Optical waveguides – With optical coupler – Switch
Reexamination Certificate
2000-05-15
2001-05-15
Ullah, Akm E. (Department: 2874)
Optical waveguides
With optical coupler
Switch
Reexamination Certificate
active
06233378
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to optical waveguide switches in general, and in particular a symmetrical two-by-two switch utilizing two waveguide couplers each having a coupling grating. More particular, still, it relates to an insulating thermo-optical switch suitable for optical communication/switching systems, interconnects and fiber based networks.
BACKGROUND OF THE INVENTION
Rapid developments and applications of communication systems are stimulating new microstructure optoelectronic technologies. Among the various microstructure optoelectronic technologies,integrated optics represents a promising approach. Future electronic systems will require on-chip signal conversion between electrical, optical and microwave media to reach speed and functionality projections. A radically different alternative concept exploits the use of photons, instead of electrons, to carry information in what is commonly referred to as “optical interconnects.” One implementation of this strategy relies on the integration of semiconductor- or polymer-based optoelectronic interconnects on a host silicon (Si) substrate, and thus requires feasible semiconductor- or polymer-based optoelectronic technologies in order to produce Si-based photonic devices for optical waveguide interconnects.
Although the technologies for some electro-optic (EO) waveguide devices based on inorganic materials such as crystals and semiconductors have had a long development history, the conditions for manufacturing and processing integrated optical devices are still seriously limited. Thermo-optic (TO) waveguide devices based on polymers and other temperature sensitive materials have shown an exciting potential in low-speed operations because of their flexibility in fabrication and processing. The TO waveguide devices can be built with glass, silica crystal and polymer because only upper modulating electrodes are needed. Especially, polymers not only have higher thermal effects but can also be directly used to fabricate multi-layer integrated optical circuits (IOC) on top of electronic substrate such as Si and Silica. Polymer-based TO waveguide devices have been successfully applied in fiber-optic communications systems and have been receiving more and more attention in this field. A variety of polymer-based new TO waveguide devices aimed at providing feasible structures with enhanced functionability have been reported. Among the active devices in optical communication systems, optical space switches are key components. Large-scale matrix switches are required to meet the increasing switching capacity. Increasing capacity is required as the number of ports increases. A basic switching unit, such as 2×2 or 1×2 switch, is a suitable unit for building various high capacity switching device.
Wavelength-division-multiplexing (WOM) lightwave systems provide optical communication in wavelength multiplex mode. Recently, research on the devices and techniques for high capability WDM systems or dense wavelength division multiplexing (DWDM) systems having effective network restoration capability, i.e., reconfigurable WDM systems, has received attention. Therefore, single and arrayed high performance optical waveguide switching devices will have wide applications in fiber-optic communication.
Currently, the adding or dropping of signals is accomplished with bulk optics. Individual components such as optical multiplexers, optical demultiplexers, 2×2 optical switches, and variable optical attenuators are used to build a programmable optical add/drop network elements. Unfortunately, this solution is costly and labor intensive. By driving integration down to the component level, it is possible to get away from bulk optics with a silicon optical bench. A Si-based array waveguide is used with optical multiplexers and demultiplexers. In this case, optical switching is done with thermo-optic switches. Interconnectivity between rings for provisioning and restoration is also necessary. Today, this function is performed at the electrical level with digital crossconnects at lower bit rates. In the future, it may take place at higher bit rates in the optical layer. In theory, this is possible with optical switching. With such systems, the challenge becomes the provision of reconfiguring an input port to any output port. The bulk optics used today in programmed optical add/drop network elements can serve as prototype systems for reconfigurable optical switches. Since these elements are large and costly to construct, miniaturization is an advantage. Si-based optical-bench technology combined with thermal-optical switches points to the possibility of smaller-scale switches.
SUMMARY OF INVENTION
The present invention provides a thermo-optical, waveguide-based, switching unit utilizing a pair of waveguide couplers with coupling gratings, which provides unidirectional and bidirectional coupling between single mode waveguides. The switch provides high isolation in a simple, symmetrical, waveguide coupler structure.
A waveguide device based on the present invention comprises two unidirectional waveguide couplers and each coupler having two waveguide channels. One channel is used for guiding the optical signal, and is called the guiding channel. The other channel is used for coupling (switching) the optical beam out (or back in) by means of a coupling grating, and is called the coupling channel. The coupling grating is an index grating made along the outside edge of the coupling channel. The coupling gratings not only couple the optical beams out from the respective coupling channel, but also couple the incoming optical beams into the coupling channels. In the present waveguide switch, the two unidirectional waveguide couplers are symmetrically placed to form a coupler-pair. One (heater) electrode is positioned to cover the two coupling gratings along the two coupling channels. When no electric power is applied to the electrode to heat it, and an optical signal is launched into the input port of the guiding channel of the first waveguide coupler, the optical signal will be coupled out from the coupling channel of the first coupler through the coupling grating; the optical signal is then coupled into the second waveguide coupler via the coupling grating along the coupling channel of the second coupler and into the guiding channel of the second waveguide coupler to exit from its output port. When, and as long as, electric power is applied to the electrode, the heat from the electrode produces a negative index modulation to eliminate the two coupling gratings, and the two original unidirectional waveguide couplers become two normal bidirectional couplers. Hence, the optical signal launched into the guiding channel of the first waveguide coupler comes out from the output port of the guiding channel of the first waveguide coupler because no coupling grating couples it out. Thus, the optical signal launched into the input port of the guiding channel of the first waveguide coupler has two possible output ports. The same switching process also occurs if an optical signal is launched into the guiding channel of the second waveguide coupler. Therefore, a 2×2 switching performance may be implemented by choosing between two alternative states, unheated and heated, of the two waveguide couplers. A high degree of isolation between the two waveguide couplers may be achieved with the structures based on the present invention. M×N switching performance may also be implemented by utilizing more than two of the present waveguide couplers with coupling gratings.
In a preferred embodiment according to the present invention, the separation between the two coupling channels of the two waveguide couplers should be large enough, such that coupling of an optical beam does not occur between the two coupling channels once coupling gratings are eliminated by the modulating power. In both waveguide couplers, the guiding channels should be longer than the coupling channels.
REFERENCES:
patent: 4106848 (1978-08-01), Conwell et al.
paten
Friedrich Kueffner
Nu-Wave Photonics Inc.
Ullah Akm E.
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