Optical waveguides – With optical coupler – Particular coupling structure
Reexamination Certificate
2002-12-17
2004-12-14
Kim, Ellen E. (Department: 2874)
Optical waveguides
With optical coupler
Particular coupling structure
C385S039000
Reexamination Certificate
active
06832029
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to electromagnetic and optical circuitry and, more particularly, impedance control elements that are implemented in conjunction with a transition region of a electromagnetic waveguide to control the impedance or the propagation velocity in the transition region.
BACKGROUND OF THE INVENTION
Microstrip line is one of the most popular types of planar transmission lines, primarily because it can be fabricated by photolithographic processes and is easily integrated with other passive and active microwave devices. Microstrip line is a kind of “high grade” printed circuit construction, consisting of a track of copper or other conductor on an insulating substrate. There is a “backplane” on the other side of the insulating substrate, formed from similar conductor. The track is considered the “hot” conductor and the backplane is considered the “return” conductor. Microstrip is therefore a variant of a two-wire transmission line.
Co-planar waveguides are also instrumental as transmission lines for microwave signals. Typically, a co-planar waveguide is formed by a circuit line bordered on each side of the line by two co-planar waveguides. The co-planar waveguides serve as the ground plane. In most embodiments the co-planar waveguides obviate the need to implement a backplane, such as used in the standard microstrip line described above. Co-planar waveguides benefit from smaller circuit size and greater design freedom in comparison to microstrip line. In addition, co-planar waveguides will typically not require backplane or via processing and, therefore fabrication costs are typically less. However, from a performance standpoint the co-planar waveguide has slightly higher losses and generally poorer power handling capabilities than microstrip line.
In the optical signal realm, an optical waveguide is similar to a microstrip in that it is used as a long transmission line, in this instance to guide an optical signal or light form. It is formed of a solid dielectric filament (i.e., optical fiber). In integrated optical circuits an optical waveguide may consist of a thin dielectric film. The optical waveguide will typically comprise a core consisting of optically transparent material of low attenuation (usually silica glass) and a cladding consisting of optically transparent material of lower refractive index than that of the core. In addition, there are planar dielectric waveguide structures in some optical components, such as laser diodes, which are also referred to as optical waveguides.
In most microstrip lines, co-planar waveguides and optical waveguides a transition region is defined in which the plan view width of the microstrip line or optical waveguide undergoes transition from a first width to a second width. In the transition region a step impedance change occurs due to the change in width. In other words, in the transition region an abrupt change to the opposition to current flow occurs. This abrupt change in impedance causes undesirable reflective pulses to be generated in the opposite direction of the signal pulse.
In previous instances, the problems related to reflective pulses in the transition region of microstrips and optical waveguides have been addressed by various means. In single frequency signal transmission applications, anti-reflective coatings have been applied to the circuits to reduce or eliminate reflective pulses. In applications in which the frequency band is narrow in range, slots have been designed into the transition region of the microstrip or waveguide to combat the problems related to reflective pulses. However, the use of such slotted transition regions is insufficient to rectify the reflective pulse problem in RF circuitry having a high bandwidth range, for example a bandwidth range of 10 Hz to about 10 GHz.
Additionally, microstrips, co-planar waveguides and optical waveguides have been used in conjunction with vertical stacks of impedance control elements, typically vertically stacked fin structures. These fins structures serve to control impedance and propagation velocity in the transition region of the circuit line. However, such structures are expensive to fabricate and typically require precise alignment during fabrication and active alignment during device use.
What is desired is a mechanism that allows for a smooth, linear impedance change in the transition region of a microstrip or optical circuit. Such a mechanism will be able diminish or eliminate problems with undesirable reflective pulses that are caused by an abrupt change in impedance. A need exists to develop such a mechanism that can be used in high bandwidth range transmission lines. Unlike the vertical stacked impedance control elements, the desired impedance control device will be easy to fabricate, low in cost and will not require precise alignments beyond conventional photolithographic fabrication.
SUMMARY OF THE INVENTION
The present invention provides for impedance control elements that are implemented in conjunction with the transition region of a microstrip, co-planar waveguide or optical waveguide (collectively referred to herein as electromagnetic waveguides) to diminish the effect of reflective pulses on the signal transmission and to create linear impedance transition in the transition region. The device of the present invention provides the stated benefits in electromagnetic waveguides that are capable of high bandwidth signal transmission.
In one embodiment of the invention a device for controlling transition and/or propagation velocity in millimeter wave circuitry includes a substrate, an electromagnetic waveguide disposed on the substrate having a first region defined by a first width, a second region extending from the first region and defined by a transitioning width and a third region extending from the second region and defined by a second width. The second width is greater than the first width. The device additionally includes a plurality of impedance control elements disposed on the substrate adjacent to the second region, the plurality of impedance control elements occupying more planar area on the substrate proximate the third region and decreasing in planar area occupancy as they approach the first region. The plurality of impedance control elements serves to control the reflection of pulses impinging from the first region onto the third region.
In one embodiment of the invention the impedance control elements are defined by line elements that are disposed generally perpendicular to the second region of the electromagnetic waveguide. The line elements will characteristically be narrowest in width proximate the first region and increase in width as they approach the third region.
In yet another embodiment of the invention the impedance control elements are more populous proximate the third region and decrease in population as they approach the first region. The plurality of impedance control elements may be configured in an array, such as a grid-like array, in a quasi-array or in random configuration. Typically the impedance control elements will be disposed on opposing sides of the microstrip/waveguide with a similar configuration on each opposing side. The impedance control elements will typically vary in pitch, density and or geometry as the elements progress from proximate the first region to proximate the third region.
In yet another embodiment of the invention, a method for controlling the impedance and propagation velocity in the transition region of an electromagnetic waveguide is defined as follows. An electromagnetic waveguide is provided that has a first region in which impedance and propagation velocity are generally constant, a second region extending from the first region in which impedance and propagation velocity are generally transitioning and a third region extending from the second region in which impedance and propagation velocity are generally constant. Impedance and velocity control elements are provided adjacent to the second region such that the elements gradually increase in p
Kim Ellen E.
MCNC
LandOfFree
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