1 and L2. By this, the laser beams S1 and S2 can be individually controlled, and the characteristics of the optical frequency combs C1 and C2 can be easily and accurately adjusted. 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 Measurement Device]
Although not shown, the measurement device of the third embodiment includes a laser device 60C shown in FIG. 4 in place of the laser device 60A of the measurement device 50 shown in FIG. The configuration of the measurement device of the third embodiment other than the laser device is the same as that of the measurement device 50. In the laser device 60C, since the optical frequency combs C1 and C2 are obtained from the polarization maintaining optical fiber 34 similarly to the laser device 60A, the measuring device of the third embodiment operates in the same manner as the measuring device 50. It produces the same effect as

Fourth Embodiment
Next, a dual optical frequency comb generation optical system, a laser apparatus, and a measurement apparatus according to a 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 introducing unit 21 in the laser device 60D of the fourth embodiment is the same as the configuration from the light source 5 to the introducing unit 21 in the laser device 60A described in the first embodiment. is there. The laser device 60D includes a dual light frequency comb generation optical system 10B in place of the dual light frequency comb generation optical system 10A described in the first embodiment.

A phase modulation unit 72 is incorporated in the polarization maintaining optical fiber 33B of the third loop unit 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 near side in the R1 direction, and an electro-optical modulator 73B provided on the far side in the R1 direction. A light emission terminal 81 and a collimator lens 82 are provided between the end of the polarization maintaining optical fiber 33B and the electro-

optic modulators

73A and 73B, respectively. A high power high frequency electric signal is supplied from the high frequency generator 84 to each of the electro-

optic modulators

73A and 73B from the outside of the third loop unit 33 via the amplifier 83. The electro-optic modulator 73A can modulate only the phase of the laser amplification light L1 whose polarization direction is the first direction. The electro-optic modulator 73B can modulate only the phase of the laser amplified 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 apparatus 60D, optical frequency combs having different repetition frequencies from the polarization maintaining optical fiber 34 according to the same guiding and operation principle as the contents 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 amplified lights L1 and L2 guided to the third loop unit 33 along the R1 and R2 directions, the phase modulation unit 72 is generated along the R1 direction. The optical path length of the incident laser amplified light L1 is changed by the electro-optical modulator 73A. 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 according to the amount of change in the optical path length of the laser amplified light L1 by the electro-

optic modulators

73A and 73B.

[Operation effect of dual optical frequency comb generation optical system and laser device]
The laser device 60D has the dual optical frequency comb generation optical system 10B, and therefore exhibits 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 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 resonator length of the laser amplification lights L1 and L2 and the optical path length difference ΔL can be controlled with high accuracy by adjusting the difference between By controlling the resonator length of the laser amplified lights L1 and L2 and the optical path length difference ΔL with high precision, it is possible to easily control only the repetition frequency f _rep1 of the optical frequency comb C1 or the repetition frequency f _{rep2 of the} optical frequency comb C2 .

[Configuration, Operation, and Effect of Measurement Device]
Although not shown, the measurement apparatus of the fourth embodiment of the present invention includes a laser apparatus 60D shown in FIG. 5 in place of the laser apparatus 60A of the measurement apparatus 50 shown in FIG. The configuration of the measurement device of the fourth embodiment other than the laser device is the same as that of the measurement device 50. In the laser device 60D, since the optical frequency combs C1 and C2 are obtained from the polarization maintaining 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. It produces the same effect as According to the laser device 60D, since the repetition frequency difference Δf _rep between the optical frequency combs C1 and C2 can be easily controlled, the frequency interval between adjacent spectra on the frequency axis in the mode decomposition spectrum can be easily controlled. The measurement resolution of the measurement apparatus of the fourth embodiment can be easily adjusted.

Fifth Embodiment
Next, a dual optical frequency comb generation optical system, a laser apparatus, and a measurement apparatus according to a 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 introducing unit 21 in the laser device 60E of the fifth embodiment is the same as the configuration from the light source 5 to the introducing unit 21 in the laser device 60A described in the first embodiment. is there. The laser apparatus 60E includes a dual light frequency comb generation optical system 10C in place of the dual light frequency comb generation optical system 10A described in the first embodiment.

The dual optical frequency comb generation optical system 10C has at least the configuration of the dual optical frequency comb generation optical system 10B described in the fourth embodiment. In addition, a polarization multiplexing non-reciprocal phase shift unit 90 is incorporated in the polarization maintaining optical fiber 32C of the second loop unit 32 of the dual optical frequency comb generation optical system 10C. Here, “polarization multiplexed type” means that it acts on both the laser amplification light L1 whose polarization direction is the first direction and the laser amplification light L2 whose polarization direction is the second direction. Show. The above-mentioned "non-reciprocal" refers to individually acting on both the laser amplified lights L1 and L2 guided in the R1 direction and the laser amplified lights L1 and L2 guided in the R2 direction. Show. 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. FIG. As shown in FIG. 7, the nonreciprocal 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 unit 90A,

collimators

100A and 100B connected to the polarization maintaining optical fiber 32C are provided at the front and back ends of the base 98 in the R1 direction. A Faraday rotator 91, a QWP 93, and a Faraday rotator 92 are arranged in this order along the R1 direction between the

collimators

100A and 100B at intervals in the base 98.

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

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

In the nonreciprocal phase shift unit 90A, the polarization direction of the laser amplified lights L1 and L2 incident on the Faraday rotator 91 from the collimator 100A through the polarization maintaining optical fiber 32C along the R1 direction is firstly 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 the third and fourth directions enter the QWP 93. The direction of polarization of the laser amplified light L1 and L2 emitted from the QWP 93 along the R1 direction and incident on the Faraday rotator 92 is 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 amplified lights L1 and L2 having passed through the Faraday rotator 92 are guided from the collimator 100B to the polarization maintaining optical fiber 32C.

In the nonreciprocal phase shift unit 90A, the direction of polarization of the laser amplified lights L1 and L2 incident on the Faraday rotator 92 from the collimator 100B through the polarization maintaining optical fiber 32C along the R2 direction is 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 QWP 93 is aligned with the direction of polarization in the R1 direction, a relative phase difference of 90 ° can be given to the laser amplified lights L1 and L2 traveling along the R2 direction. Therefore, after passing through the QWP 93, the polarization direction is returned by the Faraday rotator 91. The orientation of the crystal axis of the QWP 93 can be adjusted, for example, to the direction changed from the first direction / second direction of the laser amplification lights L1 and L2 to the third direction / the fourth direction.

According to the nonreciprocal phase shift unit 90A, both of the laser amplified lights L1 and L2 incident along the R1 direction from the polarization maintaining optical fiber 32C and the laser amplified lights L1 and L2 incident along the R2 direction A phase difference offset can be applied. The phase difference offset is based on the characteristics of QWP 93.

The number of wave plates disposed between the

Faraday rotators

91 and 92 is one 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 far 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

QWPs

93A, 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

QWPs

93A and 93B function in the same manner as the QWP 93.

In the nonreciprocal phase shift unit 90B, a series of configurations of the Faraday rotator 91, the QWP 93, and the Faraday rotator 92 in the nonreciprocal phase shift unit 90A of the first configuration example are provided in parallel. In the base 98, along the R1 direction, as a first series, the Faraday rotator 91A, the QWP 93A, and the Faraday rotator 92A are arranged in this order between the

collimators

100A and 100B at an interval. Between the

collimators

100A and 100B, the Faraday rotator 91B, the QWP 93B, and the Faraday rotator 92B as the second series are arranged in this order at intervals different from the first series along the R1 direction. In the first system, a polarization separation coupling element 97A is provided on the near side in the R1 direction of the Faraday rotator 91A. A polarization splitting / coupling element 97B is provided on the far side of the Faraday rotator 92A in the R1 direction. In the second system, a polarization maintaining mirror 99A is provided on the near side in the R1 direction of the Faraday rotator 91B. A polarization maintaining mirror 99B is provided on the far side in the R1 direction of the Faraday rotator 92B.

In the nonreciprocal phase shift unit 90B, the laser amplified lights L1 and L2 incident on the Faraday rotator 91 from the collimator 100A along the R1 direction are separated by the polarization splitting / coupling element 97A based on the difference in the direction of polarization of each other. . One of the laser amplification lights L1 of the laser amplification lights L1 and L2 travels from the polarization splitting / coupling element 97A toward the first system. The laser amplification light L1 passes through the Faraday rotator 91A, the QWP 93A, and the Faraday rotator 92A in this order, and receives a phase shift based on the characteristics of the QWP 93A. The laser amplified light L2 separated by the polarization separation coupling element 97A is turned back by the mirror 99A and travels toward the second system, and passes through the Faraday rotator 91B, QWP 93B, and Faraday rotator 92B in this order, and the characteristics of the QWP 93B Subject to 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 direction of each polarization in the first direction or the second direction, and the polarization maintaining light at the back side in the R1 direction from the collimator 100B. It enters the fiber 32C.

In the nonreciprocal phase shift unit 90B, the laser amplified lights L1 and L2 incident on the polarization separation / combination element 97B from the collimator 100B along the R2 direction travel along the R1 direction except that the traveling directions are reversed. However, nonlinear phase shift is received similarly to the laser amplified lights L1 and L2 which receive nonlinear phase shift.

According to the nonreciprocal phase shift unit 90B, the characteristics of the QWP 93A are applied to both the laser amplified light L1 incident along the R1 direction from the polarization maintaining optical fiber 32C and the laser amplified light L1 incident along the R2 direction. Based on the phase shift. Further, an offset can be given to the phase difference based on the characteristics of the QWP 93B in both the laser amplified light L2 incident from the polarization maintaining optical fiber 32C along the R1 direction and the laser amplified light L2 incident along the R2 direction. . Since the non-reciprocal phase shift unit 90B can individually apply a phase shift to the laser amplified lights L1 and L2, the repetition frequency difference Δf _rep of the optical frequency combs C1 and C2 is highly accurate compared to the non-reciprocal phase shift unit 90A. 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 apparatus 60E, optical frequency combs having different repetition frequencies from the polarization maintaining optical fiber 34 according to the same guiding and operation principle as the contents 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 60E, the non-reciprocal phase shift unit 90 causes the non-reciprocal phase shift unit 90 to nonlinearly shift the laser amplified lights L1 and L2 guided to the second loop unit 32 along the R1 and R2 directions. Receive

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

[Configuration, Operation, and Effect of Measurement Device]
Although not shown, the measurement apparatus of the fifth embodiment includes a laser apparatus 60E shown in FIG. 6 in place of the laser apparatus 60A of the measurement apparatus 50 shown in FIG. The configuration of the measurement device of the fifth embodiment other than the laser device is the same as that of the measurement device 50. In the laser device 60E, optical frequency combs C1 and C2 are obtained from the polarization maintaining optical fiber 34 as in the laser device 60A. By this, the measuring apparatus of 5th Embodiment operate | moves similarly to the measuring apparatus 50, and there exists an effect similar to the measuring apparatus 50. FIG. According to the laser device 60E, the repetition 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 measurement apparatus of the fifth embodiment can be easily and accurately adjusted.

Sixth Embodiment
Next, a dual optical frequency comb generation optical system, a laser apparatus, and a measurement apparatus according to a 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 introducing unit 21 in the laser device 60F of the sixth embodiment is the same as the configuration from the light source 5 to the introducing unit 21 in the laser device 60A described in the first embodiment. is there. The laser device 60F includes a dual light frequency comb generation optical system 10D in place of the dual light frequency comb generation optical system 10A described in the first embodiment.

The dual optical frequency comb generation optical system 10D has 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 maintaining optical fiber 32B of the second loop portion 32 of the dual optical frequency comb generation optical system 10D. The optical path lengths of the laser amplified lights L1 and L2 in the second loop section 32 can be adjusted by the resonator length control element 76. Examples of the resonator length control element 76 include a piezoelectric element, an acousto-optic element, and an electro-optic 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 apparatus 60F, optical frequency combs having different repetition frequencies from the polarization maintaining optical fiber 34 according to the same guiding and operation principle as the contents 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 guided to 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 can control the resonator length of the laser amplified lights L1 and L2 so as to easily and finely control the repetition frequency difference Δf _rep between the optical frequency combs C1 and C2.

[Configuration, Operation, and Effect of Measurement Device]
Although not shown, the measurement apparatus of the sixth embodiment includes a laser apparatus 60F shown in FIG. 6 in place of the laser apparatus 60A of the measurement apparatus 50 shown in FIG. The configuration of the measurement device of the sixth embodiment other than the laser device is the same as that of the measurement device 50. In the laser device 60F, since the optical frequency combs C1 and C2 are obtained from the polarization maintaining 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. It produces 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. By this, it is possible to control with high precision the frequency interval between adjacent spectra on the frequency axis in the mode decomposition spectrum, and to adjust the measurement resolution of the measurement apparatus of the sixth embodiment with high precision.

Seventh Embodiment
Next, a dual optical frequency comb generation optical system, a laser apparatus, and a measurement apparatus according to a 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 introducing unit 21 in the laser apparatus 60G according to the seventh embodiment of the present invention is the configuration from the light source 5 to the introducing unit 21 in the laser apparatus 60A described in the first embodiment. Is the same as The laser device 60G includes a dual light frequency comb generation optical system 10E in place of the dual light 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 introducing unit 21, an amplifying unit 40, a connecting unit 22, and a space type resonating unit 102. The first loop optical fiber 30 includes a second loop portion 32 shown on the right side of FIG. 10 and polarization maintaining

optical fibers

33A, 34, 33C shown on the left side of FIG. The polarization maintaining

optical fibers

33A and 34 are formed of a common polarization maintaining optical fiber, but may be formed of different polarization maintaining optical fibers connected to each other. The end (one end) of the incident side of the polarization maintaining optical fiber 33A is connected to the side opposite to the second loop portion 32 side of the connecting portion 22. The end (the other end) of the output side of the polarization maintaining optical fiber 33 A is connected to the polarization separation unit 52 of the measuring device 50. The end (one end) of the incident side of the polarization maintaining optical fiber 33 C is connected to the side opposite to the second loop portion 32 side of the connecting portion 22. The space type resonance unit 102 is connected to the end (the other end) of the output side of the polarization maintaining optical fiber 33C. Since light reciprocates along the longitudinal direction in the polarization maintaining optical fiber 33C, the "incident side" and the "outgoing side" are the side on which the light first enters the polarization maintaining optical fiber 33C, and the light emerges first Means the side that In the first loop optical fiber 30, an annular loop path is not configured on the left side of the connection portion 22 in FIG. That is, the first loop optical fiber 30 is configured to draw the numeral “9” with the connecting portion 22 as a knot.

The laser amplification light return unit 70 includes a connection unit 22, and a linear unit 38 configured of the polarization maintaining optical fiber 33 C and the spatial resonance unit 102.

Hereinafter, one of the linear directions separating from the end portion on the output side of the polarization maintaining optical fiber 33C with respect to the connecting portion 22 will be referred to as a P1 direction. In addition, a linear direction opposite to the P1 direction is referred to as a P2 direction. The spatial resonator 102 includes a polarization maintaining output end 104, a lens 108, and a polarization maintaining mirror 106. The emitting end 104 is provided at the end of the output side of the polarization maintaining optical fiber 33C. The lens 108 is disposed on the back side in the P1 direction from the emission end 104. The mirror 106 is disposed on the back side in the P1 direction from the lens 108. The transmittance of the laser amplification lights L1 and L2 at the reflection surface 106r of the mirror 106 is 0%. The lens 108 collimates the laser amplified lights L1 and L2 incident along the P1 direction and condenses the laser amplified lights L1 and L2 incident along the P2 direction on the emission end 104.

The guiding of the laser beams S1 and S2 and the laser amplified 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 guiding of S1 and S2 and the laser amplification lights L1 and L2.

In the connecting portion 22, the ratio of the laser amplification lights L1 and L2 incident on the connecting portion 22 to be guided to the polarization maintaining

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 the predetermined condition is satisfied), the polarization of the coupling portion 22 The laser amplified lights L1 and L2 intensified by the interference in the holding optical coupler are all guided to the polarization maintaining optical fiber 33A along the R1 direction. A part (about 50%) of the laser amplified lights L1 and L2 incident on the coupling portion 22 is guided to the polarization maintaining optical fiber 33A. The remaining portion (about 50%) of the laser amplified light L1 and L2 incident on the coupling portion 22 is guided to the polarization maintaining optical fiber 33C.

The laser amplified lights L1 and L2 guided from the connecting portion 22 to the polarization maintaining optical fiber 33C enter the spatial resonator 102 from the other end of the polarization maintaining optical fiber 33C, and the emission end 104 is 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 along the P1 direction, and are reflected by the reflection 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 condensed on the emitting end 104 by the lens 108. The laser amplified lights L1 and L2 collected at the emission end 104 pass through the emission end 104 and are guided to the polarization maintaining optical fiber 33C along the R1 direction.

The waveguides of the laser amplification lights L1 and L2 which are guided to the polarization maintaining optical fiber 33C and enter the coupling portion 22 along the R1 direction are the dual optical frequency comb generation optical system 10A described in the first embodiment and This is the same as guiding of the laser amplified lights L1 and L2 incident on the coupling portion 22 along the R1 direction in the laser device 60A. From the coupling portion 22 to the polarization maintaining

optical fibers

33A and 34, optical frequency combs C1 and C2 having different repetition frequencies are obtained.

[Operation effect of dual optical frequency comb generation optical system and laser device]
The laser device 60G has dual optical frequency comb generation optical system 10E, and exhibits the same effect as the laser device 60A. In addition, since the laser apparatus 60G includes the space type resonance unit 102, the resonator length of the laser amplification lights L1 and L2 can be adjusted by changing the separation distance between the emission end 104 and the mirror 106, and additionally, the resonator length is A large adjustment range can be secured.

[Configuration, Operation, and Effect of Measurement Device]
Although not shown, the measurement apparatus of the seventh embodiment includes a laser apparatus 60G shown in FIG. 10 in place of the laser apparatus 60A of the measurement apparatus 50 shown in FIG. The configuration of the measurement device of the second embodiment other than the laser device is the same as that of the measurement device 50. In the laser device 60G, since the optical frequency combs C1 and C2 are obtained from the polarization maintaining optical fiber 34 similarly to the laser device 60A, the measuring device of the seventh embodiment operates in the same manner as the measuring device 50 and measures 50. It produces the same effect as

Eighth Embodiment
Next, a dual optical frequency comb generation optical system, a laser apparatus, and a measurement apparatus according to an 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, a laser apparatus 60H according to the eighth embodiment includes a polarization-maintaining optical fiber 42 in place of the polarization-maintaining optical fiber 6 and the polarization separation element 12 of the laser apparatus 60G. The dual optical frequency comb generation optical system 10E of the embodiment is provided. As in the second embodiment, the polarization axis J 42 of the cladding 77 of the polarization maintaining optical fiber 42 centered on the optical axis A is the polarization of the cladding 71 of the polarization maintaining optical fiber 31 centered on the optical axis A. One of the angles 45 °, 135 °, 225 °, and 315 ° is formed with respect to the axis J31.

[Operation effect of dual optical frequency comb generation optical system and laser device]
The laser device 60H has dual optical frequency comb generation optical system 10E, and exhibits 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 separation element 12 as in the second embodiment.

[Configuration, Operation, and Effect of Measurement Device]
Although not shown, the measurement apparatus of the eighth embodiment includes a laser apparatus 60H shown in FIG. 11 in place of the laser apparatus 60A of the measurement apparatus 50 shown in FIG. The configuration of the measurement device of the eighth embodiment other than the laser device is the same as that of the measurement device 50. In the laser device 60H, the optical frequency combs C1 and C2 are obtained from the polarization maintaining optical fiber 34 similarly to the laser device 60A, so the measuring device of the eighth embodiment operates in the same manner as the measuring device 50. It produces the same effect as

The ninth embodiment
Next, a dual optical frequency comb generation optical system, a laser apparatus, and a measurement apparatus according to a 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, a laser apparatus 60I according to the ninth embodiment includes two light sources 5A, instead of one light source 5, a polarization maintaining optical fiber 6, and a polarization separation element 12 of the laser apparatus 60G. A dual optical frequency comb generation optical system 10E described in the seventh embodiment is provided as well as 5B, two polarization maintaining

optical fibers

6A and 6B, and a polarization coupling element 14.

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

[Configuration, Operation, and Effect of Measurement Device]
Although not shown, the measurement apparatus of the ninth embodiment is provided with a laser apparatus 60I shown in FIG. 12 instead of the laser apparatus 60A of the measurement apparatus 50 shown in FIG. The configuration of the measurement device of the ninth embodiment other than the laser device is the same as that of the measurement device 50. In the laser device 60I, since the optical frequency combs C1 and C2 are obtained from the polarization maintaining optical fiber 34 similarly to the laser device 60A, the measuring device of the ninth embodiment operates in the same manner as the measuring device 50. It produces the same effect as

Tenth Embodiment
Next, a dual optical frequency comb generation optical system, a laser apparatus, and a measurement apparatus according to a 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 introducing unit 21 in the laser apparatus 60J according to the tenth embodiment of the present invention is the configuration from the light source 5 to the introducing unit 21 in the laser apparatus 60A described in the first embodiment. Is the same as The laser device 60J includes a dual light frequency comb generation optical system 10F in place of the dual light 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 and the mirror 106 of the space type resonance unit 102. The phase modulation unit 72 can modulate the phases of the laser amplification lights L1 and L2 resonating in the spatial resonance unit 102. Each of the electro-

optic modulators

73A and 73B is supplied with a high power high frequency signal from the high frequency generator 84 from the outside of the spatial resonator 102 via the amplifier 83.

[Operation effect of dual optical frequency comb generation optical system and laser device]
The laser device 60J has the dual optical frequency comb generation optical system 10F, and therefore exhibits the same effect as the laser device 60G. In the laser apparatus 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. You can adjust the difference between By this, it is possible to control the resonator length of the laser amplified lights L1 and L2 and the optical path length difference ΔL 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 Measurement Device]
Although not shown, the measurement apparatus of the tenth embodiment is provided with a laser apparatus 60J shown in FIG. 13 instead of the laser apparatus 60A of the measurement apparatus 50 shown in FIG. The configuration of the measurement apparatus of the tenth embodiment other than the laser apparatus is the same as that of the measurement apparatus 50. In the laser device 60J, since the optical frequency combs C1 and C2 are obtained from the polarization maintaining optical fiber 34 similarly to the laser device 60A, the measuring device of the tenth embodiment operates in the same manner as the measuring device 50. It produces the same effect as

Eleventh Embodiment
Next, a dual optical frequency comb generation optical system, a laser apparatus, and a measurement apparatus according to an 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 introducing unit 21 in the laser apparatus 60K of the eleventh embodiment is the same as the configuration from the light source 5 to the introducing unit 21 in the laser apparatus 60A described in the first embodiment. is there. The laser device 60K includes a dual light frequency comb generation optical system 10G in place of the dual light frequency comb generation optical system 10A described in the first embodiment.

The dual optical frequency comb generation optical system 10G has at least the configuration of the dual optical frequency comb generation optical system 10F described in the tenth embodiment. In addition, the polarization multiplexing non-reciprocal phase shift unit 90 described in the fifth embodiment is incorporated in the polarization maintaining optical fiber 32C of the second loop unit 32 of the dual optical frequency comb generation optical system 10G. .

[Operation effect of dual optical frequency comb generation optical system and laser device]
The laser device 60K has the dual optical frequency comb generation optical system 10G, so that the same effect as the laser device 60J can be obtained, and the laser amplification light L1 can be obtained using the nonreciprocal phase shift unit 90 as in the fifth embodiment. , L2 and the optical path length difference ΔL, and the repetition frequency difference Δf _rep of the optical frequency combs C1 and C2 can be adjusted. In the laser device 60K, the resonator length of the laser amplification lights L1 and L2 and the optical path length difference ΔL can be individually controlled, and the repetition frequency difference Δf _rep of the optical frequency combs C1 and C2 can be finely adjusted.

[Configuration, Operation, and Effect of Measurement Device]
Although not shown, the measurement apparatus of the eleventh embodiment is provided with a laser apparatus 60K shown in FIG. 14 instead of the laser apparatus 60A of the measurement apparatus 50 shown in FIG. The configuration of the measurement apparatus of the eleventh embodiment other than the laser apparatus is the same as that of the measurement apparatus 50. In the laser device 60K, the optical frequency combs C1 and C2 are obtained from the polarization maintaining optical fiber 34 as in the laser device 60A. Therefore, the measurement device of the eleventh embodiment operates in the same manner as the measurement device 50. It produces the same effect as

(Twelfth embodiment)
Next, a dual optical frequency comb generation optical system, a laser device and a measurement apparatus according to a 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 introducing unit 21 in the laser device 60L of the twelfth embodiment is the same as the configuration from the light source 5 to the introducing unit 21 in the laser device 60A described in the first embodiment. is there. The laser device 60L includes a dual light frequency comb generation optical system 10H in place of the dual light frequency comb generation optical system 10A described in the first embodiment.

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

[Operation effect 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 same effect as the laser device 60K can be obtained, and similarly to the sixth embodiment, the second loop portion 32 is guided along the R1 and R2 directions. The optical path lengths of the waved laser amplification lights L1 and L2 can be changed by the resonator length control element 76. According to the laser device 60L, the resonator length of the laser amplified light L1 and L2 is 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 comb C1 and C2 The repetition frequency difference Δf _rep between each other can be easily and finely controlled.

[Configuration, Operation, and Effect of Measurement Device]
Although not shown, the measurement apparatus of the twelfth embodiment is provided with a laser apparatus 60L shown in FIG. 15 in place of the laser apparatus 60A of the measurement apparatus 50 shown in FIG. The configuration of the measurement apparatus of the twelfth embodiment other than the laser apparatus is the same as that of the measurement apparatus 50. In the laser device 60L, the optical frequency combs C1 and C2 are obtained from the polarization maintaining optical fiber 34 as in the laser device 60A. Therefore, the measuring device of the twelfth embodiment operates in the same manner as the measuring device 50. It produces the same effect as

(13th Embodiment)
Next, a dual optical frequency comb generation optical system, a laser apparatus, and a measurement apparatus according to a 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 introducing unit 21 in the laser apparatus 60M of the thirteenth embodiment is the same as the configuration from the light source 5 to the introducing unit 21 in the laser apparatus 60A described in the first embodiment. is there. The laser device 60M is provided with a saturable absorbing reflector 110 in place of the space type resonating portion 102 of the laser device 60G of the seventh embodiment.

The saturable absorber reflector 110 strengthens each other by the interference at the connecting portion 22, and makes only the laser amplified light L1 and L2 (pulse light) incident through the polarization maintaining optical fiber 33C into the polarization maintaining optical fiber 33C. reflect. The saturable absorbing reflector 110 is weakened due to the interference at the connecting portion 22, and absorbs the laser amplified lights L1 and L2 incident through the polarization maintaining optical fiber 33C, and the polarization maintaining optical fiber 33C Do not emit. That is, the saturable absorber reflector 110 functions in the same manner as the third loop portion 33 described in the first embodiment and the space type resonator portion 102 described in the seventh embodiment.

[Operation effect of dual optical frequency comb generation optical system and laser device]
The laser device 60M has the dual optical frequency comb generation optical system 10M, and therefore exhibits the same effects as the laser device 60A and the laser device 60G. The laser device 60M includes the saturable absorbing reflector 110 as a configuration for returning the laser amplification lights L1 and L2 intensified at the connecting portion 22 to the second loop portion 32. Therefore, the laser device 60M can be miniaturized. it can.

[Configuration, Operation, and Effect of Measurement Device]
Although not shown, the measurement apparatus of the thirteenth embodiment includes a laser apparatus 60M shown in FIG. 16 instead of the laser apparatus 60A of the measurement apparatus 50 shown in FIG. The configuration of the measurement device of the thirteenth embodiment other than the laser device is the same as that of the measurement device 50. In the laser device 60M, the optical frequency combs C1 and C2 are obtained from the polarization maintaining optical fiber 34 as in the laser device 60A. Therefore, the measuring device of the thirteenth embodiment operates in the same manner as the measuring device 50. It produces 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 according to the present invention, for example, the dual optical frequency comb generation optical system 10N shown in FIG. A 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 coupling portion, and is formed by polarization maintaining

optical fibers

30A, 30B, 30C, and 30D arranged annularly. It is configured. The first loop optical fiber 30 is provided with an introducing unit 21, an amplifying unit 40, an extracting unit 24, a saturable absorber 75, and a polarization maintaining optical isolator 25 along the R1 direction.

The laser amplification light return unit 70 in the dual optical frequency comb generation optical system 10 N is configured of a saturable absorber 75 and a polarization maintaining optical isolator 25. The saturable absorber 75 is sensitive to a wavelength band including the second wavelength. The loss of the saturable absorber 75 becomes small only when the laser amplified lights L1 and L2 having a predetermined power or more enter the saturable absorber 75, and the laser amplified lights L1 and L2 become polarization maintaining

optical fibers

30C and 30D Emit at. The polarization maintaining optical isolator 25 passes the laser amplified lights L1 and L2 incident from the polarization maintaining optical fiber 30E along the R2 direction to the polarization maintaining optical fiber 30D. The polarization maintaining optical isolator 25 removes from the first loop optical fiber 30 the laser amplification lights L1 and L2 incident from the polarization maintaining optical fiber 30D along the R1 direction.

In the dual optical frequency comb generation optical system 10N, the process until the laser beams S1 and S2 are extracted from the laser beam S0 emitted from the light source 5 and the laser beams S1 and S2 are wavelength converted by the amplification unit 40 is This is the same as the dual optical frequency comb generation optical system 10A of the embodiment. Part of the laser amplified lights L1 and L2 amplified by the amplifier 40 passes along the R1 direction through the polarization maintaining optical fiber 30B, the lead-out portion 24, and the polarization maintaining optical fiber 30C, and the saturable absorption absorption It enters the body 75. The remaining portions of the laser amplification lights L1 and L2 amplified by the amplification unit 40 are guided to the polarization maintaining optical fiber 30E along the R2 direction, pass through the polarization maintaining optical isolator 25, and The light is guided to the optical fiber 30 D and enters the saturable absorber 75.

In the saturable absorber 75, only the strong laser amplification lights L 1 and L 2 incident on the saturable absorber 75 along the R 2 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 pulse lights having high power. A part of the laser amplified lights L1 and L2 emitted from the saturable absorber 75 along the R2 direction is led out from the lead-out portion 24 to the polarization maintaining optical fiber 34. The remaining portions of the laser amplified lights L1 and L2 emitted from the saturable absorber 75 along the R2 direction are guided to the polarization maintaining optical fiber 30B, enter the amplifying unit 40, and are repeatedly amplified.

According to the above-described operation principle, in the dual optical frequency comb generation optical system 10N, the laser amplification lights L1 and L2 shift to the mode synchronization state, and the optical frequency combs C1 and C2 are generated. The total length of the polarization maintaining

optical fibers

30A, 33B, and 33C is the resonator length and the optical path of the laser amplification lights L1 and L2 in consideration of the refractive index and the second wavelength of each of the laser amplification lights L1 and L2. The length difference ΔL is set 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, in the saturable absorber 75 provided between the polarization maintaining

optical fibers

30C and 30D. Instead, a resonator length control element 76 is provided in the polarization maintaining optical fiber 30B. The resonator length control element 76 makes it possible to control the resonator length of the mode-locked laser formed of the first loop optical fiber 30. Examples of the resonator length control element 76 include a piezoelectric element, an acousto-optic element, and an electro-optic element.

In the dual optical frequency comb generation optical system 10P, the process until the laser beams S1 and S2 are extracted from the laser beam S0 emitted from the light source 5 and the laser beams S1 and S2 are amplified by the amplifier 40 is the first embodiment. It is similar to the form dual optical frequency comb generation optical system 10A. A portion of the laser amplified light L1 and L2 amplified by the amplification unit 40 passes through the polarization maintaining optical fiber 30B, the lead-out unit 24, and the polarization maintaining optical fiber 30C along the R1 direction, and the polarization maintaining , But is removed from the first loop optical fiber 30 by the polarization maintaining optical isolator 25.

The remaining portions of the laser amplification lights L1 and L2 amplified by the amplification unit 40 are guided along the R2 direction to the polarization maintaining optical fiber 30D, and the polarization maintaining optical isolator 25 and the polarization maintaining optical fiber The light passes through 30 C and enters the lead-out unit 24. A part of the laser amplified light L1 and L2 incident on the lead-out unit 24 along the R2 direction is led out of the lead-out unit 24 to the polarization maintaining optical fiber 34. The remaining portions of the laser amplification lights L1 and L2 incident on the lead-out portion 24 along the R2 direction are guided to the polarization maintaining optical fiber 30B, are incident on the amplification portion 40, and are repeatedly amplified as described in the previous stage. .

As described above, in the dual optical frequency comb generation optical systems 10N and 10P, as in the dual optical frequency comb generation optical system 10A of the first embodiment, the laser beams S1 and S2 and the laser amplification light have different polarization directions. The refractive indices of the laser amplified lights L1 and L2 are made different from each other using L1 and L2. Therefore, while making the resonators of the laser beams S1 and S2 and the laser amplified lights L1 and L2 common, the resonator lengths of the laser amplified lights L1 and L2 can be made different from each other. As a result, the 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 environmental disturbance and mechanical disturbance included in each of the optical frequency combs C1 and C2 And easily removable. When the mode-locked lasers for generating the optical frequency combs C1 and C2 are prepared in separate spaces as in the prior art by sharing one dual optical frequency comb generating optical system 10N and 10P with the laser amplified lights L1 and L2 In this case, the dual optical frequency comb generation optical systems 10N and 10P can be miniaturized.

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

Although the preferred embodiments of the present invention have been described above in detail, the present invention is not limited to the specific embodiments described above. The invention can be varied within the scope of the invention as set forth in the claims.

For example, the components of the dual optical frequency comb generating optical system described in each of the above-described embodiments are merely examples, and can be appropriately changed to known configurations having similar functions. For example, the electro-

optic modulators

73A and 73B may be changed to modulators equipped with an acousto-optic element.

5:

light source

10A, 10B, 10C, 10D, 10E, 10F, 10G, 10M, 10N, 10P, ... dual optical frequency comb generation optical system 21 ... introduction unit 22 ... connection unit 24 ... derivation unit 30 ... first loop light Fiber 32 ... second loop section 33 ... third loop section 40 ... amplification 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 part

Claims

While guiding the first laser light whose polarization direction is the first direction, the second laser light whose polarization direction is the second direction different from the first direction is guided, and the first laser light and A first loop optical fiber that holds the direction of polarization of each of the second laser light;
An introducing unit provided in the first loop optical fiber for introducing the first laser beam and the second laser beam into the first loop optical fiber;
First laser amplification provided to the first loop optical fiber, amplifying the first laser light and the second laser light while maintaining the direction of the polarization of the first laser light and the second laser light An amplification unit that generates the light and the second laser amplification light, and emits the first laser amplification light and the second laser amplification light in a circumferential direction of the first loop optical fiber and in a direction opposite to the circumferential direction;
The first laser-amplified light and the second laser-amplified light provided in the first loop optical fiber and guided along the circumferential direction, and the second laser-amplified light guided along the opposite direction to the circumferential direction The first laser amplification light and the second laser amplification light are at least in the circumferential direction and at least in a direction reverse to the circumferential direction only when the phase difference between the first laser amplification beam and the second laser amplification light satisfies a predetermined condition. A laser-amplified light return unit that emits the first loop optical fiber along one direction;
The first loop optical fiber is provided, the first loop optical fiber is generated, and the polarization direction is the first direction. The first optical frequency comb and the first loop optical fiber are generated and the polarization direction is A deriving unit that derives the second optical frequency comb that is the second direction from the first loop optical fiber;
Equipped with
Dual optical frequency comb generation optics.
The first loop optical fiber is
The second loop section,
It is comprised by the 3rd loop part connected via the connection part to the said 2nd loop part,
The introduction unit and the amplification unit are provided in the second loop unit,
The derivation unit is provided in the third loop unit,
The laser amplification light return unit includes the connection unit and the third loop unit.
The predetermined condition is that the phase difference is an odd multiple of half of the wavelength of the first laser amplified light and the second laser amplified light,
The first laser amplification light and the second laser amplification light are generated at the connection portion only when the first laser amplification light and the second laser amplification light guided from the second loop portion satisfy the predetermined condition. After being circulated 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 section,
It is comprised by the linear part connected to the said 2nd loop part via the connection part,
The introduction unit and the amplification unit are provided in the second loop unit,
The derivation unit is connected to the connection unit,
The laser amplification light return unit includes the connection unit and the linear unit.
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,
The first laser amplification light and the second laser amplification light are generated at the connection portion only when the first laser amplification light and the second laser amplification light guided from the second loop portion satisfy the predetermined condition. After being reciprocated by 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 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 4.
The first loop optical fiber is provided with a resonator length control element capable of controlling the resonator length of the first laser amplified light and the second laser amplified 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 light and the second laser light.
Laser device.
A laser device according to claim 7;
It is disposed on the far side of the traveling direction of the first optical frequency comb and the second optical frequency comb derived from the derivation unit, and the first optical frequency comb and the second optical frequency comb are separated to be different from each other A polarization separation unit to advance to
Progress of the first optical frequency comb and the second optical frequency comb from a sample disposed on the path of at least one of the first optical frequency comb and the second optical frequency comb separated from each other by the polarization separation unit A polarization interference unit disposed on the far side of the direction to cause the first optical frequency comb and the second optical frequency comb to be measured to interfere with each other;
A sample information extraction unit disposed on the back side of the traveling direction of the interference signal obtained by the polarization interference unit and extracting information of the sample from the interference signal;
Equipped with
Measuring device.