JP2007105140A - Three-dimensional measurement endoscope using self-mixing laser - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problems that, while an object is irradiated with spot light and a distance is obtained on the basis of trigonometry in order to measure the distance to the object in a conventional endoscope, a base-line length is short, there is a problem in accuracy, and measurement at multiple spots is difficult though the distance is accurately measured even in a short distance by a self-mixing semiconductor laser. <P>SOLUTION: By displacing the light emitting part of the self-mixing semiconductor laser in a direction orthogonal to an optical axis and changing the direction of a laser beam, an object surface is scanned. Or, an optical fiber is interposed in an intermediate part, the end part of the optical fiber is displaced in the direction orthogonal to the optical axis, and the direction of the laser beam is changed. Further, by two-dimensionally arraying the light emitting parts of the laser and driving them in a time division manner, the object surface is scanned. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a technique for measuring a distance to an object in an endoscope.

Conventionally, in order to measure the distance to an object in an endoscope, the object is irradiated with spot light, and the image is captured by the camera, based on the principle of triangulation from the position of the camera, the irradiator and the spot. The distance was obtained (see Patent Documents 1 and 2).
However, in this method, the base axis length between the camera and the irradiator cannot exceed the size of the distal end portion of the endoscope, and there is a problem in accuracy.
Further, a distance measurement technique that does not rely on triangulation has been considered (see Patent Documents 3 and 4 and Non-Patent Document 1). This is a technique for obtaining the distance from the change in oscillation frequency by self-interference (self-mixing) of the laser light irradiated to the object and the reflected light from the object, but requires a two-dimensional scanning means. The device was large.
Japanese Patent No. 2875832 JP-A-5-52531 JP 10-246782 A Japanese Patent Laid-Open No. 2-112784 S.Shinohara et al. "Compact and High-precision range finder with wide dynamic range and its application" IEEE Trans.Instrumrntation and Measurement.Vol.41, No.1, pp.40-44 (1992)

  As long as the triangulation method is used, it is difficult to overcome the short base length of the endoscope.

The present invention provides a proposal for downsizing in a new measurement technique that replaces the triangulation method. Until now, distance meters using laser light have existed as one of the triangulation methods. Here, a technique for measuring the distance by frequency-modulating laser light with a continuous triangular wave is adopted, and a structure for applying this technique to an endoscope is proposed.
As a non-contact type distance measuring method, the triangulation method, the light section method, and the moire topography method have been used so far. In the present invention, a distance meter using a self-mixing laser diode (hereinafter referred to as “SM-LD”) that modulates the frequency of laser light with a continuous triangular wave is used.

The principle of the distance meter using SM-LD is already known, but the outline will be described below.
FIG. 1 shows the basic configuration of the SM-LD range velocimeter. Since the triangular wave voltage generated by the oscillator (1) is applied to the laser diode current source (2), the current applied to the laser diode (3) is modulated by the triangular wave. When the injection current to the diode increases, the refractive index in the resonator decreases and the temperature rises, and the frequency of the laser light decreases. The laser light intensity is also modulated. Light emitted from the frequency-modulated laser diode passes through the lens and is irradiated onto the target surface. A part of the light scattered on the target surface reversely follows the same path as the emitted light and returns to the laser diode resonator.
Then, the return light causes self-interference (self-mixing) with the light in the resonator, and the output waveform of the photodiode (4) incorporated in the laser diode package changes to the modulation triangular wave and the resonance state of the external resonator. The resulting step-like changes (mode hops) appear to overlap.

That is, as shown in FIG. 2, the internal resonator having a length L1 constituted by the internal reflection surfaces (11, 12) of the laser diode (3) and the reflection surface of the surface of the external object (6) ( 13) and an external resonator having a length L2 constituted by the reflection surface (12) of the laser surface are combined, and interference occurs between the modulation frequency and the resonance frequency of the composite resonator. Affects the oscillation intensity.
This step-like change (mode hop) is periodic at the rising and falling portions of the modulated triangular wave. The frequency (period) of the mode hop signal depends on the distance L between the laser diode and the target and the target velocity v in the optical axis direction of the laser diode. Therefore, if the mode hop frequency (period) is measured, the distance from the laser diode to the target and the speed of the target are determined. As described above, the SM-LD distance-velocity measuring optical system can be configured to be very compact by using only a laser diode package and a condenser lens with a built-in photodiode.

The self-mixing semiconductor laser irradiates an object with light emitted from the semiconductor laser that periodically changes the oscillation frequency and returns a part of the reflected light from the object to the semiconductor laser. The optical system to be coupled, a photoelectric conversion element that measures the output of the semiconductor laser, and an arithmetic circuit that obtains the distance from the change in output of the photoelectric conversion element to the object can be miniaturized.
Although the SM-LD distance velocity measurement optical system is small, only the distance to one irradiation point can be measured with the basic structure. Therefore, the distance of a plurality of points has been measured so far by scanning with a rotating mirror or a vibrating mirror. However, it is difficult to use such a configuration for a small device such as an endoscope.

FIG. 3 shows an example in which a CCD (22) and an SM-LD (8) as an image pickup device are provided at the distal end portion of the endoscope (20). The CCD (22) is provided with an imaging lens (21), and the SM-LD (8) is provided with a projection lens (5). Since a single SM-LD irradiates light only at one point, distance measurement is performed only at one point. Therefore, it is desirable here to use a plurality of two-dimensionally arranged SM-LD elements.
If a plurality of SM-LD elements are arranged, signals from each are processed to obtain distance information up to a plurality of points. There are a form provided at the distal end of the endoscope and a form provided at the intermediate part or the operation side and transmitted by an optical fiber. The arrangement of the SM-LD elements is also preferably a two-dimensional planar arrangement, but may be a one-dimensional array arrangement due to storage space constraints.

The image of the object (6) picked up by the CCD (22) is processed by the signal processing circuit in the control device (23), and is displayed on the display device (24) together with the distance information obtained from the SM-LD (8). Is displayed. If the distance information is only one point, it is displayed as numerical information in a part of the display area. However, if the distance information is obtained at multiple points, three-dimensional display is possible.
In obtaining distance information of only one point, laser light is irradiated to a target point for which distance display is desired using one of a plurality of arranged SM-LD elements. When scanning by an actuator, which will be described later, displacement by the actuator is controlled and an arbitrary target point is irradiated with laser light. These can be considered as temporary suspension of the scanning operation.
On the other hand, for three-dimensional display, it is necessary to create a right-eye image and a left-eye image, and use a stereoscopic display device as the display device (24). If simplified, contour lines are displayed, the contour lines at the reference position are displayed in white or yellow, contour lines far from the reference position are gradually blue, and contour lines near the reference position are gradually displayed in red. A display can be used.
Further, even if a single SM-LD element is small, if it is two-dimensionally arranged for three-dimensional display, it will become large, and it will be difficult to store it at the distal end of the endoscope (20). In this case, as shown in FIG. 4, it can be solved by optical transmission using an optical fiber (23).
The laser light from the SM-LD (8) is irradiated to the end face of the optical fiber (23) by the imaging lens (10). This light passes through the optical fiber (23) and is emitted from the other end face, but is adjusted by the projection lens (5) to focus on the surface of the object (6). Similarly, the reflected light from the object follows the reverse path and is fed back to the SM-LD (8).

If a two-dimensional arrangement is made using a plurality of SM-LD elements, the size increases and the cost is high.
As a solution, the irradiation point is displaced by a small actuator such as a piezo element to obtain distance information up to a plurality of points. For this purpose, there are a form in which the SM-LD element itself is displaced and a form in which the end face of the optical fiber that has transmitted light from the SM-LD element is displaced. An example of this is shown in FIG.
In FIG. 5A, the actuator (24) is coupled to the SM-LD (8) and displaced in the direction perpendicular to the optical axis. Thereby, the displacement of the irradiation point can be expected. FIG. 5B is an example when the optical fiber (23) is used for optical relay. Similar to FIG. 5A, the SM-LD (8) is displaced. FIG. 5 (c) is an example using the optical fiber (23) as in FIG. 5 (b), but here the end surface of the optical fiber (23) is not the SM-LD (8) but the optical axis by the actuator (24). It is moved in the orthogonal direction. It will be obvious to those skilled in the art that the end face of the optical fiber (23) on the object (6) side may be displaced as a modification of FIG. 5 (c).
Further, the same effect can be obtained by displacing the lenses (5, 10) in the direction orthogonal to the optical axis instead of the displacement of the end face of the SM-LD (8) or the optical fiber (23). FIG. 5D shows an example in which a plurality of SM-LD elements described above are arranged and light is emitted sequentially in a time-division manner to irradiate different positions of the object (6). Instead of time-division driving, an equivalent sequential light emission using an electronic shutter such as a liquid crystal shutter is also possible.

Proposed here is an intermediate configuration between the configuration using the two-dimensional SM-LD elements described so far and the configuration using a single SM-LD element to displace the irradiation position of the laser beam with an actuator. To do.
The SM-LD elements are arranged in a one-dimensional array, and this element group is displaced by an actuator to obtain a signal substantially equivalent to a two-dimensional planar arrangement.
Also in this embodiment, various modifications in the second embodiment are conceivable, such as a configuration for displacing the SM-LD, a configuration for displacing the end face of the optical fiber, and a configuration for displacing the lens.

  Even if a plurality of SM-LD elements are provided, they cannot be operated simultaneously because of interference. Normal operation does not have a significant adverse effect, but is disadvantageous when high speed is required. In order to solve this problem, interference may be prevented by changing the frequency of the laser. It is also possible to employ a driving method in which the influence is canceled by shifting the phase of the driving triangular wave by about 90 degrees. Furthermore, it is also possible to employ a polarizing filter to prevent interference between the light beams.

  In the present invention, by using an SM-LD (self-mixing semiconductor laser), the distance to the object can be measured without being affected by the baseline length as compared with the conventional measurement based on triangulation. In addition, surface scanning is possible by displacing a single SM-LD element (or an optical fiber end face or lens) in a direction perpendicular to the optical axis, thereby enabling three-dimensional image display (stereoscopic view).

Diagram showing the basic configuration of a self-mixing semiconductor laser (SM-LD) The figure which shows the internal resonance circuit and external resonance circuit in SM-LD The figure which shows the structure which provided SM-LD in the front-end | tip part of an endoscope The figure which shows the structure which provided SM-LD in the operation part of the endoscope The figure which shows the various structural examples which displace an irradiation point. (a) is an example in which the SM-LD is displaced by an actuator, (b) is an example in which an optical fiber is provided in the middle, (c) is an example in which the end face of the optical fiber is displaced by an actuator, and (d) is an array of SM-LD elements. Each of the examples is arranged in the shape and sequentially irradiated.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Oscillator 2 Driver 3 Photodiode 4 Laser diode 5, 10, 21 Lens 6 Object 7 Measuring circuit 8 SM-LD (self-mixing semiconductor laser)
20 Endoscope 22 CCD
23 Optical fiber

Claims (9)

Endoscope equipped with a self-mixing laser A three-dimensional measurement endoscope that uses a self-mixing laser that measures the distance at multiple points of an object by having means for irradiating laser light to multiple points of the object mirror. An endoscope provided with a self-mixing laser is provided with an actuator that moves the position of the light-emitting portion of the self-mixing laser in a direction perpendicular to the optical axis, and by irradiating laser light to a plurality of locations on the target, A three-dimensional measuring endoscope that uses a self-mixing laser that measures distances at multiple points. In an endoscope provided with a self-mixing laser, a laser light emitting part is provided in an endoscope intermediate part or an operation part, and laser light is guided from the light emitting part to an endoscope tip part by an optical fiber. 3D using a self-mixing laser that includes an actuator that moves the optical fiber end in a direction orthogonal to the optical axis and that measures the distance at multiple points of the object by irradiating multiple points of the object with laser light Measuring endoscope. In an endoscope equipped with a self-mixing laser, a plurality of laser light emitting units are provided, and by driving these laser light emitting units in a time-sharing manner, laser light is irradiated to a plurality of locations on the object, and distances are obtained at the plurality of locations on the object. 3D measuring endoscope using self-mixing laser. In an endoscope equipped with a self-mixing laser, two or more types of laser light emitting units having different polarizations are provided, and laser light is simultaneously irradiated to a plurality of locations on the target, thereby measuring distances at the plurality of locations on the target. A three-dimensional measuring endoscope using a self-mixing laser. An endoscope equipped with a self-mixing laser is equipped with two or more types of laser light emitting units having different oscillation frequencies, and simultaneously irradiates a laser beam to a plurality of locations on the target to measure distances at a plurality of locations on the target. A three-dimensional measuring endoscope using a self-mixing laser. 7. A three-dimensional measurement endoscope using a self-mixing laser according to claim 4, wherein a laser light-emitting portion is provided at a distal end portion of the endoscope. 7. The tertiary using the self-mixing laser according to claim 4, wherein a laser light emitting part is provided in an intermediate part of the endoscope, and laser light is guided from the light emitting part to the distal end part of the endoscope by an optical fiber. Former measuring endoscope. 7. A tertiary using a self-mixing laser according to claim 4, wherein a laser light emitting part is provided in an operation part of the endoscope in the endoscope, and laser light is guided from the light emitting part to the distal end part of the endoscope by an optical fiber. Former measuring endoscope.

Images