Combined optical and electrical interconnection module and method for producing same

A combined optical and electrical interconnection module includes a flat cable comprising an optical transmission line and an electrical wire, and a printed circuit board including a light receiving module for receiving optical signals and/or a light sending module for sending optical signals and an optical waveguide for the optical signals to be transmitted therethrough or an optical block for bending the optical paths of the optical signals. The printed circuit board is electrically and optically connected to both ends or one end of the flat cable.

The present application is based on Japanese patent application No. 2009-199589 filed on Aug. 31, 2009, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a combined optical and electrical interconnection module, in which optical transmission lines for transmitting optical signals, and electrical wirings for transmitting electrical signals are combined together, to be built in an information processing device, such as a large screen imaging device, and used for signal transmission therein, or used for signal transmission between information processing devices, such as servers.

2. Description of the Related Art

In recent years, with increasing display resolution, with increasing screen size, and with increasing data amount to be managed by information transmission devices or storage devices, there have been increasing demands for high speed transmission lines capable of long distance and high speed transmission of data. As high speed transmission lines, there have been used coaxial cables having a shield function, or differential transmission lines comprising a pair of differential lines in a shield, but the transmission distance thereof has been limited due to problems of noise or skew.

As a solution to this, there has been an optical transmission method that provides optical transmission lines in portions which transfer information signals, such as between an information processing device (a main unit) and a monitor, or between servers.

As a device used for these optical transmissions, there has been a combined optical and electrical cable with an optical fiber and an electrical cable combined together. The combined optical and electrical cable is, at both ends thereof, provided with an optical device such as an LD (laser diode) or a PD (photodiode), an IC (integrated circuit) for driving the optical device, and an electrical connector for connecting to an information transmission device or a storage device.

SUMMARY OF THE INVENTION

When a flexible printed circuit board is used as the combined optical and electrical wiring cable, the flexible printed circuit board produced has however been limited in size, due to resist patterning using a mask and subsequent copper layer etching to define a copper pattern which serves as an electrical wiring pattern. It has therefore been difficult to produce the long scale flexible printed circuit boards, which are 1 or more meter long, for example. Also, its electrical wiring has large resistance due to the copper layer used being thin (approximately 6-50 μm thick), and when the entire circuit is long, the electrical wiring resistance has been innegligible. Further, the large resistance of the electrical wiring has made large (a few hundreds of mA or more) electrical current signal transmission difficult.

Also, in the case of an optical waveguide using a polymeric material (polymer or the like) for the optical transmission lines, a transmission loss of approximately 0.1 dB/cm has occurred. At transmission distances of 0.3 m or more, this has increased the optical transmission loss, and in particularly, the transmission distance exceeding 1 m has made practical implementation difficult. Also, the polymeric material (polymer or the like) used is expensive compared with general silica glass based optical fibers, and therefore costly when its amount used is increased in order to make the transmission distance long.

Accordingly, it is an object of the present invention to provide a combined optical and electrical interconnection module, capable of low cost, low loss, and long scale optical signal transmission, and large electrical current signal transmission.(1) According to one embodiment of the invention, a combined optical and electrical interconnection module comprises:

a flat cable comprising an optical transmission line and an electrical wire; and

a printed circuit board comprising a light receiving module for receiving optical signals and/or a light sending module for sending optical signals, and an optical waveguide for the optical signals to be transmitted therethrough,

wherein the printed circuit board is electrically and optically connected to both ends or one end of the flat cable.(2) According to another embodiment of the invention, a combined optical and electrical interconnection module comprises:

a flat cable comprising an optical transmission line and an electrical wire; and

a printed circuit board comprising a light receiving module for receiving optical signals and/or a light sending module for sending optical signals, and an optical block for bending the optical paths of the optical signals,

wherein the printed circuit board is electrically and optically connected to both ends or one end of the flat cable.

In the above embodiments (1) and (2) of the invention, the following modifications and changes can be made.

(i) The printed circuit board further comprises an optical transmission line groove for being engaged with a portion of the optical transmission line of the flat cable, an electrical wiring pattern for being electrically connected with the electrical wire of the flat cable, and an electrical wiring groove formed in an upper side of the printed circuit board relative to the electrical wiring pattern, the upper side being formed with the optical waveguide.

(ii) The printed circuit board further comprises an optical transmission line groove for being engaged with a portion of the optical transmission line of the flat cable, an electrical wiring pattern for being electrically connected with the electrical wire of the flat cable, and an electrical wiring groove formed in an upper side of the printed circuit board relative to the electrical wiring pattern, the upper side being formed with the optical transmission line groove.

(iii) The printed circuit board further comprises an electrical connector at its opposite end face to its end face with the optical transmission line groove formed therein, the electrical connector being insertable into or removable from an electrical connector disposed in an external device.

(iv) The optical waveguide or the optical block is disposed in the middle in the width direction thereof, the optical transmission line is disposed in the middle in the width direction thereof, and the electrical wiring wire is disposed on both sides of the printed circuit board and the flat cable.

(v) The printed circuit board is not more than 5 cm in length, and the optical transmission line of the flat cable is not less than 20 cm in length.(3) According to another embodiment of the invention, a method for producing a combined optical and electrical interconnection module comprises:

arranging a plurality of optical transmission lines in its middle, and a plurality of electrical wires on both sides of the plural optical transmission lines;

pressure bonding thereto two coverings formed with openings having a specified gap therebetween, in such a manner as to sandwich upper and lower surfaces of the optical transmission lines and the electrical wires between the two coverings, to produce a flat cable;

removing portions of the optical transmission lines and the electrical wires in the openings in the flat cable formed with the openings having the specified gap therebetween;

removing the coverings on the optical transmission lines and the electrical wires in the openings in the flat cable to bare the optical transmission lines and the electrical wires to protrude from end faces of the flat cable;

structuring a printed circuit board, the printed circuit board having electrical wiring layers laminated with an insulating layer therebetween, the laminated electrical wiring layers being electrically connected with each other through a through hole, a surface of one of the electrical wiring layers being formed with an optical waveguide layer for optical signals to be transmitted therethrough;

forming in a portion of the optical waveguide a reflective portion for bending the optical paths of the optical signals, and mounting, on a surface of an other of the electrical wiring layers above the reflective portion, a light receiving module for receiving optical signals and/or a light sending module for sending optical signals;

forming optical transmission line grooves in the printed circuit board, to be engaged onto the optical transmission lines respectively protruding from the flat cable, and thereby connected and fixed thereto with an optical adhesive, to optically connect the light receiving module and/or the light sending module and the optical transmission lines;

forming an electrical connector at an opposite end face of the printed circuit board to its end face with the optical transmission line grooves formed therein;

forming, in the printed circuit board, electrical wiring grooves and electrical wiring patterns therein, to regulate the electrical wires of the flat cable to be positioned into the electrical wiring grooves, and thereby electrically connected and fixed to the electrical wiring patterns, respectively, with solder or a conductive adhesive;

after the joining of the flat cable and the printed circuit board, covering the printed circuit board and a portion of the flat cable with a protective member; and

cutting the printed circuit board between the light receiving module or the light sending module and the light sending module or the light receiving module.

According to one embodiment of the invention, an optical fiber is mostly used as an optical transmission line and an optical waveguide of a polymeric material (polymer or the like) is used only a few cm long, so that optical signal can be transmitted at low loss and low cost, even at entire transmission distances of 0.3 m or more. Especially when the optical transmission distance exceeds 1 m, that effect is significant.

Also, electrical signals are transmitted through an electrical wire or cable disposed in a flexible flat cable, so that large (a few hundreds of mA or more) electrical current signal can be transmitted therethrough.

A combined optical and electrical interconnection module is structured to electrically and optically connect a printed circuit board mounted with a light receiving module for receiving optical signals and/or a light sending module for sending optical signals, to the flat cable comprising the optical transmission line and the electrical wire, therefore eliminating a need for wire bonding, and thereby allowing parasitic capacitances to be reduced. This permits transmission at high speeds of 5 Gbit/sec or more. Also, an optical transmission line groove and an electrical wiring groove formed in the flexible printed board are engaged onto the optical fiber and the electrical wire respectively extending from both the ends of the flat cable, thereby regulating the optical fiber and the electrical wire to be positioned, connected and fixed into the optical transmission line groove and the electrical wiring groove in such a manner that the optical transmission line groove and the electrical wiring groove overlap the optical fiber and the electrical wire respectively, therefore allowing the easy and high precision connection thereof.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Below are described the preferred embodiments of the invention in conjunction with the accompanying drawings, in which like parts are given like reference numerals.

Combined Optical and Electrical Interconnection Module100Structure

FIG. 1is a top view showing a combined optical and electrical interconnection module100, andFIG. 2is a transverse cross-sectional view showing the same.

A flat cable (FFC)101is flexible (has flexibility), and is constructed of four optical fibers102for optical transmission lines, and eight electrical wires103for power supply and electrical signal transmission. The flat cable101is structured to be protected by being covered with an outer insulating laminate film201made of a material such as a polyetherimide, a polyethylene terephthalate, or the like. The optical fibers102are a single mode optical fiber, but may use a holey fiber, which allows a reduced optical loss even due to small bend, and an increased degree of freedom of wiring, therefore aiding in wiring. On the other hand, the use of a multimode optical fiber aids in optical coupling to a light emitting device (laser diode) because the core diameter of the multimode optical fiber is 50 μm or more.

The electrical wires103are made of a metallic material such as a copper or the like, and formed in a flat rectangular cross-sectional shape being, for example, 0.1 mm thick and 0.2 mm wide. The 0.1 mm thick permits large (a few hundreds of mA) electrical current signal transmission.

Flexible printed boards104aand104bhave flexibility, and are connected to both ends respectively of the flat cable101. The flexible printed boards104aand104b(seeFIG. 3) comprise a copper layer formed of an electrical wiring301for electrical signal transmission, a polyimide layer for serving as an insulating layer302, and an optical waveguide layer303for optical signal transmission. The electrical wiring301is formed by patterning using a mask. The optical waveguide303for optical signal transmission uses a polymeric material (polymer or the like), and has flexibility. The pattern of the optical waveguide303may be formed by patterning using a mask, or by a mold.

Operation of the Combined Optical and Electrical Interconnection Module100

FIG. 4is a diagram for explaining a use of the combined optical and electrical interconnection module100. In this use, the signal transmission between external devices400and402is performed through the combined optical and electrical interconnection module100.

Though not shown, in another use of the combined optical and electrical interconnection module100, the combined optical and electrical interconnection module100may be used for signal transmission inside an information processing device. The information processing device may correspond to any of the external devices400and402inFIG. 4.

Next is described a flow of the signal transmission in conjunction withFIGS. 1 to 4.

An electrical connector401of the external device400is connected with a card edge connector304of the flexible printed board104aconnected to the left end of the flat cable101. Likewise, an electrical connector403of the external device402is connected with a card edge connector304bof the flexible printed board104bconnected to the right end of the flat cable101. An electrical signal is sent from the external device400through the electrical connector401to the flexible printed board104a, and transmitted to an light transmitting module105mounted on the flexible printed board104a. The light transmitting module105comprises a four VCSEL (vertical cavity surface emitting laser diode) array106and a laser driver IC (integrated circuit)107for driving the VCSEL array106. The electrical signal transmitted from the external device400is converted by the VCSEL array106into optical signals202. The respective optical paths of the optical signals202emitted from the VCSEL array106are bent through 90 degrees by a reflective portion305, and coupled to an optical waveguide303disposed in the flexible printed board104a. The optical signals202are propagated through the optical waveguide303, and transmitted through the optical fibers102respectively of the flat cable101, and coupled to an optical waveguide303bconnected to the right end of the flat cable101. The optical signals202are propagated through the optical waveguide303b, and their respective optical paths are bent through 90 degrees by a reflective portion305bformed in the optical waveguide303b, and transmitted into a light receiving module108mounted on the flexible printed board104b. The light receiving module108comprises a four PD (photodiode) array109and a preamplifier IC110. The received optical signals are converted by the PD array109into electrical signals. Those electrical signals are amplified by the preamplifier IC110, and one way transmitted through the card edge connector304binto the external device402.

In the above embodiment, since the four VCSEL array106and the four PD array109have been disposed, the simultaneous optical transmissions are possible for the four channels.

End Face Structure of the Flexible Printed Board104(104a,104b)

FIG. 5shows a structure of an end face of the flexible printed board104(104a,104b) to be connected with the flat cable101. In one surface of each of the flexible printed boards104aand104bare formed optical transmission line grooves306for the optical fibers102or the like, and a reflective portion305(305b) for causing the optical signals202from the optical fibers102to be reflected and transmitted into the light receiving module108, or for causing the optical signals202from the light transmitting module105to be reflected and transmitted into the optical fibers102. The reflective portion305(305b) is defined as a V-shaped groove in the optical waveguide303(303b) disposed in the surface formed with the optical transmission line grooves306of the flexible printed board104(104a,104b), where the V-shaped groove is formed by V-shape dicing the surface of the flexible printed board104(104a,104b), to form a surface slanted at 45 degrees to a perpendicular to the surface of the flexible printed board104(104a,104b), in the optical waveguide303(303b) disposed in the flexible printed board104(104a,104b). This reflective portion305(305b) allows the optical paths to be bent through 90 degrees. Further, this reflective portion305(305b) may be metallized with a metallic thin film (gold, aluminum, or the like), which is effective in enhancing reflectivity and thereby reducing optical signal loss due to reflection. The reflective portion305(305b) formed with the metallic thin film may be filled with a resin therein to thereby prevent the metallic thin film from peeling off.

Referring toFIG. 2, the opposite surfaces of the flexible printed boards104aand104bto the surfaces formed with the reflective portions305and305brespectively are mounted with the VCSEL array106or the PD array109in an extension of an optical axis of each of the reflective portions305and305b.

Also, referring toFIG. 3, the flexible printed boards104aand104bare each formed with the optical transmission line grooves306, and with electrical wiring patterns500to connect with the electrical wires103of the flat cable101. The flexible printed boards104aand104bare each structured to have two electrical wiring301layers laminated with a polyimide layer serving as an insulating layer302therebetween. The two electrical wiring301layers are electrically connected with each other via a conductive material, such as solder or the like, injected or disposed in a through hole307formed in the flexible printed boards104aand104b.

InFIG. 3, the electrical wiring patterns500are then structured to be disposed in the inner side of the flexible printed boards104aand104brelative to the optical waveguide303(303b). This causes the optical waveguide303(303b) layer lying in the lower (inFIG. 5, upper) side of the flexible printed boards104aand104brelative to the electrical wiring patterns500to obstruct the connection of the electrical wires103of the flat cable101to the electrical wiring patterns500. Accordingly, the optical waveguide303(303b) layer is formed by such patterning that no optical waveguide303(303b) layer lies in the lower (inFIG. 5, upper) side of the flexible printed boards104aand104brelative to the electrical wiring patterns500. This allows electrical wiring grooves501but no optical waveguide303(303b) layer to be formed in the lower (inFIG. 5, upper) side of the flexible printed boards104aand104brelative to the electrical wiring patterns500. This results in the exposed electrical wiring patterns500structure (seeFIG. 5). This allows the connection almost without bending of the electrical wires103of the flat cable101to the electrical wiring patterns500. The connection of the electrical wires103of the flat cable101to the electrical wiring patterns500is therefore facilitated. Further, because of not bending, the wiring is the shortest, and therefore has an advantage in high speed transmission.

The optical transmission line grooves306formed in the flexible printed boards104aand104bare engaged onto the optical fibers102, respectively, protruding from the flat cable101, thereby allowing the flexible printed boards104aand104bto be connected to the optical fibers102in such a manner that the flexible printed boards104aand104boverlap the optical fibers102. In this case, at the same time, the electrical wires103are also regulated to be positioned into the electrical wiring grooves501respectively, thereby allowing the electrical wires103to be positioned and connected to the electrical wiring patterns500. In this manner, this structure allows the easy and high precision connection of the flat cable101and the flexible printed boards104aand104b.

Referring toFIG. 1, the flexible printed boards104aand104bare each structured to have the optical waveguide303disposed in the middle in the width direction thereof, and the electrical wirings301disposed in the upper and lower sides, respectively, of the flexible printed board104aor104brelative to the optical waveguide303. Likewise, the flat cable101is structured to have the optical fibers102disposed in the middle in the width direction thereof, and the electrical wires103(103a) and103(103b) disposed in the upper and lower sides, respectively, of the flat cable101relative to the optical fibers102. For example, the electrical wires103aare disposed in the upper side of the flat cable101ofFIG. 1, while the electrical wires103bfor slow electrical signal transmission are disposed in the lower side thereof, and the space between the electrical wires103aand the electrical wires103bfor slow electrical signals is widen, thereby allowing the reduction of the effect of electrical noise.

As mentioned above, the electrical wires103aand103bof the flat cable101are for power supply and for slow electrical signal transmission, and in this embodiment, comprise four power wires (two grounds, one plus power supply, and one minus power supply), and four slow electrical signal wires (transmission speed: 10 Kbit/sec or less). Further, of the four slow electrical signal wires103b, the two middle electrical signal wires may be slow electrical signal wires, and the two side electrical signal wires may be ground wires. This configuration aids in impedance matching.

Referring toFIG. 5, the optical transmission line grooves306formed in the optical waveguide303layer are spaced at the same pitch as the pitch at which are disposed the optical fibers102in the flat cable101. In this embodiment, the pitch is 500 μm. Further, the flexible printed boards104aand104bare each formed with the electrical wiring patterns500at the same pitch and positions as the pitch and positions of the electrical wires103aand103bof the flat cable101.

Referring toFIGS. 1 and 2, on the other hand, the flexible printed boards104aand104bare formed with the electrical card edge connectors304and304brespectively at the opposite end face to the end face with the optical transmission line grooves306formed therein. The card edge connectors304and304bfor the flexible printed boards104aand104bmay then be inserted into or removed from the electrical connectors401and403provided for the external devices400and402respectively (seeFIG. 4).

Also, referring toFIG. 2, with an adhesive, a protective sheet203is mounted on the opposite surface of each of the flexible printed boards104aand104bto the surface thereof with the light transmitting module105or the light receiving module108mounted thereon. The protective sheets203are mounted to cover the entire surfaces205and205bof the flexible printed boards104aand104band the flat cable101portions (L=2 to 5 mm) respectively, and thereby ensure the strength and solidity thereof. This permits the sufficient strength thereof during attaching to or detaching from the electrical connectors401and403. The protective sheet203may be formed of a resin material, a metallic material, a plastic material, or the like, and have a thickness which satisfies strength requirements, and in the case of a resin, be 0.2 mm or more thick.

On the side of each of the flexible printed boards104aand104bon which is mounted the light transmitting module105or the light receiving module108, on the other hand, the entire flexible printed boards104aand104band the flat cable101portions are covered with a laminate204, excluding the card edge connectors304and304b. The laminate204material may use a PET (polyethylene terephthalate), a PI (polyimide), or the like. Here, the laminate204may be replaced by resin fill.

The flexible printed boards104aand104bare formed with circuit patterns (not shown) for electrical signal transmission between the light transmitting module105or the light receiving module108and the flexible printed boards104aand104b, to electrically connect the electrode patterns formed on the flexible printed boards104aand104bvia solder or the like and the light transmitting module105or the light receiving module108(seeFIG. 2).

The light transmitting module105or the light receiving module108and electronic components can therefore be electrically connected to the flexible printed boards104aand104bwithout using wire bonding, and parasitic capacitances are thereby reduced. This has an advantage especially in transmission at high speeds of 5 Gbit/sec or more.

Also, the length F of the flexible printed boards104aand104bis as short as on the order of 2 to 3 cm, preferably not more than 5 cm. A small amount of polymeric material (polymer or the like) may therefore be used for producing the optical waveguide303, and the low cost production thereof is possible. Accordingly, the optical path length of the optical waveguide303is also short, and its optical transmission loss level is negligible (on the order of 0.1 to 0.2 dB). Most of the optical transmission is then performed through the optical fibers102disposed in the flat cable101. The transmission loss of the optical fibers102is less than 0.1 dB/km, and therefore negligible at optical transmission line lengths of up to approximately 1 km. The invention is suitable for the combined optical and electrical interconnection module100having a length of not less than 0.3 m, which is low in optical transmission loss and which can be provided at a low cost. In the 0.3 m shortest combined optical and electrical interconnection module100, the total length of the flexible printed boards104aand104bis not more than 0.1 m, while the rest is the length (not less than 0.2 m) of the optical fibers102disposed in the flat cable101. At lengths of the combined optical and electrical interconnection module100of less than 0.3 m, the effect of reducing the optical transmission loss and cost is unlikely to be exhibited, compared with flexible optical waveguides in which all optical transmission lines are fabricated from a polymeric material. On the other hand, the upper limit of the length of the combined optical and electrical interconnection module100is as sufficient as on the order of 100 m in view of transmission between servers, but the invention structure allows the upper limit applied of the length of the combined optical and electrical interconnection module100to be up to approximately 1 km, because of the small transmission loss of the optical fibers102as mentioned previously.

Combined Optical and Electrical Interconnection Module100Producing Method

Next is described a process for producing the combined optical and electrical interconnection module100in reference toFIGS. 6A-6G.

Referring toFIG. 6A, the four optical fibers102to serve as optical transmission lines are arranged in the middle, and the four electrical wires103are on both sides of the optical fibers102.

Referring toFIG. 6B, this is followed by forming two coverings (laminates) formed with openings601having a specified gap G (e.g. 1 m) therebetween, in such a manner as to sandwich the upper and lower surfaces of the four optical fibers102and the eight electrical wires103ofFIG. 6Abetween the two coverings (laminates). This results in a flat cable602formed with the openings601having the specified gap G (e.g. 1 m) therebetween.

Referring toFIG. 6C, this is followed by removing portions of the optical fibers102and the electrical wires103in the openings601in the flat cable602formed with the openings601having the specified gap G therebetween.

The flat cable602is structured to have bare protrusions604of the optical fibers102and the electrical wires103in the openings601, which are caused to protrude from the end faces of the flat cable101, by removing a specified length (on the order of 2 to 5 mm as one example) of the coverings (laminates) on the optical fibers102and the electrical wires103in the openings601.

Referring toFIGS. 6D,6E and8, on the other hand, using solder, a conductive adhesive or the like, electrode patterns formed on the flexible printed board104(104a,104b) are electrically connected to the light transmitting module105or the light receiving module108and electronic components. The flexible printed board104(104a,104b) is then formed with the optical transmission line grooves306and the electrical wiring grooves501. The methods for producing these are as described in the description of the end face structure of the flexible printed board104(104a,104b). The electrical wiring grooves501are formed for the optical waveguide303(303b) side electrical wiring patterns500. This results in the exposed electrical wiring patterns500structure without the optical waveguide303(303b) layer being formed in the upper side of the flexible printed board104(104a,104b) relative to the optical waveguide303(303b) side electrical wiring patterns500.

Referring toFIG. 6F, this is followed by overlapping and connecting the surface of the flexible printed board104(104a,104b), which is formed with the optical transmission line grooves306and the electrical wiring patterns500, and the optical fibers102and the electrical wires103.

The exposed optical fibers102of the flat cable101are engaged into the optical transmission line grooves306respectively formed in the flexible printed board104(104a,104b), thereby optically connecting the light transmitting module105or the light receiving module108and the optical fibers102, while the electrical wires103of the flat cable101are regulated to be positioned into the electrical wiring grooves501respectively formed in the flexible printed board104(104a,104b), thereby allowing the electrical wires103to be positioned and connected to the electrical wiring patterns500, using solder, a conductive adhesive or the like.

Also, the optical transmission line grooves306and the optical fibers102are connected and fixed to each other respectively with an optical transparent adhesive (ultraviolet cured resin).

The joining of the flat cable101and the flexible printed board104(104a,104b) is followed by covering and protecting the joined portions thereof with the protective sheets203below and the laminates204above respectively. The protective sheets203are sized to support the entire flexible printed board104(104a,104b) and the flat cable101portions respectively.

Referring toFIG. 6G, the coupled portions of the flat cable101and the flexible printed board104(104a,104b) are laminated (covered) from above and below to cover the entire flexible printed board104(104a,104b) and the flat cable101portions. The covering of the coupled portions of the flat cable101and the flexible printed board104(104a,104b) is followed by cutting substantially in the middle of each array of the light transmitting module105column and the light receiving module108column mounted on the flexible printed boards104aand104brespectively, resulting in the completed combined optical and electrical interconnection module100.

The combined optical and electrical interconnection module100can be fabricated to have any length by varying the gap G between the openings601.

One or more light transmitting modules105and one or more light receiving modules108are mounted on the flexible printed boards104aand104bconnected to both the ends respectively of the flat cable101, thereby allowing the two-way transmitting/receiving of optical signals for one or more channels. For example, as shown inFIG. 1, the flexible printed boards104aand104bmay be mounted with the four channel VCSEL array106and the four channel PD array109respectively, and the number of the optical fibers102of the flat cable101may be eight, thereby allowing the two-way transmitting and receiving of optical signals for four channels. Further, the card edge connectors304and304bare structured to be rotationally symmetric about the central axis in the width direction of the circuits. In the use of the combined optical and electrical interconnection module100ofFIG. 4, the flexible printed board104amounted with only the light transmitting module105has to be always connected to the electrical connector401of the transmitting external device400, while the flexible printed board104bmounted with only the light receiving module108has to be always connected to the electrical connector403of the receiving external device402. However, the structures of the flexible printed boards104aand104bmay be modified to be used for either of the external device400or402, in other words, may be used regardless of directionality of signals. Also, transmitting and receiving are possible, and therefore two-way transmission is possible.

The flexible printed boards104aand104bmay be replaced by rigid (less flexible) printed boards (not shown) formed of a glass epoxy material. In this case, an optical waveguide layer is formed over one surface of each of the rigid printed boards, using a polymeric material (polymer or the like), in the same manner as the case of the flexible printed boards104aand104b. In the optical waveguide layer is then formed a reflective surface, and above the reflective surface is mounted the light transmitting module105or the light receiving module108, in the same manner as the case of the flexible printed boards104aand104b. The use of the rigid printed boards allows sufficient strength to be maintained even though using no protective sheet. Further, the rigid printed boards may be replaced by silicon boards. When the silicon boards are used, a glass optical waveguide layer is formed over the silicon boards using CVD (chemical vapor deposition). The use of the silicon boards allows the combined optical and electrical interconnection module100to have excellence in dissipating the heat of the VCSEL. As described above, the invention allows the use of the printed boards, such as the flexible printed boards, the rigid printed boards, the silicon boards or the like, formed with the optical patterns (optical waveguide layers) and the electrical patterns (electrical wiring layers) thereon.

Modification to the Embodiment

FIGS. 7A and 7Bshow a modification in which flexible printed boards104cand104dare mounted with optical blocks700and700brespectively. The flexible printed boards104cand104dare each structured to have an insulating layer302, which transmits optical signals, between copper layers formed of electrical wirings301respectively for electrical signal transmission. The flexible printed boards104cand104dare significantly different from the flexible printed boards104aand104bshown inFIG. 2, in that the flexible printed boards104cand104dhave no optical waveguides303and303b, but optical blocks700and700bdisposed in place of the reflective portions305and305bof the optical waveguides303and303b, respectively. The optical blocks700and700bare formed of an optical material such as a resin, a glass material, or the like. The optical block700(700b) is formed with a surface slanted at 45 degrees relative to optical signals202emitted from the VCSEL array106, to serve to bend their respective optical paths through 90 degrees. The slanted surface of the optical block700(700b) is metallized with a metallic thin film (gold, aluminum, or the like).

The flexible printed board104c(104d) surface mounted with the optical block700(700b) is filled with a resin, to which a protective sheet (not shown) is bonded for reinforcing. Further, it is preferred to extend the reinforcing sheet structure to a portion of the flat cable101, to thereby allow the reinforced portion connecting the flat cable101and the flexible printed board104c(104d).

Referring toFIG. 7B, the flexible printed board104cmounted with the optical block700is formed to have optical fiber positioning patterns701for positioning the optical fibers102on the same surface and with the same copper patterns as electrical wiring patterns500. Further, optical block positioning patterns702for positioning the optical block700are also formed on the same surface and with the same copper patterns as the electrical wiring patterns500.

The respective optical paths of the optical signals202emitted from the VCSEL array106are bent through 90 degrees by the optical block700, so that the optical signals202are transmitted through the optical fibers102respectively of the flat cable101mounted to the flexible printed board104c, and are reflected off the slanted surface of the optical block700bmounted to the flexible printed board104dconnected to the right end of the flat cable101, and are received in the PD array109. The other signal processing is the same as inFIG. 2.

Since no optical waveguides303and303blayers are formed, and the optical paths are bent by the optical blocks700and700b, and the optical signals202are spatially propagated into the optical fibers102, the producing process can be simplified. Further, since the optical fiber positioning patterns701and the optical block positioning patterns702are formed on the same surface and with the same copper patterns as the electrical wiring patterns500, the producing process can be simplified.

Although in the above embodiments, both the ends of the flat cable101are provided with the flexible printed boards104aand104b(or104cand104d) respectively, only one end of the flat cable101may be provided with the flexible printed board104aor104b(or104cor104d), and the other end of the flat cable101may be in the open state of the optical fibers102and the electrical wires103aand103b, or be provided with an optical connector (not shown) attached to the optical fibers102and an electrical connector (not shown) attached to the electrical wires103aand103b. When the optical fibers102and the electrical wires103aand103bare open at the other end of the flat cable101, the open ends of the optical fibers102may be connected with the ends of other optical fibers (not shown) respectively by a mechanical splice or the like, while the open ends of the electrical wires103aand103bmay also be connected to specified electrical terminals of another printed board not shown. Also, when the other end of the flat cable101is provided with an optical connector (not shown) for the optical fibers102and an electrical connector (not shown) for the electrical wires103aand103b, the optical connector and the electrical connector may respectively be connected to another optical connector not shown and an electrical connector not shown.

The invention is not limited to the above embodiments, but, for example, there may be any numbers of the optical fibers102, the arrayed PDs109, the arrayed VCSELs106, the electrical wires103aand103b. Further, various alterations should be apparent without departing from the spirit and scope of the invention.