JP2019196949A - Optical interference device and OCT device - Google Patents

Abstract

To provide an optical interference device capable of achieving a high-speed data acquisition rate as compared with before with high resolution, and to provide an OCT device using the same.SOLUTION: An optical interference device includes: an incidence optical system having a light source for emitting pulse light having a predetermined wavelength area; a measurement optical system for applying measurement light as light in which one portion of the pulse light is branched to an object to be measured; a reference optical system having a reference mirror fixed to a predetermined position to which reference light as light in which one portion of the pulse light is branched is applied; an interference optical system having a photodetector for detecting interference light obtained by compositing the measurement light reflected or scattered by the object to be measured and the reference light reflected by the reference mirror; and a delay element for delaying light such that the interference light is separated temporarily for each of a plurality of wavelengths and is detected in the photodetector.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an OCT apparatus, for example.

  An OCT (Optical Coherence Tomography) apparatus captures, for example, an internal structure of an object to be measured as an optical tomographic image using the coherence of light.

  As conventional OCT apparatus methods, TD-OCT (Time Domain Optical Coherence Tomography), SD-OCT (Spectral Domain Optical Coherence Tomography), and SS-OCT (Swept Source Optical Coherence Tomography) are known (FIG. 7). And Patent Document 1). In the following, the light emitted from the light source 11 for each method is divided into measurement light and reference light by the half mirror 5, and the measurement light reflected by the object W and the reference light reflected by the reference mirror 31 are half mirrors. As an example, an OCT apparatus 200 including an optical interference apparatus 100 configured to be combined at 5 and to detect interference light by a photodetector 41 will be described.

  In TD-OCT, by moving the reference mirror 31, the position where the measurement light and the reference light interfere and strengthen each other is changed, and information on which depth in the object W to be measured has the reflecting surface is obtained.

  In the SD-OCT, a broadband light source is used as the light source 11, and a spectrum of interference light is acquired using a spectroscopic detector including a spectroscope 41A and an area sensor 41B as the photo detector 41. In SS-OCT, a spectrum of interference light is acquired using a wavelength swept light source in which the oscillation wavelength is swept with time as the light source 11. SD-OCT and SS-OCT obtain information on the depth of the object to be measured by Fourier transforming the obtained interference light spectrum.

  In TD-OCT, since the reference mirror 31 is driven by physically moving, the sensitivity is inferior to that of SD-OCT and SS-OCT for the same measurement time.

  On the other hand, since the SD-OCT uses an area sensor to detect the spectrally separated interference light, the data acquisition rate of the interference signal is lower than that of a photodetector that detects at a single point. In SS-OCT, the scanning rate of the wavelength swept light source limits the data acquisition rate of interference signals.

  For these reasons, it is difficult to achieve higher-speed measurement while increasing the resolution by the conventional method.

JP 2014-228306 A

  The present invention has been made in view of the above-described problems, and provides an optical interference apparatus capable of realizing a higher data acquisition rate than the conventional one while having high resolution, and an OCT apparatus using the same. Objective.

  That is, an optical interference device according to the present invention receives an incident optical system having a light source that emits pulsed light having a predetermined wavelength range, and measurement light that is a part of the pulsed light. A measurement optical system for irradiating a measurement object, a reference optical system including a reference mirror fixed at a predetermined position to which a reference light that is a part of the pulsed light is branched, and the device under measurement An interference optical system comprising a photodetector that detects interference light in which the measurement light reflected or scattered by an object and the reference light reflected by the reference mirror are combined; and And a delay element that delays the light so that the interference light is detected separately in time for each of a plurality of wavelengths.

  In such a case, the delay element delays the light so that the interference light is detected in a time-separated manner for each of a plurality of wavelengths in the photodetector, so that wavelength sweeping is performed in the light source. Even if the wavelength is fixed, the spectrum of the interference light can be obtained in the same manner as SS-OCT.

  Therefore, unlike the SS-OCT, there is no limitation due to the scanning rate of the wavelength sweep, so that a higher data acquisition rate of interference signals can be realized. In addition, since the spectrum of the interference signal can be acquired, higher resolution and higher sensitivity than TD-OCT can be realized.

  As a specific configuration of the delay element that makes it possible to obtain a substantially equivalent effect without performing wavelength sweep in the light source, the delay element is configured by an optical fiber having a predetermined length. Things.

  The predetermined length is 1 km or more as the length of the optical fiber in which the pulsed light is sufficiently wavelength-dispersed so that the interference light can be separated and detected in time by a plurality of wavelengths in the photodetector. Things.

  In order to make it possible to use an optical fiber as a whole for propagation of light and to simplify the configuration of the entire apparatus, the pulse light is input from the incident optical system, and the pulse light is used as the measurement light. The optical coupler further includes an optical coupler that branches and outputs the reference light, and the optical coupler combines the measurement light reflected or scattered by the object to be measured and the reference light reflected by the reference mirror. What is necessary is just to be comprised.

  In order to be able to reduce the number of the delay elements to be provided and to configure an optical system substantially similar to the conventional SS-OCT, the delay element is provided between the light source and the optical coupler in the incident optical system. What is necessary is just to be provided.

  In order to increase the data acquisition rate of the interference signal, the photodetector is configured to detect the interference light temporally separated for each of a plurality of wavelengths at the same detection point. Good.

  In order to prevent the light source from limiting the interference signal data acquisition rate, the wavelength range of the pulsed light emitted from the light source may be fixed.

  As specific characteristics of the light source and the delay element capable of realizing OCT at a higher speed than conventional, the pulse width of the pulsed light when emitted from the light source is 1 ps or less and passed through the delay element. The pulse width of the later pulsed light is 100 ns or less.

  An OCT apparatus comprising: an optical interference apparatus according to the present invention; and a Fourier analysis unit that calculates a reflectance at each depth of the object to be measured by performing a Fourier transform on an interference signal detected by the photodetector. For example, higher resolution and higher data acquisition rate can be realized than any conventional OCT apparatus.

  As described above, according to the optical interference device of the present invention, even if the pulsed light emitted from the light source is not wavelength-swept, the delay element causes temporal chromatic dispersion in the interference light, and the light The spectrum of the interference light can be obtained by the detector. Therefore, it is possible to eliminate the limitation of the data acquisition rate as in the case where wavelength sweeping is performed in the light source while realizing high resolution and high sensitivity.

The schematic diagram which shows the optical interference apparatus and OCT apparatus which concern on 1st Embodiment of this invention. The schematic diagram shown about the effect | action of the delay element in 1st Embodiment. The schematic diagram which shows the relationship between the measurement light, reference light, and interference light in 1st Embodiment. The schematic diagram which shows the optical interference apparatus and OCT apparatus which concern on 2nd Embodiment of this invention. The schematic diagram which shows the optical interference apparatus and OCT apparatus which concern on 3rd Embodiment of this invention. The schematic diagram which shows the optical interference apparatus and OCT apparatus which concern on 4th Embodiment of this invention. The schematic diagram which shows the conventional OCT apparatus.

  An OCT apparatus 200 according to a first embodiment of the present invention will be described with reference to FIG.

  The OCT apparatus 200 according to the first embodiment obtains an interference light spectrum from the interference signal obtained by the optical interference device 100 and the interference signal obtained by the optical interference device 100, and acquires the interference signal of the measurement subject W. A calculation unit that generates an optical tomographic image.

  In the optical interference device 100, the pulsed light emitted from the light source 11 is branched into measurement light and reference light by the optical coupler 5, the measurement light is applied to the object W, and the reference light is applied to the reference mirror 31. . Further, the measurement light reflected by the object to be measured W and the reference light reflected by the reference mirror 31 are returned to the optical coupler 5 and combined to form interference light. The formed interference light is output from the optical coupler 5 and detected by the photodetector 41.

  That is, the optical interference device 100 includes an incident optical system 1 that inputs light to the optical coupler 5, a measurement optical system 2 that irradiates measurement light branched by the optical coupler 5 to the object W to be measured, A reference optical system 3 that irradiates the reference mirror 31 with the reference light branched in the optical coupler 5, and an interference optical system 4 that emits the interference light formed in the optical coupler 5 to the photodetector 41. I have. In this embodiment, each optical system includes an optical fiber for guiding light.

  Each part will be described in detail.

  The optical coupler 5 is, for example, a 2 × 2 coupler in which two optical fibers are fused. An incident optical system 1, a measurement optical system 2, a reference optical system 3, and an interference optical system 4 are connected to the four ports of the optical coupler 5, respectively.

  The incident optical system 1 includes a light source 11 that emits pulsed light, and a delay element 6 provided between the light source 11 and the optical coupler 5.

  The light source 11 is a laser light source 11 that emits pulsed light having a predetermined wavelength range. In the first embodiment, for example, the center wavelength of pulsed light is 1040 nm and has a wavelength range of 1015 nm to 1045 nm. The pulse width of the pulsed light is 1 ps or less, specifically 670 fs. The number of pulse repetitions is 40 MHz. The light source 11 is configured so that the wavelength range of the emitted pulsed light is kept substantially constant. That is, the light source 11 does not have a wavelength sweep function.

  The delay element 6 is composed of an optical fiber having a predetermined length, and generates different amounts of delay for each wavelength of light included in the pulsed light. In other words, the delay element 6 causes chromatic dispersion in the pulsed light and widens the pulse width of the pulsed light. Specifically, the delay element 6 is an optical fiber wound around a cylindrical member in a coil shape.

  As shown in FIG. 2, the pulse width of the pulsed light emitted from the light source 11 is 1 ps or less, whereas the pulse width of the pulsed light after passing through the delay element 6 is expanded to 4 ns. . That is, among the wavelength components included in the pulsed light while passing through the delay element 6, the pulse width is increased by sequentially emitting the wavelength components having the longer wavelengths. In the first embodiment, in order to cause such a delay, the delay element 6 is formed of a single mode optical fiber having a predetermined length of 1 km or more and 10 km or less. The pulse width of the pulsed light after passing through the delay element 6 may be expanded to 100 ns or less.

  The measurement optical system 2 is configured to emit the measurement light output from the optical coupler 5 to the object W and return the measurement light reflected or scattered by the object W to the optical coupler 5. ing. The irradiation point of the measurement light with respect to the part to be measured is configured to be sequentially scanned. The measurement light is also light that has been wavelength-dispersed by the delay element 6, and the light to be measured W is sequentially irradiated from the light on the long wavelength side to the light on the short wavelength side. The measurement optical system 2 can include an optical element such as a lens (not shown) provided between the light exit / incident end of the optical fiber and the object W to be measured.

  The reference optical system 3 is configured to emit the reference light output from the optical coupler 5 to the reference mirror 31 and return the reference light reflected by the reference mirror 31 to the optical coupler 5. In the first embodiment, the installation position of the reference mirror 31 is fixed and is not moved. The reference light is also light in a state of being wavelength-dispersed by the delay element 6, and the light W on the short wavelength side is sequentially irradiated to the object W to be measured from the light on the long wavelength side. The reference optical system 3 may include an optical element such as a lens (not shown) provided between the light exit / incident end of the optical fiber and the reference mirror 31.

  The interference optical system 4 is configured to cause the interference light combined in the optical coupler 5 to enter the photodetector 41. The light detector 41 is a photodiode and detects the light intensity at one point. That is, the intensity of each wavelength component of the interference light is detected at the same detection point. In addition, the interference light is detected by the photodetector 41 by separating it in time for each of a plurality of wavelengths by the action of the delay element 6. As shown in the schematic diagram of FIG. 3, when the measurement light and the reference light are combined and interference occurs, interference fringes are generated in the time direction and the wavelength direction, and the photodetector 41 detects them as a bead signal. become. Thus, since one pulse light emitted from the light source 11 is separated for each wavelength in the time direction by the delay element 6 to form interference light, each depth at one point of the object W to be measured is formed. It is possible to obtain information on the reflection surface.

  Next, the calculation unit will be described.

  The calculation unit generates an optical tomographic image of the workpiece W based on the interference signal obtained from the photodetector 41 and includes at least the Fourier analysis unit 7. The Fourier analysis unit 7 performs Fourier transform on the interference signal detected by the photodetector 41 to calculate the reflectance at each depth of the object W to be measured. An optical tomographic image can be obtained by making the reflectance at each point of the object W to be measured correspond to, for example, shading.

  As described above, according to the OCT apparatus 200 of the first embodiment, the incident optical system 1 includes the delay element 6 that wavelength-disperses the pulsed light emitted from the light source 11, so that wavelength sweeping is not performed in the light source 11. In addition, it becomes possible to sequentially irradiate the object to be measured W with a plurality of wavelengths as measurement light. For this reason, since the spectrum of interference light can be obtained for one point of the workpiece W, high resolution and high sensitivity can be realized.

  Further, for example, when the wavelength of the emitted light is swept by sweeping the voltage applied to the light source 11 itself, it is difficult to sweep the entire predetermined wavelength region in a short time of about 10 ns. Since the delay element 6 generates different delays for each wavelength due to the wavelength dependence of the refractive index, it can be separated into the respective wavelengths even if the pulse width is short.

  For this reason, there is no limitation on the data acquisition rate of the interference light due to the scanning rate of the wavelength sweep as in the case of performing the wavelength sweep in the light source 11, and it is possible to acquire data at a higher speed than in the past.

  In other words, the OCT apparatus 200 according to the first embodiment can obtain an optical tomographic image at a higher speed with the same algorithm as SS-OCT, even though the wavelength sweep function does not exist in the light source 11. Become. Further, since it is not necessary to give the light source 11 a wavelength sweep function, it is possible to use pulsed light having a very small pulse width at a very high frequency.

  An OCT apparatus 200 according to a second embodiment of the present invention will be described with reference to FIG.

  In the OCT apparatus 200 according to the second embodiment, the delay element 6 is not provided in the incident optical system 1 but the delay element 6 is provided in the interference optical system 4. In other words, the delay element 6 is provided between the optical coupler 5 and the photodetector 41 in the interference optical system 4. In this way, the interference light incident on the photodetector 41 can be separated for each wavelength component, and the spectrum of the interference light can be detected.

  An OCT apparatus 200 according to a third embodiment of the present invention will be described with reference to FIG.

  In the OCT apparatus 200 of the third embodiment, the delay element 6 is provided in each of the incident optical system 1 and the interference optical system 4. In this embodiment, the optical fiber of the delay element 6 provided in the interference optical system 4 is set longer than the optical fiber constituting the delay element 6 provided in the incident optical system 1. May be reversed.

  As described above, in the third embodiment, after the wavelength dispersion of the pulsed light emitted from the light source 11 is once performed, the wavelength dispersion is further generated with respect to the interference light. So that they can be detected separately.

  An OCT apparatus 200 according to a fourth embodiment of the present invention will be described with reference to FIG.

  In the OCT apparatus 200 of the fourth embodiment, the delay element 6 is provided in each of the measurement optical system 2 and the reference optical system 3. Here, the lengths of the optical fibers constituting the respective delay elements 6 are set to the same length, and are configured such that only the same wavelength dispersion occurs in the measurement light and the reference light.

  Any of the OCT apparatuses 200 of the second, third, and fourth embodiments configured as described above can achieve the same effects as those of the first embodiment.

  Other embodiments will be described.

  The optical interference apparatus according to the present invention can be used not only for the OCT apparatus but also for other applications. For example, you may comprise as a laser rangefinder provided with the optical interference apparatus which concerns on this invention.

  The delay element may be other than an optical fiber having a predetermined length. In other words, it is only necessary that different delays are generated in each wavelength and the interference light detected by the photodetector is wavelength-dispersed so as to be detectable for each wavelength. For example, a sufficiently large wavelength dispersion may be obtained by adjusting the refractive index of the optical fiber. Further, wavelength dispersion may be caused by scratching the optical fiber.

  In each embodiment, each optical system guides light through an optical fiber and branches and multiplexes light using an optical coupler. However, for example, a half mirror is used to divide and multiplex light. The optical interference apparatus and the OCT apparatus according to the present invention may be configured as described above.

  In addition, various combinations and modifications of the embodiments may be performed without departing from the spirit of the present invention.

DESCRIPTION OF SYMBOLS 200 ... OCT apparatus 100 ... Optical interference apparatus 1 ... Incident optical system 11 ... Light source 2 ... Measurement optical system 3 ... Reference optical system 31 ... Reference mirror 4 ... Interference Optical system 42 ... photodetector 5 ... optical coupler 6 ... delay element 7 ... Fourier analysis unit W ... device under test

Claims (9)

An incident optical system including a light source that emits pulsed light having a predetermined wavelength range;
A measurement optical system for irradiating the object to be measured with measurement light that is a part of the pulsed light; and
A reference optical system comprising a reference mirror fixed at a predetermined position to which reference light that is a part of the pulsed light that is branched is irradiated;
An interference optical system comprising a photodetector that detects interference light in which the measurement light reflected or scattered by the object to be measured and the reference light reflected by the reference mirror are combined;
And a delay element that delays the light so that the interference light is detected in a time-separated manner for each of a plurality of wavelengths in the photodetector.   The optical interference device according to claim 1, wherein the delay element is configured by an optical fiber having a predetermined length.   The optical interference apparatus according to claim 2, wherein the predetermined length is 1 km or more. An optical coupler that receives the pulsed light from the incident optical system, branches the pulsed light into the measuring light and the reference light, and outputs the optical coupler;
4. The optical coupler according to claim 1, wherein the optical coupler is configured to multiplex the measurement light reflected or scattered by the object to be measured and the reference light reflected by the reference mirror. Optical interference device.   The optical interference apparatus according to claim 1, wherein the delay element is provided between the light source and the optical coupler in the incident optical system.   The optical interference device according to claim 1, wherein the optical detector is configured to detect the interference light temporally separated for each of a plurality of wavelengths at the same detection point.   The optical interference device according to claim 1, wherein a wavelength range of the pulsed light emitted from the light source is fixed.   The optical interference device according to claim 5, wherein a pulse width of the pulsed light when emitted from the light source is 1 ps or less, and a pulse width of the pulsed light after passing through the delay element is 100 ns or less. An optical interference device according to any one of claims 1 to 8,
An OCT apparatus comprising: a Fourier analysis unit that Fourier-transforms an interference signal detected by the photodetector to calculate a reflectance at each depth of the object to be measured.