Optical waveguides – Integrated optical circuit
Reexamination Certificate
2000-07-11
2002-11-05
Lee, John D. (Department: 2874)
Optical waveguides
Integrated optical circuit
C385S049000, C385S088000, C257S433000, C257S081000
Reexamination Certificate
active
06477286
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an integrated optoelectronic device for constructing electronic equipment, and an integrated circuit device, and particularly to (i) an integrated optoelectronic device, wherein optical and electronic devices are integrated to transmit or receive signals via light or a mixture of electrical means and light, such as optical interconnections, (ii) its driving method, (iii) a method of wiring between a mixed optoelectronic substrate and the integrated optoelectronic device, and (iv) related structures.
2. Related Background Art
In recent years, the development of high-speed large scale integration (LSI) has been advanced as the speeds of computers, information processing and computer peripherals, such as displays and printers, have increased. At the same time, problems of signal delay, heat generation and electromagnetic radiation emission noise (EMI) due to the rapid switching rates of the circuits in the LSI chip, integrated circuit (IC) board, multi-chip-module (MCM), and the backplane of super computers, and connections between electronic devices such as boards, computers, peripheral equipment, and audio-visual (AV) apparatuses have proliferated. Solutions of those problems are, however, difficult. It is hence apparent that the inherent absolute physical limitations of electric wiring will be reached in the near future.
For the purposes of solving the problems in the electrical wiring, there has been developed a substrate using a micro strip-line of the Rambus system in a board, or a method of transmitting a low voltage differential signal with a small amplitude through a shield line between boards (low voltage differential signalling (LVDS)).
In the Rambus system, signal transmission of frequencies over 400 MHz has been achieved, and this system is planned to be introduced in a next generation personal computer (PC). There are, however, limitations to the manner of wiring, and the implementation and arrangement of pins on the side of LSI chips. Therefore, there are problems in that system in that the chip cost increases, the system is unsuitable for long wiring, and the size of the board increases due to the limitations as to a high density in multi-bit wiring since cross-talk must be eliminated.
In the LVDS method, high-speed serial transmission of about 1 Gbps using LVDS has been put into practice, but its range of use is restricted since the costs of its interface IC and cable are high.
As a potential method for solving the limitations inherent in electrical wiring, techniques of optical interconnections are under development. In an optical interconnection, an electric signal from the IC or the like is converted into an optical signal, the converted optical signal is transmitted through an optical channel, or “wiring”, as used hereinbelow, such as a waveguide formed in a board, to an optical receiver in another IC or board, and the optical signal is reconverted into an electric signal. Such a system removes the problem of (i) signal delay due to the parasitic capacitance that appears in electric wiring, (ii) signal degradation resulting from an unstable ground, and (iii) emission of EMI radiating from the wiring, and the system is thus expected to be used in future wiring schemes. In the optical interconnection, portions of the O (optical)/E (electrical) and E (electrical)/O (optical) conversions and the waveguide are important, and therefore, it is critical how effectively a portion of the electric wiring can be replaced by the optical wiring at a reduced cost.
As a method of optical wiring, there exists, as disclosed in Japanese Patent Application Laid-Open No. 5(1993)-67770, a structure wherein an optoelectronic IC chip, with an optical device arranged in place of the pins of the IC chip, is implemented on an optical wiring substrate provided with a waveguide and a reflective mirror.
FIG. 1
illustrates the structure. A light emitting device
1011
is provided on the bottom surface of an optoelectric IC chip
1004
, an inclined portion
1005
acting as a reflective mirror is provided on an optical wiring substrate
1001
, and an optical signal from the light emitting device
1011
is coupled to a waveguide (core)
1008
and then received by a light receiving device
1012
in another chip
1004
. In this example, a manner of the optical coupling between the optical devices
1011
and
1012
and the waveguide
1008
is illustrated, but neither the specific integration method nor the driving method of the electric circuit portion
1010
or the optical devices
1011
and
1012
is described. There is further provided in the structure of
FIG. 1
a reflective layer
1002
, a protruded portion
1006
, and a silicon-oxide layer
1007
.
As a method of driving an optical device to achieve the optical wiring, the following method is disclosed in Japanese Patent Application Laid-Open No. 9(1997)-96746. As illustrated in
FIG. 2A
, a continuous-wave output from a laser diode
1101
is divided by a coupler formed of plane waveguides into portions whose number is the number of signal lines, and electric signals are converted to optical signals by optical modulators
1102
of the electric-field absorption type or optical switches of a Mach-Zehnder type, respectively. Each optical signal is received and converted to an electric signal by a photodetector (PD)
1103
, and the electric signal is amplified by an amplifier
1104
. In this case, the substrate is not complicated and there is no need to prepare a special IC for driving the optical device, since the electric wiring portion
1106
and the optical wiring portion
1105
in the transmitter are independently designed as illustrated in FIG.
2
B and an electric wiring portion
1107
and an optical wiring portion in the receiver portion are independently designed as illustrated in FIG.
2
C. This construction can be readily applied to any electronic equipment simply by placing the optical wiring portion on a conventional electric printed circuit board (PCB), or the like.
In the system depicted in
FIGS. 2A
to
2
C, however, the thickness of the structure increases due to the optical wiring portion being provided separately from the electric circuit, as described above. Accordingly, the size is inevitably made larger, as compared with the mixed optoelectronic substrate of FIG.
1
. Further, in the case of a multi-channel device, or plurality of high-performance devices, such as an optical modulator or an optical switch, the cost increases, and problems arise with respect to the reliability of the electrode contacts of the electric signal to the modulator, to implementation, and to cross-talk between the modulators. Furthermore, the optical loss is large since light is divided by the coupler and coupled to the optical modulator, or the like, and hence, the problem arises of the electric power required to sustain the output power of the laser.
In the system of
FIG. 1
, although the detailed device construction and method of implementation are not clearly shown, it seems that the optical device and the electric device are commonly packaged, that the size is decreased due to high-density integration, and that reliability of the wiring is improved. This system is, however, impractical because of the power required to drive an ordinary light emitting device (due to the large electrical currents involved), such as a light emitting diode (LED) or a semiconductor laser. Additionally, the integrated circuit is further complicated by the addition of an IC for driving the optical device.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a practical integrated optoelectronic device which is readily adaptable to an optical interconnection and whose electric power requirements, as well as cost, can be reduced, an integrated circuit device, and related structures and methods.
The present invention is generally directed to an integrated optoelectronic device which includes an electric circuit unit, such as a bare chip of integrated electronic
Knauss Scott A
Lee John D.
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