Abstract
A method for manufacturing an electro-optically coupled switch in accordance with the present invention requires a sequential reconfiguration of a layer of semiconductor material. To begin, a base member is created wherein the semiconductor layer is positioned on a layer of insulator material with the insulator material positioned between the semiconductor layer and a semiconductor substrate. In sequence, with a first etch, the semiconductor layer is etched to create waveguides on opposite sides of a slot. In a second etch, the slot is deepened to expose the layer of insulator material in the slot. With a third contact pad doping process, pads can be positioned on top of the layer of insulator material for electrical contact with the respective waveguides. Metal contacts can then be placed on the contact pads, the slot can be filled with an electro-optical polymer and, if needed, the polymer can be poled.
Claims
1. A method for manufacturing an electro-optically coupled switch comprising the steps of: providing a layer of a conducting semiconductor material, wherein the layer is shaped as a rectangular prism and is mounted on an insulating substrate having a top silica layer, wherein the layer of semiconductor material is bounded by a pair of opposed parallel edges between a top and a bottom; removing material from the layer of semiconductor material through a same distance x.sub.e from each edge of the layer and through a same distance d.sub.1 from the top of the layer, to establish edge segments through the distance x.sub.e from the respective edge of the layer and at the distance d.sub.1 from the top thereof; creating a slot in the layer of semiconductor material along a central plane located equidistant from each edge of the layer, wherein the center of the slot is aligned with the central plane and the slot has a width x.sub.c, and the slot extends through the layer from top to bottom, to establish opposed waveguide-electrodes between the slot and the edge segments of the layer, wherein the two opposed waveguide-electrodes each has an optical input port and an optical output port; filling the slot with a non-conducting and electro-optic sensitive polymer to function as a cross-coupling material; doping the edge segments of the semiconductor material through a distance x.sub.d from each edge of the layer to establish contact pads with a respective waveguide-electrode; and interconnecting a respective metal electrode with each contact pad to selectively provide a switching voltage V.sub.π from a voltage source for the electro-optically coupled switch.
2. The method recited in claim 1 further comprising the step of poling the polymer in the slot to optimize an electro-optic coefficient for the cross-coupling material to accommodate an optical signal passing through the electro-optically coupled switch.
3. The method recited in claim 2 wherein the poling step optimizes an orientation of the electro-optic coefficient with a TE mode of the optical signal.
4. A method for manufacturing an electro-optically coupled switch comprising the steps of: creating a base member having a length L, a width W.sub.s, and a thickness T, wherein the base member defines a central plane located equidistant between opposed edges of the base member, and wherein the base member includes a layer of a non-conducting semiconductor substrate and a layer of a doped semiconductor conducting material, with a layer of an insulator material positioned therebetween; performing a first etch using a self-aligned first mask by removing material from the layer of semiconductor material on the base member to a depth d.sub.1, along the length L through a distance x.sub.e extending from each edge of the base member toward the central plane and a slot region along the length L through a distance x.sub.c symmetrically centered on the central plane; performing a second etch, using the self-aligned first mask and a second mask to remove material from the layer of semiconductor material on the base member to a depth d.sub.2 in the slot region which is along the length L and through the distance x.sub.c to expose the insulator material in the slot region between opposed waveguide-electrodes, wherein each waveguide-electrode has an optical input port and an optical output port, and each waveguide-electrode has a width of at least x.sub.w and a length L, and wherein d.sub.2>d.sub.1, and W.sub.s=2x.sub.e+2x.sub.w+x.sub.c; filling the slot with a non-conducting and electro-optic sensitive polymer to function as a cross-coupling material; doping the semiconductor material through a distance x.sub.d from each edge of the base member to establish respective contact pads along each edge of the base member, for connection of each contact pad with a respective waveguide-electrode, wherein x.sub.d is less than x.sub.e (x.sub.d<x.sub.e); and interconnecting a respective metal electrode with each contact pad to selectively provide a switching voltage V.sub.π from a voltage source for the electro-optically coupled switch.
5. The method recited in claim 4 further comprising the step of poling the polymer in the slot to optimize an electro-optic coefficient for the cross-coupling material to accommodate an optical signal passing through the electro-optically coupled switch.
6. The method recited in claim 5 wherein the poling step optimizes an orientation of the electro-optic coefficient with a TE mode of the optical signal.
7. The method recited in claim 4 further comprising the step of passivating the layer of semiconductor material and the electro-optic sensitive polymer material.
8. The method recited in claim 4 wherein the semiconductor material is selected from the group consisting of silicon, compound semiconductor InP, GaAs, GaN, and quantum well semiconductors.
9. The method recited in claim 4 wherein the doping step further comprises the steps of: performing a second doping process into the layer of semiconductor material through the distance x.sub.d to the depth d.sub.2 along the length L at each edge of the base member in its respective edge segment to create respective contact pads for connection with a metal electrode; and N.sup.+ doping the contact pads to reduce switch series resistance.
10. The method recited in claim 4 further comprising the steps of: providing the self-aligned first mask for the first etch, wherein the first mask is formed with a central cutout and a pair of rectangular shaped side cutouts positioned on opposite sides of the central cutout from each other to define a pair of parallel strips, with each strip having the length L and a width x.sub.w with the distance x.sub.c therebetween; aligning the self-aligned first mask to cover the base member with the parallel strips symmetrically positioned to straddle the central plane; providing a second mask for the second etch, wherein the second mask is formed with a single rectangular shaped cut-out having a length L and a width equal to W.sub.c wherein x.sub.c<W.sub.c<x.sub.c+2x.sub.w; aligning the second mask to cover the first mask pattern which is imposed on the base member with the rectangular shaped cut-out symmetrically positioned relative to the central plane; providing a third mask for the heavily doped region to reduce switch series resistance wherein the third mask is a panel having a length L and a width equal to W.sub.s-2x.sub.d; and aligning the third mask symmetrically on the base member to dope the edge segments of the base member.
11. The method recited in claim 10 wherein the self-aligned first mask, the second mask, and the third mask are made using a photo-lithography process.
12. The method recited in claim 4 wherein the first etch and the second etch are accomplished using a chemical/physical process.
13. A method for manufacturing an electro-optically coupled switch comprising the steps of: providing a base member having a non-conducting semiconductor substrate and a layer of a conducting semiconductor material, with a layer of insulator material positioned therebetween; positioning a first mask against the layer of semiconductor material; etching the layer of semiconductor material behind the first mask to remove the layer of semiconductor material to a depth d.sub.1, and to form a slot straddled by opposed waveguide-electrodes; positioning a second mask against the opposed waveguide-electrodes; etching the layer of semiconductor material in the slot to a depth d.sub.2 to expose insulator material in the slot between the opposed waveguide-electrodes, and d.sub.2 is greater than d.sub.1 (d.sub.2>d.sub.1), and wherein each waveguide-electrode has an optical input port and an optical output port; positioning a third mask over the slot and over the opposed waveguide-electrodes to expose an edge segment for each waveguide-electrode, wherein each edge segment is at a respectively same distance from the slot; doping the exposed segments of each waveguide-electrode in the layer of semiconductor material to the depth d.sub.2 and to the edge segments beyond the waveguide-electrode from the slot to create respective contact pads; connecting an electrode with each contact pad; filing the slot with a non-conducting polymer material; and poling the polymer material in the slot.
14. The method recited in claim 13 wherein the layer of semiconductor material is selected from the group consisting of silicon, compound semiconductor such as InP, GaAs, GaN, and quantum well compound semiconductor materials.
15. The method recited in claim 13 wherein the layer of semiconductor material is a doped N material and the contact pads are heavily N.sup.+ doped material to reduce the switch series resistance.
16. The method recited in claim 13 wherein the insulator material is silica.
17. The method recited in claim 13 wherein the polymer material used in the poling step is an electro-optic cross-coupling polymer, and the poling step is accomplished to optimize an alignment of the electro-optic coefficient of the polymer material.
18. The method recited in claim 13 wherein the base member is rectangular shaped having a length L, a width W.sub.s, and wherein the base member defines a central plane located equidistant between opposed edges of the base member, the method further comprising the steps of: forming the first mask, wherein the first mask is formed with a central cutout and a pair of rectangular shaped side cutouts, wherein the side cutouts are on opposite sides of the central cutout from each other to define a pair of parallel strips, with each strip having the length L and a width x.sub.w with the distance x.sub.c therebetween; and aligning the first mask to cover the base member with the parallel strips symmetrically positioned relative to the central plane.
19. The method recited in claim 18 further comprising the steps of: forming the second mask for a second etch, wherein the second mask is formed with a single rectangular shaped central cutout having a length L and a width equal to W.sub.c, wherein x.sub.c<W.sub.c<x.sub.c+2x.sub.w; and aligning the second mask to cover the first mask pattern imposed on the base member with the rectangular shaped cut-out symmetrically positioned relative to the central plane.
20. The method recited in claim 19 further comprising the steps of: forming the third mask for heavy doping into the contact pads wherein the third mask is a panel having a length L and a width equal to W.sub.s-2x.sub.d; and aligning the third mask symmetrically on the base member to expose edge segments of the base member.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0032] The novel features of this invention, as well as the invention itself, both as to its structure and its operation, will be best understood from the accompanying drawings, taken in conjunction with the accompanying description, in which similar reference characters refer to similar parts, and in which:
[0033] FIG. 1 is a perspective-schematic view of a system for transmitting optical signals, which includes an electro-optically coupled switch in accordance with the present invention;
[0034] FIG. 2 is a cross-section view of an embodiment of the electro-optically coupled switch for the present invention as seen along the line 2-2 in FIG. 1;
[0035] FIG. 3 is a cross-section view of an exemplary switch in accordance with the present invention, as seen along the line 3-3 in FIG. 1, showing the switch/modulation functionality of the present invention;
[0036] FIG. 4 is a cross-section view of another embodiment of the electro-optically coupled switch for the present invention as seen along the line 4-4 in FIG. 1;
[0037] FIG. 5 is a cross-section view of still another embodiment of the electro-optically coupled switch for the present invention as seen along the line 5-5 in FIG. 1;
[0038] FIG. 6 is a perspective view of a work piece used for a manufacture of the electro-optically coupled switch of the present invention;
[0039] FIG. 7A is a cross-section of the work piece as seen along the line 7-7 in FIG. 6, with the work piece in an intermediate configuration during a manufacturing process;
[0040] FIG. 7B is a view of the work piece as seen in FIG. 7A after manufacture and ready for subsequent assembly in an operational switch;
[0041] FIG. 8 is a sequence of evolving cross-sections of the work piece as seen in FIGS. 7A and 7B, with the sequence showing eight different manufacturing steps, respectively numbered (1) through (8), in a manufacture of the present invention;
[0042] FIG. 9A is a top plan view of a first mask for use in the manufacture of the present invention;
[0043] FIG. 9B is a top plan view of a second mask for use in the manufacture of the present invention; and
[0044] FIG. 9C is a top plan view of a third mask for use in the manufacture of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0045] Referring initially to FIG. 1, an electro-optically coupled switch in accordance with the present invention is shown and is generally designated 10. As shown, the switch 10 includes an enclosure 12 for holding and protecting the electro-optic components of the switch 10. Also, an access connector 14 is provided for connecting the electro-optic components (not shown in FIG. 1) with an external voltage source 16. A queue control 18 and a routing control 20 are incorporated with the voltage source 16 to respectively provide for the sequencing, routing and modulation of optical signals, λ, as they pass through the electro-optically coupled switch 10.
[0046] Still referring to FIG. 1, it will be seen that the enclosure 12 includes an input port 22 for optically connecting an optical waveguide 24 with the switch 10. Similarly, an input port 26 is provided by the enclosure 12 for optically connecting an optical waveguide 28 with the switch 10. It is to be appreciated that the optical waveguides 30 and 32 will have similar connections with the enclosure 12.
[0047] In FIG. 2 the internal, electro-optic components for a preferred embodiment of the switch 10 are shown. There it will be seen that the switch 10 includes a waveguide 34 and a waveguide 36 that are respectively protected by a cladding 38 and a cladding 40. In more detail, each waveguide 34 and 36 has a width, W, and a length, L, and they are vertically aligned in parallel with each other. Further, as shown, the switch 10 includes a metal connector 42 (e.g. +V) and a metal connector 44 (e.g. −V) which are respectively connected with a transparent electrical contact 46 and a transparent electrical contact 48. Further, a cross-coupling material 50 is positioned between the transparent electrical contacts 46 and 48. In accordance with the present invention, the transparent electrical contacts 46 and 48 are in direct contact with the cross-coupling material 50, and are everywhere separated from each other by a distance, d. Further, the transparent electrical contacts 46 and 48 are positioned opposite each other from the cross-coupling material 50. And, they are each positioned between the cross-coupling material 50 and a respective waveguide 34 and 36. Additionally, a filler material 52 is provided to electrically confine the cross-coupling material 50 between the transparent electrical contacts 46 and 48.
[0048] Within the combination of components for the switch 10 shown in FIG. 2, the differences in the refractive index of the various materials used are important. In detail, the refractive index of waveguide 34 (a first waveguide), n.sub.wg1, will be equal to, or nearly equal to, the refractive index of waveguide 36 (a second waveguide), n.sub.wg2. For purposes of the present invention, the refractive indexes of the waveguides 34 and 36 will be the same, or nearly the same, n.sub.wg1≈n.sub.wg2. Importantly, however, the refractive index of the cross-coupling material 50, n.sub.c, (also sometimes noted herein as n.sub.eo) needs to be much greater than the respective indexes n.sub.wg1 and n.sub.wg2 of the first and second waveguides 34 and 36 (i.e. n.sub.wg1<<n.sub.c>>n.sub.wg2). As noted above, this arrangement is made to achieve strong waveguide cross-coupling, good optical confinement in the cross-coupling material, and efficient electro-optic modulation, with a proper waveguide separation distance, d. For example, n.sub.c=1.7, n.sub.wg=1.57, and d=0.5 μm. Also, the refractive index of the filler material 52, n.sub.f, needs to be smaller than all of the others (i.e. n.sub.c>>n.sub.wg(1 and 2)>n.sub.f, and n.sub.wg1≈n.sub.wg2).
[0049] As shown, the metal connector 42 and the metal connector 44 are separately connected with the voltage source 16. Thus, a +V can be provided to the metal connector 42 by the voltage source 16, and a −V can be provided to the metal connector 44. The result is that a switching voltage, ΔV.sub.π, can be applied through the cross-coupling material 50 that will change its refractive index, n.sub.c. As envisioned for the present invention, the cross-coupling material 50 may be a polymer, when the waveguides 34 and 36 are also polymers, or when the waveguides 34 and 36 are made of a SiON/silica material.
[0050] An operation of the switch 10 will be best appreciated with reference to FIG. 3. There it will be seen that, depending on the influence of the switching voltage, V.sub.π, an optical signal, λ, can be directed either onto a pathway 54 (solid arrows) or a pathway 56 (dashed arrows). The consequence of this is that, the switching voltage, V.sub.π, can be used to guide an optical signal, λ, which enters the switch 10 through the input port 22 to exit the switch 10 from either the output port 58 of waveguide 36 or the output port 60 of waveguide 34.
[0051] With the above in mind, and by returning to FIG. 1, it will be appreciated that the routing control 20 can influence the voltage source 16 to selectively establish the switching voltage, V.sub.π, and thereby generate the electrical field, E. Importantly, the electrical field, E, when generated, is uniform with the flux lines of the field oriented substantially perpendicular to the length, L, of the waveguides 34 and 36. As mentioned above, the purpose here is to influence the transit of an optical signal, λ, through the switch 10.
[0052] For an exemplary operation of the switch 10, refer back to FIG. 1. In this example, consider an optical signal, λ.sub.in-a, as input from optical waveguide 24, into the waveguide 36 via input port 22. Also consider an optical signal, λ′.sub.in-b, as input from optical waveguide 28, into the waveguide 34 via input port 26. For purposes of this example, subscript “a” pertains to waveguide 36, while subscript “b” pertains to waveguide 34.
[0053] With cross-reference between FIG. 1 and FIG. 3, and first considering only the optical signal, λ, it is to be appreciated that with no switching voltage, V.sub.π, there is no electric field, E, through the cross-coupling material 50. Accordingly, optical signal, λ.sub.in-a, in optical waveguide 24 will enter switch 10 via input port 22, transit switch 10 on pathway 54, and exit from switch 10 via the output port 58 (FIG. 3) and into the optical waveguide 30 as optical signal, λ.sub.out-a. On the other hand, with a switching voltage, V.sub.π, imposed on the cross-coupling material 50, an electric field, E, is generated through the cross-coupling material 50 to change the refractive index, n.sub.c(n.sub.eo), of the cross-coupling material 50. In this case, the optical signal, λ.sub.in-a, will transit switch 10 on pathway 56, and exit from switch 10 via the output port 60 (FIG. 3), and into the optical waveguide 32 as optical signal, λ.sub.out-b.
[0054] Similarly, when considering the optical signal, λ′, it is to be appreciated that with no switching voltage, V.sub.π, optical signal, λ′.sub.in-b, will enter switch 10 from optical waveguide 28 via input port 26. Optical signal, λ′.sub.in-b, will then transit switch 10 and exit via the output port 60 (FIG. 3) and into the optical waveguide 32 as optical signal, λ′.sub.out-b. With a switching voltage, V.sub.π, imposed on the cross-coupling material 50, however, the optical signal, λ′.sub.in-b, will transit switch 10 to exit from switch 10 via the output port 58 (FIG. 3), and into the optical waveguide 30 as optical signal λ′.sub.out-a.
[0055] Still referring to FIG. 1 it is to be appreciated that the switch 10 can be used either as a switch or as a modulator. Further, it will be appreciated that the queue control 18 can be used as a gate to provide for alternating or sequential access of the optical signals, A and A′, to the switch 10. As will be appreciated by the skilled artisan, when switch 10 is used as a modulator, only one continuous wave (CW) light input port 22 and one optical output port (e.g. output port 58, FIG. 3) are required.
[0056] FIG. 4 shows an alternate embodiment for the present invention wherein the waveguide 34 and the waveguide 36 are each made of a same, lightly-doped, electrically-conductive material. As shown, the waveguides 34 and 36 are individually positioned in contact with the voltage source 16. For one alternate embodiment of the present invention, both the waveguide 34 and the waveguide 36 are N doped. Accordingly, the means for imposing the switching voltage, V.sub.π, includes an N.sup.+ doped layer 62 that is positioned in electrical contact between the N doped waveguide 34 and the metal connector 44. Similarly, an N.sup.+ doped layer 64 is positioned in electrical contact between the N doped waveguide 36 and the metal connector 42. Preferably, for this alternate embodiment of the present invention, the cross-coupling material 50 is a polymer.
[0057] FIG. 5 shows another alternate embodiment of the present invention wherein the waveguide 34 is P doped and the waveguide 36 is N doped. In this case, the means for imposing V.sub.π includes a P.sup.+ doped layer 66 positioned in electrical contact between the P doped waveguide 34 and the metal connector 44. Also included is an N.sup.+ doped layer 68 which is positioned in electrical contact between the N doped waveguide 36 and the metal connector 42. In this case, the cross-coupling material 50 can be either a PIN planar-diode-structure semiconductor, or a PIN multiple-quantum-well semiconductor.
[0058] Referring now to FIG. 6, a method for manufacturing an electro-optically coupled switch in accordance with the present invention is disclosed. In FIG. 6 it will be appreciated that the method first requires providing a base member that has been generally designated 80. As shown, the base member 80 includes a layer 82 of a semiconductor material. Also, the base member 80 includes a layer 84 of an insulator material that is positioned between the semiconductor layer 82 and a substrate 86 that is also made of a semiconductor material. For purposes of the present invention, the semiconductor material that is used for the layer 82 may be of any type well known in the pertinent art, such as silicon, or compound semiconductors such as InP, GaAs, GaN, or a quantum well composition of various compound semiconductors.
[0059] When constructed, the base member 80 will have a length L, a width W.sub.s and a thickness T. The base member 80 will also have opposite edges 88a and 88b which straddle the central plane 90 that is defined by the base member 80.
[0060] As an overview of the methodology for the present invention, FIG. 7A shows that the semiconductor layer 82 is to be reconfigured to form a slot 92 which is positioned along the central plane 90 between opposed waveguides 94a and 94b. Note: the depth of the slot 92 extends through the semiconductor layer 82 to expose the layer 84 of insulator material. Still referring to FIG. 7A it will be appreciated that the slot 92 will have a width x.sub.c along the length L of the slot 92, and that the waveguides 94a and 94b each have an operational width x.sub.w adjacent the slot 92, as well as an extension of width x.sub.e that extends from the waveguides 94a and 94b toward the edges 88a and 88b of the base member 80.
[0061] FIG. 7B shows that the semiconductor layer 82 will be further reconfigured to form contact pads 96a and 96b at the edges 88a and 88b of the base member 80. Additionally, metal electrodes 98a and 98b are then to be positioned in electrical contact with the respective contact pads 96a and 96b. Further, FIG. 7B shows that the slot 92 is filled with a cross-coupling material 100. For purposes of the present invention, the cross-coupling material 100 can be of any type material known in the pertinent art for the specified purposes of the present invention. Preferably, the cross-coupling material 100 will be a polymer. With the above overview in mind, the methodology of the present invention is best appreciated with reference to FIG. 8 and FIGS. 9A, 9B and 9C.
[0062] FIG. 8 shows that the method for manufacturing an electro-optically coupled switch is essentially an eight step process. In FIG. 8, these steps are designated sequentially as (1), (2), (3) . . . (8). To begin, as shown in FIG. 8(1), a base member 80 is constructed as disclosed above. Then, a first mask 102 is positioned on the layer 82 of semiconductor material and it is aligned on the layer 82 relative to the central plane 90 substantially as shown in FIG. 9A. As best seen in FIG. 9A, the first mask 102 is formed with a central cutout 104 and a pair of side cutouts 106a and 106b. Between the central cutout 104 and the side cutouts 106a and 106b are two parallel strips 108a and 108b that are separated from each other by the distance x.sub.c. With the first mask 102 in position on the layer 82, FIG. 8(2) shows that, in a first etch, the semiconductor material in the layer 82 is etched to a depth of d.sub.1. The result here is to create a reconfigured layer 82′ that is formed with the slot 92.
[0063] FIG. 8(3) shows that after the first etch, a second mask 110 is positioned over the first mask 102. FIG. 9B shows that this second mask 110 is formed with only a central cutout 104′. For purposes of the present invention, this central cutout 104′ can be formed with a width W.sub.e where x.sub.c<W.sub.c<x.sub.c+2X.sub.w. In any event, the second mask 110 is intended to mask the entire layer 82′ with the exception of the slot 92. Accordingly, in a second etch, with the second mask 110 in place, the layer 82′ of semiconductor material can be further reconfigured. Specifically, as shown in FIG. 8(3), semiconductor material in the slot 92 can be removed through the depth d.sub.2 to expose insulator material in the layer 84. The second mask 110 and the first mask 102 can then be removed.
[0064] In the next sequential step, FIG. 8(4) shows that a third mask 112 is positioned over the layer 82 of semiconductor material to cover the slot 92 and portions of the waveguides 94a and 94b. For the present invention, the third mask 112 is essentially a solid panel 114 (See FIG. 9C). This effectively exposes the edge segments 116a and 116b shown in FIG. 8(4). Thus, semiconductor material in the edge segments 116a and 116b of layer 82 can be heavily doped in this process. As shown in FIG. 8(5), after the doping of edge segments 116a and 116b, the respective contact pads 96a and 96b can be formed. As noted above, the contact pads 96a and 96b are preferably formed by N.sup.+ doped semiconductor material.
[0065] With the above in mind, it follows as shown in FIG. 8(6) that metal electrodes 98a and 98b can be positioned on respective contact pads 96a and 96b. FIG. 8(7) then indicates that the next step in the methodology is to fill the slot 92 with a cross-coupling material 100, such as an electro-optical polymer. A final step, which is appreciated with reference to FIG. 8(8), is that the cross-coupling material 100 (i.e. electro-optical polymer) can be poled in the slot 92 to optimize its electro-magnetic coefficient for cross-coupling optical signals as they pass through the waveguides 94a and 94b.
[0066] While the particular Method for Configuring an Optical Modulator as herein shown and disclosed in detail is fully capable of obtaining the objects and providing the advantages herein before stated, it is to be understood that it is merely illustrative of the presently preferred embodiments of the invention and that no limitations are intended to the details of construction or design herein shown other than as described in the appended claims.
