Optical waveguides – With optical coupler – With alignment device
Reexamination Certificate
2001-07-13
2002-11-12
Nasri, Javaid (Department: 2839)
Optical waveguides
With optical coupler
With alignment device
Reexamination Certificate
active
06480651
ABSTRACT:
FIELD OF THE INVENTION
The present application relates to a method and apparatus for aligning optical components.
BACKGROUND OF THE INVENTION
Optical components such as optical fibres, lenses, integrated optical systems, etc. are frequently aligned and coupled to one another. In general, the alignment is performed passively and/or actively. During passive alignment, the two optical components may be placed according to the expected desired orientation. During active alignment, the two optical components may be moved relative to one another while light transmitted therethrough is simultaneously monitored to determine an optimum coupling efficiency.
For integrated optical systems, such as optical integrated circuits (OICs), arrayed waveguide gratings (AWGs), planar waveguides (PW), etc., which generally have multiple channels extending to an array of ports at an end of the component, active alignment can be quite difficult. For example, consider the pigtailing of an integrated optical system, wherein each output port of the integrated optical system must be aligned and coupled to a specific optical fibre in a fibre array unit (FAU).
In many cases, to achieve optimum coupling of such multi-port components via active alignment, it is preferred that alignment be performed to a fraction of a micron and within six degrees of freedom, namely, three translational degrees of freedom and three rotational degrees of freedom.
According to one common prior art method of active alignment, an optical component having an input beam of light launched therethrough is mounted to a first jig, an integrated optical system which for example is an AWG is mounted to a second jig or post, and an FAU is mounted to a third jig. Relative movement between the optical components is controlled manually and/or automatically one degree of freedom at a time until an output signal indicating maximum coupling efficiency is achieved. More specifically, maximum coupling efficiency is determined typically for a first optical port/fibre pair, and subsequently for a second optical port/fibre pair.
Unfortunately, alignment in a first degree of freedom usually destroys alignment in a second degree of freedom. For example, alignment of the second optical port/fibre pair almost always unaligns the alignment of the first optical port/fibre pair. In the worst case scenario, the optical signal is lost and must be found again. This is usually due to the fact that the pivot points of relative movement cannot be disposed at the end of the fibre being aligned within sub-micron tolerances and/or the fact that the jigs have linear tolerances (e.g., the x, y, and z axes are not generally 100% orthogonal).
Accordingly, the prior art method typically involves moving one of the components in a first degree of freedom until optimum coupling is achieved, moving the component in a second degree of freedom until optimum coupling is achieved, repeating the step of moving the component in the first degree of freedom until optimum coupling is achieved, repeating the step of moving the component in the second degree of freedom until optimum coupling is achieved, moving the component in a third degree of freedom until optimum coupling is achieved, etc . . . This recursive process can make prior art methods of alignment very time consuming and difficult to automate.
A second disadvantage of the prior art alignment relates to the apparatuses used to provide the relative movement, which traditionally, have been based only on thumb screw drives, differential drives, and/or stepping motors. For example, stepping motors that achieve the required stepping quality are excessively slow.
Since the prior art active alignment methods have traditionally been very slow, as discussed above, alignment errors associated with the use of adhesives for securing the optically aligned components, have also arisen. For example, if an adhesive, such as epoxy, is applied after the optical components have been initially aligned, then as the epoxy hardens, it may shrink and pull the optical components out of alignment. As a result, prior art methods have compensated by using relatively low temperatures to set the epoxy so that the optical components can be finely aligned during the curing of the epoxy. This increases the time of the alignment.
Another disadvantage of prior art method/apparatuses relates to the fact that they are not easily adaptable to multi-component alignment. For example, it is common to provide only two jigs for mounting only two optical components at a time.
Melles Griot Ltd., has proposed a positioning apparatus for aligning waveguides and optical fibres that may alleviate some of the above disadvantages. The positioning apparatus uses a signal optimization system referred to as “NanoTrak”, to scan and search for an optimum signal. More specifically, the apparatus includes positioners that radially move one of the components in a first search plane such that an optimum signal intensity is measured at the detector, and subsequently move the origin of the scan circle in the direction of the optimum signal intensity. The procedure is repeated iteratively until no appreciable signal gradient exists between iterations. It is further repeated for a plurality of search planes. For example, see UK Pat. Appl. GB 2 345 154, incorporated herein by reference. However, although the proposed apparatus may reduce the initial alignment time over traditional auto-alignment systems, it is limited in that in many cases the scan and track method loses the optimum signal and must find it again. This is particularly important in the alignment of multi-channel optical devices. Moreover, the proposed apparatus uses a combination of piezoelectric and stepping motors, which are used sequentially, to perform the alignment. Disadvantageously, this sequential and radial action slows down the alignment process. Further disadvantageously, piezoelectric motion is associated with hysteresis and/or drift.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a method and apparatus that obviates the above disadvantages.
It is another object of the present invention to provide a method and apparatus for efficiently aligning optical components.
Thus the present invention provides a method and apparatus for aligning optical components that effectively locks pairs of ports in alignment, while simultaneously allowing further alignment of the same or a different pair of ports. For example, in one embodiment the locked pair of ports includes a fibre end and a waveguide channel end. The effective locking of pairs of ports is achieved by providing a virtual pivot point close to the ports being aligned, via a relatively fast compensating movement of at least one of the optical components being aligned. For example, as the fibre end and waveguide channel end are moved/positioned relative to one another to improve the alignment, a relatively fast and simultaneous movement is provided to compensate for instances when the positioning movement destroys the alignment. More specifically, when the positioning movement destroys the alignment and the optical signal would otherwise be lost, the relatively fast compensating movement provides means for continuously monitoring the optical signal and recording the coordinates corresponding to the maximum optical signal. The coordinates are used to determine subsequent positioning movements.
Since the ports are locked, i.e., are always aligned with being affected by any other activities, the instant method and apparatus for alignment is suitable for automation. In the preferred embodiment, the relatively fast compensating movement is provided with at least one electromagnetic actuator.
Advantageously, the instant invention is applicable to the alignment of multi-channel optical components, multi-port optical components, and/or multi-component optical devices. With respect to the latter, the instant invention provides means for aligning three or more optical components at one time, which are sequentially positioned on the aligning jig
JDS Uniphase Inc.
Nasri Javaid
Teitelbaum Neil
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