Patent ID: 12189183

It is noted that the drawings of the disclosure are not necessarily to scale. The drawings are intended to depict only typical aspects of the disclosure, and therefore should not be considered as limiting the scope of the disclosure. In the drawings, like numbering represents like elements between the drawings.

DETAILED DESCRIPTION

In the following description, reference is made to the accompanying drawings that form a part thereof, and in which is shown by way of illustration specific illustrative embodiments in which the present teachings may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the present teachings, and it is to be understood that other embodiments may be used and that changes may be made without departing from the scope of the present teachings. The following description is, therefore, merely illustrative.

It will be understood that when an element such as a layer, section, or substrate is referred to as being “on” or “over” another element, it may be directly on the other element or intervening elements may also be present. In contrast, when an element is referred to as being “directly on” or “directly over” another element, there may be no intervening elements present. It will also be understood that when an element is referred to as being “connected” or “coupled” to another element, it may be directly connected or coupled to the other element or intervening elements may be present. In contrast, when an element is referred to as being “directly connected” or “directly coupled” to another element, there are no intervening elements present.

Reference in the specification to “one embodiment” or “an embodiment” of the present disclosure, as well as other variations thereof, means that a particular feature, structure, characteristic, and so forth described in connection with the embodiment is included in at least one embodiment of the present disclosure. Thus, the phrases “in one embodiment” or “in an embodiment,” as well as any other variations appearing in various places throughout the specification are not necessarily all referring to the same embodiment. It is to be appreciated that the use of any of the following “/,” “and/or,” and “at least one of,” for example, in the cases of “A/B,” “A and/or B” and “at least one of A and B,” is intended to encompass the selection of the first listed option (a) only, or the selection of the second listed option (B) only, or the selection of both options (A and B). As a further example, in the cases of “A, B, and/or C” and “at least one of A, B, and C,” such phrasing is intended to encompass the first listed option (A) only, or the selection of the second listed option (B) only, or the selection of the third listed option (C) only, or the selection of the first and the second listed options (A and B), or the selection of the first and third listed options (A and C) only, or the selection of the second and third listed options (B and C) only, or the selection of all three options (A and B and C). This may be extended, as readily apparent by one of ordinary skill in the art, for as many items listed.

Embodiments of the disclosure includes a structure including a polarization splitter, a polarization combiner, or a polarization splitter rotator (PSR) including a waveguide having an end section with at least a hook shape. The structure also includes another waveguide adjacent the noted waveguide. The hook shape, which can in certain embodiments be spiral shaped, acts as a light absorber to reduce undesired optical noise such as excessive light insertion loss and/or light scattering. The hook or spiral shape may also be used on supplemental waveguides used to further filter and/or refine an optical signal in one of the waveguides of the polarization splitter or PSR, e.g., downstream of an output section of the polarization splitter or PSR.

FIG.1shows a schematic top-down view of a structure100including a polarization splitter or combiner110(hereafter “PSC110”) according to embodiments of the disclosure.FIG.2shows a cross-sectional view of structure100along view line2-2inFIG.1. PSC110, also referred to as a polarization beam splitter or polarization beam combiner, is an optical component that is bi-directional and either splits a beam of light (optical signal) into TE polarization light and TM polarization light if light passes from left-to-right as shown (see solid arrows), or combines two beams of light (TE or TM polarization light beams) into a single light beam if light passes from right-to-left as shown (see dashed arrows). For purposes of description, PSC110will be described mainly as a splitter with an input region112, a coupling region114and an output region116.

PSC110includes a first, “input” waveguide120(hereinafter “first waveguide120”) through which an optical signal121(light) is input. PSC110also includes a stacked “splitter” or “combiner” waveguide130(herein “second waveguide130”). First waveguide120may be coupled to optical signal121in any now known or later developed fashion. For example, an optical fiber or laser may be attached to structure100using a V-groove connection.

As shown inFIG.2, structure100can include a substrate101. Substrate101can be, for example, a semiconductor substrate, such as a silicon substrate. Substrate101can have a first surface (e.g., a bottom surface) and a second surface (e.g., a top surface) opposite the first surface. Optionally, structure100can further include an insulator layer104(dashed box) on the second surface of substrate101. Insulator layer104can be, for example, a silicon dioxide layer (also referred to herein as a buried oxide (BOX) layer) or a layer of some other suitable insulator material.

First waveguide120may include first end sections122and a first coupling section126between first end section122. First waveguide120includes any now known or later developed core material, e.g., silicon. Second waveguide130includes second end sections132and a second coupling section136between second end sections132. Second waveguide130includes a second core138positioned laterally adjacent first core124of first waveguide120and an additional second core140stacked vertically with second core138. Note,FIG.1shows additional (upper) second core140smaller than (lower) second core138for illustration purposes. The cores138,140may have the same width, or additional second core140may be thinner in width than second core138(seeFIG.2). While second waveguide130is shown including two second cores138,140, more than two second cores can be used, e.g., three or more cores can be vertically positioned. Each first end section122and second end section132can have a corresponding I/O port distal to the respective coupling sections126,136.

In the example shown, first waveguide120includes a core material for its first core124including silicon, e.g., crystalline silicon or amorphous silicon with a refractive index of 3 or larger and typically between 3.3 and 3.6. First core material for first core124and a second core material for second core138may both include the same material, e.g., crystalline silicon or amorphous silicon. Additional second core material of additional second core140includes a different material than the material(s) of first core124and second core138. Second cores138,140can include any combination of core materials suitable for forming second waveguide130. For example, as shown inFIGS.1and2, second core138could include silicon, e.g., crystalline silicon or amorphous silicon with a refractive index of 3 or larger and typically between 3.3 and 3.6, and additional second core140could include a silicon nitride with a refractive index of approximately 2.0.FIG.3Ashows a schematic top-down view of a structure100including PSC110, andFIG.4shows a cross-sectional view of structure100along view line4-4inFIG.3Aaccording to other embodiments of the disclosure. As shown inFIGS.3A and4, in an alternative embodiment, first core124and second core138include silicon and additional second core140includes polysilicon.

Other combinations of suitable core materials may be selected from but are not limited to: crystalline silicon (c-Si), amorphous silicon (a-Si), polysilicon (polySi), silicon germanium (SiGe), polysilicon germanium (polySiGe), silicon nitride (SiN), silicon oxynitride (SiON), gallium nitride (GaN), and aluminum nitride (AlN). Waveguides120,130can further include waveguide cladding125surrounding and immediately adjacent to the surfaces of cores124,138,140. The function of waveguide cladding125is to confine the optical signals within the waveguide core by reflection at interfaces between the core and cladding materials. Waveguide cladding125adjacent to the cores can be a single cladding material. Alternatively, waveguide cladding125can be made up of different cladding materials adjacent to different regions and/or different surfaces of the cores. In any case, to facilitate and control optical signal propagation within the cores, the refractive index of the cladding material used (or the refractive indices of the different cladding materials used, if applicable) should be smaller than the refractive index (or the multiple refractive indices) of the core material. Those skilled in the art will recognize that the same material may be incorporated into one waveguide for a respective core and in another waveguide for the waveguide cladding. For example, if first core124is silicon with a refractive index between 3.3 and 3.6, cladding125surrounding core124could be silicon dioxide (SiO2), which as a refractive index of less 1.6, or silicon nitride, which has a refractive index of approximately 2. If additional second core140is silicon nitride with a refractive index of approximately 2.0, cladding125surrounding additional second core140could also be silicon dioxide. The various cladding materials mentioned above are provided for illustration purposes. Alternatively, any other suitable cladding material could be used, depending upon the core material. The following is a list of possible materials (including the refractive indices (n) thereof) that could potentially be incorporated into a waveguide as cladding material or core material, depending upon the selected materials and the refractive index differential between them (i.e., as long as the cladding material has a smaller refractive index than the core material it clads): hafnium dioxide (HfO2), n=2.0754 @1.31 um, n=2.0709 @1.55 um; zirconium dioxide (ZrO2), n=2.1155 @1.31 um, n=2.1103 @1.55 um; silicon nitride (Si3N4) n=˜2; silicon oxide nitride (SiON) n=˜1.46 to ˜2.1; aluminum nitride (AlN), n=˜2.1 to ˜2.4; titanium dioxide (TiO2), n=2.4622 @1.31 um, n=2.4538 @1.55 um; zinc monoxide (ZnO), n=1.9318 @1.31 um, n=1.9267 @1.55 um; aluminum oxide (Al2O3), n=1.7503 @1.31 um, n=1.7462 @1.55 um; magnesium oxide (MgO), n=1.7178 @1.31 um, n=1.7146 @1.55 um; silicon dioxide (SiO2), n<1.6, n=1.45 @1.31 um; calcium fluoride (CaF2), n=1.4272 @1.31 um, n=1.4260 @1.55 um; octamethylcyclotetrasiloxane (OMCTS) [(CH3)2SiO]4(SiCOH), n=1.406 @1.31 um; and magnesium fluoride (MgF2), n=1.3718 @1.31 um, n=1.3705 @1.55 um.

Each waveguide120,130generally has a linear, strip/wire geometry. That is, waveguides120,130can include an elongated body with a vertical cross-sectional shape of this elongated body cutting across its width that is essentially rectangular with a planar bottom surface, a planar top surface opposite the planar bottom surface, and opposing sidewalls. Alternatively, waveguides120,130could have some other suitable cross-sectional geometry, e.g., a rib geometry. The height of the elongated body of first core124and second cores138,140can be essentially uniform from one end to the other. The width of the elongated body of first core124can also be essentially uniform (as illustrated). Alternatively, as will be described further herein, the width of the elongated body of first core124and/or second cores138,140could be tapered. Optionally, one or both of the various I/O ports can also be tapered (as discussed in greater detail below regardingFIGS.7-8). Within first coupling section126, first core124can be essentially linear. Within one or both of first end sections122, first core124can be curved.

In accordance with embodiments of the disclosure, second waveguide130includes a selected one of second end sections132having a light absorber148thereon. More particularly, second waveguide130has a selected one of second end sections132having at least a hook shape150(hereafter “hook end150”) that creates light absorber148.FIGS.5and6show enlarged views of illustrative embodiments of a hook end150. As shown inFIGS.5and6, as used herein, “at least hook shape” indicates cores138,140curve back from a point at which they start to turn in their final direction of turn (e.g., clockwise) from end section132to extend about an angle α of at least 120°, but do not reach 360° (circular). In other embodiments, as shown inFIG.3A, hook shape150on end section132may be a spiral shape (hereinafter “spiral end152”) having at least a (generally) circular path with a radially overlapping portion.FIG.3Bshows an enlarged view of a light absorber for an end section of a waveguide having spiral end152as inFIG.3A. As used herein, “spiral” indicates cores138,140curve in a continuous and gradually widening (or tightening) curve around a central point on a flat plane, and have at least one radially overlapping portion, i.e., at least circular path with overlapping portion. Hook end150or spiral end152include the same cores138,140as the rest of second waveguide130.

During use, a vertical polarization (denoted transverse magnetic (TM) mode in a waveguide) couples more strongly with second waveguide130than a horizontal polarization (denoted transverse electric (TE) mode in a waveguide). Positioning first waveguide120in proximity to second waveguide130in coupling region114, as shown inFIGS.1and3A, causes TM polarization light142(see also arrows between waveguides120,130) to be removed from first waveguide120and propagate through second waveguide130. At the same time, TE polarization light144continues to propagate in first waveguide120. Outside of coupling region114, waveguides120,130may diverge from one another, see for example, curved second end section122in first waveguide120in output region116. As noted, process induced defects from formation of waveguides120,130can result in defects that can create undesired optical noise such as excessive light insertion loss and/or light scattering. Light absorber148in the form of hook end150or spiral end152minimizes or eliminates light insertion loss and light scattering. In the example shown, light absorber148is in input region112of PSC110, and thus acts to minimize or eliminate light insertion loss and light scattering in input region112.

FIGS.7and8show schematic top-down views of structure100including PSC110, according to alternative embodiments. InFIGS.7and8, at least one of first end sections122of first waveguide120(both shown) may optionally include a tapered end154, i.e., I/O ports thereat are tapered. As shown inFIG.7, second waveguide130includes a tapered end156in at least one of second core138and additional second core140(latter shown), i.e., an I/O port thereat may be at least partially tapered. As used herein, “tapered” indicates the width of the respective core(s) decrease or increases along their respective length(s) in a given direction.

InFIGS.1,3A,7and8, and as shown in an enlarged top-down view inFIG.9, first waveguide120is linear and second waveguide130tapers along its length in a manner that a spacing S between first waveguide120and second waveguide130is uniform in coupling region114, i.e., in first coupling section126and second coupling section136. That is, spacing S does not change in coupling region114where TM polarization light142is captured from first waveguide120. In theFIG.9example, second waveguide130widens left-to-right on the page; it could also narrow.FIG.10shows an enlarged top-down view of waveguides120,130according to an alternative embodiment. In other embodiments, first waveguide120is linear and second waveguide130tapers along its length in a manner that a spacing S between second waveguide130and first waveguide120is non-uniform in coupling region114, i.e., in first coupling section126and second coupling section136. That is, spacing S changes in coupling region114where TM polarization light142is captured from first waveguide120. In the example shown, spacing S decreases in coupling region114as light passes through waveguides120,130from input region112to output region116. The opposite arrangement is also possible.FIG.9also shows a first sidewall158of first core124in first coupling section126(e.g.,FIGS.1,3A,7) may be angled relative to at least one of a sidewall160of second core138(shown) and a sidewall162of additional second core140in second coupling section136(e.g.,FIGS.1,3A,7).FIG.10also shows first sidewall158of first core124in first coupling section126(e.g.,FIGS.1,3A,7) may be angled relative to at least one of sidewall160of second core138and sidewall162(shown) of additional second core140in second coupling section136(e.g.,FIGS.1,3A,7). That is, they are not parallel. Sidewalls158,160,162are also labeled inFIG.2for reference purposes.

As shown inFIG.1, first waveguide120and/or second waveguide130can have respective first and second end sections122,132in output region116extending to, for example, a functional circuit block170,172of structure100, i.e., a PIC structure. Each end section122,132can be configured to function as a coupler on one side of an optical interface that facilitates communication of light signals between waveguide(s)120,130and an optical device174,176, e.g., a photodetector, within or operatively coupled to functional circuit blocks170,172. It will be recognized that optical signals from each waveguide120,130may be used in a variety of applications, and in other arrangements as show, e.g., they could be outputted from structure100.

FIG.11shows a schematic top-down view of structure100also including a polarization rotator180operatively coupled to second waveguide130. Hence, structure100inFIG.11constitutes a polarization splitter rotator (PSR)200. Polarization rotator180may include any now known or later developed structure for converting TM polarization light142to TE polarization light178. Polarization rotator180is operatively coupled to the other end section132of second waveguide130opposite light absorber148, e.g., hook end150or spiral end152. As shown inFIG.11, first waveguide120and/or polarization rotator180can have a respective end section122,182extending to, for example, functional circuit block(s)170,172of structure100, i.e., PIC structure. Each end section122,182can be configured to function as a coupler on one side of an optical interface that facilitates communication of light signals between waveguide(s)120,130and optical device(s)174,176, e.g., a photodetector, within or operatively coupled to functional circuit block(s)170,172. It will be recognized that TE polarization light144from first waveguide120and TE polarization light178from polarization rotator180may be input into a single functional circuit block with a single optical device. Alternatively, TE polarization light144from first waveguide120and TE polarization light178from polarization rotator180may be combined prior to input into a single functional circuit block with a single optical device, e.g., as will be described herein, using a polarization combiner having similar structure to PSC110but operated in reverse.

Spiral end152can have a variety of alternative configurations of spiral shapes.FIGS.12-15show top-down views of various embodiments of spiral end152. As noted, “spiral” indicates cores138,140curve in a continuous and gradually widening (or tightening) curve around a central point on a flat plane. In certain embodiments, spiral end152has a spiral shape having at least one radially overlapping portion or round. In certain embodiments, the spiral shape has at least a (generally) circular path with a radially overlapping portion.FIGS.3A,7,8and11, for example, show spiral end152with at least a generally circular path with a radially overlapping portion extending in a counterclockwise direction from end section132of second waveguide130.FIG.12shows an alternative embodiment of spiral end152with at least a generally circular path with radially overlapping portion extending in a clockwise direction from end section132of second waveguide130.FIG.13shows spiral end152with at least a generally circular path with overlapping portion extending in a counterclockwise path from end section132of second waveguide130, but with only one short, partially radially overlapping portion.FIG.14shows spiral end152with a spiral shape having a plurality of linear segments190forming a polygonal path. Any polygonal shape can be used, e.g., square, rectangular, pentagonal, etc.FIG.15shows spiral end152with a spiral shape having a plurality of linear segments190forming a polygonal path, similar toFIG.14, but with a corner194of at least one pair of adjacent linear segments190(four shown) of plurality of linear segments190forming the polygonal path being curved. That is, spiral end152includes linear segments190with at least one pair of adjacent linear segments190joined by corner194of second cores138,140that is curved, e.g., with any desired radius.

FIG.16shows a perspective view of a structure100according to alternative embodiments. While spiral end152is shown in the previous embodiments as used on an input region112of structure100in the form of PSC110or PSR200, a light absorber248including an at least hook end250, e.g., a hook or spiral end, may also be used in structure100in any location in which process induced defects can cause optical noise. For example, as shown inFIG.16, hook end250may be used on a downstream end252of polarization rotator180.

FIG.16also shows structure100including at least one supplemental waveguide210adjacent one of second waveguide130and first waveguide120. In the example shown, two supplemental waveguides210A,210B (collectively210) are illustrated, one adjacent first waveguide120and one adjacent second waveguide130. Supplemental waveguides210can include any dielectric core material listed herein, e.g., silicon nitride. Supplemental waveguides210may be used to further filter and/or refine an optical signal in one of the waveguides120,130of PSC110, PSR200and/or polarization rotator180. For example, supplemental waveguide210A may filter and/or refine an optical signal in first waveguide120by further separating any remaining TM polarization light therein from first waveguide120. In another example, supplemental waveguide210B may filter and/or refine an optical signal in second waveguide130, e.g., downstream of polarization rotator180, by further separating any remaining TE polarization light from second waveguide130. Supplemental waveguides210may suffer from the same challenges as second waveguide130, e.g., process induced defects that cause light scattering. In accordance with embodiments of the disclosure, supplemental waveguide(s)210may include an end section with at least a hook shape, e.g., hook shape or spiral shape, creating a light absorber248, similar to that described previously herein. Light absorber248can be used wherever process induced defects create undesired optical noise such as excessive light insertion loss and/or light scattering.FIG.16shows light absorber248, such as a spiral end250, on an upstream end of supplemental waveguide210A, on a downstream end of supplemental waveguide210A, and on an upstream end of supplemental waveguide210B.

Returning toFIG.11, PSR200includes PSC110including first waveguide120having end section122in input region112of the PSR, and second waveguide130including end section132having light absorber148, e.g., hook end150as inFIG.1or spiral end152(shown). Light absorber148is adjacent end section122of first waveguide120in input region112. PSR200also includes polarization rotator180operatively coupled to second waveguide130, i.e., in optical communication therewith. Second waveguide130includes second core138and additional second core140of different materials, as previously described.

Structure100can be formed using any now known or later developed semiconductor fabrication techniques. Forming PSC110may include forming second waveguide130having end section132thereof with at least a hook shape and forming first waveguide120adjacent second waveguide130. First core124of first waveguide120and second core138of second waveguide130may be formed as part of a patterning an active region for functional circuit blocks170,172and/or other CMOS devices. Additional second core140can be, for example, a middle-of-line (MOL) SiN core. Additional second core140can be formed in the MOL some distance above the level of any front end of the line (FEOL) active or passive semiconductor devices and below the level of any back end of the line (BEOL) metal levels. Alternatively, additional second core140can be, for example, a back-end-of-line (BEOL) SiN core. Additional second core140may be formed using any now known or later developed technique, e.g., by forming a trench in a relevant interlayer dielectric over second core138, depositing silicon nitride and planarizing.

With further reference toFIGS.1,3A,7and8, those with skill in the art will recognize that PSC110may be bi-directional. That is, while PSC110is described herein as a splitter that takes a random optical signal and splits it into two light beams (see solid arrows), it can also be used in an opposite direction to combine light beams (see dashed arrows). In a combining operation, output region116becomes an input region, and input region112becomes an output region. More particularly, polarization combiner has essentially the same input and second waveguide120,130configuration. However, in this case, as shown by dashed arrows pointing to the left inFIGS.1,3A,7and8, light signals of one mode (e.g., TE polarization light143) are received at a first input of first end section122(right side) of first waveguide120and propagate toward a first output of the opposite first end section122(left side). Light signals of the opposite mode (e.g., TM polarization light145) are received at a second input of second end section132(right side) of second waveguide130and propagate toward a second output at the opposite second end section132(left side). However, prior to these light signals reaching the respective opposite end sections122,132, some form of mode matching (e.g., TM-mode matching) occurs between first coupling section126and second coupling section136such that matched mode light signals pass from second waveguide130into first waveguide120and propagate toward the first output (left first end section122). Thus, light signals of both modes (i.e., TE polarization light143and TM polarization light145) are output from the first output (left first end section122) of first waveguide120, as a combined light147.

Embodiments of the disclosure provide various technical and commercial advantages, examples of which are discussed herein. Structure100provides a splitter, combiner (PSC110) or PSR200with a second waveguide with an end section having light absorber, e.g., a hook or spiral shape, which reduces undesired optical noise such as excessive light insertion loss and/or light scattering. Structure100also has a cleaner layout compared to conventional devices, removing design rule conflict issues when connecting with waveguides or other components. The hook or spiral shape light absorber may also be used on supplemental waveguides used to further filter and/or refine an optical signal in one of the waveguides of the polarization splitter, e.g., downstream of an output section of the polarization splitter and/or rotator. Light absorber148lowers scattering loss, especially when used in a combiner application. Light absorber148especially lowers excess light loss associated with silicon nitride cores. Structure100is fully compatible with CMOS fabrication techniques.

The structure and method as described above are used in the fabrication of photonics integrated circuit chips. The resulting integrated circuit chips can be distributed by the fabricator in raw wafer form (that is, as a single wafer that has multiple unpackaged chips), as a bare die, or in a packaged form. In the latter case the chip is mounted in a single chip package (such as a plastic carrier, with leads that are affixed to a motherboard or other higher-level carrier) or in a multichip package (such as a ceramic carrier that has either or both surface interconnections or buried interconnections). In any case the chip is then integrated with other chips, discrete circuit elements, and/or other signal processing devices as part of either (a) an intermediate product, such as a motherboard, or (b) an end product. The end product can be any product that includes integrated circuit chips, ranging from toys and other low-end applications to advanced computer products having a display, a keyboard or other input device, and a central processor.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. “Optional” or “optionally” means that the subsequently described event or circumstance may or may not occur, and that the description includes instances where the event occurs and instances where it does not.

Approximating language, as used herein throughout the specification and claims, may be applied to modify any quantitative representation that could permissibly vary without resulting in a change in the basic function to which it is related. Accordingly, a value modified by a term or terms, such as “about”, “approximately” and “substantially”, are not to be limited to the precise value specified. In at least some instances, the approximating language may correspond to the precision of an instrument for measuring the value. Here and throughout the specification and claims, range limitations may be combined and/or interchanged, such ranges are identified and include all the sub-ranges contained therein unless context or language indicates otherwise. “Approximately” as applied to a particular value of a range applies to both values, and unless otherwise dependent on the precision of the instrument measuring the value, may indicate +/−10% of the stated value(s).

The corresponding structures, materials, acts, and equivalents of all means or step plus function elements in the claims below are intended to include any structure, material, or act for performing the function in combination with other claimed elements as specifically claimed. The description of the present disclosure has been presented for purposes of illustration and description, but is not intended to be exhaustive or limited to the disclosure in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the disclosure. The embodiment was chosen and described in order to best explain the principles of the disclosure and the practical application, and to enable others of ordinary skill in the art to understand the disclosure for various embodiments with various modifications as are suited to the particular use contemplated.