Optical waveguides – Directional optical modulation within an optical waveguide – Acousto-optic
Reexamination Certificate
2002-03-22
2004-04-06
Healy, Brian (Department: 2874)
Optical waveguides
Directional optical modulation within an optical waveguide
Acousto-optic
C385S004000, C385S011000, C385S032000, C359S285000, C359S305000, C381S337000, C372S013000
Reexamination Certificate
active
06718076
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to optical devices. In particular, the present invention relates to optical devices that include optical interaction regions, such as optical filters and optical modulators.
BACKGROUND OF THE INVENTION
Acousto-optic tunable filters (AOTFs) are electrically-tunable optical filters. Wavelength tuning is accomplished by varying the surface acoustic wave frequency applied to the AOTFs. AOTFs are useful for optical filtering and add-drop multiplexing in wavelength division multiplexing (WDM) optical transport systems. WDM is an optical transport technology that propagates many wavelengths in the same optical fiber, thus effectively increasing the aggregate bandwidth per fiber to the sum of the bit rates of each wavelength. Dense Wavelength Division Multiplexing (DWDM) is a technology that implements WDM technology with a large number of wavelengths. DWDM is typically used to describe WDM technology that propagates more than 40 wavelengths in a single optical fiber.
As the number of wavelengths increases, the channel width and channel spacing decreases. To achieve the required channel width and channel spacing in DWDM communication systems, high quality, high performance optical filters are required. In order to function properly, these optical filters generally must exhibit low loss and narrow band transmission characteristics over the wavelength spectrum of 1.3 &mgr;m to 1.55 &mgr;m. These filters generally must also have good mechanical properties and must be stable in typical operating environments.
AOTFs are particularly advantageous for use in WDM optical transport systems because they can achieve narrow passbands and broad tuning ranges. In fact, an AOTF can have a tuning range that is substantially the entire wavelength range of an optical fiber communication system, which can typically be approximately from 1.3 &mgr;m to 1.6 &mgr;m. Also, AOTFs have the unique capability of simultaneous multi-channel filtering. By simultaneous multi-channel filtering we mean that an AOTF can select several wavelength channels simultaneously by applying multiple acoustic wave signals. In addition, AOTFs can be configured as add-drop multiplexers. Add-drop multiplexers are used in WDM optical transport systems for adding and dropping one or more channels while preserving the integrity of the other channels.
AOTFs include a narrowband polarization converter that is positioned between an input and an output polarizing element. The polarization converter changes one polarization mode to an orthogonal polarization mode. Light having a wavelength range within the passband of the filter propagates through the input polarizing element and then is converted to an orthogonal state of polarization. The converted light then propagates through the output polarization element.
The degree of polarization transformation depends on the magnitude of the polarization conversion, which is a function of the applied acoustic power density. However, the polarization converter is inoperative outside of the passband of the filter. Light having a wavelength range outside of the passband does not get converted by the polarization converter and, therefore, is blocked from propagating through the AOTF.
Known AOTFs have several practical limitations that have prevented them from being used in commercial WDM optical transport systems. For example, known AOTFs have relatively wide channel bandwidth and have relatively poor out-of-band signal suppression. Also, known AOTFs that are configured as multi-wavelength add/drop multiplexers experience coherent beating between multiple drive frequencies when performing multi-wavelength add/drops. This can lead to undesirable wavelengths being included when performing multi-wavelength add/drops.
SUMMARY OF THE INVENTION
The present invention relates to optical devices that include multi-segment optical interaction regions. In one embodiment, the present invention relates to AOTF devices having long interaction lengths. An AOTF according to the present invention divides the optical interaction region into a plurality of segments, such that the total combined length of the plurality of segments is the desired interaction length. In one embodiment, the plurality of segments comprises segments that are positioned adjacent to each other in numerous folded configurations.
AOTFs according to the present invention have a relatively low aspect ratio. By aspect ratio we mean the ratio of the physical length of the device to its physical width. Devices having low aspect ratios generally are more physically robust and axe generally easier to package. In addition, an AOTF according to the present invention can use smaller heaters or thermoelectric coolers and less complex temperature controllers compared with devices having higher aspect ratios. In one embodiment, AOTFs according to the present invention have a relatively high yield because the materials they are fabricated from are generally more uniform and generally the fabrication tolerances ate less demanding for devices with low aspect ratios. In one embodiment, devices with low aspect ratios are less expensive to manufacture because more or the devices can occupy a given sized substrate compared with devices having standard or higher aspect ratios
Accordingly, in one aspect, the present invention is embodied in an acousto-optic tunable filter that includes a polarization beamsplitter for receiving an optical signal at a first optical input. The polarization beamsplitter generates a first and a second polarized optical signal at a first and a second optical output, respectively. In one embodiment, the polarization beamsplitter is formed in a substrate. In another embodiment, the polarization beamsplitter is a discrete planar device. In other embodiments, the polarization beamsplitter is a prism or other known polarization splitter device. In one embodiment, the first polarized optical signal is orthogonally polarized relative to the second polarized optical signal.
The acousto-optic tunable filter also includes a first optical interaction region having a first and a second optical waveguide optically coupled to the first and the second output of the polarization beamsplitter, respectively. The first optical interaction region also includes a first acoustic wave generator for generating acoustic waves in the first and the second optical waveguides. In one embodiment, the first optical interaction region is formed in a substrate. In another embodiment, the first optical interaction region is a discrete planar device. In another embodiment, the first optical interaction region includes a first and a second segment that are physically separate.
The acousto-optic tunable filter further includes a second optical interaction region having a third and a fourth optical waveguide optically coupled to the first and the second optical waveguide of the first optical interaction region, respectively. The second optical interaction region also includes a second acoustic wave generator for generating acoustic waves in the third and the fourth optical waveguides. The second optical interaction region is non-collinear relative to the first optical interaction region, thereby reducing the aspect ratio of the acousto-optic tunable filter.
In one embodiment, the second optical interaction region is formed in a substrate. In another embodiment, the second optical interaction region is a discrete planar device. In another embodiment, the second optical interaction region includes a first and a second segment that are physically separate. In one embodiment, the first optical interaction region and the second optical interaction region are discrete planar devices that are formed in a first and second physically separate substrate, respectively. In another embodiment, the first optical interaction region and the second optical interaction region are positioned adjacent to each other in a folded configuration. In yet another embodiment, the first optical interaction region is positioned in a non-parallel configur
Bures Kenneth J.
Gunes Dogan
Lee Chunghsin
Maki Paul
Sferlazzo Piero
Healy Brian
Petkovsek Daniel
Rauschenbach Kurt
Rauschenbach Patent Law Group, LLC
Unaxis USA Inc.
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