JP2009031238A - Optical coherence tomography device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical coherence tomography device capable of rapidly and continuously scanning the wavelength of a light source having a narrow band spectrum, in a wide band without carrying out signal processing for calibration to an optical CT signal. <P>SOLUTION: The optical coherence tomography device includes a wavelength scanning laser light source 10 for outputting laser light scanning the wavelength temporally by varying the resonator length of at least one of two Fabry-Perot resonators 13A, 13B periodically within a predetermined range to allow the Fabry-Perot resonators 13A, 13B to function as narrow band variable wavelength filters capable of varying the selection wavelength by vernier effect; an interference optical system 20 for branching the output laser light into reference light and observation light irradiating an observation object 60 and generating interference light between the reference light and the reflection light from the observation object 60; and a signal processing section 50 for receiving the interference light obtained from the interference optical system 20, converting it into an electric signal and calculating the optical tomography information of the observation object 60. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an optical coherence tomography apparatus having a wavelength scanning light source that temporally scans a wavelength.

  In recent years, with the advancement of medical techniques such as endoscopic treatment, a diagnostic method that performs non-intrusive and real-time diagnosis of a pathological tissue is desired. Conventionally, for example, an electronic endoscope using a CCD, imaging using CT, MRI, and ultrasonic waves are used as diagnostic methods. The electronic endoscope is limited to observation of the surface of a living body, and the latter diagnostic imaging system has a technical limit in observing with a resolution of micron order.

  In addition, as one of the non-destructive tomographic techniques used in the medical field, etc., optical tomography method using optically low-coherence light as a probe (probe) (OCT: Optical Coherence Tomography) It has been known. Since OCT uses light as a measurement probe, OCT has an advantage that it can measure the refractive index distribution, spectral information, polarization information (birefringence distribution), etc. of the object to be measured (see, for example, Patent Document 1).

  The OCT 800 is based on a Michelson interferometer, and its principle is shown in FIG.

  The light emitted from the light source 801 is collimated by a collimator lens 802 and then split into reference light and object light by a beam splitter 803. The object light is collected on the measurement object 805 by the objective lens 804 in the object arm, scattered and reflected there, and then returns to the objective lens 804 and the beam splitter 803 again.

  On the other hand, the reference light is reflected by the reference mirror 807 after passing through the objective lens 806 in the reference arm, and returns to the beam splitter 803 through the objective lens 806 again. The object light and the reference light that have returned to the beam splitter 803 in this way are incident on the condenser lens 808 together with the object light, and are collected on the photodetector 809 (photodiode or the like).

  The light source 801 of the OCT 800 uses a light source of temporally low coherence light (light emitted from the light source at different times is extremely difficult to interfere). In a Michelson interferometer using temporally low coherence light as a light source, an interference signal appears only when the distance between the reference arm and the object arm is approximately equal. As a result, when the intensity of the interference signal is measured by the photodetector 809 while changing the optical path length difference (τ) between the reference arm and the object arm, an interference signal (interferogram) for the optical path length difference is obtained.

  The shape of the interferogram shows the reflectance distribution in the depth direction of the measured object 805, and the structure in the depth direction of the measured object 805 can be obtained by one-dimensional axial scanning. Thus, in the OCT 800, the structure in the depth direction of the measurement object 805 can be measured by optical path length scanning.

  In addition to the scanning in the axial direction, a two-dimensional cross-sectional image of the object to be measured can be obtained by performing a two-dimensional scanning by adding a horizontal mechanical scanning. The scanning device that performs the horizontal scanning includes a configuration in which the object to be measured is directly moved, a configuration in which the objective lens is shifted while the object is fixed, and a pupil of the objective lens while the object to be measured and the objective lens are fixed. The structure etc. which rotate the angle of the galvanometer mirror in the surface vicinity are used.

  The basic OCT has been developed as follows: a wavelength scanning type OCT that obtains a spectral interference signal by scanning the wavelength of a light source, and a spectral domain OCT that obtains a spectral signal using a spectroscope. The latter is a Fourier domain OCT. There is.

  As described in Non-Patent Document 1, the wavelength scanning type OCT irradiates a living body with light, continuously changes the wavelength of the irradiation light, and returns from the reference light and a different depth in the living body. This system obtains a tomographic image by causing light to interfere with an interferometer and analyzing the frequency component of the interference signal. This technology is expected as an advanced system because it can construct a tomographic image with extremely high resolution from frequency analysis of signals from inside the object. The wavelength scanning type OCT is suitable for practical use such as an endoscope in that it has high measurement sensitivity and is resistant to dynamic noise. Here, the wider the wavelength scanning band of the irradiated light, the higher the frequency analysis band, so that the resolution in the depth direction increases.

  In the Fourier domain OCT, the wavelength spectrum of the reflected light from the object to be measured is acquired with a spectrometer (spectrum spectrometer), and Fourier transform is performed on this spectrum intensity distribution, so that the real space (OCT signal space) is obtained. This Fourier domain OCT does not need to scan in the depth direction, and can measure the cross-sectional structure of the object to be measured by scanning in the x-axis direction.

  Like the Fourier domain OCT, the polarization-sensitive OCT acquires the wavelength spectrum of the reflected light from the object to be measured with a spectrum spectrometer. For example, horizontal linearly polarized light, vertical linearly polarized light, 45 ° linearly polarized light, and circularly polarized light passed through a four-wavelength plate, etc. Only the horizontally polarized component is incident on the spectrum spectrometer to cause interference, and only the component having a specific polarization state of the object light is extracted and subjected to Fourier transform. This polarization sensitive OCT also does not need to be scanned in the depth direction.

  Conventionally, as a wavelength scanning type fiber laser light source capable of continuously scanning a wavelength of a light source having a narrow band spectrum in a wide band at a high speed, a gain medium having an oscillation wavelength gain and an optical circulator are provided in an optical fiber loop. The light extracted by the optical circulator is magnified by the collimator lens, the polygon mirror provided on the optical axis is rotated, and the light reflected by the polygon mirror is reflected in the same direction as the incident light. A wavelength scanning fiber laser light source having a Littrow diffraction grating has been proposed. In this wavelength scanning fiber laser light source, the selection wavelength changes depending on the incident angle to the diffraction grating, and the selectivity increases by two incidences. Therefore, even if the polygon mirror is rotated at a high speed and the selection wavelength is changed, it is narrow. The oscillation wavelength can be changed in the band (see, for example, Patent Document 2).

  A wavelength tunable light source using a ring laser using an erbium-doped fiber has also been proposed. For example, as shown in FIG. 40, the wavelength tunable light source 2000 uses a fiber amplifier 2012 using an erbium-doped fiber (EDF) as a gain medium, and a tunable bandpass filter 2014 is provided in the optical fiber loop 2011. The wavelength of the laser light extracted through the optical coupler 2015 connected to the optical fiber loop 2011 is varied by changing the wavelength of the bandpass filter 2014. In this case, since the resonator length of the optical fiber loop 2011 can be increased to, for example, 30 m, the longitudinal mode interval can be reduced. Therefore, the influence of the mode hop can be eliminated without changing the resonator length. Therefore, strictly speaking, it is not single mode oscillation, but it is possible to perform quasi-continuous wavelength tuning only by changing the selected wavelength of the bandpass filter 2014 (see, for example, Non-Patent Document 2).

  Further, in the type in which the wavelength variable mechanism is provided in the laser element, a DBR-LD (Distributed Bragg reflector laser diode) in which an active region that generates gain and a DBR region that generates reflection by a diffraction grating are formed in the same laser element. ) Has been proposed. The wavelength variable range of this DBR-LD is about 10 nm at the maximum. In addition, a DBR-LD using a non-uniform diffraction grating in which an active region that generates a gain and a DBR region sandwiching the active region between the front and the rear is formed in the same laser element has been proposed. In the front and rear DBR regions, a large number of reflection peaks are generated by the non-uniform diffraction grating, and the interval between the reflection peaks is slightly shifted between the front and the rear. With this structure, a so-called “vernier effect” can be obtained, so that an extremely wide wavelength variation is possible. In the DBR-LD using this non-uniform diffraction grating, wavelength variable operation exceeding 100 nm is realized. In the DBR-LD using this non-uniform diffraction grating, a wavelength variable operation exceeding 100 nm and a quasi-continuous wavelength variable operation of 40 nm are realized (for example, see Patent Document 3).

JP 2007-101365 A JP 2006-237359 A JP 2006-278770 A Handbook of Optical Coherence Tomography, p41-43, Mercel Dekker, Inc. 2002 YAMASHITA ET AL., IEEE JOURAL ON SELECTED TOPICS IN QUANTUM ELECTRONICS, VOL.7, NO.1 JANUARY / FEBRUARY 2001, PP41 ~ 43

  By the way, the Fourier transform of the time signal in the wavelength scanning OCT becomes a scattering distribution in the depth direction of the measurement object, that is, an optical tomographic image. In order to obtain an accurate optical tomographic image, the original signal needs to be equally spaced with respect to the wave number of light (2π / wavelength).

  In general, the wavelength scanning light source and the spectroscope are often designed linearly with respect to the wavelength. Moreover, its linearity was not perfect and calibration was difficult. If this calibration and conversion to wave number are not performed, the resolution of the obtained optical tomographic image is significantly reduced, and the linearity in the depth direction is lost. Therefore, it is essential to calibrate the output of the scanning characteristic of the light source to the wave number.

  These wavelength scanning light sources were calibrated in advance by measuring the time characteristics of the wavelength scanning light source (using equipment such as an oscilloscope or an interference filter, or by the method of Patent Document 1, etc. Interference signals are rearranged at equal intervals with respect to the wave number (2π / wavelength) of light, and signal processing is performed, and it takes time to output an image for the time required for signal processing.

  Further, in general, the wavelength scanning light source is wavelength scanning by a mechanical wavelength selection element, and there is a limit to high speed, and at most 20 kHz is realized. Therefore, it took several seconds to obtain a 3D OCT signal.

  In addition, when using a tunable light source as a light source for an analyzer, it is necessary to change the wavelength at high speed and to narrow the width of the oscillation spectrum, and characteristics corresponding to this are also required for the bandpass filter. Is done. For example, when high-speed wavelength scanning becomes available in optical coherence tomography (OCT), dynamic analysis such as high-speed image processing, blood flow observation, and oxygen saturation concentration change can be performed. Is required.

  As a product adopting the disclosed technique of Patent Document 2, for example, Santec Corporation provides a wavelength scanning laser light source HSL-2000 capable of repeatedly scanning wavelengths at a scan rate of a maximum of 20 kHz. However, at present, 20 kHz is only practically used as the wavelength scanning period.

  This requires several seconds to obtain a stereoscopic image by optical coherence tomography (OCT).

  Further, as described in Patent Document 3, in the DBR-LD, by performing carrier injection in the DBR region, the refractive index in this portion is changed to realize the wavelength variable operation. For this reason, if crystal defects grow due to current injection, the rate of change in the refractive index with respect to current injection varies significantly, so that it is difficult to maintain laser oscillation at a stable wavelength over a long period of time. Further, with the current compound semiconductor process technology, an inch-up of 2 inches or more is impossible. For this reason, it is difficult to reduce the price of the laser element that has become complicated and large in size. However, if it is a small element of 1 mm or less, the longitudinal mode interval is large, for example, 100 GHz, and if the wavelength of the tunable filter that changes the wavelength at high speed is simply changed, the wavelength tunable operation is performed every longitudinal mode interval. It becomes. Such a large and discrete wavelength tunable operation is too large for application to optical coherence tomography. Furthermore, if the wavelength of the tunable filter is simply changed, it becomes unstable between the longitudinal modes. For example, discontinuous mode hops may occur between modes, or oscillation may occur in multiple modes.

  Furthermore, the disclosed technique of Patent Document 2 is a configuration in which a plurality of optical resonators are adopted as a wavelength filter by a ring-type optical resonator, and the wavelength can be varied by the vernier effect, but the wavelength can be varied by a heater. Not suitable for high speed scanning. In addition, it is difficult to adjust the resonator lengths of a plurality of ring-type optical resonators on the same substrate. Further, since the entire length of the laser including the ring type optical resonator is short, simply changing the wavelength of the wavelength tunable filter makes it unstable between the longitudinal modes. For example, discontinuous mode hops may occur between modes, or oscillation may occur in multiple modes.

  Therefore, in view of the conventional problems as described above, the object of the present invention is to perform a high-speed wavelength of a light source having a narrow-band spectrum without performing signal processing for calibration on the optical CT signal, Another object of the present invention is to provide an optical coherence tomography apparatus capable of continuous scanning.

  Other objects of the present invention and specific advantages obtained by the present invention will become more apparent from the description of embodiments described below.

  An optical coherence tomography device according to the present invention includes a resonator length of at least one Fabry-Perot resonator of two Fabry-Perot resonators having FSR (Free Spectral Range) provided in a laser oscillation optical path and close to each other. By periodically changing the frequency in a certain range, the two Fabry-Perot resonators function as narrow-band tunable filters capable of varying the selected wavelength by the vernier effect, and the wavelengths are scanned in time. A wavelength scanning light source that outputs laser light, and a laser beam output from the wavelength scanning light source is split into reference light and observation light that irradiates the observation object, and reflection of the observation light that irradiates the observation object An interference optical system that generates interference light between the light and the reference light, and the interference light obtained by the interference optical system is received and converted into an electrical signal, and the light of the object to be observed Signal processing means for calculating tomographic image information.

  In the optical coherence tomography device according to the present invention, the wavelength scanning light source is calibrated so that, for example, the wave number of the laser beam being scanned is linear with respect to time.

  In the optical coherence tomography device according to the present invention, the wavelength scanning light source includes, for example, an optical fiber loop serving as the laser oscillation optical path, an optical amplifier provided in the optical fiber loop and having a gain at an oscillation wavelength, and the above Two Fabry-Perot resonators provided in the optical fiber loop and having close free spectral ranges (FSRs), an optical element connected to the optical fiber loop and extracting a part of the light passing through the optical fiber loop, and And a resonator length controller that periodically changes the resonator length of at least one of the two Fabry-Perot resonators having adjacent FSRs within a certain range.

  Further, in the optical coherence tomography device according to the present invention, the Fabry-Perot resonator in which the resonator length is periodically changed in a certain range by the resonator length control unit is, for example, a Fabry-Perot electric having a structure with an electrode attached. An optical modulator is used, and light passing therethrough is modulated by a periodic scanning signal given by the resonator length controller.

  Also, in the optical coherence tomography device according to the present invention, the two Fabry-Perot resonators having the adjacent FSRs are each composed of, for example, a Fabry-Perot electro-optic modulator, and are adjusted to the adjacent FSRs by temperature control. Yes.

  Also, in the optical coherence tomography device according to the present invention, the resonator length control unit, for example, provides the two Fabry-Perot resonators having the adjacent FSRs with mutually inverted scanning signals to provide each Fabry-Perot resonance. The resonator length of the resonator is changed reciprocally.

  Further, in the optical coherence tomography device according to the present invention, the resonator length control unit, for example, superimposes a control voltage on a scanning signal to superimpose a light passing through the two Fabry-Perot resonators having the adjacent FSRs. Control the center wavelength.

  Further, in the optical coherence tomography apparatus according to the present invention, for example, the optical amplifier is provided in each subsequent stage of the two Fabry-Perot resonators.

  In the optical coherence tomography device according to the present invention, for example, the light is separated by the direction or polarization of the light passing through the optical fiber loop, and each of the two Fabry-Perot resonators is separated by one optical amplifier. Optical amplification is performed at a later stage.

  In the optical coherence tomography device according to the present invention, the wavelength scanning light source may be configured such that the resonator length control unit adjusts a waveform of the periodic scanning signal given to the Fabry-Perot resonator. Is calibrated so that the wave number of the laser light taken out via is linear with respect to time.

  Further, in the optical coherence tomography apparatus according to the present invention, the laser oscillation optical path includes, for example, two Fabry Peripheries in which electro-optic crystals are incorporated in a Fabry-Perot resonator in a space having FSR (Free Spectral Range) close to each other. A Perot electro-optic modulator, an optical amplifier having a gain at an oscillation wavelength, and an optical element for extracting output light are connected by an optical fiber.

  Further, in the optical coherence tomography device according to the present invention, the two Fabry-Perot electro-optic modulators may each be, for example, a ring-type resonance that obtains a ring-type resonance with a Fabry-Perot resonator containing an electro-optic crystal. It consists of a Fabry-Perot electro-optic modulator.

  Further, in the optical coherence tomography apparatus according to the present invention, the two Fabry-Perot resonators may be, for example, V-type resonant Fabry-Perots, each of which obtains a V-type resonance with a Fabry-Perot resonator containing an electro-optic crystal. It consists of an electro-optic modulator.

  Further, in the optical coherence tomography device according to the present invention, the two Fabry-Perot electro-optic modulators each have, for example, the curvature of each concave mirror so that the Fabry-Perot resonator containing the electro-optic crystal is confocal. Consists of a set confocal Fabry-Perot electro-optic modulator.

  Also, in the optical coherence tomography device according to the present invention, the Fabry-Perot electro-optic modulator is formed, for example, by arranging two electro-optic crystals so that the C-axis is orthogonal between the concave mirrors constituting the Fabry-Perot resonator. .

  In the optical coherence tomography device according to the present invention, the wavelength scanning light source may be configured to adjust the waveform of the periodic scanning signal that the resonator length control unit applies to the Fabry-Perot resonator, for example. Calibration is performed so that the wave number of the laser light extracted through the optical element is linear with respect to time.

  Also, in the optical coherence tomography device according to the present invention, the laser oscillation optical path includes, for example, a Fabry-Perot electro-optic modulator in which an electro-optic crystal is contained in a spatial Fabry-Perot resonator and an optical amplifier having a gain in oscillation wavelength. And a polarization conversion element that rotates the polarization direction of the light emitted from the Fabry-Perot electro-optic modulator by 90 ° and an optical element for extracting output light, and the Fabry-Perot electro-optic modulator includes: For example, it functions as two Fabry-Perot resonators having FSR (Free Spectral Range) close to each of the polarized light components orthogonal to each other, and by the periodic scanning signal given by the resonator length control unit, Each of the polarized light components orthogonal to each other is modulated.

  Further, in the optical coherence tomography device according to the present invention, the Fabry-Perot electro-optic modulator may be, for example, a ring-type resonant Fabry-Perot electro-optic that obtains a ring-type resonance with a Fabry-Perot resonator including the electro-optic crystal. It consists of a modulator.

  Further, in the optical coherence tomography apparatus according to the present invention, the Fabry-Perot resonator is, for example, a V-type resonant Fabry-Perot electro-optic modulator configured to obtain a V-type resonance with a Fabry-Perot resonator including the electro-optic crystal. Consists of.

  Further, in the optical coherence tomography device according to the present invention, the Fabry-Perot electro-optic modulator is, for example, a confocal type in which the curvature of each concave mirror is set so that the Fabry-Perot resonator containing the electro-optic crystal is confocal. It consists of a Fabry-Perot electro-optic modulator.

  Also, in the optical coherence tomography device according to the present invention, the Fabry-Perot electro-optic modulator is formed, for example, by arranging two electro-optic crystals so that the C-axis is orthogonal between the concave mirrors constituting the Fabry-Perot resonator. .

  In the optical coherence tomography device according to the present invention, the wavelength scanning light source may be configured to adjust the waveform of the periodic scanning signal that the resonator length control unit applies to the Fabry-Perot resonator, for example. Calibration is performed so that the wave number of the laser light extracted through the optical element is linear with respect to time.

  In the optical coherence tomography device according to the present invention, each of the two Fabry-Perot electro-optic modulators is a ring-type resonant Fabry-Perot that obtains a ring-type resonance with a Fabry-Perot resonator containing an electro-optic crystal. It consists of an electro-optic modulator.

  Furthermore, in the optical coherence tomography device according to the present invention, each of the two Fabry-Perot electro-optic modulators includes a polarization-independent ring-type resonant Fabry-Perot electro-optic modulator, and the wavelength scanning light source includes: A polarization-independent optical amplifier having a gain at the oscillation wavelength is provided in the laser oscillation optical path.

  An optical coherence tomography device according to the present invention includes a broadband light source and two Fabry-Perot resonators having free spectral ranges (FSRs) close to each other provided in an optical path of light emitted from the broadband light source. A narrow-band tunable filter capable of changing the selected wavelength of the two Fabry-Perot resonators by the vernier effect by periodically changing the resonator length of at least one of the Fabry-Perot resonators in a certain range. A wavelength scanning light source including a wavelength variable filter unit that outputs light whose wavelength is scanned temporally, and irradiates the reference light and the object to be observed with the laser light output from the wavelength scanning light source. An interference optical system that branches into observation light and generates interference light between the reflected light of the observation light irradiated on the object to be observed and the reference light; and the interference optical system Signal processing means for receiving the interference light obtained by the above and converting it into an electrical signal and calculating optical tomographic image information of the object to be observed.

  According to the present invention, two Fabry-Perot resonators function as a narrow-band wavelength tunable filter that can vary the selected wavelength by the vernier effect, and output light with a wavelength scanned at high speed. By using a wavelength scanning light source capable of scanning, high-speed OCT signal acquisition is possible, and by adjusting the waveform of the periodic scanning signal given to the Fabry-Perot resonator by the resonator length control unit, Since the wave number (2π / wavelength) of the light extracted via the optical element is calibrated so as to be linear with respect to time, the obtained interference signal can be obtained with respect to the wave number (2π / wavelength) of the light, etc. Since it is not necessary to rearrange and arrange signal intervals, it is not necessary to perform signal processing for calibration on the OCT signal, and the wavelength of the light source having a narrow-band spectrum is widened. It is possible to provide an optical coherence tomography apparatus capable of continuous scanning at a high speed in a band.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Needless to say, the present invention is not limited to the following examples, and can be arbitrarily changed without departing from the gist of the present invention.

  An optical coherence tomography apparatus 100 according to the present invention has a basic configuration as shown in FIG. 1, a wavelength scanning laser light source 10, and interference optics connected to the wavelength scanning laser light source 10 via an optical fiber 1. A system 20, a scanning optical system 30 connected to the interference optical system 20 via an optical fiber 2, a reference optical system 40 connected to the interference optical system 20 via an optical fiber 3, and the interference optical system 20 The signal processing unit 50 is connected via an optical fiber 4.

  The wavelength scanning laser light source 10 in the optical coherence tomography apparatus 100 is configured to vary the selection wavelength of the two Fabry-Perot resonators previously proposed by the present applicant, for example, as Japanese Patent Application No. 2007-018168, by the vernier effect. It functions as a tunable narrow-band tunable filter and outputs laser light whose wavelength is scanned temporally, the details of which will be described later.

  The interference optical system 20 branches the laser light output from the wavelength scanning laser light source 10 into reference light and observation light for irradiating the observation object 60, and reflected light of the observation light irradiated to the observation object 60. For example, the laser beam output from the wavelength scanning laser light source 10 includes a fiber coupler 21 through which the laser beam is incident.

  In the interference optical system 20, an observation light that sends the laser light incident from the wavelength scanning laser light source 10 through the optical fiber 1 to the scanning optical system 30 through the optical fiber 2 in the fiber coupler 21, and the optical fiber 3. And the reference light to be sent to the reference optical system 40 via the optical fiber 2, the observation light is sent to the scanning optical system 30 via the optical fiber 2, and the reference light is sent to the reference optical system 40 via the optical fiber 3. Interfering light between the reflected light of the observation light irradiated from the system 30 through the optical fiber 2 and the reference light returned from the reference optical system 30 through the optical fiber 3 is converted into the fiber coupler 21. The generated interference light is transmitted to the signal processing unit 50 through the optical fiber 4.

  The scanning optical system 30 spatially scans the observation light branched in the interference optical system 20 and irradiates the object 60 to be observed, and returns the reflected light from the object 60 to the interference optical system 20. The lens 31 includes a scanning mirror 32 and a lens 33 that can change the angle.

  Observation light branched by the fiber coupler 21 in the interference optical system 20 and sent to the scanning optical system 30 via the optical fiber 2 is observed via a lens 31, a scanning mirror 32 having a variable angle, and a lens 33. The reflected light that is irradiated onto the body 60 and reflected by the object to be observed 60 is returned to the fiber coupler 21 through a reverse route.

  The reference optical system 40 reflects the reference light branched in the interference optical system 20 by the fixed reference mirror 43 and returns it to the interference optical system 20. The reference optical system 40 includes a lens 41, a lens 42, and a fixed reference mirror 43.

  The reference light branched by the fiber coupler 21 in the interference optical system 20 and sent to the reference optical system 40 via the optical fiber 3 is irradiated to the fixed reference mirror 43 via the lens 41 and the lens 42, and this fixed reference. The light is reflected by the mirror 43 and returned to the fiber coupler 21 through a reverse route.

  Then, in the fiber coupler 21 of the interference optical system 20, interference light between the reflected light of the observation light irradiated on the object 60 and the reference light is generated, and the generated interference light is transmitted through the optical fiber 4 to the signal processing unit. 50.

  The signal processing unit 50 receives the interference light obtained by the interference optical system 20 and converts it into an electrical signal, and calculates optical tomographic image information of the object 60 to be observed. It comprises an arithmetic processing unit 52 and a display unit 53.

  In the signal processing unit 50, the interference light transmitted from the fiber coupler 21 of the interference optical system 20 via the optical fiber 4 is received by the light detector 51 and converted into an electrical signal, which is detected as a spectrum interference signal. Then, the arithmetic processing unit 52 takes in the spectral interference signal detected by the photodetector 51 and performs Fourier transform on the spectral interference signal at equal frequency intervals, so that the depth direction of the object to be observed 60 and the scanning mirror 32 The optical section image information in the scanning direction is calculated, and the optical tomographic image is displayed on the display unit 53.

  Here, in the optical coherence tomography apparatus 100, the wavelength scanning laser light source 10 is a light source that scans by changing the wavelength with time, that is, a light source whose wavelength is time-dependent, and scans the reference mirror 43. Without obtaining the depth distribution of the observation object 60 in the depth direction, the structure in the depth direction can be obtained, and a two-dimensional tomographic image can be formed simply by scanning in the primary direction. .

  In this optical coherence tomography apparatus 100, a wavelength scanning laser light source 10 that scans by changing the wavelength with time is two Fabry-Perots having FSRs (Free Spectral Ranges) provided in the laser oscillation optical path close to each other. By narrowing the resonator length of at least one Fabry-Perot resonator among the resonators periodically within a certain range, the two Fabry-Perot resonators can change the selected wavelength by the vernier effect. 2 to output a laser beam whose wavelength is scanned in time, and as shown in FIG. 2, an optical fiber loop 11 serving as a laser oscillation optical path, An optical amplifier 12 provided in the optical fiber loop 11 and having a gain at an oscillation wavelength, and the optical fiber loop The two Fabry-Perot resonators 13A and 13B provided in the optical fiber 11 and having close FSR (Free spectral range) are connected to the optical fiber loop 11 and a part of the light passing through the optical fiber loop 11 is taken out. One of the optical elements such as the optical coupler 14 and the two Fabry-Perot resonators 13A and 13B having the adjacent FSRs, here, the resonance of the Fabry-Perot resonator 13A is periodically changed in a certain range. And a device length control unit 15.

  In this wavelength scanning laser light source 10, the two Fabry-Perot resonators 13A and 13B having adjacent FSRs function as wavelength selection filters. At least one of the two Fabry-Perot resonators 13A and 13B, here the Fabry-Perot resonator 13A, can change the selected wavelength by changing the resonator length.

  The two Fabry-Perot resonators 13A and 13B having the adjacent FSRs can narrow the selection wavelength by the vernier effect by changing the resonator length of one Fabry-Perot resonator 13A. It functions as a bandpass filter having a wavelength selection characteristic of the band.

  In this wavelength scanning laser light source 10, the light that has passed through the band-pass filter by the two Fabry-Perot resonators 13 A and 13 B having the adjacent FSR provided in the optical fiber loop 11 is amplified by the optical amplifier 12, and It oscillates by being fed back through the optical fiber loop 11. In the wavelength scanning laser light source 10, the oscillation length is periodically changed by periodically changing the resonator length of the Fabry-Perot resonator 13A within a certain range by the resonator length control unit 15. The wavelength of the laser light taken out via the coupler 14 changes periodically.

  The optical coupler 14 for extracting laser light from the optical fiber loop 11 is provided after the optical amplifier 12, but is provided in front of the optical amplifier 12 or between the two Fabry-Perot resonators 13A and 13B. It may be.

  In the wavelength scanning laser light source 10 having such a configuration, the resonator length of the optical fiber loop 11 can be increased. By setting the resonator length of the optical fiber loop 11 to 1000 m, for example, the longitudinal mode interval of the entire laser is set to, for example, It can be as narrow as 200 kHz. As a result, the longitudinal mode interval of the entire laser can be made sufficiently narrower than the bandwidth (FSR / finesse, for example, 2.5 GHz / 50 = 50 MHz) of each Fabry-Perot resonator 13A, 13B. The effect of mode hop can be eliminated without changing the resonator length. Therefore, although it is not strictly single mode oscillation, it is possible to tune the wavelength continuously in a pseudo manner simply by changing the selected wavelength of the bandpass filter.

  Here, the transmission spectrum of a normal optical resonator is shown in FIGS. The horizontal axis represents the frequency of light, and is normalized as FSR = 1 and indicates a range of 100 × FSR. You can see 100 modes per FSR. 3B is an enlarged view of FIG. 3A.

  4A to 4G show transmission spectra when two optical resonators having different FSRs of 1% are connected in cascade. The respective horizontal axes are the same as those in FIG. 3A. However, since the mode intervals of the two optical resonators are different, the vernier effect is caused, and the envelope of the spectrum that is configured in the mode with a small FSR is Equivalent to an optical resonator with a large FSR. The difference of 1% FSR makes the FSR of the moire fringe envelope 100 times. It can also be seen that when the resonator length is changed by about the wavelength, the peak changes by the FSR of the moire fringe envelope. A partially enlarged view of FIG. 4 is shown in FIG.

  Therefore, even if an optical resonator having a small FSR is used, if the vernier effect of the spectrum of the two optical resonators is used, the FSR of the moire fringe envelope is inversely proportional to the difference between the FSRs of the two optical resonators. And get bigger.

  That is, even if an optical resonator having a small FSR is used, a wavelength tunable laser light source can be configured by utilizing the vernier effect of the spectrum of two optical resonators.

  In this case, the wavelength of the laser jumps every FSR (for example, 2.5 GHz) at an interval corresponding to the FSR of the two optical resonators. However, in the case of applications such as optical CT, the measurement range in the depth direction is c If the range is sufficiently narrower than / FSR (about 10 cm), it can be regarded as a quasi-continuous variable wavelength.

It is also called a Fabry-Perot electro-optic modulator (or optical comb generator) with a structure in which an electrode is attached to a Fabry-Perot resonator constructed of an electrically variable refractive index material such as LN (LiNbO ₃ ). By using the modulator, the wavelength can be varied by the electro-optic effect. Since it is an electrical modulation, it has excellent linearity and reproducibility.

  Therefore, a Fabry-Perot electro-optic modulator is used for the Fabry-Perot resonator 13A in which the resonator length in the wavelength scanning laser light source 10 is variable. Then, a periodic signal such as a sawtooth wave is given to the Fabry-Perot electro-optic modulator by the resonator length control unit 15 and optically modulated, so that the oscillation wavelength of the wavelength scanning laser light source 10 can be adjusted with high accuracy. Scanning can be performed at high speed.

  In addition, the Fabry-Perot electro-optic modulator can be adjusted in length by polishing, and the resonator length can be accurately controlled by controlling the temperature of each. Therefore, the absolute value of the resonator length is desired by controlling the temperature. The range can be controlled at 1 ppm. Therefore, for example, it is easy to prepare two Fabry-Perot electro-optic modulators having FSR = 2.5 GHz and two Fabry-Perot electro-optic modulators having different FSR by 1/4000. Thus, a 10 THz FSR wavelength selection element of 4000 times can be easily realized by the vernier effect.

Therefore, Fabry-Perot electro-optic modulators whose lengths are uniformed by polishing are used for the two Fabry-Perot resonators 13A and 13B having adjacent FSRs in the wavelength scanning laser light source 10, and the lengths of the resonators are the same. Is adjusted by temperature control.
For example, if the optical resonator can be manufactured by changing the length by the required amount accurately, the difference between the FSRs can be constant by bringing the two optical resonators into thermal contact with each other at the same temperature. Therefore, it is not necessary to perform temperature control. For example, by adjusting the waveguide process, the FSR can be differentiated. In the case of a waveguide based on Ti diffusion of LN, for example, by adjusting the doping amount of Ti so that the refractive index changes by 1/4000. , Waveguide Fabry-Perot electro-optic modulators with different FSR by 1/4000 can be fabricated.

  FIG. 6 shows an actual configuration example of the wavelength scanning laser light source 10 using the Fabry-Perot electro-optic modulators 13A ′ and 13B ′ for the two Fabry-Perot resonators 13A and 13B.

  Since the Fabry-Perot electro-optic modulator currently on the market has reflection, optical isolators 17A, 17B, 17C, and 17D are inserted in the wavelength scanning laser light source 10 shown in FIG. A delay line 18 is inserted. For example, the delay line is a 1 km fiber. As a result, the time for the light to travel around the optical fiber loop 11 is 5 μs, so that the mode interval is 200 kHz. The entire system of this wavelength scanning laser light source 10 is constructed with polarization conservation, and a polarizer 19 is connected to an optical amplifier 12 and an optical isolator in order to determine the polarization state of light passing through an optical fiber loop 11 which is an optical path for laser oscillation. It is inserted between 17C. For the delay, a Faraday mirror, an SM fiber, and a PBS coupler can be used. The scanning frequency can be an integer multiple of 200 kHz.

  The polarizer 19 is used to determine the polarization state of light passing through the optical fiber loop 11 serving as an optical path for laser oscillation, and may be inserted at any position in the loop.

  Here, as the optical amplifier 12, the Fabry-Perot resonators 13A and 13B, and the optical coupler 14 in the wavelength scanning laser light source 10, the optical fiber amplifier EFDA for the wavelength band of 1.5 μm, the two comb generator modules OFCG1, The fiber ring laser shown in FIG. 7 is configured using OFCG2 and an optical coupler PC, and the wavelength variable characteristic by the bias voltage applied to the comb generator module OFCG1 is measured. As a result, it functions as a scanning laser light source capable of high-speed wavelength scanning. The results shown in FIG. 8 were obtained.

  When the temperature difference is large, the difference in FSR is large, so that the wavelength change with respect to the voltage is gradual and the wavelength variable band becomes narrow. When the temperature difference is reduced, the wavelength change becomes sensitive to the bias voltage, and the wavelength variable band is also expanded. The wavelength variable band was about 33 nm when the temperature difference was 15 ° C., and about 15 nm when the temperature difference was 25 degrees.

  As the optical amplifier 12, an optical fiber amplifier (PM EDFA) manufactured by IPG Photonics was used at Pout = + 22.6 dBm. In addition, as Fabry-Perot resonators 13A and 13B, a waveguide-type Fabry-Perot electro-optic modulator (waveguide-type FP-EO modulator WR-250-03 manufactured by Optical Com Co., Ltd.) having an FSR of 2.5 GHz at room temperature is used. Two units are used, the temperature of the first waveguide type Fabry-Perot electro-optic modulator 13A ′ and the second waveguide type Fabry-Perot electro-optic modulator 13B ′ are shifted by temperature control, and the FSR is shifted. Configured. Each waveguide-type Fabry-Perot electro-optic modulator 13A ′, 13B ′ uses an FSR whose FSR changes by about 0.08 MHz per 1 ° C., and is controlled by temperature control using a Peltier element or the like. The temperature of the electro-optic modulator 13A ′ was 20 ° C. (fixed), and the temperature of the second waveguide Fabry-Perot electro-optic modulator 13B ′ was 33 ° C. to 45 ° C. (variable).

  The optical coupler 14 used was 10:90, that is, 10% output.

  The optical isolators 17A, 17B, and 17C were used in one place for input / output of the waveguide type Fabry-Perot electro-optic modulators 13A 'and 13B'.

  Here, the waveguide-type Fabry-Perot electro-optic modulators 13A ′ and 13B ′ have a loss of about 7 dB, and the two waveguide-type Fabry-Perot electro-optic modulators 13A ′ and 13B ′ together have a loss of 14 dB. Since the loss increases the spontaneous emission light (ASE) of the laser light, the two optical amplifiers 12A and 12B are respectively arranged after the waveguide type Fabry-Perot electro-optic modulators 13A ′ and 13B ′ as shown in FIG. Spontaneously emitted light (ASE) due to loss in the waveguide Fabry-Perot electro-optic modulators 13A ′ and 13B ′ by performing optical amplification after the respective waveguide-type Fabry-Perot electro-optic modulators 13A ′ and 13B ′ Can be reduced.

  Also, for example, as shown in FIGS. 10 and 11, the polarization components are separated by polarization conversion elements 19A and 19B and PBS couplers 20A and 20B that rotate the polarization direction of the light passing through the optical fiber loop 11 by 90 °. The path may be determined, and one optical amplifier 12 may be used as the two optical amplifiers 12A and 12B, and optical amplification may be performed after the waveguide type Fabry-Perot electro-optic modulators 13A ′ and 13B ′, respectively. The increase in spontaneous emission light (ASE) due to loss in the waveguide Fabry-Perot electro-optic modulators 13A ′ and 13B ′ can be reduced.

  For example, an optical amplifier such as SOA can amplify both polarizations in either direction, so that it can be used to amplify light twice during one round of light, as shown in FIG. In the wavelength scanning laser light source 10, light is separated by direction and polarization, and light amplification is performed by a single optical amplifier 12 using SOA. A circulator may be used instead of the PBS couplers 20A and 20B. In the wavelength scanning laser light source 10 shown in FIG. 11, the direction of passing through the optical amplifier 12 is the same, but the light is separated by polarized light.

  Here, a measurement system 200 as shown in FIG. 12 is constructed, and the wavelength of the laser beam output from the wavelength scanning laser light source 10 due to the vernier effect is measured by the interferometer 210 to constitute the bandpass filter. The result of obtaining the relationship between the scanning signal voltage and the laser frequency given by the resonator length control unit 15 that changes the resonator length of one of the two Fabry-Perot resonators 13A and 13B is shown. FIG. 13A shows the result of plotting the deviation amount from the linear approximation of the measured value shown in FIG. 13A. Each of the horizontal axes in FIGS. 13A and 13B represents the scanning signal voltage, and the vertical axis in FIG. 13A represents the laser frequency corresponding to the wavelength obtained as a measurement result. The vertical axis of B) is the amount of deviation of the laser frequency measurement value from the linear approximation value.

  Further, when the waveform of the scanning signal given to the Fabry-Perot resonator 13A by the resonator length control unit 15 and the waveform of the interference signal obtained by the interferometer 210 are observed, (A), (B), ( As shown in (C), the waveform of the interference signal following the waveform of the scanning signal (triangular wave, sine wave, sawtooth wave) was obtained.

  In the measurement system 200 shown in FIG. 12, an SOA (semiconductor optical amplifier) is used as the optical amplifier 12 of the wavelength scanning fiber laser light source 10, and a 1 km SM fiber and a Faraday mirror are used as the delay line 18. A delay line using a PBS coupler was inserted. Further, the synchronized function generator 2 channels are used as the resonator length control unit 15 so that the Fabry-Perot resonators 13A and 13B can be modulated with arbitrary waveforms.

  In the measurement system 200, the wavelength tunable range is increased by using the SOA for the optical amplifier 12. 13A shows the result of measuring the change in the frequency (wavelength) of the laser by applying a voltage to the bias of one Fabry-Perot resonator 13A. Looking at the data, the variable wavelength reaches 10 THz. You can see that 10 THz is approximately 80 nm, which is larger than the experimental data 33 nm of FIG. 8 obtained with the system of FIG. Here, as a temperature condition, the temperature difference between the two Fabry-Perot resonators 13A and 13B is set to 8 degrees.

  In the measurement system 200, modulation is possible at an integral multiple of 100 kHz by inserting a delay line 18 into the wavelength scanning laser light source 10. In the case of a delay line using a 1 km SM fiber, a Faraday mirror, and a PBS coupler, light travels back and forth through the fiber, which is equivalent to a 2 km delay line. The data in FIG. 14 is data at a scanning frequency of 200 kHz, and the temperature condition is the same 8 degrees. The scanning range is 10 THz.

  Further, at this time, by using a synchronized two-channel function generator as the resonator length control unit 15 and applying an inverted scanning signal to each of the Fabry-Perot resonators 13A and 13B, the wavelength change direction is affected. Good modulation was obtained as shown in FIG. When a scanning signal exceeding 100 kHz was applied to only one Fabry-Perot resonator 13A, the light intensity varied depending on the direction of the wavelength change, and the laser oscillation did not occur. By adding an inverted scanning signal to 13A and 13B, the degree of these problems was greatly reduced. Thereby, the scanning frequency could be confirmed up to at least 1 MHz.

  In addition, when an inverted scanning signal is applied to each Fabry-Perot resonator 13A, 13B, the distance between the two Fabry-Perot resonators 13A, 13B cannot be ignored, particularly at a high scanning frequency (about 1 MHz). It is necessary to adjust the phase difference between the inverted scanning signals applied to the respective Fabry-Perot resonators 13A and 13B.

  As is apparent from the above measurement results, the laser frequency in the wavelength scanning laser light source 10 due to the vernier effect is substantially proportional to the scanning signal voltage by the resonator length control unit 15.

  That is, in the wavelength scanning laser light source 10 based on the vernier effect, the wavelength of the light is proportional to the input voltage signal. Therefore, for example, if the input electric signal is modulated by a linear sawtooth wave or the like, the sawtooth wavelength can be modulated. In particular, since the wavelength can be controlled by an electrical EO effect, there is no hysteresis caused by mechanical modulation.

Here, in the case where the wavelength scanning laser light source 10 is used in the optical coherence tomography apparatus, the maximum FSR (FSRmax) of the Fabry-Perot electro-optic modulator is the sampling theorem, where the required coherent length is δL and the speed of light is c. From
FSRmax = c / δL (1) is given by equation (1).

  Since each of the two Fabry-Perot electro-optic modulators has a loss of 7 dB, the total loss is 14 dB or more, the output power does not reach the saturation limit, and the optical power of each Fabry-Perot electro-optic modulator is Sensitive to dynamic response characteristics.

Therefore, the frequency scanning speed (Srate), that is, the cut-off (Srate-cut) of the frequency at which the laser beam scans per unit time, is a function of the maximum scanning range (FSRv).
Srate-cut = FSRv / Fδt (2) It is estimated that it is given by equation (2). Here, δt (= F / FSR) is a photon lifetime in the Fabry-Perot electro-optic modulator.

  The cut-off (Srate-cut) of the frequency scanning speed (Srate) obtained as a result of the experiment was 12 THz / μs.

The limit (δLlimit) of the coherent length (δL) is
δLlimit = c / Srateδt (3) It was estimated to be given by equation (3).

From this result, it can be predicted that the coherent length (δL) and the frequency scanning speed (Srate) are in a trade-off relationship, and the coherent length (δL) in the cutoff (Srate-cut) of the frequency scanning speed (Srate). The limit of (δLlimit-cutoff) is
δLlimit-cutoff = cF / FSRv (4) Equation (4)

  Thus, given the coherent length (δL), frequency scan rate (Srate), and maximum scan range (FSRv) given system requirements, the resonator conditions, ie, finesse (F) and free spectral region (FSR) Conditions can be determined as follows.

That is, the range that Finesse (F) can take is generally calculated from the above equation (3). CFSR / SrateδL> F
The possible range of the free spectral region (FSR) is
c / δL> FSR
It becomes.

Here, in an actual device, the range that the finesse (F) can take is as follows:
c / δL>FSR> SrateF ² / FSRv / 2
That is, good operation could be confirmed when the frequency scanning speed (Srate) was in the range of 1/2 to 2 times the cutoff (Srate-cut).

  In this wavelength scanning type light source 10, intensity noise was generated when the scanning speed was slow, particularly when the frequency scanning speed (Srate) was slower than cut-off (Srate-cut) / 2. This phenomenon is considered as mode competition noise, and mode competition noise can be reduced by performing high frequency superposition on the SOA, and the scanning speed is low. The characteristics can be improved. When the frequency scanning speed (Srate) is faster than cut-off (Srate-cut) / 2, it can be improved by increasing the loop gain by the method shown in FIG. 8, FIG. 9, FIG.

  Further, in the wavelength scanning light source 10 based on this vernier effect, in principle, since the laser wavelength is proportional to the scanning signal voltage, the laser frequency is not completely proportional to the scanning signal voltage. Therefore, the linear scan signal cannot scan at equal intervals in time with respect to the wave number (laser frequency × 2π ÷ light speed), but scans at equal intervals in time with respect to the wave number by adjusting the waveform of the scan signal. be able to.

  That is, the wavelength scanning laser light source 10 based on the vernier effect can perform sawtooth modulation such that the wave number is equally spaced in time by adjusting the electrical signal to a non-linear sawtooth wave.

That is, when α is a constant, the wavelength with respect to the voltage V is
λ = α ・ V + λ0
It is. On the other hand, the wave number K of light is
K = 2π / λ = 2π / (α · V + λ0)
Therefore, in order to realize a wave number that is a function K (t) for an arbitrary time, a function V (t) for a voltage time is expressed as V (t) = (2π / K (t) −λ0) / α
And it is sufficient.

  Therefore, in the wavelength scanning laser light source 10, the resonator length control unit 15 sets the resonator length of at least one Fabry-Perot resonator 13A out of the two Fabry-Perot resonators 13A and 13B constituting the bandpass filter. In order to periodically scan the wavelength of the laser light extracted through the optical coupler 14 by periodically changing the range in a certain range, the scanning signal given to the Fabry-Perot resonator by the resonator length control unit in advance Is adjusted so that the wave number of the laser light extracted via the optical coupler 14 is linear with respect to time, so that the laser light whose wave number is linear with respect to time is converted via the optical coupler 14. Obtainable.

  Then, for example, as in the wavelength scanning laser light source 10 shown in FIG. 15, the resonator length control unit 15 reads calibration data for obtaining laser light whose wave number is linear with respect to time from the ROM 15A, and the waveform of the scanning signal. With this configuration, laser light whose wave number is linear with respect to time can be obtained via the optical coupler 14.

  Here, a wavelength scanning laser light source 210 obtained by improving the wavelength scanning laser light source 10 is shown in FIG.

  The wavelength scanning laser light source 210 includes two Fabry-Perot resonators 130A and 130B having close free spectral ranges (FSRs), an optical amplifier 12 having a gain at an oscillation wavelength, and a polarizer 19 in the optical amplifier 12. And the optical coupler 14 connected to the optical fiber via the optical isolator 17 and at least one of the two Fabry-Perot resonators 130A and 130B, here, the resonator length of the Fabry-Perot resonator 130A is periodically varied within a certain range. And one Fabry-Perot resonance via an incident side optical system 18A comprising a collimator and a convex lens designed so that the optical coupler 14 matches the resonance mode of the optical resonator. One Fabry-Perot resonator 130A is connected to the resonator 130A as a fiber. An output side optical system 18B composed of a convex lens and a collimator designed to match the optical mode and an incident side optical system 18C composed of a collimator and a convex lens designed to match the resonance mode of the optical resonator. An optical fiber loop serving as a laser oscillation optical path that is fiber-connected to the Fabry-Perot resonator 130B and the other Fabry-Perot resonator 130B is fiber-connected to the optical amplifier 12 via the output side optical system 18D having a collimator function. The fiber ring laser which has this is comprised.

  Here, the polarizer 19 is for determining the polarization state of the light passing through the optical fiber loop, which is an optical path for laser oscillation, and may be inserted at any position in the loop.

  In the wavelength scanning laser light source 210, the two Fabry-Perot resonators 130A and 130B are confocal with the Fabry-Perot resonator including the electro-optic crystal 110, as shown in FIG. 17, for example. As described above, the ring-type resonant Fabry-Perot electro-optic modulator 130 is used in which the curvatures of the concave mirrors 111 and 112 are set to obtain a ring-type resonance.

  In the ring-type resonant Fabry-Perot electro-optic modulator 130 in which the curvatures of the concave mirrors 111 and 112 are set to be confocal as described above, the direct reflected light Lr with respect to the incident light Lin does not return to the incident side. Do not need.

  Therefore, in the wavelength scanning laser light source 210, the confocal ring-type resonant Fabry-Perot electro-optic modulator 130 in which the direct reflected light Lr with respect to the incident light Lin does not return to the incident side is provided with two Fabry having the adjacent FSRs. By using the Perot resonators 130A and 130B, the optical isolator at the input / output portion of each Fabry-Perot resonator 130A and 130B can be omitted, and the optical isolator 17 is provided only on the input side of the optical amplifier 12.

  That is, in this wavelength scanning laser light source 210, the confocal ring type in which the direct reflected light Lr with respect to the incident light Lin does not return to the incident side as the two Fabry-Perot resonators 130A and 130B having close FSRs as described above. Since the resonant Fabry-Perot electro-optic modulator 130 is used, the influence of reflection is low, but light is applied only to the input side of the optical amplifier 12 in order to determine the clockwise or counterclockwise oscillation direction of the ring laser. An isolator 17 is inserted. The optical isolator 17 has a purpose different from that for reducing the influence of reflection from a conventional Fabry-Perot electro-optic modulator, and has a performance that only needs to be given a gain difference between clockwise and counterclockwise. Only required. Further, this optical isolator 17 may be basically inserted at any position in the loop.

  In this wavelength scanning laser light source 210, the two Fabry-Perot resonators 130A and 130B having adjacent FSRs function as wavelength selection filters. At least one of the two Fabry-Perot resonators 130A and 130B, here, the Fabry-Perot resonator 130A can change the selected wavelength by changing the resonator length by the resonator length control unit 15. It can be done.

  Then, the two Fabry-Perot resonators 130A and 130B having the adjacent FSRs can be selected so that the selected wavelength can be varied by the vernier effect by varying the resonator length of one Fabry-Perot resonator 130A. It functions as a bandpass filter having a wavelength selection characteristic of the band.

  In this wavelength scanning laser light source 210, the light that has passed through the band-pass filter by the two Fabry-Perot resonators 130A and 130B having the adjacent FSRs provided in the optical fiber loop 11 is amplified by the optical amplifier 12, It oscillates by being fed back through the optical fiber loop 11. In the wavelength scanning laser light source 210, the oscillation wavelength is periodically changed by periodically changing the resonator length of the Fabry-Perot resonator 130A within a certain range by the resonator length control unit 15. The wavelength of the laser light taken out via the coupler 14 changes periodically.

  The optical coupler 14 for extracting laser light from the optical fiber loop 11 is provided after the optical amplifier 12, but is provided before the optical amplifier 12 or between the two Fabry-Perot resonators 130A and 130B. It may be.

  In the wavelength scanning laser light source 210 having such a configuration, the resonator length of the optical fiber loop 11 can be increased. By setting the resonator length of the optical fiber loop 11 to 1000 m, for example, the longitudinal mode interval of the entire laser is set to, for example, It can be as narrow as 200 kHz. As a result, the longitudinal mode interval of the entire laser can be made sufficiently narrower than the bandwidth (FSR / finesse, for example, 2.5 GHz / 50 = 50 MHz) of each of the Fabry-Perot resonators 130A and 130B. The effect of mode hop can be eliminated without changing the resonator length. Therefore, although it is not strictly single mode oscillation, it is possible to tune the wavelength continuously in a pseudo manner simply by changing the selected wavelength of the bandpass filter.

  In this wavelength scanning laser light source 210, the wavelength of a light source having a narrow band spectrum can be scanned continuously in a wide band at high speed, and the direct reflected light Lr with respect to the incident light Lin does not return to the incident side. Since the above-mentioned two Fabry-Perot resonators 130A and 130B are used as the ring-type resonant Fabry-Perot electro-optic modulator 130, the optical isolators at the input / output portions of the Fabry-Perot resonators 130A and 130B can be omitted. The increase in noise due to optical loss in the optical isolator can be reduced.

  Here, the length of the waveguide-type Fabry-Perot electro-optic modulator can be adjusted by polishing, and the resonator length can be accurately controlled by controlling the temperature of each, so the absolute value of the resonator length is controlled by temperature control. It is possible to control at 1 ppm within the desired range. Therefore, for example, by using a Fabry-Perot electro-optic modulator with FSR = 2.5 GHz and a Fabry-Perot electro-optic modulator with a different FSR by 1/4000, a 10 THz FSR wavelength selection element 4000 times easier due to the vernier effect. realizable. However, in a spatial Fabry-Perot electro-optic modulator that uses a concave mirror, it is difficult to adjust the length with high precision by polishing. Therefore, the position of the concave mirror is adjusted with an accuracy of several microns, and two optical resonators are used. It is necessary to adjust the temperature with high accuracy.

In addition, the FSR (Free Spectral Range) of the confocal ring-type resonant Fabry-Perot electro-optic modulator 130 is as follows.
FSR = c / (4 ng · L)
It becomes. Here, c is the speed of light in vacuum, and L is the resonator length.

In lithium niobate (LN: LiNbO ₃ ) often used for electro-optic modulation, the group refractive index of ordinary light is nog and the group refractive index of extraordinary light is both about 2 but the difference is 4%. is there.

Therefore, the FSR of the confocal ring-type resonant Fabry-Perot electro-optic modulator 130 that modulates ordinary light by the electro-optic crystal (LN) 110 is:
FSR1 = c / (4 nog · L)
The FSR of the confocal ring-type resonant Fabry-Perot electro-optic modulator 130 that modulates extraordinary light by the electro-optic crystal (LN) 110 is
FSR2 = c / (4 neg · L)
It becomes.

Also, as shown in FIG. 18, a length L1 electro-optic crystal (LN) 110A and a length L2 electro-optic crystal (LN) 110B are inserted into a confocal ring-type resonant Fabry-Perot electro-optic modulator 130. Then, by arranging the C-axis to be orthogonal, the ordinary light is modulated by the electro-optic crystal (LN) 110A having the length L1, and the extraordinary light is modulated by the electro-optic crystal (LN) 110B having the length L2. The FSR of the confocal ring-type resonant Fabry-Perot electro-optic modulator 130 is
FSR1 = c / (4nog · L1 + 4neg · L2)
A confocal ring-type resonant Fabry-Perot electro-optic modulation in which extraordinary light is modulated by an electro-optic crystal (LN) 110A having a length L1 and ordinary light is modulated by an electro-optic crystal (LN) 110B having a length L2. The FSR of the vessel 130 is
FSR2 = c / (4 neg · L1 + 4 nog · L2)
It becomes.

  In this case, if L1 = L2, FSR1 = FSR2, and the difference between FSR1 and FSR2 can be finely set by the difference between the lengths L1 and L2 of the electro-optic crystals (LN) 110A and 110B.

  Here, for the FSR of the ring-type resonant Fabry-Perot electro-optic modulator 130, the calculation formula is shown on the assumption that the crystal length and the resonator length are the same, ignoring the space for the principle explanation.

  Thus, when two crystals are inserted into one Fabry-Perot resonator, the entire resonator length is shared. Originally, what is important for the vernier effect is that the difference between the two FSRs and the ratio between the FSRs is important, so the absolute value of the length is essentially not important, and the difference between the lengths of the two crystals is important. . The difference in length between the two crystals can be adjusted by polishing. Some deviations in the position of the external mirror can be ignored.

  Here, in the wavelength scanning laser light source 210, the resonator length of the one Fabry-Perot resonator 130A of the two Fabry-Perot resonators 130A and 130B constituting the bandpass filter is set as the resonator length control unit 15. Thus, the wavelength of the laser light extracted via the optical coupler 14 is periodically scanned by periodically changing in a certain range. For example, the resonator length in the wavelength scanning laser light source 210 shown in FIG. Like the control unit 15, the sawtooth wave signal generated by the sawtooth wave signal generator 150 as a periodic scanning signal is directly supplied to the Fabry-Perot resonator 130B, and the inverting amplifier 151 is supplied to the Fabry-Perot resonator 11A. To both the electro-optic modulators in the two Fabry-Perot resonators 130A and 130B. Then, by applying an inverted scanning signal and reciprocally changing the resonator length of each Fabry-Perot resonator, the modulation voltage can be halved, and by adding the inverted scanning signal, the modulation voltage can be halved. In addition, since the phase change that occurs when a voltage is applied to the electro-optic modulator in the Fabry-Perot resonator is canceled out, the wavelength can be scanned more accurately and stably.

  Further, in the wavelength scanning laser light source 210, since the center wavelength is extremely sensitive to the temperature difference of each Fabry-Perot electro-optic modulator, the resonator length control unit 15 in the wavelength scanning laser light source 210 shown in FIG. Laser light extracted through the optical coupler 14, that is, a part of the light that has passed through the band filter that transmits the center wavelength, is guided from the optical coupler 14 ′ to the photodetector 152 through the band pass filter 16 to detect the light. The phase difference between the timing and the periodic scanning signal is detected by the lock-in amplifier 153, and the control signal is superimposed on the periodic signal and fed back so that the phase difference becomes a constant value. Thus, the center wavelength is controlled. As a result, modulation can always be performed at a constant wavelength.

  In addition, as shown in FIG. 18, a length L1 electro-optic crystal (LN) 110A and a length L2 electro-optic crystal (LN) 110B are inserted into a confocal ring-type resonant Fabry-Perot electro-optic modulator 120. Then, when the C-axis is arranged so as to be orthogonal, as shown in FIG. 20, the electrodes 125A and 125B of the two electro-optic crystals (LN) 110A and 110B are connected in parallel and modulated by giving a modulation signal. By doing so, the optical distance changes relative to the polarization direction by making the voltages opposite to each other with respect to the C-axis of the crystal.

  Therefore, the change in the optical distance that occurs during one transmission through the crystal is (γ31 · L1) for the polarized light on the FSR1 side when the electro-optic constants γ33, γ31, crystal lengths L1, L2, and crystal thickness d are used. −γ33 · L2) · V / d, and for polarized light on the FSR2 side, (γ33 · L1−γ31 · L2) · V / d, and the difference between them is (γ31−γ33) · (L1 + L2) · The optical distance is modulated by V / d.

  That is, even when two Fabry-Perot electro-optic modulators are used, the inverting amplifier 151 is not necessary if the electrodes can be replaced.

  The crystal selection method is to select a crystal having a large difference between γ33 and γ31. For example, in the case of LN or LT, the stoichiometric composition crystal is more advantageous than the coincidence melt composition crystal.

  Here, a confocal ring-type resonant Fabry-Perot electro-optic modulator 11 in which two electro-optic crystals are inserted into one Fabry-Perot resonator has, for example, a structure as shown in FIG. It is fabricated as a monolithic Fabry-Perot electro-optic modulator.

  First, as shown in FIG. 22A, long crystals 1101 and 1102 whose C-axis is orthogonal to the light beam direction and orthogonal to each other, and thin crystals 1201 whose C-axis is the light beam direction. 1202 is manufactured, each end face orthogonal to the light beam direction is polished, and the length of the electro-optic crystal (LN) 1101 is adjusted to L1, and the length of the electro-optic crystal (LN) 1102 is adjusted to L2.

  Next, as shown in FIG. 22 (B), the refractive index match between the electro-optic crystal (LN) 1101 of length L1 and the electro-optic crystal (LN) 1102 of length L2 with the C axes orthogonal to each other. Are bonded with an adhesive or an optical contact, and crystals 1201 and 1201 whose thin C-axis is in the light beam direction are bonded to both ends thereof to produce a joined body 1000 having a length of L as a whole. . The crystals 1201 and 1202 in which the thin C-axis at both ends are in the direction of the light beam are isotropic media with respect to the light beam.

  Then, as shown in FIG. 22C, the joined body 1000 is diced to form a base body 1001 of a monolithic Fabry-Perot electro-optic modulator 130.

  Next, as shown in FIG. 22D, the above-mentioned crystals 120A and 120B of the substrate 1001 composed of the electro-optic crystals (LN) 110A and 110B and the crystals 120A and 120B at both ends thus fabricated are shared. The convex surface is polished with a curvature R that becomes a focal point.

Next, as shown in FIG. 22E, opposite confocal concave mirrors 111 and 112 that form Fabry-Perot resonators by coating both end surfaces of the base body 1001 having a convex surface polished with the curvature R by vapor deposition. Form. Here, the concave mirrors 111 and 112 are formed by coating the end face of the crystal 120A on one side with less than 100% and the end face of the opposite crystal 120B with 100%. The curvature R when the overall length is L is
R = (no / ne-1). (L1 + L2) / 2 + L
It is.

  Then, as shown in FIG. 22F, electrodes are formed on the side surfaces orthogonal to the C-axis of each electro-optic crystal (LN) 110A, 110B of the substrate 1001 on which the concave mirrors 111, 112 are formed on both end surfaces by vapor deposition. By forming 125A and 125B, a monolithic Fabry-Perot electro-optic modulator 130 having a structure as shown in FIG. 21 is manufactured.

  In the case of the monolithic Fabry-Perot electro-optic modulator 130, since the crystal size is smaller than that of the collimator, it is difficult to arrange two collimators as the input / output optical systems 18A and 18B. For example, as shown in FIG. In addition, the input / output optical systems 16A and 16B having a prism type mirror 18C on the input surface, or a fiber is mounted on a two-core ferrule as shown in FIG. 24, and a two-core ferrule is formed by the prism 18D. An input / output optical system 18 having a structure in which a fiber mounted on the ring and a ring resonator are coupled to each other is used.

  Here, since the confocal ring-type resonant Fabry-Perot electro-optic modulator 130 can be used as a bidirectional electro-optic modulator, for example, a wavelength scanning laser light source 210 ′ shown in FIG. As the optical amplifier 12 in the wavelength scanning laser light source 210 shown in FIG. 16, a directional optical amplifier 12 ′ such as SOA that can amplify both polarizations in either direction is used. Instead, a total reflection mirror 14A and a half mirror 14B are provided, and the above-mentioned confocal ring-type resonant fabric in which the two Fabry-Perot resonators 130A and 130B having adjacent FSRs function as bidirectional electro-optic modulators, respectively. By using the Perot electro-optic modulator 130, optical amplification is performed twice during one round of the optical fiber loop. Can Unisuru.

  In the wavelength scanning laser light source 210 ′, light emitted from one Fabry-Perot resonator 130A via the incident / exit optical system 18A ′ is totally reflected by the total reflection mirror 14A and passes through the incident / exit optical system 18A ′. Is incident on the Fabry-Perot resonator 130A, and the light emitted from the Fabry-Perot resonator 130A via the incident / exit optical system 18B ′ enters the other Fabry-Perot resonator 130B via the incident / exit optical system 18C ′. The light emitted from the Fabry-Perot resonator 130B via the incident / exit optical system 18D ′ is amplified by the bidirectional optical amplifier 12 ′. Then, light having a predetermined polarization component extracted from the light amplified by the bidirectional optical amplifier 12 ′ via the polarizer 19 is reflected by the half mirror 14 B, and the bidirectional optical amplifier 12 is transmitted via the polarizer 19. The light of a predetermined polarization component that is incident on 'and passes through the polarizer 19 is amplified by the bidirectional optical amplifier 12' and is incident on the Fabry-Perot resonator 130B via the input / output optical system 17B '. The light emitted from the Fabry-Perot resonator 130B via the incident / exit optical system is incident on the Fabry-Perot resonator 130A via the incident / exit optical system, and the laser light is extracted through the half mirror 14B.

  In the wavelength scanning laser light source 210 ′ having such a configuration, while the light goes around the fiber loop, each of the Fabry-Perot resonators 130A and FSR2 of the FSR1 including the confocal ring-type resonant Fabry-Perot electro-optic modulator 130, respectively. Since it passes through the Fabry-Perot resonator 130B twice, the resolution of the optical filter as the vernier effect can be improved, the wavelength selection becomes stronger, the line width is narrow, and the coherent length can be increased. The bidirectional optical amplifier 12 may be inserted at any position in the loop.

  In addition, the confocal ring-type resonant Fabry-Perot electro-optic modulator 130 has a different FSR depending on the polarization direction, and the electro-optic modulation is strongly applied to the polarization in the c-axis direction. Therefore, the wavelength scanning type shown in FIG. Like the laser light source 220, by providing an optical system 180 that separates and synthesizes the polarization components, one confocal ring-type resonant Fabry-Perot electro-optic modulator 130 is provided with two Fabry having the adjacent FSRs. It can function as Perot resonators 130A and 130B.

  That is, the wavelength scanning laser light source 220 shown in FIG. 26 is an improvement of the wavelength scanning laser light source 210 shown in FIG. 16, and is a single confocal ring-type resonant fabric provided in the optical fiber loop. Perot electro-optic modulator 130, optical amplifier 12 having gain in oscillation wavelength, optical coupler 14 connected to the optical amplifier 12 through an optical isolator 17, and the confocal ring-type resonant Fabry-Perot electro-optic modulator 130 The resonator length control unit 15 that periodically changes the relative resonator length of the P-polarized light and the S-polarized light within a certain range, the optical amplifier 12, the optical coupler 14, and the incident side optical system 18A and the output side optical system 18B. And an optical system 180 that separates and combines the polarization components.

  The optical system 180 includes a first PBS coupler 181 to which light emitted from the confocal ring-type resonant Fabry-Perot electro-optic modulator 130 is incident via an output-side optical system 18B. A first polarization converter 182 to which light of a P-polarized component separated from incident light is incident, and a second polarization converter 183 to which light of an S-polarized component separated from the emitted light by the PBS coupler 181 is incident. The second PBS coupler 184 into which the S-polarized component light is incident via the optical coupler 14.

  In this optical system 180, the first PBS coupler 181 includes light of P-polarized component and light of S-polarized component from the ring-type resonant Fabry-Perot electro-optic modulator 130 that is incident through the output-side optical system 16B. To separate. The P-polarized component light separated from the outgoing light by the first PBS coupler 181 is incident on the first polarization converter 182, and the S-polarized component light is incident on the second polarization converter 183. The

  The first polarization converter 182 rotates the polarization direction of the P-polarized component light separated from the emitted light by the first PBS coupler 181 by 90 ° and converts it into S-polarized component light. The S-polarized component light converted by the first polarization converter 182 is incident on the optical amplifier 12.

  In the wavelength scanning laser light source 220, the S-polarized component light incident via the first polarization converter 182 is amplified by the optical amplifier 12 having a gain at the oscillation wavelength, and the optical isolator 17 and the optical coupler are coupled. 14 and enters the second PBS coupler 184.

  The second polarization converter 183 rotates the polarization direction of the S-polarized light component separated from the emitted light by the first PBS coupler 181 by 90 ° and converts it into P-polarized light. The P-polarized component light converted by the second polarization converter 183 is incident on the second PBS coupler 184.

  Here, the first and second polarization converters 182 and 183 can use a Faraday element, a wavelength plate, or the like, and also connect the PM fiber to the optical element, and select the PM axis at appropriate times to change the polarization direction by 90. It can also be set as the structure rotated by a degree.

  The second PBS coupler 184 combines the S-polarized component light incident through the optical coupler 14 and the P-polarized component light incident through the second polarization converter 183.

  Then, the combined light by the second PBS coupler 184 is incident on the confocal ring-type resonant Fabry-Perot electro-optic modulator 130 as incident light through the incident side optical system 18A.

  A circulator may be used instead of the first and second PBS couplers 181 and 184.

  In the wavelength scanning laser light source 220, the confocal ring-type resonant Fabry-Perot electro-optic modulator 130 has different FSR depending on the polarization direction, and the electro-optic modulation is strongly applied to the polarization in the c-axis direction. It functions as two Fabry-Perot resonators having different degrees of modulation in the adjacent FSRp and FSRs with respect to incident light, that is, P-polarized component light and S-polarized component light constituting the combined light.

  In this wavelength scanning laser light source 220, one confocal ring-type resonant Fabry-Perot electro-optic modulator 130 that functions as two Fabry-Perot resonators having different modulation degrees by adjacent FSRp and FSRs includes a wavelength selective filter. It functions as a band-pass filter having a narrow-band wavelength selection characteristic in which the selected wavelength can be varied by the vernier effect by varying the relative resonator lengths of P-polarized light and S-polarized light.

  In this wavelength scanning laser light source 220, light that has passed through a bandpass filter by one confocal ring-type resonant Fabry-Perot electro-optic modulator 11 having the above-mentioned close FSRp and FSRs provided in an optical fiber loop. That is, light emitted from the ring-type resonant Fabry-Perot electro-optic modulator 130 is separated into light of P-polarized component and light of S-polarized component by the first PBS coupler 181, and the first PBS coupler 181 The P-polarized component light separated from the emitted light is converted into S-polarized component light by the first polarization converter 182, amplified by the optical amplifier 12, fed back through the optical fiber loop, and the first The S polarization component light separated from the emitted light by the PBS coupler 181 is sent by the second polarization converter 183. It is converted into light of the polarized component to oscillate by being fed back. In this wavelength scanning laser light source 220, the resonator length control unit 15 sets the relative resonator lengths of the P-polarized light and the S-polarized light of the single confocal ring-type resonant Fabry-Perot electro-optic modulator 130 within a certain range. By periodically changing the oscillation wavelength, the oscillation wavelength periodically changes, and the wavelength of the laser light extracted via the optical coupler 14 changes periodically.

  This wavelength scanning laser light source 220 uses a single confocal ring-type resonant Fabry-Perot electro-optic modulator 11 in which direct reflected light Lr with respect to incident light Lin does not return to the incident side. The wavelength of a light source having a narrow-band spectrum that generates chromatic light can be continuously scanned in a wide band at high speed.

Here, as described above, in the case of two Fabry-Perot resonators, FSR1 = c / (4 ng · L1)
FSR2 = c / (4 ng · L2)
Therefore, approximately (FSR1-FSR2) / FSR = (L2-L1) / L
For example, if a difference of 1/1000 is to be made, the difference between L1 and L2 is set to a difference of 1/1000. Therefore, the length is adjusted with an accuracy of 1/1000 or less of L by polishing, and the temperature difference In the case of one Fabry-Perot resonator, FSR1 = c / (4nog · L1 + 4neg · L2)
FSR2 = c / (4 neg · L1 + 4 nog · L2)
Therefore, approximately (FSR1-FSR2) / FSR = (L2-L1) / L (nog-neg) / ng
Since (nog−neg) / ng is about 0.04, even if the polishing accuracy is the same, the difference in length may be set to 1/40 of L. Since the polishing accuracy is about 1/1000, the FSR difference can be realized with an accuracy of 1/1000 ± 1/40000 or less by polishing alone. At this time, it is possible to thermally couple the two crystals because they are close to each other, and the accuracy of the difference in FSR obtained by polishing can be maintained without temperature control. There is no need for temperature control to make the FSR difference constant as used in the waveguide type. Therefore, there is no need for two temperature controllers, and there is a cost merit.

  Further, as described above, the confocal ring-type resonant Fabry-Perot electro-optic modulator 130 can be used as a bi-directional electro-optic modulator, so that, for example, a wavelength scanning laser light source 220 ′ shown in FIG. As the optical amplifier 12 in the wavelength scanning laser light source 220 shown in FIG. 26, a bidirectional optical amplifier 12 ′ such as SOA that can amplify both polarizations in either direction is used. 14 is provided with a total reflection mirror 14A and a half mirror 14B, and one confocal ring-type resonant Fabry-Perot electro-optic that functions as two Fabry-Perot resonators with different degrees of modulation in the above-mentioned adjacent FSRp and FSRs. The modulator 11 may be configured to be used in both directions.

  In this wavelength scanning laser light source 220 ′, light extracted from the confocal ring-type resonant Fabry-Perot electro-optic modulator 130 via the incident / exit optical system 18 A ′ passes through the second PBS coupler 184 and is totally reflected. The light incident on the mirror 14A and reflected by the total reflection mirror 14A passes through the second PBS coupler 184 and passes through the incident / exit side optical system 18A ′ so that the confocal ring-type resonant Fabry-Perot electro-optics. The light incident on the modulator 11 and extracted from the confocal ring-type resonant Fabry-Perot electro-optic modulator 11 via the incident / exit optical system 18B ′ is converted into the first PBS coupler 181 and the first and polarization conversions. The light that has passed through the optical device 182 and entered the bidirectional optical amplifier 12 ′ and amplified by the bidirectional optical amplifier 12 ′ enters the half mirror 14B. Then, the light reflected by the half mirror 14B is incident on the bidirectional optical amplifier 12 ′, and the light amplified by the bidirectional optical amplifier 12 ′ is the first and polarization converters 182 and the first PBS coupler. It oscillates by being incident on the confocal ring-type resonant Fabry-Perot electro-optic modulator 130 from the incident / exit side optical system 16B ′ via 181 and takes out the laser light via the half mirror 14B.

  In the wavelength scanning laser light source 220 ′ having such a configuration, one confocal ring-type resonant Fabry-Perot electro-optic modulation functioning as two Fabry-Perot resonators having different modulation degrees in the above-mentioned adjacent FSRp and FSRs. By using the resonator 130 in both directions, the FSR1 Fabry-Perot resonator and the FSR2 Fabry-Perot resonator comprising the confocal ring-type resonant Fabry-Perot electro-optic modulator 130 can be used while the light goes around the fiber loop. Since the light filter passes twice, the resolution of the optical filter as the vernier effect can be improved, the wavelength selection becomes stronger, the line width is narrow, and the coherent length can be increased. The bidirectional optical amplifier 12 may be inserted at any position in the loop. For example, if the bidirectional optical amplifier 12 is inserted before or after the second polarization converter 183, the light goes around the fiber loop, that is, is shared. Since it can be optically amplified twice during two passes through the Fabry-Perot resonator of the FSR1 and the FSR2 Fabry-Perot resonator comprising the focal ring-type resonant Fabry-Perot electro-optic modulator 130, it is advantageous for SN.

  Further, since the confocal ring-type resonant Fabry-Perot electro-optic modulator 130 can be used as a bidirectional electro-optic modulator, for example, as in a wavelength scanning laser light source 230 shown in FIG. Light is incident / exited to / from one confocal ring-type resonant Fabry-Perot electro-optic modulator 130 having FSRp and FSRs via the entrance / exit side optical system 18A ′ and the entrance / exit side optical system 36B. Light emitted through the incident / exit side optical system 18A ′ is incident on the incident / exit side optical system 18A ′ via the first optical fiber loop 331, and emitted through the incident / exit side optical system 18B ′. May be configured to be incident on the incident / exit side optical system 18B ′ via the second optical fiber loop 332.

  In this wavelength scanning laser light source 230, the light emitted from the confocal ring-type resonant Fabry-Perot electro-optic modulator 11 through the incident / exit side optical system 18 A ′ is converted into a P-polarized component by the first PBS coupler 311. The P-polarized component light is separated by the first polarization converter 312 and rotated by 90 ° by the first polarization converter 312 to be converted to S-polarized component light and incident on the optical amplifier 12. The first optical fiber loop 331 is configured so that the S-polarized component light amplified by the optical amplifier 12 is returned to the first PBS coupler 311 via the optical isolator 17 and the optical coupler 14. The confocal ring-type resonant Fabry-Perot electro-optic modulator 130 enters the confocal ring from the first PBS coupler 311 via the input / output side optical system 18A ′. It is. Further, the light emitted from the confocal ring-type resonant Fabry-Perot electro-optic modulator 130 via the incident / exit side optical system 18B ′ is reflected by the second PBS coupler 321 with the P-polarized component light and the S-polarized component light. The P-polarized component light and the S-polarized component light separated into light are rotated by 90 ° by the second polarization converter 322 and synthesized by the second PBS coupler 321. Two optical fiber loops 332 are configured, and the combined light from the second PBS coupler 321 is incident on the confocal ring-type resonant Fabry-Perot electro-optic modulator 130 via the incident / exit-side optical system 18B ′. The

  That is, in the wavelength scanning laser light source 230, the light emitted through the incident / exit side optical system 18 A ′ of the confocal ring-type resonant Fabry-Perot electro-optic modulator 130 is transmitted through the first optical fiber loop 331. The light is amplified by the optical amplifier 12 and is incident on the confocal ring-type resonant Fabry-Perot electro-optic modulator 130 through the incident / exit-side optical system 18A ′, and the confocal ring-type resonant Fabry-Perot electro-optic modulator 130. The light emitted from the incident / exit side optical system 18B ′ is rotated by 90 ° in the polarization direction in the second optical fiber loop 332 and the confocal ring-type resonance is obtained via the incident / exit side optical system 18B ′. An optical fiber loop is configured to be incident on the Fabry-Perot electro-optic modulator 130.

  In this wavelength scanning laser light source 230, one confocal ring-type resonant Fabry-Perot electro-optic modulator 130 in which the direct reflected light Lr with respect to the incident light Lin does not return to the incident side is used as a bidirectional electro-optic modulator. Thus, the wavelength of a light source having a narrow-band spectrum that generates monochromatic light with extremely low noise can be continuously scanned at a high speed in a wide band.

  The polarization direction of the light emitted from the confocal ring-type resonant Fabry-Perot electro-optic modulator 130 via the incident / exit side optical system 18B ′ is rotated by 90 ° and the incident / exit side optical system 18B ′. Instead of the first optical fiber loop returned to the confocal ring-type resonant Fabry-Perot electro-optic modulator 130, a Faraday rotator 323 and a total reflection mirror 324 are used as in the wavelength scanning laser light source 230 'shown in FIG. Can also be used.

  This wavelength scanning laser light source 230 ′ is an improvement of the wavelength scanning laser light source 230 shown in FIG. 28, except that the second optical fiber loop 332 is replaced with a Faraday rotator 323 and a total reflection mirror 324. Since it is the same as the wavelength scanning laser light source 230, the same reference numerals are given to the same components, and detailed description thereof is omitted.

  In this wavelength scanning laser light source 230 ′, the light emitted from the confocal ring-type resonant Fabry-Perot electro-optic modulator 130 through the incident / exit side optical system 18 B ′ is rotated by 45 ° by the Faraday rotator 323. Then, the light incident on the total reflection mirror 324 and totally reflected by the total reflection mirror 324 is further rotated by 45 ° in the polarization direction by the Faraday rotator 323 so that the confocal ring is transmitted from the incident / exit side optical system 18B ′. It is incident on the type resonant Fabry-Perot electro-optic modulator 130.

  Also in this wavelength scanning laser light source 230 ′, one confocal ring-type resonant Fabry-Perot electro-optic modulator 130 in which the direct reflected light Lr with respect to the incident light Lin does not return to the incident side is replaced with a bidirectional electro-optic modulator. Can be used to scan the wavelength of a light source having a narrow band spectrum that generates monochromatic light with extremely low noise in a wide band at high speed and continuously.

  Further, for example, an optical amplifier such as SOA can amplify both polarizations in either direction, so that, for example, bidirectional light such as SOA is used like the wavelength scanning laser light source 240 shown in FIG. By providing the amplifier 41, optical amplification can be performed twice during one round of the optical fiber loop.

  A wavelength scanning laser light source 240 shown in FIG. 30 is an improvement of the wavelength scanning laser light source 230 ′ shown in FIG. 29, and includes a first optical fiber loop 331, a bidirectional optical amplifier 41, a Faraday rotator 42, and the like. Since it is the same as the wavelength scanning laser light source 230 ′ except that it is replaced with the half mirror 43, the same components are denoted by the same reference numerals, and detailed description thereof is omitted.

  In this wavelength scanning laser light source 240, the light emitted from the confocal ring-type resonant Fabry-Perot electro-optic modulator 130 via the incident / exit side optical system 18 A ′ is amplified by the bidirectional optical amplifier 41, and is Faraday rotator. The polarization direction is rotated 45 ° by 42 and incident on the half mirror 43, and the light reflected by the half mirror 43 is further rotated 45 ° by the Faraday rotator 42 and incident on the bidirectional optical amplifier 41. The light amplified by the bi-directional optical amplifier 41 oscillates when it enters the confocal ring-type resonant Fabry-Perot electro-optic modulator 130 from the incident / exit optical system 18A ′, and passes through the half mirror 43. Laser light is extracted.

  Further, in the confocal resonant Fabry-Perot electro-optic modulator, V-shaped resonance can be obtained by adjusting the incident direction of incident light. For example, the confocal V-shaped resonant Fabry-Perot electro-optic modulation shown in FIG. The curvature of each concave mirror 511, 512 is set so that the Fabry-Perot resonator containing the electro-optic crystal 510 is confocal, and the incident light Lin is adjusted by adjusting the incident direction of the incident light Lin. V-shaped resonance in which the outgoing light Lout returns in the incident direction without the direct reflected light Lr of Lin returning in the incident direction can be obtained.

  Therefore, a confocal V-type resonant Fabry-Perot electro-optic modulator 251 that can obtain a V-shaped resonance in which outgoing light returns in the incident direction without direct reflection of incident light returning in the incident direction is used. Thus, for example, a linear resonance type wavelength scanning laser light source 250 as shown in FIG. 32 can be configured.

  This wavelength scanning laser light source 250 includes two confocal V-type resonant Fabry-Perot electro-optic modulators 251A and 251B, and one V-type resonant Fabry-Perot electro-optic modulator 251A via an input / output side optical system 252A. A bi-directional optical amplifier 253 connected to an optical fiber, an optical coupler 254 connected to the other V-type resonant Fabry-Perot electro-optic modulator 251B via an input / output optical system 252B, and the two V-type resonances. One of the Fabry-Perot electro-optic modulators 251A and 251B, here, a resonator length control unit 255 for periodically changing the resonator length of the V-type resonant Fabry-Perot electro-optic modulator 251A within a certain range, and The bidirectional optical amplifier 253 and the optical coupler 254 are optically connected.

  The two confocal V-shaped resonant Fabry-Perot electro-optic modulators 251A and 251B have close free spectral ranges (FSRs), and each function as a wavelength selection filter. Then, at least one of the two confocal V-shaped Fabry-Perot resonators 251A and 251B, here, the Fabry-Perot resonator 251A can change the selected wavelength by changing the resonator length. It has become.

  The two V-type resonant Fabry-Perot electro-optic modulators 251A and 251B having the FSRs close to each other have their vernier effect by changing the resonator length of one V-type resonant Fabry-Perot electro-optic modulator 251A. Therefore, it functions as a band pass filter having a narrow band wavelength selection characteristic that can change the selection wavelength.

  In the wavelength scanning laser light source 250, the light that has passed through the band-pass filter formed by the two V-type Fabry-Perot resonators 251A and 251B having the adjacent FSR passes between the V-type Fabry-Perot resonators 251A and 251B. It oscillates by being amplified by the bidirectional optical amplifier 253 having a gain at the oscillation wavelength when reciprocating. In this wavelength scanning laser light source 250, the oscillation wavelength is periodically changed by periodically changing the resonator length of the V-type Fabry-Perot resonator 251A by a resonator length control unit 255 within a certain range. The wavelength of the laser light taken out via the optical coupler 254 changes periodically.

  In the wavelength scanning laser light source 250 having such a configuration, the resonance length can be increased by increasing the length of the optical path connected to the optical fiber, thereby reducing the longitudinal mode interval of the entire laser and changing the resonance length. The effect of mode hopping can be eliminated, and strictly speaking, it is not single-mode oscillation, but it is possible to tune the wavelength continuously in a pseudo manner simply by changing the selected wavelength of the bandpass filter. .

  In this wavelength scanning laser light source 250, the wavelength of a light source having a narrow band spectrum can be scanned continuously at a high speed in a wide band, and the direct reflected light Lr with respect to the incident light Lin does not return to the incident side. Since the V-type resonant Fabry-Perot electro-optic modulator Fabry-Perot resonators 251A and 251B are used, the optical isolator can be omitted, and an increase in noise due to optical loss in the optical isolator can be reduced.

  Similarly to the confocal ring-type resonant Fabry-Perot electro-optic modulator 251, the confocal V-type resonant Fabry-Perot electro-optic modulator 251 also includes two electro-optic crystals such that the C-axis is orthogonal between the concave mirrors. By arranging, the difference in FSR can be set finely by the difference in length.

  Further, the confocal V-type resonant Fabry-Perot electro-optic modulator 251 has different FSR depending on the polarization direction, and the electro-optic modulation is strongly applied to the polarization in the c-axis direction. For example, as shown in FIG. In addition, the linear resonance type wavelength scanning laser light source 260 can be constituted by one confocal V-type resonance Fabry-Perot electro-optic modulator 251.

  This wavelength scanning laser light source 260 is an improvement of the wavelength scanning laser light source 250 shown in FIG. 32, and includes a single confocal V-type resonant Fabry-Perot electro-optic modulator 251 and the V-type resonant Fabry-Perot. A bidirectional optical amplifier 253 connected to the electro-optic modulator 251 via an input / output optical system 252, a Faraday rotator 264 connected to the bidirectional optical amplifier 253 by optical fiber, and an optical fiber connected to the Faraday rotator 264 A half mirror 265.

  In this wavelength scanning laser light source 260, the light emitted from the confocal V-type resonant Fabry-Perot electro-optic modulator 251 through the incident / exit side optical system 252 is amplified by the bidirectional optical amplifier 253, and the Faraday rotator 264 is used. When the polarization direction is rotated by 45 °, the light is incident on the half mirror 265, and the light reflected by the half mirror 265 is further rotated by 45 ° by the Faraday rotator 265 and incident on the bidirectional optical amplifier 253. The light amplified by the bidirectional optical amplifier 253 is incident on the confocal V-type resonant Fabry-Perot electro-optic modulator 251 from the incident / exit side optical system 252.

  In the wavelength scanning laser light source 250, the confocal V-type resonant Fabry-Perot electro-optic modulator 251 has different FSR depending on the polarization direction, and electro-optic modulation is strongly applied to the polarization in the c-axis direction. It functions as two Fabry-Perot resonators having different degrees of modulation in the adjacent FSRp and FSRs with respect to incident light, that is, P-polarized component light and S-polarized component light constituting the combined light.

  One confocal V-type resonant Fabry-Perot electro-optic modulator 251 that functions as two Fabry-Perot resonators having different modulation degrees in the adjacent FSRp and FSRs functions as a wavelength selection filter, and is configured to have P polarization and S By varying the relative resonator length of the polarized light, it functions as a bandpass filter having a narrow band wavelength selection characteristic that can vary the selected wavelength by its vernier effect.

  In the wavelength scanning laser light source 260, the light emitted from the confocal V-type resonant Fabry-Perot electro-optic modulator 251 is reflected by the half mirror 265 and is reflected by the confocal V-type resonant Fabry-Perot electro-optic modulator 251. Oscillated by being amplified by the bidirectional optical amplifier 253 having a gain at the oscillation wavelength. In the wavelength scanning laser light source 260, the relative resonator lengths of the P-polarized light and the S-polarized light of the V-type resonant Fabry-Perot electro-optic modulator 251 are periodically changed within a certain range by the resonator length control unit 55. As a result, the oscillation wavelength changes periodically, and the wavelength of the laser light extracted through the half mirror changes periodically.

  In the wavelength scanning laser light source 260 having such a configuration, the resonance length can be increased by increasing the length of the optical path connected to the optical fiber, thereby reducing the longitudinal mode interval of the entire laser and changing the resonance length. The effect of mode hopping can be eliminated, and strictly speaking, it is not single-mode oscillation, but it is possible to tune the wavelength continuously in a pseudo manner simply by changing the selected wavelength of the bandpass filter. .

  Therefore, this wavelength scanning laser light source 260 uses a single confocal V-type resonant Fabry-Perot electro-optic modulator 51 in which the direct reflected light Lr with respect to the incident light Lin does not return to the incident side. The wavelength of a light source having a narrow band spectrum that generates monochromatic light can be continuously scanned in a wide band at high speed.

  In the embodiment of the invention described above, the confocal ring-type resonant Fabry-Perot electro-optic modulator 130 (130A, 130B) or the confocal V-type resonant Fabry-Perot electro-optic modulator 251 (251A, 251) 251B) has been described, but the ring-type resonant Fabry-Perot electro-optic modulator 130 (130A, 130B) and the V-type resonant Fabry-Perot electro-optic modulator 251 (251A, 251B) In principle, the light beam may not be confocal as long as light can be coupled to the single transverse mode.

  That is, a spatial Fabry-Perot electro-optic modulator can also be used as the ring-type resonant Fabry-Perot electro-optic modulator 130 (130A, 130B) or the V-type resonant Fabry-Perot electro-optic modulator 251 (251A, 251B).

  Using a spatial Fabry-Perot electro-optic modulator has the advantage of reducing loss and increasing finesse. In the optical path, the loss is about 7 dB per unit and the finesse is about 50, but the loss is about 1 dB and the finesse is about 400 in the spatial type. In this case, the SN ratio is improved by reducing the loss, and the finesse improvement increases the resolution as a wavelength filter, so that the coherent length of the wavelength tunable laser can be increased.

  By making the Fabry-Perot electro-optic modulator in the above space “ring type” or “V-shaped”, direct reflection can be prevented, thereby reducing the number of optical isolators.

  A "ring-type" or "V-shaped" Fabry-Perot electro-optic modulator is theoretically not confocal as long as it can couple light into a single transverse mode. If the light cannot be coupled into a single transverse mode with slight adjustments, the unwanted transverse mode will appear and will be different from the desired mode frequency, thus disturbing the vernier effect. In a confocal "ring-type" or "V-shaped" Fabry-Perot electro-optic modulator, the resonance frequency of the transverse mode is degenerated, so even if there is a lack of adjustment, use it without causing unnecessary modes. Can do.

  Further, in the wavelength scanning laser light source using the confocal “ring type” or “V-shaped” Fabry-Perot electro-optic modulator, similarly to the wavelength scanning laser light source 10 shown in FIG. Laser light whose wave number is linear with respect to time is configured so that the resonator length controller reads the calibration data for obtaining laser light whose wave number is linear with respect to time from the ROM and generates the waveform of the scanning signal. Can be obtained.

  Therefore, as described above, the two Fabry-Perot resonators function as narrow-band wavelength tunable filters that can vary the selected wavelength by the vernier effect, and wavelength scanning that outputs laser light whose wavelength is temporally scanned. In the optical coherence tomography apparatus 100 using a scanning laser light source, high-speed OCT signal acquisition is possible, and the waveform of the periodic scanning signal applied to the Fabry-Perot resonator is adjusted, via the optical element. By calibrating so that the wave number (2π / wavelength) of the extracted laser light is linear with respect to time, the obtained interference signal is rearranged so that the wave number (2π / wavelength) of the light is evenly spaced. However, since it is not necessary to add signal processing, the wavelength of the light source having a narrow-band spectrum without performing signal processing for calibration on the OCT signal. Can be continuously scanned in a wide band at high speed.

  As described above, as an embodiment capable of reducing the number of optical isolators, a space in which direct reflection can be prevented by making the Fabry-Perot electro-optic modulator of the space “ring-shaped” or “V-shaped”. The case of using a Fabry-Perot electro-optic modulator in which an electro-optic crystal is incorporated in a Fabry-Perot resonator is described. However, a waveguide-type Fabry-Perot electro-optic modulator, that is, a bulk type other than a Fabry-Perot resonator in a space, for example, The wavelength scanning laser light source may be configured using a Fabry-Perot electro-optic modulator in which an electro-optic crystal is incorporated in the Fabry-Perot resonator.

  Further, in the ring-type Fabry-Perot electro-optic modulator, the characteristics of the resonator do not depend on the direction in which the laser light rotates in the resonator, so that the wavelength scanning laser light sources 270 and 280 shown in FIGS. Two ring-type Fabry-Perot electro-optic modulators can be made polarization independent, and a polarization independent optical amplifier having a gain at the oscillation wavelength can be provided in the laser oscillation optical path.

  Polarization-dependent optical amplifiers are expensive and have poor characteristics such as extinction ratio, but this problem can be solved by using polarization-independent optical amplifiers.

  A wavelength scanning laser light source 270 shown in FIG. 34 is a polarization-independent configuration obtained by improving the wavelength scanning laser light source 210 ′ shown in FIG. 25, and has two units having FSRp and FSRs close to each other. The ring-type Fabry-Perot electro-optic modulators 130A and 130B, a polarization conversion element 271, a PBS coupler 272, an SM fiber 273, a polarization-independent bidirectional optical amplifier 274, and a half mirror 275 are provided.

  The polarization-independent bidirectional optical amplifier 274 is a polarization-independent bidirectional optical amplifier such as an SOA that can amplify in either direction with respect to any polarization. Amplifying the light incident via the fiber 273, outputting a part of the emitted light to the outside via the half mirror 275, amplifying the light reflected back by the half mirror 275, The light enters the PBS coupler 272 through the SM fiber 273.

  The PBS coupler 272 transmits the P-polarized component of the incident light and reflects the S-polarized component, thereby separating the incident light by the polarized component, and also incident P-polarized component light and S-polarized component light. Is synthesized.

  Here, the PBS coupler 272 separates incident light incident via the SM fiber 273 into a P-polarized component and an S-polarized component.

  The incident light that has entered the PBS coupler 272 via the SM fiber 273 is such that the P-polarized component transmitted through the PBS coupler 272 enters the ring-type Fabry-Perot electro-optic modulator 130B via the input / output optical system. Is done.

  The P-polarized component of the incident light incident on the ring-type Fabry-Perot electro-optic modulator 130B is extracted from the ring-type Fabry-Perot electro-optic modulator 130B via the entrance / exit optical system, and the entrance / exit optical system is The P-polarized light component of the incident light that is incident on the ring-type Fabry-Perot electro-optic modulator 130A via the ring-type Fabry-Perot electro-optic modulator 130A is converted into the ring-type Fabry-Perot electro-optic modulator 130A. Is taken out via an incident / exit optical system.

  The P-polarized component of the incident light extracted from the ring-type Fabry-Perot electro-optic modulator 130A through the input / output optical system is rotated by 90 ° by the polarization conversion element 271 and converted into an S-polarized component. The light enters the PBS coupler 272.

  The PBS coupler 272 reflects the light whose polarization direction is rotated by 90 ° by the polarization conversion element 271 and converted into the S-polarized component, and the polarization-independent bidirectional light is transmitted through the SM fiber 273. The light enters the amplifier 274.

  Of the incident light incident on the PBS coupler 272 via the SM fiber 273, the S-polarized component reflected by the PBS coupler 272 is rotated by 90 ° in the polarization direction by the polarization conversion element 271 and is P-polarized. It is converted into a component and incident on a ring-type Fabry-Perot electro-optic modulator 130A via an incident / exit optical system.

  The P-polarized component incident on the ring-type Fabry-Perot electro-optic modulator 130A via the incident / exit optical system, that is, the P-polarized component obtained by converting the S-polarized component of the incident light by the polarization converting element 271 is Is extracted from the Fabry-Perot electro-optic modulator 130A via the incident / exit optical system, and is incident on the ring-type Fabry-Perot electro-optic modulator 130B via the incident / exit optical system. The P-polarized component of the incident light incident on the device 130B is extracted from the ring-type Fabry-Perot electro-optic modulator 130A via the input / output optical system and is incident on the PBS coupler 272.

  The PBS coupler 272 transmits the P-polarized component light extracted from the ring-type Fabry-Perot electro-optic modulator 130A through the incident / exit optical system and passes through the SM fiber 273 to prevent polarization. It enters the dependent bidirectional optical amplifier 274.

  In this wavelength scanning laser light source 270, the light reflected by the half mirror is amplified by the polarization-independent bidirectional optical amplifier 274 and is incident on the PBS coupler 272 via the SM fiber 273 to be P-polarized component and S-polarized light. The light separated into the P-polarized component and the S-polarized component is returned to the PBS coupler 272 via the two ring-type Fabry-Perot electro-optic modulators 130A and 130B having the adjacent FSRp and FSRs. The combined light is incident on the polarization-independent bidirectional optical amplifier 274 via the SM fiber 273 and amplified. The light amplified by the polarization-independent bidirectional optical amplifier 274 is incident on the half mirror 14B. The light reflected by the half mirror 14B enters the polarization-independent bidirectional optical amplifier 274 and emits light. And the laser beam is taken out through the half mirror 14B.

  A wavelength scanning laser light source 280 shown in FIG. 35 is improved from the above-described wavelength scanning laser light source 270 shown in FIG. 34, and one ring type Fabry-Perot electro-optic modulator 130 is bidirectionally modulated. By being used as a detector, it is made to function as two ring-type Fabry-Perot electro-optic modulators 130A and 130B having adjacent FSRp and FSRs.

  This wavelength scanning laser light source 270 includes one ring-type Fabry-Perot electro-optic modulator 130, polarization conversion elements 271A and 271B, PBS couplers 272A, 271B and 272C, SM fiber 273, polarization-independent bidirectional light. An oscillation optical path provided with an amplifier 274 and a half mirror 275 is provided.

  The polarization-independent bidirectional optical amplifier 274 is a polarization-independent bidirectional optical amplifier such as an SOA that can amplify in either direction with respect to any polarization. Amplifying the light incident via the fiber 273, outputting a part of the emitted light to the outside via the half mirror 275, amplifying the light reflected back by the half mirror 275, The light enters the PBS coupler 272A through the SM fiber 273.

  The PBS coupler 272A separates incident light incident through the SM fiber 273 into a P-polarized component and an S-polarized component.

  The incident light that has entered the PBS coupler 272A via the SM fiber 273 has a P-polarized component transmitted through the PBS coupler 272A, incident on the PBS coupler 272B, and a P-polarized component transmitted through the PBS coupler 272B. The light is incident on a ring-type Fabry-Perot electro-optic modulator 130 via an input / output optical system.

  Of the incident light incident on the PBS coupler 272A via the SM fiber 273, the S-polarized component reflected by the PBS coupler 272A is rotated by 90 ° in the polarization direction by the polarization conversion element 271A, and becomes P-polarized light. The P-polarized component that is converted into the component and incident on the PBS coupler 272C and transmitted through the PBS coupler 272C is rotated by 90 ° in the polarization direction by the polarization conversion element 271B, converted into the S-polarized component, and passed through the entrance / exit optical system. The light enters the ring-type Fabry-Perot electro-optic modulator 130.

  The P-polarized component of the incident light incident on the ring-type Fabry-Perot electro-optic modulator 130 via the incident / exit optical system is extracted from the ring-type Fabry-Perot electro-optic modulator 130 via the incident / exit optical system. Then, the polarization direction is rotated by 90 ° by the polarization conversion element 271B, converted into an S-polarized component, incident on the PBS coupler 272C, reflected by the PBS coupler 272C, incident on the PBS coupler 272B, and the PBS coupler 272C. And is incident on a ring-type Fabry-Perot electro-optic modulator 130 via an incident / exit optical system.

  The S-polarized component light extracted from the ring-type Fabry-Perot electro-optic modulator 130 via the incident / exit optical system is rotated by 90 ° by the polarization conversion element 271B and converted into a P-polarized component. Light of the P-polarized component that is incident on the PBS coupler 272C and transmitted through the PBS coupler 272C is rotated by 90 ° in the polarization direction by the polarization conversion element 271A, converted into an S-polarized component, and incident on the PBS coupler 272A.

  The PBS coupler 272 reflects the light whose polarization direction is rotated by 90 ° by the polarization conversion element 271 and converted into the S-polarized component, and the polarization-independent bidirectional light is transmitted through the SM fiber 273. The light enters the amplifier 274.

  In addition, the S-polarized component of the incident light that has entered the ring-type Fabry-Perot electro-optic modulator 130 via the incident / exit optical system is transmitted from the ring-type Fabry-Perot electro-optic modulator 130 via the incident / exit optical system. And is incident on the PBS coupler 272B, reflected by the PBS coupler 272B, incident on the PBS coupler 272C, reflected by the PBS coupler 272C, and rotated by 90 ° by the polarization conversion element 271B. The light is converted into a P-polarized component and is incident on a ring-type Fabry-Perot electro-optic modulator 130 via an incident / exit optical system.

  Then, the P-polarized component light extracted from the ring-type Fabry-Perot electro-optic modulator 130 via the incident / exit optical system is incident on the PBS coupler 272B, passes through the PBS coupler 272C, and passes through the PBS coupler 272A. Is incident on.

  The PBS coupler 272A transmits the P-polarized component light and enters the polarization-independent bidirectional optical amplifier 274 via the SM fiber 273.

  In this wavelength scanning laser light source 270, the light reflected by the half mirror is amplified by the polarization-independent bidirectional optical amplifier 274 and is incident on the PBS coupler 272 A via the SM fiber 273 to be P-polarized component and S-polarized light. The light separated into the P-polarized component and the S-polarized component is returned to the PBS coupler 272A via the ring-type Fabry-Perot electro-optic modulator 130 and synthesized, and is polarized via the SM fiber 273. The light is incident on the wave-independent bidirectional optical amplifier 274 and amplified. The light amplified by the polarization-independent bidirectional optical amplifier 274 is incident on the half mirror 14B, and the light reflected by the half mirror 14B is reflected. The laser beam oscillates when incident on the polarization-independent bidirectional optical amplifier 274, and the laser beam is received through the half mirror 14B. It is issued.

  Here, in the embodiment described above, two Fabry-Perot resonators function as a narrow-band wavelength tunable filter that can vary the selected wavelength by the vernier effect, and the light whose wavelength is scanned in time is used. Although the optical coherence tomography apparatus using the wavelength scanning laser light source including the wavelength tunable filter means for output has been described, the light source like the optical coherence tomography apparatus is not necessarily a laser light source, and has a configuration as shown in FIG. A non-laser wavelength scanning light source 300 may be used.

  A non-laser wavelength scanning light source 300 shown in FIG. 36 includes a broadband light source 310 that emits broadband light that covers a wavelength scanning range required by an optical coherence tomography apparatus, and broadband light emitted from the broadband light source 310. The wavelength tunable filter unit 320 extracts light in a desired wavelength band.

  The non-laser wavelength scanning light source 300 includes a broadband light source 310 that emits broadband light that covers a wavelength scanning range required for an optical coherence tomography apparatus, and a desired wavelength band from the broadband light emitted from the broadband light source 310. It comprises a wavelength tunable filter unit 320 for extracting the light.

  The wavelength tunable filter unit 320 includes two Fabry-Perot resonators 321A and 321B having FSRs (Free Spectral Ranges) close to each other provided in the optical path of broadband light emitted from the broadband light source 310, and The optical amplifiers 323A and 323B that amplify the output light of the Fabry-Perot resonators 322A and 322B and the resonance of the Fabry-Perot resonator 323A, one of the two Fabry-Perot resonators 323A and 323B having the adjacent FSRs, here. And a resonator length control unit 324 that periodically changes the length of the device within a certain range.

  In the non-laser wavelength scanning light source 300, the two Fabry-Perot resonators 321A and 321B having adjacent FSRs function as wavelength selection filters, respectively. At least one of the two Fabry-Perot resonators 321A and 321B, here the Fabry-Perot resonator 321A, can change the selected wavelength by changing the resonator length.

  The two Fabry-Perot resonators 321A and 321B having the FSRs close to each other can narrow the selection wavelength by changing the resonator length of one of the Fabry-Perot resonators 321A. It functions as a bandpass filter having a wavelength selection characteristic of the band.

  In this non-laser wavelength scanning light source 300, the light that has passed through the band-pass filter by the two Fabry-Perot resonators 321A and 321B having the adjacent FSR is amplified by the optical amplifiers 323A and 323B such as SOA and fiber amplifier. Is output.

It is called a Fabry-Perot electro-optic modulator (or an optical comb generator) having a structure in which an electrode is attached to a Fabry-Perot optical resonator constructed of an optically variable refractive index material such as LN (LiNbO ₃ ). By using the modulator, the wavelength can be varied by the electro-optic effect. Moreover, since it is an electrical modulation, it has excellent linearity and reproducibility.

  Therefore, a Fabry-Perot electro-optic modulator is used as the Fabry-Perot resonator 321A in which the resonator length in the non-laser wavelength scanning light source 300 is variable. The two Fabry-Perot resonators 321A having the adjacent FSRs are optically modulated by applying a periodic signal such as a sawtooth wave to the Fabry-Perot electro-optic modulator by the resonator length control unit 324. The 321B can function as a bandpass filter having a narrow band wavelength selection characteristic capable of changing the selection wavelength by the vernier effect, and the center frequency can be scanned with high accuracy and high speed within a predetermined range. Therefore, by periodically changing the resonator length of the Fabry-Perot resonator 321A within a certain range by the resonator length control unit 324, the wavelength of the extracted light can be periodically changed to scan at high speed. .

  That is, in this non-laser wavelength scanning light source 300, as shown in FIG. 37 (A), the two Fabry-Perot resonators 321A and 321B having the adjacent FSRs can be changed in wavelength by the vernier effect. Functioning as a band pass filter having a narrow band wavelength selection characteristic, and extracting narrow band light corresponding to the wavelength selection characteristic of the band pass filter from the broadband light emitted from the broadband light source 310, and By scanning the center frequency within a predetermined range, as shown in FIG. 37 (B), it is possible to obtain narrowband light whose wavelength is continuously scanned within the predetermined scanning range.

  Here, when a linear (waveguide-type) Fabry-Perot electro-optic modulator is used as the two Fabry-Perot resonators 321A and 321B, laser oscillation is caused by reflected light from the Fabry-Perot electro-optic modulator. In order to prevent this, the optical amplifiers 323A and 323B must have an optical isolator built therein.

  Further, as the two Fabry-Perot resonators 321A and 321B, for example, the curvatures of the concave mirrors 111 and 112 are set so that the Fabry-Perot resonator including the electro-optic crystal 110 shown in FIG. In the case of using the ring-type resonant Fabry-Perot electro-optic modulator 130 in which the ring-type resonance is obtained by setting, the ring-type resonant fabric in which the curvatures of the concave mirrors 111 and 112 are set to be confocal in this way. In the Perot electro-optic modulator 130, since the direct reflected light Lr with respect to the incident light Lin does not return to the incident side, an optical isolator is not required, so that the optical isolators at the input / output portions of the Fabry-Perot resonators 321A and 321B are omitted. It is only necessary to provide an optical isolator on the output side of the optical amplifier 323B.

  Further, when the Fabry-Perot electro-optic modulator is a ring type, spontaneous emission light (ASE) generated from the optical amplifiers 323A and 323B can be regarded as a broadband light source. For example, a wavelength scanning laser light source shown in FIG. As in 350, the spontaneous emission is provided by reflecting a spontaneous emission light (ASE) emitted from the optical amplifier 323A323B instead of the broadband light source 310 and entering the wavelength tunable filter unit 320. The optical amplifiers 323A and 323B that emit light (ASE) can be used as the broadband light source 310.

  In the wavelength scanning laser light source 350 shown in FIG. 38, spontaneous emission light (ASE) generated by the optical amplifier 323A is reversely directed toward the Fabry-Perot resonator 321B, the optical amplifier 323A, the Fabry-Perot resonator 321A, and the reflecting mirror 351. , And reflected by the reflecting mirror 351, are returned through the Fabry-Perot resonator 321A, the optical amplifier 323A, and the Fabry-Perot resonator 321B and output. In this case, since the number of optical isolators, broadband light sources 310, and the like can be reduced, there is a cost merit. In addition, since the light passes through the filter twice, the SN ratio of light can be improved.

Here, in the case where the wavelength scanning laser light source 10 is used in the optical coherence tomography apparatus, the maximum FSR (FSRmax) of the Fabry-Perot electro-optic modulator is the sampling theorem, where the required coherent length is δL and the speed of light is c. From
FSRmax = c / δL (1) is given by equation (1).

  Since the two Fabry-Perot electro-optic modulators each have a loss of 7 dB, the total loss is 14 dB or more, the output power does not reach the saturation limit, and the optical power of each Fabry-Perot electro-optic modulator is Sensitive to response characteristics.

Therefore, the frequency scanning speed (Srate), that is, the cut-off (Srate-cut) of the frequency at which the laser beam scans per unit time, is a function of the maximum scanning range (FSRv).
Srate-cut = FSRv / Fδt (2) It is estimated that it is given by equation (2). Here, δt (= F / FSR) is a photon lifetime in the Fabry-Perot electro-optic modulator.

  The cut-off (Srate-cut) of the frequency scanning speed (Srate) obtained as a result of the experiment was 12 THz / μs.

The limit (δLlimit) of the coherent length (δL) is
δLlimit = c / Srateδt (3) It was estimated to be given by equation (3).

From this result, it can be predicted that the coherent length (δL) and the frequency scanning speed (Srate) are in a trade-off relationship, and the coherent length (δL) in the cutoff (Srate-cut) of the frequency scanning speed (Srate). The limit of (δLlimit-cutoff) is
δLlimit-cutoff = cF / FSRv (4) Equation (4)

  Thus, given the coherent length (δL), frequency scan rate (Srate), and maximum scan range (FSRv) given system requirements, the resonator conditions, ie, finesse (F) and free spectral region (FSR) Conditions can be determined as follows.

That is, the range that Finesse (F) can take is generally calculated from the above equation (3). CFSR / SrateδL> F
The possible range of the free spectral region (FSR) is
c / δL> FSR
It becomes.

Here, in an actual device, the range that the finesse (F) can take is as follows:
c / δL>FSR> SrateF ² / FSRv / 2
That is, good operation could be confirmed when the frequency scanning speed (Srate) was in the range of 1/2 to 2 times the cutoff (Srate-cut).

  In the wavelength scanning laser light source 10, intensity noise was generated when the scanning speed was slow, particularly when the frequency scanning speed (Srate) was slower than cut-off (Srate-cut) / 2. This phenomenon is considered as mode competition noise, and mode competition noise can be reduced by performing high frequency superposition on the SOA, and the scanning speed is low. The characteristics can be improved. When the frequency scanning speed (Srate) is faster than cut-off (Srate-cut) / 2, it can be improved by increasing the loop gain by the method shown in FIG. 9, FIG. 10, FIG.

1 is a block diagram showing a basic configuration of an optical coherence tomography device according to the present invention. It is a block diagram which shows the basic composition of the wavelength scanning laser light source used for the said optical coherence tomography apparatus. It is a figure which shows the transmission spectrum of a normal optical resonator. It is a figure which shows the transmission spectrum at the time of connecting two optical resonators in which FSR differs 1% in cascade. It is the figure which expanded and showed a part of transmission spectrum shown in FIG. It is a block diagram which shows the actual structural example of the wavelength scanning laser light source which used the Fabry-Perot electro-optic modulator for the said 2 Fabry-Perot resonators. It is a block diagram which shows the structure of the fiber ring laser which uses the optical fiber amplifier for wavelength 1.5 micrometer band, two comb generator modules, and an optical coupler. It is a figure which shows the measurement result of the said fiber ring laser. It is a block diagram which shows the structural example of the wavelength scanning laser light source which arrange | positions two optical amplifiers in the back | latter stage of a Fabry-Perot electro-optic modulator, respectively. It is a block diagram which shows the structural example of the wavelength scanning laser light source made to optically amplify in the back | latter stage of two Fabry-Perot electro-optic modulators with one optical amplifier. It is a block diagram which shows the other structural example of the wavelength scanning laser light source made to optically amplify in the back | latter stage of two Fabry-Perot electro-optic modulators with one optical amplifier. It is a block diagram which shows the structure of the measurement system for measuring the relationship between the scanning signal voltage and laser frequency in a wavelength scanning laser light source. It is a figure which shows the result of having measured the relationship between the said scanning signal voltage and a laser frequency. It is a figure which shows the observation result of the waveform of the scanning signal which the said resonator length control part gives to a Fabry-Perot resonator, and the waveform of the interference signal obtained with an interferometer. It is a block diagram which shows the structural example of the wavelength scanning laser light source which can obtain a laser beam with a wave number linear with respect to time via an optical coupler. It is a block diagram which shows the fundamental structure of a wavelength scanning laser light source provided with two confocal Fabry-Perot electro-optic modulators. It is sectional drawing which shows typically the structure of the confocal ring-type resonant Fabry-Perot electro-optic modulator used for the said wavelength scanning laser light source. It is sectional drawing which shows typically the structure of the confocal Fabry-Perot electro-optic modulator formed by arrange | positioning two electro-optic crystals so that C-axis may be orthogonally crossed between concave mirrors. It is a block diagram which shows the structural example of the resonator length control part made to control the center wavelength of the band pass filter comprised by two Fabry-Perot resonators. It is a figure which shows typically the connection structure for supplying the modulation | alteration signal of the confocal Fabry-Perot electro-optic modulator formed by arrange | positioning two electro-optic crystals so that C axis may be orthogonally crossed between concave mirrors. It is a figure which shows typically the manufacture example of a monolithic type Fabry-Perot electro-optic modulator. It is a figure which shows typically the manufacture process of the said monolithic type Fabry-Perot electro-optic modulator. It is a figure which shows typically the manufacture example of a monolithic type Fabry-Perot electro-optic modulator. FIG. 2 is a diagram schematically illustrating a monolithic Fabry-Perot electro-optic modulator including an input / output optical system having a structure in which a prism type mirror is provided on an input surface. It is a figure which shows typically the monolithic Fabry-Perot electro-optic modulator provided with the incident / exit optical system of the structure which couple | bonds the fiber mounted in the two-core ferrule with a prism, and a ring type resonator. It is a block diagram which shows the other structural example of the wavelength scanning laser light source provided with two confocal Fabry-Perot electro-optic modulators. It is a block diagram which shows the basic composition of a wavelength scanning laser light source provided with one confocal Fabry-Perot electro-optic modulator. It is a block diagram which shows the other structural example of the wavelength scanning laser light source provided with one confocal Fabry-Perot electro-optic modulator. It is a block diagram which shows the other structural example of the wavelength scanning laser light source provided with one confocal Fabry-Perot electro-optic modulator. It is a block diagram which shows the other structural example of the wavelength scanning laser light source provided with one confocal Fabry-Perot electro-optic modulator. It is a block diagram which shows the other structural example of the wavelength scanning laser light source provided with one confocal Fabry-Perot electro-optic modulator. It is sectional drawing which shows typically the structure of the confocal V-type resonant Fabry-Perot electro-optic modulator used for a wavelength scanning laser light source. It is a block diagram which shows the structure of the linear resonance type | mold wavelength scanning laser light source comprised using two confocal V-type resonant Fabry-Perot electro-optic modulators. It is a block diagram which shows the structure of the linear resonance type | mold wavelength scanning laser light source comprised using one confocal V-type resonant Fabry-Perot electro-optic modulator. FIG. 2 is a block diagram showing a configuration of a wavelength scanning laser light source including a polarization-independent ring-type resonant Fabry-Perot electro-optic modulator and a polarization-independent optical amplifier in a laser oscillation optical path. FIG. 35 is a block diagram illustrating a configuration of a wavelength scanning laser light source including one ring-type Fabry-Perot electro-optic modulator obtained by improving the wavelength scanning laser light source illustrated in FIG. 34. It is a block diagram which shows the structure of the non-laser wavelength scanning light source with which the said optical coherence tomography apparatus is equipped. It is a figure which shows typically the characteristic of the narrowband light obtained in the said non-laser wavelength scanning light source. It is a block diagram which shows the other structural example of the non-laser wavelength scanning light source with which the said optical coherence tomography apparatus is equipped. It is a block diagram which shows the principle of the optical coherence tomography apparatus based on a Michelson interferometer. It is a block diagram which shows the structure of the wavelength variable light source by the ring laser using an erbium doped fiber.

Explanation of symbols

  1, 2, 3, 4 Optical fibers 10, 10 ′, 210, 210 ′, 220, 220 ′, 230, 230 ′, 240, 250, 260 Wavelength scanning laser light source, 11 Optical fiber loop, 12, 12A, 12B, Optical amplifier, 12 ', 41, 253 Bidirectional optical amplifier, 13A, 13B Fabry-Perot resonator, 13A', 13B 'Fabry-Perot electro-optic modulator, 14,254 optical coupler, 15, 255 Cavity length controller, 15A ROM, 16 band pass filter, 17, 17A, 17B, 17C, 17D, 17E optical isolator, 20 interference optical system, 21 fiber coupler, 30 scanning optical system, 31, 33 lens, 32 scanning mirror, 40 reference optical system, 41 , 42 lens, 43 fixed reference mirror, 50 signal processing unit, 51 photodetector, 52 Arithmetic processing unit, 60 object to be observed, 100 optical coherence tomography apparatus, 130, 130A, 130B ring-type resonant Fabry-Perot electro-optic modulator, 150 sawtooth wave signal generator, 151 inverting amplifier, 152 photodetector, 153 lock-in Amplifier, 180 Optical system for separating and synthesizing polarization components, 110, 110A, 110B, 510 Electro-optic crystal, 111, 112, 511, 512, concave mirror, 181, 184, 311, 321 PBS coupler, 182, 183, 312 , 322 Polarization conversion element, 251, 251A, 251B V-type resonant Fabry-Perot electro-optic modulator

Claims (28)

Periodically changing the resonator length of at least one Fabry-Perot resonator out of two Fabry-Perot resonators having FSR (Free Spectral Range) provided in the laser oscillation optical path close to each other within a certain range. Accordingly, the two Fabry-Perot resonators function as narrow-band tunable filters capable of varying the selected wavelength by the vernier effect, and a wavelength scanning light source that outputs laser light that has been scanned in terms of time, ,
The laser light output from the wavelength scanning light source is branched into reference light and observation light for irradiating the object to be observed, and interference light between the reflected light of the observation light irradiated on the object to be observed and the reference light is generated. Interference optical system
An optical coherence tomography apparatus comprising: signal processing means that receives interference light obtained by the interference optical system, converts the interference light into an electrical signal, and calculates optical tomographic image information of the object to be observed.   2. The optical coherence tomography apparatus according to claim 1, wherein the wavelength scanning light source is calibrated so that the wave number of the laser beam being scanned is linear with respect to time. The wavelength scanning light source is
An optical fiber loop serving as the laser oscillation optical path;
An optical amplifier provided in the optical fiber loop and having a gain at an oscillation wavelength;
Two Fabry-Perot resonators provided in the optical fiber loop and having close free spectral range (FSR);
An optical element connected to the optical fiber loop and extracting a part of the light passing through the optical fiber loop;
And a resonator length controller that periodically changes the resonator length of at least one of the two Fabry-Perot resonators having the adjacent FSRs within a certain range. Item 4. The optical coherence tomography device according to Item 1.   The Fabry-Perot resonator, in which the resonator length is periodically changed within a certain range by the resonator length control unit, is composed of a Fabry-Perot electro-optic modulator having an electrode structure, and is given by the resonator length control unit. 4. The optical coherence tomography apparatus according to claim 3, wherein light passing therethrough is modulated by a periodic scanning signal.   5. The optical coherence tomography according to claim 4, wherein each of the two Fabry-Perot resonators having adjacent FSRs is a Fabry-Perot electro-optic modulator, and is adjusted to the adjacent FSR by temperature control. apparatus.   The resonator length control unit applies reciprocal scanning signals to the two Fabry-Perot resonators having the adjacent FSRs to reciprocally change the resonator lengths of the Fabry-Perot resonators. The optical coherence tomography apparatus according to claim 5.   7. The resonator length control unit controls a center wavelength of light passing through the two Fabry-Perot resonators having the adjacent FSRs by superimposing a control voltage on a scanning signal. Optical coherence tomography device.   4. The optical coherence tomography apparatus according to claim 3, wherein the optical amplifier is provided at each subsequent stage of the two Fabry-Perot resonators.   4. The light is separated by the direction or polarization of light passing through the optical fiber loop, and optical amplification is performed at each subsequent stage of the two Fabry-Perot resonators by one optical amplifier. The optical coherence tomography device described.     The wavelength scanning light source adjusts the waveform of the periodic scanning signal given to the Fabry-Perot resonator by the resonator length control unit, so that the wave number of the laser light taken out through the optical element can be changed over time. 4. The optical coherence tomography apparatus according to claim 3, wherein the optical coherence tomography apparatus is calibrated so as to be linear.   The laser oscillation optical path includes two Fabry-Perot electro-optic modulators in which an electro-optic crystal is incorporated in a Fabry-Perot resonator in a space having an FSR (Free Spectral Range) close to each other, and an optical amplifier having a gain in oscillation wavelength. 2. The optical coherence tomography apparatus according to claim 1, wherein an optical element for extracting output light is connected to an optical fiber.   Each of the two Fabry-Perot electro-optic modulators includes a ring-type resonant Fabry-Perot electro-optic modulator configured to obtain a ring-type resonance with a Fabry-Perot resonator including an electro-optic crystal. Item 12. An optical coherence tomography device according to Item 11.   12. The two Fabry-Perot resonators each include a V-type resonant Fabry-Perot electro-optic modulator configured to obtain a V-type resonance with a Fabry-Perot resonator including an electro-optic crystal. The optical coherence tomography device described.   Each of the two Fabry-Perot electro-optic modulators comprises a confocal Fabry-Perot electro-optic modulator in which the curvature of each concave mirror is set so that the Fabry-Perot resonator containing the electro-optic crystal is confocal. 14. The optical coherence tomography apparatus according to claim 12 or claim 13.   12. The optical coherence tomography apparatus according to claim 11, wherein the Fabry-Perot electro-optic modulator is formed by arranging two electro-optic crystals so that the C-axis is orthogonal between the concave mirrors constituting the Fabry-Perot resonator. .   The wavelength scanning light source includes a resonator length controller that periodically changes the resonator length of at least one of the two Fabry-Perot resonators having the adjacent FSRs within a certain range. By adjusting the waveform of the periodic scanning signal given to the Fabry-Perot resonator by the resonator length control unit, the wave number of the laser light extracted through the optical element becomes linear with respect to time. The optical coherence tomography apparatus according to claim 11, wherein the optical coherence tomography apparatus is calibrated. The laser oscillation optical path includes a Fabry-Perot electro-optic modulator in which an electro-optic crystal is contained in a spatial Fabry-Perot resonator, an optical amplifier having a gain at an oscillation wavelength, and light emitted from the Fabry-Perot electro-optic modulator. A polarization conversion element that rotates the polarization direction by 90 ° and an optical element for extracting output light are connected to an optical fiber,
The Fabry-Perot electro-optic modulator functions as two Fabry-Perot resonators having FSRs (Free Spectral Ranges) close to each of the polarized light components orthogonal to each other, and is provided by the resonator length control unit. The optical coherence tomography apparatus according to claim 1, wherein each of light components having mutually orthogonal polarization components is modulated by a periodic scanning signal.   18. The Fabry-Perot electro-optic modulator comprises a ring-type resonant Fabry-Perot electro-optic modulator configured to obtain a ring-type resonance with a Fabry-Perot resonator including the electro-optic crystal. Optical coherence tomography device.   18. The optical coherence according to claim 17, wherein the Fabry-Perot resonator comprises a V-type resonant Fabry-Perot electro-optic modulator configured to obtain a V-type resonance with a Fabry-Perot resonator including the electro-optic crystal. Tomography device.   The Fabry-Perot electro-optic modulator comprises a confocal Fabry-Perot electro-optic modulator in which the curvature of each concave mirror is set so that a Fabry-Perot resonator containing an electro-optic crystal is confocal. Item 20. The optical coherence tomography device according to Item 18 or Item 19.   18. The optical coherence tomography apparatus according to claim 17, wherein the Fabry-Perot electro-optic modulator is formed by arranging two electro-optic crystals so that the C-axis is orthogonal between concave mirrors constituting the Fabry-Perot resonator. .   The wavelength scanning light source adjusts the waveform of the periodic scanning signal given to the Fabry-Perot resonator by the resonator length control unit, so that the wave number of the laser light taken out through the optical element can be changed over time. The optical coherence tomography apparatus according to claim 17, wherein the apparatus is calibrated so as to be linear.   2. The two Fabry-Perot resonators each comprising a ring-type resonant Fabry-Perot electro-optic modulator configured to obtain a ring-type resonance with a Fabry-Perot resonator containing an electro-optic crystal. The optical coherence tomography device described. Each of the two Fabry-Perot resonators comprises a polarization-independent ring-type resonant Fabry-Perot electro-optic modulator,
24. The optical coherence tomography apparatus according to claim 23, wherein the wavelength scanning light source includes a polarization independent optical amplifier having a gain at an oscillation wavelength in a laser oscillation optical path. The Fabry-Perot resonator has a required coherent length of δL and a frequency scanning speed of Srate.
cFSR / SrateδL> F
Having a range finesse (F) indicated by
c / δL> FSR
The optical coherence tomography apparatus according to claim 1, wherein the optical coherence tomography apparatus has an FSR indicated by: Resonance of at least one Fabry-Perot resonator out of two Fabry-Perot resonators having a FSR (Free Spectral Range) close to each other provided in the optical path of the light emitted from the broadband light source and the broadband light source By periodically changing the length of the filter in a certain range, the two Fabry-Perot resonators function as narrow-band tunable filters that can change the selected wavelength by the vernier effect, and the wavelength is changed with time. A wavelength scanning light source comprising wavelength tunable filter means for outputting scanned light;
The laser light output from the wavelength scanning light source is branched into reference light and observation light for irradiating the object to be observed, and interference light between the reflected light of the observation light irradiated on the object to be observed and the reference light is generated. Interference optical system
An optical coherence tomography apparatus comprising: signal processing means that receives interference light obtained by the interference optical system, converts the interference light into an electrical signal, and calculates optical tomographic image information of the object to be observed.   Each of the two Fabry-Perot electro-optic modulators of the wavelength scanning light source comprises a ring-type resonant Fabry-Perot electro-optic modulator in which a ring-type resonance is obtained by a Fabry-Perot resonator containing an electro-optic crystal. 27. The optical coherence tomography device according to claim 26.   The wavelength scanning light source includes an optical amplifier provided in the outgoing light path of the wavelength tunable filter unit, and spontaneous emission light (ASE) emitted from the optical amplifier to be incident on the wavelength tunable filter unit. 28. The optical coherence tomography apparatus according to claim 27, wherein the optical amplifier that includes a reflecting mirror that emits spontaneous emission light (ASE) is used as the broadband light source.

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