Patent Publication Number: US-2015088000-A1

Title: Method for manufacturing optical device, optical device, and biological information detector

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This is a continuation application of U.S. patent application Ser. No. 13/022,177 filed on Feb. 7, 2011. This application claims priority to Japanese Patent Application No. 2010-033058 filed on Feb. 18, 2010. The entire disclosures of U.S. patent application Ser. No. 13/022,177 and Japanese Patent Application No. 2010-033058 are hereby incorporated herein by reference. 
    
    
     BACKGROUND 
     1. Technical Field 
     The present invention relates to a method for manufacturing an optical device, an optical device, a biological information detector, and the like. 
     2. Background Technology 
     A biological information measuring device measures human biological information such as, for example, pulse rate, blood oxygen saturation level, body temperature, or heart rate, and an example of a biological information measuring device is a pulse rate monitor for measuring the pulse rate. Also, a biological information measuring device such as a pulse rate monitor may be installed in a clock, a mobile phone, a pager, a PC, or another electrical device, or may be combined with the electrical device. The biological information measuring device has a biological information detector for detecting biological information, and the biological information detector includes a light-emitting element for emitting light towards a detection site of a test subject (i.e., a user), and a light-receiving element for receiving light having biological information from the detection site. Thus, a biological information detector or the biological information measuring device may have an optical device and be capable of detecting or measuring biological information. A common detector or a measuring device (or in a broader sense, an electronic device) other than a biological information detector or a biological. 
     In Patent Citation 1, there is disclosed a pulse rate monitor (or in a broader sense, a biological information measuring device). A light-receiving element (e.g., a light-receiving element  12  in  FIG. 16  of Patent Citation 1) of the pulse rate monitor receives light reflected at a detection site (e.g., dotted line in  FIG. 16  of Patent Citation 1) via a diffusion reflection plane (e.g., reflecting part  131  in  FIG. 16  of Patent Citation 1). In an optical probe  1  in Patent Citation 1 (or in a broader sense, a biological information detector), a light-emitting element  11  and the light-receiving element  12  overlap in plan view, and the size of the optical probe is reduced. 
     JP-A 2004-337605 (Patent Citation 1) is an example of the related art. 
     SUMMARY 
     Problems to be Solved by the Invention 
       FIG. 4  in Patent Citation 1 shows an electrode (or in a narrower sense, a bonding pad) and a wiring (or in a narrower sense, a bonding wire) for the light-receiving element  12 . In an instance in which the light-emitting element  11  and the light-receiving element  12  overlap each other with respect to a plan view, a first light-emitting element  111  of the light-emitting element  11  is positioned directly below the bonding pad, as shown in  FIG. 5  of Patent Citation 1. According to a configuration described above, when the bonding wire is attached to the bonding pad, it is difficult for the attaching to be made more reliable. Also, the light-emitting element  111  may be damaged during a manufacturing process of such description. 
     According to several modes of the invention, it is possible to provide a method for manufacturing an optical device, an optical device, and a biological information detector in which the attaching can be performed more reliably when a bonding wire is attached to a bonding pad. 
     Means Used to Solve the Above-Mentioned Problems 
     A biological information detector in accordance with one aspect of the invention comprises a substrate, a light-emitting element having a thickness of 20 μm to 1000 μm, a light-receiving element having a thickness of 20 μm to 1000 μm, and a bonding pad disposed at a position that overlaps the light-emitting element and that is displaced relative to a center of the light-emitting element in a plan view as viewed in a perpendicular direction perpendicular to an emitting surface of the light-emitting element. A wavelength of light emitted by the light-emitting element is within a range of 470 nm to 600 nm. 
     The biological information detector according to the aspect of the invention further comprises a reflecting part disposed around the light-emitting element. 
     In the biological information detector according to the aspect of the invention, the light-emitting element has a quadrilateral shape in the plan view, and a length of one side of the light-emitting element is 100 μm to 10,000 μm. 
     The biological information detector according to the aspect of the invention further comprises a light-transmitting film disposed on the substrate. 
     In the biological information detector according to the aspect of the invention, the maximum transmittance rate of light passing through the light-transmitting film falls within a range of ±10% of the maximum intensity value of the wavelength of the light emitted by the light-emitting element. 
     In the biological information detector according to the aspect of the invention, the light-transmitting film increases smoothness of a surface of the substrate. 
     In the biological information detector according to the aspect of the invention, the reflecting part includes metal or resin. 
     The biological information detector according to the aspect of the invention further comprises a support part supporting the light-emitting element, and the support part has a thickness of 50 μm to 1000 μm. 
     A biological information measuring device comprises the biological information detector according to the aspect of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A and 1B  are an example of a configuration of an optical device according to a present embodiment; 
         FIGS. 2A ,  2 B,  2 C, and  2 D are an example of steps according to a method for manufacturing the optical device of the present embodiment; 
         FIG. 3  is a comparative example of an optical device; 
         FIGS. 4A and 4B  are examples of an arrangement of the optical device; 
         FIGS. 5A and 5B  are schematic diagrams showing a distance between a first center and a second center; 
         FIGS. 6A and 6B  are examples of a configuration of a biological information detector according to the present embodiment; 
         FIGS. 7A and 7B  are plan views showing the biological information detector of  FIG. 6A ; 
         FIGS. 8A ,  8 B,  8 C, and  8 D are another example of steps according to the method for manufacturing the optical device of the present embodiment; 
         FIG. 9  is an example of intensity characteristics of light emitted by a light-emitting element; 
         FIG. 10  is an example of transmission characteristics of light passing through a contact part; 
         FIG. 11  is another example of a configuration of the biological information detector according to the present embodiment; 
         FIG. 12  is an example of transmission characteristics of light passing through a substrate coated with a light-transmitting film; 
         FIGS. 13A ,  13 B, and  13 C are examples of a configuration of a first reflecting part; 
         FIGS. 14A and 14B  are examples of an outer appearance of the first reflecting part and the light-emitting element with respect to a plan view; 
         FIGS. 15A and 15B  are examples of an outer appearance of a biological information measuring device comprising the biological information detector; and 
         FIG. 16  is an example of a configuration of the biological information measuring device. 
     
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     A description shall now be given for the present embodiment. The present embodiment described below is not intended to unduly limit the scope of the claims of the present embodiment. Not every configuration described in the present embodiment is necessarily an indispensible constituent feature of the invention. 
     1. Optical Device 
       FIGS. 1A and 1B  are an example of a configuration of an optical device according to a present embodiment. In  FIGS. 1A and 1B , the dimensions of each of the members are not intended to accurately represent actual dimensions. Specifically, in FIGS.  1 A and  1 B, the dimensions of each of the members have been expanded or reduced in order to facilitate understanding of the descriptions given below. Similarly, drawings other than  FIGS. 1A and 1B  are not intended to necessarily represent actual dimensions. 
       FIG. 1A  shows a cross-section view, and  FIG. 1B  shows a plan view. As shown in  FIG. 1A , the optical device comprises a substrate  11 , a light-emitting element  14 , and a light-receiving element  16 . The substrate  11  has a first surface  11 A and a second surface  11 B that is opposite the first surface  11 A. The light-emitting element  14  is installed on the first surface  11 B, and the light-receiving element  16  is installed on the second surface  11 A. As shown, e.g., on  FIG. 1B , the light-emitting element  14  has a first center  14 - 1  and the light-receiving element  16  has a second center  16 - 1  with respect to the plan view. 
     In the example shown in  FIGS. 1A and 1B , the entirety of the light-emitting element  14  is arranged in a position that completely overlaps the light-receiving element  16  with respect to the plan view. However, at least a part of the light-emitting element  14  may be arranged in a position that overlaps the light-receiving element  16  with respect to the plan view. Specifically, with respect to the plan view, the light-emitting element  14  falls within the light-receiving element  16 , but a part of the light-emitting element  14  may protrude from the light-receiving element  16  with respect to the plan view. 
     Although in the example shown in  FIGS. 1A and 1B , both of the light-emitting element  14  and the light-receiving element  16  are already attached to the substrate  11 , in reality, the light-receiving element  16  is attached to the substrate  11  in a state in which the light-emitting element  14  has been attached to the substrate  11 . The light-receiving element  16 , which is installed after the light-emitting element  14 , has a bonding pad  16 A′. The bonding pad  16 A′ is provided at a position that is displaced relative to the second center  16 - 1  towards a first direction DR 1  with respect to the plan view. Also, the first center  14 - 1  is provided at a position that is displaced relative to the second center  16 - 1  towards a second direction DR 2 , which is opposite the first direction DR 1 , with respect to the plan view. 
     The bonding pad  16 A′ of the light-receiving element  16  is displaced relative to a center of the light-receiving element  16  (i.e., the second center  16 - 1 ) towards the first direction DR 1  with respect to the plan view, and a center of the light-emitting element  14  (i.e., the first center  14 - 1 ) is displaced relative to the center of the light-receiving element  14  (i.e., the second center  16 - 1 ) towards the second direction DR 2  with respect to the plan view. Therefore, when the bonding wire  61 - 1  is attached to the bonding pad  16 A′, a position directly below the bonding pad  16 A′ can be supported using a jig or a similar tool. The bonding wire  61 - 1  can thereby be attached in a reliable manner. 
     In the example shown in  FIGS. 1A and 1B , the bonding wire  61 - 1  provides an electrical connection between the bonding pad  16 A′ of the light-receiving element  16  and a pad  61 ′ for providing a connection to the light-receiving element  16  (or in a broader sense, wiring for the light-receiving element  16 ). Also, examples of configurations of the optical device are not limited by that shown in  FIGS. 1A and 1B , and the shape, or a similar attribute, of a part of the example of configuration (e.g., the light-emitting element  14 , the light-receiving element  16 , the bonding pad  16 A′, and other components) may be modified. 
     1.1 Method for Manufacturing Optical Device 
       FIGS. 2A ,  2 B,  2 C, and  2 D are an example of steps according to a method for manufacturing the optical device of the present embodiment. While in the example shown in  FIGS. 1A and 1B , both of the light-emitting element  14  and the light-receiving element  16  are already attached to the substrate  11 , as shown in  FIG. 2A , the substrate  11  having a first surface  11 A and a second surface  11 B that is opposite the first surface  11 A is readied. In an instance in which the first surface  11 A refers to, e.g., a front surface, and the second surface  11 B refers to, e.g., a reverse surface, in the example shown in  FIG. 2A , the substrate  11  is upside down. 
     As shown in  FIG. 2B , the light-emitting element  14  is installed on the second surface  11 B. Then, the substrate  11  to which the light-emitting element  14  is attached is turned over, and the light-receiving element  16  is installed on the first surface  11 A. As shown in  FIG. 2C , the following conditions (a) through (c) are satisfied (see  FIG. 1B ). 
     (a) The light-receiving element  16  having the second center  16 - 1  and the bonding pad  16 A′ overlaps with at least a part of the light-emitting element  14  with respect to a plan view; 
     (b) the bonding pad  16 A′ is displaced relative to the second center  16 - 1  towards the first direction DR 1  with respect to the plan view; and 
     (c) the first center  14 - 1  is displaced relative to the second center  16 - 1  towards the second direction DR 2  with respect to the plan view. 
     As shown in  FIG. 2   b , a position directly below the bonding pad  16 A′ of the light-receiving element  16  can be supported by a jig  74 . Since the position directly below the bonding pad  16 A′ of the light-receiving element  16  is being supported, even when the bonding pad  16 A′ is restrained with a bonding tool  72 , the bonding pad  16 A′ of the light-receiving element  16  can be immobilized. 
       FIG. 3  is a comparative example of an optical device. In the example shown in  FIG. 3 , the above-mentioned condition (c) is not satisfied. As shown in  FIG. 3 , the jig  74  must provide a space at a position directly below the bonding pad  16 A′ of the light-receiving element  16  so that the light-emitting element  14  is not destroyed. Therefore, the position directly below the bonding pad  16 A′ of the light-receiving element  16  cannot be directly supported by the jig  74 . Since the position directly below the bonding pad  16 A′ of the light-receiving element  16  is not supported, when the bonding pad  16 N is restrained using the bonding tool  72 , the substrate  11  is caused to bend. The position of the bonding pad  16 A′ of the light-receiving element  16  changes with the bending of the substrate  11 . Since the bonding pad  16 A′ cannot be immobilized, the bonding wire  61 - 1  cannot be attached to the bonding pad  16 A′ in a reliable manner. 
     In contrast to the example shown in  FIG. 3 , in the example shown in  FIG. 2D , the bonding wire  61 - 1  is attached to the bonding pad  16 A′ while the position directly below the bonding pad  16 A′ is supported. Thus, in the example shown in  FIG. 2D , the bonding wire  61 - 1  can be attached to the bonding pad  16 A′ in a reliable manner. As a result, in the method for manufacturing the optical device in which the bonding wire  61 - 1  is attached to the bonding pad  16 A′, the attaching can be performed more reliably. 
       FIGS. 4A and 4B  are examples of an arrangement of the optical device. As with  FIG. 1B , in the example shown in  FIG. 4A  and the example shown in  FIG. 4B , the light-emitting element  14  and the light-receiving element  16  are shown as an optical device. As shown in  FIGS. 4A and 4B , the light-emitting element  14  has a rectangular profile with respect to the plan view, and one side of the rectangle is tangent to a circle having a given radius and having a center on the bonding pad  16 A′ (or in a narrower sense, a center of the bonding pad  16 A′) with respect to the plan view. The light-emitting element  14  can be separated, by the given radius, from the position directly below the bonding pad  16 A′ of the light-receiving element  16 . Therefore, a space can he created at the position directly below the bonding pad  16 N of the light-receiving element  16 . For example, as shown, e.g., in  FIG. 2D , the substrate  11  can be directly supported by the jig  74 . 
     The given radius of the circle having a center on the bonding pad  16 N shown in  FIG. 4A  is equal to the given radius of the circle having a center on the bonding pad  16 N shown in  FIG. 4B , and the light-emitting element  14  can be separated from the position directly below the bonding pad  16 A′ of the light-receiving element  16  by the same given radius. While in the example shown in  FIG. 4A , the light-emitting element  14  completely overlaps the light-receiving element  16  with respect to the plan view, in the example shown in  FIG. 4B , a part of the light-emitting element  14  overlaps the light-receiving element  16  with respect to the plan view. In an instance in which light emitted by the light-emitting element  14  is transmitted through the substrate  11  and received by the light-receiving element  16 , the light-emitting element  14  with respect to the plan view forms a light-blocking region, and the light-receiving element  16  with respect to the plan view also forms a light-blocking region. In the example shown in  FIG. 4A , a light-blocking region as a whole corresponds only to the light-blocking region of the light-receiving element  16 . In the example shown in  FIG. 4B , the light-blocking region as a whole corresponds to, in addition to the light-blocking region of the light-receiving element  16 , the light-blocking region of the light-emitting element  14  that protrudes from the light-blocking region of the light-receiving element  16  (i.e., the light-blocking region of the light-emitting element  14  that does not overlap with the light-blocking region of the light-receiving element  16 ). The light-blocking region as a whole in the example shown in  FIG. 4A  is smaller than the light-blocking region as a whole in the example shown in  FIG. 4B . Therefore, in the example shown in  FIG. 4A , light can more readily reach the light-receiving element  16  compared to the example shown in  FIG. 4B . 
       FIGS. 5A and 5B  are schematic diagrams showing a distance between the first center  14 - 1  and a second center  16 - 1 . As shown in  FIGS. 5A and 5B , the light-emitting element  14  has a rectangular (or in a narrower sense, a square) profile with respect to the plan view, and the length of one side of a square shown in  FIG. 5A  is equal to the length of one side of a square shown in  FIG. 5B . In the example shown in  FIG. 5A , one side (e.g., a side that is nearest to the bonding pad  16 A′) of the square (or in a broader sense, a rectangle) is perpendicular to a direction that connects the first center  14 - 1  and the second center  16 - 1  with respect to the plan view. In the example shown in  FIG. 5B , no side, i.e., none of the four sides, of the square (or in a broader sense, the rectangle) is perpendicular to the direction that connects the first center  14 - 1  and the second center  16 - 1  with respect to the plan view. 
     The given radius of the circle having a center on the bonding pad  16 A′ shown in  FIG. 5A  can be made smaller than the given radius of the circle having a center on the bonding pad  16 A′ shown in  FIG. 5B . Thus, in an instance in which one side of the rectangle that represents the profile of the light-emitting element  14  is perpendicular to the direction that connects the first center  14 - 1  and the second center  16 - 1  with respect to the plan view, the distance between the first center  14 - 1  and the second center  16 - 1  can be decreased. In an instance in which light emitted by the light-emitting element  14  is transmitted through the substrate  11  and received by the light-receiving element  16 , the light-receiving element  16  can receive light more effectively with a shorter distance between the first center  14 - 1  and the second center  16 - 1 . 
     2. Biological Information Detector 
       FIGS. 6A and 6B  are examples of a configuration of a biological information detector according to the present embodiment. As shown in  FIGS. 6A and 6B , the biological information detector comprises the optical device shown, e.g., in  FIG. 1A .  FIGS. 6A and 6B  can also be said to show other examples of a configuration of the optical device according to the present embodiment. As shown in  FIGS. 6A and 6B , the biological information detector (or in a broader sense, the optical device) may further comprise a first reflecting part  92 . Structures that are identical to those in the example described above are affixed with the same numerals, and a description of the structures is not provided. 
     While in  FIG. 6A , the light-emitting element  14  is arranged on a side towards a detection site O of a test subject (e.g., a user), in  FIG. 6B , the light-receiving element  16  is arranged on a side towards the detection site O of the test subject. All of the light-receiving element  16  and other components arranged on the first surface  11 A of the substrate  11  in  FIG. 6A  are arranged on the second surface  11 B of the substrate  11  in  FIG. 6B ; however,  16 A′ and other numerals shown in  FIG. 6A  are not shown in  FIG. 6B . Also, all of the light-emitting element  14  and other components arranged on the second surface  11 B of the substrate  11  in  FIG. 6A  are arranged on the first surface  11 A of the substrate  11  in  FIG. 6B ; however,  14 A and other numerals shown in  FIG. 6A  are not shown in  FIG. 6B . Also, the light-emitting element  14  in  FIG. 6A  emits a first light R 1  and a second light R 2 ; however, the second light R 2  is not shown in  FIG. 6B . 
     The light-emitting element  14  emits light RI directed at the detection site O of the test subject (e.g., the user). The light-emitting element  14  also emits the second light R 2  directed at a direction other than that of the detection site O (i.e., directed at the first reflecting part  92 ). The first reflecting part  92  reflects the second light R 2  towards the detection site O. The light-receiving element  16  receives light R 1 ′ (i.e., reflected light) having biological information, the light R 1 ′ being light RI emitted by the light-emitting element  14  reflecting at the detection site O. The light-receiving element  16  also receives light R 2 ′ (i.e., reflected light) having biological information, the light R 2 ′ being the second light R 2  reflecting at the detection site O. 
     The biological information detector (or in a broader sense, the optical device) may further comprise a second reflecting part  18 . In the examples shown in  FIGS. 6A and 6B , the second reflecting part  18  reflects the light RI emitted by the light-emitting element  14  or the light R 1 ′ (i.e., reflected light) having biological information. In the example shown in  FIG. 6A , the second reflecting part  18  reflects the light R 1 ′ and R 2 ′ (i.e., reflected light) having biological information from the detection site O towards the light-receiving element  16 . In  FIG. 6B , the second reflecting part  18  reflects the light R 1  emitted by the light-emitting element  14  towards the detection site O. The second reflecting part  18  may have a reflecting surface on a dome surface provided between the light-emitting element  14  and the light-receiving element  16 . 
     The biological information detector (or in a broader sense, the optical device) may further comprise a contact part  19 . The contact part  19  has a surface  19 A that comes into contact with the test subject, and is formed from a material that is transparent with respect to the wavelength of the light R 1  emitted by the light-emitting element  14  (e.g., glass). The substrate  11  is also formed from a material that is transparent with respect to the wavelength of the light R 1  emitted by the light-emitting element  14  (e.g., polyimide), and the substrate  11  is formed from, e.g., a flexible substrate. 
     In the example shown in  FIGS. 6A and 6B , the detection site O (e.g., a blood vessel) is within the test subject. The first light R 1  travels into the test subject and diffuses or scatters at the epidermis, the dermis, and the subcutaneous tissue. The first light R 1  then reaches the detection site O, and is reflected at the detection site O. The reflected light R 1 ′ reflected at the detection site O diffuses or scatters at the subcutaneous tissue, the dermis, and the epidermis. In  FIG. 6A , the reflected light R 1 ′ travels to the reflecting part  18 . In  FIG. 6B , the first light RI travels to the detection site O via the second reflecting part  18 . The first light R 1  is partially absorbed at the blood vessel. Therefore, due to an effect of a pulse, the rate of absorption at the blood vessel varies, and the amount of the reflected light R 1 ′ reflected at the detection site O also varies. Biological information (e.g. pulse rate) is thus reflected in the reflected light R 1 ′ reflected at the detection site O. 
     In  FIG. 6A , the second light R 2  travels into the test subject, and the reflected light R 2 ′ reflected at the detection site O travels to the second reflecting part  18 . The biological information (i.e., pulse rate) is also reflected in the reflected light R 2 ′ reflected at the detection site O. 
     Examples of configurations of the biological information detector (or in a broader sense, the optical device) are not limited by those shown in  FIGS. 6A and 1B , and the shape, or a similar attribute, of a part of the example of configuration (e.g., the first reflecting part  92 , the second reflecting part  18 , and other components) may be modified. The biological information may also be blood oxygen saturation level, body temperature, heart rate, or a similar variable; and the detection site O may be positioned at a surface SA of the test subject. In the example shown in  FIG. 6A , the first light R 1  and the second light R 2  are each shown by a single line, and in the example shown in  FIG. 6B , the first light R 1  is shown by a single line; however, in reality, the light-emitting element  14  emits many light beams in a variety of directions. 
     In the example shown in  FIG. 6A , a part of the wiring for the light-receiving element  16  is shown, and the pad  61 ′ for providing a connection to the light-receiving element  16  is shown. The bonding pad  16 A′ (or in a broader sense, an electrode) is, e.g., an anode of the light-receiving element  16 . In the example shown in  FIG. 6A , a connecting part  62 ′ for providing a connection to, e.g., an electrode pad  16 C′ (or in a broader sense, an electrode) of the light-receiving element  16  is also shown as a part of the wiring for the light-receiving element  16 . The electrode pad  16 C′ is, e.g., a cathode of the light-receiving element  16 . In the example shown in  FIG. 6A , the connecting part  62 ′ is directly connected to an electrode pad  16 C′. 
     Also, in the example shown in  FIG. 6A , a part of the wiring for the light-emitting element  14  is shown, and a pad  64 ′ for providing a connection to the light-emitting element  14  is shown. The connecting pad  64 ′ is connected to a bonding pad  14 A′ (or in a broader sense, an electrode) of the light-emitting element  14  via a bonding wire  64 - 1 . The bonding pad  14 A′ is, e.g., an anode of the light-emitting element  14 . The example shown in  FIG. 6A  shows a cross-section view corresponding to one cut plane. In the example shown in  FIG. 6A , a connecting pad  63 ′ that is not, in reality, present on the cut plane is represented by a dotted line. The connecting pad  63 ′ is connected to a bonding pad  14 C′ (or in a broader sense, an electrode) of the light-emitting element  14  via a bonding wire  63 - 1 . The bonding pad  14 C′ is, e.g., a cathode of the light-emitting element  14 . 
       FIGS. 7A and 7B  are plan views showing the biological information detector (or in a broader sense, the optical device) of  FIG. 6A .  FIG. 7A  corresponds to a plan view of a side towards the light-receiving element  16 , and  FIG. 7B  corresponds to a plan view of a side towards the light-emitting element  14 . Structures that are identical to those in the examples described above are affixed with the same numerals, and a description of the structures is not provided. 
     In  FIG. 7A , each of the light-emitting element  14  and the first reflecting part  92  is shown by a dotted line. As shown in  FIG. 7A , the first reflecting part  92  has a third center  92 -C, and the third center  92 -C coincides with the first center  14 - 1  of the light-emitting element  14  with respect to the plan view. In an instance in which the third center  92 -C coincides with the first center  14 - 1 , the first reflecting part  92  is capable of reflecting light emitted by the light-emitting element  14  in an efficient manner. The example shown in  FIG. 7A  satisfies a positional relationship shown in  FIG. 1B . Therefore, the third center  92 -C (i.e., the first center  14 - 1 ) is provided at a position that is displaced, relative to the second center  16 - 1 , towards the second direction DR 2 , which is opposite the first direction DR 1 , with respect to the plan view. 
     As shown in  FIG. 7A , a wiring  61  for the light-receiving element  16  has a connecting pad  61 ′ and the bonding wire  61 - 1  at one end. Also, a wiring  62  for the light-receiving element  16  has the connecting part  62 ′ at one end. As shown in  FIG. 7B , a wiring  63  for the light-emitting element  14  has the connecting pad  63 ′ and the bonding wire  63 - 1  at one end. Also, a wiring  64  for the light-emitting element  14  has the connecting pad  64 ′ and the bonding wire  64 - 1  at one end. Electrical power can be fed to the light-emitting element  14  from the wiring  63  and the wiring  64 , and an electrical signal from the light-receiving element  16  can be extracted from wiring  63  and the wiring  64 . In  FIG. 7A , the wiring  63  and the wiring  64  are not shown. In  FIG. 7B , the light-receiving element  16  and similar components are each shown by a dotted line. 
     The configuration of the wiring  63  and the wiring  64  for the light-emitting element  14  and the wiring  61  and the wiring  62  for the light-receiving element  16  are not limited by the examples shown in  FIGS. 7A and 7B . For example, the shape of the connecting pad  61 ′ of the wiring  61  may, instead of being circular as shown in  FIG. 7A , be, e.g., square, elliptical, polygonal, or describing another shape. The shape of, e.g., the connecting pad  63 ′ of the wiring  63  may, instead of being square as shown in  FIG. 7B , also be, e.g., circular, elliptical, polygonal, or describing another shape. 
     2.1 Method for Manufacturing Optical Device in Biological Information Detector 
       FIGS. 8A ,  8 B,  8 C, and  8 D are another example of steps according to the method for manufacturing the optical device of the present embodiment. Structures that are identical to those in the examples described above are affixed with the same numerals, and a description of the structures is not provided. The example differs, in general, from the example shown in  FIG. 2D  in that the light-emitting element  14  is installed on the second surface  11 B with the first reflecting part  92  for reflecting light emitted by the light-emitting element  14  interposed therebetween, and the bonding wire  61 - 1  is attached to the bonding pad  16 A′ while the position directly below the bonding pad  16 A′ is supported by the first reflecting part  92  ( FIG. 8D ). 
     Adding the first reflecting part  92  to the light-emitting element  14  makes it possible to support the position directly below the bonding pad  16 A′ of the light-receiving element  16  using the first reflecting part  92  and the jig  74  or a similar tool. Therefore, the bonding wire  16 - 1  can be attached to the bonding pad  16 A′ in a reliable manner. Also, the first reflecting part  92  makes it possible to prevent the jig  74  from coming into contact with the light-emitting element  14 , and as a result, it is possible to prevent the light-emitting element  14  from being damaged. 
     As shown in  FIGS. 8A ,  6 A, and  7 B, the connecting pad  64 ′ and the connecting pad  63 ′ (or in a broader sense, the wirings  64 ,  63  for the light-emitting element  14 ) are arranged in advance on the second surface  11 B of the substrate  11 . Also, the connecting pad  61 ′ and the connecting part  62 ′ (or in a broader sense, the wirings  61 ,  62  for the light-receiving element  16 ) are arranged in advance on the first surface  11 A of the substrate  11 . 
     As shown in  FIG. 8B , the first reflecting part  92 , to which the light-emitting element  14  has been attached in advance, is arranged on the second surface  11 B of the substrate  11 , and the bonding wire  64 - 1  is attached to the bonding pad  14 A′ while the first surface  11 A of the substrate  11  is supported a jig or a similar tool (not shown). Also, the bonding wire  63 - 1  is attached to the bonding pad  14 C′. 
     As shown in  FIG. 8C , the following conditions (a) through (c) are satisfied. 
     (a) The light-receiving element  16  having the second center  16 - 1  and the bonding pad  16 A′ overlaps with at least a part of the light-emitting element  14  with respect to the plan view; 
     (b) the bonding pad  16 A′ is displaced relative to the second center  16 - 1  towards the first direction DR 1  with respect to the plan view; and 
     (c) the third center  92 -C (and the first center  14 - 1 ) are displaced relative to the second center  16 - 1  towards a second direction DR 2  with respect to the plan view. 
     As shown in  FIG. 8C , when a wire bonding step in the optical device is complete, the second reflecting part  18  and the contact part  19  are attached to the substrate  11  as shown, e.g., in  FIG. 6A . 
     As shown in  FIG. 6A  or  FIG. 6B , the substrate  11  is arranged between the second reflecting part  18  and the contact part  19 . Therefore, even in an instance in which the light-emitting element  14  and the light-receiving element  16  are arranged on the substrate  11 , there is no need to separately provide a mechanism for supporting the substrate  11  itself, and the number of components is smaller. Also, since the substrate  11  is formed from a material that is transparent with respect to the emission wavelength, the substrate  11  can be arranged on a light path from the light-emitting element  14  to the light-receiving element  16 , and there is no need to accommodate the substrate  11  at a position away from the light path, such as within the second reflecting part  18 . A biological information detector (or in a broader sense, an optical device) that can be readily assembled can thus be provided. Also, the second reflecting part  18  is capable of increasing the amount of light reaching the light-receiving element  16  or the detection site O, and the detection accuracy (i.e., the signal-to-noise ratio) of the biological information detector increases. 
     In Patent Citation 1, it is necessary to install the light-emitting element  11 , the light-receiving element  12 , the substrate  15 , and the transparent material  142  in the interior of the reflecting part  131 . Therefore, a small optical probe  1  cannot be assembled with ease. Also, according to paragraph [0048] in Patent Citation 1, the substrate  15  is formed so that an interior-side of the reflecting part  131  is a diffuse reflection surface. In other words, the substrate  15  in Patent Citation 1 is not required to be formed from a transparent material. 
     The thickness of the substrate  11  is e.g., 10 μm to 1000 μm. The substrate  11  is, e.g., a printed circuit board; however, a printed circuit board is not generally formed from a transparent material, as with the substrate  15  of Patent Citation 1. Specifically, the inventors purposefully used a configuration in which the printed circuit board is formed from a material that is transparent at least with respect to the emission wavelength of the light-emitting element  14 . The thickness of the contact part  19  is, e.g., 1 μm to 3000 μm. 
     The light-emitting element  14  is, e.g., an LED. The light emitted by the LED has a maximum intensity (or in a broader sense, a peak intensity) within a wavelength range of, e.g., 425 nm to 625 nm, and is, e.g., green in color. The thickness of the light-emitting element  14  is, e.g., 20 μm to 1000 μm. The light-receiving element  16  is, e.g., a photodiode, and can generally be formed by a silicon photodiode. The thickness of the light-receiving element  16  is, e.g., 20 μm to 1000 μm. The silicon photodiode has a maximum sensitivity (or in a broader sense, a peak sensitivity) for received light having a wavelength within a range of, e.g., 800 nm to 1000 nm. Ideally, the light-receiving element  16  is formed by a gallium arsenide phosphide photodiode, and the gallium arsenide phosphide photodiode has a maximum sensitivity (or in a broader sense, a peak sensitivity) for received light having a wavelength within a range of, e.g., 550 nm to 650 nm. Since biological substances (water or hemoglobin) readily allow transmission of infrared light within a wavelength range of 700 nm to 1100 nm, the light-receiving element  16  formed by the gallium arsenide phosphide photodiode is more capable of reducing noise components arising from external light than the light-receiving element  16  formed by the silicon photodiode. 
       FIG. 9  shows an example of intensity characteristics of the light emitted by the light-emitting element  14 . In the example shown in  FIG. 9 , the intensity is at a maximum for light having a wavelength of 520 nm, and the intensity of light having other wavelengths is normalized with respect thereto. Also, in the example shown in  FIG. 9 , the wavelengths of light emitted by the light-emitting element  14  are within a range of 470 nm to 600 nm. 
       FIG. 10  shows an example of transmission characteristics of light passing through the contact part  19 . As shown in  FIG. 10 , at the wavelength of light (520 nm) emitted by the light-emitting element  14  at which the intensity is at a maximum shown, e.g., in  FIG. 9 , the transmittance is 50% or above. Also, although an example of transmission characteristics of light passing through the substrate  11  itself is not shown, transmittance of the substrate  11  with respect to a wavelength of 520 nm can be set to, e.g., 50% or above, as with the transmission characteristics shown in  FIG. 10 . The contact part  19  and the substrate  11  can be formed from a material that is transparent with respect to the wavelength of light R 1  emitted by the light-emitting element  14 . 
       FIG. 11  is another example of a configuration of the biological information detector according to the present embodiment. As shown in  FIG. 11 , the light-transmitting film  11 - 1  can be formed on the first surface  11 A and the second surface  11 B, which is opposite the first surface, of the substrate  11 . Structures that are identical to those in the example described above are affixed with the same numerals, and a description of the structures is not provided. The light-transmitting film  11 - 1  may be formed only on the first surface  11 A, or may be formed only on the second surface  11 B. Also, in the example shown in  FIG. 11 , the light-transmitting film  11 - 1  is formed on a light-transmitting region of the substrate  11  on which the light-emitting element  14  and the light-receiving element  16  (or in a narrower sense, the first reflecting part  92 , the connecting pad  64 ′ (i.e., wirings  63 ,  64  for the light-emitting element  14  in  FIG. 7B ), the connecting part  62 ′, and the connecting pad  61 ′ (i.e., wirings  61 ,  62  for the light-receiving element  16  in  FIG. 7B )) are not arranged. Although  FIG. 11  corresponds to  FIG. 6A , the light-transmitting film  11 - 1  may be formed on at least one of the first surface  11 A and the second surface  11 B of the substrate  11  in  FIG. 6B . The light-transmitting film  11 - 1  may be formed from, e.g., a solder resist (or in a broader sense, a resist). 
     In the example shown in  FIG. 11 , the first surface  11 A and the second surface  11 B of the substrate  11  may be processed so as to form a rough surface so that the wirings  61 ,  62 ,  63 ,  64  (including the connecting pads  61 ′,  64 ′, the connecting part  62 ′, and similar components) on the substrate  11  do not peel off. Therefore, the light-transmitting film  11 - 1  is formed on the first surface  11 A and the second surface  11 B, whereby the roughness on the surface of the substrate  11  is filled with the light-transmitting film, and the smoothness of the entire substrate  11  is increased. Specifically, the light-transmitting film  11 - 1  on the substrate  11  is smooth, and can therefore reduce dispersion of light on the roughness on the surface of the substrate  11  during transmission of the light through the substrate  11 . Specifically, the presence of the light-transmitting film  11 - 1  increases the transmittance of the substrate  11 . Therefore, the amount of light reaching the light-receiving element  16  or the detection site O increases, and the detection accuracy of the biological information detector increases further. 
     The refractive index of the light-transmitting film  11 - 1  is preferably between the refractive index of air and the refractive index of the substrate  11 . Further preferably, the refractive index of the light-transmitting film  11 - 1  is preferably closer to the refractive index of the substrate  11  than the refractive index of air. In such an instance, it is possible to reduce reflection of light on an interface. 
       FIG. 12  is an example of transmission characteristics of light passing through the substrate  11  coated with a light-transmitting film. In the example shown in  FIG. 12 , transmittance is calculated using the intensity of light before being transmitted through the substrate  11  and the intensity of light after being transmitted through the substrate  11 . In the example shown in  FIG. 12 , in the range of wavelength the equal to or less than 700 nm, which is the lower limit of the optical window in biological tissue, the transmittance is at a maximum for light having a wavelength of 525 nm. Or, in the example shown in  FIG. 12 , in the range of wavelength equal to or less than 700 nm, which is the lower limit of the optical window in biological tissue, the wavelength of the maximum transmittance of light passing through the light transmission film  11 - 1  falls within a range of ±10% of the wavelength of the maximum intensity of light generated by the light-emitting part  14  in  FIG. 9 , for example. It is preferable that the light-transmitting film  11 - 1  thus selectively transmit light generated by the light-emitting element  14  (e.g., the first light R 1  (or in a narrower sense, the reflected light R 1 ′ produced by the first light R 1  being reflected) in  FIG. 6A ). The presence of the light-transmitting film  11 - 1  makes it possible to enhance the smoothness of the substrate  11  and prevent, to a certain extent, a decrease in efficiency of the light-emitting element  14  and the light-receiving element  16 . In an instance in which transmittance has a maximum value (or in a broader sense, a peak value) within, e.g., a visible light region for light having a wavelength of 525 nm, as shown in the example in  FIG. 12 , the light-transmitting film  11 - 1  is, e.g., green. 
     In the example shown in  FIG. 6A , the light-emitting element  14  may have a first light-emitting surface  14 A that faces the detection site O and emits the first light R 1 . The light-emitting element  14  may also have a second light-emitting surface  14 B that is a side surface of the first light-emitting surface  14 A and emits the second light R 2 . In such an instance, the first reflecting part  92  may have a wall part that surrounds the second light-emitting surface  14 B. 
       FIGS. 13A ,  13 B, and  13 C are examples of a configuration of the first reflecting part  92  shown in  FIG. 6A . As shown in  FIG. 13A , the first reflecting part  92  may have a support part  92 - 1  for supporting the light-emitting element  14 , and an inner wall surface  92 - 2  and a top surface  92 - 3  of the wall part surrounding the second light-emitting surface  14 B of the light-emitting element  14 . The light-emitting element  14  is not shown in  FIGS. 13A through 13C . In the example shown in  FIG. 13A , the first reflecting part  92  can reflect the second light R 2  on the inner wall surface  92 - 2  towards the detection site O (see  FIG. 6A ), the first reflecting part  92  having a first reflecting surface on the inner wall surface  92 - 2 . The thickness of the support part  92 - 1  is, e.g., 50 μm to 1000 μm, and the thickness of the wall part ( 92 - 3 ) is, e.g., 100 μm to 1000 μm. 
     In the example shown in  FIG. 13A , the inner wall surface  92 - 2  has an inclined surface ( 92 - 2 ) which, with increasing distance in a width direction (i.e., a first direction) from a center of the first reflecting part  92 , inclines towards the detection site O in a height direction (i.e., a direction that is perpendicular to the first direction), in cross-section view. The inclined surface ( 92 - 2 ) in  FIG. 13A  is formed by, in cross-section view, an inclined plane, but may also be a curved surface shown in, e.g.,  FIG. 13C , or a similar inclined surface. The inner wall surface  92 - 2  may also be formed as a plurality of inclined flat surfaces whose angle of inclination vary from one another, or by a curved surface having a plurality of curvatures. In an instance in which the inner wall surface  92 - 2  of the first reflecting part  92  has an inclined surface, the inner wall surface  92 - 2  of the first reflecting part  92  is capable of reflecting the second light R 2  towards the detection site O. In other words, the inclined surface on the inner wall surface  92 - 2  of the first reflecting part  92  can be said to be the first reflecting surface for improving the directivity of the light-emitting element  14 . In such an instance, the amount of light reaching the detection site O increases further. The top surface  92 - 3  shown in  FIGS. 13A and 13C  may be omitted as shown, e.g., in  FIG. 13B . In an instance in which the first reflecting part  92  has the top surface  92 - 3 , the top surface  92 - 3  may be supported by the jig  74  (see  FIG. 8D ). In  FIGS. 13A through 13C , a range indicated by label  92 - 4  function as a mirror surface part. 
       FIGS. 14A and 14B  respectively show an example of an outer appearance of the first reflecting part  92  and the light-emitting element  14  of  FIG. 6A  in plan view. In the example shown in  FIG. 14A , with respect to the plan view (when viewed from, e.g., towards the detection site O shown in  FIG. 6A ), an outer circumference of the first reflecting part  92  is circular, where the diameter of the circle is, e.g., 200 μm to 11,000 μm. In the example shown in  FIG. 14A , the wall part ( 92 - 2 ) of the first reflecting part  92  surrounds the light-emitting element  14  (see  FIG. 6A ). The outer circumference of the first reflecting part  92  may also be a quadrilateral (or specifically, a square) with respect to the plan view as shown, e.g., in  FIG. 14B . Also, in the examples shown in  FIGS. 14A and 14B , with respect to the plan view (when viewed from, e.g., towards the detection site O shown in  FIG. 6A ), the outer circumference of the light-emitting element  14  is a quadrilateral (or specifically, a square), where the length of one side of the square is, e.g., 100 μm to 10,000 μm. The outer circumference of the light-emitting element  14  may also be circular. 
     The first reflecting part  92  is made of metal whose surface is polished to a mirror finish, and thereby has a reflective structure (or specifically, a mirror reflection structure). The first reflecting part  92  may also be formed from, e.g., a resin whose surface is polished to a mirror finish. Specifically, for example, a base metal forming a base of the first reflecting part  92  is readied, and a surface of the base metal is then, e.g., subjected to plating. Alternatively, a mold of the first reflecting part  92  (not shown) is filled with a thermoplastic resin, molding is performed, and a metal film, for example, is then deposited by vapor deposition on a surface of the mold. 
     In the examples shown in  FIGS. 14A and 14B , in plan view (when viewed from, e.g., towards the detection site O shown in  FIG. 6A ), a region of the first reflecting part  92  other than that directly supporting the light-emitting element  14  (i.e., the inner wall surface  92 - 2  and the top surface  92 - 3  of the wall part, and a part of the support part  92 - 1 ) is exposed. The exposed region is shown as a mirror surface part  92 - 4  in  FIG. 13A . Although in the example shown in  FIG. 13A , a dotted line representing the mirror surface part  92 - 4  is shown within the first reflecting part  92 , the mirror surface part  92 - 4  is actually formed on a surface of the first reflecting part  92 . 
     In the examples shown in  FIGS. 13A ,  13 B, and  13 C, the mirror surface part  92 - 4  preferably has a high reflectivity. The reflectivity of the mirror surface part  92 - 4  is, e.g., 80% to 90% or higher. It is possible for the mirror surface part  92 - 4  to be formed only on the inclined surface of the inner wall surface  92 - 2 . In an instance in which the mirror surface part  92 - 4  is formed not only on the inclined surface of the inner wall surface  92 - 2  but also on the support part  92 - 1 , the directivity of the light-emitting element  14  increases further. 
     The second reflecting part  18  is formed from, e.g., a resin whose surface (i.e., a reflecting surface on a side towards the light-receiving element  16  in  FIG. 6A ) is polished to a mirror finish, and thereby has a reflective structure (or specifically, a mirror reflection structure). In other words, the second reflecting part  18  is capable of causing mirror reflection of light without causing diffuse reflection of light. In an instance in which the second reflecting part  18  has a mirror reflection structure, the second reflecting part  18  is also capable of not causing reflected light R 1 ″ (i.e., directly reflected light; invalid light) produced by reflection of the first light R 1  to reflect towards the light-receiving element  16 , the reflected light R 1 ″ having a reflection angle that is different to that of the reflected light R 1 ′ produced by reflection of the first light R 1  (see  FIG. 6A ). In such an instance, the detection accuracy of the biological information detector is further increased. As shown in  FIG. 6A , since the reflected light R 1 ′ produced by reflection of the first light R 1  originates from the detection site O, which is within the test subject, the reflection angle of the reflected light R 1 ′ produced by reflection of the first light R 1  (i.e., a reflection angle relative to a straight line perpendicular to the surface SA of the test subject) is generally small. Meanwhile, since the reflected light R 1 ″ produced by reflection of the first light R 1  originates from the surface SA of the test subject, the reflection angle of the reflected light R 1 ″ produced by reflection of the first light R 1  is generally large. 
     In  FIG. 16  of Patent Citation 1, there is disclosed a reflecting part  131 ; and according to paragraphs [0046], [0059], and [0077] in Patent Citation 1, the reflecting part  131  has a diffuse reflection structure, and the reflectivity is increased to improve the efficiency of the light-receiving element  12 . However, at the time of filing, it had not been recognized by those skilled in the art that in the reflecting part  131  according to Patent Citation 1, directly reflected light (or in a broader sense, noise) is also reflected towards the light-receiving element  12 . In other words, the inventors recognized that reducing a noise component arising from the directly reflected light from a light reception signal increases the efficiency of the light-receiving element. Specifically, the inventors recognized that the detection accuracy of the biological information detector is further increased in an instance in which the second reflecting part  18  has a mirror reflection structure. 
     3. Biological Information Measuring Device 
     3.1 Pulse Rate Monitor 
       FIGS. 15A and 15B  are examples of the outer appearance of a biological information measuring device comprising the biological information detector such as that shown in  FIG. 1  and other drawings. As shown in  FIG. 15A , the biological information detector shown, e.g., in  FIG. 6A  may further comprise a wristband  150  capable of attaching the biological information detector to an arm (or specifically, a wrist) of the test subject (i.e., the user). In the example shown in  FIG. 15A , the biological information is the pulse rate indicated by, e.g., “72.” The biological information detector is installed in a wristwatch showing the time (e.g., “8:15 am”). As shown in  FIG. 15B , an opening part is provided to a back cover of the wristwatch, and the contact part  19  shown in, e.g.,  FIG. 6A  is exposed in the opening part. In the example shown in  FIG. 15B , the second reflecting part  18  and the light-receiving element  16  are installed in a wristwatch. In the example shown in  FIG. 15B , the first reflecting part  92 , the light-emitting element  14 , the wristband  150 , and other components are not shown. 
       FIG. 16  is an example of a configuration of the biological information measuring device. The biological information measuring device includes the biological information detector as shown, e.g., in  FIG. 6A , and a biological information measuring part for measuring biological information from a light reception signal generated at the light-receiving element  16  of the biological information detector. As shown in  FIG. 16 , the biological information detector may have the light-emitting element  14 , the light-receiving element  16 , and a circuit  161  for controlling the light-emitting element  14 . The biological information detector may further have a circuit  162  for amplifying the light reception signal from the light-receiving element  16 . The biological information measuring part may have an A/D conversion circuit  163  for performing A/D conversion of the light reception signal from the light-receiving element  16 , and a pulse rate computation circuit  164  for calculating the pulse rate. The biological information measuring part may further have a display part  165  for displaying the pulse rate. 
     The biological information detector may have an acceleration detecting part  166 , and the biological information measuring part may further have an A/D conversion circuit  167  for performing A/D conversion of an acceleration signal from the acceleration detecting part  166  and a digital signal processing circuit  168  for processing a digital signal. The configuration of the biological information measuring device is not limited to the example shown in  FIG. 16 . The pulse rate computation circuit  164  in  FIG. 16  may be, e.g., an MPU (i.e., a micro processing unit) of an electronic device installed with the biological information detector. 
     The control circuit  161  in  FIG. 16  drives the light-emitting element  14 . The control circuit  161  is, e.g., a constant current circuit, delivers a predetermined voltage (e.g., 6 V) to the light-emitting element  14  via a protective resistance, and maintains a current flowing to the light-emitting element  14  at a predetermined value (e.g., 2 mA). The control circuit  161  is capable of driving the light-emitting element  14  in an intermittent manner (e.g. at 128 Hz) in order to reduce consumption current. The control circuit  161  is formed on, e.g., a motherboard, and wiring between the control circuit  161  and the light-emitting element  14  is formed, e.g., on the substrate  11  shown in  FIG. 6A . 
     The amplification circuit  162  shown in  FIG. 16  is capable of removing a DC component from the light reception signal (i.e., an electrical current) generated in the light-receiving element  16 , extracting only an AC component, amplifying the AC component, and generating an AC signal. The amplification circuit  162  removes the DC component at or below a predetermined wavelength using, e.g., a high-pass filter, and buffers the AC component using, e.g., an operational amplifier. The light reception signal contains a pulsating component and a body movement component. The amplification circuit  162  or the control circuit  161  is capable of feeding a power supply voltage for operating the light-receiving element  16  at, e.g., reverse bias to the light-receiving element  16 . In an instance in which the light-emitting element  14  is intermittently driven, the power supply to the light-receiving element  16  is also intermittently fed, and the AC component is also intermittently amplified. The amplification circuit  162  is formed on, e.g., the mother board, and wiring between the amplification circuit  162  and the light-receiving element  16  is formed on, e.g., the substrate  11  shown in  FIG. 6A . The amplification circuit  162  may also have an amplifier for amplifying the light reception signal at a stage prior to the high-pass filter. In an instance in which the amplification circuit  162  has an amplifier, the amplifier is formed, e.g., on the substrate  11 . 
     The A/D conversion circuit  163  shown in  FIG. 16  converts an AC signal generated in the amplification circuit  162  into a digital signal (i.e., a first digital signal). The acceleration detecting part  166  shown in  FIG. 16  calculates, e.g., acceleration in three axes (i.e., x-axis, y-axis, and z-axis) and generates an acceleration signal. Movement of the body (i.e., the arm), and therefore movement of the biological information measuring device, are reflected in the acceleration signal. The A/D conversion circuit  167  shown in  FIG. 16  converts the acceleration signal generated in the acceleration detecting part  166  into a digital signal (i.e., a second digital signal). 
     The digital signal processing circuit  168  shown in  FIG. 16  uses the second digital signal to remove or reduce the body movement component in the first digital signal. The digital signal processing circuit  168  may be formed with, e.g., an FIR filter or another adaptive filter. The digital signal processing circuit  168  inputs the first digital signal and the second digital signal into the adaptive filter and generates a filter output signal in which noise has been removed or reduced. 
     The pulse rate computation circuit  164  shown in  FIG. 16  uses e.g. fast Fourier transform (or in a broader sense, discrete Fourier transform) to perform a frequency analysis on the filter output signal. The pulse rate computation circuit  164  identifies a frequency that represents a pulsating component based on a result of the frequency analysis, and calculates a pulse rate. 
     3.2 Pulse Oximeter 
     A description will now be given for a pulse oximeter as another example of the biological information measuring device. A biological information detector (or in a broader sense, an optical device) that is installed in the pulse oximeter can be obtained using a configuration that is identical to that used in the above-described embodiment (i.e., the configuration shown in, e.g.,  FIG. 6A  or  FIG. 1A ). 
     A description will now be given based on the configuration shown in  FIG. 6A . The pulse oximeter (or in a broader sense, the biological information detector) comprises the light-emitting element  14  and the light-receiving element  16 . The light-emitting element  14  emits, e.g., a red light and infrared light. Reflected light, produced by the light emitted by the light-emitting element  14  reflecting at the detection site O (e.g., a blood vessel), is measured using the light-receiving element  16 . Red-light and infrared absorbance of haemoglobin in the blood differ depending on presence of a bond with oxygen. Therefore, the arterial oxygen saturation (S p O 2 ) can be measured by measuring the reflected light at the light-receiving element  16  and analyzing the reflected light. 
     The configuration of the biological information measuring part (i.e., the A/D conversion circuit  163 , the pulse rate computation circuit  164 , the display part  165 , the acceleration detecting part  166 , the A/D conversion circuit  167 , and the digital signal processing circuit  168 ) for use in a pulse rate monitor as shown in  FIG. 16  can be used as a configuration of the biological information measuring part for use in the pulse oximeter. However, the pulse rate computation circuit  164  shown in  FIG. 16  is replaced by an arterial oxygen saturation analysis circuit  164  in which a pulse rate computation circuit and an FFT or another approach is used. 
     Although a detailed description was made concerning the present embodiment as stated above, persons skilled in the art should be able to easily understand that various modifications can be made without substantially departing from the scope and effects of the invention. Accordingly, all of such examples of modifications are to be included in the scope of the invention. For example, terms stated at least once together with different terms having broader sense or identical sense in the specification or drawings may be replaced with those different terms in any and all locations of the specification or drawings. 
     A first aspect of the embodiment relates to a method for manufacturing an optical device, comprises: 
     readying a substrate having a first surface and a second surface that is opposite the first surface; 
     installing on the second surface a light-emitting element having a first center; 
     installing a light-receiving element having a second center and a bonding pad so that 
     (a) the light-receiving element overlaps with at least a part of the light-emitting element with respect to a plan view; 
     (b) the bonding pad is displaced relative to the second center towards a first direction with respect to the plan view; and 
     (c) the first center is displaced relative to the second center towards a second direction, which is opposite the first direction, with respect to the plan view; and 
     attaching a bonding wire to the bonding pad while supporting a position directly below the bonding pad. 
     According to the first aspect of the embodiment, the bonding pad of the light-receiving element is displaced relative to a center of the light-receiving element (i.e., the second center) towards the first direction with respect to the plan view, and a center of the light-emitting element (i.e., the first center) is displaced relative to the center of the light-receiving element (i.e., the second center) towards the second direction with respect to the plan view. Therefore, the position directly below the bonding pad of the light-receiving element can be supported using a jig or a similar tool. Since a position directly below the bonding pad of the light-receiving element is supported, the bonding pad of the light-receiving element can be immobilized even when the bonding pad is restrained with a bonding tool. The bonding wire can thereby be reliably attached to the bonding pad. As a result, when the bonding wire is attached to the bonding pad, the attaching can be performed more reliably. In an instance in which a space is created in the position directly below the bonding pad of the light-receiving element, it is possible to avoid installing the light-emitting element in the position directly below the bonding pad of the light-receiving element. Therefore, it is possible to prevent the light-emitting element from being damaged when the bonding wire is attached to the bonding pad. 
     According to a second aspect of the embodiment, 
     the light-emitting element may be installed on the second surface with a first reflecting part interposed between, the first reflecting part adapted for reflecting light emitted by the light-emitting element and 
     the bonding wire may be attached to the bonding pad while the position directly below the bonding pad is supported by the first reflecting part. 
     Thus, adding the first reflecting part to the light-emitting element makes it possible to support the position directly below the bonding pad of the light-receiving element using the first reflecting part and a jig or a similar tool. Therefore, the bonding wire can be attached to the bonding pad in a reliable manner. Also, the first reflecting part makes it possible to prevent the jig from coming into contact with the light-emitting element, and as a result, it is possible to prevent the light-emitting element from being damaged. 
     A third aspect of the embodiment relates to an optical device, characterized in comprising: 
     a substrate having a first surface and a second surface that is opposite the first surface; 
     a light-emitting element having a first center, the light-emitting element being installed on the second surface; and 
     a light-receiving element having a second center, the light-receiving element being installed on the first surface; wherein 
     at least a part of the light-emitting element is arranged at a position that overlaps the light-receiving element with respect to a plan view; 
     the light-receiving element installed subsequent to the light-emitting element has a bonding pad; 
     the bonding pad is provided at a position that is displaced relative to the second center towards a first direction with respect to the plan view; and 
     the first center is provided at a position that is displaced relative to the second center towards a second direction, which is opposite the first direction, with respect to the plan view. 
     According to the third aspect of the embodiment, the bonding pad of the light-receiving element is provided to the position that is displaced relative to a center of the light-receiving element (i.e., the second center) towards the first direction with respect to the plan view, and a center of the light-emitting element (i.e., the first center) is displaced relative to the center of the light-receiving element (i.e., the second center) towards the second direction with respect to the plan view. Therefore, the bonding wire can be attached to the bonding pad in a reliable manner. 
     According to a fourth aspect of the embodiment, 
     the light-emitting element may have a rectangular profile with respect to the plan view; wherein 
     one side of the rectangle may be tangent to a circle having a given radius and having a center on the bonding pad with respect to the plan view. 
     Thus, the light-emitting element may be separated from the position directly below the bonding pad of the light-receiving element by the given radius. Therefore, a space can be created at the position directly below the bonding pad of the light-receiving element. 
     According to a fifth aspect of the embodiment, 
     the light-emitting element may have a rectangular profile with respect to the plan view; wherein 
     one side of the rectangle may be perpendicular to a direction in which the first center and the second center are connected, with respect to the plan view. 
     Thus, the light-emitting element can be separated from the position directly below the bonding pad of the light-receiving element in an effective manner. Therefore, a space can be created at the position directly below the bonding pad of the light-receiving element. 
     According to a sixth aspect of the embodiment, the entirety of the light-emitting element may be arranged at a position at which there is a complete overlapping of the light-receiving element with respect to the plan view. 
     Thus, the light-emitting element completely overlaps the light-receiving element with respect to the plan view, and whereby light can readily reach the light-receiving element. Specifically, a light-blocking region formed by the light-emitting element overlaps a light-blocking region formed by the light-receiving element, and a light-blocking region as a whole corresponds only to the light-blocking region formed by the light-receiving element. 
     According to a seventh aspect of the embodiment, the optical device may further comprise a first reflecting part for reflecting light emitted by the light-emitting element, the first reflecting part having a third center, wherein the third center may coincide with the first center with respect to the plan view. 
     Thus adding the first reflecting part to the light-emitting element makes it possible to support the position directly below the bonding pad of the light-receiving element with the first reflecting part and a jig or a similar tool. Therefore, the bonding wire can be attached to the bonding pad in a reliable manner. 
     An eighth aspect of the embodiment relates to a biological information detector, characterized in comprising: 
     the optical device described above; 
     a contact part formed from a material that is transparent with respect to a wavelength of light emitted by the light-emitting element, the contact part having a contact surface in contact with a test subject; and 
     a second reflecting part for reflecting light having biological information; wherein 
     the light-emitting element emits light directed at a detection site of the test subject; 
     the light-receiving element receives light having biological information, the light being light emitted by the light-emitting element and reflected at the detection site; 
     the substrate is a flexible substrate formed from a material that is transparent with respect to the wavelength of light emitted by the light-emitting element; and 
     the biological information is a pulse rate. 
     According to the eighth aspect, applying an optical device to a biological information detector makes it possible to provide a biological information detector (i.e., a pulse rate monitor) in which, when the bonding wire is attached to the bonding pad, the attaching can be performed. 
     The entire disclosure of Japanese Patent Application No. 2010-33058, filed Feb. 18, 2010 is expressly incorporated by reference herein.