WO2005012983A1

WO2005012983A1 - Variable spectral light generation device

Info

Publication number: WO2005012983A1
Application number: PCT/JP2004/011167
Authority: WO
Inventors: Masatoshi Fujimoto; Yutaka Tsuchiya; Tsuneyuki Urakami; Shinichiro Aoshima
Original assignee: Hamamatsu Photonics K.K.
Priority date: 2003-08-04
Filing date: 2004-08-04
Publication date: 2005-02-10
Also published as: JP2005055652A

Abstract

A basic wave light A having a constant phase relationship over a predetermined band is outputted from a light source section (11) and inputted to a light modulation section (12). In the light modulation section (12), parameters of the respective wavelength components are modulated into a modulated light B. The modulated light B outputted from the light modulation section (12) is inputted to a wavelength conversion section (13). Light C obtained by the wavelength conversion is outputted from the wavelength conversion section (13). Thus, it is possible to realize a variable spectral light generation device having a large degree of freedom of output light spectrum variation.

Description

Specification

Variable spectrum light generator

Technical field

The present invention relates to a variable spectrum light generator in which the shape of the spectrum of output light is variable.

Background art

[0002] There are various light generating devices whose output light wavelength is variable. For example, the laser oscillation device can change the output light wavelength by changing the resonator length. However, changing the resonator length requires a mechanical drive. This is not preferable in maintaining the stability of the device, and it is difficult to control the output light wavelength at a high speed of about nanosecond. In the case of a semiconductor laser device, the output light wavelength can be changed by utilizing the change in the bandgap accompanying the temperature change, but it requires time for temperature control and is affected by the surrounding environment. large.

[0003] A light generator using optical parametric oscillation as described in Non-Patent Document 1 can change the output light wavelength over a wide wavelength range by changing the orientation of the nonlinear optical crystal. . However, this light generation device requires a mechanical drive unit for changing the orientation of the nonlinear optical crystal. This is not preferable in maintaining the stability of the device.

[0004] A light generator that generates and outputs high-order harmonics from a fundamental wave as described in Non-Patent Document 2 can generate harmonics of various orders. Therefore, the output light wavelength can be made variable by setting conditions for optimizing the harmonic generation efficiency of the required order. Non-Patent Document 2 describes that the 27th harmonic generation efficiency could be optimized.However, the spectrum of the 27th harmonic has a broad spectrum. It has not been possible to perform detailed control within the band.

[0005] Although the conventional light generating devices including those described above have variable output light wavelengths, the degree of change is limited. For example, light that has sharp intensity peaks at arbitrary adjacent wavelengths and has no other wavelength components is output by high-speed control. It is not possible.

Non-Patent Document 1: "Laser Handbook", pp. 143-145, edited by The Laser Society of Japan, Ohmsha, 1982

^^ Patent Aiden 2: R. Bartels, et al., Shaped-pulse optimization of coherent emission of high-harmonic softX-rays ", Nature, Vol.406, pp.164-166 (2000)

Disclosure of the invention

Problems to be solved by the invention

[0006] The present invention has been made to solve the above problem, and an object of the present invention is to provide a variable spectral light generator capable of increasing the degree of freedom in changing the shape of an output light spectrum. And

Means for solving the problem

[0007] The variable spectrum light generation device according to the present invention includes: (1) a light source unit that outputs light having a predetermined wavelength band and a phase relationship between wavelength components that is temporally constant; The light output from the light source unit is input, the parameters of each wavelength component of the light are modulated, and the light modulation unit that outputs the modulated light; and (3) the light output from the light modulation unit is output. A wavelength conversion unit that inputs and wavelength-converts the light, and outputs the light obtained by the wavelength conversion; and (4) a control unit that controls modulation of a meter of each wavelength component of the light in the light modulation unit. It is characterized by the following. Here, it is preferable that the light modulating unit modulates at least one of amplitude, phase, polarization, and wavefront as parameters.

[0008] In this variable spectrum light generator, the light output from the light source section has a predetermined wavelength band, the phase relationship between the wavelength components is temporally constant, and the parameters (for example, As described above, any one of the amplitude, phase, polarization, and wavefront is modulated in the light modulation unit, and the modulated light is output from the light modulation unit. The light output from the light modulator is input to the wavelength converter and wavelength-converted, and the light obtained by the wavelength conversion is output from the wavelength converter. The modulation of the parameters of the wavelength components of the light in the light modulator is controlled by the controller, so that the spectrum of the light output from the wavelength converter becomes variable.

[0009] In the above-described light generating device, "the light generating device has a predetermined wavelength band, and `` Light whose phase relationship is temporally constant '' is not limited to the case where the phase waveform force of each pulse is the same even after the lapse of time. (A) In the phase component of the spectral waveform, the temporal (B) When the same constant value is superimposed as an offset, the case where the value of cZ Zx A is superimposed as a temporal offset for each pulse in the phase component of the spectrum waveform is also included (λ: wavelength, c: speed of light) , A: any constant). Here, in the case (a), the intensity waveform does not change for each pulse, but this corresponds to the case where the phase within the pulse called the carrier envelope phase drifts. In the case of (b) above, the intensity waveform does not change for each pulse, indicating a state in which a temporal drift occurs.

[0010] Here, regarding the configuration of the light modulating unit, (1) a light branching unit that spatially branches the light output from the light source unit, and (2) a wavelength branching unit by the light branching unit. A spatial light modulating means for modulating and outputting parameters of each wavelength component of light; and (3) an optical multiplexing means for multiplexing and outputting each wavelength component of light modulated by the spatial light modulating means. It is preferable to use a configuration. In this case, the light output from the light source unit and input to the light modulation unit is first spatially wavelength-branched by the light demultiplexing unit in the light modulation unit. Then, the parameters of the respective wavelength components of the wavelength-branched light are modulated by the spatial light modulator, and the respective wavelength components of the modulated light are multiplexed by the optical multiplexing means and output. As each of the optical demultiplexing means and the optical multiplexing means, for example, a diffraction grating is suitably used.

[0011] Further, the light modulation unit is an element utilizing the acousto-optic effect (A〇PDF; Acousto-Optic

It is also possible to configure a single Programmable Dispersion Filter). When an element utilizing the acousto-optic effect is used, a small system can be realized. Further, a configuration other than the above may be used as the light modulation unit.

[0012] It is preferable that the wavelength conversion unit includes a nonlinear optical medium, and emits light having a wavelength different from the wavelength of light incident on the nonlinear optical medium from the nonlinear optical medium. In this case, the light output from the light modulator and input to the wavelength converter is wavelength-converted by the nonlinear optical medium and output from the wavelength converter. Here, the nonlinear optical medium includes a nonlinear optical crystal, a nonlinear optical waveguide (for example, a photonic crystal optical fiber, a tapered single optical fiber, a hollow optical fiber, etc.), a gas having appropriate pressure and temperature conditions. A medium, or a combination thereof, is preferably used. In addition, the nonlinear optical medium When performing wavelength conversion using phenomena, phenomena such as the generation of second and higher harmonics, the generation of sum and difference frequencies, optical parametric oscillation, self-phase modulation, and cross-phase modulation are used. can do.

[0013] Further, the variable spectrum light generation device further includes a measurement unit that measures light output from the wavelength conversion unit, and the control unit controls each wavelength of light in the light modulation unit based on the measurement result by the measurement unit. Also good for controlling the modulation of component parameters. In this case, the spectrum or the like of the light output from the wavelength conversion unit is measured by the measurement unit. Based on the measurement result, the control unit can control the modulation of the parameters of each wavelength component of the light in the light modulation unit so that the spectrum or the like of the output light from the wavelength conversion unit approaches a predetermined value. Become.

[0014] Alternatively, the variable spectrum light generation device further includes a detection unit that detects a change accompanying the irradiation of the object irradiated with the light output from the wavelength conversion unit, and the control unit controls the detection by the detection unit. Based on the result, the configuration may be such that the modulation of the parameter of each wavelength component of the light in the light modulation unit is controlled. In this case, a change accompanying the irradiation of the object irradiated with the light output from the wavelength conversion unit is detected by the detection unit. Then, based on this detection result, the modulation of the parameters of each wavelength component of the light in the light modulation unit can be feedback-controlled by the control unit so that the change of the target object becomes a desired state. At this time, the spectrum or the like of the output light from the wavelength converter also approaches the desired value. Here, it is not necessary to know in advance the desired values such as the spectrum of the output light from the wavelength converter.

[0015] The control unit controls one or more of the pressure, temperature, current value, voltage value, position, and angle of both or one of the components of the light source unit and the wavelength conversion unit. Is preferred. In this case, the control of the light source unit and / or the wavelength conversion unit, which is not limited to the light modulation unit, further enhances the degree of freedom of control. The degree of freedom is further increased.

The invention's effect

The variable spectrum light generating device according to the present invention can increase the degree of freedom of the output light spectrum variable. Brief Description of Drawings

FIG. 1 is a block diagram showing a schematic configuration of a variable spectrum light generation device 1 according to a first embodiment.

FIG. 2 is a block diagram showing a schematic configuration of a variable spectrum light generating device 2 according to a second embodiment.

FIG. 3 is a block diagram showing a schematic configuration of a variable spectrum light generating device 3 according to a third embodiment.

FIG. 4 is a configuration diagram of a variable spectrum light generation device 4 of the embodiment.

FIG. 5 is a graph showing the intensity and phase of each wavelength component of the modulated light B in the variable spectrum light generator 4 of the embodiment.

FIG. 6 is a graph showing the intensity and phase of each wavelength component of output light C in the variable spectrum light generation device 4 of the example.

Explanation of symbols

[0018] 1-4: variable spectrum light generator, 11: light source unit, 12: light modulation unit, 13: wavelength conversion unit, 14: control unit, 15: measurement unit, 16: beam splitter, 17: detection unit, 21 ... Reflector, 22 ... Diffraction grating, 23 ... Cylindrical lens, 24 ... Spatial light modulator, 25 ... Cylindrical lens, 26 ... Diffraction grating, 27 ... Reflector, 31 ... Lens, 32 ... Nonlinear optical crystal, 33 · ·-Lens.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to the accompanying drawings. In the description of the drawings, the same elements will be denoted by the same reference symbols, without redundant description.

(First Embodiment)

First, a first embodiment of the variable spectrum light generator according to the present invention will be described.

. FIG. 1 is a block diagram showing a schematic configuration of the variable spectrum light generating device 1 according to the first embodiment. The variable spectrum light generator 1 shown in FIG.

12, a wavelength conversion unit 13 and a control unit 14.

The light source unit 11 outputs the fundamental light A having a constant phase relationship over a predetermined band. Therefore, it is possible to output the fundamental light A over a certain wide band (for example, a bandwidth of 10 nm or more). The light source unit 11 is preferably, for example, a laser light source that outputs a femtosecond light pulse as the fundamental light A.

The optical modulator 12 receives the fundamental light A output from the light source 11, modulates the parameters of the wavelength components of the light, and outputs the modulated light B. Here, it is preferable that the light modulating unit 12 modulates any one or more of the above parameters as amplitude, phase, polarization and wavefront. Further, the light modulation unit 12 modulates the parameters of each wavelength component of the light that is wavelength-branched by the light branching unit that spatially branches the light output from the light source unit 11 into wavelengths. It is preferable to include spatial light modulating means for outputting, and optical multiplexing means for multiplexing and outputting each wavelength component of light modulated by the spatial light modulating means.

The light modulation unit 12 is an element using an acousto-optic effect (A〇PDF; Acousto-Optic

It is also possible to configure a single Programmable Dispersion Filter). When an element utilizing the acousto-optic effect is used, it is possible to realize a compact system.

[0024] The wavelength conversion unit 13 receives the modulated light B output from the light modulation unit 12, converts the wavelength, and outputs light C obtained by the wavelength conversion. For example, it is preferable that the wavelength conversion unit 13 includes a nonlinear optical medium and emits light having a wavelength different from the wavelength of light incident on the nonlinear optical medium. Here, as the nonlinear optical medium, in addition to the nonlinear optical crystal, an optical waveguide having nonlinearity (for example, a photonic crystal optical fiber, a taper optical fiber, a hollow optical fiber, etc.), appropriate pressure conditions and temperature conditions A gas medium having: or a combination thereof is preferably used. In addition, when performing wavelength conversion using a nonlinear optical medium, generation of second harmonics and higher harmonics, generation of sum frequency and difference frequency, optical parametric oscillation, self-phase modulation, mutual phase modulation, etc. Can be used.

The control unit 14 modulates the parameters of each wavelength component of light (for example, any one of amplitude, phase, polarization, and wavefront, as described above, one or more) in the light modulation unit 12. Control. When the light modulator 12 includes the spatial light modulator as described above, it is sufficient for the controller 14 to control the spatial light modulator. [0026] The variable spectrum light generation device 1 according to the first embodiment operates as follows. The fundamental light A having a constant phase relationship over a predetermined band is output from the light source unit 11 and input to the optical modulation unit 12, where the parameters of each wavelength component are modulated. It is considered to be dimming B. The variable-length light B output from the optical modulation unit 12 is input to the wavelength conversion unit 13 where the wavelength conversion is performed, and the light C obtained by the wavelength conversion is output from the wavelength conversion unit 13.

Each wavelength component of the light C output from the wavelength conversion unit 13 receives contribution from almost all the wavelength components of the fundamental light A output from the light source unit 11. Therefore, the control of the control of the parameter of each wavelength component of light in the light modulation unit 12 by the control unit 14 allows each wavelength over a certain wide band in the modulated light B obtained by modulating the fundamental light A. The parameters of the components are set, whereby the spectrum of the output light C can be made variable. Since the degree of freedom in modulating the parameters of each wavelength component of the light in the light modulation unit 12 is large, the degree of freedom in changing the spectrum of the output light C is large.

[0028] When modulating the parameters of each wavelength component of light in the light modulation unit 12, an electric control mechanism that does not use a mechanical driving unit can be used. In this case, it is preferable to maintain the stability of the device, and it is possible to perform high-speed control.

[0029] Further, unnecessary wavelength components can be prevented from being generated during wavelength conversion from the fundamental light A to the output light C. The fundamental light A is used only for conversion of the output light C into the necessary wavelength components. Can be used. As a result, when the wavelength conversion efficiency is saturated in the state where the optical modulation is not performed, by performing the optical modulation, only the conversion from the fundamental light A to the required wavelength component in the output light C is performed with high efficiency. Can do it.

[0030] By using such a variable spectrum light generator 1, for example, in an application in which a bond of a photoreactive material is selectively cut, output light of one or more wavelengths corresponding to a band to be cut is used. While generating C, it is also easy to prevent the output light C from including components in the wavelength range corresponding to the band that the user does not want to cut. This allows the variable spectrum light generator 1 to be used for industrial applications such as photochemical reaction control.

[0031] The light C output from the variable spectrum light generation device 1 can include only a desired wavelength component. Therefore, if this output light C is used for reactions such as excitation, Generation of necessary heat can be suppressed.

The control unit 14 controls the pressure of both or one of the components of the light source unit 11 and the wavelength conversion unit 13 as shown by a broken line in FIG. It may be configured to control any one or more of force, temperature, current value, voltage value, position and angle. For example, when the wavelength of the fundamental light A output from the light source unit 11 is variable, control may be performed to change the wavelength of the fundamental light A. When the wavelength conversion unit 13 uses optical parametric oscillation, the direction of incidence of light on the nonlinear optical medium may be controlled. In this case, since the degree of freedom of control is further increased, the degree of freedom of changing the spectrum of the output light C is further increased.

(Second Embodiment)

Next, a second embodiment of the variable spectrum light generator according to the present invention will be described. FIG. 2 is a block diagram illustrating a schematic configuration of the variable spectrum light generation device 2 according to the second embodiment. The variable spectrum light generator 2 shown in this figure further includes a measurement unit 15 and a beam splitter 16 in addition to the light source unit 11, the light modulation unit 12, the wavelength conversion unit 13, and the control unit 14.

[0034] The beam splitter 16 splits the light C output from the wavelength conversion unit 13, transmits most of the light C, and reflects part of the light. The measuring unit 15 receives the light C arriving after being branched by the beam splitter 16, and measures the light C. Here, it goes without saying that a configuration in which the transmitted light and the reflected light of the beam splitter 16 are replaced may be employed. For example, a spectrometer can be used as the measuring unit 15, and the measuring unit 15 may be configured to measure the spectrum of the received light C in the entire band or a part of the band. A configuration for measuring the intensity at one or two or more wavelengths of interest may be used.

The control unit 14 controls the modulation of the parameter of each wavelength component of light in the light modulation unit 12 based on the measurement result by the measurement unit 15. At this time, the control unit 14 can also perform feedback control of the optical modulation unit 12 so that the measurement result by the measurement unit 15 approaches a desired value. As an algorithm for this control, for example, an optimization algorithm such as a simulated annealing method or a genetic algorithm is preferably used. If the control conditions are not complicated, set this control manually. It is also possible to carry out.

The variable outside light generator 2 according to the second embodiment operates as follows. The fundamental light A having a constant phase relationship over a predetermined band is output from the light source unit 11 and input to the optical modulation unit 12, where the parameters of each wavelength component are modulated. It is considered to be dimming B. The modulated light B output from the optical modulation unit 12 is input to the wavelength conversion unit 13 and wavelength-converted, and the light C obtained by the wavelength conversion is output from the wavelength conversion unit 13. A part of the light C output from the wavelength conversion unit 13 is branched by the beam splitter 16 and reaches the measurement unit 15, and the spectrum and the like are measured by the measurement unit 15. Based on the measurement result, the control unit 14 modulates the parameters of the respective wavelength components of the light in the light modulation unit 12 so that the spectrum of the output light C from the wavelength conversion unit 13 approaches a predetermined value. Controlled.

Therefore, the variable spectrum light generation device 2 according to the second embodiment can obtain the same effect as that obtained by the variable spectrum light generation device 1 according to the first embodiment. Even if the relationship between the modulation in the light modulating unit 12 and the spectrum of the output light C is not clear, or in some cases, the spectrum of the output light C from the wavelength conversion unit 13 is set to a desired value. You can get closer.

(Third Embodiment)

Next, a third embodiment of the variable spectrum light generator according to the present invention will be described. FIG. 3 is a block diagram illustrating a schematic configuration of the variable spectrum light generation device 3 according to the third embodiment. The variable spectrum light generation device 3 shown in this figure further includes a detection unit 17 in addition to the light source unit 11, the light modulation unit 12, the wavelength conversion unit 13, and the control unit 14.

The detection unit 17 detects a change in the object 9 irradiated with the light C output from the wavelength conversion unit 13 due to the irradiation. The control unit 14 controls the modulation of the parameter of each wavelength component of light in the light modulation unit 12 based on the detection result by the detection unit 17. In this control, for example, an optimization algorithm such as a simulated annealing method or a genetic algorithm is preferably used.

For example, in a case where a reaction product is generated in the target object 9 by irradiating the output light C to the target object 9 and it is desired to control the generation amount of the reaction product, Raw The control unit 14 controls the light modulation unit 12 so that the amount approaches the desired value, whereby the spectrum of the output light C from the wavelength conversion unit 13 can be made close to the desired value. At this time, the desired values of the output light C, such as the spectrum, need to be known in advance.

Next, an embodiment of the variable spectrum light generating apparatus according to the present invention will be described. FIG. 4 is a configuration diagram of the variable spectrum light generator 4 of the embodiment. The variable staple light generator 4 shown in this figure has a more specific configuration than the variable spectrum light generator 2 according to the above-described second embodiment. The variable spectrum light generation device 4 of the embodiment includes a light source unit 11, a light modulation unit 12, a wavelength conversion unit 13, a control unit 14, a measurement unit 15, and a beam splitter 16.

The light source unit 11 outputs the fundamental wave light A having a constant phase relationship over a predetermined band. In this embodiment, a titanium sapphire laser light source is used. The fundamental wave light A output from the titanium sapphire laser light source is a pulse light having a pulse width of 100 fs or less, a bandwidth of 10 nm or more, and a constant phase relationship over the band.

The light modulating unit 12 receives the fundamental wave light A output from the light source unit 11, modulates a meter of each wavelength component of the light, and outputs the modulated light B. In the present embodiment, the reflector includes a reflecting mirror 21, a diffraction grating 22, a cylindrical lens 23, a spatial light modulator 24, a cylindrical lens 25, a diffraction grating 26, and a reflecting mirror 27.

The reflecting mirror 21 receives the fundamental light A output from the light source unit 11 and causes the fundamental light A to be incident on the diffraction grating 22. The diffraction grating 22 is a reflection type, which receives the fundamental wave light A arriving from the reflecting mirror 21 and diffracts each wavelength component of the fundamental wave light A at a diffraction angle corresponding to the wavelength. Therefore, the wavelength division of the fundamental light A is realized according to the spatial direction. The cylindrical lens 23 spatially separates the wavelength components by condensing each wavelength component branched by the diffraction grating 22 in only one axial direction. The spatial light modulator 24 is arranged on the light condensing surface in a direction perpendicular to the light beam.

The spatial light modulator 24 is capable of adjusting the phase of transmitted light for each of a plurality of arranged pixels, and modulates the phase of light of each wavelength component input from the cylindrical lens 23. Then, the phase-modulated light of each wavelength component is output to the cylindrical lens 25. The phase modulation in the spatial light modulator 24 is given from the control unit 14. It is controlled based on an electrical control signal.

The cylindrical lens 25 receives the light of each wavelength component output from the spatial light modulator 24 and focuses the light on the diffraction surface of the diffraction grating 26. At this time, each wavelength component is collimated. The diffraction grating 26 is of a reflection type, receives light of each wavelength component output from the cylindrical lens 25 and collected, and diffracts each wavelength component at a diffraction angle corresponding to the wavelength. Accordingly, light is multiplexed. The reflecting mirror 27 receives the light multiplexed by the diffraction grating 26, reflects the light, and outputs the reflected light to the wavelength converter 13 as modulated light B.

In order to realize a desired operation, it is preferable that the diffraction grating 22, the cylindrical lens 23, the spatial light modulator 24, the cylindrical lens 25, and the diffraction grating 26 form a 4f system. Not limited.

[0048] The configuration of the light modulation unit 12 may have various modifications. For example, the diffraction gratings constituting the light demultiplexing means and the light multiplexing means may be either reflection type or transmission type, and the spatial light modulation element may be either reflection type or transmission type. Further, a concave mirror or the like may be used instead of the cylindrical lens 23, 25.

[0049] The wavelength conversion unit 13 receives the modulated light B output from the light modulation unit 12, converts the wavelength, and outputs the light C obtained by the wavelength conversion. Including lens 31, nonlinear optical crystal 32 and lens 33.

The lens 31 receives the modulated light B output from the light modulator 12, condenses the modulated light B, and makes the modulated light B enter the nonlinear optical crystal 32. The nonlinear optical crystal 32 is capable of generating a second harmonic having a frequency twice the frequency of the incident light. The modulated light B collected by the lens 31 is input to the Generates the second harmonic of The lens 33 receives the second harmonic generated by the nonlinear optical crystal 32, collimates the second harmonic, and outputs the collimated light as output light C.

The amplitude E (V) of the electric field of the output light C obtained as the second harmonic in the nonlinear optical crystal 32 in this way is equal to the amplitude E (V) of the electric field of the modulated light B incident on the nonlinear optical crystal 32. )

SH i is expressed by the following relational expression. Here, V is the light frequency, and the electric field amplitudes E (V) and E (V) of the output light C and the modulated light B are expressed as a function of the light frequency V.

SH i Has been.

[Equation 1]) = J (') ^-') '…

For example, suppose that the center frequency of the modulated light B incident on the nonlinear optical crystal 32 is 375 THz (the center wavelength is 800 nm), and the center frequency of the output light C obtained as the second harmonic in the nonlinear optical crystal 32 Is 750 THz. At this time, the electric field amplitude E (750) of the frequency 750 THz component of the output light C is equal to the frequency (375 + ν ′) ΤΗζ component of the modulated light B.

SH

Product of the electric field amplitude and the frequency (375-V ') of the ΤΗζ component (Ε (375 + ν') · Ε (375_ l i

V ')) is obtained by integrating V'.

Therefore, by modulating the phase relationship of each frequency component (each wavelength component) of the fundamental light A by the spatial light modulation element 24 of the light modulation unit 12, each frequency component (each wavelength component) of the modulated light B is By appropriately setting the phase relationship, the intensity of each frequency component (each wavelength component) of the output light C can be set to a desired value.

In order to modulate the fundamental light A to obtain the modulated light B, the number of control parameters is large and the degree of freedom of control is large. Therefore, the intensity of each frequency component (each wavelength component) of the output light C is increased such that the intensity of a certain frequency component of the output light C is increased while the intensity of another certain frequency component is decreased. Can be set freely. As described above, according to the present embodiment, it is possible to increase the degree of freedom in changing the spectrum of the output light C, as well as to make the spectrum of the output light C variable.

[0055] Actually, the phase modulation of the spatial light modulation element 24 for obtaining a desired spectrum of the output light C for which the relationship between the modulation in the light modulation unit 12 and the spectrum of the output light C is clear is clear. It may be difficult to find specific conditions in advance. Therefore, using a spectroscope as the measuring unit 15, the spectrum of the output light C is measured by the measuring unit 15, and the spatial light modulation is performed so that the spectrum of the output light C obtained by this measurement approaches a desired value. It is preferable that the phase modulation in the element 24 is feedback-controlled by the control unit 14.

For example, a personal computer is used as the control unit 14 that performs such control, As a control algorithm, an optimization algorithm such as a simulated annealing method or a genetic algorithm is preferably used. Further, once the specific conditions of the phase modulation in the spatial light modulator 24 for obtaining the output light c having a certain spectrum are obtained, then, in order to obtain the output light C having the same spectrum, Phase modulation in the spatial light modulator 24 may be performed under the determined specific conditions.

Next, a simulation result of the modulated light B and the output light C in the variable spectrum light generator 4 of the embodiment will be described. FIG. 5 is a graph showing the intensity and phase of each wavelength component of the modulated light B in the variable spectrum light generation device 4 of the embodiment, and graphs (a) and (b) show the intensity and phase of each wavelength component, respectively. ing. FIG. 6 is a graph showing the intensity and phase of each wavelength component of the output light C in the variable spectrum light generator 4 of the embodiment, and graphs (a) and (b) show the respective wavelength components. Shows the intensity and phase.

Here, in the output light C, the components at the wavelengths of 397.7 nm, 400.0 nm, and 401.2 nm are increased, and the intensity of the other wavelength components is decreased. The simulated annealing method was used as the optimization algorithm. As a result, by setting the intensity distribution and the phase distribution of the modulated light B as shown in the graphs (a) and (b) of FIG. 5, the output light C is represented by an arrow in the graph (a) of FIG. As shown, it had an intensity peak at the desired three wavelengths.

Note that the broken line in the graph (a) of FIG. 6 represents the intensity distribution of the output light C obtained when the phases of all the wavelength components of the modulated light B are all equal. It indicates the maximum strength that can be obtained from the component. Also, in the simulations shown in FIGS. 5 and 6, the intensity distribution of the output light C is set to a desired value, but the phase distribution of the output light C can be set to a desired value. In addition, the simulations shown in FIGS. 5 and 6 were to modulate the fundamental light A to obtain a modulated light B, but to modulate the fundamental light A to obtain an output light C having a desired spectrum. In order to realize this, any one of the intensity, polarization, and wavefront of each wavelength component of the fundamental wave light A may be modulated, and the phase, intensity, polarization, and wavefront of each wavelength component of the fundamental wave light A may be modulated. Two or more may be modulated.

The variable spectrum light generator according to the present invention can be suitably used as a light source in, for example, optical coherence tomography (OCT). [0061] The OCT irradiates a multi-scattering object (eg, an eyeball) such as a living body with a low-coherent light having a wide spectrum width and highly sensitively reflects back-scattering light generated inside the multi-scattering object. This is a method of measuring the three-dimensional tomographic image of the multiple scattering object by detecting it (for example, the document “Satoshi Sato, et al., Basics of Optical Coherence Tomography”, Optics, Vol. 32, No. 4, p. 268) 1 p. 274, 2003 ”). In this OCT, by preparing in advance a light source that outputs light suitable for the object to be measured, which is a multiple scattering object, the light output from the light source is not subjected to any special modulation or the like. In general, measurement is performed by irradiating an object to be measured. The resolution of the measurement in the depth direction of the measurement object depends on the coherence length of the irradiation light. OCT uses light in the wavelength range of 0.7 μm to 1.3 μm, which is the spectroscopic window region of living organisms with relatively low absorption.

[0062] In the variable spectrum light generating device according to the present invention, a laser light source that outputs an optical fiber (fundamental wave light A) having a center wavelength of 1.56 xm including an optical fiber to which an Er element and a Yb element are added as an optical amplification medium. For example, an IMRA model B-150) is used as the light source unit 11, and a light source including a nonlinear optical medium that generates the second harmonic is used as the wavelength conversion unit 13. At this time, the output light C output from the variable spectrum light generator has a center wavelength of 0.78 μm and is included in the biological spectroscopic window region.

In the variable spectrum light generating device having such a configuration, each of the light source unit 11 and the wavelength conversion unit 13 can be downsized, so that it can be downsized as a whole. The spectrum of the output light C can be changed with a high degree of freedom in the spectroscopic window region. Furthermore, this variable spectrum light generator has the following advantages when used in OCT.

As a first advantage, the coherence length of the output light C output from the variable spectrum light generator can be adjusted. Generally, the coherence length is shorter as the spectrum width is wider, and the coherence length is longer as the spectrum width is smaller. When the variable spectrum light generator according to the present invention is used, the coherence length of the output light C is also variable because the spectrum width of the output light C is variable. Note that in order to shorten the coherence length of the output light C, it is necessary to increase the sturtle width of the output light C. For this purpose, the nonlinear optical medium included in the wavelength conversion unit 13 is required. It is preferable to use a photonic crystal optical fiber with high nonlinearity It is.

[0065] If the coherence length of the light applied to the measurement target is short, when the measurement target is long in the depth direction, a long sweep time is required to measure the entire measurement target. Absent. In addition, if a rough sweep is performed with a high resolution, a situation may occur in which a structure in the object to be measured cannot be detected. Therefore, in order to perform a coarse sweep, the resolution must be reduced.

[0066] By using the variable spectrum light generator according to the present invention, the coherence length of the output light C can be changed by changing the spectrum width of the output light C, and therefore, the resolution can also be changed. Power S can. In addition, by changing the resolution, the roughness of the sweep can be adjusted.For example, a rough sweep with a low resolution can be used to measure the entire measurement object, and a specific structure that needs to be measured in detail can be specified. The site can be measured by performing a fine sweep with high resolution. This can increase the dynamic range of OCT measurement. This corresponds to a zoom in the depth direction of the measurement target.

At this time, the horizontal zoom of the measurement object can be performed at the same time. In other words, when focusing the output light C output from the variable outside light generator and irradiating the object to be measured, performing long focal focusing requires a large focusing diameter. And the Rayleigh length (confocal length) also increases, so that a uniform beam diameter can be achieved over a relatively long distance in the depth direction. Conversely, when short focal point focusing is performed, the lateral resolution is increased because the focusing diameter is small, but the distance at which a uniform beam diameter is realized in the depth direction is shortened. Therefore, after performing a long-distance sweep in both directions under the condition of low resolution in both the depth direction and the lateral direction, perform detailed measurement of a specific part under the condition of high resolution in both the depth direction and the lateral direction. be able to.

As a second advantage, the coherence of the output light C output from the variable spectrum light generation device can be variously adjusted. In the present invention, the shape of the output light C (wavelength and number of intensity peaks) can be freely changed. From this, the optical coherence function can be changed freely. The optical coherence function indicates the degree of the degree of coherence for each delay time difference (for example, the reference "Kazuo Hotate," Application of synthesized coherence mnction to distributed optical sensing, Measurement Science and Technology, Vol.13, No.11, pp.1746-1755 (2002) ").

[0069] Then, by changing the optical coherence function of the output light C, the depth component that contributes to the OCT interference signal changes. For example, when an object to be measured exists near a part where the light reflection at the interface of the measurement object is large, the spectrum of the output light C is adjusted by adjusting the spectrum of the output light C so that the reflection from the interface does not contribute to the interference signal. The measurement of the object can be performed effectively.

[0070] As a third advantage, it is easy to specify the constituent substance of the measurement object. What kind of substance the measurement object is made of can be known by performing spectroscopic measurement. Here, in OCT, scattering, absorption-reflection, and the like change complicatedly according to the size and shape of the measurement target. Therefore, sufficient information cannot be obtained simply by irradiating the object to be measured with light having a fixed wavelength and performing spectroscopic measurement, as is usually done.

On the other hand, if the variable spectrum light generating device according to the present invention is used, the vector shape (wavelength and number of intensity peaks) of the output light C can be freely changed. Therefore, for example, by setting the output light C to have a sharp intensity peak at two wavelengths, it is possible to easily perform an operation of obtaining a ratio of the interference signals of the two wavelengths. Then, information peculiar to the constituent substance of the measurement object can be obtained from the interference signal, thereby making it possible to specify the constituent substance.

[0072] As a fourth advantage, it is possible to electrically change the spectrum of light irradiating the object to be measured. Changing the wavelength of light usually has the problem of slow modulation of both the force made by mechanical adjustment and the temperature adjustment, and it is not possible to realize a complicated spectrum. In addition, mechanical adjustments require moving parts in the device, which impair overall stability. In particular, in OCT, it is necessary to perform sweeping in both the depth direction and the lateral direction of the measurement object, so that it is not practical to use a method that requires a long time to operate the wavelength. However, in the variable spectrum light generation device according to the present invention, the spectrum of the output light C can be changed electrically at a high speed, so that the measurement time by the OCT can be reduced.

[0073] A fifth advantage is that the three-dimensional tomographic image obtained by the OCT is optimized to be optimal. The spectrum of the force light c can be feedback-controlled. For example, it is difficult to determine in advance the spectrum condition of the irradiation light for reducing strong reflection from a position at a specific distance. However, in the variable spectrum light generating apparatus according to the present invention, even if the conditions under which the optimum measurement can be performed are not known in advance, the output is controlled so that the interference signal is optimum while referring to the measurement result. The spectrum of light C can be changed.

Industrial applicability

INDUSTRIAL APPLICABILITY The variable spectrum light generation device of the present invention can be used as a variable spectrum light generation device capable of increasing the degree of freedom in changing the output light spectrum shape.

Claims

The scope of the claims

[1] a light source unit that outputs light having a predetermined wavelength band and a phase relationship between wavelength components that is temporally constant;

An optical modulator that receives light output from the light source, modulates parameters of each wavelength component of the light, and outputs the modulated light;

A wavelength converter that inputs the light output from the light modulator, converts the wavelength, and outputs the light obtained by the wavelength conversion;

A control unit that controls modulation of parameters of each wavelength component of light in the light modulation unit.

2. The variable spectrum light generation device according to claim 1, wherein the light modulator modulates any one or more of amplitude, phase, polarization, and wavefront as the parameter.

[3] The light modulation unit comprises:

Light demultiplexing means for spatially branching the light output from the light source unit, and spatial light modulation means for modulating and outputting parameters of each wavelength component of the light wavelength-branched by the light demultiplexing means. ,

Optical multiplexing means for multiplexing and outputting each wavelength component of the light modulated by the spatial light modulation means,

3. The variable spectrum light generator according to claim 1, further comprising:

4. The variable spectrum light generating device according to claim 1, wherein the light modulating unit comprises an element utilizing an acousto-optic effect.

[5] The claim according to claim 11, wherein the wavelength conversion unit includes a nonlinear optical medium, and emits light having a wavelength different from the wavelength of light incident on the nonlinear optical medium from the nonlinear optical medium. 5. The variable spectrum light generator according to any one of the items 4 to 4.

[6] The nonlinear optical medium is characterized by being constituted by one or more of a nonlinear optical crystal, an optical waveguide having nonlinearity, and a gas medium having appropriate pressure and temperature conditions. The variable spectrum light generator according to claim 5.

[7] The apparatus further includes a measurement unit that measures light output from the wavelength conversion unit, The control unit controls the modulation of the parameter of each wavelength component of light in the light modulation unit based on the measurement result by the measurement unit.

7. The variable spectrum light generating device according to claim 1, wherein:

[8] The image processing apparatus further includes a detection unit that detects a change accompanying the irradiation of the object irradiated with the light output from the wavelength conversion unit,

The controller feedback-controls the modulation of the parameter of each wavelength component of light in the light modulator based on a detection result by the detector.

8. The variable spectrum light generating device according to claim 4, wherein the variable spectrum light generating device includes:

[9] The control unit may be one or more of a pressure, a temperature, a current value, a voltage value, a position, and an angle of at least one of the light source unit and the wavelength conversion unit. 19. The variable spectrum light generator according to claim 18, wherein the variable spectrum light generator is controlled.