Optical waveguides – Polarization without modulation
Reexamination Certificate
2000-10-02
2002-10-01
Ngo, Hung N. (Department: 2874)
Optical waveguides
Polarization without modulation
C385S024000, C370S351000
Reexamination Certificate
active
06459827
ABSTRACT:
BACKGROUND
1. The Field of the Invention
This invention relates to photonic processing and, more particularly, to novel systems and methods for switching and routing photonic signals.
2. Background
Communication signals must be routed through networks from a source to a destination. One form of signal is a photonic signal. Photonic signals may be a series of pulses, or other serial data, and may also be carried in a two dimensional array of pixels, a parallel flow of data.
Fundamental to transmission of any signal over a multiplicity of locations, such as through elements of a network, is routing and switching of signals between potential alternative paths. Photonic signals are electromagnetic waves modulated in some fashion to carry information. Electronic signals are typically routed by electronic switches. Optical signals or photonic signals are typically switched by electro-optical mechanisms. Switches for optical signals or photonic signals do not work well with signals that have variations in state of polarization. For example if polarization is modulated as a mechanism for transmitting information in a photonic signal, the variations in polarization must pass through all elements of a switching or routing network in order to preserve the information embodied in the switched outputs.
Various signal routers have been produced. Particular technologies include micro-mirrors, bubble-jet bubbles, and electronic switches or electro-optical mechanisms. The prior art lacks an effective high speed switching structure for routing a photonic signal through basic switching elements of a network while preserving or stabilizing a state of polarization of the photonic signal. If polarization-sensitive elements exist, including elements that benefit from polarization modulation, then preservation or stabilization of the state of polarization of a photonic signal may be critical.
Switches for routing optical or photonic data have made recent advances. For example, Bergland et al., U.S. Pat. No.: 5,317,658, characterize an optical switch as “Polarization independent.” According to Bergland, certain specific difficulties associated with polarization dependence are addressed by a switch capable of switching both TE and TM components of a lightwave received by a switch.
However, Bergland et al. state that “Although the polarization-independent switch may switch both the TE and TM components of a light wave in an arbitrary polarized condition, it has the disadvantage of requiring a higher operating voltage than the polarization-dependent photonic switch. Moreover, the level of performance in each individual switch element in the polarization-independent photonic switch is inferior to that of the individual switch elements in the polarization-dependent photonic switch.” The requirement for using this type of photonic switch inherently limits the usefulness and switching speed.
Another problem is dependence on high birefringence fiber as a required component. Bergland teaches the necessity of using this fiber in order to provide the polarization rotation needed to accommodate his polarization-dependent switches. This requirement introduces specific problems that may not be observed with the older, slower communications equipment, but as bit rates go up, and throughput becomes more important, the signals being switched become more critical. High time division multiplexed (TDM) bit rates require shorter and shorter pulses. These pulses may require special processing both before they are launched into the fiber, and at the various nodes along the way.
A “high birefringence fiber” is a nonlinear optical element. The introduction of such nonlinearity can be a severe detriment in high bit rates systems because it tends to exacerbate the problems of four-wave mixing between the various optical signals, that might otherwise be manageable.
Every extra element inserted into an optical path introduces losses. So, by providing an optical switch that does not require these extra components, losses can be reduced, which becomes increasingly important as the number of switching elements in a switching fabric increases.
The present invention addresses these disadvantages by producing a photonic switch that does not favor one polarization over another. It eliminates the need both for the high birefringence fiber, and even for the need to rotate the polarization in one of the light paths, simplifying the design, reducing losses, and reducing manufacturing costs. The present invention goes on to provide high speed switching even when using low speed components. It introduces the use of optically-controlled, all optical switching, plus a simplified routing arrangement that is compatible with photonic transistor technology and other all optical methods of directing data packets through all optical switching fabrics.
Carlsen et al, U.S. Pat. No. 4,474,435 also rotates one of the polarization-separated beams in order to use a “polarization sensitive interferometric multimode fiber optic switch and modulator.” It suffers from the same kinds of difficulties as Bergland. Additionally, Carlsen uses expensive specially made crystals.
Transparency is a very important consideration in the design of photonic communications equipment, and photonic signal switching matrices use in optical computers and the like. In order to provide reliable, high speed, practical switching all aspects of an incoming signal must be effectively transmitted through the switch and into the output. In order to prevent the introduction of noise, and as a result, produce unfavorable bit error rates, all phase, frequency, amplitude, spatial and polarization variations of the original input signal must be reliably transmitted through the switch and into the output.
In other words, a router must be transparent, switching an entire wavefront, not just binary data. When free space optics are used, even beam quality and profile becomes important when interconnecting a number of switches into a matrix or network. Full images with their massive amounts of spatial information also need to be switched. The prior art does not address these issues.
BRIEF SUMMARY AND OBJECTS OF THE INVENTION
In view of the foregoing, it is a primary object of the present invention to provide a polarization-preserved or alternatively polarization-stabilized router for photonic signals.
It is another object of the invention to provide a phase-preserving, and phase-and-polarization-preserving router for photonic signals.
One object of the present invention is to provide means and method of transparent switching of photonic signals including all their aspects and information content as represented by a series of wavefronts along with their temporal waveforms.
Another object is to provide means and method of switching and routing images based on their temporal and/or spatial content.
It is a further object of the invention to provide a photonic switching mechanism capable of switching entire arrays of pixels maintained in a coherent pattern. Accordingly, it is an object of the invention to transmit and switch photonic images. It is yet another object of the invention to switch a parallel image or pattern of electromagnetic energy, such as light as an array of photonic signals switched in parallel as a single photonic data signal. It is also an object of the invention to provide a photonic switch for switching serialized packets of photonic data embodied in electromagnetic radiation (e.g. visible light, laser light, infrared, etc). It is a further object of the invention to provide packetized addressing integrated within a packet in order to switch a photonic signal in a photonic switch, based upon an address portion of the photonic signal itself. Accordingly, it is an object of the invention to provide a switch mechanism capable of reading, in real time, an address portion of a photonic data packet, and switching a photonic data packet in accordance with the address therein.
Consistent with the foregoing objects, and in accordance with the invention as embodied and broadly described
Eastman Gary L.
Ngo Hung N.
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