Multiple channel optical assembly and method of manufacture

A collimator array is disclosed that carries forward its alignment characteristics to optical devices that incorporate it. Little, if any active alignment need be performed in the manufacturing of such optical devices, such as switching arrays and optical add/drop arrays that employ a plurality of such collimator arrays in each device. The collimator array includes a fiber array having a plurality of regularly spaced optical fibers such that an output axis of each optical fiber has a predetermined spatial position and orientation with respect to a reference edge of the fiber array. The collimator array also includes an array of lenses separated from the fiber array by an air gap and aligned with the fiber array at an alignment position. The aligned position is such that collimated light exiting each lens has a predetermined position and direction with respect to the reference edge of the fiber array.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to optical components and, in particular, to optical components that direct multiple optical channels or perform optical switching from one channel to another, including add and drop functions for optical wavelength channels and to methods for manufacturing such optical components.

2. Description of the Related Art

Optical networks use a variety of optical components, including wavelength channel add/drop modules, optical wavelength multiplexer/demultiplexers, optical attenuators, optical isolators and optical switches. Such components are fundamental to the next generation WDM network. To make the network practical, the necessary optical devices generally must be in the form of arrays of optical elements that physically include multiple communication channels. Functional examples of such components are provided in our co-pending applications entitled “Reconfigurable Optical Add/Drop Module,” filed on May 18, 2001, having Ser. No. 09/861,117 and “Switch and Variable Optical Attenuator for Single Or Arrayed Optical Channels,” filed on Jul. 16, 2001, and having Ser. No. 09/907,496, both of which are hereby incorporated by reference as though fully set forth herein.

Present implementations of these components remain bulky and expensive and have low levels of integration, despite the continued efforts of optical component designers to improve the quality and cost-effectiveness of these optical components. The unavailability of reliable and cost-effective components has retarded the implementation of optical networks and has limited optical networks to very high traffic systems.

Currently, one area of focus for the development of commercially practical components is optical interconnect technology, and in particular, free-space optical interconnection, where signals travel through space to communicably connect optical elements with each other. Free-space based optical devices advantageously minimize the use of optically undesirable materials, such as epoxy adhesives, which when present in a light path can cause distortions that reduce component reliability and useful life. Free-space based fiber optic collimators, which are fundamental components for free-space optical interconnection, advantageously operate with a large separation distance, in comparison with the optical wavelength, between communicating collimators and with relatively low signal attenuation or loss. Such collimator arrays include an array of optical fibers that communicate through space with an array of light collimating lenses. Because of the inherent low-loss advantages of these collimator arrays, substantial resources are being applied to make them cost effective to mass-produce and package in optical devices.

Nevertheless, cost-effective and reliable free-space based collimator arrays and the optical devices that could employ them remain unavailable. The steps of performing optical alignment and attachment at each stage of device assembly continue to be difficult and labor-intensive. Misalignment loss in the space between the optical fiber array and collimating lens array due to scattering, divergence and other distortions of light continues to be problematic. Shrinkage and expansion of the adhesives that are used to join the fiber array with the lens array due to adhesive curing, temperature, aging, or other effects are also major issues because of their short and long-term effects on optical alignment. A related issue is the effect of uneven distributions of adhesive that can stress optical elements and reduce overall reliability. When balanced against the manufacturing priorities of yield and manufacturing cost per unit, these issues become even more difficult to overcome.

A need exists, therefore, for optical devices, such as collimator arrays and switching arrays, including optical add-drop switch arrays and variable optical attenuator (VOA) arrays, that can be easily and cost-effectively manufactured for optical communication applications.

SUMMARY OF THE INVENTION

The present invention provides, in one aspect, arrayed optical devices and methods for their manufacture and packaging.

In one aspect, the present invention provides a method of manufacturing a collimator array including providing an array of lenses and a fiber array comprising regularly-spaced optical fibers such that an output axis of each optical fiber has a predetermined spatial position and orientation with respect to a reference edge of the fiber array. The fiber array is aligned with the array of lenses at an alignment position such that collimated light from each lens has a predetermined position and direction with respect to the reference edge, where the array of lenses is separated from the fiber array by a gap. The fiber array is coupled to the lens array at the alignment position.

In a second separate aspect, the present invention provides a method of assembling an optical switching array. The method preferably includes the steps of providing a first collimator array having a right reference edge with respect to its array of collimated output, and a second collimator array having a left reference edge, where each collimator array includes a fiber array and a lens array. The collimator arrays are aligned and then coupled to each other at an alignment position.

Another distinct aspect of the present invention provides a method of manufacturing a low loss optical fiber collimator array. A lens array is provided and mounted between the fiber array and a mirror so that a position of the lens array can be adjusted in a plurality of dimensions, the mirror having a first position with respect to the lens array. A baseline alignment position is identified for the lens array using retroreflection from the mirror at the first position. The mirror is moved to a second position spaced farther from the lens array and a second baseline alignment position is identified for the lens array using retroreflection from the mirror at the second position. The fiber array is aligned with the array of lenses beginning from the second baseline alignment position such that collimated light from each lens has a predetermined position and direction with respect to the reference edge, the lens array being separated from the fiber array by a gap. The fiber array is rigidly fixed with respect to the lens array after alignment.

In a fourth separate aspect, the present invention provides a method of manufacturing optical array switching devices. In the case of an optical add/drop array switch, the method includes providing at least four collimator arrays, where each collimator array includes a set of beam waists with a predetermined position with respect to a reference edge of the collimator array. The method couples at an aligned position two of the collimator arrays into a first switching array having a switching array reference edge. The two remaining collimator arrays are similarly coupled into a second switching array. The first switching array is coupled with a second switching array via an alignment guide, such as a wedge, such that the four sets of beam waists for the collimator arrays are substantially co-located.

In a specific example for the fourth aspect implemented to provide a 1×2 or 2×1 array switch, the three sets of beam waists for the collimator arrays preferably are similarly co-located. In another specific example for the fourth aspect, implementing the case of an array VOA switch, the two sets of beam waists for the input and output collimator arrays are co-located, with or without an extra wedge alignment guide to couple the pair of collimators.

Further embodiments as well as modifications, variations and enhancements of the invention are also described herein.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A fiber optical collimator is an optical device that converts the highly divergent output beam of an optical fiber into a wider beam of very low divergent or convergent angles, usually employing some lensing method. Fiber optical collimators are usually used to couple light from one fiber (in a transmitting fiber collimator) to another fiber (in a receiving fiber collimator, usually of identical construction) over a relatively long working distance. One desirable quality of fiber collimator light coupling is low loss, which is attained by matching the optical beam mode of the transmitting collimator to that of the receiving collimator at the mid-point of the working distance. With identical or similar transmitting and receiving collimators, this mode matching is equivalent to locating the necked-down point (beam waist) of the collimated beam at the mid-point of the working distance. Such alignment of each collimator could be done by placing a mirror at the half working distance point, retro-reflecting the light back and adjusting the lens to fiber gap until the backward coupled light is maximized.

Given a fiber and collimating lens of a certain focal length, there is a maximum collimator working distance that will allow nearly 100% coupling. For a working distance greater than this maximum value, mode matching between the transmitting and receiving collimators is not possible and coupling is less than 100%. In general, for a fixed collimator working distance (equivalent to twice the fiber to mirror distance) less than the maximum value, there are two positions of the lens that will locate the collimated beam waist at the mirror and maximize the retro-coupling to nearly 100%.

The first position, with the lens closer to the fiber, has the advantage that the beam spot on the lens is smaller so that the clear aperture of the lens, over which any lens aberration has to be minimized for low loss, is smaller. The second position, with the lens farther away from the fiber, has the advantage that the beam waist at the mirror is smaller. Hence the clear aperture of any switching mirror can be smaller. A smaller beam waist also means that collimator coupling is more tolerant to any directional error of the beam axis. In the context of an array collimator with closely spaced fiber channels, a small clear aperture requirement for either the lens array or the mirror array is desirable. In general, either the first or second position can provide optimal low loss coupling. For a working distance greater than the maximum value, an adjustment of the lens to fiber gap distance will produce only a single instead of two retro-coupling peak positions. However, under this configuration, the collimator is very sensitive to any lateral position error of the lens, so that it could be utilized to adjust the x and y transverse positions together with the pitch and yaw of the lens array to maximize the retro-coupling across the full array of channels.

FIG. 1Ais a conceptual illustration of one preferred embodiment of a collimator array122. The collimator array122includes a fiber array110separated from a lens array112by a spatial gap114. The gap may contain air, a vacuum, or contain another gas, preferably a substantially transparent gas for the light used in the fibers. InFIG. 1A, the fiber array110includes eight optical fibers124corresponding to eight independently switchable communication channels configured as an 8×1 array, although any convenient number of fibers (or channels) configured as a one or potentially two-dimensional array may be provided. Similarly, the collimator array122includes a lens array112having eight corresponding lenses for collimating light that emerges from an optical fiber124of the fiber array110, travels through the spatial gap114and enters a lens. A rigid coupling device116preferably joins the fiber array110with the lens array112. The coupling device116fixes the relative positions of the fiber array110and the lens array112once the output of each fiber is sufficiently aligned with its corresponding light-collimating lens.

The collimating array122exhibits a design feature that a side edge, such as side edge118, is a reference edge with respect to collimated beams120of light that emerge from each lens. That is, the emerging point and direction of each beam120is precisely determined (e.g., to preferably within about a few micrometers (um) in the x, y and z dimensions and preferably within about 0.5 milliradians (mrad) in the θx, θy and θz orientations) with respect to the reference edge118. Preferably, each beam120is parallel to the reference edge118in two dimensions (i.e., in the x and z dimensions inFIG. 1A) and has the same specific downward angle (e.g., 2.4°) relative to the reference edge118in a third dimension (y dimension in FIG.1A). Furthermore, each beam120is preferably separated from its nearest neighboring beam120by the same predetermined distance.

In a preferred embodiment, any optical devices that combine multiple collimating arrays having the above-described design feature may be assembled without having to repeat any significant active alignment procedure. As an elemental component of other optical devices such as switching arrays, optical add/drop arrays and variable optical attenuators for arrayed optical channels, use of such a collimating array122facilitates the manufacturing processes for these devices.

FIG. 1Bdepicts a preferred method100of assembling a collimator array, such as the collimator array122functionally represented in FIG.1A. The method100preferably includes two initial steps102,104of providing a fiber array and a lens array such as the arrays110,112conceptually illustrated in FIG.1A.

FIG. 2illustrates an example of one preferred embodiment of a fiber array200that may be manufactured and provided in step102for assembling a collimating array. The fiber array200includes a set of preferably equal length optical fibers202, a substrate204and a cover plate206. The substrate204illustratively includes a front end208, a top side209, a bottom side211and a reference edge212. The optical fiber202preferably is typical telecommunications grade optical fiber that has been stripped of the conventionally applied plastic outer coating. Each optical fiber strand202illustratively includes an input end214and an output end216.

FIG. 3illustrates preferred basic steps in a method300of providing a fiber array200such as that depicted inFIG. 2. Afirst step302in the method300is to provide the substrate204, where the substrate204preferably is a wafer of silicon, ceramic, glass or other convenient material with a similar thermal expansion coefficient and rigidity and includes a set of parallel grooves210, preferably V-shaped, which run the length of the substrate204. Each of the V-grooves210in the substrate204is preferably sufficiently deep and wide to permit a portion of a length of optical fiber202to be fully inset within the groove210.

In a second step304, an end of a strand of optical fiber202is set within each V-groove210of the substrate204. Preferably, each strand of optical fiber202rests firmly below the top and throughout the length of each V-groove220, with the output end216of each fiber202being flush with the front side208of the substrate204. The remaining length of each strand of fiber202preferably extends from the back side of the substrate204.

In a third step306, the cover plate206is set on the top side209of the substrate206. The cover plate206is preferably made of Pyrex or other similar material and covers all of the V-grooves209to hold each strand of optical fiber202in place. Although the cover plate206may cover all or substantially all of the top side209of the substrate204, the cover plate206may cover the top side209of the substrate204at and/or near its front end208as shown inFIG. 2, where the output ends216of the optical fiber202are positioned. By so placing the cover plate206, the output ends216of the optical fiber202are fixed in position, with the output ends216of the optical fiber202fixed substantially parallel to each other.

The fiber array200is preferably specified and assembled with a threshold level of machined precision. For example, in one preferred embodiment, the grooves210in the substrate204are preferably manufactured to be equally spaced apart with a tolerance of ±0.5 micrometers (um). Furthermore, the front end208of the substrate204is preferably also machined such that along the front end208of the substrate204a predetermined distance is provided between each groove210(and thereby each optical fiber's core) and the reference edge212to a tolerance of ±5 um. The reference edge212is preferably also substantially parallel to the direction of the V-grooves210, and optionally, only substantially parallel near the front end208of the substrate204, to within at most about 0.25°. Furthermore, the substrate204is preferably machined such that its bottom surface211is parallel to within 0.5 milliradians (mrad) of an imaginary plane defined by the optical fibers202once they are fixed in position at the front end208of the substrate204. The cover plate206is also preferably precisely machined so that its top surface is parallel to the bottom surface211of the substrate204.

The surface of each optical fiber202at its output end216is preferably angled upward with respect to the fiber plane (e.g., 8 degrees from normal) to avoid retro-reflection of light back through the fiber202. The front sides208,216of the substrate204and the cover plate206are similarly angled so that the front face of the fiber array200preferably is a uniformly angled surface. The output ends216of the fiber202are preferably polished and coated with an anti-reflecting material, such as silicon nitride (Si3N4), silica (SiO2) or amorphous silicon. Once assembled, the fiber array200includes a set of fibers, where each fiber202, including each fiber's output axis216, most preferably is held in position relative to, regularly spaced from, and parallel to the reference edge212of the substrate204.

Returning toFIG. 1B, once the fiber array110,200and the lens array112are provided, the fiber array110,200is optically aligned with the lens array112in a step106.FIG. 4Adepicts a preferred embodiment of a method400for performing the step106of aligning the lens array112with the fiber array110,200. In a first step402in the aligning method400, the fiber array110,200, the lens array112and preferably an array of mirrors are mounted such that light exiting an optical fiber124,202of the fiber array110,200is directed towards a corresponding lens of the lens array112, and travels through the lens to a corresponding mirror of the mirror array. Any convenient mirror array may be used to assist in the alignment process400, although a microelectro-mechanical (MEM) mirror array is preferably used. Such mirrors are known in the art and can be made to precise tolerances.

FIG. 4Bprovides conceptual illustrations of a fiber array420, a lens array422and a mirror array424in their relative positions so as to align a fiber array420with a lens array422.FIG. 4Bprovides further explanation of the alignment method400. WhileFIG. 4Bdepicts an eight independent switch configuration, the same alignment process400may be performed for any two or more independent channels. As shown inFIG. 4B, the lens array422is preferably mounted to allow adjustment with respect to at least five degrees of freedom, represented in Cartesian coordinates as x, y, z, θy (yaw) and θz (roll). Freedom with respect to θx (pitch) may be restricted such that the lens array422is set to about a 90°-pitch with respect to an incident beam originating from the output side of an optical fiber. Mounting devices for mounting and adjusting the components, including actuators and drive electronics that provide precise adjustment of components in five or six degrees of freedom, are readily available and known in the art.

In a second step404of the alignment method400, one lens, preferably at one end of the lens array, is selected for alignment adjustment. Such a selected lens may be, for example, lens426depicted in FIG.4B. Any convenient alignment methodology may be used including maximizing the signal that retro-reflects back into the optical fiber from the mirror and detecting that signal, using, for example, a splitter at the optical fiber's input side. In a next step406, the selected end lens426is adjusted in the x, y and z dimensions. The position sought for the lens426relative to the corresponding fiber in the z dimension is approximately at the focal length for the lens426such that, with the mirror positioned at half the working distance of the collimator, the collimated beam waist is at the mirror.

In a next step408, the lens array422is then preferably adjusted to optimize the signal for a channel at the other end of the lens array422. In this step408, the lens array422is adjusted in orientation, preferably only in roll and yaw as those orientations are represented in FIG.4B. This adjustment of the lens array422, first in position and then in orientation, preferably establishes a baseline alignment position. Optionally, the order in which the alignment steps are performed may be reversed.

In the next step410, the mirror for each channel is adjusted in yaw and pitch (and optionally roll) to identify the maximum signal for each channel within ±0.5 mrad of the baseline alignment pitch and yaw. The next step412identifies the channel with the median pitch angle adjustment so as to obtain a signal maximum and identifies the channel with the median yaw adjustment to obtain the signal maximum. These adjustment values represent a center of gravity of the error in the positioning and machining of each lens as well as other factors.

Then, in a step414, the lens array422is adjusted according to the determined median yaw and pitch positions. In this step414, the lens array422is adjusted to optimize the yaw of the collimated output beam from the channel with the median yaw adjustment. This adjustment of the lens array422is performed by adjusting the lens array422in the x dimension, as represented in FIG.4B. Similarly, the lens array422is adjusted to optimize the pitch of the collimated output beam based on the channel with the median pitch angle adjustment. This adjustment of the lens array422is performed by translating the lens array422in the y dimension. Once this final adjustment is made, the lens array422is in its final alignment position with respect to the reference edge of the fiber array420.

Referring again toFIGS. 1A & B, once the fiber array110,200and the lens112array are in their optimally aligned positions and orientations, another step108is performed to permanently join the fiber array110,200and the lens array112. This completes assembly and fixing of a collimator subassembly according to a first alignment procedure. A second, presently preferred, alignment process is now discussed. This alignment process differs somewhat from the process illustrated in FIG.4A.

As in the alignment process discussed above, the fiber array420is held on a base fixed to a work bench with no degrees of freedom. The lens array422preferably is mounted in a holder connected to computer-controlled actuators that provide five degrees of freedom for positioning. These degrees of freedom are along three orthogonal translational directions (x is side-to-side along the lens array direction, y is up and down, z is along the optical axis of the fiber) and about two rotational axes (one about the optical z axis and one about the up and down y axis). The missing rotational axis (about the side-to-side x axis) would pitch the lens array back and forth and is of little consequence for the optical alignment. The lens array422preferably is fixed by the tooling in a plane normal to the optical z axis of the fiber. For alignment ease, the tooling is designed so that the two adjustable rotational axes (θy and θz) intersect precisely at the center of the primary alignment lens426at one end of the lens array, although other lenses of the array could be used in the alignment process.

Beam positioning and coupling efficiency for this alignment process are monitored by retro-reflecting the light exiting the lens array422back into itself and back along the input fiber. This is the same technique discussed above. A monitoring signal is derived from a backward facing fiber splitter in the fiber input line. The retro-reflecting mirror424is nominally placed at a distance from the lens array422equal to half the desired working distance for the collimator.

This alignment process first uses the three translational degrees of freedom to optimize back coupling for the primary alignment lens422in the array. At this stage, translation of the z position of the lens along the optical axis will produce two maxima in the coupling efficiency; at this stage in alignment the exact position of the lens array along the z dimension is not critical but is preferably somewhere between z positions corresponding to these maxima in coupling efficiency.

The alignment process next preferably rotates the lens array422about the optical z axis extending through the center of the primary alignment lens426so that the position of the lens at the other end of the array from the primary alignment lens426is optimized. Note that this action will not affect the position of the primary lens because the axis of rotation most preferably passes through the center of this lens.

The alignment process continues by rotating the lens array422about the up and down axis y so that the position of the lens at the other end of the array from the primary alignment lens422is optimized. Again, this will not change the position of the primary lens because the axis of rotation also was built to pass through the center of this lens. These initial rotations can be done in reverse order.

In a particularly preferred further process in aligning the collimator for low loss, this alignment process positions the lens array422on the optical z axis close enough to its final position so that final optimization of all the degrees of freedom can be made individually and independently. In other words, the lens array422can be guided into its overall optimum position and not a local minimum within a five-parameter space. First the retro-reflecting mirror424is moved several centimeters back from its nominal position at half the desired working distance for the collimator. The lens array422z position along the optical axis is then scanned so that the back-coupled signal can be seen passing through a maximum. If a double peak is seen in the coupling efficiency, then the retro-reflecting mirror424should be moved further back and the scanning repeated. The lens array422is most preferably positioned at the z position corresponding to this maximum and the retro-reflecting mirror is returned to its nominal position at half the desired working distance for the collimator. When the lens array422is now scanned in z position about this new placement, a double peaked curve in the coupling efficiency should be observed with a shallow saddle. The new placement of the lens array422should appear close to the one of the peaks that is closer to the fiber array420. It is from this position that the other four degrees of freedom can be independently optimized for example, the in the manner discussed above with respect to the first alignment process to give the final position for the lens array.

The lens array422is now preferably attached to the fiber array by means of a rectangular joining plate. Because the sixth degree of freedom (rotation about the side-to-side x axis) was fixed in a plane normal to the fiber axis, the surfaces of the joining plate butt up against the top cover plate on the fiber array and the back surface of the lens array without any wedged glue joints.

FIG. 5Adepicts an exploded view of a preferred embodiment of components of a collimator array500, including a fiber array520, a lens array506and a joining plate504for coupling the arrays520,506.FIG. 5Bdepicts a preferred embodiment of the collimator array500once the components are assembled in an aligned configuration according to either of the preceding first or second alignment processes.FIG. 6is a flow diagram illustrating a preferred method600of performing the step108of joining the lens array506with the fiber array520to obtain the form depicted in FIG.5B.

In a first step602, a coupling material, such as wax, glue, epoxy (preferably curable by ultraviolet (UV) light or heat) or another adhesive as is widely available and known in the art is applied to the bottom side512of the joining plate504or on the top side516of the cover plate518for the fiber array512. While the fiber array512and the lens array506are mounted in the aligned position, the joining plate504, in a next step604, is placed on the cover plate518and in a position such that the front side522of the joining plate504is pushed against the back side508of the rigidly mounted lens array506. After completing this step604, the joining plate504and the fiber array520are preferably rigidly coupled. However, the joining plate504and the lens array506, while in contact, preferably remain movable with respect to each other because no adhesive has yet been applied between them.

In a next step606, a check of the positional alignment of the lens array506is performed in two dimensions (i.e., the x and y dimensions in FIGS.5A & B). Because the front side522of the joining plate504meets the back side508of the lens array506, such an alignment is readily performed while maintaining the potential for thin and uniform adhesive lines502(seeFIG. 5B) once the joining plate504and the lens array506are rigidly joined.

If, for example, the bonding is provided between the bottom side512of the joining plate504and the top side514of the lens array506, such a positional adjustment either could not be performed or would risk requiring a substantial additional amount of adhesive to provide the rigid bonding. Such a bonding configuration is disclosed in H. Zhou, et al., “Packaging of Fiber Collimators,”Advanced Packaging, January 2002. A minimum amount and use of adhesive is, for most optical devices, preferred so as to avoid exacerbating negative optical performance effects caused by thermal expansion, aging, creep or bubbling in the adhesive.

Whether or not a final dimensional alignment of the lens array with the fiber array has been required, a next step608is preferably the application of the adhesive between the joining plate504and the lens array506. Preferably, a minimal amount of adhesive is uniformly applied and provides a rigid bond between the joining plate504and the lens array506. Preferably, the adhesive has a useful lifetime that exceeds that of the device into which the collimator array500is incorporated.

If the adhesives used in the preceding steps602,608are curable, such as a UV-curable epoxy, then the applied adhesives are cured in the next step610. This step610preferably hardens the temporarily established bonds between the components504,506,518without disturbing the components from their aligned relative positions.

When in use, the properly constructed collimator array500emits an array of parallel and regularly-spaced collimated beams524that are also parallel to a reference edge510of the collimator array500in two dimensions (i.e., y and z dimensions inFIGS. 5A & B) and have the same downward angle (e.g., 2.4°) with respect to the reference edge510in the third dimension (i.e., x dimension in FIGS.5A & B). Furthermore, the collimated beams524originate from regularly spaced predetermined points in space with respect to the reference edge.

With a collimator500having the alignment features discussed herein, many arrayed optical devices that include such a collimator array500may be easily manufactured.FIG. 7, for example, depicts a switching array700that employs two such collimating arrays702,704. To perform as a signal switching device, the switching array700preferably includes an array of mirrors positioned about one to two cm from the collimating arrays (i.e, at the line of beam waists714of the collimating arrays702,704) to direct signals from a channel of one collimating array702into or away from a corresponding channel of the other collimating array704.

FIG. 8illustrates a preferred method800for assembling a switching array such as the switching array700depicted in FIG.7. In a first step802, the two collimator arrays702,704are provided, where one collimator array704includes a reference edge on one side (e.g., left side) of the array704and the other collimating array702includes a reference edge on the opposite side (e.g., right side) of the array702. The collimating arrays702,704may be identical if they are manufactured with both left side and right side reference edges. InFIG. 5B, for example, the reference edge510for the collimator array500is on the viewable left side.

Returning toFIGS. 7 and 8, in the next step804, the collimator arrays702,704with opposing reference surfaces are mated so that their reference surfaces line up. That is, preferably the bottom surface of one collimator array702is mated with the bottom surface of the other collimator array704. InFIG. 7, numeral710identifies the location where the bottom surfaces of the collimator arrays702,704meet. Optionally, the top surfaces706,708of the collimator arrays702,704are mated. In a top-surface mating configuration, the collimating beams of each collimator array rather than having a downward angle relative to the reference edge as discussed above in connection withFIGS. 6 and 7, have an upward angle with respect to the reference edge. The objective of either form of switching array is that the arrays of beam waists714for the pair of collimator arrays will be easily co-located once the collimator arrays702,704are fixed in position relative to each other. The mating of top or bottom surfaces fixes the relative positions of the collimator arrays702,704in one dimension (i.e., the y dimension as represented in FIG.7).

Because the collimator arrays702,704are manufactured to have their beams aligned to a reference surface, no active alignment procedure is required as a step in the manufacture of the switching array700. Thus, in a next step806, the collimator arrays702,704may be passively aligned in a second dimension (i.e., the x dimension as represented inFIG. 7) by, for example, passively aligning each collimator array's reference side edge against a flat stop. Furthermore, the alignment in the third dimension may be obtained by, for example, pushing the front side of the fiber array portion of the collimator arrays702,704against a flat stop. The relatively straightforward assembling steps of pushing the collimator arrays702,704against stops and against each other perform the alignment between them702,704such that the collimator arrays' sets of beam waists714are co-located.

Nevertheless, in a manufacturing context, a quality control step808of checking the alignment of the switching array is preferably performed. If for any reason the switching array is not aligned, the components are preferably discarded or remachined. The collimator arrays, however, are preferably manufactured with precision sufficient to maintain a high yield. In a mass production context, a cost analysis is performed to optimize cost of level of precision per unit against yield.

Assuming the check of alignment meets specifications, a next step810is performed of permanently joining the collimator arrays to each other at the aligned position. This step810may be performed, as in previous steps, using a minimal amount of a convenient adhesive, such as UV-curable epoxy.

In an alternative embodiment, rather than coupling two collimator arrays together for the switching array, the switching array is formed from a single substrate, preferably having approximately double the normal width and having grooves on opposing sides to hold the optical fiber for two sets of channels. Although formed from a single substrate, a fiber array pair is provided that appears similar to the bottom surface-to-bottom surface array configuration depicted in FIG.7. The fiber array pair preferably includes a single reference edge on one side (i.e., left or right side). The alignment procedure in this embodiment comprises aligning the fiber array pair with two lens arrays such that the sets of beam waists for the collimating arrays that are formed when the alignment is completed are co-located.

FIG. 9depicts a preferred embodiment of an optical add/drop array900which may be manufactured using a pair of switching arrays904,912such as the switching array700illustrated in FIG.7. To perform as an optical add/drop device, the optical add/drop array900preferably includes an array of mirrors positioned at a line of beam waists (indicated by line914inFIG. 9) of the collimating arrays to direct signals according mirror position. Preferably, each mirror includes three-reflection positions corresponding to two alternative in/out positions and an add/drop position as is commonly provided in an add/drop module.

FIG. 10is a flow diagram illustrating three basic steps in assembling such an add/drop array900from a set of four collimator assemblies having the alignment characteristics discussed herein. In the first step1002, a set of four collimator assemblies are provided, two with reference edges on their left side and two with reference edges on their right side. In the second step1004, a pair of switching arrays902,904is assembled, each requiring a collimator with one left reference edge and one collimator with a right reference edge, preferably using the method800discussed in connection with FIG.8. Then, in a third step1006, the switching arrays902,904are used to form the optical add/drop array900.

FIG. 11details a method1100for assembling the optical add/drop array900from the pair of switching arrays904,912. In a first step1102, the two switching arrays904,912are positioned on opposing surfaces of a wedge902such as is depicted in FIG.9. The wedge902may be of any convenient rigid material, and in one preferred embodiment is a Pyrex prism. As shown inFIG. 9, the wedge902has an angle of about 25°, although the wedge902may have any convenient angle, and may even be in the form of a block having a corresponding angle of greater than 90°. Alternatively, instead of a wedge, another guide for aligning the switching arrays is used, such as wedge-shaped rails on which the switching arrays rest. InFIG. 11, the wedge902is also specified to have its side (triangular) surfaces be perpendicular to its bottom surface916and have its side surface and bottom surface916be planar to preferably within about ±5 um.

As with the assembly of a switching array discussed above, an active alignment step is preferably unnecessary to the assembly of the optical add/drop array900. Thus, in a next step1104, the reference edges906,908of the switching arrays912,904with the wedge902between them912,904may be passively aligned against a flat stop. As represented inFIG. 9, this alignment is performed in the x′ direction. The switching arrays912,904include such reference side edges906,908because these edges are provided by the collimator arrays that comprise each switching array912,904.

In a next step1106, as shown inFIG. 9, the switching arrays912,904are preferably aligned with each other in the z′ direction910by preferably pushing the switching arrays912,904against flat stops. In the embodiment depicted inFIG. 9, alignment in the z′ direction910may be achieved passively because alignment within about ±50 um in this direction is sufficient and generally readily obtainable without precise instrumentation. Alternatively, however, an active alignment step is performed such as by using MEM mirrors to reflect or retro-reflect light beams into appropriate collimators.

Once the switching arrays are aligned in the z′ direction, a next step1108is preferably performed of checking the alignment of the switching arrays912,904to verify co-location of the four sets of beam waists. Again, as with the assembly of the switching array, if the check determines that optical add/drop array900is not aligned, the components are preferably discarded or remachined. With the switching arrays912,904in a final alignment position, the switching arrays912,904are preferably bonded to the wedge902at the aligned position using an adhesive material such as the UV-curable epoxy discussed herein to form the optical add/drop array900.

While preferred embodiments of the invention have been described herein, many variations are possible that remain within the concept and scope of the invention. Such variations would become clear to one of ordinary skill in the art after inspection of the specification and drawings. The invention therefore is not to be restricted except within the spirit and scope of any appended claims.