Optical waveguides – Accessories – Attenuator
Reexamination Certificate
1999-09-02
2001-06-12
Spyrou, Cassandra (Department: 2872)
Optical waveguides
Accessories
Attenuator
C385S019000
Reexamination Certificate
active
06246826
ABSTRACT:
FIELD OF INVENTION
The invention relates to variable optical attenuators, and in particular, to variable optical attenuators having profiled blades.
BACKGROUND OF THE INVENTION
An optical attenuator is a device which is widely used in a variety of modern telecommunications applications. It provides balance of optical power levels of data transmission, including balancing of signal-to-noise ratio and power levelling between different wavelengths in a wavelength division multiplexing (WDM) system. Usually there is a large number of attenuators distributed throughout the system, the particular patterns dictated by the geometry of the network (long haul, ring, metro, etc.). Because of an increasing use of these elements, small, efficient and easily controllable attenuators become an important requirement.
There is a variety of types of optical attenuators developed up to date. As an example, they include waveguides with electronically variable properties, macroscopic mechanical means of attenuating light, and micro-mechanical structures brought by the rapid advances of the micro-electro-mechanical system (MEMs) technology during the past ten years. Material thicknesses and feature sizes of 1 micron and sub-micron dimensions are typical as a result of the use of high definition photolithography techniques, but having the ability to fabricate these structures is only the first step. The next is to provide an efficient use of such devices by an easy and controllable attenuation of light up to sub-dB range of accuracy.
SUMMARY OF THE INVENTION
It is therefore an object of the invention to provide a variable optical attenuator which would provide an easy and controllable attenuation of light.
According to one aspect of the invention there is provided a variable optical attenuator device, comprising:
a light input means for receiving a light beam and directing said light beam along an optical path;
an attenuator comprising an actuator carrying a blade whose front edge is moveable across said light beam to provide an attenuated light beam, the front edge of the blade being profiled so that the attenuation of the beam is a predetermined function of the displacement of the blade; and
a light output means disposed along said optical path for receiving said attenuated light beam.
Conveniently, the device further comprises a mounting base, the base having a locating structure, e.g. trenches, grooves, slots, pins, edges, shelves, for receiving the light input and output means. Preferably, the front edge of the blade is profiled so that to partially block the beam and provide that the attenuation of the beam is substantially proportional to the displacement of the blade, desirably the attenuation being linear versus the displacement of the blade. For some applications it may be convenient to have the blade profiled so that the attenuation of the beam is logarithmic versus the displacement of the blade. First and second embodiments of the invention use a monolithic semiconductor electrostatic actuator carrying the profiled blade. The blade of the first embodiment has a triangular protrusion at its front edge, the size of the protrusion being of the order of several FWHM of the laser beam. Accordingly, the blade of the second embodiment has a triangular notch at its front edge, the notch having a size similar the above protrusion. It is understood that the blade may have any other shape, e.g. include a protrusion and/or a notch of rectangular, trapezoidal, square, oval, circular, semi-oval, semi-circular or any other required profile. The blade is made of a semiconductor opaque material and covered with a thin layer of metal. Alternatively, the blade may be made of a semi-transparent material, e.g. doped glass. It required, the device may be integrated into a package, either alone and/or with other opto-electronic components.
In modifications to the above embodiments the electrostatic actuator may be replaced with another known actuator capable of carrying and moving the blade to the required accuracy, e.g. electromagnetic actuator, thermal actuator, piezoelectric actuator, and micro-gears actuator. Light input and output means may include fiber, such as cleaved fiber, angle cleaved fiber, expanded core fiber and fiber bundle, or a lensed source, such as ball lens, index graded lens, fiber with a lens and tapered fiber. Conveniently, the input and output means are made symmetrical to each other. Optionally, the device may include a thermal management system for maintaining a constant temperature of the device. If required, the device may be integrated into an optical fiber transmission system. A set of VOA devices
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may be arranged into one- or two-dimensional array according to a predetermined pattern, depending on the requirements of the system.
According to another aspect of the invention there is provided an optical attenuator comprising:
a base; and
an actuator formed thereon, the actuator carrying a blade whose front edge to be moved across a light beam to attenuate the light beam, the front edge of the blade being profiled so that the attenuation of the beam is a predetermined function of the displacement of the blade.
Optionally, the optical attenuator has a locating structure, e.g. trenches, grooves, slots, pins, edges, shelves, for receiving light input and light output means formed on the base. Preferably, the front edge of the blade is profiled so that the blade partially blocks the beam so that the attenuation of the beam is substantially proportional to the displacement of the blade, desirably being linear versus the displacement of the blade. For some applications it may be convenient to have the blade profiled so that the attenuation of the beam is logarithmic versus the displacement of the blade. Similar to the above, the blade may have any other shape, e.g. include a protrusion and/or a notch of a triangular, rectangular, trapezoidal, square, oval, circular, semi-oval, semi-circular or any other required profile. Preferably, the typical size of the protrusion and/or the notch is of the order of several full width half maximum (FWHM) of the laser beam. The blade may be made of an opaque material, e.g. semiconductor material, or semi-transparent material, e.g. doped glass. If required, the attenuator may be integrated into a package, either alone and/or with other opto-electronic components. Other types of actuators are also suitable to be implemented into the attenuator of the present invention. They include electromagnetic actuator, thermal actuator, piezoelectric actuator, micro-gears actuator or any other known actuator capable of carrying and moving the blade to the required accuracy. If required, attenuators may be arranged into one- or two-dimensional array.
According to yet another aspect of the invention there is provided an actuator for a variable optical attenuator, the actuator carrying a blade whose front edge to be moved across a light beam to attenuate the beam, the actuator being characterized in that the front edge of the blade is profiled so that the attenuation of the beam is a predetermined function of the displacement of the blade. Preferably, the blade is profiled so that the attenuation of the beam is substantially proportional to the displacement of the blade.
The use of the optical actuator with the profiled blade in an optical attenuator provides the attenuation of light which can be controlled easily and accurately. By patterning the required profile of the blade, it is ensured that the attenuation is a predetermined function of the displacement of the blade. For most applications, it provides a big advantage, especially where a substantially linear response of the device is required.
REFERENCES:
patent: 4925273 (1990-05-01), Maisenbacher et al.
patent: 5226104 (1993-07-01), Unterleitner et al.
patent: 5325459 (1994-06-01), Schmidt
patent: 5745634 (1998-04-01), Garrett et al.
patent: 5900983 (1999-05-01), Ford et al.
patent: 6061235 (2000-05-01), Cromwell et al.
Anderson Keith Douglas
O'Keefe Sean Sebastian
Cherry Euncha
Donnelly Victoria
Nortel Networks Limited
Spyrou Cassandra
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