Method for making hermetically sealed transmitter optical subassembly

A method for making a transmitter optical subassembly (TOSA) is provided. In the method, an alignment in the Z-direction between a fiber stub array (FSA) and a VCSEL array is performed first. Then, an alignment in the X-Y direction is performed. A rough prealignment in the X-Y direction may also be performed prior to the alignment in Z-direction. A vertical cavity surface emitting laser (VCSEL) array may be hermetically sealed using a lens assembly or by using a separate lid assembly. The hermetic sealing and attaching of different components may be achieved by laser welding and/or soldering or any other suitable method.

FIELD OF THE INVENTION

The present invention relates to an optical subassembly, and particularly to a hermetically sealed optical subassembly, and a method of assembling the same.

BACKGROUND OF THE INVENTION

In an optical communication system, components on the transmission side are typically packaged in a transmitter optical subassembly (TOSA). While assembling a TOSA, optical transmitting elements (e.g., vertical cavity surface emitting lasers (VCSELs)) are aligned with optical fibers so as to provide sufficient coupling efficiency. The optical transmitting elements and the optical fibers may also need to be aligned with lenses disposed therebetween. It is often difficult to align all of the optical components to each other since a three dimensional alignment, in which these components are aligned in a Z-direction as well as X and Y directions, is typically required.

In addition, when moisture and/or other gases are allowed to enter a TOSA, they can damage the optical transmitting elements and/or other components enclosed therein. Since polymers are generally not gas hermetic, encapsulation may not be sufficient to provide effective hermiticity to keep out moisture and other gases.

SUMMARY OF THE INVENTION

One embodiment of the present invention includes a hermetically sealed TOSA for a VCSEL array. In another embodiment, a method of assembling a TOSA is provided. In this embodiment, alignment in the Z-direction between a fiber stub assembly (FSA) and a VCSEL array is performed substantially independently of alignment in the X-Y direction.

In an exemplary embodiment according to the present invention, an optical subassembly is provided. The optical subassembly comprises a ceramic substrate comprising at least one layer having an electrically conductive portion; a metallic plate mounted on the ceramic substrate, the metallic plate having a cavity disposed therethrough; at least one optoelectronic device mounted on the metallic plate proximate the cavity, wherein said at least one optoelectronic device is electrically coupled to the ceramic substrate though the cavity; a lens frame having a receptacle and at least one first alignment means; a lens assembly capable of being coupled to the receptacle, said lens assembly comprising a lens array including at least one lens optically aligned with said at least one optoelectronic device; an alignment plate having a cavity disposed therethrough and at least one second alignment means arranged for cooperatively engaging the first alignment means; and a retainer mounted on the alignment plate for retaining a fiber stub assembly.

Although described herein with respect to an exemplary TOSA, it will be appreciated by those of ordinary skill in the art that the principles disclosed herein may be applied to receiver optical subassemblies (ROSAs) as well.

DETAILED DESCRIPTION OF THE INVENTION

In an exemplary embodiment according to the present invention, an optical subassembly is hermetically sealed (for example, through laser welding and/or soldering) so as to prevent moisture and/or other gases from entering it and causing damages to optical components enclosed therein. Further, in order to reduce complexity associated with a three dimensional alignment between a fiber stub array and an array of optoelectronic devices during the assembly process of the optical subassembly, an alignment in X-Y direction is performed separately from an alignment in Z-direction. By separating the three dimensional alignment into two separate alignments, time and cost savings can be realized.

FIG. 1is a perspective view of a TOSA100illustrating certain components in an exemplary embodiment according to the present invention. The TOSA100is mounted in an enclosure, here partially illustrated as a TOSA container102, and electrically coupled to a printed circuit board (PCB)104. The TOSA100also includes screws107for holding the TOSA container102together to enclose the components of the TOSA, and screws106for mounting the PCB104to the TOSA container102. The TOSA may comprise an OC-48 TOSA that transmits data at 2.5 Giga bit per second (Gbps) per channel. The TOSA may also comprise an OC-192 TOSA or OC-768 TOSA, which transmit data at 10 Gbps and 40 Gbps, respectively, or other rates.

The PCB104is electrically connected to a ceramic substrate108via a flex connector122. The ceramic substrate has multiple layers for routing electrical leads and for providing one or more ground planes. A metallic plate110is mounted on the ceramic substrate108, through brazing, for example.

The metallic plate110, which may be laser weldable, may be machined or metal-injection molded. In one embodiment, the metallic plate110is fabricated from Kovar®, which has a CTE (coefficient of thermal expansion) that is matched to the ceramic substrate108. Kovar® is a registered trademark of CRS Holdings, Inc., Wilmington, Del. The metallic plate110may also be fabricated from other suitable laser weldable metal, such as, for example, stainless steel. In other embodiments, the metallic plate110may be referred to as a seal ring or as a weld ring. In addition to providing a laser weldable interface to the ceramic substrate108, the metallic plate110may also function as a heat sink for the components of the TOSA.

An array of optoelectronic devices (i.e., optical transmitting elements, such as a VCSEL array216ofFIG. 2) is mounted on the metallic plate110. The array of optoelectronic devices may comprise, e.g., long wave (LW) VCSELs. The metallic plate110, for example, may have an opening (or cavity) formed therethrough for wire bonding or otherwise (e.g., flip-chip bonding) electrically coupling the optoelectronic devices to electrically conducting portions of the underlying ceramic substrate108for communication with other system components. The array of optoelectronic devices, for example, may be picked and placed on the metallic plate110during passive alignment with alignment marks on the ceramic substrate108or the metallic plate110using machine vision.

In an exemplary embodiment, the center-to-center distance between VCSELs in the array may be 250 μm. Thus, for example, with thirteen VCSELs in the array, the total length of the VCSEL array may be approximately 3 mm. Other dimensions used in the art also suffice. In other embodiments, a single VCSEL rather than a VCSEL array may be used for serial data transmission. In further embodiments, the optoelectronic devices may comprise short wave (SW) lasers.

The VCSEL array in the described embodiment is hermetically sealed using a glass lid transparent at the optical wavelength, such as a glass lid218ofFIG. 2. The glass lid may be anti-reflection (AR) coated to allow the VCSEL output to pass through it more effectively. The glass lid may be any commercially available glass lid suitable for hermetic sealing.

A lens frame112is also mounted on the metallic plate110. A lens assembly comprising a lens array (such as a lens array212ofFIG. 2) may be mounted on the lens frame112. The lens array should align with the VCSEL array to focus the VCSEL outputs onto corresponding fiber stubs of a fiber stub assembly (FSA), such as an FSA220ofFIG. 2. The fiber stubs interface with fibers from a fiber/ferrule assembly to propagate VCSEL outputs over an optical transmission medium.

The lens array, for example, may comprise an optical grade glass, such as COSSO™ available from Geltech, Orlando, Fla., or any other commercially available, suitable lens array fabricated from glass, plastic or other suitable material. In other embodiments, the VCSEL array may be hermetically sealed by the lens array.

The TOSA100also includes a weld plate114, which is held in place by a retainer116. For example, the weld plate114may be laser welded or soldered to the retainer116. The weld plate114may be laser welded to a lens frame112so that the VCSEL outputs are properly focused onto the fiber stubs of the FSA, which may be retained by the retainer116. The weld plate may also be referred to as an alignment plate.

The FSA in the described embodiment contains short fiber stubs corresponding to and aligned with the VCSELs, and is used to interface the VCSELs with a fiber/ferrule assembly. In other embodiments, the fiber/ferrule assembly may interface (with or without a lens array) directly with the VCSELs without an FSA disposed therebetween.

The TOSA100also includes a plastic cap118, which enables the TOSA to snap with the interfacing fiber/ferrule assembly. For example, the plastic cap118in the described embodiment includes snapping members119for holding the fiber/ferrule assembly in place. In addition, the TOSA100includes a nose receptacle120, which may be spring loaded, and into which a fiber/ferrule assembly may be inserted during use.

FIG. 2is a cross-sectional view of a TOSA200in an exemplary embodiment according to the present invention.FIG. 2, for example, may represent a cross-sectional view of the TOSA100inFIG. 1.

The TOSA200includes a retainer202for holding the optical components in place. The retainer holds the FSA220for interfacing with a fiber/ferrule assembly. The FSA220includes guide pins222aand222bfor guiding the FSA220to mate properly with the fiber/ferrule assembly. The FSA220also includes embedded fiber stubs224, which may be used to interface between a VCSEL/lens array and the fiber/ferrule assembly.

The TOSA200includes a multi-layered ceramic substrate204, on which a laser weldable metallic plate206is mounted. The metallic plate206, for example, may be fabricated from Kovar®. The metallic plate206may also be fabricated from stainless steel or any other suitable, laser weldable material. A VCSEL array216is mounted on the metallic plate206.

The VCSEL array216may be fabricated from a suitable Group III-V system, Group II-VI system, or any other suitable material known to those skilled in the art. For example, the VCSEL array may be fabricated on a gallium arsenide (GaAs) or indium phosphate (InP) substrate, or any other suitable substrate material. The VCSEL array216in the described embodiment may include thirteen VCSELs fabricated thereon, although it will be appreciated that the present invention may be used with a single VCSEL or an array of VCSELs having a different number of lasers. The VCSEL array may also be referred to as a VCSEL die.

A monitor photodetector214is mounted on one of the VCSELs of the VCSEL array216. Any one of the thirteen VCSELs, and not just the one at the edge, may be monitored by the monitor photodetector214. In other embodiments, the VCSEL array216may include other number of VCSELs, e.g., nine, fabricated thereon, with one or more of the VCSELs being monitored by one or more photodetectors.

The monitor photodetector214may be a back-illuminated photodetector for detecting VCSEL output at its backside. Unlike most photodetectors that have contact pads and active area on the same side, the bond pads of the back-illuminated monitor photodetector214in the exemplary embodiment are on an opposite side of the active area on the backside. In this way, the monitor photodetector may be wire bonded or otherwise electrically coupled to the ceramic substrate in a similar manner as the VCSELs.

Even though the monitor photodetector is monitoring a VCSEL that is not being used to transmit data over the optical fiber, due to substantial similarities between operations of the VCSELs in a VCSEL array on a common substrate, and due to the fact that they all make good contacts with the heat conductive metallic plate206, monitoring the spare VCSEL should provide sufficient information for feedback and automatic power control in the exemplary embodiment.

The VCSEL array216is enclosed in a lid assembly comprising a lid218and a lid frame217. The lid218may be made of glass transparent at the optical wavelength of the VCSELs, and the lid frame217may be fabricated from laser weldable material, such as stainless steel or Kovar®. The lid218may be AR-coated to more effectively pass through VCSEL outputs. The lid frame217may be laser welded and/or soldered to the metallic plate206. The hermetic sealing of the VCSEL array may be effected by applying solder, resistance or laser welding at the seam between the lid assembly and the metallic plate.

In other embodiments, the lid218may have a lens array formed thereon. In these embodiments, the hermetic seal would actually be formed by the lens array.

A lens frame208is also mounted on the metallic plate206. The lens frame208may be fabricated from a laser-weldable material for welding to the metallic plate206and to a weld plate114. For example, the lens frame may be fabricated from stainless steel, iron-copper alloy, iron-nickel alloy (“Alloy52”) or any other suitable material.

As illustrated onFIG. 2, the lens frame208has formed thereon a couple of grooves209aand209b. The grooves209aand209bmay be used during alignment between the weld plate210and the lens frame208. The grooves may also be referred to as notches or as alignment notches. In other embodiments, the lens frame208may have an O-ring groove formed on the bottom side opposite the side with the grooves209aand209b. The O-ring groove may be useful during solder-sealing of the lens frame208to the metallic plate206, for example, for trapping excess flux or solder.

The lens frame208holds a lens assembly213, which comprises a lens array212. In one embodiment, the number of lenses in the lens array212is the same as the number of active VCSELs used to transmit data over the optical fibers. The lenses of the lens array should be aligned with the VCSELs of the VCSEL array216.

As illustrated inFIG. 2, the weld plate210in the exemplary embodiment includes a couple of protruding portions that interface with the grooves209aand209b, respectively. The protruding portions may also be referred to as alignment members. It can also be seen inFIG. 2that the edges of the weld plate210leading to the protruding portions are slanted at an angle. The angling of the edges may be useful to bring the edges of the weld plate proximately to the walls of the grooves209aand209b, respectively, for laser welding. In other embodiments, the lens frame208may have protruding portions (alignment members) and the weld plate210may have grooves (alignment notches), to facilitate alignment between the two.

The weld plate210is mounted (laser welded, soldered or otherwise attached) on the retainer202, so that the weld plate210, and therefore the lens frame208and other components, are substantially fixed in relation to the interfacing fiber/ferrule assembly once the assembly of the TOSA and interfacing between the TOSA and the fiber/ferrule assembly is completed.

FIG. 3is a top view300of a partially assembled TOSA illustrating hermetic sealing of a VCSEL array308within a lid assembly306. In the exemplary embodiment, the lid assembly306is laser welded, and then solder sealed onto a metallic plate304, which in turn is mounted on a ceramic substrate302. A monitor photodetector310is mounted on one of the VCSELs to monitor and provide feedback for automatic control of the VCSEL operation.

FIG. 4is a top view320of a partially assembled TOSA illustrating a lens frame312in addition to the components illustrated inFIG. 3. The lens frame312may be laser welded to the metallic plate304. The lens frame312has grooves313aand313bformed thereon. These grooves may be used for alignment during laser welding.

In the described exemplary embodiment, as can be seen inFIG. 4, the width of the lens frame is slightly less than the width of the underlying metallic plate304, and the side walls of the lens frame312may form a 90° angle with respect to the top plane of the metallic plate304. This way, when laser welding is applied between the metallic plate304and the lens frame312, the forces applied to the seam are balanced. For example, the weld laser may be applied at 45° into that joint.

FIG. 5is a top view340of a partially assembled TOSA illustrating a lens assembly314in addition to the components illustrated inFIG. 4. The lens assembly314comprises a lens array that should be aligned with the VCSEL array308. The portion of the lens assembly314that holds the lens array may be fabricated from metal (e.g., stainless steel, iron-copper alloy or iron-nickel alloy), and may be laser welded and/or soldered to the lens frame312.

FIG. 6is a top view360of a partially assembled TOSA illustrating a weld plate316in addition to the components illustrated inFIG. 5. In this embodiment, the weld plate316is mounted on the lens frame312. The weld plate316includes protruding portions317aand317bto interface with the grooves313aand313b, respectively, of the lens frame312.

FIG. 7is a flow diagram illustrating a process of assembling the TOSA using laser welding in an exemplary embodiment according to the present invention.FIG. 7may be best described in reference toFIGS. 2–6.

In step400, the VCSEL array308is hermetically sealed by the lid assembly306as illustrated inFIG. 2. The lid assembly306may be laser welded and/or soldered to the metallic plate306to create the hermetic seal.

In step402, the lens array is aligned to the VCSEL array in X-Y direction by adjusting the position of the lens frame312with respect to the metallic plate304, on which the VCSEL array is fixedly mounted. The lens array may also be rotatably aligned (in a θ-direction indicated inFIG. 2) to the VCSEL array by rotating the lens assembly314with respect to the metallic plate304. The alignment between the lens array and the VCSEL array, for example, may be realized through an active alignment, during which the VCSELS are activated (e.g., turned on or pumped up).

Upon achieving substantial alignment between the VCSEL array and the lens array, the lens frame312is laser welded to the metallic plate304using any suitable, commercially available laser welder. The lens frame312and the metallic plate304may be laser welded at multiple locations along the boundary between the two to generate a sufficiently strong bond. For example, the laser welder used may be a LW-4200™ laser welder available from Newport Corporation, Irvine, Calif.

In one embodiment, the laser welder used should be suitable for applying laser beams that exert opposing forces of equal magnitude to two opposing sides of objects being welded. This way, potential for misalignment between welded objects may be reduced. For example, two laser beams may be applied at junctions between the metallic plate304and the lens frame312on two opposing sides for laser welding.

As discussed above, the width of the lens frame312may be slightly less than the width of the metallic plate304, so as to form a 90° angle at the laser welding joint on each side. For example, the laser beams may be applied at 45° at these joints to balance the forces exerted on them. In other embodiments, the lens frame312may be soldered to the metallic plate304rather than being laser welded. In still other embodiments, a combination of laser welding and soldering may be used.

After the lens frame312is fixedly attached to the metallic plate304, a weld plate316is placed on top of the lens frame312in step406. Further a retainer containing an FSA (e.g., the retainer202and the FSA220ofFIG. 2) is placed on top of the weld plate316. The weld plate316is not laser welded or otherwise attached to the retainer until the alignment in Z-direction is completed. During the alignment in the Z-direction, the weld plate316and the retainer are moved together in the Z-direction to adjust the focal point of the lenses on the fiber stubs of the FSA.

When the VCSELs are turned on, the lens array would focus the VCSEL outputs at a point in space. In step408, the FSA is aligned to the VCSEL array (via the lens array) in the Z-direction (ofFIG. 2) with the goal of optimizing the coupling efficiency (e.g., towards maximizing VCSEL outputs detected at the other end) between the VCSELs and the fiber stubs within the FSA. This may be referred to as an active alignment since at least one VCSEL output is detected and used during the alignment.

When the coupling efficiency between the VCSELs and the fiber stubs are substantially optimized, lower power may be used for transmission over the same distance with same probability of error (e.g., bit error rate (BER)) than with inefficient coupling. Thus, the VCSELs may operate at cooler temperature, and may result in longer operating life of the VCSELs.

As illustrated inFIG. 6, in the described exemplary embodiment, the protruding portions317aand317bof the weld plate slidably interface with the grooves313aand313b, respectively, of the lens frame312. The distance between the weld plate316and the lens frame312in the Z direction are adjusted until the desirable coupling efficiency between the VCSEL array and the FSA is attained; then the weld plate316is laser welded to the lens frame312to fix the distance between the FSA and the VCSEL array in Z-direction.

Prior to welding the weld plate316to the lens frame312, alignments other than the alignment in Z-direction may also be performed. For example, the weld plate316may be tilted in an X-Z plane about the Y-direction to correct any non-uniformity in the VCSEL output strength detected on the other side of the FSA. For example, if the surface of the FSA facing the VCSEL array is not parallel to the VCSEL array and is at even a slight angle, the fiber stub at one end of the FSA may detect lower-strength VCSEL output than the fiber stub at the other end, or vice versa, when in actuality, all the VCSEL outputs have equal intensity.

Therefore, by tilting the weld plate316in the X-Z plane, slight variations in distance between the VCSELs and the corresponding fiber stubs may be corrected. Further, the weld plate316may be tilted in Y-Z plane to correct reduction in coupling efficiency due to the VCSEL output hitting the fiber stubs at an angle.

Due to the fact that the edges of the weld plate316are slanted at an angle, slight tilting of the weld plate in X-Z plane with respect to the lens frame may not change the distance between weld plate and the lens frame at the welding spot. In this embodiment, this is desirable since the distance (i.e., gap) between two surfaces being laser welded should not be greater than 20 μm.

In other embodiments, the slanted edges of the weld plate316may be replaced by curved surfaces that are aligned with a curvature of a common cylinder that has a circular cross-section on the X-Z plane. This way, the weld plate may be tilted in X-Z plane with the both curved edges of the weld plate316touching the lens frame312over a range of tilting angles.

Once the distance between the FSA and the VCSEL array is substantially fixed in the Z-direction, in step412the FSA is aligned to the VCSEL array in an X-Y direction. The FSA may also be aligned to the VCSEL array in a θ-direction. In the described embodiment, the alignment in the X-Y direction may be an active alignment. Once the FSA is substantially aligned with the VCSEL array, the weld plate316is laser welded in step414to the retainer. In this embodiment, the laser welder may provide laser beams of equal power from two opposing sides to reduce potential for misalignment during laser welding. In other embodiments, the retainer and weld plate316may be attached to each other by soldering or any other suitable method known to those skilled in the art.

FIG. 8is a perspective view of a subassembly500of a TOSA illustrating certain components in another exemplary embodiment according to the present invention. The subassembly500comprises a ceramic substrate502, a metallic plate504, a sealing container506, a lens frame508, a lens array510and a weld ring512. The lens frame508and the lens array510together may be referred to as a lens assembly. The weld ring512may also be referred to as an alignment ring.

The lens array510, and therefore an underlying VCSEL array is mounted substantially at the center of the sealing container506, with one of the VCSELs positioned on the center axis of the sealing container506. This way, regardless of the orientation of the sealing container506with respect to the weld ring512, a VCSEL is always aligned with the center axis of the weld ring512.

FIG. 9is an exploded view of the subassembly500ofFIG. 8. A VCSEL array505is mounted on the metallic plate504, which may be made from a laser weldable material, such as, for example, Kovar® or stainless steel. The sealing container506is also made of a laser weldable material in this exemplary embodiment.

The VCSEL array505in this exemplary embodiment, which may have an array of nine, thirteen, or any other desired number of VCSELs, is hermetically sealed using the sealing container506, the lens frame508and the lens array510. The hermetic sealing may be achieved by laser welding, soldering, combination of the two, or any other sealing method known to those skilled in the art. The glass lens array510can be hermetically mounted to the sealing container506by means of lens frame508. The lens frame508can be in form of a metal frame that is seam welded to the container, or it can be in form of a glass frit or solder ring that hermetically seals the lens array510to the container506.

FIG. 10is a cross-sectional view of a TOSA600in an exemplary embodiment according to the present invention.FIG. 10, for example, may include the subassembly500ofFIG. 8.

The TOSA600includes a retainer602for holding the optical components in place. The retainer holds the FSA620for interfacing with a fiber/ferrule assembly. The FSA620includes guide pins622aand622bfor guiding the FSA620to mate properly with the fiber/ferrule assembly. The FSA620also includes embedded fiber stubs624, which may be used to interface between a VCSEL/lens array and the fiber/ferrule assembly.

The TOSA600includes a multi-layered ceramic substrate604, on which a laser weldable metallic plate606is mounted. The metallic plate606, for example, may be fabricated from Kovar®. The metallic plate606may also be fabricated from stainless steel or any other suitable, laser weldable material. A VCSEL array616is mounted on the metallic plate606.

A monitor photodetector614is mounted on one of the VCSELs of the VCSEL array216. Any one of the VCSELs in the array may be monitored by the monitor photodetector614. The monitor photodetector614may be a back-illuminated photodetector for detecting VCSEL output at its backside.

In this exemplary embodiment, the VCSEL array616is hermetically sealed within a sealing container610, a lens array612and a lens frame613. The sealing between the sealing container and the metallic plate606is achieved through soldering, laser welding and/or any other suitable method known to those skilled in the art. Prior to being fixedly attached to the metallic plate606, the sealing container may be rotatably aligned about the center of the VCSEL array on ball bearings624, for example.

In one embodiment, the number of lenses in the lens array612is the same as the number of active VCSELs used to transmit data over the optical fibers. The lenses of the lens array612should be aligned with the VCSELs of the VCSEL array616.

The weld ring608is mounted (laser welded, soldered or otherwise attached) on the retainer602, so that the weld ring608, and therefore the sealing container610and other components, are substantially fixed in relation to the interfacing fiber/ferrule assembly once the assembly of the TOSA and interfacing between the TOSA and the fiber/ferrule assembly is completed.

FIG. 11is a flow diagram illustrating a process of assembling the TOSA using laser welding in an exemplary embodiment according to the present invention.FIG. 11may be best described in reference toFIGS. 10.

In step700, the lens array612is aligned with the VCSEL array616. During this process, the sealing container610may be rotated about the VCSEL array. Once the lens array612is substantially aligned with the VCSEL array616, the sealing container is fixedly attached to the metallic plate606. Then in step702, the VCSEL array616is hermetically sealed.

The fixedly attaching and hermetic sealing between the sealing container610and the metallic plate606may be achieved by laser welding, soldering and/or any other suitable hermetic sealing method. Since the sealing container610has generally cylindrical shape, forces with substantially the same magnitude exerted by the welding laser beams should be applied substantially simultaneously at three locations, 120 degrees apart from each other. The laser welding, for example, may be performed using a LW4000™ laser welder available from Newport Corporation, Irvine, Calif., or any other suitable, commercially available laser welder.

In step704, the weld ring608is placed around the sealing container610, and the retainer602is placed on the weld ring608. Then in step706, the retainer602and the weld ring608are held together and aligned with the VCSEL/lens assembly in the Z-direction towards maximizing the output power of the VCSELs detected through the FSA620. This may be referred to as an active alignment since at least one VCSEL output is detected and used during the alignment.

Since one of the VCSELs is aligned with the center axis of the weld ring608, it may suffice to try to optimize the detected output from such center-aligned VCSEL. This alignment used in the described embodiment may be referred to as an active alignment where one or more VCSELs are turned on, and at least one VCSEL output is detected and used during alignment.

In the described exemplary embodiment, the alignment in Z-direction between the VCSEL array616and the FSA620may involve Z-direction movement of the weld ring608and the retainer602with respect to the VCSEL array. The alignment in Z-direction may also involve tilting the weld ring608with respect to the sealing container610. By designing the sealing container610to have a shape of a center section of a sphere rather than a section of a cylinder, as illustrated inFIG. 10, the sealing container610may have a curvature over which the weld ring608may tilt in any direction over a range of angles.

Once a satisfactory alignment is achieved between the FSA and the VCSEL array in the Z-direction, in step708the weld ring is laser welded to the sealing container by applying laser beams having substantially the same power from three directions that are 120 degrees apart from each other. The laser beams may be applied on the outer surface of the weld ring608to weld to the sealing container610inside the weld ring, since the laser beams can typically weld through metal.

In step710, the retainer602, and therefore the FSA620is aligned with the VCSEL/lens array in an X-Y direction. The FSA may be aligned with the VCSEL/lens array in a θ-direction as well. In the described embodiment, the alignment in the X-Y direction may be an active alignment. Once a satisfactory alignment is achieved, the weld ring608is laser welded to the retainer602to fix the alignment. Since the retainer and the weld ring have rectangular surfaces at their interface, the laser welding may be achieved by applying laser beams having power with substantially the same magnitude from two opposing directions. The weld ring608may also be attached to the retainer602by soldering or any other suitable method known to those skilled in the art.

Although this invention has been described in certain specific embodiments, many additional modifications and variations would be apparent to those skilled in the art. It is therefore to be understood that this invention may be practiced otherwise than as specifically described. Thus, the present embodiments of the invention should be considered in all respects as illustrative and not restrictive, the scope of the invention to be determined by the appended claims and their equivalents.

For example, even though the present invention has been described in reference to TOSAs comprising VCSELs, the principles of the present invention may also be applied to TOSAs comprising edge emitting lasers. When the edge emitting lasers are used, for example, the laser substrates would be oriented differently so as to align the emitting edges with an FSA or a fiber/ferrule assembly.