Optical waveguides – Accessories – Attenuator
Reexamination Certificate
1998-11-20
2001-01-09
Healy, Brian (Department: 2874)
Optical waveguides
Accessories
Attenuator
C383S014000, C383S015000, C383S019000, C383S025000, C383S126000
Reexamination Certificate
active
06173105
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to an optical attenuator and more particularly to an optical attenuator that uses a micro-electro-mechanical system (MEMS) device for control of the attenuation.
BACKGROUND OF THE INVENTION
Optical components in optical communication networks need to operate over a wide range of power levels, varying from those emanating from high power sources and amplifiers that may be tens of watts to signals of fractions of microwatts arriving at receivers for detection. Moreover, there is often the need in such networks for a wide dynamic range of optical power sources and receivers. For example, in wavelength division multiplexed (WDM) systems, the power needs are dependent on the number of channels present at a particular time in a WDM system. Also fixed optical attenuators are frequently used to add attenuation to short optical fiber spans to reduce the power impinging on the receiver's detector and variable attenuators have been proposed for use in WDM networks to regulate the signal power to a level appropriate to the number of channels then active.
It is important for a variable optical attenuator to add little excess insertion loss when the signal power is already as low as desirable.
It is also important for a variable optical attenuator to be able to respond rapidly to sudden increases in power levels since excessive power levels that are allowed to persist too long often can do considerable damage or otherwise impair operation.
The present invention provides a variable optical attenuator that should be able to meet these various requirements. In particular, the invention provides a variable power attenuator that is especially useful for power regulation.
The invention involves the use of a novel micro-electro-mechanical system (MEMS) device to provide control of the attenuation. MEMS technology is now a well-recognized technology. Basically, it involves forming a multilayer structure by sequentially depositing and shaping on a silicon substrate a plurality of polysilicon layers that are separated by layers of silicon oxide and/or silicon nitride. The shaping of the layers is generally done by the techniques used in the manufacture of silicon integrated circuits and generally involves the patterning of the layers by photolithographic techniques. The basic principles of MEMS technology are described in a paper entitled “MEM'S the Word for Optical Beam Manipulation” that was published in
Circuits and Devices
, July 1997, pp. 11-18. MEMS devices are available from many sources, such as, for example, the MEMS Technology Application Center at North Carolina (MCNC) that custom makes devices on order.
Various applications of MEMs devices are described in copending application Ser. No. 09/088,182, filed Jun. 1, 1998 by five of the present applicants and having a common assignee.
SUMMARY OF THE INVENTION
A variable optical attenuator in accordance with the invention comprises first and second optical waveguides, for example optical fibers that are positioned end to end, preferably slightly offset from coaxial alignment, and spaced apart to define a small gap between adjacent ends of the two optical fibers. These adjacent ends are preferably angle cleaved and coated to be anti-reflective so that an optical signal introduced at the far end of the first or source fiber will pass through the gap and continue along the second fiber with little loss of power, the offset in alignment of cleaved end surfaces of the fiber sections largely compensating for the bending of the optical signal as it exits and enters the cleaved surfaces. To vary the insertion loss introduced by the gap between fiber sections, a MEMS device that includes a movable shutter element is positioned so that the shutter may be interposed in controlled amounts into the gap quickly and easily to vary the amount of optical signal that traverses the gap. Advantageously, typically the shutter surface on which optical signal power to be controlled is incident is coated to be highly opaque or reflective of such incident signal, preferably scattering such signal so that little of it either traverses the gap to enter into the second fiber or is reflected back into the first fiber.
Alternatively, if it is desired to utilize such reflected energy, it may be captured by the source fiber and later diverted to a different wave path in any of the known ways to separate out this backward traveling light.
For use in optical power regulation, the variable attenuator described is positioned at the output of the power source or amplifier being regulated and a known fraction of the power level at the output of the attenuator is abstracted and detected. The resulting detected signal level is compared with a known reference level that corresponds to the desired power at the output of the attenuator were at the level desired. The two signals are compared and any difference signal is used to control the attenuation provided by the attenuator.
The invention will be better understood from the following more detailed description.
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patent: 5052777 (1991-10-01), Ninnis et al.
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patent: 5745634 (1998-04-01), Garrett et al.
patent: 5923798 (1999-07-01), Aksyuk et al.
Aksyuk Vladimir A.
Barber Bradley P.
Bishop David J.
Giles Clinton R.
Ruel Rene R.
Healy Brian
Lucent Technologies
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