US 7425286 B2
An optical waveguide apparatus includes an optical waveguide, such as an optical sheet of a two-dimensional slab waveguide, and an appropriately-shaped plated structure provided in the optical waveguide. Typically, the plated structure is constructed so as to serve as an optical-path converting unit for optically coupling the optical waveguide and an optical device, which is to be provided on or in the vicinity of the optical waveguide, or as at least a part of a via penetrating the optical waveguide.
1. A method for making an optical waveguide apparatus, which includes an optical waveguide and an optical path converter provided in the optical waveguide, the method comprising the steps of:
preparing a substrate having a conductor;
forming a first resin material layer on the conductor;
forming a window for exposing a portion of the conductor by removing a portion of the first resin material; and
forming the optical path converter made of metal on the window and on the first resin material through the window by electroplating; and
forming a second resin material layer as a core layer of the optical waveguide on the optical path converter,
wherein the optical path converter has a semispherical shape, horizontal semicylindrical shape, or semicylindrical shape having a concave surface on its recessed portion.
2. The method according to
3. The method according to
4. The method according to
This application is a division of application Ser. No. 10/388,431, filed Mar. 17, 2003, which is based on Japanese Patent Application No. 2002-82295, filed Mar. 25, 2002. The entire disclosures of these applications are incorporated herein by reference.
1. Field of the Invention
The present invention relates to an optical waveguide apparatus that includes an optical waveguide, such as an optical waveguide sheet, apparatuses using the optical waveguide apparatus, and a method for making the optical waveguide apparatus. As disclosed herein, the optical waveguide sheet or the optical sheet is a waveguide that permits, for example, an optical transmission from a light-transmitting unit that is not directed at a light-receiving unit, as well as an optical transmission from the light-transmitting unit to the light-receiving unit.
2. Description of the Related Background Art
In recent years, performance of portable equipment, such as personal computers, cellular phones and personal digital assistants (PDAs), and digital audio-visual devices, significantly improved. Different means for interconnecting this equipment are being developed using all kinds of frequency bands in both wireless and wire forms. Therefore, appropriate and prompt ways are needed to cope with malfunctions of digital equipment due to electromagnetic interference from electrical substrates (electromagnetic interference: EMI), external electrical waves (resistance), and signal errors resulting from defective connections (signal integrity (SI)). In view of these electromagnetic wave problems, products prior to shipment are required to meet the standards prescribed by the Radio Law. Development costs for taking these measures continuously increase. In this situation, the optical wiring or interconnection without any electromagnetic induction is expected to radically solve the above regulatory and technical problems.
Further, in the near future, high-speed interconnections will undoubtedly be incorporated into homes. Hence, there is a need to prevent the malfunctions and noise intervention even when high-speed electronic equipment is freely connected in a variety of ground environments. Also, in this respect, the optical interconnection is an effective means that can readily achieve an electrical isolation from the ground.
Various methods for the optical interconnections have been proposed.
In the structure of
It is an object of the present invention to provide an optical waveguide apparatus that includes an appropriately-shaped plated structure for, for example, facilitating an alignment between an optical device and an optical waveguide, such as an optical waveguide sheet, apparatuses including the optical waveguide apparatus, and a method for making the optical waveguide apparatus.
According to one aspect of the present invention, there is provided an optical waveguide apparatus that includes an optical waveguide and an appropriately-shaped plated structure provided in the optical waveguide. Typically, the plated structure is constructed so as to serve as an optical-path converting unit for optically coupling the optical waveguide, such as an optical sheet of a two-dimensional slab waveguide, and an optical device provided on or in the vicinity of the optical waveguide, as at least a part of a via penetrating the optical waveguide, as both a via and an optical path converting unit, or as an optical path converting unit for changing a direction or conditions of light propagating in the waveguide.
The following more specific structures are possible. The plated structure can be encased in the optical waveguide. The plated structure can have an approximately semispherical shape, an approximately horizontal semicylindrical shape, or an approximately horizontal semicylindrical shape having a concave surface on its recessed portion. A patterned metal usable for driving the optical device, and/or a patterned metal for electrical wiring can be further provided on the waveguide. The plated structure can have an approximately semispherical shape such that light emitted from a light-emitting device is reflected by the plated structure in all directions in the optical sheet to perform an optical transmission in the optical waveguide sheet in a broadcasting manner. The plated structure can have an approximately semispherical shape such that light propagating from any direction in the optical sheet is reflected by the plated structure toward a light-receiving device to be received thereby. The plated structure can have an approximately horizontal semicylindrical shape, or an approximately horizontal semicylindrical shape having a concave surface on its recessed portion such that light emitted from a light-emitting device is reflected by the plated structure in a set (predetermined) direction in the optical sheet to perform an optical transmission in the optical waveguide sheet in a set region. The plated structure can have an approximately horizontal semicylindrical shape, or an approximately horizontal semicylindrical shape having a concave surface on its recessed portion such that light propagating from a set direction in the optical sheet is reflected by the plated structure toward a light-receiving device to be received thereby. The optical sheet can include a line-shaped or linear waveguide for performing an optical transmission and reception along a set channel independent from another optical transmission and reception in the optical sheet. The optical waveguide apparatus can further include an optical device (light-emitting device or light-receiving device) provided on the optical waveguide. The plated structure can be located immediately below the optical device.
According to another aspect of the present invention, there is provided an optoelectrical mixture wiring apparatus that includes an electrical circuit substrate including a plurality of electronic devices and electrical wires for connecting the electronic devices to each other; and an optical circuit including: (a) a light-emitting device for converting an electrical signal from an electronic device into an optical signal, (b) the above-discussed optical waveguide apparatus of the present invention, and (c) a light-receiving device for converting an optical signal transmitted in the waveguide into an electrical signal. In the optoelectrical mixture wiring apparatus, the optical waveguide apparatus can be flexible so that it is approximately tightly stacked on the electrical circuit substrate. Further, at least one electrical circuit board and at least one optical circuit can be layered, and the optical waveguide apparatus can include a via for electrical wiring provided in the optical waveguide.
According to yet another aspect of the present invention, there is provided a high-speed optical serial bus in which a plurality of the optical waveguide apparatuses are layered, arranged in a lateral direction, or constructed in their combination form so as to connect multiple-bit wiring between electrical chips, such as CPUs and memories, and/or connect peripheral equipment, such as storing apparatuses or visual instruments.
According to still yet another aspect of the present invention, there is provided a method for making an optical waveguide apparatus, which includes an optical waveguide and a plated structure provided in the optical waveguide, having an appropriate shape, such as an approximately semispherical shape, an approximately horizontal semicylindrical shape, or an approximately semicylindrical shape with a concave surface on its recessed portion. The fabrication method includes a step of forming an electrode on a substrate, a step of patterning an electrode-exposing window having a set shape on the electrode, a step of selectively plating only on and around the window, and a step of coating the patterned and plated surface with a liquefied resin material. The window can have an approximately circular shape, an approximately rectangular shape, or an approximately rectangular shape with long sides each having a recessed central portion, whose diameter (or short side) and thickness are less than about a tenth of those of the plated structure. The electrode-exposing window is made sufficiently small in such a way that the plated structure can have a sufficiently upward-rising profile. The production method can further include a step of drying the resin material and a step of removing the substrate from the dried resin material to obtain the plated structure encased in the resin material. Alternately, in the fabrication method, the substrate can be an electrical circuit substrate, and the plated structure can be formed directly on the electrical circuit substrate such that an optoelectrical mixture substrate with the encasing resin material and electrical circuit substrate can be obtained.
More specifically, a protrusion of the optical-path converting unit or the like can be formed on the substrate (or cladding layer) by plating Ni, Sn, Cr, Cu, Au or the like, and a transparent resin of a waveguide core layer can be formed on the substrate or cladding layer by dipping, casting, spin-coating, or the like. Also, another cladding layer can be formed on the core layer, and a guide hole for mounting an optical device can be formed by photography and etching, molding, laser-beam processing, or the like. Further, an electrical wiring for flip-chip mounting a device can be formed. When an optical device is mounted in the vicinity of the plated structure and the resin core layer is then removed from the above substrate, the core layer with the plated structure encased therein can be obtained. Therefore, an optical waveguide apparatus with the plated structure (for example, the optical-path converting unit such as a metal mirror) encased at a desired location can be accomplished by simple processing at a relatively low cost.
Where a single two-dimensional slab waveguide is used, signal multiplexing is basically performed using time sharing, i.e., parallel-serial conversion. However, when a line-shaped waveguide (linear waveguide) or a thin bar-shaped waveguide for performing lateral spatial division is provided in the two-dimensional slab waveguide, parallel transmission with independent channels can be employed only for necessary lines.
When electrical wires are further formed on the optical sheet and the optical sheet has a bendable, flexible structure, a portion of the electrical wiring in an electrical board with large scale integration (LSI) or the like mounted thereon can be replaced by the optical wiring of the optical waveguide apparatus of the present invention. Accordingly, the EMI problem can be overcome by such an optoelectrical mixture apparatus at a relatively low cost without any extensive design alterations.
Further, when a plurality of signal interconnections are to be simultaneously executed, a plurality of layered optical waveguide apparatuses need only to be integrated with the electrical circuit board. Here, the electrical interconnection for driving the optical device can be constructed by mounting the optical device and the optical-path converting unit on the optical sheet and forming the via filled with a conductor in the stacked optical sheets. Thus, a multi-layer optoelectrical mixture wiring apparatus can be achieved at a relatively low cost.
These advantages, as well as others, will be more readily understood in connection with the following detailed description of the preferred embodiments and examples of the invention in connection with the drawings.
Embodiments of an optical waveguide apparatus of the present invention will be described with reference to
As a light source, a surface light-emitting device 6, such as an LED and a surface-emitting laser, is provided. A guide hole 8 for fitting the light-emitting device 6 therein is formed in the optical sheet. The shape of the guide hole 8 corresponds to the outer profile of the device 6 such that the device 6 can be guided in the hole 8 in a self-aligning manner. Metal wires are further formed on the optical sheet, and the end of each wire extends into the guide hole 8 such that electrodes 4 and 5 of the light emitting device 6 can be brought into contact with the ends of the metal wires when the device 6 is set in the hole 8. The surface light-emitting device 6 can be, for example, a vertical cavity surface-emitting laser (VCSEL) in which a GaAs/AlGaAs MQW (multi-quantum well) active layer, a spacer layer of a one-wavelength cavity, a pair of AlAs/AlGaAs DBR (distributed Bragg reflector) mirrors sandwiching the active layer are grown on a GaAs substrate using a crystal growth method such as MOCVD.
An approximately semispherical plated structure 3 for converting an optical path is formed at a location of the core layer 1 under the surface light-emitting device 6. When the light-emitting device 6 is set in the guide hole 8, the device 6 is aligned with the plated structure 3 such that light emitted from the device 6 can enter the optical sheet 12 through the plated structure 3. In this embodiment, a radiation center of the light-emitting device 6 is aligned right above the top of the semispherical plated structure 3 to transmit light from the light-emitting device 6 in all directions in the optical sheet 12 of the two-dimensional slab waveguide.
A portion of light coupled to the optical sheet 12 propagates as a light beam 9, as illustrated in
This embodiment, however, cannot be applied to simultaneous transmission of multiple bits. In this case, parallel signals need to be converted into a serial signal. Nevertheless, a highly-functional optoelectrical mixture substrate can be obtained by constructing an appropriate circuit design for replacing some signal lines, which require a solution of the EMI problem, with the optical sheet 12. In
A fabrication method of the optical waveguide apparatus of the first embodiment will be described with reference to
Plating can be performed using other metal, such as Cu, Cr, Au, or chemical compounds. A multi-layer plated structure of different materials can likewise be adopted. Further, the plated structure can also be formed by electroless plating. In a step shown in
A polymer core layer 26 is formed by dipping, molding, coating, or the like so as to cover the semispherical structure 25, as illustrated in
Electrodes and electrical wires 27 are metal wires made of aluminum, copper, or the like. These wires can be formed by forming a wiring pattern of Al, Cu, Ag, Au or the like using vacuum evaporation and lithography. The electrical wires 27 can also be formed in the following manner. A conductive paste of Cu, Ag, Au or the like is printed on the substrate by a screen printing method to form a circuit conductor pattern, and the circuit conductor is then formed by sintering or hardening the conductive paste. Alternatively, a metal foil, such as an electrolytic copper foil, is deposited and chemically etched using an etching resist with a desired pattern to form the circuit conductor pattern. Further, the interconnection can be formed with a conductive polymer that has a thermal expansion coefficient and an elastic constant sufficiently matching those of the polymer waveguide.
In mounting the light emitting or light-receiving device 28, the device can be flip-chip bonded on the optical sheet and brought into contact with the electrode 27 as follows. An Ag paste or a cream solder is coated on a predetermined location by printing or using a dispenser. The device 28 is inserted into the guide hole 30 and heated to a temperature of about 120° C. In
The electrical circuit board 37 has a multi-layer built-up structure, and electrical wires 34 and via holes 35 are highly densely formed therein. An RF circuit portion 36 for wireless communication is covered with a shield cover to prevent the electromagnetic interference. Conventionally, when the signal line is drawn out from the RF circuit portion, an antenna is likely to be created depending on the length of the signal line. Hence, due to the common-mode noise radiation, a malfunction of the circuit is caused, requiring a considerable amount of time to satisfy the regulations prescribed by the Radio Law. In this construction, since the signal interconnection is established using the above-discussed optical waveguide apparatus 40, no antenna is formed and unwanted radiation can be vastly reduced.
An optical device 32 is in contact with electrodes on the substrate 37. An electrical wiring 39 and an electrical device chip 33 can also be mounted on the optical sheet, if necessary. In this case, the optical sheet can be an optoelectrical mixture wiring substrate by itself. In the above discussion, the optical waveguide sheet is a flexible wiring substrate. However, a core layer having a thickness of about 1 mm can be injection-molded, and the optical sheet can be constructed as a rigid substrate.
In the second embodiment, a plated structure 59 for converting an optical path is formed by plating on the surface of an electrical circuit substrate 50 including electrical wires 51 and 53 and via wiring 52, similar to the first embodiment. The electrical circuit substrate 50 can be formed of glass epoxy, polyimide, ceramics, or the like, which can be used for an ordinary substrate. An optical layer 57 of a transparent polymer, such as PCZ, is formed on the circuit substrate 50, similar to the first embodiment. The optical interconnection is established when optical information from a light-emitting device 56 connected to an electrode 54 is transmitted through the optical layer 57 and the plated structures 59, and detected by a light-receiving device 55 connected to another electrode 54.
A plated structure 58 can be used as a via wiring penetrating the optical layer 57. Further, a plated structure 58′ can serve as both an optical-path converting unit and a via penetrating the optical sheet 57.
A method for making the second embodiment will be described with reference to
After the electrical wiring is completed, an optical waveguide layer 66 of optical polymer is formed by dipping, molding, coating, or the like so as to encase the semispherical structure 64 and 65 therein. Then, as illustrated in
The EMC design becomes important for compact, portable equipment if plural high-speed systems with different frequencies, such as IEEE 802.11a (5-GHz band to 54 Mbps), Bluetooth (2.4 GHz to 1 Mbps), and 4th-generation cellular phones (5-GHz band to 100 Mbps), are involved. The above-discussed optoelectrical mixture substrate with the integrated optical sheet of this embodiment can increase flexibility of such a design and reduce the cost.
In the structure of
Using the above structure, plural electrical circuit boards 90 a and 90 b can be connected through cables formed by an optical waveguide apparatus 91 a, as illustrated in
In the above embodiments, the resist mask for plating has a circular opening for forming an approximately semispherical plated structure, and light emission and reception in the two-dimensional slab waveguide are conducted with respect to all directions in the optical sheet.
In many actual cases, however, light need only propagate in a certain predetermined direction from the standpoint of the wiring architecture. Also, in cases of bus wiring, it is desirable from the viewpoint of effective use of optical power to transmit light in a predetermined direction and output the light. In other words, when light is transmitted in a two-dimensional manner and reaches a position at a distance of R (mm), its optical power receivable per 1-mm arc attenuates by 10*log(1/2πR)+R*α (dB), where α is the propagation loss in the optical sheet (dB/mm). Accordingly, when light propagates 20 mm and is detected by a detector with a diameter of 1 mm, its loss is 21 dB even if α is neglected. Hence, directive transmission is often advantageous in power consumption and cost in cases other than one-to-multiplicity transmission, such as transmission of clock signals.
In a fourth embodiment, a mask pattern with an elongated slit-like opening 95 a, as illustrated in
For example, when plating is performed to a thickness of 80 microns using a mask with a 5 μm×50 μm slit-like opening 95 a, a horizontal semicylindrical plated structure 95 with rounded ends can be formed as illustrated in
Actually, where interconnections are close to each other, i.e., the inter-wiring distance is less than several tens microns, there is a possibility of cross-talk. Accordingly, the line waveguide 99 can be jointly used in the optical sheet.
The line waveguide 99 can be formed, for example, as follows. In the case of polycarbonate Z, monochlorobenzene mixed with monomer is coated, and the coated material is then exposed to radiation through a photo mask having a pattern, as illustrated in
The fourth embodiment can achieve an optical wiring apparatus in which directive transmission can be jointly performed in the two-dimensional optical sheet 93 with less power loss.
As illustrated in
In the fifth embodiment, an optical waveguide apparatus of the present invention is bonded to the electrical circuit board 205, and disposed below a substrate 220 on which the LSI 210 is mounted. The LSI 210 packaged by micro BGA (ball grid array) and the like is mounted so as to be connected to pads 212 with solder balls 211. A portion of its terminals is connected to a light-emitting device 216 in the optical waveguide apparatus through a via 214 to drive the device. Another electrode of the light-emitting device 216 is connected to a common electrode (ground, or power source voltage) through an electrical wire 218 formed in a cladding layer 207. The electrical wire 218 also has divides optical waveguide layers 206 and shields light. In such a structure, an electrical signal from the LSI 210 is converted into an optical signal by the light-emitting device 216, and the optical signal is reflected by an optical-path converting plated structure 217 and transmitted in a direction indicated by the arrow in the optical waveguide layer 206.
The optical waveguide apparatus of this embodiment has a four-layer structure, but it is not limited thereto. As a wiring to an optical device in a lower layer, a via 215, such as the via 58 illustrated in
When a 64-bit output of the CPU 231 is parallel-serial converted into 16-bit signals and an optical transmission of 10 Gbps per one bit is performed, serial-bus connection with a 2.5 GHz operation per one bit (converted into a 64-bit parallel), i.e., totally 160 Gbps (20 GB/sec) in one channel, can be achieved. Even in such high-speed connections, the EMI noises can be oppressed, and multi-CPU systems, such as direct network connections between plural remote CPUs and between peripheral equipment, can be established. The 16-bit bus width is discussed in the above structure, but the structure is not limited thereto.
In recent built-up substrates using only electrical wiring, there exist the following problems in a transmission wiring for high-speed signals. These problems are cross-talk noises due to proximate wiring, signal degradation due to reflections caused by the impedance mismatching, and electromagnetic radiation noises resulting therefrom. The problems can be solved when the multi-layer optical waveguide apparatus of this embodiment applicable to a built-up substrate is used in a portion of high-speed signal transmission. Further, a high-speed serial transfer is under development as a bus for next-generation high-speed LSI interconnection, and RapidIO (U.S. Motrola, et al.), Hyper Transport (U.S. AMD), 3GI0 (U.S. Intel), and so forth are presently targeting 1 GB/sec at 8 bit-1 GHz. In the event that the next-generation interconnections require more than 10 GB/sec under the same standards, high-speed serial bus using the optical waveguide apparatus of the present invention becomes in dispensable even from the viewpoint of electromagnetic radiation noises, board design, and power consumption.
In the fifth embodiment, the optical waveguide apparatus is sandwiched by the electrical circuit boards 205 and 220. However, there can also be provided a structure in which the electrical circuit board is mounted on one side of the optical waveguide apparatus only, or a structure in which optical waveguide apparatuses and electrical circuit boards are alternately stacked.
As described in the foregoing, in the optical waveguide apparatus of the present invention usable to solve the EMI problem and the like, the plated structure can be flexibly arranged at any desired location of the optical sheet at a relatively low cost.
Further, in establishing high-speed multi-CPU systems, super-high-speed bus wiring for increasing flexibility of board designing can be accomplished using the optoelectrical mixture wiring substrate of the present invention.
While the present invention has been described with respect to what is presently considered to be the preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. The present invention is intended to cover various modifications and equivalent arrangements included within the spirit and the scope of the appended claims.