Compact multi-output optical module

Abstract

An optical module for providing and detecting a plurality of split light beams from a light source is provided. A method for assembling the optical module is also provided. By reducing the assembly steps that require active component alignment, and by constraining the possible degrees of freedom for performing the alignment, the method may allow for the efficient construction of the optical module.

Description

COMPACT MULTI-OUTPUT OPTICAL MODULECROSS-REFERENCE TO RELATED APPLICATIONS[00011 This application claims the benefit of U.S. provisional application Serial No. 63 / 556,941 filed February 23, 2024, the disclosure of which is hereby incorporated in its entirety by reference herein.TECHNICAL FIELD

[0002] Aspects of the disclosure generally relate to an optical module and a method for assembly of the optical module.BACKGROUND|'00031 In order to meet optical system requirements, it may be desirable to position and align optical components in the six possible degrees of freedom. These six degrees of freedom include three degrees of translation in X, Y, and Z, as well as three degrees of rotation along each of the X, Y, and Z axes. Passive alignment refers to an alignment process without powering a system to perform the positioning. Active alignment, in comparison, refers to an alignment operation that requires a laser, detector, and or other components to be powered to perform the alignment.SUMMARY

[0004] In one or more illustrative examples, a method is performed for assembling an optical module providing and detecting a plurality of split light beams from a light source. A fiber assembly is constructed holding a plurality of fibers for receiving the split light beams, the plurality of fibers being assembled to the fiber assembly with constrained translational freedom. A subset of beam splitters are passively aligned to a beam splitter assembly. The remaining beam splitters of the beam splitter assembly are actively aligned.

[0005] In one or more illustrative examples, the method further includes placing each of the plurality of fibers into a respective V-shaped groove of the fiber assembly to provide passive translational alignment of the plurality of fibers; actively aligning rotation of the plurality of fibers around the longitudinal axis of the fibers to establish proper orientation of the fibers within the respective V-shaped grooves; and bonding the fibers into the respective V-shaped grooves once oriented.

[0006] In one or more illustrative examples, passively placing the subset of beam splitters to the beam splitter assembly includes applying vacuum to the subset of the beam splitters to hold the subset of the beam splitters in place in a fixture with respect to a beam splitter base; and bonding the beam splitters, as held into place, onto the beam splitter base, thereby securing the subset of the beam splitters to the beam splitter base within tolerance of the fixture.

[0007] In one or more illustrative examples, the subset of the beam splitters includes two beam splitters along one of the light beams, and one of the two beam splitters along each of the remaining light beams.

[0008] In one or more illustrative examples, the method further includes actively aligning a collimating lens to collimate the light source; securing the collimating lens into position once aligned; with the collimating lens into position, actively aligning a focusing lens for the light entering the respective fiber for the light beam having two passively-placed beam splitters; and securing the focusing lens into position once aligned.

[0009] In one or more illustrative examples, the method further includes for the light beams having one of the two beam splitters passively aligned, actively aligning the remaining beam splitter along the light beam in combination with a focusing lens for focusing light entering the respective fiber, wherein active alignment of the focusing lens is performed via translation but not rotation, and active alignment of the remaining beam splitter is performed via rotation.

[0010] In one or more illustrative examples, each of the remaining beam splitters comprises a kovar sliver, and further comprising magnetically chucking each of the remaining beam splitters during assembly using the respective kovar sliver of the beam splitter being actively aligned.(0011 ] In one or more illustrative examples, the method further includes actively aligning detectors along return light beam paths of the optical module to optimize signal -to-noise.(0012] In one or more illustrative examples, the method further includes actively aligning polarizers along the light beams for controlling the light beams.[001.3] In one or more illustrative examples, the method further includes no components of the optical module through which the light beams pass are aligned with more than three degrees of freedom.

[0014] In one or more illustrative examples, an optical module for providing and detecting a plurality of split light beams from a light source includes a fiber assembly comprising a plurality of fibers and a ferrule holder defining a series of V-shaped grooves. The fiber assembly is configured to receive the plurality of split light beams. The V-shaped grooves are configured to provide constrained translational freedom to the plurality of fibers while allowing for active rotational alignment of the plurality of fibers.

[0015] In one or more illustrative examples, the optical module further includes a beam splitter assembly comprising a beam splitter base and a plurality of beam splitters, wherein a first subset of the plurality of beam splitters are passively aligned when mounted to the beam splitter assembly and a second subset of the plurality of beam splitters are actively aligned in combination with corresponding collimating lenses when mounted to the beam splitter assembly.

[0016] In one or more illustrative examples, the first subset of the plurality of beam splitters includes two beam splitters along one of the light beams and one of the two beam splitters along each of the remaining light beams.(0017] In one or more illustrative examples, each of the second subset of the plurality of beam splitters comprises a kovar sliver configured to be magnetically chucked during active alignment of the respective beam splitter of the second subset.

[0018] In one or more illustrative examples, the optical module further includes a base plate configured to receive the fiber assembly and the beam splitter assembly, wherein the fiber assembly and the beam splitter assembly are passively mounted to the base plate.

[0019] In one or more illustrative examples, the optical module further includes a lens assembly including a plurality of lenses, wherein each of the lenses is configured to be actively aligned to focus light entering a respective one of the plurality of fibers, and wherein the base plate is configured to mount the lens assembly between the fiber assembly and the beam splitter assembly.

[0020] In one or more illustrative examples, active alignment of the lenses is performed via translation but not rotation, and active alignment of the second subset of the plurality of beam splitters is performed via rotation.|0021| In one or more illustrative examples, the optical module further includes a lens to collimate the light source, the base plate being configured to mount the lens between the light source and the beam splitter assembly, all lenses configured to be actively aligned into position and secured to the base plate once aligned, wherein the plurality of lenses includes a collimating lens corresponding to the light beam having two passively aligned beam splitters, the collimating lens being configured to be actively aligned and secured before the focusing lens is actively aligned into position.

[0022] In one or more illustrative examples, the optical module further includes a polarization rotator assembly including a plurality of polarizers configured to be actively aligned along the light beams, the base plate being configured to mount the rotator assembly between the collimator assembly and the beam splitter assembly.

[0023] In one or more illustrative examples, the optical module further includes a plurality of detectors configured to be mounted to the base plate and actively aligned along a return light beam path of the optical module.BRIEF DESCRIPTION OF THE DRAWINGS

[0024] FIG. 1A illustrates the example perspective view of the optical module in an assembled state;

[0025] FIG. IB illustrates a perspective view the components of rotator assembly, the beam splitter assembly, the collimator assembly, and the fiber assembly;[0026| FIG. 1C illustrates a perspective view the components of the thermoelectric cooler (TEC) and base plate assembly;

[0027] FIG. ID illustrates a perspective view the components of the housing assembly;[0028| FIG. 2A illustrates an example plan view of the outgoing light path of the assembled optical module;

[0029] FIG. 2B illustrates an example plan view of the incoming light path of the assembled optical module;

[0030] FIG. 3 illustrates an example process for the construction of the optical module;

[0031] FIG. 4A illustrates an exploded perspective view of the attachment of the fiber assembly;

[0032] FIG. 4B illustrates a plan view of the fiber assembly assembled onto the base plate;

[0033] FIG. 5 illustrates aspects of the active alignment of the fibers into the fiber assembly;

[0034] FIG. 6 illustrates an example of the beam splitter assembly partially constructed using the fixture;

[0035] FIG. 7A illustrates an exploded perspective view of the attachment of the beam splitter assembly onto the base plate of the TEC and base plate assembly;

[0036] FIG. 7B illustrates example plan view of the beam splitter and fiber assembly having been installed into the base plate assembly;

[0037] FIG. 7C illustrates an example of the beam splitter assembly and the fiber assembly being secured to the base plate during assembly;

[0038] FIG. 8A illustrates an example exploded perspective view of the installation of the TEC into the package of the housing assembly;

[0039] FIG. 8B illustrates an example perspective view of the TEC having been installed into the housing assembly;

[0040] FIG. 9A illustrates an example exploded perspective view of the installation of the partially completed TEC and base plate assembly from FIGS. 7A-7C into the package of FIGS. 8A-8B;

[0041] FIG. 9B illustrates an example plan view of the partially completed TEC and base plate assembly having been installed into the into the package;

[0042] FIG. 10A illustrates an example exploded perspective view of the installation of the superluminescent diode (SLD) and thermistor;

[0043] FIG. 10B illustrates an example close-up plan view of the SLD and thermistor as installed to the base plate;

[0044] FIG. 11 illustrates an example plan view of a simplified schematic of one of the light path channels;

[0045] FIG. 12A illustrates an example exploded perspective view of the first light path Pl;

[0046] FIG. 12B illustrates the rotation angles in a front view with respect to the SLD;

[0047] FIG. 13 A illustrates an example exploded perspective view of the additional light paths Pn;(0048) FIG. 13B illustrates the rotation angles in a back view with respect to the optical module;

[0049] FIG. 14A illustrates am example of the clocked rotators under a scope with the rotators at first orientations;

[0050] FIG. 14B illustrates an example of the clocked rotators under a scope with the rotators at second orientations;|0051[ FIG. 14C illustrates an example of two rotators of the rotator assembly being oriented;

[0052] FIG. 14D illustrates the clocked rotators as installed into the optical module;

[0053] FIG. 15 illustrates an example plan view of the optical module showing placement of the collimating lens in front of the SLD and the P4 fiber collimating lens;

[0054] FIG. 16 illustrates an example closeup plan view of a portion of the optical module showing attachment of the aligned P4 fiber collimating lens;

[0055] FIG. 17 illustrates an example plan view of the installation of the remaining beam splitters;

[0056] FIG. 18 illustrates an example plan view of the installation of the remaining collimating lenses;

[0057] FIG. 19 illustrates an example perspective view of a pair of hexapod devices for active alignment of the beam splitters and lenses;

[0058] FIG. 20 illustrates an example top view of the photodetectors as bonded to the optical module; and

[0059] FIG. 21 illustrates an example photodetector alignment station for active alignment of the photodetectors.DETAILED DESCRIPTION[0060| As required, detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of theinvention that may be embodied in various and alternative forms. The figures are not necessarily to scale; some features may be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present invention.[00611 Various applications, such as fiber optic gyroscopes, require the use of a plurality of split beams from a light source. These types of applications may employ the use of multiple, spatially separated, parallel laser beams for producing the interferometer interaction. For example, a set of fiber optic connections may be used to power a plurality of sense loops.|0062| FIGS. 1A-1D illustrates an example optical module 100 constructed to facilitate the production and meaning of such light beams. FIG. 1 A illustrates the example perspective view of the optical module 100 in an assembled state without fibers.

[0063] The optical module 100 may be constructed of a plurality of assemblies, including a housing assembly 110, a lighting assembly 120, a rotator assembly 130, a beam splitter assembly 140, a collimator assembly 150, a fiber assembly 160, and a cooling and base plate assembly 170. FIG. IB illustrates a perspective view the components of rotator assembly 130, the beam splitter assembly 140, the collimator assembly 150, and the fiber assembly 160. FIG. 1C illustrates a perspective view of the components of the cooling and base plate assembly 170. FIG. ID illustrates a perspective view the components of the housing assembly 110.

[0064] As best seen in FIG. ID, the housing assembly 110 may include a package 112 having bottom and side walls, as well as a lid 114 for enclosing the top of the optical module 100. The housing assembly 110 may accordingly define enclosure for holding the components discussed herein.

[0065] Turning to FIG. IB, the lighting assembly 120, may include an aluminum nitride plate 121 for use in mounting of the components. The lighting assembly 120 may further include a superluminescent diode (SLD) 122, a focusing lens 123 for focusing the SLD 122, a thermistor 124, an H holder 125, and a glass T 126. It should be noted that in other variations, a fiber-coupledlight input may be used as the illumination source for the optical module 100 instead of the lighting assembly 120. In some cases, the lighting assembly 120 can be disposed within the housing assembly 110, or can be external to the housing assembly 110.|0066] The rotator assembly 130 may include an optics cradle 132. The optics cradle 132 may define features for holding a plurality of rotators 134. These rotators 134 may include a SLD polarizer placed and aligned to receive the light beam output from the lighting assembly 120. The rotators 134 may also include a series of polarizers with rotators 134-134.

[0067] The beam splitter assembly 140 may include a beam splitter base 142, as well as a plurality of beam splitters 144. Significantly, each of the series of polarizers with rotators 134 may correspond to at least one of the beam splitters 144 of the beam splitter assembly 140. A light path may thus be defined from each of the beam splitters 144 to a corresponding one of the rotators 134. In one non-limiting example, the beam splitters 144 include a 30:70 beam splitter, a 70:30 beam splitter, and a 50:50 beam splitter. A subset of the beam splitters 144 may include a kovar sliver 146 attached to their upper faces. Kovar is a nickel-cobalt ferrous alloy that is magnetic and that has a coefficient of thermal expansion similar to that of glass. These kovar slivers 146 may allow for magnetic chucking of these beam splitters 144 during assembly, e.g., via an electromagnet that is powered to hold the kovar sliver 146 and unpowered to release the kovar sliver 146.

[0068] The collimator assembly 150 may include a collimator holder 152, a U-shaped glass lens mount 154 and a collimating lens 156. The collimator assembly 150 may be oriented within the housing assembly 110 to receive light beams from each of the polarizers of the rotator assembly 130, and to provide a series of collimated beam outputs.

[0069] The fiber assembly 160 may include a ferrule holder 161 defining a series of V-shaped grooves 162, one V-shaped groove 162 for holding each of a plurality of fibers 163. For each fiber 163, the fiber assembly 160 may also include a fiber boot 165, a ferrule snout 166, and a ferrule hermetic plug (not shown).

[0070] As shown in FIG. 1C, the cooling and base plate assembly 170 may include a base plate 171. A plurality of photodetector pedestals 172 may be mounted to the upper surface of the base plate 171, where each photodetector pedestal 172 defines a holder for a respective photodetector 173. The cooling and base plate assembly 170 may also include a TEC 174 to allow for heat dissipation from the lighting assembly 120, once installed to the base plate assembly 170, during operation of the SLD 122 (or other light-producing component). The base plate assembly 170 may also define a first set of electrical pins 175 for connection to the thermistor 124 and the SLD 122 (e.g., thermistor lo, thermistor hi, SLD P and SLD N). The base plate assembly 170 may also define a second set of electrical pins 176 for connection to the TEC 174 and photodetectors 173 (e g., a pair of TEC 174 power pins, a pair of Hi and Lo pins for each of the photodetectors 173, one or more ground pins, etc.).

[0071] FIG. 2A illustrates an example plan view of the outgoing light path 202 of the assembled optical module 100. As shown, the lighting assembly 120 provides a collimated output that is rotated by the rotator assembly 130, split by the beam splitter assembly 140, focused by the lens assembly 150, and applied as the light outputs into the fiber assembly 160.

[0072] FIG. 2B illustrates an example plan view of the returning light path 204 of the assembled optical module 100. As shown, the returning light paths 204 begin from light outputs of the fiber assembly 160, through the collimator assembly 150, through the beam splitter assembly 140 and into the cooling and base plate assembly 170 for detection. The photodetectors 173 may also include a photodetector 173 measuring the input signal as well, as noted above. In some variations, the light source may be external to the optical module 100, which instead may include a light input (not specifically shown). For sake of explanation, the first light path from the SLD 122 may be referred to herein as Pl, and the second, third and fourth paths to the three outputs may be referred to as P2, P3, and P4, with P2 closest to Pl, and P4 the furthest from PL While the example optical module 100 discussed herein illustrates three outputs to three fibers 163, this is only an example and optical modules 100 having a greater quantity of outputs may be constructed and used.

[0073] Maintaining the alignment of the components of the optical module 100 may be critical to avoid sensor drift and / or loss of signal. However, the alignment of these optical modules 100can be affected by various external factors such as temperature variation and system perturbation. To minimize these effects, it may be desirable to package the components of the optical module 100 as tightly as possible. However, such packaging is a challenge due to the complexity of performing alignment of each of the components to a micron or less among the six possible degrees of freedom. These six degrees of freedom include three degrees of translation in X, Y, and Z, as well as three degrees of rotation along each of the X, Y, and Z axes.

[0074] To facilitate building, it may be desirable to construct the optical module 100 with a specific sequence of assembly and alignment that constrains the degrees of freedom to be adjusted. In one example, it may be desirable ensure that no components of the optical module 100 through which the light beams pass are aligned with more than three degrees of freedom.

[0075] Certain of the steps may involve passive alignment, which refers to an alignment process without powering the system to perform the positioning. Other steps require active alignment, which refers to an alignment operation that requires the laser, detector, and or other components to be powered to perform the alignment.

[0076] FIG. 3 illustrates an example process 300 for the construction of the optical module 100. By reducing the assembly steps that require active component alignment, and by constraining the possible degrees of freedom for performing the alignment, the process 300 may allow for the efficient construction of the optical module 100. It should be noted that the operations of the process 300 are only an example, and more, fewer, and / or differently ordered operations may be performed to assemble the optical module 100.

[0077] At operation 302, the fiber assembly 160 is constructed. The assembling of the fiber assembly 160 includes the attachment of the fiber boots 164, ferrule snout 165, and ferrule hermetic plugs 166 to each of the fibers 163. Additionally, each of the fibers 163 is placed into a respective one of the V-shaped grooves 162 of the ferrule holder 161. Thus, construction of the fiber assembly 160 holding the plurality of fibers 163 for receiving the split light beams is performed such that the plurality of fibers 163 are assembled to the fiber assembly 160 with constrained translational freedom.

[0078] FIG. 4A illustrates an exploded perspective view of the attachment of the fiber assembly 160. As shown, the ferrule holders 161 are aligned to the V-shaped grooves 162 on the ferrule holder 161, e.g., using microscope and custom software. An adhesive 402 is then applied between the base plate 171 and the fiber assembly 160 with the base plate 171 once the base plate 171 is within -0.5° of the right edge of the fiber assembly 160. The adhesive 402 may, for example, be EMI Optocast 3408-XTP, as high thermal conductivity is not required. These operations may be performed passively. FIG. 4B illustrates a plan view of the fiber assembly 160 assembled onto the base plate 171.10079] FIG. 5 illustrates aspects of the active alignment of the fibers 163 into the fiber assembly 160. As shown, the fiber ferrule snouts 165 may be clocked to establish orientation of the fast and slow axes. Image based software used to view front of polished ferrule showing stress rods. With orientation of stress rods visible, the rotation stage allows each fiber 163 to be rotated around its longitudinal axis to establish proper orientation, e g., for polarization control. The three-axis stage allows a needle to contact the ferrule 165 and be set in V-groove for epoxy application. Thus, the placement of the fibers 163 is accomplished passively, except for the rotation alignment of the ferrules 165 which is performed actively.

[0080] Referring back to FIG. 3, at operation 304, a portion of the beam splitter assembly 140 is passively constructed. The beam splitter base 142 (sometimes referred to as the optical bench), as well as subset of the beam splitters 144 may be assembled passively, using a fixture. Because this subset of the beam splitters 144 is installed passively, these beam splitters 144 do not require the kovar slivers 146 on their upper faces. This subset of beam splitters 144 may thus be passively aligned to the beam splitter assembly 140.

[0081] FIG. 6 illustrates an example of the beam splitter assembly 140 partially constructed using the fixture. The fixture (not shown) may use vacuum is used to hold the pieces in place, in an example. For instance, the three left splitters and the rightmost splitter may be held by vacuum on their backs and glued in place. This allows this subset of the beam splitters 144 to be fixed onto the optical bench with the tolerance of the precision fixture. The reminder of the beam splitters144 may be aligned actively (e.g., the beam splitters 144 having the kovar slivers 146), as discussed below.(0082] Referring back to FIG. 3, at operation 306, a portion of the light path is passively assembled. This includes passive installation of the fiber assembly 160, beam splitter assembly 140, TEC 174, aluminum nitride bench, and related components to the package 112 of the housing assembly 110.

[0083] FIG. 7A illustrates an exploded perspective view of the attachment of the beam splitter assembly 140 onto the base plate 171 of the cooling and base plate assembly 170. The attachment may be performed using an epoxy 702 between the bottom of the beam splitter assembly 140 and the top of the base plate 171. The components may then be baked to ensure curing of the epoxy 702. As with the epoxy 402, the epoxy 702 may be an epoxy suitable for when high thermal conductivity is not required, such as EMI Optocast 3408-XTP.

[0084] As shown, the fiber assembly 160 is also already installed to the base plate 171. It should be noted that while all the beam splitters 144 are shown in beam splitter assembly 140 in FIG. 7A, this is for sake of illustration of their final positions, and at this stage of assembly only the passively placed subset of the beam splitters 144 would be installed.10085] FIG. 7B illustrates an example plan view of the beam splitter and fiber assembly 160 having been installed into the base plate assembly 170. FIG. 7C illustrates an example of the beam splitter assembly 140 and the fiber assembly 160 being secured to the base plate 171 during assembly.

[0086] FIG. 8A illustrates an example exploded perspective view of the installation of the TEC 174 into the package 112 of the housing assembly 110. As shown, the TEC 174 is attached to the bottom of the housing package 112 using thermal conductive adhesive 802. The thermal conductive adhesive 802 may be a thermally conductive and electrically insulating material that remains compliant after curing, such as Bacon Adhesives Flexobond 442.

[0087] FIG. 8B illustrates an example perspective view of the TEC 174 having been installed into the housing assembly 1 10. The first set of electrical pins 175 for connection to the thermistor124 and the SLD 122 and the second set of electrical pins 176 for connection to the TEC 174 and photodetectors 173 have also been installed to the housing assembly 110 at this point.(0088] FIG. 9A illustrates an example exploded perspective view of the installation of the partially completed cooling and base plate assembly 170 from FIGS. 7A-7C into the package 112 of FIGS. 8A-8B. As shown, the cooling and base plate assembly 170 is attached to the top of the TEC 174 using an epoxy 902. The epoxy 902 may be a silver-filled thermally and electrically conductive epoxy, such as Bacon Adhesives LCA-24 / BA-9, that is rigid after curing.

[0089] FIG. 9B illustrates an example plan view of the partially completed cooling and base plate assembly 170 having been installed into the into the package 112.

[0090] FIG. 10A illustrates an example exploded perspective view of the installation of the SLD 122 and thermistor 124. As shown, each of the SLD 122 and the thermistor 124 is attached to a pedestal area of the base plate 171 using an epoxy 1002. The epoxy 1002 may be a silver-filled thermally and electrically conductive epoxy, such as Bacon Adhesives LCA-24 / BA-9, that is rigid after curing. Again, while all the beam splitters 144 are shown in beam splitter assembly 140 in FIG. 10A, this is for sake of illustration of their final positions, and at this stage of assembly only the passively placed subset of the beam splitters 144 would be installed.

[0091] FIG. 10B illustrates an example close-up plan view of the SLD 122 and thermistor 124 as installed to the base plate 171. This accordingly shows the placement of the SLD 122 and thermistor 124 components after the curing of the epoxy 1002.

[0092] Referring back to FIG. 3, at operation 308, the rotators 134 of the rotator assembly 130 are clocked and bonded into the optical module 100. This allows the rotators 134 to be aligned with the various light paths as well as be rotated to the correct angles for operation of the optical module 100.| 0093| FIG. 11 illustrates an example plan view of a simplified schematic of one of the light path channels. As shown, the SLD 122 provides light, e.g., as opposed to a light input receiving from an external light source. Next, the light is applied to the rotator 134A, e.g., first to the polarizer 1102 and then to the rotator 1 104. Next, the light passes through a half-wave plate 1106. The half-wave plate 1106, sometimes referred to as a retarder, transmits light and modifies its polarization state without attenuating, deviating, or displacing the beam. Next, the light passes through a beam splitter 144A, which may be a non-polarizing plate beamsplitter (as shown) or cube beamsplitter (NPBS). A photodetector 173A may be used to detect the light passing through the NPBS beam splitter 144A. Additionally, the light may be directed from the NPBS beam splitter 144A to second beam splitter 144B, which may be a polarizing beam splitter (PBS). The light may reflect and continue through a second polarizer with rotator 134B and out the fiber 163. A second photodetector 173B may receive the incoming light from the fiber 163, having returned through the polarizer with rotator 134B and the second beam splitter 144B.

[0094] FIG. 12A illustrates an example exploded perspective view of the first light path Pl . FIG. 12B illustrates the rotation angles in a front view with respect to the SLD 122. As shown, the SLD 122 provides an SLD output 1202, which passes into the polarizer 1102. The polarizer 1102 has notches 1204 on its endcap to indicate the polarization axis direction. The light then passes through the Faraday rotator 1104. Next, the rotated light 1206 passes through the half-wave plate 1106 resulting in additional rotation of 45°. The resulting light 1210 continues to the non-polarizing beam splitter 144A, where a first portion of the light 1214 is transmitted towards RIN detector, and a second portion of the light 1216 is reflected.|0095] FIG. 13 A illustrates an example exploded perspective view of the additional light paths Pn. FIG. 13B illustrates the rotation angles in a back view with respect to the optical module 100. As shown, the second portion of the light 1216 from FIG. 12A is received to the PBS second beam splitter 144B. Reflected light 1302 from the second beam splitter 144B is then directed through the rotator 1104 and then the polarizer 1102. This results in light aligned to the fast axis of the fiber assembly as shown 1304. This light 1304 is then sent out the fiber 163, e g., to a gyroscope. Light may be returned, e.g., from the gyroscope, and may enter the second polarizer with rotator 134B, be rotated to light 1306, pass through the second beam splitter 144B, and be measured by the photodetector 173B.

[0096] FIGS. 14A and 14B illustrates example of the clocked rotators 134 under a scope. The different orientation of the polarizer 1102 of the rotators 134 can be clearly seen. FIG. 14Cillustrates an example of two rotators 134 of the rotator assembly 130 being oriented. The notches 1204 of the polarizer 1102 can be seen on the leftmost rotators 134. FIG. 14D illustrates the clocked rotators 134 as installed into the optical module 100.

[0097] Referring back to FIG. 3, at operation 310, active alignment of the beam splitters 144 and lenses is performed. The alignment may begin with using hexapods to align the focusing lens 123 in front of the SLD 122 and the P4 fiber collimating lens 156. (An illustration of a set of hexapods is shown in FIG. 19.) Significantly, by aligning the collimating lens 156 going into the respective fiber 153 and also aligning the associated beam splitter 144 in a pairwise manner, fewer degrees of freedom may be adjusted on each component without losing accuracy. For example, the beam splitter 144 may be aligned through rotational alignment, e.g., tipping and tilting via a first hexapod, while the collimating lens 156 may be aligned through translational movement via a second hexapod. It should also be noted that the ordering of alignment of the beam splitter 144 and collimating lens 156 may be performed in any sequence.

[0098] FIG. 15 illustrates an example plan view of the optical module 100 showing placement of the focusing lens 123 in front of the SLD 122 and the P4 fiber collimating lens 156. Significantly, this active alignment of the focusing lens 123 and the P4 fiber collimating lens 156 is performed using the three degrees of translation in X, Y, and Z, but not using the three degrees of rotation along each of the X, Y, and Z axes. This allows for a simplified alignment and attachment of the lenses 123, 156. After a dry fit check is completed, and after actively confirming adequate coupling efficiency is achieved, the lenses 123, 156 are bonded into place.

[0099] FIG. 16 illustrates an example closeup plan view of a portion of the optical module 100 showing attachment of the aligned P4 fiber collimating lens 156. As shown, the collimating lens 156 is now bonded into place on either side of the light path using epoxy 1602. At this point, the light paths Pl and P4 are complete and aligned. However, the light paths P2 and P3 have yet to receive the remaining beam splitters 144, and the P2 and P3 collimating lenses 156 require alignment and installation.

[0100] FIG. 17 illustrates an example plan view of the installation of the remaining beam splitters 144. As shown, the beam splitters 144 for P2 and P3 are being installed to the beam splitter base142. These beam splitters 144 are the beam splitters 144 having kovar slivers 146, as best seen in context in FIG. IB. Each of the illustrated beam splitters 144 may be aligned with one of the like of beam splitters 144 in Pl, and may also be aligned with one of the fiber collimating lenses 156. Thus, P2 and P3 alignment is achieved by aligning a beam splitter 144 and the fiber collimating lens 156 in each of the channels.[01011 FIG. 18 illustrates an example plan view of the installation of the remaining collimating lenses 156. As shown, the P2 and P3 collimating lens 156 are now also bonded into place on either side of their respective light paths, using the epoxy 1602. While not shown in FIG. 18, the beam splitters 144 for P2 and P3 are similarly bonded in place to the beam splitter base 142 in combination with the attachment of the P2 and P3 collimating lenses 156.

[0102] Hexapods 1900, such as the pair shown in FIG. 19, may be used to grab the kovar slivers 146 attached to the top of the beam splitters 144. This may be accomplished using electromagnets as an example, which may be powered to secure the beam splitters 144 to the hexapod 1900 for manipulation, and then unpowered once the beam splitters 144 are bonded into place. Hexapods in general are alignment devices that facilitate precise controlled movement in the six degrees of freedom discussed herein, referring to the three degrees of translation in X, Y, and Z, as well as pitch, roll, yaw.

[0103] Referring back to FIG. 3, at operation 312, the photodetectors 173 are actively installed to the optical module 100. As noted above, photodetector pedestals 172 may be mounted to the upper surface of the base plate 171. The photodetectors 173 may be placed onto the photodetector pedestals 172 and then aligned and bonded into place.

[0104] FIG. 20 illustrates an example top view of the photodetectors 173 as bonded to the optical module 100. Additionally, the pins of the photodetectors 173 are wired to the electrical pins 176 for electrical connection to external equipment.

[0105] FIG. 21 illustrates an example photodetector alignment station 2100. The photodetector alignment station 2100 may be utilized for active alignment of the photodetector 173. To do so, the photodetector alignment station 2100 implements custom tweezers with pogo pins sized tohold the photodetector 173 diodes to make electrical contact while the three-axis positioning stage allows adjustment of position of the photodetector 173 to achieve maximum received intensity of respective light beams.

[0106] Once installed, the components of the optical module 100 are complete. At this point, the lid 114 may be attached to enclose the top of the optical module 100, and the optical module 100 may be used.[01(17] While exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms of the invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention. Additionally, the features of various implementing embodiments may be combined to form further embodiments of the invention.

Claims

WHAT IS CLAIMED IS:

1. A method for assembling an optical module, the optical module providing and detecting a plurality of split light beams from a light source, comprising: constructing a fiber assembly holding a plurality of fibers for receiving the split light beams, the plurality of fibers being assembled to the fiber assembly with constrained translational freedom; passively aligning a subset of beam splitters to a beam splitter assembly; and actively aligning the remaining beam splitters of the beam splitter assembly.

2. The method of claim 1, further comprising: placing each of the plurality of fibers into a respective V-shaped groove of the fiber assembly to provide passive translational alignment of the plurality of fibers; actively aligning rotation of the plurality of fibers around the longitudinal axis of the fibers to establish proper orientation of the fibers within the respective V-shaped grooves; and bonding the fibers into the respective V-shaped grooves once oriented.

3. The method of claim 1, wherein passively placing the subset of beam splitters to the beam splitter assembly includes: applying vacuum to the subset of the beam splitters to hold the subset of the beam splitters in place in a fixture with respect to a beam splitter base; and bonding the beam splitters, as held into place, onto the beam splitter base, thereby securing the subset of the beam splitters to the beam splitter base within tolerance of the fixture.

4. The method of claim 1, wherein the subset of the beam splitters includes two beam splitters along one of the light beams, and one of the two beam splitters along each of the remaining light beams.

5. The method of claim 4, further comprising: actively aligning a collimating lens to collimate the light source; securing the collimating lens into position once aligned;with the collimating lens into position, actively aligning a focusing lens for the light entering the respective fiber for the light beam having two passively-placed beam splitters; and securing the focusing lens into position once aligned.

6. The method of claim 5, further comprising: for the light beams having one of the two beam splitters passively aligned, actively aligning the remaining beam splitter along the light beam in combination with a focusing lens for focusing light entering the respective fiber, wherein active alignment of the focusing lens is performed via translation but not rotation, and active alignment of the remaining beam splitter is performed via rotation.

7. The method of claim 6, wherein each of the remaining beam splitters comprises a kovar sliver, and further comprising magnetically chucking each of the remaining beam splitters during assembly using the respective kovar sliver of the beam splitter being actively aligned.

8. The method of claim 1, further comprising actively aligning detectors along return light beam paths of the optical module to optimize signal-to-noise.

9. The method of claim 1, further comprising actively aligning polarizers along the light beams for controlling the light beams.

10. The method of claim 1, wherein no components of the optical module through which the light beams pass are aligned with more than three degrees of freedom.

11. An optical module for providing and detecting a plurality of split light beams from a light source, the optical module comprising: a fiber assembly comprising a plurality of fibers and a ferrule holder defining a series of V-shaped grooves, the fiber assembly configured to receive the plurality of split light beams,wherein the V-shaped grooves are configured to provide constrained translational freedom to the plurality of fibers while allowing for active rotational alignment of the plurality of fibers.

12. The optical module of claim 11, further comprising: a beam splitter assembly comprising a beam splitter base and a plurality of beam splitters, wherein a first subset of the plurality of beam splitters are passively aligned when mounted to the beam splitter assembly and a second subset of the plurality of beam splitters are actively aligned in combination with corresponding collimating lenses when mounted to the beam splitter assembly.

13. The optical module of claim 12, wherein the first subset of the plurality of beam splitters includes two beam splitters along one of the light beams and one of the two beam splitters along each of the remaining light beams.

14. The optical module of claim 12, wherein each of the second subset of the plurality of beam splitters comprises a kovar sliver configured to be magnetically chucked during active alignment of the respective beam splitter of the second subset.

15. The optical module of claim 12, further comprising a base plate configured to receive the fiber assembly and the beam splitter assembly, wherein the fiber assembly and the beam splitter assembly are passively mounted to the base plate.

16. The optical module of claim 15, further comprising a lens assembly including a plurality of lenses, wherein each of the lenses is configured to be actively aligned to focus light entering a respective one of the plurality of fibers, and wherein the base plate is configured to mount the lens assembly between the fiber assembly and the beam splitter assembly.

17. The optical module of claim 16, wherein active alignment of the lenses is performed via translation but not rotation, and active alignment of the second subset of the plurality of beam splitters is performed via rotation.

18. The optical module of claim 16, further comprising a lens to collimate the light source, the base plate being configured to mount the lens between the light source and the beam splitter assembly, wherein the lenses are configured to be actively aligned into position and secured to the base plate once aligned, wherein the plurality of lenses includes a collimating lens corresponding to the light beam having two passively aligned beam splitters, the collimating lens being configured to be actively aligned and secured before the focusing lens is actively aligned into position.

19. The optical module of claim 16, further comprising a polarization rotator assembly including a plurality of polarizers configured to be actively aligned along the light beams, the base plate being configured to mount the rotator assembly between the collimator assembly and the beam splitter assembly.

20. The optical module of claim 16, further comprising a plurality of detectors configured to be mounted to the base plate and actively aligned along a return light beam path of the optical module.

Images