Optical waveguide having core partially formed in S-shape, and position sensor and optical circuit board including the same

Provided are an optical waveguide capable of propagating light, and a position sensor and an optical circuit board including the same. The optical waveguide includes cores each partially formed in an S-shape. The S-shaped portion includes a first curved portion upstream as seen in the direction of light propagation, and a second curved portion downstream as seen in the direction of light propagation and curved in a direction opposite to the first curved portion. The first curved portion and the second curved portion are connected to each other via a straight portion having a length in the range of from 0 mm to 30 mm. One of the width of the exit of the first curved portion and the width of the entrance of the second curved portion is smaller than the width of a core portion upstream of the S-shaped portion.

TECHNICAL FIELD

The present invention relates to an optical waveguide, a position sensor which optically senses a pressed position with the use of the optical waveguide, and an optical circuit board which propagates light to and from an optical element or the like with the use of the optical waveguide.

BACKGROUND ART

The present applicant has heretofore proposed a position sensor which optically senses a pressed position with the use of an optical waveguide (see PTL 1, for example). As shown inFIG. 17A, this position sensor includes a rectangular sheet-like optical waveguide W10configured such that a sheet-like core pattern member is held between a rectangular sheet-like under cladding layer11and a rectangular sheet-like over cladding layer13. The aforementioned core pattern member includes: a lattice-shaped portion12A including a plurality of linear cores12serving as an optical path and arranged vertically and horizontally; a first outer peripheral core portion12B disposed along a first horizontal side and a first vertical side of the outer periphery of the lattice-shaped portion12A; and a second outer peripheral core portion12C disposed along a second horizontal side and a second vertical side which are opposed to the first horizontal side and the first vertical side, with the lattice-shaped portion12A therebetween. The first outer peripheral core portion12B includes a single core26. The vertical and horizontal cores12of the lattice-shaped portion12A have respective front ends branching off from the single core26. The second outer peripheral core portion12C includes cores27extending from the rear ends of the respective cores12of the lattice-shaped portion12A. In the position sensor, a light-emitting element14is connected to an end surface of the first outer peripheral core portion12B of the core pattern member, and a light-receiving element15is connected to an end surface of the second outer peripheral core portion12C thereof.

In the position sensor including such an optical waveguide, light emitted from the light-emitting element14branches from the core26of the first outer peripheral core portion12B into the cores12of the lattice-shaped portion12A, passes through the cores27of the second outer peripheral core portion12C, and is received by the light-receiving element15. A surface portion (a rectangular portion indicated by dash-and-dot lines in the center ofFIG. 17A) of the over cladding layer13corresponding to the lattice-shaped portion12A serves as an input region13A for the position sensor.

Input to the position sensor is performed by pressing the input region13A, for example, with a pen tip for input. This deforms at least one of the cores12which corresponds to the pressed part to decrease the amount of light propagating in the at least one core12. The intensity of light received by the light-receiving element15is accordingly decreased in the at least one core12corresponding to the pressed part. In this manner, the position sensor senses the pressed position. The position sensor is also capable of sensing the input of a character and the like through the use of the position sensing.

With the increase in the amount of transmission information, an optical circuit board in addition to an electrical circuit board has been employed in recent electronic devices and the like. An example of such electronic devices is shown inFIG. 18. In this electronic device, the aforementioned optical circuit board is stacked on the electrical circuit board. Specifically, the electrical circuit board80includes an insulative layer81, and an electrical interconnect line82formed on the front surface of the insulative layer81. The optical circuit board70includes an optical waveguide W20(a first cladding layer71, a core (optical path)72, and a second cladding layer73) stacked on the back surface (the surface opposite from the surface with the electrical interconnect line82formed thereon) of the insulative layer81, and optical elements (a light-emitting element74and a light-receiving element75) mounted on portions of the front surface (the surface with the electrical interconnect line82formed thereon) of the insulative layer81which correspond to opposite end portions of the optical waveguide W20(see PTL 2, for example). In this optical circuit board70, the opposite end portions of the optical waveguide W20are formed into inclined surfaces inclined at 45 degrees with respect to the axial direction of the core72. Portions of the core72positioned at the inclined surfaces function as light reflecting surfaces72aand72b. Portions of the insulative layer81corresponding to the light-emitting element74and the light-receiving element75have respective through holes81aand81bformed therein. The through holes81aand81ballow light L (indicated by dash-double-dot lines) to propagate (allow optical connection) therethrough between the light-emitting element74and the light reflecting surface72aprovided in a first end portion and between the light-receiving element75and the light reflecting surface72bprovided in a second end portion.

The propagation of light in the aforementioned optical circuit board70is performed in a manner to be described below. First, the light L emitted from the light-emitting element74passes through the through hole81aof the insulative layer81, and then passes through a first end portion (the right-hand end portion as seen inFIG. 18) of the first cladding layer71. Then, the light L is reflected from the light reflecting surface72ain a first end portion of the core72(or the optical path is changed by 90 degrees), and is propagated in the core72. Then, the light L propagated in the core72is reflected from the light reflecting surface72bin a second end portion (the left-hand end portion as seen inFIG. 18) of the core72(or the optical path is changed by 90 degrees), and passes through a second end portion of the first cladding layer71outwardly. Then, the light L passes through the through hole81bof the insulative layer81, and is thereafter received by the light-receiving element75.

In some cases, an optical fiber is used in place of the light-receiving element75in a second end portion of the optical circuit board70. In this case, the propagation of light is performed in the same manner as described above.

RELATED ART DOCUMENT

Patent Document

SUMMARY OF INVENTION

Unfortunately, there have been cases in which the position sensor (with reference toFIG. 17A) fails to precisely sense the pressed position depending on the circumstances. As a result of the investigation into the cause of the failure, the present inventors have found that, when the pressed position cannot be precisely sensed, a portion having a low intensity of light received by the light-receiving element15exists while the input region13A is not pressed.

When a character or the like is inputted in the case where the portion having a low intensity of light received by the light-receiving element15exists without pressing the input region13A, a portion pressed by the input also has a low intensity of light received by the light-receiving element15. Thus, the pressed position cannot be precisely sensed. The position sensor including the aforementioned optical waveguide still has room for improvement in these regards.

There have also been cases in which the optical circuit board70(with reference toFIG. 18) has a low intensity of light received by the light-receiving element15depending on the circumstances. When an optical fiber is used in place of the light-receiving element75, there have been cases in which the amount of light propagating to the optical fiber is decreased. In such cases, an electronic device or the like incorporating the optical circuit board70does not properly operate because of the failure to properly propagate light (transmit information).

In view of the foregoing, it is therefore an object of the present invention to provide an optical waveguide capable of propagating light properly, and a position sensor and an optical circuit board including the same.

To accomplish the aforementioned object, a first aspect of the present invention is intended for an optical waveguide comprising: a linear core serving as an optical path; and upper and lower cladding layers holding the core therebetween, wherein the core is partially formed in an S-shape, wherein the S-shaped portion includes a first curved portion upstream as seen in the direction of light propagation, and a second curved portion downstream as seen in the direction of light propagation and curved in a direction opposite to the first curved portion, wherein the first curved portion and the second curved portion are connected to each other via a straight portion having a length in the range of from 0 mm to 30 mm, and wherein one of the width of the exit of the first curved portion and the width of the entrance of the second curved portion is smaller than the width of a core portion upstream of the S-shaped portion.

A second aspect of the present invention is intended for a position sensor comprising: a sheet-like optical waveguide including a sheet-like core pattern member, and upper and lower sheet-like cladding layers holding the core pattern member therebetween, the sheet-like core pattern member including a lattice-shaped portion having a plurality of linear cores, a first outer peripheral core portion positioned on a first horizontal side and a first vertical side of an outer periphery of the lattice-shaped portion and optically connected to front ends of respective vertical cores of the lattice-shaped portion and to front ends of respective horizontal cores of the lattice-shaped portion, and a second outer peripheral core portion positioned on and extending along a second horizontal side and a second vertical side which are opposed respectively to the first horizontal side and the first vertical side, with the lattice-shaped portion therebetween, and extending from rear ends of the respective vertical cores of the lattice-shaped portion and from rear ends of the respective horizontal cores of the lattice-shaped portion; a light-emitting element connected to an end surface of the first outer peripheral core portion of the optical waveguide; and a light-receiving element connected to an end surface of the second outer peripheral core portion, wherein part of the optical waveguide corresponding to at least a portion of the second outer peripheral core portion is an optical waveguide as recited in the first aspect, wherein light emitted from the light-emitting element passes through the first outer peripheral core portion, the lattice-shaped portion and the second outer peripheral core portion, and is received by the light-receiving element, wherein a surface portion of the position sensor corresponding to the lattice-shaped portion of the core pattern member serves as an input region, and wherein a pressed position in the input region is determined based on the amount of light propagating in the cores which is varied by the pressing.

A third aspect of the present invention is intended for an optical circuit board comprising: an optical waveguide as recited in the first aspect; and an optical member optically connected to an end portion of the core of the optical waveguide.

The term “S-shape” as used in the present invention refers to a portion in which the first curved portion and the second curved portion are connected to each other via the straight portion having a length in the range of from 0 (zero) mm to 30 mm as described above, and shall be meant to include an inverted S-shape. The expression “the straight portion has a length of 0 (zero) mm” shall mean that the first curved portion and the second curved portion are directly connected to each other without the straight portion. The first curved portion and the second curved portion shall be meant to include those that are curved even slightly.

In the optical circuit board according to the third aspect of the present invention, the optical member is a member responsible for emitting light, receiving light, propagating light or the like. Examples of the optical member include optical elements (a light-emitting element and a light-receiving element) for opto-electric conversion, optical fibers responsible for propagating light, and optical fiber connecting connectors for use in connection of the optical fibers.

To equalize the intensity of light received by the light-receiving element while the input region is not pressed, the present inventors have made investigation into the cause of the occurrence of a location where the intensity of light received by the light-receiving element15is low without pressing the input region13A in the related art technique shown inFIG. 17A. As a result, it has turned out that light leakage occurs in an S-shaped core portion in the second outer peripheral core portion12C between the lattice-shaped portion12A and the light-receiving element15, which in turn is the cause. The light-receiving element15connected to an end surface of the second outer peripheral core portion12C is disposed in the periphery of the sheet-like optical waveguide W10. Depending on the position of the light-receiving element15, at least some of the cores27of the second outer peripheral core portion12C are partially formed in the S-shape near the light-receiving element15(in a region surrounded by an ellipse D0ofFIG. 17A) in some cases.

Then, the present inventors have made investigation into the cause of the light leakage in the S-shaped portion of the cores27. In the course of the investigation, it has turned out that light L leans toward the outside portion of the curve of an upstream first curved portion S11in the aforementioned S-shaped portion (with reference toFIG. 17B). In the position sensor, the greater width of the cores12,26and27allows the greater amount of light propagating in the cores12,26and27and the greater amount of decrease in the propagating light due to the pressing of the input region13A. This facilitates the sensing of the pressed position. For this reason, the cores12,26and27having a greater width are formed in the position sensor of the related art. As shown inFIG. 17B, when the core27has a greater width in the S-shaped portion, the light L (indicated by dash-double-dot lines) leaning toward the outside portion of the curve of the upstream first curved portion S11as mentioned above is propagated to a downstream second curved portion S12while leaning toward the inside of the curve near the entrance of the downstream second curved portion S12, and reaches the outside side surface of the curve of the second curved portion S12in a concentrated manner. It has turned out that, when the core27has a greater width as described above, most of the light L reaching the aforementioned side surface is transmitted through the side surface (leaks from the core27) without reflecting from the side surface because the incident angle θ of the light L is smaller than the critical angle. That is, it has turned out that the cause of the leakage of the light L in the S-shaped portion lies in the greater width of the core27in the S-shaped portion.

Also, it has turned out that the optical circuit board has a problem similar to that of the aforementioned position sensor. That is, when the intensity of light received by the light-receiving element is low in the optical circuit board of the related art, the cores are partially formed in the aforementioned S-shape, and light leakage occurs in the S-shaped portion. In the optical circuit board of the related art, the cores are formed to have a greater width because the greater width of the cores allows the greater amount of light propagating in the cores (the greater amount of transmitted information). It has turned out that the light L leaks in the S-shaped portion due to this fact (with reference toFIG. 17B).

It has also turned out that light leaks in the second curved portion in the same manner as described above when the first curved portion and the second curved portion are connected to each other via the straight portion having a length of not greater than 30 mm. On the other hand, it has turned out that light leaks little in the second curved portion when the straight portion has a length of greater than 30 mm. In this case, the light leaning toward the outside portion of the curve of the first curved portion is repeatedly reflected from the side surface of the straight portion because of the sufficient length of the straight portion, and the leaning of the light is eliminated near the exit of the straight portion. Thus, the light leans little toward the inside of the curve near the entrance of the second curved portion, and is little concentrated on the outside side surface of the curve of the second curved portion when reaching the side surface. The light leaks accordingly little in the second curved portion.

In view of these findings, the present inventors have hit upon the idea of making the core width of the downstream second curved portion smaller in the S-shaped portion, and have made one of the width of the exit of the first curved portion and the width of the entrance of the second curved portion smaller than the width of a core portion upstream of the S-shaped portion. As a result, the present inventors have found out that most of the light reaching the outside side surface of the curve of the second curved portion is reflected from the side surface because the incident angle of the light is greater than the critical angle in the second curved portion, so that the leakage of light is reduced. That is, the present inventors have found out that, even if the cores in the second outer peripheral core portion between the lattice-shaped portion and the light-receiving element are partially formed in the S-shape in the position sensor, the propagating light reaches the light-receiving element, with leakage of the propagating light reduced in the cores in the second outer peripheral core portion, by setting the aforementioned specific widths of the S-shaped portion. The present inventors have found that the intensity of light received by the light-receiving element is thus equalized while the input region is not pressed, and have attained the present invention.

The problem of the leakage of light from the S-shaped portion of the cores in the optical circuit board is also solved in the same manner as in the position sensor. That is, the present inventors have found out that, even if the cores are partially formed in the S-shape in the optical circuit board, the leakage of the propagating light is reduced in the S-shaped portion by setting the aforementioned specific widths of the S-shaped portion. The present inventors have found that the decrease in the intensity of light received by the light-receiving element or the decrease in the amount of light propagating to an optical fiber is thus suppressed, and have attained the present invention.

The present inventors have found that not only the optical waveguide for use in the aforementioned position sensor and the aforementioned optical circuit board but also an optical waveguide used for other applications, e.g. for opto-electric hybrid boards, achieves light propagation more properly when the cores are partially formed in the aforementioned S-shape.

The expression “the intensity of light received by the light-receiving element is equal” in the aforementioned position sensor shall be meant to include not only being absolutely equal but also being roughly equal to such an extent that the pressed position in the input region of the position sensor can be sensed if precisely sensed.

In the optical waveguide according to the present invention, the core is partially formed in an S-shape. In the S-shaped portion, one of the width of the exit of the upstream first curved portion and the width of the entrance of the downstream second curved portion is smaller than the width of a core portion upstream of the S-shaped portion. Thus, when the light propagating in the first curved portion reaches the outside side surface of the curve of the second curved portion, the incident angle of the light is greater than the critical angle. Most of the light is reflected from the side surface, so that the leakage of the light is reduced. In other words, the optical waveguide according to the present invention is capable of propagating the light in the core more properly.

In the position sensor according to the present invention, part of the optical waveguide corresponding to at least a portion of the second outer peripheral core portion between the lattice-shaped portion and the light-receiving element is the aforementioned optical waveguide of the present invention. Thus, when light propagating in the first curved portion in each core in the part of the optical waveguide reaches the outside side surface of the curve of the second curved portion, the incident angle of the light is greater than the critical angle. Most of the light is reflected from the side surface, so that the leakage of the light is reduced. That is, light propagating in the cores in the second outer peripheral core portion reaches the light-receiving element, with the leakage of the propagating light reduced. Thus, the intensity of light received by the light-receiving element is equalized while the input region is not pressed. Thus, the location where the intensity of light received by the light-receiving element is decreased is made clear when the input region is pressed. As a result, the position sensor according to the present invention is capable of precisely sensing the pressed position in the input region.

In the optical circuit board according to the present invention, an optical waveguide for optical connection to an optical member is the aforementioned optical waveguide according to the present invention. Thus, when light propagating in the first curved portion in the S-shaped portion of each core in the optical waveguide reaches the outside side surface of the curve of the second curved portion, the incident angle of the light is greater than the critical angle. Most of the light is reflected from the side surface, so that the leakage of the light is reduced. That is, when the optical member receives light from end portions of the cores of the optical waveguide, the leakage of the propagating light is reduced in the cores of the optical waveguide. This suppresses the decrease in the intensity of light received by the optical member. The formation of the S-shaped portion in each of the cores improves flexibility in layout design of the cores to allow the layout design of the cores in accordance with the layout of the optical member. Also, the proper operation of electronic devices and the like incorporating the optical circuit board according to the present invention is achieved with reliability.

In particular, in the case where the width of the entrance of the second curved portion is smaller than the width of the core portion upstream of the S-shaped portion, and where a relationship between the width (B1; in μm) of the entrance of the second curved portion, the radius of curvature (R2; in mm) of the second curved portion, the refractive index (K1) of the core with the S-shaped portion formed therein, and the refractive index (K2) of one of the cladding layers which covers the side surface of the core satisfies Formula (1) below, the amount of leakage of propagating light is further reduced in the second curved portion in the optical waveguide according to the present invention. This equalizes the intensity of light received by the light-receiving element to improve the precision of the sensing of the pressed position in the position sensor according to the present invention. It should be noted that the radius of curvature (R2) of the second curved portion is the radius of curvature of a widthwise center line of the second curved portion.
[MATH. 1]
B2/R2≤800×(K1−K2)  (1)

Further, in the case where the relationship between the width (B1; in μm) of the entrance of the second curved portion, the radius of curvature (R2; in mm) of the second curved portion, the refractive index (K1) of the core with the S-shaped portion formed therein, and the refractive index (K2) of one of the cladding layers which covers the side surface of the core satisfies Formula (2) below, the amount of leakage of propagating light is further reduced in the second curved portion in the optical waveguide according to the present invention. This further equalizes the intensity of light received by the light-receiving element to further improve the precision of the sensing of the pressed position in the position sensor according to the present invention.
[MATH. 2]
B2/R2≤800×(K1−K2)−4  (2)

Also, in the case where the width of the entrance of the second curved portion is smaller than the width of the core portion upstream of the S-shaped portion, where the width of the first curved portion decreases gradually from the entrance of the first curved portion toward the exit thereof, where the width of the straight portion and the width of the second curved portion are constant in the longitudinal direction thereof, and where the width of the exit of the first curved portion, the width of the straight portion, and the width of the second curved portion are equal to each other, the amount of leakage of propagating light is also reduced in the second curved portion, so that the light is propagated in the core more properly. In the position sensor according to the present invention, the intensity of light received by the light-receiving element is equalized, whereby the pressed position is sensed precisely.

Also, in the case where the width of the entrance of the second curved portion is smaller than the width of the core portion upstream of the S-shaped portion, where the width of the first curved portion, the width of the straight portion, and the width of the second curved portion are constant in the longitudinal direction thereof, where the width of the first curved portion is greater than the width of the second curved portion, where the width of the straight portion and the width of the second curved portion are equal to each other, and where the entrance of the straight portion is disposed in part of the exit of the first curved portion which corresponds to the outside of the curve of the first curved portion as seen in the width direction, the amount of leakage of propagating light is also reduced in the second curved portion, so that the light is propagated in the core more properly. In the position sensor according to the present invention, the intensity of light received by the light-receiving element is equalized, whereby the pressed position is sensed precisely.

Also, in the case where the width of the entrance of the second curved portion is smaller than the width of the core portion upstream of the S-shaped portion, where the width of the first curved portion, the width of the straight portion, and the width of the second curved portion are constant in the longitudinal direction thereof, where the width of the first curved portion is greater than the width of the second curved portion, where the width of the first curved portion and the width of the straight portion are equal to each other, and where the entrance of the second curved portion is disposed in part of the exit of the straight portion which corresponds to the outside of the curve of the first curved portion as seen in the width direction, the amount of leakage of propagating light is also reduced in the second curved portion, so that the light is propagated in the core more properly. In the position sensor according to the present invention, the intensity of light received by the light-receiving element is equalized, whereby the pressed position is sensed precisely.

Also, in the case where the width of the entrance of the second curved portion is smaller than the width of the core portion upstream of the S-shaped portion, where the width of the first curved portion and the width of the second curved portion are constant in the longitudinal direction thereof, where the width of the first curved portion is greater than the width of the second curved portion, where the width of the entrance of the straight portion is equal to the width of the first curved portion, and where the width of the exit of the straight portion is equal to the width of the second curved portion, the amount of leakage of propagating light is also reduced in the second curved portion, so that the light is propagated in the core more properly. In the position sensor according to the present invention, the intensity of light received by the light-receiving element is equalized, whereby the pressed position is sensed precisely.

Also, in the case where the width of the entrance of the second curved portion is smaller than the width of the core portion upstream of the S-shaped portion, and where all of the width of the first curved portion, the width of the straight portion, and the width of the second curved portion are constant and equal in the longitudinal direction thereof, the amount of leakage of propagating light is also reduced in the second curved portion, so that the light is propagated in the core more properly. In the position sensor according to the present invention, the intensity of light received by the light-receiving element is equalized, whereby the pressed position is sensed precisely.

On the other hand, in the case where the width of the exit of the first curved portion is smaller than the width of the core portion upstream of the S-shaped portion, and where a relationship between the width (B1; in μm) of the exit of the first curved portion, the radius of curvature (R1; in mm) of the first curved portion, the refractive index (K1) of the core with the S-shaped portion formed therein, and the refractive index (K2) of one of the cladding layers which covers the side surface of the core satisfies Formula (3) below, the amount of leakage of propagating light is further reduced in the second curved portion in the optical waveguide according to the present invention. Thus, when the optical member receives light from end portions of the cores of the optical waveguide in the optical circuit board according to the present invention, the decrease in the intensity of light received by the optical member is further suppressed. The reliability of the achievement of the proper operation of electronic devices and the like incorporating the optical circuit board is improved. It should be noted that the radius of curvature (R1) of the first curved portion S1is the radius of curvature of a widthwise center line of the first curved portion S1.
[MATH. 3]
B1/R1≤800×(K1−K2)  (3)

Also, in the case where the width of the exit of the first curved portion is smaller than the width of the core portion upstream of the S-shaped portion, where the width of the first curved portion decreases gradually from the entrance of the first curved portion toward the exit thereof, where the width of the straight portion and the width of the second curved portion are constant in the longitudinal direction thereof, and where the width of the exit of the first curved portion, the width of the straight portion, and the width of the second curved portion are equal to each other, the amount of leakage of propagating light is also reduced in the second curved portion, so that the light is propagated in the core more properly. Thus, the decrease in the intensity of light received by the optical member is suppressed in the optical circuit board according to the present invention. Also, the proper operation of electronic devices and the like incorporating the optical circuit board is achieved with reliability.

DESCRIPTION OF EMBODIMENTS

Next, embodiments according to the present disclosure will now be described in detail with reference to the drawings.

FIG. 1Ais a plan view of a first embodiment of a position sensor according to the present disclosure.FIG. 1Bis an enlarged view of a midsection taken along the line X-X ofFIG. 1A. The position sensor according to this embodiment includes: a rectangular sheet-like optical waveguide W; two light-emitting elements4disposed in two adjacent corner portions (two upper corner portions as seen inFIG. 1A) of the rectangular shape of the optical waveguide W; and two light-receiving elements5disposed in the remaining two corner portions (two lower corner portions as seen inFIG. 1A) thereof.

The optical waveguide W includes: a rectangular sheet-like under cladding layer1; a sheet-like core pattern member formed on a surface of the under cladding layer1; and a rectangular sheet-like over cladding layer3formed on the surface of the under cladding layer1while covering the core pattern member. The core pattern member includes: a lattice-shaped portion2A including a plurality of linear cores2serving as an optical path and arranged vertically and horizontally; a first outer peripheral core portion2B positioned on and extending along a first horizontal side and a first vertical side (upper and right-hand sides as seen inFIG. 1A) of the outer periphery of the lattice-shaped portion2A; and a second outer peripheral core portion2C positioned on and extending along a second horizontal side and a second vertical side (lower and left-hand sides as seen inFIG. 1A) which are opposed respectively to the first horizontal side and the first vertical side, with the lattice-shaped portion2A therebetween.

The first outer peripheral core portion2B includes a single core21, and is optically connected to front ends (upper ends as seen inFIG. 1A) of respective vertical cores2of the lattice-shaped portion2A and to front ends (right-hand ends as seen inFIG. 1A) of respective horizontal cores2of the lattice-shaped portion2A. Thus, the vertical cores2and the horizontal cores2branch off from the first outer peripheral core portion2B. The second outer peripheral core portion2C includes cores22extending from rear ends (lower ends as seen inFIG. 1A) of the respective vertical cores2and from rear ends (left-hand ends as seen inFIG. 1A) of the respective horizontal cores2. The light-emitting elements4are connected to end surfaces of the first outer peripheral core portion2B, and the light-receiving elements5are connected to end surfaces of the second outer peripheral core portion2C.

InFIG. 1A, the cores2,21and22are indicated by chain-dotted lines. Also, inFIG. 1A, the number of cores2in the lattice-shaped portion2A and the number of cores22in the second outer peripheral core portion2C which extend from the cores2are shown as abbreviated. Arrows of the cores2inFIG. 1Aindicate the directions in which light travels.

A feature of the position sensor according to this embodiment is the core widths of an S-shaped portion of certain ones of the cores22of the second outer peripheral core portion2C which is formed near the light-receiving elements5(in regions surrounded by ellipses D1ofFIG. 1A), as shown in enlarged plan view ofFIG. 1C.FIG. 1Cshows the S-shaped portion of one of the cores22of the second outer peripheral core portion2C in enlarged plan view. The S-shaped portion in this embodiment includes a first curved portion S1upstream as seen in the direction of light propagation, and a second curved portion S2downstream as seen in the direction of light propagation and curved in a direction opposite to the first curved portion S1. The first curved portion S1and the second curved portion S2are connected in contiguous relation. The width of the entrance (the entrance of the first curved portion S1) of the S-shaped portion is equal to the width B0of a core portion upstream of the S-shaped portion. In the S-shaped portion, the width of the first curved portion S1decreases gradually from the entrance of the first curved portion S1toward the exit thereof. The width of the exit of the first curved portion S1is equal to the width B2of the entrance of the second curved portion S2. The second curved portion S2has a width constant in the longitudinal direction thereof. Thus, the width B2of the entrance of the second curved portion S2is smaller than the width B0of the core portion upstream of the S-shaped portion.

In this manner, setting the characteristic core widths of the S-shaped portion reduces leakage of light L in the S-shaped portion (reduces the propagation loss of the light L). When the light L (indicated by dash-double-dot lines) leans toward an outside portion of the curve of the upstream first curved portion S1and is propagated to the downstream second curved portion S2in the S-shaped portion, the light L is propagated near the entrance of the second curved portion S2while leaning toward the inside of the curve, and reaches the outside side surface of the curve of the second curved portion S2in a concentrated manner. The incident angle θ of the light L reaching the side surface is greater than the critical angle because the core width of the second curved portion S2is smaller in accordance with the setting of the characteristic core widths of the S-shaped portion as mentioned above. For this reason, most of the light L is reflected from the aforementioned side surface, so that the leakage of the light L is reduced. The light L reaches the light-receiving elements5while leakage of the propagating light L is reduced in the cores22of the second outer peripheral core portion2C.

In such a position sensor, light emitted from the light-emitting elements4branches from the core21of the first outer peripheral core portion2B into the cores2of the lattice-shaped portion2A, passes through the cores22of the second outer peripheral core portion2C, and is received by the light-receiving elements5, as shown inFIG. 1A. A surface portion (a rectangular portion indicated by dash-and-dot lines in the center ofFIG. 1A) of the over cladding layer3corresponding to the lattice-shaped portion2A of the core pattern member serves as an input region3A.

The input of a character or the like to the position sensor is performed by writing the character or the like into the input region3A with an input element such as a pen either directly or through a resin film, paper or the like. At this time, the input region3A is pressed with the tip of the pen or the like, so that at least one of the cores2corresponding to the pressed part is deformed. The deformation decreases the amount of light propagating in the at least one core2. Thus, the intensity of light received by the light-receiving elements5is decreased in the at least one core2corresponding to the pressed part. In this manner, the position sensor senses the pressed position (X and Y coordinates).

As mentioned above, light propagating in the cores22of the second outer peripheral core portion2C reaches the light-receiving elements5while leakage of the propagating light is reduced. This equalizes the intensity of light received by the light-receiving elements5while the input region3A is not pressed. Thus, the location where the intensity of light received by the light-receiving elements5is decreased is made clear when the input region3A is pressed. As a result, the position sensor is capable of precisely sensing the pressed position in the input region3A.

From the viewpoints of further reducing the amount of leakage of propagating light in the second curved portion S2and thereby further equalizing the intensity of light received by the light-receiving elements5to improve the precision of the sensing of the pressed position, it is preferable that a relationship between the width (B2; in μm) of the entrance of the second curved portion S2, the radius of curvature (R2; in mm) of the second curved portion S2, the refractive index (K1) of the cores22with the S-shaped portion formed therein, and the refractive index (K2) of the over cladding layer3covering the side surfaces of the cores22is established so as to satisfy Formula (1) below. More preferably, the relationship is established so as to satisfy Formula (2) below. It should be noted that the radius of curvature (R2) of the second curved portion S2is the radius of curvature of a widthwise center line of the second curved portion S2.
[MATH. 4]
B2/R2≤800×(K1−K2)  (1)
[MATH. 5]
B2/R2≤800×(K1−K2)−4  (2)

The light-receiving elements5, which are in general small, have a narrow light-receiving region for connection to the cores22. Accordingly, there is a limit to the number of cores22for connection to the narrow light-receiving region. In the position sensor, the core width of the downstream second curved portion S2is smaller in the S-shaped portion formed near the light-receiving elements5, as mentioned above. The formation of the cores22having the smaller width to the front ends thereof allows the increase in the number of cores22for connection to the light-receiving region. As a result, this allows the increase in the number of cores2of the lattice-shaped portion2A corresponding to the input region3A to achieve an improvement in positional accuracy of the pressed position sensed in the input region3A.

In the optical waveguide W, it is preferable that the cores2of the lattice-shaped portion2A have an elasticity modulus higher than the elasticity moduli of the under cladding layer1and the over cladding layer3. The reason for this is as follows. If the elasticity modulus of the cores2is lower than the elasticity moduli of the under cladding layer1and the over cladding layer3, the surroundings of the cores2are hard, so that part of the optical waveguide W having an area significantly greater than the area of the pen tip or the like which presses part of the input region3A of the over cladding layer3is depressed. As a result, it tends to be difficult to precisely sense the pressed position. For this reason, it is preferable that the elasticity moduli are as follows: the cores2have an elasticity modulus in the range of 1 GPa to 10 GPa; the over cladding layer3has an elasticity modulus in the range of 0.1 GPa to less than 10 GPa; and the under cladding layer1has an elasticity modulus in the range of 0.1 MPa to 1 GPa, for example. In this case, the cores2are not crushed (the cross-sectional area of the cores2is not decreased) with a small pressing force because of the high elasticity modulus of the cores2. However, the optical waveguide W is depressed by the pressing, so that light leakage (scattering) occurs from the bent part of the cores2corresponding to the depressed part. Thus, the intensity of light received by the light-receiving elements5is decreased in these cores2. In this manner, the pressed position is sensed. The aforementioned values of the elasticity moduli are values of tensile elasticity moduli measured using a dynamic mechanical analyzer RSA III available from TA Instruments Japan Inc.

Examples of materials for the formation of the under cladding layer1, the cores2,21and22, and the over cladding layer3include photosensitive resins and thermosetting resins. The optical waveguide W may be produced by a manufacturing method depending on the materials. The cores2,21and22have a refractive index higher than the refractive indices of the under cladding layer1and the over cladding layer3. The adjustment of the refractive indices and the elasticity moduli may be made, for example, by adjusting the selection of the types of the materials for the formation of the cores2,21and22, the under cladding layer1and the over cladding layer3, and the composition ratio thereof. Examples of the thicknesses of the respective layers are as follows: the under cladding layer1has a thickness in the range of 10 to 500 μm; the cores2,21and22have a thickness in the range of 5 to 100 μm; and the over cladding layer3has a thickness (a thickness as measured from the top surfaces of the cores2,21and22) in the range of 1 to 200 μm. A rubber sheet may be used as the under cladding layer1, and the cores2,21and22may be formed on the rubber sheet.

FIG. 2is an enlarged plan view (a view corresponding toFIG. 1C) of the S-shaped portion in a second embodiment of the position sensor of the present disclosure. In the second embodiment, the S-shaped portion is formed in such a manner that the first curved portion S1and the second curved portion S2in the first embodiment shown inFIGS. 1A to 1Care connected to each other via a straight portion T having a length in the range of greater than 0 (zero) mm to 30 mm. The straight portion T has a width constant in the longitudinal direction thereof and equal to the width of the exit of the first curved portion S1(the width B2of the entrance of the second curved portion S2). The remaining parts of the second embodiment are similar to those of the first embodiment described above. Like reference numerals and characters are used in the second embodiment to designate parts similar to those of the first embodiment.

In the second embodiment, the straight portion T is formed between the first curved portion S1and the second curved portion S2, but has a short length of not greater than 30 mm. For this reason, light L (indicated by dash-double-dot lines) propagated from the first curved portion S1to the straight portion T is reflected little from the side surface of the straight portion T and is propagated to the second curved portion S2. The light L propagated to the second curved portion S2reaches the light-receiving elements5while leakage of the propagating light L is reduced as in the first embodiment because the second curved portion S2in the second embodiment is similar to that in the first embodiment. That is, the position sensor in the second embodiment produces functions and effects similar to those of the first embodiment.

FIG. 3is an enlarged plan view (a view corresponding toFIG. 1C) of the S-shaped portion in a third embodiment of the position sensor of the present disclosure. In the third embodiment, the first curved portion S1of the S-shaped portion in the first embodiment shown inFIGS. 1A to 1Chas a width constant in the longitudinal direction thereof and equal to the width B0of the core portion upstream of the S-shaped portion. The second curved portion S2has a width constant in the longitudinal direction thereof as in the first embodiment, and the width B2of the entrance of the second curved portion S2is smaller than the width B0of the core portion upstream of the S-shaped portion. The entrance of the second curved portion S2is disposed in part of the exit of the first curved portion S1which corresponds to the outside of the curve of the first curved portion S1as seen in the width direction. That is, the connecting portion between the first curved portion S1and the second curved portion S2in the S-shaped portion is formed in a stepped shape, and the width of the connecting portion is abruptly narrowed down to the outside of the curve of the first curved portion S1(the inside of the curve of the second curved portion S2). The remaining parts of the third embodiment are similar to those of the first embodiment described above. Like reference numerals and characters are used in the third embodiment to designate parts similar to those of the first embodiment.

In the third embodiment, the width of the connecting portion between the first curved portion S1and the second curved portion S2is abruptly narrowed down to the outside of the curve of the first curved portion S1. However, the light L (indicated by dash-double-dot lines) propagating in the first curved portion S1leans toward the outside portion of the curve thereof as in the first embodiment. For this reason, most of the light L is propagated to the second curved portion S2. The light L propagated to the second curved portion S2reaches the light-receiving elements5while leakage of the propagating light L is reduced as in the first embodiment because the second curved portion S2in the third embodiment is similar to that in the first embodiment. That is, the position sensor in the third embodiment produces functions and effects similar to those of the first embodiment.

FIG. 4is an enlarged plan view (a view corresponding toFIG. 1C) of the S-shaped portion in a fourth embodiment of the position sensor of the present disclosure. In the fourth embodiment, the S-shaped portion is formed in such a manner that the first curved portion S1and the second curved portion S2in the third embodiment shown inFIG. 3are connected to each other via the straight portion T having a length in the range of greater than 0 (zero) mm to 30 mm. The entrance of the straight portion T is disposed in part of the exit of the first curved portion S1which corresponds to the outside of the curve of the first curved portion S1as seen in the width direction. The straight portion T has a width constant in the longitudinal direction thereof and equal to the width B2of the entrance of the second curved portion S2. That is, the connecting portion between the first curved portion S1and the straight portion T is formed in a stepped shape, and the width of the connecting portion is abruptly narrowed down to the outside of the curve of the first curved portion S1. The remaining parts of the fourth embodiment are similar to those of the third embodiment described above. Like reference numerals and characters are used in the fourth embodiment to designate parts similar to those of the third embodiment.

In the fourth embodiment, the width of the connecting portion between the first curved portion S1and the straight portion T is abruptly narrowed down to the outside of the curve of the first curved portion S1. However, the light L (indicated by dash-double-dot lines) propagating in the first curved portion S1leans toward the outside portion of the curve thereof as in the third embodiment. For this reason, most of the light L is propagated to the straight portion T. In addition, the light L is reflected little from the side surface of the straight portion T and is propagated to the second curved portion S2as in the second embodiment shown inFIG. 2. The light L propagated to the second curved portion S2reaches the light-receiving elements5while leakage of the propagating light L is reduced as in the first embodiment because the second curved portion S2in the fourth embodiment is similar to that in the first embodiment. That is, the position sensor in the fourth embodiment produces functions and effects similar to those of the first embodiment.

FIG. 5is an enlarged plan view (a view corresponding toFIG. 1C) of the S-shaped portion in a fifth embodiment of the position sensor of the present disclosure. In the fifth embodiment, the width of the first curved portion S1and the width of the straight portion T in the fourth embodiment shown inFIG. 4are equal to each other. The entrance of the second curved portion S2is disposed in part of the exit of the straight portion T which corresponds to the outside of the curve of the first curved portion S1as seen in the width direction. That is, the connecting portion between the straight portion T and the second curved portion S2is formed in a stepped shape, and the width of the connecting portion is abruptly narrowed down to the outside of the curve of the first curved portion S1. The remaining parts of the fifth embodiment are similar to those of the fourth embodiment described above. Like reference numerals and characters are used in the fifth embodiment to designate parts similar to those of the fourth embodiment.

In the fifth embodiment, the light L (indicated by dash-double-dot lines) propagating while leaning toward the outside portion of the curve of the first curved portion S1is also propagated in the straight portion T while leaning toward part of the straight portion T which corresponds to the outside portion without any change. In addition, the light L propagated to the straight portion T is reflected little from the side surface of the straight portion T and is propagated to the second curved portion S2as in the fourth embodiment. Thus, most of the light L propagating in the straight portion T is propagated to the second curved portion S2although the width of the connecting portion between the straight portion T and the second curved portion S2is abruptly narrowed down to the outside portion of the straight portion T as described above. The light L propagated to the second curved portion S2reaches the light-receiving elements5while leakage of the propagating light L is reduced as in the first embodiment because the second curved portion S2in the fifth embodiment is similar to that in the first embodiment. That is, the position sensor in the fifth embodiment produces functions and effects similar to those of the first embodiment.

FIG. 6is an enlarged plan view (a view corresponding toFIG. 1C) of the S-shaped portion in a sixth embodiment of the position sensor of the present disclosure. In the sixth embodiment, the width of the entrance of the straight portion T in the fifth embodiment shown inFIG. 5is equal to the width of the first curved portion S1, and the width of the exit of the straight portion T is equal to the width of the second curved portion S2. That is, the straight portion T is formed in such a tapered shape that the width thereof gradually decreases from the entrance thereof toward the exit thereof. The remaining parts of the sixth embodiment are similar to those of the fifth embodiment described above. Like reference numerals and characters are used in the sixth embodiment to designate parts similar to those of the fifth embodiment.

In the sixth embodiment, the light L (indicated by dash-double-dot lines) propagating while leaning toward the outside portion of the curve of the first curved portion S1is also propagated in the straight portion T while leaning toward part of the straight portion T which corresponds to the outside portion without any change. In addition, the light L propagated to the straight portion T is reflected little from the side surface of the straight portion T and is propagated to the second curved portion S2as in the fifth embodiment. The light L propagated to the second curved portion S2reaches the light-receiving elements5while leakage of the propagating light L is reduced as in the first embodiment because the second curved portion S2in the sixth embodiment is similar to that in the first embodiment. That is, the position sensor in the sixth embodiment produces functions and effects similar to those of the first embodiment.

FIG. 7is an enlarged plan view (a view corresponding toFIG. 1C) of the S-shaped portion in a seventh embodiment of the position sensor of the present disclosure. In the seventh embodiment, the width of the first curved portion S1in the third embodiment shown inFIG. 3is equal to the width of the second curved portion S2and is smaller. That is, the width of the S-shaped portion is constant and equal throughout in the longitudinal direction thereof, and is smaller than the width B0of the core portion upstream of the S-shaped portion. The remaining parts of the seventh embodiment are similar to those of the third embodiment described above. Like reference numerals and characters are used in the seventh embodiment to designate parts similar to those of the third embodiment.

In the seventh embodiment, the width of the S-shaped portion is constant and equal in the longitudinal direction thereof, and is smaller than the width B0of the core portion upstream of the S-shaped portion. For this reason, the light L (indicated by dash-double-dot lines) propagating while leaning toward the outside portion of the curve of the first curved portion S1is also propagated to the second curved portion S2without any change also in the seventh embodiment. The light L propagated to the second curved portion S2reaches the light-receiving elements5while leakage of the propagating light L is reduced as in the first embodiment because the second curved portion S2in the seventh embodiment is similar to that in the first embodiment. That is, the position sensor in the seventh embodiment produces functions and effects similar to those of the first embodiment.

FIG. 8is an enlarged plan view (a view corresponding toFIG. 1C) of the S-shaped portion in an eighth embodiment of the position sensor of the present disclosure. In the eighth embodiment, the S-shaped portion is formed in such a manner that the first curved portion S1and the second curved portion S2in the seventh embodiment shown inFIG. 7are connected to each other via the straight portion T having a length in the range of greater than 0 (zero) mm to 30 mm. The straight portion T has a width constant in the longitudinal direction thereof and equal to the width of the first curved portion S1(the width of the second curved portion S2). The remaining parts of the eighth embodiment are similar to those of the seventh embodiment described above. Like reference numerals and characters are used in the eighth embodiment to designate parts similar to those of the seventh embodiment.

In the eighth embodiment, the light L (indicated by dash-double-dot lines) propagating while leaning toward the outside portion of the curve of the first curved portion S1is also propagated in the straight portion T while leaning toward part of the straight portion T which corresponds to the outside portion without any change. In addition, the light L propagated to the straight portion T is reflected little from the side surface of the straight portion T and is propagated to the second curved portion S2as in the second embodiment shown inFIG. 2. The light L propagated to the second curved portion S2reaches the light-receiving elements5while leakage of the propagating light L is reduced as in the first embodiment because the second curved portion S2in the eighth embodiment is similar to that in the first embodiment. That is, the position sensor in the eighth embodiment produces functions and effects similar to those of the first embodiment.

Although the cores22having the S-shaped portion formed therein are part of the second outer peripheral core portion2C in the aforementioned embodiments, all of the cores22may have the S-shaped portion formed therein.

The optical waveguide W has a cross-sectional structure shown inFIG. 1Bin the aforementioned embodiments, but may have other cross-sectional structures. For example, as shown in sectional view inFIG. 9, the optical waveguide W may have a cross-sectional structure obtained by turning the cross-sectional structure shown inFIG. 1Bupside down. Specifically, the optical waveguide W is configured such that the cores2are buried in a front surface portion of the sheet-like under cladding layer1so that the top surface of the cores2is flush with the front surface of the under cladding layer1, and such that the sheet-like over cladding layer3is formed while covering the front surface of the under cladding layer1and the top surface of the cores2.

Each intersection of the cores2in the lattice-shaped portion is generally configured to be continuous in all of the four intersecting directions as shown in enlarged plan view inFIG. 10Ain the aforementioned embodiments, but may be of other configurations. For example, each intersection may be separated by a gap G to become discontinuous only in one of the intersecting directions, as shown inFIG. 10B. The gap G is made of the material for the formation of the under cladding layer1or the over cladding layer3. The gap G has a width d greater than 0 (zero) (it is only necessary that the gap G is formed) and generally not greater than 20 μm. Likewise, as shown inFIGS. 10C and 10D, each intersection may be discontinuous in two intersecting directions (in two opposed directions inFIG. 10C, and in two adjacent directions inFIG. 10D). Alternatively, each intersection may be discontinuous in three intersecting directions, as shown inFIG. 10E. Also, each intersection may be discontinuous in all of the four intersecting directions, as shown inFIG. 10F. Further, the cores2may be in a lattice-shape including two or more types of intersections shown inFIGS. 10A to 10F. The term “lattice-shape” formed by the linear cores2as used in the present disclosure shall be meant to include a lattice-shape in which part or all of the intersections are formed in the aforementioned manner.

In particular, intersections which are discontinuous in at least one intersecting direction as shown inFIGS. 10B to 10Fare capable of reducing intersection losses of light. At an intersection which is continuous in all of the four intersecting directions as shown inFIG. 11A, attention will be given on one intersecting direction (an upward direction as seen inFIG. 11A). Then, part of light incident on the intersection reaches a side surface2aof a first core2perpendicular to a second core2through which the light travels, and is transmitted through the first core2(with reference to dash-double-dot arrows inFIG. 11A) because the incident angle at the side surface2ais smaller than the critical angle. Such light transmission occurs also in the opposite intersecting direction (a downward direction as seen inFIG. 11A). As shown inFIG. 11B, on the other hand, when an intersection is made discontinuous by the gap G in one intersecting direction (an upward direction as seen inFIG. 11B), an interface between the gap G and a core2is formed. Then, part of light transmitted through the core2with reference toFIG. 11Ais not transmitted through the interface but is reflected from the interface to continue traveling through the core2(with reference to dash-double-dot arrows inFIG. 11B) because the incident angle at the interface is greater than the critical angle. Based on these facts, the reduction in intersection losses of light is achieved by making the intersection discontinuous in at least one intersecting direction as mentioned above. As a result, the sensitivity for sensing of the pressed position with the tip of the pen or the like is increased.

The optical waveguide W has a rectangular sheet-like shape in the aforementioned embodiments, but may have other polygonal sheet-like shapes so long as the optical waveguide W includes the cores2arranged in a lattice shape.

FIG. 12Ais a plan view of a first embodiment of an optical circuit board according to the present disclosure.FIG. 12Bis a vertical sectional view taken along the central axis of a core shown inFIG. 12A(a sectional view taken along the line Y-Y ofFIG. 12A). Like the optical circuit board70of the related art (with reference toFIG. 18), an optical circuit board30according to this embodiment is also stacked on an electrical circuit board40. As shown in plan view ofFIG. 12A, the optical circuit board30includes two light-emitting elements34on a first end side (the upper end side as seen inFIG. 12A), and two light-receiving elements35on a second end side (the lower end side as seen inFIG. 12A). The distance between the two light-receiving elements35on the second end side is greater than the distance between the two light-emitting elements34on the first end side. Thus, the optical circuit board30has a smaller width on the first end side and a greater width on the second end side, and the distance between adjacent cores32which propagate light between the light-emitting elements34and the light-receiving elements35is greater on the light-receiving elements35side than on the light-emitting elements34side. Accordingly, the cores32are curved in an S-shape in a longitudinally middle portion (regions surrounded by ellipses D2inFIG. 12A). It should be noted that the width of the cores32is shown in exaggeration.

As shown in enlarged plan view inFIG. 12C, the S-shaped portion of each core32in this embodiment includes the first curved portion S1upstream as seen in the direction of light propagation, and the second curved portion S2downstream as seen in the direction of light propagation and curved in a direction opposite to the first curved portion S1. The first curved portion S1and the second curved portion S2are connected in contiguous relation. The width of the entrance (the entrance of the first curved portion S1) of the S-shaped portion is equal to the width B0of the core portion upstream of the S-shaped portion. The width of the first curved portion S1decreases gradually from the entrance of the first curved portion S1toward the exit thereof. The width B1of the exit of the first curved portion S1is equal to the width B2of the entrance of the second curved portion S2. The second curved portion S2has a width constant in the longitudinal direction thereof.

The remaining parts are similar to those of the electrical circuit board80and the optical circuit board70of the related art shown inFIG. 18. Specifically, inFIG. 12B, the reference numeral41designates an insulative layer;42designates an electrical interconnect line (not shown inFIG. 12A) formed on the front surface of the insulative layer41; the reference characters41aand41bdesignate through holes formed in the insulative layer41; W2designates an optical waveguide;32aand32bdesignate light reflecting surfaces formed in opposite end portions of each core32;31designates a first cladding layer; and33designates a second cladding layer. The cores32have respective first end portions optically connected to the light-emitting elements34, and respective second end portions optically connected to the light-receiving elements35. Light L (indicated by dash-double-dot lines) is propagated from the light-emitting elements34through the cores32to the light-receiving elements35.

Setting the characteristic core widths of the S-shaped portion in each of the cores32reduces leakage of light L in the S-shaped portion (reduces the propagation loss of the light L). Specifically, the width B1of the exit of the upstream first curved portion S1in the S-shaped portion is smaller than the width B0of the core portion upstream of the S-shaped portion, as shown inFIG. 12C. Thus, the propagating light L (indicated by dash-double-dot lines) is propagated to the downstream second curved portion S2while leaning toward the outside portion of the curve of the upstream first curved portion S1. Then, the light L is propagated near the entrance of the second curved portion S2while leaning toward the inside of the curve, and reaches the outside side surface of the curve of the second curved portion S2in a concentrated manner. The incident angle θ of the light L reaching the outside side surface of the curve of the second curved portion S2is greater than the critical angle because the width B2of the entrance of the second curved portion S2is equal to the width B1of the exit of the first curved portion S1and smaller and because the width of the second curved portion S2is constant in the longitudinal direction thereof. For this reason, most of the light L is reflected from the aforementioned side surface, so that the leakage of the light L is reduced. The light L reaches the light-receiving elements35while leakage of the propagating light L is reduced in the cores32.

From the viewpoints of further reducing the amount of leakage of propagating light in the second curved portion S2and thereby further suppressing the decrease in the intensity of light received by the light-receiving elements35, it is preferable that a relationship between the width (B1; in μm) of the exit of the first curved portion S1, the radius of curvature (R1; in mm) of the first curved portion S1, the refractive index (K1) of the cores32with the S-shaped portion formed therein, and the refractive index (K2) of the second cladding layer33covering the side surfaces of the cores32is established so as to satisfy Formula (3) below. It should be noted that the radius of curvature (R1) of the first curved portion S1is the radius of curvature of a widthwise center line of the first curved portion S1.
[MATH. 6]
B1/R1≤800×(K1−K2)  (3)

The core width of the first curved portion S1at both the entrance and the exit is preferably in the range of 1 to 80 μm, for example. The radius of curvature (R1) of the first curved portion S1is preferably in the range of 0.5 to 5.0 mm, for example. The difference (K1−K2) in refractive index is preferably in the range of 0.005 to 0.05, for example.

FIG. 13is an enlarged plan view (a view corresponding toFIG. 12C) of the S-shaped portion in a second embodiment of the optical circuit board of the present disclosure. In the second embodiment, the S-shaped portion is formed in such a manner that the first curved portion S1and the second curved portion S2in the first embodiment shown inFIGS. 12A to 12Care connected to each other via the straight portion T having a length in the range of greater than 0 (zero) mm to 30 mm. The straight portion T has a width constant in the longitudinal direction thereof and equal to the width B1of the exit of the first curved portion S1(the width B2of the entrance of the second curved portion S2). The remaining parts of the second embodiment are similar to those of the first embodiment described above. Like reference numerals and characters are used in the second embodiment to designate parts similar to those of the first embodiment.

In the second embodiment, the width B1of the exit of the upstream first curved portion S1in the S-shaped portion is smaller than the width B0of the core portion upstream of the S-shaped portion. Thus, the light L (indicated by dash-double-dot lines) propagating in the S-shaped portion is propagated to the straight portion T while leaning toward the outside portion of the curve of the upstream first curved portion S1. The straight portion T has a short length of not greater than 30 mm. For this reason, light L propagated from the first curved portion S1to the straight portion T is reflected little from the side surface of the straight portion T and is propagated to the second curved portion S2while leaning. Then, the light L is propagated near the entrance of the second curved portion S2while leaning toward the inside of the curve, and reaches the outside side surface of the curve of the second curved portion S2in a concentrated manner, as in the first embodiment. Most of the light L reaching the side surface is reflected from the aforementioned side surface, so that the leakage of the light L is reduced because the second curved portion S2in the second embodiment is similar to that in the first embodiment. In this manner, the light L propagated to the second curved portion S2reaches the light-receiving elements35while leakage of the propagating light L is reduced as in the first embodiment. That is, the optical circuit board in the second embodiment produces functions and effects similar to those of the first embodiment.

FIG. 14is a plan view of a third embodiment of the optical circuit board of the present disclosure. In the third embodiment, a large number of electronic components50including optical elements54, IC chip interfaces, resistors, capacitors, coils and the like are disposed in dispersed locations on a surface of an insulative layer61. An optical waveguide W3includes cores S2having respective first end portions optically connected to the optical elements54, and respective second end portions optically connected to an optical fiber connecting connector55. Part (regions surrounded by ellipses D3inFIG. 14) of each of the cores52is formed in an S-shape because the cores52are arranged and formed so as to be clear of the dispersed electronic components50. The characteristic core widths of the S-shaped portion are set as in the first embodiment shown inFIG. 12Cor the second embodiment shown inFIG. 13. The remaining parts of the third embodiment are similar to those of the first or second embodiment described above. The optical circuit board in the third embodiment produces functions and effects similar to those of the first or second embodiment.

The cross-sectional structure (a cross-sectional structure corresponding to those ofFIGS. 1B and 9) of each of the optical waveguides W2and W3in the aforementioned embodiments of the optical circuit board may be a cross-sectional structure shown inFIG. 15Aor a cross-sectional structure shown inFIG. 15B. In the cross-sectional structure shown inFIG. 15A, the cores32in a protruding shape are formed on the lower surface of the first cladding layer31, and the second cladding layer33is formed on the lower surface of the first cladding layer31while covering the side and lower surfaces of the cores32. The cross-sectional structure shown inFIG. 15Bis obtained by turning the cross-sectional structure shown inFIG. 15Aupside down. Specifically, the cores32are buried in the lower surface portion of the first cladding layer31so that the lower surface of the cores32is flush with the lower surface of the first cladding layer31, and the second cladding layer33is formed while covering the lower surface of the first cladding layer31and the lower surface of the cores32.

In the aforementioned embodiments of the position sensor and the optical circuit board, the width of the downstream second curved portion S2of the S-shaped portion is constant in the longitudinal direction thereof. However, the width of the downstream second curved portion S2may be gradually decreased from the entrance thereof toward the exit thereof because the light propagation loss in the S-shaped portion tends to decrease with the decreasing width of the second curved portion S2.

The optical waveguides W, W2and W3including the cores22and32each having the S-shaped portion are employed for the position sensor and the optical circuit board in the aforementioned embodiments. However, the optical waveguides W, W2and W3may be optical waveguides used for other applications, e.g. for opto-electric hybrid boards.

Next, inventive examples of the present disclosure will be described in conjunction with comparative examples. It should be noted that the present disclosure is not limited to the inventive examples.

EXAMPLES

[Material for Formation of Under Cladding Layer and Over Cladding Layer]

Component a: 60 parts by weight of an epoxy resin (YX7400 available from Mitsubishi Chemical Corporation).

Component b: 40 parts by weight of an epoxy resin (EHPE3150 available from Daicel Corporation).

Component c: 1 part by weight of a photo-acid generator (CPI-101A available from San-Apro Ltd.).

A material for the formation of an under cladding layer and an over cladding layer was prepared by mixing these components a to c together.

[Material for Formation of Cores]

Component d: 100 parts by weight of an epoxy resin (EHPE3150 available from Daicel Corporation).

Component e: 1 part by weight of a photo-acid generator (SP-170 available from ADEKA Corporation).

Component f: 50 parts by weight of ethyl lactate (a solvent available from Wako Pure Chemical Industries, Ltd.).

A material for the formation of cores was prepared by mixing these components d to f together.

An optical waveguide in which a portion of each of the cores was formed in an S-shape was produced with the use of the aforementioned materials. The S-shaped portion included a first curved portion S1having a width decreasing gradually from the entrance thereof toward the exit thereof, and a second curved portion S2having an entrance with a width B2smaller than the width B0of a core portion upstream of the S-shaped portion (with reference toFIG. 1C). The width B2of the entrance of the second curved portion S2was set to a variety of values listed in TABLE 1 below. Other dimensions, refractive indices and the like were also listed in TABLE 1. The width B0of the core portion upstream of the S-shaped portion was 200 μm. The under cladding layer had a thickness of 25 μm. The cores had a thickness of 30 μm. The over cladding layer had a thickness of 70 μm as measured from the top surface of the cores.

Comparative Example 1

Comparative Example 1 was provided in which the S-shaped portion in Inventive Example 1 had a greater constant width of 200 μm. The remaining parts of Comparative Example 1 were similar to those of Inventive Example 1.

[Measurement of Light Propagation Loss]

A light-emitting element (XH85-S0603-2s available from Optowell Co., Ltd.) was connected to a first end surface of the cores of the aforementioned optical waveguide, and alight-receiving element (s10226 available from Hamamatsu Photonics K.K.) was connected to a second end surface of the cores thereof. Then, a light propagation loss (α) was calculated in accordance with Formula (4) below based on the intensity (E) of light emitted from the light-emitting element and the intensity (F) of light received by the light-receiving element, and was listed in TABLE 1 below.
[MATH. 7]
α=−10 log10(F/E)  (4)

The results in TABLE 1 show that the light propagation loss is low in Inventive Example 1 as compared with that in Comparative Example 1. From this, it is found to be effective in lowering the light propagation loss that the width B2of the entrance of the second curved portion of the S-shaped portion is smaller than the width B0of the core portion upstream of the S-shaped portion. It should be noted that Inventive Example 1 satisfies Formula (1) described above.

Inventive Examples 2 to 4 and Comparative Examples 2 and 3

Inventive Examples 2 to 4 and Comparative Examples 2 and 3 were provided by changing the material for the formation of the over cladding layer in Inventive Example 1 and Comparative Example 1 to thereby change the refractive index of the over cladding layer. Then, the light propagation loss was calculated in the same manner as in Inventive Example 1. The results were listed in TABLES 2 and 3 below.

The results in TABLES 2 and 3 show that the light propagation loss is low in Inventive Examples 2 to 4 as compared with that in Comparative Examples 2 and 3. From this, it is found to be effective in lowering the light propagation loss that the width B2of the entrance of the second curved portion of the S-shaped portion is smaller than the width B0of the core portion upstream of the S-shaped portion. It should be noted that Inventive Examples 2 to 4 satisfy Formula (1) described above.

An optical waveguide including cores having each of the S-shaped portions shown inFIGS. 2 to 8provided results having tendencies similar to those in Inventive Examples 1 to 4.

A position sensor shown inFIG. 1Aincluding a second outer peripheral core portion with each S-shaped portion formed therein was produced. A light-emitting element and a light-receiving element employed in the position sensor were similar to those described above.

[Measurement of Intensity of Received Light]

In the position sensor, the intensity of light received by the light-receiving element was measured while an input region was not pressed. As a result, in the position sensor including the second outer peripheral core portion having each of the S-shaped portions shown inFIG. 1CandFIGS. 2 to 8, the intensity of the received light was equal throughout the input region. On the other hand, in the position sensor including the second outer peripheral core portion having each of the S-shaped portions of Comparative Examples 1 to 3, the intensity of the received light was low and unequal in portions corresponding to the cores having each of the S-shaped portions.

Experimental Example 1

An optical waveguide in which a portion of each core was formed in an S-shape was produced with the use of the same materials as in Inventive Example 1. The S-shaped portion included: a first curved portion having an entrance with a width of 200 μm, an exit with a width of 40 μm, and a radius of curvature of 10 mm; and a second curved portion having an entrance with a width of 40 μm, an exit with a width of 15 μm, and a radius of curvature of 10 mm. The width of the entrance of the first curved portion was equal to the width of a core portion upstream of the S-shaped portion. A straight portion was provided between the first curved portion and the second curved portion. The length of the straight portion was increased from 0 (zero) mm in increments of 1.2 mm. The light propagation loss was calculated for each length of the straight portion in the same manner as in Inventive Example 1. The results were shown in the graph ofFIG. 16.

Experimental Example 2

The first curved portion in Experimental Example 1 had a greater constant width of 200 μm. The second curved portion in Experimental Example 1 had an entrance with a width of 200 μm, an exit with a width of 15 μm, and a radius of curvature of 10 mm. The light propagation loss was calculated in the same manner as in Experimental Example 1. The results were shown in the graph of FIG. 16 in conjunction with the results of Experimental Example 1.

The graph ofFIG. 16shows that the light propagation loss in Experimental Example 1 is substantially constant independently of the length of the straight portion. The graph ofFIG. 16also shows that the light propagation loss in Experimental Example 2 tends to increase with the decreasing length of the straight portion when the length of the straight portion is not greater than 30 mm, and that the light propagation loss in Experimental Example 2 is substantially constant as in Experimental Example 1 when the length of the straight portion is greater than 30 mm. From these results, it is found to be effective in lowering the light propagation loss when the length of the straight portion is not greater than 30 mm that the width of the entrance of the second curved portion is smaller than the width of the core portion upstream of the S-shaped portion.

An optical waveguide in which a portion of each core was formed in an S-shape was produced with the use of new materials to be described below as an optical waveguide for an optical circuit board to be stacked on an electrical circuit board (with reference toFIGS. 12A and 12B).

[Material for Formation of First Cladding Layer and Second Cladding Layer]

Component g: 60 parts by weight of an epoxy resin (jER1001 available from Mitsubishi Chemical Corporation).

Component h: 30 parts by weight of an epoxy resin (EHPE3150 available from Daicel Corporation).

Component i: 10 parts by weight of an epoxy resin (EXA-4816 available from DIC Corporation).

Component j: 0.5 part by weight of a photo-acid generator (CPI-101A available from San-Apro Ltd.).

Component k: 0.5 part by weight of an antioxidant (Songnox1010 available from Kyodo Chemical Co., Ltd.).

Component l: 0.5 part by weight of an antioxidant (HCA available from Sanko Co., Ltd.).

Component m: 50 parts by weight of ethyl lactate (a solvent available from Wako Pure Chemical Industries, Ltd.).

A material for the formation of a first cladding layer and a second cladding layer was prepared by mixing these components g to m together.

[Material for Formation of Cores]

Component n: 50 parts by weight of an epoxy resin (YDCN-700-3 available from Nippon Steel & Sumikin Chemical Co., Ltd.).

Component o: 30 parts by weight of an epoxy resin (jER1001 available from Mitsubishi Chemical Corporation).

Component p: 20 parts by weight of an epoxy resin (OGSOL PG-100 available from Osaka Gas Chemicals Co., Ltd.).

Component q: 0.5 part by weight of a photo-acid generator (CPI-101A available from San-Apro Ltd.).

Component r: 0.5 part by weight of an antioxidant (Songnox1010 available from Kyodo Chemical Co., Ltd.).

Component s: 0.125 part by weight of an antioxidant (HCA available from Sanko Co., Ltd.).

Component t: 50 parts by weight of ethyl lactate (a solvent available from Wako Pure Chemical Industries, Ltd.).

A material for the formation of cores was prepared by mixing these components n to t together.

Inventive Examples 5 to 9

In the S-shaped portion in Inventive Examples 5 to 9, the width of the first curved portion S1was decreased gradually from the entrance thereof toward the exit thereof, and the width B1of the exit of the first curved portion S1was smaller than the width B0of the core portion upstream of the S-shaped portion (with reference toFIGS. 12C and 13). Then, the width B1of the exit of the first curved portion S1, the radius of curvature R1thereof and the like were set to a variety of values listed in TABLE 4 below. The width of the entrance of the first curved portion S1was equal to the width B0of the core portion upstream of the S-shaped portion. The width of the straight portion T (Inventive Examples 6 to 9) and the width of the second curved portion S2were constant in the longitudinal direction thereof and were equal to the width B1of the exit of the first curved portion S1. The radius of curvature of the second curved portion S2was 0.5 mm in each of Inventive Examples 5 to 9. The first cladding layer had a thickness of 25 μm. The cores had a thickness (a height of protrusions from the lower surface of the first cladding layer) of 30 μm. The second cladding layer had a thickness of 70 μm as measured from the lower surface of the cores.

Comparative Examples 4 to 6

As listed in TABLE 4 below, the width of the first curved portion was decreased gradually from the entrance of the first curved portion toward the exit thereof in Comparative Example 4, and the width of the first curved portion was constant in the longitudinal direction thereof in Comparative Examples 5 and 6. The radius of curvature R1and the like of the first curved portion S1were set to a variety of values listed in TABLE 4 below. The remaining parts of Comparative Examples 4 to 6 were similar to those of Inventive Examples 5 to 9.

[Measurement of Light Propagation Loss]

Prepared were a graded index (GI) type multimode optical fiber (FFP-GI20-0500 available from Miki Inc.; a first optical fiber) having a diameter of 50 μm and connected to a VCSEL light source (OP250-LS-850-MM-50-SC available from Miki Inc.; having an emission wavelength of 850 nm), and a similar graded index (GI) type multimode optical fiber (a second optical fiber) having a diameter of 50 μm and connected to a photodetector (multimeter Q8221 available from Advantest Corporation). Then, the front end of the first optical fiber and the front end of the second optical fiber were brought into abutment with each other. The photodetector received light coming from the VCSEL light source to measure the intensity (H) of the received light.

Next, the front end of the first optical fiber was optically connected to a light reflecting surface (a light entrance portion) of a first end portion of one core in the optical waveguide of each of Inventive Examples 5 to 9 and Comparative Examples 4 to 6. The front end of the second optical fiber was optically connected to a light reflecting surface (a light exit portion) of a second end portion of the one core. In that state, the photodetector received light to measure the intensity (I) of the received light.

A light propagation loss (β) was calculated in accordance with Formula (5) below based on the measured intensities (H and I) of the received light, and was listed in TABLE 4 below.
[MATH. 8]
β=−10 log10(I/H)  (5)

The results in TABLE 4 show that the light propagation loss is low in Inventive Examples 5 to 9 as compared with that in Comparative Examples 4 to 6. From this, it is found to be effective in lowering the light propagation loss that the width B1of the exit of the first curved portion of the S-shaped portion is smaller than the width B0of the core portion upstream of the S-shaped portion. In particular, it is found that the light propagation loss is lower in Inventive Examples 7 to 9 which satisfy Formula (3) above.

Results having tendencies similar to those in Inventive Examples 5 to 9 were obtained when the optical waveguide in which a portion of each core was formed in an S-shape in each of Inventive Examples 1 to 4 was used as an optical waveguide for an optical circuit board as in Inventive Examples 5 to 9.

Although specific forms in the present disclosure have been described in the aforementioned examples, the aforementioned examples should be considered as merely illustrative and not restrictive. It is contemplated that various modifications evident to those skilled in the art could be made without departing from the scope of the present disclosure.

The optical waveguide according to the present disclosure is usable for propagating light in the cores more properly, and may be used for optical communication applications. The optical waveguide according to the present disclosure is effective at reducing the light propagation loss for optical communication applications and at saving space for routing of the cores. The position sensor according to the present disclosure is usable for equalizing the intensity of light received by the light-receiving element while the input region is not pressed. The optical circuit board according to the present disclosure is usable for suppressing the decrease in the intensity of light received by an optical member such as an optical element.

REFERENCE SIGNS LIST

W2Optical waveguide32CoresS1First curved portionS2Second curved portionB0Width of upstream core portionB1Width of exit of first curved portionB2Width of entrance of second curved portion