Optical waveguides – Temporal optical modulation within an optical waveguide – Electro-optic
Reexamination Certificate
2000-11-22
2003-09-02
Ullah, Akm Enayet (Department: 2874)
Optical waveguides
Temporal optical modulation within an optical waveguide
Electro-optic
C385S014000, C385S015000, C385S019000, C385S024000, C385S027000
Reexamination Certificate
active
06614947
ABSTRACT:
FIELD OF THE INVENTION
The present invention is directed to small-scale Mach-Zehnder interferometer (“MZI”) devices and structures. The present invention is also directed to digital optical switches.
BACKGROUND OF THE INVENTION
An optical network, in its simplest representation, consists of an optical source, a destination, and a matrix of devices (e.g., fiber-optical cables, waveguides, cross-connects, amplifiers, etc.) for causing an optical signal generated by the source to reach a desired destination. Physical and geographic boundaries present no impediment to telecommunication, data communication and computing, all of which may utilize all or part of an optical network. Consequently, the number or sources and destinations, and the combinations of sources and destinations and the communication paths therebetween, may be nearly infinite. Optical switches are used in the optical network for facilitating the routing of an optical signal to its desired destination.
By way of example,
FIG. 1
depicts a block diagram of a part of an optical component
1
comprising a plurality of optically interconnected optical devices
3
(e.g., switches, filters, etc.), shown in
FIG. 1
as switches. As used herein, the terms “optical component” and “component” refer to any and all of a plurality of interconnected devices which may operate using any combination of optical, opto-electrical, and/or electrical technologies and which may be constructed as an integrated circuit. Devices
3
can be optically interconnected by waveguides
5
. Various other optical, opto-electrical, and/or electrical devices may also be included in the optical component, as a matter of design choice. As used herein, the terms “optical”, “opto-electrical”, and “electrical” devices may include, by way of non-limiting example, lasers, waveguides, couplers, switches, filters, resonators, interferometers, amplifiers, modulators, multiplexers, cross-connects, routers, phase shifters, splitters, fiber-optic cables, and various other optical, opto-electrical, and electrical devices. The optical component
1
and devices
3
depicted in
FIG. 1
are merely illustrative.
Although a single wavelength of light can be transmitted through the network, in order to increase the network's data-carrying capacity it is preferable to transmit multiple wavelengths of light at the same time. This is currently accomplished using techniques known as wave-division-multiplexing (“WDM”), dense WDM (“DWDM”), and ultra-dense wave-division-multiplexing (“UDWDM”).
The ability to separate one optical signal from a plurality of optical signals (or one wavelength from a plurality of wavelengths in an optical signal) propagating within an optical network becomes more important as the number of signals transmitted through a single optical fiber (or waveguide) increases. As optical transmission evolves from WDM to DWDM to UDWDM, and beyond, more and more data contained in a multi-wavelength optical signal is transmitted over the optical network. Optical filters are one component that may be used to extract a desired signal (i.e., a desired wavelength) at a particular point or location in the network and route that signal to its desired destination, while also permitting other signals to continue along the network.
Optical networks transmit data as pulses of light through waveguides in a manner similar to electrical networks, which send pulses of electricity through wiring. Transmitting an optical signal between waveguides, which may occur in various devices employed in an optical network, may require the optical signal to leave one waveguide and propagate through one or more materials (mediums) before entering another waveguide. It is likely that at least one of the devices will have an index of refraction different than the index of refraction of the waveguides (which typically have approximately the same refractive index). It is known that the transmission characteristics of an optical signal may change if that signal passes through materials (mediums) having different indices of refraction. For example, a phase shift may be introduced into an optical signal passing from a material having a first index of refraction to a material having a second index of refraction due to the difference in velocity of the signal as it propagates through the respective materials and due, at least in part, to the materials' respective refractive indices. As used herein, the term “medium” is intended to be broadly construed and to include a vacuum.
If two materials (or mediums) have approximately the same index of refraction, there is no significant change in the transmission characteristics of an optical signal as it passes from one material to the other. Accordingly, one solution to the mismatch of refractive indices in an optical switch involves providing an index matching or collimation fluid to offset any difference in refractive indices. Consequently, the optical signal does not experience any significant change in the index of refraction as it passes from one waveguide to another.
An example of this approach may be found in international patent application number WO 00/25160. That application describes a switch that uses a collimation matching fluid in the chamber between the light paths (i.e., between waveguides) to maintain the switch's optical performance. The use of an index matching fluid introduces a new set of design considerations, including the possibility of leakage and a possible decrease in switch response time due to the slower movement of the switching element in a fluid.
In addition, the optical signal will experience insertion loss as it passes between waveguides. A still further concern is optical return loss caused by the discontinuity at the waveguide input/output facets and the trench. In general, as an optical signal passes through the trench, propagating along a propagation direction, it will encounter an input facet of a waveguide which, due to physical characteristics of that facet (e.g., reflectivity, verticality, waveguide material, etc.) may cause a reflection of part (in terms of optical power) of the optical signal to be directed back across the trench (i.e., in a direction opposite of the propagation direction). This is clearly undesirable because the reflected signal will interfere with the optical signal propagating along the propagation direction.
Reflection of the optical signal back across the trench also can create problems if the facets not only are coaxial, but also are parallel to one another. That arrangement forms a Fabry-Perot resonator cavity, which, under the appropriate circumstances, allows for resonance of the reflected signal, in known fashion.
Size is also an ever-present concern in the design, fabrication, and construction of optical components (i.e., devices, circuits, and systems) for use in optical networks. It is strongly desirable to provide smaller optical components so that optical devices, circuits, and systems may be fabricated more densely, consume less power, and operate more efficiently.
Currently, optical switches can be constructed using a directional coupler or a Mach-Zehnder interferometer (“MZI”), as is generally known in the art. Mach-Zehnder interferometers are known devices which take an input optical signal, split the signal in half (generally, in terms of optical power), direct the split signals along different optical paths, apply a phase shift to one of those split signals, recombine the signals and then feed those combined signals as a single signal to an output. The amount by which the phase of one of the signals is changed will, in known fashion, affect the nature of the output signal.
Conventional Mach-Zehnder interferometers shift the phase of light traveling along one of the interferometers in one of several ways. If the electro-optic effect is used, one of the interferometer arms is made from a medium having an index of refraction which changes in the presence of an applied electrical field. Similarly, if the electro-thermal effect is used, the interferometer has an a
Doan Jennifer
Edwards & Angell LLP
LNL Technologies, Inc.
Ullah Akm Enayet
LandOfFree
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