Optical waveguides – Accessories – Attenuator
Reexamination Certificate
2000-03-30
2002-10-15
Ullah, Akm E. (Department: 2874)
Optical waveguides
Accessories
Attenuator
C385S092000
Reexamination Certificate
active
06466729
ABSTRACT:
TECHNICAL FIELD
The present invention relates to controllable attenuators and attenuation systems for attenuating optical energy transmitted through a fiber optic, and in particular to the use of tapered fiber optic portions suspended in controllable materials to effect attenuation.
BACKGROUND OF THE INVENTION
Fiber optic systems often require precise control of optical signal levels entering various system components. This is particularly true for systems at test and characterization stages of deployment. A controllable optical attenuator can be used, for example, to characterize and optimize the optoelectronic response of high-speed photoreceivers, wherein the detection responsivity is dependent on the average optical power incident on the photodiode.
The majority of controllable fiber optic attenuators currently commercially available rely on thin-film absorption filters, which require breaking the fiber and placing the filters in-line. Controllable attenuation is then achieved mechanically by, for example, rotating or sliding the filter to change the optical path length within the absorptive material. This adversely impacts the response speed of the device, the overall mechanical stability, zero attenuation insertion loss and optical back reflection. In general, broken fiber designs suffer numerous disadvantages such as high insertion loss, significant back reflection, and large size. These factors can be minimized, although such corrective measures typically result in added cost and/or size.
Additional issues have impeded the development of thermo-optic variable attenuators, including: (i) the thermal mass of surrounding materials and/or structures which significantly degrade device response time; and (ii) spectrally non-uniform attenuation, resulting from a dispersion mis-match between the optical mode index of the underlying transmission media and a controllable overlay material.
As disclosed in the above-noted, commonly assigned, U.S. patent applications, techniques have been proposed to overcome these weaknesses by providing a “blockless” attenuator implementation. The “blockless” technique of suspending a portion of a fiber optic within a dispersion-controlled, controllable material, addresses the thermal mass responsivity and spectral uniformity problems. The portion of the fiber is modified to allow extraction of optical energy therefrom by the controllable material.
Now, additional species techniques of this fiber modification are desirable to improve the predictability, producibility, and costs of these attenuator devices.
What is required, therefore, are techniques which maintain the advantages of the blockless, dispersion-controlled variable optical attenuators previously disclosed, while at the same time providing increased producibility and improved performance. Tapering or etching the fiber optics, as discussed herein, provides these and other advantages.
SUMMARY OF THE INVENTION
The shortcomings of the prior approaches are overcome, and additional advantages are provided, by the present invention, which in one aspect relates to an attenuator having a tapered or etched portion of a fiber optic through which optical energy can be extracted. A controllable material is formed around the portion of the fiber optic for controllably extracting the optical energy in accordance with a changeable stimulus applied thereto. In the thermo-optic embodiment of the present invention, the changeable stimulus is temperature, and the tapered portion of the fiber optic is suspended through the controllable material and thereby substantially insulated from any heat sink structures in the attenuator.
The attenuator disclosed herein may be used as part as an attenuation system, which includes a control circuit coupled to the attenuator for controlling the amount of the changeable stimulus applied to the controllable material, and a level sense circuit, for sensing the optical energy in the fiber optic and/or the level of changeable stimulus and providing a result thereof to the control circuit.
To improve spectral uniformity of the response of the attenuator across a given wavelength band (e.g., 1520 nm to 1580 nm), the controllable material may have its optical dispersion properties controlled (e.g., matched) in accordance with those of the fiber in this band. Preferably, the controllable material has its optical dispersion properties substantially matched to those of the fiber in the band of interest. The control of the dispersion properties is effected using, for example, polymers with added dyes, discussed in detail in the above incorporated Application entitled “DISPERSION CONTROLLED POLYMERS FOR BROADBAND FIBER OPTIC DEVICES.”
The present invention, in another aspect, relates to methods for attenuating optical energy in a fiber optic using the attenuator discussed above, as well as methods for forming the attenuator discussed above.
The “blockless,” dispersion controlled attenuator of the present invention provides a high performance design with wide flexibility. The use of tapered or etched fiber optics provides additional cost, producibility and performance advantages.
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McCallion, K. et al., “Investigation o
Chan Kwok Pong
Gascoyne David G.
Johnstone Walter
McCallion Kevin J.
Wagoner Gregory A.
Connelly-Cushwa Michelle R.
Heslin Rothenberg Farley & & Mesiti P.C.
Molecular Optoelectronics Corporation
Radigan, Esq. Kevin P.
Ullah Akm E.
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