V-groove chip with wick-stop trench for improved fiber positioning

[0002] The present invention relates generally to optical fiber arrays and micromachined chips used in optical fiber arrays. More specifically, it relates to a V-groove chip having a wick stop trench to prevent the uncontrolled wicking and movement of adhesive during manufacture of a V-groove fiber array.

[0003] Micromachined V-groove chips are commonly used in the optical fiber industry and photonics industry to align and position optical fibers. Typically, V-groove fiber arrays are made by placing optical fibers in V-grooves of a V-groove chip, placing a lid on the fibers, and then securing the assembly with adhesive. The lid can be a V-groove chip or a flat silicon or glass plate. The adhesive is typically a UV-curable or heat-curable epoxy.

[0004] The optical fibers must be carefully located in the V-grooves during manufacture of the array. Specifically, the optical fibers must be disposed in contact with the surfaces of the V-grooves. Also, for fiber arrays having polarization-maintaining fiber, the optical fibers must have an accurate rotational alignment. Also, some fiber arrays need to have optical fibers placed so that the fiber endfaces are fixed at different longitudinal positions.

[0005] It can be difficult to position optical fibers in conventional V-groove chips. This is because adhesive used to secure the fibers wicks by capillary action into the small spaces between the fibers and V-grooves. Since the adhesive wicks into these spaces, the entire length of the fiber is secured to the V-groove chip in a single step. It is not possible to secure the fiber in the V-groove in multiple gluing steps. This is a problem for certain fiber arrays because multiple gluing steps can improve the alignment of optical fibers.

[0006] U.S. Pat. No. 5,257,332 to Pimpinella discloses a fiber coupler having v-groove chips.

[0007] U.S. Pat. No. 5,748,822 to Miura et al. discloses a module for connecting an optical fiber to an optical element such as a laser diode. The module has a vertical groove cut perpendicular to the V-grooves. The vertical groove is positioned to abut the fiber endface and provide longitudinal positioning of the optical fiber.

[0008] Accordingly, it is a primary object of the present invention to provide a V-groove chip that:

[0009] 1) controls wicking of adhesive so that optical fibers can be glued in multiple gluing steps;

[0010] 2) provides for improved alignment of optical fibers in a V-groove chip;

[0011] 3) provides for improved longitudinal alignment of optical fibers;

[0012] 4) provides for improved rotational alignment optical fibers.

[0013] These and other objects and advantages will be apparent upon reading the following description and accompanying drawings.

[0014] The present invention includes a method for making a fiber array having a wick stop trench. In this method, an optical fiber is disposed in the V-groove. The fiber is glued to front and rear groove sections in separate gluing steps. Optionally, different adhesives are used in gluing the front and rear groove sections. Also, rotational or longitudinal alignment can be provided for the fiber before the fiber is glued to the front groove section.

[0015] FIG. 1 is a V-groove chip according to the present invention.

[0016] FIG. 2 is a side view of a V-groove chip of the present invention.

[0017] FIGS. 3a-bare side views of V-groove arrays of the present invention.

[0018] FIGS. 4a-billustrate a preferred method for making the present invention.

[0019] FIGS. 5a-dillustrate a preferred method of the present invention.

[0020] FIG. 6 is a top view illustrating longitudinal positioning according to the present invention.

[0021] FIG. 7 is a side view of a V-groove chip having two wick stop trenches.

[0022] FIG. 8 is a top view of an embodiment where the wick stop trench is not perpendicular to the V-grooves.

[0023] A V-groove chip according to the present invention has a wick stop trench that prevents adhesive from wicking the entire length of a V-groove. The wick stop trench is perpendicular to the V-groove and preferably deeper than the V-groove. The wick stop trench divides the V-groove into groove sections which can be glued separately in distinct gluing steps. The ability to secure a fiber in multiple gluing steps facilitates improved fiber positioning. The present invention is particularly well suited for accurate longitudinal and rotational positioning of an optical fiber in a V-groove.

[0024] FIG. 1 shows a V-groove chip according to a preferred embodiment of the present invention. The V-groove chip has a substrate 20 with a top surface 22. V-grooves 24a-fare disposed in the substrate 20. A wick stop trench 26 intersects the V-grooves 24a-f. Groove sections 24a-bare aligned across the wick stop trench 26 and in the present application are considered to comprise a single V-groove. Similarly, groove sections 24c-dand 24e-fare aligned and considered to comprise single V-grooves.

[0025] V-groove sections 24a-fare aligned in a longitudinal direction 28, and the wick stop trench 26 is aligned in a transverse direction 30. Preferably, the wick stop trench 26 is perpendicular to the V-grooves 24a-f.

[0026] Also preferably, the substrate 20 is made of single crystal silicon, and the top surface 22 is aligned with the <100>crystal plane. V-grooves 24a-fare preferably made by wet anisotropic orientation dependent etching, (e.g. using KOH) as is known in the art of silicon micromachining. The wick stop trench 26 is preferably made by a dicing saw, and can have a wide range of depths and widths. The wick stop trench 26 is preferably deeper than the V-grooves 24a-f. Alternatively, the wick stop can be made by any other micromachining technique (e.g. reactive ion etching is a possibility). The location and dimensions of the wick stop trench do not need to be precisely defined.

[0027] It is noted that V-groove chips are sometimes made from quartz or similar materials with V-grooves formed by grinding. The present invention is equally applicable to such V-groove chips.

[0028] FIG. 2 shows a side view of the wick stop trench 26. Dotted lines 32 indicate the bottom corners of the V-grooves 24a-f. The wick stop trench has sidewalls 38. In some embodiments, the sidewalls 38 are vertical (i.e. perpendicular to the top surface). The sidewalls 38 are vertical in embodiments where the trench is made using a dicing saw. The wick stop trench 26 has a width 34 and a depth 36. As noted, the wick stop trench is preferably deeper than the V-grooves (i.e. deeper than the dotted lines 32). The wick stop trench may be slightly deeper than the V-grooves (e.g. 50, 100, or 200 microns deeper than the V-grooves); the wick stop trench may also be slightly shallower then the V-grooves (e.g. 5, 10, or 20 microns shallower. In either case, the wick stop trench must be deep enough to stop capillary action of adhesive between the V-groove and a fiber disposed in the V-groove. The required depth may depend on the size of the optical fiber, the viscosity of the adhesive, and the wetting properties of the chip, optical fiber and adhesive.

[0029] The trench width 34 can be in the range of 20-500 microns. Preferably, the width 34 is about 150 microns, or in the range of 100-200 microns. The trench width should be kept relatively short to prevent microbending of an optical fiber in the V-groove. The trench can be relatively wide (e.g. 1-3 millimeters) although this is not preferred.

[0030] Preferably, the wick stop trench 26 is centered on a midpoint 39 of the v-grooves so that the V-grooves are divided into sections 40 of equal length. Alternatively, the wick stop trench 26 is located off the midpoint 39 so that the V-grooves are divided into unequal lengths. In this case, each section of the V-grooves should be at least 50-200-500 microns long. More preferably, each length is at least 2-4 millimeters long.

[0031] FIG. 3ashows a side view of an optical fiber array according to the present invention. An optical fiber 42 is disposed in the V-groove 24. Dotted line 32 indicates the bottom of the V-groove 24. A lid 44 is disposed on top of the optical fiber and holds the fiber 42 in the V-groove. The lid 44 can be made of glass, silica or silicon, for example. The wick stop trench 26 may be filled with adhesive, or may be empty. Also, the lid 44 can be replaced with a V-groove chip (with or without a wick stop trench). A front face 47 of the array is preferably polished for optical connection to other optical components.

[0032] FIG. 3bshows an alternative embodiment where the lid 44 only covers one front length 45 of the V-groove. This embodiment may be useful if hardened adhesive residue 43 is adhered to the optical fiber 42 because such adhesive residue can prevent the proper placement of the lid.

[0033] FIGS. 4a-billustrate a method for making the chips of the present invention. In FIG. 4a, a V-groove 24 is formed in a single crystal silicon substrate 20 using wet anisotropic etching. Optionally, a recessed area 46 for bonding coated fibers is etched to a level deeper than the V-grooves. Next, in FIG. 4b, the wick stop trench 26 is cut across the V-groove 24, dividing the V-groove into front and rear groove sections 24kand 24t. Groove sections 24kand 24tcan be equal or unequal in length. Preferably, the trench 26 is cut using a dicing saw or similar device. Preferably, a large number of V-groove chips are cut with the dicing saw while still connected in wafer form.

[0034] FIGS. 5a-5cillustrate a preferred method of the present invention for securing an optical fiber in a V-groove chip according to the present invention. First, in FIG. 5a, the optical fiber 42 is disposed in the front and rear V-groove sections 24k-t. The rotational alignment of the fiber may be adjusted, and the longitudinal alignment of the fiber may be adjusted. Next, in FIG. 5b, adhesive 48 (e.g. UV curable epoxy) is disposed in the rear groove section 24k. The adhesive 48 travels by capillary action (wicking) along the rear groove section 24kand stops at the wick stop trench 26. The adhesive may partially fill the wick stop trench 26. The adhesive does not travel to the front groove section 24tbecause of the wick stop trench 26. Next, the adhesive in the rear groove section 24kis hardened using UV illumination. Hardening the adhesive 48 secures the rotational and longitudinal alignment of the optical fiber 42. At this point, the fiber 42 is not attached to the front groove section 24t.

[0035] It is noted that the fiber may not be accurately disposed in the front groove section 24tduring or after adhesive 48 is set in the rear groove section 24k. This is because the fiber 42 is not pressed into the front groove section 24t. FIG. 5cillustrate a possible mispositioning of the fiber in the front groove section 24t.

[0036] Next, in FIG. 5d, a lid 44 is placed on top of the fiber 42. In the embodiment shown, the lid 44 only covers the front groove section and does not cover the rear groove section 24k. Placement of the lid presses the optical fiber into the front groove section 24tthereby providing accurate positioning of the fiber. The rotational and longitudinal alignment of the fiber is fixed by the adhesive 48 in the rear groove section before the lid is placed. After the lid is placed, adhesive is disposed in the front groove section 24tfrom either the wick stop trench 26 or the front face 47 and hardened using UV illumination. Since the rotational/longitudinal alignment and position of the fiber with in the V-groove are set independently in two separate gluing steps, each alignment can be done with higher precision. In the prior art, rotational/longitudinal alignment and pressing of the fiber into the groove must be performed in the same gluing step.

[0037] The ability of the wick stop trench 26 to stop the adhesive travel is an essential feature of the present invention. Since the wick stop trench can control the movement of adhesive, different portions of the optical fiber 42 can be glued in distinct gluing steps. The ability to glue different portions of the fiber in distinct steps provides for improved fiber alignment and other benefits in certain kinds of fiber arrays. This is because longitudinal/rotational alignment can be fixed in a separate step from pressing the fiber into the groove.

[0038] The present invention is particularly well suited for making polarization-maintaining (PM) optical fiber V-groove arrays. A method for making PM fiber V-groove arrays according to the present invention includes the following steps:

[0039] 1) Place a PM fiber in the rear groove section and front groove section.

[0040] 2) Rotate the PM fiber until properly aligned.

[0041] 3) Apply adhesive to the rear groove section and cure the adhesive, thereby fixing the rotational alignment.

[0042] 4) Place a lid on the PM fiber and press the fiber into the front groove section to accurately position the fiber in the front groove section.

[0043] 5) Apply adhesive to the front groove section and cure adhesive.

[0044] FIG. 6 shows an optical fiber array where the optical fibers 42a-care located longitudinally. Endfaces 50 are not flush (coplanar) with the front face 47 of the array and substrate. A method for making fiber V-groove arrays with longitudinally located fibers according to the present invention includes the following steps:

[0045] 1) Place a fiber in the rear groove section and front groove section.

[0046] 2) Longitudinally move the fiber until properly aligned.

[0047] 3) Apply adhesive to the rear groove section and cure the adhesive, thereby fixing the longitudinal alignment.

[0048] 4) Place a lid on the fiber and press the fiber into the front groove section to accurately position the fiber in the front groove section.

[0049] 5) Apply adhesive to the front groove section and cure adhesive.

[0050] It is noted that a jig having fiber stops can be used to longitudinally locate the optical fibers in this embodiment. It is noted that the present invention can be used in any situation where multiple gluing steps are desired. For example, different adhesives can be used in different groove sections. This may be useful, for example, where an adhesive having good polishing properties is used in the front groove section and a different adhesive having good adhesion/expansion properties is used in the rear groove section.

[0051] It is also noted that the present invention includes embodiments having more than one wick stop trench. FIG. 7, for example, shows a side view of a V-groove chip having two wick stop trenches 26a, 26bdividing the V-groove into three groove sections 24x, 24y, 24z.

[0052] It is also noted that the wick stop trench does not need to be perpendicular to the v-groove. The wick stop trench can be located at almost any angle provided that the wick stop prevents the wicking of adhesive. The wick stop trench could be oriented at 60 degrees with respect to the V-grooves, for example. FIG. 8 shows a top view of an embodiment with a nonperpendicular wick stop trench.

[0053] It is further noted that the V-groove does not necessarily have a pointed, V-shaped bottom. The V-groove can have a flat bottom. V-grooves with flat bottoms are commonly used in the art and are readily made in silicon using wet anisotropic etching techniques.

[0054] Although the present invention has been described with reference to using V-grooves, the present invention can be used with grooves of any cross sectional shape. For example, the present invention can be used with grooves having U-shapes or rectangular shapes. Also, the wick stop trench can have essentially any shape (e.g. V-shaped, U-shaped), provided that it functions as a wick stop.

[0055] Also, the V-groove chips of the present invention can be made of materials other than silicon including ceramic, quartz, plastic and metal.

[0056] It will be clear to one skilled in the art that the above embodiment may be altered in many ways without departing from the scope of the invention. Accordingly, the scope of the invention should be determined by the following claims and their legal equivalents.