Abstract:
A portable electronic device includes: an operating section; a display section configured to perform display based on information transmitted from the operating section; a light emitting element provided in one of the operating section and the display section; and a light receiving element provided in other of the operating section and the display section. The operating section and the display section are enabled to be in an open state and a closed state by changing a superposition condition thereof. An optical path interconnecting the light emitting element and the light receiving element in the open state is different from an optical path interconnecting the light emitting element and the light receiving element in the closed state.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2006-000053, filed on Jan. 4, 2006; the entire contents of which are incorporated herein by reference. 
       BACKGROUND 
       [0002]    A portable electronic device such as a mobile phone, notebook personal computer, and PDA (Personal Digital Assistant) is composed of an operating section and a display section, which are often superposed on each other in a folding, rotating, or sliding design. Any of these designs requires signals to be correctly transmitted and received between the display section and the operating section. In folding and sliding designs, flexible substrates (or flexible cables) or the like have been used for maintaining electrical connection. 
         [0003]    With the enhancement of communication features such as full-color video transmission, the amount of data transmission is increased, which requires a wider transmission bandwidth up to 400 MHz, for example. Such high-speed transmission involves susceptibility to external noise, which increases malfunctions as well. One method of solving these problems is to use optical fiber transmission. However, in optical fiber transmission, movable portions similar to the flexible substrate in electrical connection decrease reliability of transmission paths due to their wear and breaking. 
         [0004]    Instead of optical fibers having movable portions, a technology for using free-space optical transmission has been disclosed (US 2003/0087610 A1). However, in this publication, an infrared communication unit must be housed inside a connecting portion, which significantly constrains the device design and the device assembly process. Moreover, while the technology is applicable to a rotating structure in which the connecting portion is composed of a hinge portion, it is not suitable to sliding structures. 
       SUMMARY 
       [0005]    According to an aspect of the invention, there is provided a portable electronic device including: an operating section; a display section configured to perform display based on information transmitted from the operating section; a light emitting element provided in one of the operating section and the display section; and a light receiving element provided in other of the operating section and the display section, the operating section and the display section being enabled to be in an open state and a closed state by changing a superposition condition thereof, and an optical path interconnecting the light emitting element and the light receiving element in the open state being different from an optical path interconnecting the light emitting element and the light receiving element in the closed state. 
         [0006]    According to an aspect of the invention, there is provided a portable electronic device including: an operating section; a display section configured to perform display based on information transmitted from the operating section; a first light emitting element provided in one of the operating section and the display section; and a first light receiving element provided in other of the operating section and the display section, the operating section and the display section being enabled to be in an open state and a closed state by changing a superposition condition thereof, a first optical path interconnecting the first light emitting element and the first light receiving element in the open state being different from a second optical path interconnecting the first light emitting element and the first light receiving element in the closed state, and a first optical guide being provided in at least a part of the first optical path and in at least a part of the second optical path. 
         [0007]    According to an aspect of the invention, there is provided a portable electronic device including: an operating section; a display section configured to perform display based on information transmitted from the operating section; a first light emitting element provided in one of the operating section and the display section; and a first light receiving element provided in other of the operating section and the display section, the operating section and the display section being enabled to be in an open state and a closed state by changing a superposition condition thereof, at least one of the operating section and the display section being provided with a space for propagating light emitted from the light emitting element, and different optical paths being formed in the open state and in the closed state by a reflecting plate provided in at least one of the operating section and the display section. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  is a cross section showing a folding mobile phone in a first example; 
           [0009]      FIG. 2  is a view showing the optical path in the molded transparent resin portion; 
           [0010]      FIG. 3  is a cross section showing a sliding mobile phone in a second example; 
           [0011]      FIG. 4  is a cross section showing a rotating mobile phone in a third example; 
           [0012]      FIG. 5  is a plan view of the rotating mobile phone in the third example; 
           [0013]      FIG. 6  is a plan view of a mobile phone in a fourth example; 
           [0014]      FIG. 7  is a cross section of a sliding mobile phone in a fifth example; 
           [0015]      FIG. 8  is a cross section showing a variation of the fifth example; 
           [0016]      FIG. 9A  is a partial plan view in the vicinity of a hinge portion of a folding mobile phone in a sixth example, and 
           [0017]      FIG. 9B  is a partial cross section thereof; 
           [0018]      FIG. 10  shows an operating section optical element mounting substrate of the folding mobile phone in the sixth example; 
           [0019]      FIG. 11  shows an operating section optical element mounting substrate of the folding mobile phone in a first variation of the sixth example; 
           [0020]      FIG. 12A  is a view of a notebook personal computer in a second variation of the sixth example, and 
           [0021]      FIG. 12B  is a partial cross section in the vicinity of a hinge portion thereof; 
           [0022]      FIG. 13A  is a partial plan view of a rotating mobile phone in a third variation of the sixth example, and 
           [0023]      FIG. 13B  is a partial cross section thereof; 
           [0024]      FIG. 14  shows an electronic device in its closed state in a fourth variation of the sixth example, where 
           [0025]      FIG. 14A  is a view of an operating section optical element mounting substrate, 
           [0026]      FIG. 14B  is a view of a display section optical element mounting substrate, and 
           [0027]      FIG. 14C  is a side view in the vicinity of a hinge portion; 
           [0028]      FIG. 15  shows the electronic device in its intermediate position between the closed and open states in the fourth variation of the sixth example, where 
           [0029]      FIG. 15A  is a view of the operating section optical element mounting substrate, 
           [0030]      FIG. 15B  is a view of the display section optical element mounting substrate, and 
           [0031]      FIG. 15C  is a side view in the vicinity of the hinge portion; 
           [0032]      FIG. 16  shows the electronic device in its intermediate position between the closed and open states in the fourth variation of the sixth example, where 
           [0033]      FIG. 16A  is a view of the operating section optical element mounting substrate, 
           [0034]      FIG. 16B  is a view of the display section optical element mounting substrate, and 
           [0035]      FIG. 16C  is a side view in the vicinity of the hinge portion; and 
           [0036]      FIG. 17  shows the electronic device in its open state in the fourth variation of the sixth example, where 
           [0037]      FIG. 17A  is a view of the operating section optical element mounting substrate, 
           [0038]      FIG. 17B  is a view of the display section optical element mounting substrate, and 
           [0039]      FIG. 17C  is a side view in the vicinity of the hinge portion. 
       
    
    
     DETAILED DESCRIPTION 
       [0040]    Embodiments of the invention will now be described with reference to the drawings. 
       FIRST EXAMPLE  
       [0041]      FIG. 1A  is a cross section showing a folding mobile phone in its open state in a first example, and  FIG. 1B  is a cross section showing the mobile phone of this example in its closed state. This mobile phone has a structure in which two housings are superposed on each other. One of the housings, an operating section  10 , and the other, a display section  12 , are connected via a hinge portion  20 , and can be opened and closed by rotating around the central axis of the hinge portion  20  in foldable manner. 
         [0042]    In the open state, the operating section  10  and the display section  12  are maximally opened as illustrated in  FIG. 1A . In the closed state, the operating section  10  and the display section  12  are substantially superposed on each other as shown in  FIG. 1B . While they are superposed in a folding design in this example, sliding and rotating designs can also be used as described later. 
         [0043]    The operating section  10  includes a control substrate  22  fixed in its housing and having thereon a transceiver, a memory element, a control circuit, key switches  16 , and a power switch  18 . The operating section  10  further includes a light emitting element  26  for free-space optical communication with the display section  12  and a connecting line  24  for electrically connecting the control substrate  22  to the light emitting element  26 . 
         [0044]    The display section  12  includes a liquid crystal display  14  for displaying the transmitting/receiving state and email content, a light receiving element  28  for receiving data from the operating section  10 , a connecting line  24  for electrically connecting the liquid crystal display  14  to the light receiving element, and a camera section  70 . The display may be an organic EL display, for example. 
         [0045]    The light emitting element  26  for transmitting data from the operating section  10  to the display section  12  by free-space optical transmission can be an LED (Light Emitting Diode) or VCSEL (Vertical Cavity Surface Emitting Laser). An optical signal from the light emitting element  26  is introduced into an optical guide  30  which may be a molded transparent resin provided in the vicinity of the hinge portion  20 . Part of the light introduced into the molded transparent resin portion (optical guide)  30 , which illustratively has a generally circular cross section adapted to the shape of the hinge portion  20 , propagates with repeated reflections at the interface with the exterior (air). The light is then incident on the light receiving element  28  in the display section  12 . In this way, the data from the operating section  10  is transmitted to the display section  12 . 
         [0046]    Here the optical path inside the molded transparent resin portion  30  is described.  FIG. 2  is a view showing the optical path. An LED chip  34  is mounted on a lead  32  and sealed with a mold resin  44 , thereby configuring the light emitting element  26 . Furthermore, a photodiode chip  35  is mounted on a lead  40  and sealed with a mold resin  44 , thereby configuring the light receiving element  28 . 
         [0047]    As illustrated in  FIG. 2 , if the surface of the molded transparent resin portion  30  facing to the light emitting element  26  is made generally perpendicular to the central axis of the light emitting element  26 , the incident light L 1  spreads entirely in the molded transparent resin portion  30 . The incident light can be further spread by using a light emitting element  26 , which has a large orientation angle. The light can then propagate in the molded transparent resin portion  30  by repeating total reflection at the interface with exterior. 
         [0048]    However, the light receiving element  28  changes its position between the open state illustrated in  FIG. 1A  and the closed state illustrated in  FIG. 1B . In the open state, the transmitted light L 2  from the molded transparent resin portion  30  is incident on the light receiving element  28 . Even after rotation, the light L 3  emitted after propagating in the molded transparent resin  30  by reflection is incident on the light receiving element  28 . In this way, light can be transmitted at a position between the open state and the closed state. 
         [0049]    One of the features of this example is that the optical path differs between the open state and the closed state. This substantially prevents durability issues such as mechanical wear due to motion of flexible substrates (or flexible cables) at each time of folding. Such an optical path can exploit the space in the housings and thus increases the flexibility of arrangement of parts on the control substrate  22  in the housing. 
         [0050]    Advantages of using optical transmission are now described. Full-color video display is increasingly demanded in mobile phones and PDAs. This requires a transmission bandwidth as wide as about 400 MHz. To achieve this with an electrical cable, at least ten cables are needed. It is difficult for a portable device limited in size to enclose such many electrical cables and flexible substrates. Free-space optical transmission can overcome these problems. 
         [0051]    Moreover, optical transmission can also reduce the effect of external noise. For example, free-space optical transmission can prevent potential deterioration of the bit error rate of a mobile phone due to external noise. Free-space optical transmission can also prevent the effect of external noise on the control signal which may result in malfunctions of the device and disturbances of the image on the liquid crystal display  14 . Free-space optical transmission can prevent adverse effects on other electronics due to external emission of noise from long flexible substrates and electrical cables. 
         [0052]    An optical fiber may be used instead of the flexible substrate  24  in order to reduce noise emission and the effect of external noise. However, an optical fiber has an admissible minimum radius of curvature, which must be greater than the radius of curvature of the hinge portion  20 . This leads to a large hinge portion  20  and insufficient mechanical durability of the optical fiber at its rotating portion. Therefore, it is more preferable to use free-space optical transmission as in this example, which is free from rotating portions. 
         [0053]    In this example, the light emitting element  26  may include a light transmitting module incorporating an LED driving circuit or the like. The light receiving element  28  may include a light receiving module incorporating a waveform shaping circuit, current amplifying circuit, or the like. These modules can be used to simplify circuitry in the operating section  10  and the display section  12 , thereby further reducing the effect of external noise and emission noise. 
         [0054]    The light emitted from the light emitting element  26  can be in the infrared region, but is not limited thereto. For example, a preferable wavelength range is from 400 to 1000 nm. When the light receiving element  28  is an integrated circuit incorporating an amplifier circuit and a silicon photodiode, a range of 780 to 1000 nm is more preferable, which is in the vicinity of the sensitivity peak of the silicon photodiode. 
       SECOND EXAMPLE  
       [0055]      FIG. 3A  is a cross section of a sliding mobile phone in its open state in the second example, and  FIG. 3B  is a cross section in its closed state. In these figures and the following figures, components similar to those in  FIG. 1  are marked with like reference numerals and not described in detail. This example has a structure in which the display section  12  is slid back and forth relative to the operating section  10 . 
         [0056]    In this example, a signal from the control substrate  22  placed in the operating section  10  is transmitted via the connecting line  24  to the light emitting element  26  placed on the bottom of the housing of the operating section  10 . The light emitted generally perpendicularly from the bottom of the housing propagates (L 4 ) in a generally horizontal direction in the molded transparent resin portion  30  placed along the bottom of the housing of the display section  12 . Here, while the cross section of the molded transparent resin portion  30  may be rectangular, a circular or elliptical shape is more preferable in view of consistency with luminous intensity distribution characteristics of the light emitting element. In the open state illustrated in  FIG. 3A , the light L 4  is directed to the light receiving element  28  as indicated by the arrow while being subjected to reflection or transmission at the interface with air. 
         [0057]    In the closed state illustrated in  FIG. 3B , the light L 5  from the light emitting element  26  is incident on the vicinity of the tip of the molded transparent resin portion  30  and then spreads to the light receiving element  28 , where it is incident thereon in the direction indicated by the arrow. In this case again, the optical path differs between the open state and the closed state. However, mechanical wear or the like will not occur as with the first example because there are no movable portions such as flexible substrates. 
       THIRD EXAMPLE  
       [0058]      FIG. 4A  is a cross section showing a rotating mobile phone in its open state in the third example, and  FIG. 4B  is a cross section in its closed state. 
         [0059]    In this example, slide rotation around DD′ axis allows for an open state illustrated in  FIG. 4A , or a closed state illustrated in  FIG. 4B  in which the operating section  10  and the display section  12  are superposed on each other. The light from the light emitting element  26  placed in the operating section  10  is incident on a molded annular transparent resin (optical guide)  31  and then spreads and propagates to the light receiving element  28 , where it is incident thereon. 
         [0060]      FIG. 5A  is a plan view of the mobile phone in the open state illustrated in  FIG. 4A ,  FIG. 5B  is a plan view showing one position in process of slide rotation, and  FIG. 5C  is a plan view of the mobile phone in the closed state. 
         [0061]    In the open state, the light L 6  from the light emitting element  26  spreads and propagates in the annular transparent resin portion  31  as illustrated in  FIGS. 4A and 5A , and is emitted outside. Part of the emitted light is incident on the light receiving element  28 , and then converted into an electrical signal, which causes the liquid crystal display  14  to display desired data. 
         [0062]    In process of slide rotation illustrated in  FIG. 5B  as well, the light L 7  from the light emitting element  26  is transmitted to the light receiving element  28  via the annular transparent resin  31  as indicated by the arrow. Therefore, correct data can be displayed even at a position in process of slide rotation. 
         [0063]    In the closed state, the light L 8  from the light emitting element  26  spreads and propagates in the annular transparent resin  31  as illustrated in  FIGS. 4B and 5C , and is emitted outside. Part of the emitted light is incident on the light receiving element  28 , and then converted into an electrical signal, which causes the liquid crystal display  14  to display desired data. In the third example as well, the optical path L 6  in the open state is different from the optical path L 8  in the closed state. Furthermore, there is no mechanical wear of flexible substrates due to slide rotation. Moreover, data can be transmitted with reduced effect of external noise thereon, irrespective of the relative spatial position between the operating section  10  and the display section  12 . 
       FOURTH EXAMPLE  
       [0064]      FIG. 6  is a plan view showing a mobile phone in the fourth example. In this example, which is in a sliding design similar to the second example, an independent optical transmission path is arranged between the operating section  10  and the display section  12 . More specifically, in addition to the first optical transmission path composed of the light emitting element  26  placed in the operating section  10 , the molded transparent resin portion  30 , and the light receiving element  28  placed in the display section  12 , a second optical transmission path composed of a light emitting element  26  placed in the display section  12 , a molded transparent resin portion  30 , and a light receiving element  28  placed in the operating section  10  is provided generally in parallel. 
         [0065]    Data can be transmitted also from the display section  12  to the operating section  10 . Data transmitted from the display section  12  include an image from the camera section  70  provided in the display section  12  and data stored in a semiconductor memory section provided in the display section. This example allows for bidirectional data transmission. 
       FIFTH EXAMPLE  
       [0066]      FIG. 7A  is a cross section in the open state, and  FIG. 7B  is a cross section in the closed state. In this example, the light emitting element  26  is provided on the control substrate  22  placed in the housing of the operating section  10 . 
         [0067]    First, in the open state illustrated in  FIG. 7A , an in-housing space  11  is provided above the operating section  10 . The light Log emitted upward from the light emitting element  26  is reflected from a half mirror  52  and propagates along the in-housing space  11 . The light L 11  reflected from a reflecting plate  50  placed at the other end of the in-housing space  11  is reflected from a reflecting plate  50  placed in the display section  12  and propagates along an in-housing space  13  in the display section  12 . The light L 11  reflected upward by a reflecting plate  50  placed at the other end of the in-housing space  13  is incident on the light receiving element  28  placed on a display section substrate  23 . In this way, by electro-optically converting data from the operating section  10 , the data can be transmitted to the display section  12  with reduced effect of external noise and reduced noise emission. The data, after opto-electrical conversion, is displayed on the liquid crystal display  14 . 
         [0068]    In the closed state where the display section  12  is slid as illustrated in  FIG. 7B , the light L 12  emitted upward from the light emitting element  26  is transmitted through the half mirror  52 , then reflected by the reflecting plate  50  placed in the display section  12 , and propagates along the in-housing space  13 . The light L 12  reflected upward by the reflecting plate  50  placed at the other end of the in-housing space  13  is incident on the light receiving element  28 . 
         [0069]      FIG. 7C  is a cross section along dot-dashed line EE′ in  FIG. 7A . The light L 11  transmitted from the operating section  10  travels along the in-housing space  13 , is bent upward by the reflecting plate  50 , and reaches the light receiving element  28 . In this case, the in-housing space  13  can be shaped as a U-groove as illustrated in  FIG. 7C  to prevent parts placed on the display section substrate  23  from obstructing the optical path. Alternatively, a tunnel-like space can be used instead of the U-groove. 
         [0070]    In this case, the light emitting element  26  can be an LED or VCSEL. A VCSEL is more preferable for ensuring a bandwidth as wide as 400 MHz and transmitting light in the in-housing spaces  11  and  13  without divergence under low-current operation. 
         [0071]    In this way, in the closed state as well, by electro-optically converting a signal from the operating section  10 , data can be transmitted to the display section  12 . The data, after opto-electrical conversion, is displayed on the liquid crystal display  14 . In this example as well, the optical path for the light L 11  in the open state can be varied from that for the light L 12  in the closed state to eliminate flexible substrates or the like. 
         [0072]    Next, a variation of the fifth example is described.  FIG. 8A  is a cross section in the open state in the variation, and  FIG. 8B  is a cross section in the closed state. In this variation, movable reflecting plates  54  are provided instead of the reflecting plates  50  and half mirror  52 . In the open state as illustrated in  FIG. 8A , the light L 13  from the light emitting element  26  is bent by the movable reflecting plate  54  and propagates along the in-housing space  11  of the operating section  10 . The light L 13  is bent by the movable reflecting plate  54  or reflecting plate at the other end of the in-housing space  11  and incident on the light receiving element  28 . 
         [0073]    In the closed state illustrated in  FIG. 8B , slide motion of the display section  12  causes the movable reflecting plate  54  to change its orientation so that the light L 14  from the light emitting element  26  travels in a straight line. As a result, the light L 15  is incident on the light receiving element  28 . In this case again, the optical path differs between the open state and the closed state. 
       SIXTH EXAMPLE  
       [0074]      FIG. 9A  is a view showing the vicinity of a hinge portion  20 , and  FIG. 9B  is a partial cross section thereof. In this example, the light emitting element  26  and the light receiving element  28  are facing to each other at one end of the hinge portion  20 . An electrical signal from the control substrate  22  in the operating section  10  is converted into an optical signal, which is transmitted in free space. The light receiving element performs opto-electrical conversion, and the resulting data is transmitted via the display section substrate  23  to the liquid crystal display  14 . 
         [0075]      FIG. 10  is a cross section for illustrating optical transmission in the open and closed states in accordance with rotation of the hinge portion  20 .  FIG. 10A  shows an operating section optical element mounting substrate  60 , and is a view as viewed from the right side of the rotation axis FF′ in  FIG. 9A . 
         [0076]    The operating section optical element mounting substrate  60  illustrated in  FIG. 10A  is electrically connected to the control substrate  22  in the operating section  10 , where the light emitting element  26  performs electro-optical conversion. Here, the emission center of the light emitting element  26  substantially coincides with the rotation axis FF′ of the hinge portion  20 . Two light receiving elements  28  are placed substantially on an identical circle R around the rotation axis FF′ of the hinge portion  20 , and thereby can receive an optical signal from the display section  12 . 
         [0077]      FIG. 10B  shows a display section optical element mounting substrate  62  in the closed state in which it is facing to the operating section optical element mounting substrate  60 , and is a view as viewed from the right side of the rotation axis FF′ in  FIG. 9 . On the display section optical element mounting substrate  62 , a light receiving element  28  receiving light from the light emitting element  26  of the operating section  10  is placed in a plane generally perpendicular to the rotation axis FF′ of the hinge portion  20 . The light receiving element  28  receives an optical signal from the operating section  10  and converts it into an electrical signal. A light emitting element  26  is placed around the rotation axis FF′ of the hinge portion  20 . The light emitting element  26  electro-optically converts the signal from the display section  12  and then transmits the resulting optical signal to the left one of the two light receiving elements  28  in  FIG. 10A  on the operating section optical element mounting substrate  60 . 
         [0078]      FIG. 10C  shows a display section optical element mounting substrate  62  in the open state. This is the state rotated from the closed state illustrated in  FIG. 10B , and the position of the light emitting element  26  is different from that in the closed state. Because the position facing to the operating section optical element mounting substrate  60  is rotated, the right one of the light receiving elements  28  in FIG.  10 A is now responsible for reception in contrast to the closed state. In this way, optical transmission and reception can be performed both at the open and closed positions by placing two or more light receiving elements  28  on an identical circle R, each corresponding to the rotation angle. Here, the optical path for transmission from the display section  12  differs between the open state ( FIG. 10C ) and the closed state ( FIG. 10B ). Note that what is placed in the vicinity of the rotation axis on the hinge portion  20  of the operating section  10  is not limited to the light emitting element  26 , where the light receiving element  28  can be placed alternatively. In this case, the light emitting element  26  should all be interchanged with the light receiving elements  28  in the example. In this way, this example also allows for bidirectional optical transmission between the operating section  10  and the display section  12 . By applying a driving voltage to both the two light receiving elements  28 , either one of the light receiving elements can detect an optical signal. 
         [0079]      FIG. 11  is a view showing a first variation of the sixth example. In the sixth example described above, two light receiving elements  28  are placed on the identical circle R around the rotation axis FF′ of the operating section optical element mounting substrate  60 . In this variation, however, two light emitting elements  26  are placed on the identical circle R around the rotation axis FF′ of the display section optical element mounting substrate  62 . 
         [0080]      FIG. 11A  shows the operating section optical element mounting substrate  60 , where a light emitting element  26  is placed in the vicinity of the rotation axis FF′, and one light receiving element  28  is placed on the circle R. In contrast, on the display section optical element mounting substrate  62 , a light receiving element  28  is placed in the vicinity of the rotation axis FF′, and two light emitting elements  26  are placed on the identical circle R around the rotation axis FF′. 
         [0081]      FIG. 11B  shows the closed state, where an optical signal from the display section  12  is transmitted from the right one of the light emitting elements  26  in  FIG. 11B  to the light receiving element  28  in  FIG. 11A .  FIG. 11C  shows the open state, where an optical signal from the display section  12  is transmitted from the upper one of the light emitting elements  26  in  FIG. 11C  to the light receiving element  28  in  FIG. 11A . In the first variation as well, what is placed in the vicinity of the rotation axis on the hinge portion  20  of the operating section  10  is not limited to the light emitting element, where the light receiving element can be placed alternatively. In this case, the light emitting element  26  should all be interchanged with the light receiving elements in the example. The light emitting element  26  is more suitable for downsizing because it is typically smaller in area than the light receiving element  28 . 
         [0082]      FIG. 12  shows a second variation of the sixth example, where  FIG. 12A  is a view of a personal computer, and  FIG. 12B  is a side view in the vicinity of the hinge portion  20 . When the angle in the open state is different from that for the folding phone, the light receiving elements  28  can be placed accordingly to achieve similar advantageous effects. 
         [0083]      FIG. 13  shows a rotating phone in a third variation of the sixth example.  FIG. 13A  is a partial plan view thereof, and  FIG. 13B  is a partial cross section thereof. Advantageous functions and effects similar to those in the sixth example are achieved except for horizontal arrangement of the operating section optical element mounting substrate  60  and the display section optical element mounting substrate  62 . 
         [0084]      FIGS. 14 to 17  show a portable electronic device in a fourth variation of the sixth example.  FIGS. 14A ,  15 A,  16 A, and  17 A are views of the operating section optical element mounting substrate  60 ,  FIGS. 14B ,  15 B,  16 B, and  17 B show the display section optical element mounting substrate  62 , and  FIGS. 14C ,  15 C,  16 C, and  17 C are side views in the vicinity of the hinge portion  20 .  FIG. 14  shows the closed state,  FIGS. 15 and 16  show intermediate positions between the closed and open states, and  FIG. 17  shows the open state. Even if the angle in the open state reaches 180 degrees, bidirectional optical transmission can be achieved in accordance with the rotation angle by placing, for example, four light receiving elements  28  on an identical circle. On the rotation axis, the light emitting element  26  and the light receiving element  28  are provided. This implementation is not limited to the slide rotating portable device, but may be applied to a folding design as shown in  FIGS. 9A and 9B , for example. Further, instead of providing a plurality of light receiving elements, a plurality of light emitting elements may be provided. In the sixth example described above as well, the optical path between the light emitting element  26  and the light receiving element  28  can be changed from the closed state to the open state and vice versa to transmit an optical signal in both directions. 
         [0085]    As described above, in the first to sixth examples, a signal is electro-optically converted in the operating section  10 . The resulting optical signal from the light emitting element  26  reaches the display section  12  via free-space transmission without the intermediary of movable portions such as flexible substrates. The optical signal is opto-electrically converted by the light receiving element  28  in the display section  12 , and the resulting data is displayed on a liquid crystal display or the like. 
         [0086]    Here, when the device is carried about, it requires to be downsized by changing the relative position of the operating section  10  and the display section  12  by folding, sliding, or rotation. In both the open and closed states by such folding, sliding, or rotation, data transmission is required between the operating section  10  and the display section  12 . To this end, conventionally, a flexible substrate or the like has been used. However, the flexible substrate or the like is mechanically worn as the number of opening/closing motions increases. Furthermore, as the communication system becomes more sophisticated, the amount of data transmission tends to increase, which requires increasing the number of signal lines. The increase of signal lines hinders downsizing. 
         [0087]    In the first to sixth examples, different optical paths can be formed in the free-space optical transmission path in the open and closed states to allow for data transmission without movable portions such as flexible substrates, electrical cables, and optical fibers. Furthermore, because of great flexibility in placing the light emitting element and the light receiving element, the invention is applicable to any of the folding, rotating, and sliding designs. As a result, mechanical durability is improved, and the increased amount of data transmission can be addressed. 
         [0088]    Moreover, use of optical transmission allows for reducing the effect of external noise, which results in improved bit error rate and reduced malfunctions. Reduction of noise emission allows for reducing EMI (Electro-Magnetic Interference) to other electronics. 
         [0089]    Embodiments of the invention have been described with reference to the drawings. However, the invention is not limited to thereto. Any size, shape, and material of various components including the light emitting element, light receiving element, reflecting plate, half mirror, and molded transparent resin that are variously adapted by those skilled in the art are also encompassed within the scope of the invention as long as they meet the requirements of the invention.