This is a National Stage of Application No. PCT Application No. PCT/JP2016/051210, filed Jan. 18, 2016.

TECHNICAL FIELD

The present invention relates to an optical element for propagating light in a set direction, and to a display device and photoreceptor device using such an optical element, relating in particular to a display device suitable for monitors for information appliances that can be used outside of a desktop environment, such as wearable computers which are worn on the body by means of a waist belt, personal accessories and the like, and communication devices such as portable telephones which can be carried by placing in a knapsack or pocket.

BACKGROUND ART

Among display devices for information appliances of the type worn on the body, the goggle type format which also allows the outside world to be seen is becoming mainstream.FIG. 3is an external view showing a goggle type display (display device) worn by a viewer, andFIG. 4is a drawing illustrating the general configuration of a conventional goggle type display and the optical path in the XY plane.

Here, the goggle type display101is for the right eye, and defines an XYZ coordinate system having its origin at the center of the right eye E of a viewer viewing into the distance. The Y direction is to the front of the viewer, the Z direction is above the viewer, and the X direction (set direction) is to the left of the viewer.

The goggle type display101has an appearance similar to goggles, and comprises an output unit (output optical system)40which outputs image display light L, a light guide (optical element)10which is a substrate that internally reflects the image display light L from the output unit40and guides it to the eye E of the viewer, and a frame part F to which the output unit40and light guide10are attached (for example, see patent literature 1).

The output unit40has a housing as shown inFIG. 3, and inside this housing, comprises an output mechanism including a transmissive liquid crystal display41, an optical system42and a light source (not illustrated), and a control unit (not illustrated) which outputs an image signal to the output mechanism.

The transmissive liquid crystal display41, based on an image signal from the control unit, forms an image in a display region perpendicular to the output direction, and outputs an image display light L.

Optical system42transmits the image display light L of the display region. Optical system42is furthermore arranged at a distance in front of the transmissive liquid crystal display41. As a result, the optical system42forms a virtual image of the observed object while transmitting image display light L of the display region.

Light guide10is a substrate fashioned from a light transmitting material such as glass (BK7, etc.), resin (polycarbonate, polymethacrylic acid (PMMA), cycloolefin, etc.) or the like and comprises a front surface10a, a rear surface10blocated opposite the front surface10ain the −Y direction, a right surface10c, a left surface10dlocated opposite the right surface10cin the X direction, a top surface (not illustrated) and a bottom surface (not illustrated) located opposite the top surface in the Z direction, and furthermore has a beam splitter surface11formed inside. Here, the front surface10a, the rear surface10b, the top surface and the bottom surface are parallel to the X direction (set direction), while the left surface10dis perpendicular to the X direction (set direction).

Furthermore, the right surface10cis arranged so as to have an angle at to the X direction (set direction) when viewed from the Z direction. The output unit40is moreover arranged so as to cause the image display light L from the output mechanism to be inputted through the right surface10cof the light guide10into the light guide10in a direction perpendicular to the right surface10c. As a result, when image display light L from the output unit40enters inside the light guide10through the right surface10cin a direction perpendicular to the right surface10c, it advances substantially in the X direction (set direction).

The beam splitter surface11comprises three planar beam splitter surfaces, arranged in the X direction in the sequence: first beam splitter surface11a, second beam splitter surface11b, third beam splitter surface11c. Furthermore, each of the beam splitter surfaces11athrough11care arranged at the same angle β to the X direction when viewed from the Z direction.

The first beam splitter surface11a, second beam splitter surface11band third beam splitter surface11cfurthermore make it possible to reflect a predetermined fraction of the luminous flux of the inputted image display light L and to transmit a predetermined fraction of the luminous flux of the image display light L.

In such a goggle type display101, first, the image display light L of the display region from the output unit40is inputted into the light guide10through the right surface10c. Here, the image display light L from the output unit40is inputted through the right surface10cinto the light guide10in a direction perpendicular to the right surface10c, and the right surface10ccauses the image display light L of the display region from the output unit40to be inputted such that it advances substantially in the X direction (set direction).

The front surface10aand rear surface10bcause the image display light L of the display region to advance in the X direction (set direction) while reflecting it in alternation multiple times, thereby leading it to the first beam splitter surface11a. The first beam splitter surface11athen reflects a predetermined fraction of the luminous flux of the inputted image display light L and transmits a predetermined fraction of the luminous flux of the image display light L. Namely, the luminous flux of image display light La is guided to the eye E of the viewer.

Furthermore, the image display light L which has passed through the first beam splitter surface11areaches the second beam splitter surface11b. Here, the second beam splitter surface11breflects a predetermined fraction of the luminous flux of the inputted image display light L and transmits a predetermined fraction of the luminous flux of the image display light L. Namely, the luminous flux of image display light Lb is guided to the eye E of the viewer.

Moreover, the image display light L which has passed through the second beam splitter surface11breaches the third beam splitter surface11c. Here, the third beam splitter surface11creflects a predetermined fraction of the luminous flux of the inputted image display light L and transmits a predetermined fraction of the luminous flux of the image display light L. Namely, the luminous flux of image display light Lc is guided to the eye E of the viewer.

PRIOR ART LITERATURES

Patent Literatures

Patent literature 1: Japanese Unexamined Patent Application Publication 2011-186332Patent literature 2: Japanese Unexamined Patent Application Publication 2011-164545Patent literature 3: WO2011/24291A1

SUMMARY OF THE INVENTION

Problem to be Solved by the Invention

However, in a goggle type display101as described above, images with a shadow generated in a portion thereof would sometimes be seen.FIG. 5is an example of an image in which a shadow seen by the viewer has been generated by the goggle type display101ofFIG. 4.

Means for Solving the Problem

The present applicant investigated methods that would allow the viewer to properly see the image, and found that in a goggle type display101as described above, the size of the luminous flux of the image display light L (the display region) is limited by the size of the right surface10c, and with a luminous flux size that has been limited by the size of the right surface10cshown inFIG. 4, regions occur in which luminous flux of image display light L propagating through the inside of the light guide10is not present (dropouts).

Here,FIG. 6is a drawing illustrating the propagation range of luminous flux in the XY plane of the goggle type display101ofFIG. 4, where symbols A in the drawing indicate luminous flux dropouts.

The occurrence of such regions in which luminous flux of the image display light propagating through the inside of the light guide is not present (dropouts) could conceivably be prevented by increasing the size of the right surface of the light guide and increasing the size of the inputted luminous flux.FIG. 7is a plan view illustrating a light guide in which the size of the right surface and the size of the light flux have been increased. However, this sort of light guide300has protruding parts and is thus difficult to manufacture and also makes the output unit340larger and heavier.

Furthermore, Japanese Unexamined Patent Application Publication 2011-164545 discloses a display device comprising a first light guide for guiding image display light from a first output unit and a second light guide for guiding image display light from a second output unit, but since this device comprises two output units, it has the problem that it becomes larger and heavier. Furthermore, International Publication No. WO2011/24291 discloses a display device comprising a first light guide which reflects image display light by means of four surfaces—a front surface, rear surface, top surface and bottom surface, in order to guide it to a second light guide, and a second light guide for guiding the image display light from the first light guide, but this has the problem of making the device large and heavy.

Thus, the applicant discovered how to arrange a substance (secondary substrate) across a beam splitter surface (secondary beam splitter) in front of the light guide (main substrate) in order to prevent dropouts of luminous flux of the image display light propagating through the inside of the light guide without providing protruding parts as in light guide300and without increasing the size of the output unit340, etc. It will be noted that the term beam splitter surface here refers to a surface having the function of reflecting a portion of the luminous flux and transmitting a portion of the luminous flux.

Accordingly, the image display light of the display region is reflected in alternation multiple time at the front surface and rear surface of the light guide, and when it reaches the front surface (secondary beam splitter surface) of the light guide, 100% of the luminous flux of the image display light is not reflected, but rather a predetermined fraction of the luminous flux of the image display light is reflected and advances into the light guide, and a predetermined fraction of the luminous flux of the image display light is transmitted and advances into the secondary substrate. Namely, a difference (offset) occurs between the optical path of the image display light advancing inside the light guide and the optical path of the image display light advancing inside the secondary substrate (the image display light is split by the secondary beam splitter surface and is magnified), and the occurrence of regions where luminous flux of image display light propagating through the inside of the light guide is not present (dropouts) can be prevented by making use of this difference (offset).

Namely, the optical element of the present invention comprises a main substrate fabricated from light transmitting material, whereof the front surface and rear surface are parallel to a set direction, and having at least one main beam splitter surface formed diagonally to the set direction inside the main substrate, which optical element further comprises a secondary substrate fabricated from light transmitting material, whereof the front surface and rear surface are parallel to a set direction, wherein a secondary beam splitter surface is arranged between the front surface of the secondary substrate and the rear surface of said main substrate or between the rear surface of the secondary substrate and the front surface of said main substrate.

Here, “set direction” is an arbitrary direction determined in advance by the designer, etc., and could be, for example, the left direction, right direction, top direction or bottom direction.

Effect of the Invention

With the optical element of the present invention, as described above, light is split and magnified by a secondary beam splitter surface, thus making it possible to prevent the occurrence of regions where luminous flux propagating through the inside of the main substrate is not present (dropouts).

(Other Means for Solving the Problem, and Effects)

Furthermore, in the optical element of the present invention, light may be inputted or outputted through a surface other than the front surface and rear surface of the main substrate and the front surface and rear surface of the secondary substrate.

With the optical element of the present invention, when the right surface, etc. of the secondary substrate is formed diagonally, the concentration of complex processing on a single substrate can be avoided, so productivity is improved.

Furthermore, when the width of the output mechanism is to be reduced, in the case where the image display light is inputted through the right surface of the main substrate, if the main substrate is made thinner, it is necessary to increase the number of main beam splitter surfaces in the main substrate in order to maintain the output range outputted by the main beam splitter surface, but by inputting the image display light through the right surface, etc. of the secondary substrate, the need to increase the number of main beam splitter surfaces of the main substrate is eliminated even if the secondary substrate is made thinner, so productivity is better.

Furthermore, in the optical element of the present invention, a reflective surface may be formed inside the main substrate or the secondary substrate, so that light enters through at least one surface from among the front surface and rear surface of the main substrate and the front surface and rear surface of the secondary substrate and either reaches the reflective surface or, after reaching the reflective surface, is outputted from at least one surface from among the front surface and rear surface of the main substrate and the front surface and rear surface of the secondary substrate.

The optical element of the present invention makes it possible to increase the degree of freedom in respect of the location where light enters inside the main substrate and secondary substrate and the location where it is outputted from inside the main substrate and secondary substrate.

Furthermore, in the optical element of the present invention, the secondary beam splitter surface may be arranged so that light is not reflected two or more times from the reflective surface.

In the display device of the present invention, a substrate of a fixed minimum thickness is arranged in front of the reflective surface, so luminous flux which is reflected two or more times from the reflective surface can be eliminated and the occurrence of stray light can be prevented.

The display device of the present invention may comprise an optical element as described above and an output optical system which outputs light.

With the display device of the present invention, regions where luminous flux is not present (dropouts) do not occur and the output mechanism can be made smaller and lighter.

Furthermore, as light progresses in a set direction, since there exists light which passes through the inside of the secondary substrate without being transmitted through the main beam splitter surface, the difference between the light quantity outputted to the outside from the first main beam splitter surface near the input location and the light quantity outputted to the outside from the Nth main beam splitter surface from the input location becomes smaller, making it possible to make the brightness (light quantity) more uniform.

Moreover, the photoreceptor device of the present invention may comprise an optical element as described above and a photoreceptor optical system which detects light.

With the photoreceptor device of the present invention, [sic] when optical components such as shown inFIG. 4are used for a photoreceptor device, missing regions occur in the luminous flux (light flux which cannot be received), but with the photoreceptor device of the present invention, the total luminous flux reaching the main beam splitter surface can be received. Thus, the photoreceptor device of the present invention is able to sense objects of sensing located in any region of the luminous flux.

