JP5735674B2 - Optical connector and endoscope system - Google Patents

Description

  The present invention relates to an optical connector, and more particularly to an optical connector that optically couples a light source side optical fiber and a light receiving side optical fiber, and an endoscope system using the optical connector.

  Conventionally, as a non-contact type optical connector, an optical fiber having a core portion having a refractive index distribution (abbreviated as GI type optical fiber) or an optical fiber having a core portion having a constant refractive index (abbreviated as SI type optical fiber). What is also known as). A GI collimator, which is an optical connector using a GI type optical fiber, has a remarkable wavelength dependence in the rear focal length, and the optical transmission efficiency is greatly reduced by the expansion of the wavelength range of light passing therethrough. Used to transmit light.

  In addition, a technique is known in which light having a wavelength range wider than that of monochromatic light, for example, light having different wavelengths in the infrared region, is passed through such a GI collimator (see Patent Document 1).

  Further, the laser light emitted from the semiconductor laser element is condensed through a convex lens, and the end face on the large diameter side of the tapered optical fiber is arranged at the condensing point of the laser light, and the large diameter side is arranged from this large diameter side. There is also known a light propagation device that transmits incident laser light through the tapered narrow diameter side (see Patent Document 2).

JP 2006-524845 A JP 2006-309146 A

  However, the GI collimator that transmits light having different wavelengths in the infrared region does not fundamentally eliminate the decrease in the light transmission efficiency due to the expansion of the wavelength range of the transmitted light, and includes, for example, a wider wavelength range. In the case of passing white light, the light transmission efficiency is greatly reduced for a specific wavelength. In addition, the light propagation device having the optical fiber having the tapered shape on the light receiving side can be applied to a detachable optical connector, but in order to eliminate the wavelength dependence of the light transmission efficiency, Since it is necessary to use a lens or the like that suppresses the occurrence, there is a problem that the size of the device increases and the cost of the device increases.

  The present invention has been made in view of the above circumstances, and an optical connector that can suppress a decrease in optical transmission efficiency due to an increase in the wavelength range of light to pass through without increasing the device cost or increasing the size of the device. An object of the present invention is to provide an endoscope system using the same.

  The optical connector of the present invention includes an SI-type light source-side optical fiber disposed on the light source side and an SI-type light-receiving side optical fiber disposed on the light-receiving side, and an end face of the light source-side optical fiber and the light-receiving side optical fiber. An optical connector that optically couples the two optical fibers with the end face of the optical fiber facing each other, wherein the light source side optical fiber and the light receiving side optical fiber are detachable, and the light source side optical fiber is the light source side light. It has a taper part formed so that the diameter of a core part may become large, so that the said end surface of a fiber is approached.

  The SI type optical fiber means a step index type optical fiber. That is, the refractive indexes of the core portion of the light source side optical fiber and the core portion of the light receiving side optical fiber are constant and do not have a refractive index distribution. Therefore, the light propagating in each core part propagates in each optical fiber while being reflected by the outer wall surface of the core part.

  Detachable means that the optical fiber is positioned so that the optical coupling between the two optical fibers can be maintained opposite to each other, and that the optical fibers are positioned so that they are in a mounted state. It means that it can be in a state.

  Further, “a tapered portion formed such that the diameter of the core portion increases as it approaches the end surface of the light source side optical fiber” means any region on the outer wall surface (reflective surface) of the core portion constituting the tapered portion. Also, the outer wall surface (reflection surface) is formed so that the light propagating in the direction orthogonal to the optical axis in the core portion is reflected to the side having a larger diameter (the end surface side from which the light is emitted). . That is, the tapered portion is not limited to a conical shape, and may be a polygonal pyramid shape, or a shape combining a free-form surface, a polyhedron, and the like. In addition, the said optical axis can be made into the center axis which passes along the gravity center position of the cross section of a core part. Moreover, the cross section of the said core part can be made into the cross section cut | disconnected by the plane orthogonal to the direction where this core part is extended.

  The tapered portion of the light source side optical fiber is preferably formed so that the central axis passing through the center of gravity of the cross section of the core portion is a straight line.

  The light receiving side optical fiber may have a tapered portion formed such that the diameter of the core portion increases as the end surface of the light receiving side optical fiber is approached.

  In addition, "the taper part formed so that the diameter of a core part becomes large so that the said end surface of the light reception side optical fiber is approached" is any area | region in the outer wall surface (reflection surface) of the core part which comprises this taper part. The outer wall surface (reflection surface) is formed so that the light propagating in the direction perpendicular to the optical axis in the core portion is reflected to the side having the larger diameter (the side of the end face receiving the light). That is, the tapered portion is not limited to a conical shape, and may be a polygonal pyramid shape, or a shape combining a free-form surface, a polyhedron, and the like. In addition, the said optical axis can be made into the center axis which passes along the gravity center position of the cross section of a core part. The cross section of the core portion is a cross section cut along a plane orthogonal to the extending direction of the core portion.

  The tapered portion of the light source side optical fiber is preferably formed so that the central axis passing through the center of gravity of the cross section of the core portion is a straight line.

  The light receiving side optical fiber may be formed such that the shape and size of the cross section of the core portion are constant.

  The optical connector may be configured such that when the two optical fibers are optically coupled, the end face of the light source side optical fiber and the end face of the light receiving side optical fiber are arranged to face each other without contact.

  The optical connector may transmit light of two or more different wavelengths.

  The optical connector may pass white light.

  The optical connector may be configured such that the area of the core portion at the end face of the light receiving side optical fiber is larger than the area of the core portion at the end face of the light source side optical fiber.

  The optical connector is disposed so that the end surface of the core portion of the light receiving side optical fiber and the end surface of the core portion of the light source side optical fiber are overlapped with each other when the optical fibers are optically coupled. It can be configured.

  Note that “overlapping without excess or deficiency” means not only when there is complete overlap without excess or deficiency, but also when 90% or more of the regions overlap each other.

  It is desirable that the light source side optical fiber satisfy the conditional expression (1): 0.5 ≦ L1 / ε1, and satisfy the conditional expression (1A): 2.6 ≦ L1 / ε1. Is more desirable. However, L1 is the length (mm) of the taper portion of the light source side optical fiber, and ε1 is the taper ratio of the light source side optical fiber. Here, the taper ratio ε1 is a value obtained by an equation represented by ε1 = (maximum core diameter of the tapered portion in the light source side optical fiber / minimum core diameter of the tapered portion in the light source side optical fiber).

  The light receiving side optical fiber preferably satisfies conditional expression (2): 0.5 ≦ L2 / ε2, and satisfies conditional expression (2A): 2.6 ≦ L2 / ε2. Is more desirable. However, L2 is the length (mm) of the tapered portion of the light receiving side optical fiber, and ε2 is the taper ratio of the light receiving side optical fiber. Here, the taper ratio ε2 is a value obtained by an equation represented by ε2 = (maximum core diameter of the tapered portion in the light receiving side optical fiber / minimum core diameter of the tapered portion in the light receiving side optical fiber).

  An endoscope system according to the present invention includes the optical connector, a light source, and an endoscope body, and transmits a light beam emitted from the light source to the endoscope body through the optical connector. It is comprised so that the said light beam may be inject | emitted from.

  According to the optical connector of the present invention and the endoscope system using the optical connector, there are an emission-side end surface that is an emission-side end surface of the light source-side optical fiber and an incident-side end surface of the light-receiving-side optical fiber. In optical connectors that are optically coupled with the incident side end face facing each other, the light source side optical fiber is tapered so that the diameter of the core portion increases toward the exit side end face. In addition, it is possible to efficiently pass light through the optical connector without causing an increase in the size of the apparatus and a decrease in light transmission efficiency (coupling efficiency) due to an increase in the wavelength range of light passing therethrough.

  That is, since the core portion of the light source side optical fiber has a tapered shape as described above, the angle of the light beam reflected by the outer wall surface of the core portion with respect to the extending direction of the core portion (that is, with respect to the optical axis) The divergence angle (also referred to as the divergence angle) of the light beam emitted from the exit side end face of the core portion can be reduced. As a result, when the two optical fibers are optically coupled, the angle of the light beam incident on the light receiving side optical fiber with respect to the direction in which the light receiving side optical fiber extends (relative to the optical axis) can be further reduced. The amount of light incident on other than the core portion can be suppressed. Therefore, light can efficiently pass through this optical connector.

  Furthermore, since the light passing through the optical connector can be transmitted only by the action of reflection, not by the action of refraction like a GI collimator, the wavelength of light can be changed by changing the wavelength of light or increasing the type of wavelength. Even if the wavelength range is expanded, the optical transmission efficiency can be prevented from being lowered.

  In addition, since the core portion of the light source side optical fiber has a tapered shape and the area of the emission side end surface of the core portion is increased, the energy density of light passing through the emission side end surface of the core portion can be reduced. it can. Thereby, the effect which suppresses adsorption | suction of the pollutant in this injection | emission side end surface can be acquired. For this “effect of suppressing the adsorption of contaminants”, reference can be made to JP-A-2006-309146.

  Further, even if the diameter of the large diameter side of the core portion forming the taper shape of the light source side optical fiber (the diameter of the end surface on the exit side of the core portion) is increased, the diameter of the small diameter side of the core portion forming the taper shape is reduced. Since it can be made small, the diameter of the optical transmission section can be reduced as a whole, and its flexibility can be ensured.

  When laser light is used as the light source, the laser light emitted from the light source and incident on the light source side optical fiber is emitted from the emission side end surface (end surface on the large diameter side) of the tapered core portion. The light intensity of the laser light per viewing angle can be reduced. Here, in determining the laser class of the device, it is advantageous to increase the viewing angle of the emission side end face. That is, it becomes possible to use laser light having a larger light intensity in the same class.

Sectional drawing which shows the state by which the optical connector by embodiment of this invention was connected and optically coupled Sectional drawing which shows the state from which the said optical connector was separated and the optical coupling was cancelled | released The figure which shows the optical connector which relaxed the gradient of the taper part of the optical fiber of the light receiving side The figure which shows the optical connector which made the taper angle of the light-receiving side optical fiber 0, and enlarged the diameter of the whole core part The figure which shows the optical connector which enlarged the diameter of the incident side end face while making the gradient of the taper part of the light receiving side optical fiber loose It is a figure which shows the optical connector which made the inclination of the taper part of the light reception side optical fiber steep, and enlarged the diameter of the incident side end surface. The figure which shows the mode of the light ray which passes through the core part of the light source side optical fiber which is the object of the computer simulation It is a figure which shows the relationship between the taper rate in the light source side optical fiber, and the divergence angle of the light beam inject | emitted from the taper part which has the taper rate. The figure which shows a mode that the optical fiber which has a taper part is formed. The figure which compares and compares the light intensity distribution of the light beam inject | emitted from a straight optical fiber and a taper optical fiber The figure which shows a mode when applying a straight optical fiber to both the light source side optical fiber and the light receiving side optical fiber and optically coupling The figure which shows a mode when applying a taper optical fiber to both a light source side optical fiber and a light receiving side optical fiber, and carrying out optical coupling The figure which shows a mode when applying a taper optical fiber to a light source side optical fiber, and applying a straight optical fiber to a light reception side optical fiber, and carrying out optical coupling The figure which shows the relationship between the separation distance and optical transmission efficiency when both optical fibers are optically coupled The figure which shows the simulation result of the light intensity distribution of the light beam inject | emitted when only the taper angle of the light source side optical fiber is changed The figure which compares and shows the measured value of the light intensity distribution of the light beam inject | emitted from a taper optical fiber and a straight optical fiber The figure which shows the simulation result of the divergence angle of the light beam which fluctuates according to the change of the length of a taper part regarding the light source side optical fiber. The figure which shows the result of having simulated the optical path of the light ray which passes along the light source side optical fiber The figure which shows the result of having fixed the length of the taper part and simulating the relation between taper rate and optical transmission efficiency The figure which shows the result of having simulated the optical path of the light ray which passes through the optical fiber which carried out optical coupling The figure which shows the endoscope system which uses only a laser light source as a light source for illumination The figure which shows the endoscope system which uses a laser light source and a xenon lamp together as a light source for illumination The figure which shows the endoscope system containing the laser light source for fluorescence illumination as a light source for illumination

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. 1A and 1B are sectional views showing a schematic configuration of an optical connector of the present invention. FIG. 1A is a sectional view showing a state where the optical connector of the present invention is connected and optically coupled. FIG. 1B is a cross-sectional view showing a state in which the optical connectors of the present invention are separated from each other and the optical coupling is released.

  All optical connectors described in the embodiments of the present invention employ step index type (SI type) optical fibers for the light source side optical fiber and the light receiving side optical fiber.

  An optical connector 100 according to the embodiment of the present invention shown in FIGS. 1A and 1B includes a light source side optical fiber 10 that is an optical fiber disposed on a light source side (arrow Z side in the figure) and a light receiving side (arrow in the figure). A light receiving side optical fiber 20 that is an optical fiber disposed on the + Z side), and the end surface 11 of the light source side optical fiber 10 and the end surface 21 of the light receiving side optical fiber 20 are arranged to face each other. Is for optical coupling.

  The light source side optical fiber 10 disposed on the light source side is a step index type optical fiber, and the light source side optical fiber 10 is optically connected to the light emitted from the light source 1. The light receiving side optical fiber 20 disposed on the light receiving side is also a step index type optical fiber, and the light receiving side optical fiber 20 is optically connected to the illumination unit 5. When the light source side optical fiber 10 and the light receiving side optical fiber 20 are optically coupled, the light emitted from the light source 1 is transmitted to the illumination unit 5 through the optical connector 100. The optical connector 100 includes an optical path formed by the light source side optical fiber 10 so that light emitted from the light source 1 and passed through the light source side optical fiber 10 is propagated to the light receiving side optical fiber 20 and transmitted to the illumination unit 5. The optical path formed by the light receiving side optical fiber 20 is optically coupled. That is, the optical connector 100 optically couples both optical fibers 10 and 20 so that the light emitted from the light source side optical fiber 10 enters the light receiving side optical fiber 20.

  The optical connector 100 is configured such that the light source side optical fiber 10 and the light receiving side optical fiber 20 are detachable (the light receiving side optical fiber 20 is detachable from the light source side optical fiber 10). That is, the optical connector 100 fixes the positional relationship between the optical fibers 10 and 20 so as to maintain the optical coupling between the optical fibers 10 and 20 facing each other (see FIG. 1A), The fiber 10 and the light-receiving-side optical fiber 20 can be separated from each other so as not to face each other (see FIG. 1B). Here, in an optically coupled state, an air layer is formed between the end surface 11 of the light source side optical fiber 10 and the end surface 21 of the light receiving side optical fiber 20.

  The light source side optical fiber 10 has a tapered portion 14 formed such that the diameter of the core portion 12 increases as it goes from the light source side toward the end face 11 to be optically coupled.

  The light source side optical fiber 10 satisfies the conditional expression (1): 0.5 ≦ L1 / ε1, where L1 is the length of the tapered portion 14 (length in the optical axis C1 direction) and ε1 is the taper ratio. Is configured to do.

  The taper ratio ε1 is a value obtained by a mathematical formula of ε1 = φ1max / φ1min. Here, φ1max is the maximum diameter (maximum core diameter) of the core portion 12 in the tapered portion 14, and φ1min is the minimum diameter (minimum core diameter) of the core portion 12 in the tapered portion 14.

  Further, it is desirable that the light source side optical fiber 10 satisfies the conditional expression (1A): 2.6 ≦ L1 / ε1.

  On the other hand, the light-receiving side optical fiber 20 has a tapered portion 24 in which the diameter of the core portion 22 increases as it approaches the end face 21 to be optically coupled. That is, the light receiving side optical fiber 20 has a tapered portion 24 in which the diameter of the core portion 22 decreases as the distance from the end face 21 to be optically coupled to the light receiving side (the arrow + Z side in the drawing) increases (towards the illumination unit 5 side). It is what has.

  Similarly to the above, this light receiving side optical fiber 20 also has conditional expression (2): 0.5 ≦ L2 / ε2 when L2 is the length of the taper portion 24 in the optical axis C2 direction and ε2 is the taper ratio. Furthermore, it is desirable that the conditional expression (2A): 2.6 ≦ L2 / ε2 is satisfied.

  The taper angle θ1 shown in FIGS. 1A and 1B is an angle formed by the outer wall surface of the taper portion 14 in the core portion 12 and the optical axis C1, and the length L1 of the taper portion 14, the maximum core diameter φ1max, and the minimum core diameter. An angle determined by φ1 min.

  Further, the taper angle θ2 shown in FIG. 1 is an angle formed by the outer wall surface of the taper portion 24 in the core portion 22 and the optical axis C2, and the length L2 of the taper portion 24, the maximum core diameter φ2max, and the minimum core diameter. An angle determined by φ2 min.

  The light source side optical fiber 10 has a cladding portion 18 disposed on the outer periphery of the core portion 12, and the light receiving side optical fiber 20 has a cladding portion 28 disposed on the outer periphery of the core portion 22. is there. And it is comprised so that light may be reflected in the outer wall surface of the core part 12 (22) which is a boundary of the core part 12 (22) and clad part 18 (28) from which refractive indexes mutually differ. Here, when the taper angles θ1 and θ2 become smaller, the boundary with respect to the optical axis C1 (C2), that is, the gradient of the outer wall surface of the core portion 12 (22) becomes gentler.

  The optical connector 100 is configured such that the optical axis C1 of the light source side optical fiber 10 and the optical axis C2 of the light receiving side optical fiber 20 coincide when the optical fibers 10 and 20 are optically coupled. Yes. In other words, the center axis G1 of the core portion 12 of the light source side optical fiber 10 and the center axis G2 of the core portion 22 of the light receiving side optical fiber 20 are configured to coincide with each other when optically coupled.

  When the optical fibers 10 and 20 are optically coupled, the end surface 11 of the light source side optical fiber 10 and the end surface 21 of the light reception side optical fiber 20 are interposed with an air layer (separation distance d) therebetween as described above. The optical connector 100 is configured so as to be opposed to each other without contact.

  Since this optical connector 100 employs a method of optical coupling by reflecting and propagating light, it is possible to reduce wavelength dependency when optical coupling is performed, and light having a large wavelength range, for example, white Light or the like can pass through without being deteriorated in color.

  Furthermore, according to the optical connector 100, the divergence angle (also referred to as the divergence angle) of the light beam emitted from the light source side optical fiber can be reduced without using a refractive optical system such as a lens. Since it is possible to reduce a decrease in light transmission performance due to a positional shift of the light receiving side optical fiber in the direction perpendicular to the optical axis, it is possible to suppress a decrease in light transmission efficiency due to the attachment / detachment of both optical fibers.

  Note that when the optical fibers 10 and 20 are optically coupled, the separation distance d, which is the distance between the end surface 11 of the light source side optical fiber 10 and the end surface 21 of the light receiving side optical fiber 20 that are opposed to each other, is, for example,. It can be 5 mm or more and 3 mm or less. Moreover, the taper length L which is the length of a taper part can be 2 mm or more and 10 mm or less, for example.

  2A to 2D show a modification of the optical connector of the present invention, and show only the core portions 12 and 22 by omitting the clad portions 18 and 28 of the optical fiber. For the optical fibers shown in FIG. 3 and subsequent drawings, the cladding portion is similarly omitted and only the core portion is shown.

  FIG. 2A is a diagram showing an optical connector 100A in which the slope of the taper portion of the light receiving side optical fiber is relaxed, and FIG. 2B is a light in which the diameter of the entire core portion is increased and made constant without providing the taper portion in the light receiving side optical fiber. FIG. 2C is a diagram showing the connector 100B, FIG. 2C is a diagram showing the optical connector 100C in which the diameter of the incident side end face is increased while the slope of the tapered portion of the light receiving side optical fiber is loosened, and FIG. 2D is the slope of the tapered portion of the light receiving side optical fiber. It is a figure which shows optical connector 100D which made the diameter of the incident side end surface large steep.

  Hereinafter, the optical connectors 100A to 100D will be individually described. The description of each optical connector is based on the case where both the light-receiving side optical fiber 10 and the light source-side fiber 20 have tapered portions and have the same shape. Here, when the shapes are the same, the shapes of both optical fibers are the maximum core diameter φ1max = φ2max, the minimum core diameter φ1min = φ2min, the taper length L1 = L2 that is the length of the taper portion, and the taper angle θ1 = θ2. This is the case. Here, the reference optical connector is referred to as a reference optical connector.

The distance d and the dimensions related to the light source side optical fiber 10 (maximum core diameter φ1max, minimum core diameter φ1min, taper length L1, taper angle θ1) are the same for the optical connectors 100A to 100D.
<About optical connector 100A>
In the optical connector 100A of Modification A shown in FIG. 2A, the maximum core diameter φ2max and the minimum core diameter φ2min of the light receiving side optical fiber 20 are made equal to the reference optical connector, and the length L2 of the tapered portion 24 is made longer. (That is, the taper angle θ2 is made smaller).

  As described above, the maximum core diameter φ1max of the light source side optical fiber 10 and the maximum core diameter φ2max of the light reception side optical fiber 20 are made the same diameter (and the end faces 11 and 21 of the core portion overlap each other without excess or deficiency). ) By reducing the taper angle θ2 at the core portion 22 of the light receiving side optical fiber 20, the light loss of the optical connector 100A when optically coupled can be further reduced. That is, when the light receiving side optical fiber is shaped as described above, the light amount loss can be made smaller than when the light receiving side and light source side fibers have the same shape.

The advantage of the optical connector 100A is that mode conversion is advantageous when optically coupled. Moreover, since the thick part of the light-receiving side optical fiber becomes long, a fault is that handling becomes a little worse (flexibility falls a little).
<About optical connector 100B>
In the optical connector 100B of the modified example B shown in FIG. 2B, the maximum core diameter φ2max of the light receiving side optical fiber 20 is made equal to that of the reference optical connector so that no taper portion is provided (taper angle θ2 = 0). Is.

  In this way, the maximum core diameter φ1max of the light source side optical fiber 10 and the maximum core diameter φ2max of the light reception side optical fiber 20 are made the same diameter (in addition, the end surfaces 11 and 21 of the core portion are overlapped without excess or deficiency). ) By making the thickness of the core portion 22 of the light receiving side optical fiber 20 constant (straight optical fiber), the light amount loss of the optical connector 100B when optically coupled is determined by the optical fibers on the light receiving side and the light source side. It is possible to reduce the light loss as compared with the case where the shapes are equal.

The advantage of the optical connector 100B is that the attenuation of the amount of light passing through the light receiving side optical fiber can be reduced. Moreover, since a whole light receiving side optical fiber becomes a large diameter, a fault is that handling becomes worse (flexibility falls).
<About optical connector 100C>
In the optical connector 100C of Modification C shown in FIG. 2C, the length L2 of the tapered portion 24 is increased and the maximum core diameter φ2max is increased without changing the taper angle θ2 and the minimum core diameter φ2min with respect to the reference optical connector. It is a thing.

  Thus, by increasing the maximum core diameter φ2max of the light receiving side optical fiber 20 relative to the maximum core diameter φ1max of the light source side optical fiber 10, the light amount loss of the optical connector 100C when optically coupled is reduced. can do. That is, the light-receiving side optical fiber 20 can be made incident with a reduced amount of light (leakage light) emitted from the light source-side optical fiber 10, so that the light amount loss can be reduced.

The advantages of the optical connector 100C are that light loss (leakage light) when optically coupled can be reduced, and mode conversion when optically coupled is advantageous. Moreover, since the thick part of the light-receiving side optical fiber becomes long, a fault is that handling becomes a little worse (flexibility falls a little).
<About optical connector 100D>
In the optical connector 100D of Modification D shown in FIG. 2D, the maximum core diameter φ2max is increased (the taper angle θ2 is increased) while the length L2 of the taper portion 24 and the minimum core diameter φ2min are made equal to the reference optical connector. ).

  In this way, by increasing the maximum core diameter φ2max of the light receiving side optical fiber 20 relative to the maximum core diameter φ1max of the light source side optical fiber 10, the light amount loss of the optical connector 100C when optically coupled is further reduced. (Similar to the case of the optical connector 100C). On the other hand, increasing the taper angle θ2 increases the light amount loss in the taper portion 24.

  The advantage of the optical connector 100D is that it is possible to reduce light leakage (leakage light) when optically coupled. A drawback is that the loss of mode conversion becomes large.

Next, examples of the present invention will be further described.
<Computer simulation of light source side optical fiber by BPM method>
The BPM method is a method for computer simulation of the state of an electric field propagating in an optical waveguide or an optical fiber.

  FIG. 3 is a schematic diagram showing a core portion of a light source side optical fiber to be subjected to computer simulation and a state of light rays passing through the core portion. 4 shows a taper ratio in the light source side optical fiber and its taper ratio on a coordinate plane in which the horizontal axis indicates the taper ratio ε and the vertical axis defines the spread half angle α (full angle 2α) of the light beam emitted through the taper portion. It is a figure which shows the relationship with the divergence angle of the light beam inject | emitted from the taper part which has.

  Here, FFP (far field pattern: far field image) when the taper length L1 is 10 mm and 20 mm was calculated.

  As can be seen from FIGS. 3 and 4, when the taper length is 10 mm, the spreading half angle α of the light beam Ku1 emitted from the taper portion 14 is increased until the taper ratio ε increases to 3.8. It is inversely proportional to the taper rate. That is, the effect of decreasing the divergence angle was observed. Further, it can be seen that when the taper ratio ε is 6.5 or more, the above-described inversely proportional relationship is largely lost, and the lower limit of the spread half angle α is constant at about 2 °.

  When the taper length was 20 mm, the lower limit of the spread angle was slightly improved when the taper ratio ε was 6.5 or more, and the spread half angle α was constant at about 1.6 °.

  In this experiment, since the taper ratio ε is 3.8 (φ1 min = 60 μm, φ1max = 230 μm), it can be seen that it is close to the limit of etendue storage.

  The conditions when this computer simulation is performed are shown below.

  For the computer simulation, an optical waveguide simulation program developed by OPTIWAVE was used.

Incident beam Kn1: Gaussian beam with a wavelength of 780 nm and a spot diameter of 0.5 μm Straight section length: 40 mm (20 mm)
Taper length L1: 10mm, 20mm
Refractive index of the core part: 1.45
Refractive index of the cladding part: 1.433
Medium refractive index: 1.00
Tapered shape: exp ^(-1)
The numerical value in parentheses indicates a case where the taper ratio ε is 6.5 or more.

Note that NA × core diameter (core part diameter) is constant, the cladding mode equal to or greater than the fiber NA is removed on the incident side, and NA decreases at the tapered part on the emission side. Further, the trajectory (optical path) of the light beam Le that propagates in the core portion 12 is shown in the drawing.
<Manufacture of optical fiber having tapered portion>
Hereinafter, fabrication of an optical fiber having a tapered portion will be described.

  FIG. 5 is a diagram showing a state in which a large-diameter optical fiber is heated and stretched and welded to a small-diameter optical fiber to form an optical fiber having a tapered portion. The upper diagram in FIG. 5 shows a state where a large-diameter optical fiber is heated and stretched. The middle figure shows a state where the large-diameter optical fiber F and the small-diameter optical fiber H that have been heated and stretched are fused. The lower diagram shows a state in which the large diameter side of the tapered portion of both the fused optical fibers is cut and the end surfaces thereof are polished.

  When manufacturing an optical fiber having a tapered portion, a large-diameter optical fiber F and a small-diameter optical fiber H are prepared.

  Here, the large-diameter optical fiber F is a straight optical fiber having an NA of 0.22, a core diameter of 230 μm, a cladding diameter of 250 μm, and a core forming material made of quartz.

The thin optical fiber H has an NA of 0.22, a core diameter of 60 μm, a cladding diameter of 80 μm, and the core material is quartz.
First, the large-diameter optical fiber F is heated and stretched with a ceramic heater of about 1400 ° to form a tapered portion Ft having a tapered shape.

  Next, the core portion on the end surface of the tapered portion Ft and the core portion on the end surface of the small-diameter optical fiber are aligned.

Next, the end surface of the tapered portion in the large-diameter optical fiber and the end surface of the small-diameter optical fiber are fused and joined. After the large-diameter side of the tapered portion is cut, it is fused and integrated with the small-diameter optical fiber. The end surface of the tapered portion is optically polished and fixed to the FC connector.

  In this way, an optical fiber having a tapered portion with a taper length L = 10 mm and a taper ratio ε = 3.8 is obtained.

  In addition, the core diameter and clad diameter of a large diameter optical fiber and a small diameter optical fiber are not restricted to said case.

  Since the outer peripheral size of a general optical fiber FC connector ferrule is φ2.5 mm, the maximum clad diameter is preferably φ2.5 mm or less.

The optimum value of the taper length L will be described later.
<Measurement of divergence angle of light beam emitted from taper part>
Next, measurement of the divergence angle of the light beam emitted from the light source side optical fiber having the tapered portion will be described.

  FIG. 6 is a diagram comparing the light intensity distributions of light beams emitted from a straight optical fiber and a tapered optical fiber on a coordinate plane in which the horizontal axis represents the angle formed with the optical axis and the vertical axis represents the light intensity.

  The straight optical fiber has a constant core diameter of 60 μm.

  The tapered optical fiber has the smallest core diameter (minimum core diameter) in the tapered portion of 60 μm, the thickest core diameter of the tapered portion (maximum core diameter) is 230 μm, and the taper ratio ε is 3.8. (Ε = 3.8≈230 / 60).

As can be seen from FIG. 6, when the NA is calculated by setting the angle at which the light intensity is 5% of the peak value of the light intensity distribution as the divergence angle, the NA of the tapered optical fiber is 0.058, and the NA of the straight optical fiber is 0.169. Thus, the NA of the tapered optical fiber is reduced to 1/3 of the NA of the straight optical fiber.
<Measurement of optical transmission efficiency>
Next, measurement of optical transmission efficiency when optical fibers are optically coupled will be described.

  FIG. 7A is a diagram showing a state in which a straight optical fiber is applied to both the light source side optical fiber and the light receiving side optical fiber and optically coupled, and FIG. 7B shows both the light source side optical fiber and the light receiving side optical fiber. FIG. 7C is a diagram showing a state when optical coupling is performed by applying a tapered optical fiber. FIG. 7C is a diagram when optical coupling is performed using a tapered optical fiber as a light source side optical fiber and a straight optical fiber as a light receiving side optical fiber. It is a figure which shows a mode.

  FIG. 8 is a diagram showing the relationship between the separation distance and the light transmission efficiency when both optical fibers are optically coupled on the coordinate plane with the separation distance d on the horizontal axis and the light transmission efficiency E on the vertical axis. .

  Two types of light source side optical fibers were prepared. That is, a tapered optical fiber (minimum core diameter of taper portion 60 μm, maximum core diameter 230 μm) and a thin straight optical fiber (constant at a core diameter of 60 μm) were prepared.

  Three types of light receiving side optical fibers were prepared. That is, a tapered optical fiber (minimum core diameter of taper portion 60 μm, maximum core diameter 230 μm), a thin straight optical fiber (constant at a core diameter of 60 μm), and a large straight optical fiber (constant at a core diameter of 230 μm) were prepared.

  Two types of laser light wavelengths were prepared. That is, laser light sources that emit laser beams having wavelengths of 405 nm and 785 nm were prepared.

  The separation distance as a measurement parameter is set in a stepwise manner from a state where the end faces of both optical fibers are in close contact (separation distance d = 0) to a distance where the separation distance is 3 mm (d = 3 mm). And measured.

  Laser light was passed through an optical connector formed by combining and combining the above optical fibers, and the optical transmission efficiency was measured while changing the separation distance stepwise.

  In addition, the aspect of the optical connector used as the measuring object of optical transmission efficiency is three types shown to FIG. FIG. 7A shows an optical connector in which the light source side is made of a thin straight optical fiber Sh and the light receiving side is made of a thin straight optical fiber Sh. FIG. 7B shows an optical connector in which the light source side is a tapered optical fiber Te and the light receiving side is also a tapered optical fiber Te. FIG. 7C shows an optical connector including a tapered optical fiber Te on the light source side and a large-diameter straight optical fiber Sf on the light receiving side.

  As can be seen from FIG. 8, when both optical fibers are thin straight optical fibers (see FIG. 7A), the light source side is a tapered optical fiber and the light receiving side is a large straight optical fiber (FIG. 7C). It can be seen that the light transmission efficiency is higher in the case of the reference) at any separation distance and wavelength.

In the same manner as described above, when both optical fibers are thin straight optical fibers as a reference, when the separation distance is between 0 and 0.5 mm, both optical fibers are tapered optical fibers. Although the transmission efficiency is low, when the distance is 0.5 to 1.0 mm, the optical transmission efficiency is higher when both optical fibers are tapered optical fibers.
<Optimal taper length>
Hereinafter, the result of examining the optimum length of the tapered portion provided in the light source side optical fiber will be described.

  In FIG. 9, only the taper angle is changed without changing the minimum core diameter and the maximum core diameter of the taper portion of the light source side optical fiber on the coordinate plane in which the horizontal axis indicates the taper angle θ1 and the vertical axis indicates the light intensity. It is a figure which shows the result of having simulated the light intensity distribution of the light beam inject | emitted from a taper part at the time (namely, when only taper length is changed).

  FIG. 10 compares measured values of light intensity distributions of light beams emitted from a straight optical fiber and a tapered optical fiber having a taper length of 10 mm on a coordinate plane in which the horizontal axis indicates the taper angle and the vertical axis indicates the light intensity. FIG. The core diameter of the straight optical fiber and the minimum core diameter of the tapered portion of the tapered optical fiber are the same diameter.

  FIG. 11 is a diagram showing a simulation result of the spread angle of the light beam that fluctuates in accordance with the change of the taper length on the coordinate plane that represents the taper length on the horizontal axis and the full angle 2α of the light beam emitted from the taper portion on the vertical axis. is there.

  FIG. 12 is a diagram showing the result of simulating the trajectory (light path) of the light beam passing through the light source side optical fiber. The simulation result obtained here is obtained by a ray tracing simulation using a general-purpose optical design tool developed by ZEMAX.

  In this computer simulation and actual measurement, the minimum core diameter of the tapered portion was set to 60 μm and the maximum core diameter was set to 230 μm. Therefore, the taper ratio ε of this taper portion is 3.8.

  Further, the calculation was made assuming that the incident angle (full angle) of the light flux on the light source side optical fiber was 20 ° and the NA of this optical fiber was 0.23. 11 was calculated as an angle including 63% light intensity in the plot shown in FIG. 9 (description of “beam divergence angle (1D d63) (deg)” in FIG. 11). reference).

  As can be seen from the simulation results of FIGS. 9 and 11, when the taper ratio ε is 3.8, the length of the tapered portion is preferably at least 2 mm or more, and more preferably 10 mm or more. In other words, it can be seen that the value obtained by dividing the taper length by the taper rate (the value obtained by the formula of taper length / taper rate) is preferably 0.5 mm or more, and more preferably 2.6 mm or more.

Further, as can be seen from the simulation result of FIG. 9 and the actual measurement result of FIG. 10, the simulation result and the actual measurement result are approximately the same.
<Optimal taper ratio>
Next, the result of studying the optimum taper ratio of the tapered portion provided in the optical fiber to be optically coupled will be described.

  FIG. 13 shows the relationship between the taper ratio and the optical transmission efficiency when optical coupling is performed with the taper length of the two optical fibers fixed to 10 mm on the coordinate plane where the horizontal axis represents the taper ratio and the vertical axis represents the optical transmission efficiency. It is a figure which shows the result of simulation.

  FIG. 14 is a diagram showing the result of simulating the trajectory (optical path) of the light beam passing through the optically coupled optical fiber.

  The simulation result obtained here is obtained by a ray tracing simulation using a general-purpose optical design tool developed by ZEMAX.

  In this computer simulation, for both the light source side optical fiber and the light receiving side optical fiber, the minimum core diameters φ1min and φ2min of the tapered portion are 60 μm, the taper lengths L1 and L2 are 10 mm, and the maximum core diameter φ1max of the tapered portion of both optical fibers is The change in optical transmission efficiency when the size was changed while matching φ2max was obtained by calculation. In addition, the separation interval d was constant at 500 μm.

As can be seen from FIG. 13, the optical transmission efficiency is 0.67 when the taper ratio is 1, the optical transmission efficiency is 0.91 when the taper ratio is 2.2, and then the optical transmission efficiency increases as the taper ratio increases. It turns out that falls.
<Application to endoscope system>
Next, the case where the optical connector of the present invention is applied to an endoscope system will be described.

  FIG. 15 is a diagram showing an endoscope system of Example A that uses only a laser light source as a light source for illumination, and FIG. 16 shows an endoscope of Example B that uses a laser light source and a xenon lamp in combination as a light source for illumination. FIG. 17 is a diagram showing the system, and FIG. 17 is a diagram showing an endoscope system of Example C that uses only a laser light source as a light source for illumination but includes a laser light source for fluorescent illumination.

  As shown in FIG. 15, the endoscope system of Example A is in a state in which a combined light beam obtained by combining light beams emitted from laser light sources emitting different wavelengths with an optical coupler is optically coupled. The signal is transmitted to the endoscope main body through the optical connector of the present invention, and the combined light flux (laser light) is irradiated from the endoscope main body.

  Further, as shown in FIG. 16, the endoscope system of Example B was transmitted from the laser light source through the optical connector of the present invention to the endoscope body and emitted from the xenon lamp. A luminous flux (white light) is transmitted to an endoscope main body through a normal connector (bundle fiber), and each transmitted luminous flux is individually irradiated from this endoscope main body.

  As shown in FIG. 17, the endoscope system of Example C combines the light beams emitted from a plurality of laser light sources and the light beams emitted from the laser light sources for fluorescent illumination by an optical coupler. The combined light beam is transmitted to the endoscope main body through the optical connector of the present invention in an optically coupled state, and the combined light beam (laser light) is irradiated from the endoscope main body.

  In addition, this invention is not limited to the said embodiment and each Example, A various deformation | transformation implementation is possible unless the summary of invention is changed.

DESCRIPTION OF SYMBOLS 10 Light source side optical fiber 11 End surface of light source side optical fiber 12 Core part of light source side optical fiber 14 Tapered part of light source side optical fiber 20 Light receiving side optical fiber 21 End surface of light receiving side optical fiber

Claims (6)

An SI-type light source-side optical fiber disposed on the light source side and an SI-type light-receiving side optical fiber disposed on the light-receiving side are provided, and the end surface of the light-source-side optical fiber and the end surface of the light-receiving-side optical fiber are opposed to each other An optical connector for arranging and optically coupling the two optical fibers,
The light source side optical fiber and the light receiving side optical fiber are detachable,
The light source side optical fiber has a tapered portion formed such that the diameter of the core portion increases as it approaches the end face of the light source side optical fiber,
The light receiving side optical fiber has a tapered portion formed such that the diameter of the core portion increases as it approaches the end face of the light receiving side optical fiber,
A taper angle at the tapered portion of the light source side optical fiber, such that the diameter of the core portion at the end surface of the light receiving side optical fiber is larger than the diameter of the core portion at the end surface of the light source side optical fiber; The light receiving side optical fiber is configured so that the taper angle at the taper portion is equal, and the minimum core diameter of the light source side optical fiber is equal to the minimum core diameter of the light receiving side optical fiber. Yes,
An optical connector characterized in that, when the two optical fibers are optically coupled, the end face of the light source side optical fiber and the end face of the light receiving side optical fiber are opposed to each other without contact.   The optical connector according to claim 1, wherein the optical connector allows light having two or more different wavelengths to pass through.   The optical connector according to claim 1, wherein the optical connector transmits white light. The optical connector according to claim 1, wherein the light source side optical fiber satisfies the following conditional expression (1).
0.5 ≦ L1 / ε1 (1)
However,
L1: Length of tapered portion of light source side optical fiber ε1: Taper ratio of light source side optical fiber The optical connector according to claim 1, wherein the light receiving side optical fiber satisfies the following conditional expression (2).
0.5 ≦ L2 / ε2 (2)
L2: Length of taper portion of light receiving side optical fiber ε2: Tapered ratio of light receiving side optical fiber It comprises the optical connector according to any one of claims 1 to 5 , a light source, and an endoscope body, and transmits a light beam emitted from the light source to the endoscope body through the optical connector, An endoscope system configured to emit the light beam from the endoscope body.