Optical waveguides – Integrated optical circuit
Reexamination Certificate
2001-04-18
2003-07-15
Kim, Robert H. (Department: 2882)
Optical waveguides
Integrated optical circuit
C385S015000, C385S049000, C385S088000
Reexamination Certificate
active
06594409
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to optical communications of the type used in communication over optical networks and particularly relates to optical communications through fiber optic links using multiple wavelength or broad spectrum light for communication.
2. Discussion of the Related Art
Optical communications networks have become prevalent in long distance communication networks, including for the backbone of the Internet. Demand for additional bandwidth in all manner of optical networks continues to grow and a variety of different strategies have been adopted to improve the utilization of the bandwidth within existing optical fiber networks. There is, for example, increasing utilization of multiple wavelength or broad-spectrum light communication over optical fiber links, generally using the technology known as wavelength division multiplexing (“WDM”). Presently the most common implementation of WDM communication uses a plurality of different lasers as light sources, with each laser emitting light at a wavelength different from the wavelengths emitted by the other lasers in the system. Each of the different wavelengths of light represents a different, substantially independent communication channel and symbols can be transmitted on each of these different communication channels using a modulation and encoding stream appropriate to the channel. For example, each of the channels might be modulated and encoded using time domain techniques.
As an alternate to using lasers to define a plurality of distinct communication channels, a broader spectrum light source might be used and distinct optical channels defined within the broader spectrum light source. Different channels are defined to include a range of wavelengths about a central wavelength, with each channel extending across a range of wavelengths sufficient for reliable detection and separated from the one or more other channels by sufficient wavelength separation to allow for discrimination of adjacent channels. Examples of a broad-spectrum source might include, for example, a super luminescent diode (SLD). The definition of different channels from this broadband light source might be accomplished using a wavelength dispersive grating and a filter or by using one or more Bragg grating filters cascaded within an optical fiber.
Multiple wavelength systems such as WDM systems require that the various communication channels associated with the different wavelengths of light be separated out at different points along a transmission path. For example, an optical fiber having two channels defined as distinct wavelengths or as distinct wavelength ranges might, at different points in time, have signals bound for distant nodes on the network. At some switching node along the communication path, it is necessary for the network to separate these channels so that the signals on these channels can be routed appropriately. This is accomplished, for example, by separating out the wavelengths or wavelength ranges associated with the desired channels using an add/drop filter connected to the fiber. Successive add/drop filters are used to successively select desired channels from the fiber, for example to route the signal on that channel to a different node of the network.
An alternate strategy to the use of add/drop filters includes the use of an array waveguide grating to disperse and separate the broad spectrum light. The separated light is then passed through a set of optical switches such as an array of Mach-Zehnder switching elements. One or more of the outputs from the array of switching elements is then combined into an optical fiber for further transmission. In this way, an array waveguide in combination with other optical elements can provide switching within a multi-wavelength, multi-channel optical communication system. Such a system is described for example in U.S. Pat. No. 5,937,117 to Ishida, et al., entitled “Optical Cross-Connect Device.” The Ishida patent shows a number of different configurations for switches based on array waveguide gratings.
A difficulty with the various devices shown in the Ishida patent is that the array waveguide grating receives inputs and couples its outputs to other devices through optical fibers. Coupling optical fibers to devices such as array waveguide gratings presently involves a largely manual process called “pigtailing” in which each fiber is separately connected to the array waveguide grating. An optical element processing N channels of light typically requires 2N manual pigtail connections to couple light into and out of the element. This assembly work is particularly time consuming and difficult because the pigtailed fibers must be aligned carefully with the input optics of the array waveguide grating. Assembling the devices shown in the Ishida patent is time consuming and undesirably increases the cost of the illustrated switches. The expense of such switches presently limits the possibility of using such switches in many applications.
A similar problem arises when array waveguide gratings are used in combination with detectors to form an analyzer or a channel receiver. Receiving the signals from a channel is accomplished by separating the different channels of light in the optical fiber through a wavelength dispersion and separation element. The separated channel is then provided to a detector that converts the encoded light within the channel into an electrical signal. Such a device is illustrated in U.S. Pat. No. 5,617,234 to Koga, et al., entitled “Multiwavelength Simultaneous Monitoring Circuit Employing Arrayed-Waveguide Grating.” As can be seen in the Koga patent, input and output connections are also made through pigtailed fiber connections to and from the array waveguide grating. Assembly of the illustrated devices requires considerable precise manual labor, undesirably increasing the cost of the components.
It is consequently an object of the present invention to provide optical networking elements having a higher degree of integration that might facilitate less expensive networks and wider application of optical switches.
SUMMARY OF THE PREFERRED EMBODIMENTS
An aspect of the present invention provides an optical component with a substrate having one or more waveguide structures formed on a surface. The substrate comprises a first semiconductor material. An optical detector is bonded to a surface of a first of the waveguide structures and comprises a second semiconductor material different from the first semiconductor material and adapted so that light from the first waveguide structure is coupled into the optical detector and converted into an electrical signal.
Another aspect of the invention provides an optical component with a substrate having an plurality of waveguide structures formed on a surface, at least a portion of the array comprising substantially parallel waveguide structures. The substrate comprises a first semiconductor material. The component includes an array of optical detectors, each optical detector bonded to a surface of a corresponding one of the waveguide structures. The optical detectors comprise a second semiconductor material different from the first semiconductor material and are adapted so that light from a corresponding waveguide structure is coupled into a corresponding optical detector and converted into an electrical signal.
Still another aspect provides an optical component with a silicon on insulator substrate having an plurality of waveguide structures formed on a surface, at least a portion of the array comprising substantially parallel waveguide structures, the substrate further comprising an array waveguide coupled to the plurality of waveguide structures. The optical component includes N optical detectors. Each optical detector is bonded to a surface of a corresponding one of the waveguide structures. The N optical detectors comprise a second semiconductor material different from a surface of the silicon on insulator substrate. The array waveguide separates an input light beam into N
Chan James
Dutt Birendra
APIC Corporation
Hogan & Hartson LLP
Kim Richard
Kim Robert H.
LandOfFree
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