Optical waveguides – With optical coupler – Input/output coupler
Reexamination Certificate
2000-11-27
2002-12-03
Ullah, Akm E. (Department: 2874)
Optical waveguides
With optical coupler
Input/output coupler
C385S014000, C385S024000, C359S571000
Reexamination Certificate
active
06490393
ABSTRACT:
TECHNICAL FIELD
This invention relates generally to wavelength division optical transmission of information and more particularly to wavelength division optical multiplexers and demultiplexers for use in optical transmission systems.
BACKGROUND
Wavelength division multiplexing (WDM) is a valuable technique for increasing the information carrying capacity of optical transmissions for voice communications as well as high density transmission of data. In essence, WDM involves modulating light beams of multiple discrete wavelengths with information to be transmitted, combining or multiplexing the beams into a single polychromatic light beam, and transmitting the polychromatic beam to a receiving location by means, for example, of optical fibers or waveguides. At the receiving location, the beam is demultiplexed or separated back into its component discrete wavelength beams, each of which may then be demodulated to extract the information carried by the beam. Thus, many channels of information can be transmitted simultaneously thereby multiplying the information carrying capacity of the transmission.
Wavelength division optical transmission requires an optical multiplexer for combining individual optical signals into a multiplexed signal and an optical demultiplexer for separating the multiplexed signal back into its discrete wavelength components. A variety of optical multiplexers and demultiplexers have been developed for this purpose, many of which for use in the telecommunications industry. Some of these devices make use of optical gratings because such gratings inherently diffract and/or reflect light beams of different wavelengths at different angles. For example, U.S. Pat. No. 6,011,884 of Dueck et al. discloses an optical wavelength division multiplexer that integrates an axial gradient refractive index element with a diffraction grating. Enhanced efficiency multiplexing of discrete wavelength optical beams into a single polychromatic beam for transmission is asserted. U.S. Pat. No. 4,923,271 of Henry et al. discloses an optical multiplexer/demultiplexer having a plurality of focusing Bragg reflectors, each including a plurality of confocal elliptical grating lines. U.S. Pat. No. 5,818,986 of Asawa et al. discloses a optical wavelength demultiplexer incorporating angular back reflection from a series of Bragg gratings in the optical signal path to separate a polychromatic optical beam into its constituent wavelengths. Devices such as these generally are used in the telecommunications industry for the transmission of voice and similar signals over optical communications networks. The size of such devices generally is not an issue in the telecommunications industry and, thus, optical multiplexers and demultiplexers such as those disclosed in the above patents and others tend to be relatively large and bulky.
The past four decades have been a time during which microelectronics, including the integrated circuit chip, has advanced at exponential rates. Microelectronics has entered into almost all aspects of human life through the invention of small electronic devices such as watches, hearing aids, implantable cardiac pacemakers, pocket calculators, and personal computers. The advance of microelectronics has become the principal driving force of innovation in modern information technologies and high-density data communications such as fiber communications, global satellite communications, cellular phones, the Internet, and the World Wide Web. As microelectronics techniques advance, nano-electronics (feature scales on the order of 10
−9
meters) are being realized.
Based on the current growth rate of data communication traffic, the microelectronic chip of 2010 likely will be an array of parallel processors consisting of at least 1024 channels with processing speeds of 40 Giga bytes per second (Gb/s) or faster for each channel. This pushes semiconductor technology towards gigascale and terascale integration with smaller component or feature sizes and larger chip sizes. At the same time, interconnections between circuit components on the chip must support the data transfer rates of 40 Gb/s or faster. As integrated circuit feature sizes continue to decrease and chip sizes to increase, interconnections formed of conventional electrical interconnects and switching technology are rapidly becoming a critical issue in the realization of microelectronic systems. It is believed that the maximum length of interconnection required for a chip is proportional to one half of the square root of the chip area. This parameter thus will be approximately constant while the circuit feature size and required interconnection data throughput scales down. As a consequence, the interconnection delay will be kept approximately constant while device delay is reduced as feature sizes are scaled down. The interconnection delay can even increase if chip size is scaled up. At some point in this scaling process, interconnection delay will dominate system speed; i.e. system speed will not be able to track increasing device speed performance due to the interconnection delay. Conventional conductor and semiconductor interconnects are not able to sustain the required future data rates of 40 Gb/s or higher. Thus conventional interconnects between features on future chips will be an insurmountable bottleneck to the throughput of high-density data communication systems and will be unworkable in future high-speed microelectronics.
To handle the unprecedented growth of data and telecommunications traffic, many novel transmission mechanisms have been proposed, including 3D structures with multiple levels of transistors and conventional interconnects, wireless RF interconnections using co-planar waveguides and capacitive couplers to obtain a “micro-area network on a chip,” and on chip optical interconnections. Of these proposals, optical interconnections, which has proven itself in large scale telecommunications networks, appears to hold the most promise. This is due to a number of factors including the fact that the propagation speed of an optical signal is independent of the number of electronic components that receive the signal, the fact that optical interconnections do not suffer mutual interference effects, and that optical interconnect paths can cross each other without significant interaction. As a result, optical interconnections between microchip features promises to enhance communication performance by providing larger fan-outs at higher bandwidths.
There are two major challenges to the introduction of optical interconnections to microelectronic data communication systems such as computer chips. First, the optical systems and the electronic systems have different architectures since they operate under different physical principals. Second, optical component technology on a micro- or nano-optical scale necessary for implementation of on-chip optical interconnects is not mature and it is costly. Thus, the key to successful application of optical interconnections to high-density microelectronic systems is to perform very effective integration of exceedingly small but highly efficient optical devices with increasingly smaller microelectronic circuitry components.
In order to maximize the potential of micro-optical interconnects for data communications, wavelength division multiplexing of multiple optical signals on a micro- or nano-scale will be employed just as it has been on a macro scale in the telecommunications industry. This requirement calls for exceedingly small optical multiplexers and demultiplexers for combining and separating discrete wavelength optical signals. Further, due to power and heat dissipation constraints present in a microelectronic circuit environment, these micro-optical multiplexers and demultiplexers must operate with virtually no optical transmission losses, otherwise the data throughput will be compromised. Finally, the micro-optical multiplexers and demultiplexers must be highly integrated with micro-optical transmitters for generating the optical signals to be multiplexed and tr
Advanced Interfaces, LLC
Connelly-Cushwa Michelle R.
Ullah Akm E.
LandOfFree
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