Patent Application
20250155639
Embodiments presented in this disclosure generally relate photonic components. More specifically, embodiments disclosed herein relate to adiabatic splitters.
Adiabatic splitters, such as adiabatic 2×2 3 dB splitters, are photonic components used to split or cross optical signals. Adiabatic splitters can be implemented in a number of applications, including switches, modulators, interfometers, etc. As one example, an adiabatic 2×2 3 dB splitter can be used as an input and/or an output splitter of a photonic switch. Further, adiabatic splitters can be used as standalone devices. Generally, adiabatic splitters are desired to be minimal loss, compact, and fabrication tolerant. Adiabatic splitters are also designed to have a precise split ratio. Improvements to these metrics is desirable as improved optical performance, packaging, and/or manufacturability can result.
So that the manner in which the above-recited features of the present disclosure can be understood in detail, a more particular description of the disclosure, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate typical embodiments and are therefore not to be considered limiting; other equally effective embodiments are contemplated.
To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements disclosed in one embodiment may be beneficially used in other embodiments without specific recitation.
One embodiment presented in this disclosure is an adiabatic splitter. The adiabatic splitter includes a first waveguide and a second waveguide spaced from the first waveguide by a gap. The second waveguide has a first layer and a second layer. In a first stage of the adiabatic splitter, the first and second waveguides converge toward one another and the first and second layers are in a stacked arrangement. In a second stage of the adiabatic splitter, the second layer tapers and translates so that the first and second layers are, at least at an output of the adiabatic splitter, no longer in the stacked arrangement.
Another embodiment presented in this disclosure is a crossover adiabatic splitter. The crossover adiabatic splitter includes a first region, a second region, a first waveguide traversing through the first region and the second region, and a second waveguide traversing through the first region and the second region. In the first region, the first waveguide has a first layer and the second waveguide has a first layer and a second layer. The first waveguide and the second waveguide converge toward one another over a first stage of the first region and the second layer and the first layer of the second waveguide traverse through the first stage in a stacked arrangement, and in a second stage of the first region, the second layer tapers and translates. In the second region, the second layer inverse tapers and translates over a third stage of the second region, and in a fourth stage of the second region, the first layer of the first waveguide and the first layer of the second waveguide diverge from one another and the second layer and the first layer of the first waveguide traverse through the fourth stage in a stacked arrangement.
A further embodiment presented in this disclosure is an adiabatic splitter. The adiabatic splitter includes a first waveguide a second waveguide spaced laterally from the first waveguide by a gap. The second waveguide has a first layer and a second layer. With the first and second layers in a vertically stacked arrangement, the first and second waveguides laterally converge toward one another over a first portion of a longitudinal length of the adiabatic splitter. Over a second portion of the longitudinal length of the adiabatic splitter, the second layer tapers in width and translates so as to laterally cross an inner edge or an outer edge of the first layer.
Various embodiments of adiabatic splitters are disclosed herein that can provide improved optical performance, packaging, and/or manufacturability over conventional adiabatic splitters. The disclosed adiabatic splitters can be used as standalone devices or can be implemented into various products, including, without limitation, switches (e.g., thermos-optic switches), modulators, interfometers, other FR4 standard products, Co-Packaged Optics (CPO) applications, etc., and can be used in receiver, transmitter, and/or transceiver applications.
In one example aspect, an adiabatic 2×2 3 dB splitter with a 50:50 split ratio is disclosed. The adiabatic splitter has two waveguides, including a first waveguide and a second waveguide. Each waveguide has an inlet port and an outlet port; hence, the 2×2 configuration. The first waveguide includes a single layer while the second waveguide includes two layers, including a first layer and a second layer. Along a first stage of the adiabatic splitter, the first waveguide and the second waveguide approach one another. Specifically, the first waveguide and the second waveguide laterally converge toward one another in the first stage, e.g., to enable optical coupling of the first and second waveguides. In the first stage, the first and second layers of the second waveguide are in a stacked arrangement and, in one embodiment, both have a same width, which can be fixed in the first stage. The single layer of the first waveguide can taper slightly in the first stage. Notably, in the first stage, the second waveguide has a different effective refractive index than the first waveguide due to the stacked layers of the second waveguide. That is, the incoming light in the second waveguide experiences a greater impedance than in the first waveguide. The thicker refractive index of the second waveguide prevents light from jumping from the second waveguide to the first waveguide, or rather, prevents light scattering. Light traversing through the first waveguide is phase-mismatched with respect to light traversing through the second waveguide. The unique arrangement of the second waveguide in the first stage allows for the first and second waveguides to rapidly approach one another without or with minimal light scatter, compared to conventional designs. In this regard, such an adiabatic splitter can be made with a shorter longitudinal length, which results in the use of less material and better packaging, which is particularly beneficial for forward-looking applications, such as CPO applications. Moreover, the stacked arrangement does not extend the lateral footprint of the adiabatic splitter.
Once the first and second waveguides meet or approach one another, e.g., at a coupling region, the second layer of the second waveguide begins to taper and translate in a second stage of the adiabatic splitter. In the second stage, the single layer of the first waveguide and the first layer of the second waveguide can have substantially fixed widths and a constant or substantially constant edge-to-edge lateral separation between them. The second layer of the second waveguide can taper in width and translate so that, at least at the output of the adiabatic splitter, the second layer is no longer in a stacked arrangement with the first layer of the second waveguide. As one example, the second layer can taper in width and translate toward a center of the adiabatic splitter, e.g., so that a tip of the second layer is positioned laterally between the first waveguide and the second layer of the second waveguide. As another example, the second layer can taper in width and translate away from the center of the adiabatic splitter, e.g., to a position laterally outward of an outer edge of the first layer of the second waveguide. Accordingly, the second layer of the second waveguide tapers and translates so that, after facilitating a refractive index differential between the first and second waveguides in the first stage, the second layer “disappears” so that photonic symmetry can be achieved at the output of the adiabatic splitter, or rather, so that a 50:50 split (or near 50:50 split) can be achieved.
Accordingly, such an adiabatic splitter can advantageously have improved optical performance, packaging, and/or manufacturability over conventional adiabatic splitters. Specifically, minimal loss can be achieved due to the refractive index differential of the first and second waveguides in the first stage, which also allows for the adiabatic splitter to be fabricated shorter in length because the first and second waveguides can more rapidly approach one another. Further, because of the stacked arrangement and resulting refractive index differential between the first and second waveguides, the waveguides can be made of the same material, which can reduce manufacturing complexity. Also, the tapering and translating of the second layer of the second waveguide to make the second layer “disappear” can facilitate a precise splitting ratio at the output of the adiabatic splitter despite the multilayer stacked arrangement of the second waveguide in the first stage.
In yet another example aspect of the present disclosure, a crossover adiabatic splitter is disclosed. The crossover adiabatic splitter can be constructed with two adiabatic splitters having the same topology as described above but arranged in a face-to-face or mirrored configuration so as to enable an optical crossover, such as crossover of two different Transverse Electric (TE) signals or crossover of a TE signal and a Transverse Magnetic (TM) signal, among other possibilities. The same or similar advantages set forth above are applicable to the crossover adiabatic splitter.
Example embodiments of adiabatic splitters and crossover adiabatic splitters are provided below.
With reference now to
The adiabatic splitter 100 depicted in
The first layer 112 of the first waveguide 110 has a width W1 (e.g., a lateral width). In some embodiments, the width W1 of the first layer 112 can vary along the length L of the adiabatic splitter 100. For instance, the width W1 of the first layer 112 can be 900 nanometers at the inlet port 114 and can taper to 700 nanometers as the first layer 112 extends along the longitudinal direction Z toward the outlet port 116. In some embodiments, the width W1 of the first layer 112 can remain constant over the length L of the adiabatic splitter 100. The first layer 112 can each have a vertical thickness of 250 nanometers, for example.
Further, the first layer 122 of the second waveguide 120 has a width W2-1 (e.g., a lateral width). In some embodiments, the width W2-1 of the first layer 122 can vary or remain constant along the length L of the adiabatic splitter 100. In some embodiments, the width W2-1 of the first layer 122 can be 700 nanometers. The second layer 124 of the second waveguide 120 has a width W2-2 (e.g., a lateral width). As will be explained below, the width W2-2 of the second layer 124 can track with the width W2-1 of the first layer 122 over a first portion of the length L of the adiabatic splitter 100 but can taper over a second portion of the length L. In some embodiments, the width W2-1 of the first layer 122 and the width W2-2 of the second layer 124 can both be 700 nanometers over the first portion of the length L (e.g., over the first stage S1). The first layer 122 and the second layer 124 can each have a vertical thickness of 250 nanometers, for example.
With respect to the first stage S1 of the adiabatic splitter 100, the first waveguide 110 and the second waveguide 120 converge toward one another (e.g., laterally) along the first stage S1. That is, in the first stage S1, the first and second waveguides 110, 120 converge laterally toward one another as they extend along longitudinal direction Z from an inlet plane P1 to a reference plane P2. The reference plane RP is orthogonal to the longitudinal direction Z and is located along the length L of the adiabatic splitter 100 where the second layer 124 begins to taper. Accordingly, the gap G between the first waveguide 110 and the second waveguide 120 is greater at the inlet plane P1 than at the reference plane P2. Further, the first layer 122 and the second layer 124 of the second waveguide 120 have a same width along the first stage S1. That is, W2-1-W2-2 over the first stage S1. The widths W2-1, W2-2 of the first and second layers 122, 124 can be fixed over the first stage S1.
With respect to the second stage S2 of the adiabatic splitter 100, the width W2-2 of the second layer 124 tapers along the second stage S2. Stated another way, in the second stage S2, the second layer 124 of the second waveguide 120 tapers in width from the reference plane P2 to an outlet plane P3. The second layer 124 can taper in a non-linear manner along the second stage S2 as shown in
Unlike the second layer 124, the first layer 122 of the second waveguide 120 does not taper along the second stage S2. Rather, the width W2-1 of the first layer 122 of the second waveguide 120 remains substantially constant along the second stage S2. Moreover, the first layer 112 of the first waveguide 110 and the first layer 122 of the second waveguide 120 can have a substantially constant lateral edge-to-edge separation along the second stage S2. A width W1 of the first layer 112 of the first waveguide 110 can remain substantially constant along the first and second stages S1, S2, but can taper slightly in the first stage S1 as noted previously.
Further, for the depicted embodiment of
The arrangement of the adiabatic splitter 100 provides certain advantages, benefits, and/or technical effects. Particularly, the stacked arrangement of the second waveguide 120 enables the second waveguide 120 to have a different effective refractive index than the first waveguide 110, which prevents light scattering between the first and second waveguides 110, 120. Consequently, the first and second waveguides 110, 120 can approach one another in a more rapid manner than in conventional adiabatic splitters. In this regard, the adiabatic splitter 100 can be fabricated with a shorter longitudinal length L than conventional designs, which makes the adiabatic splitter 100 more compact and less material is needed. Moreover, the stacked arrangement of the first and second layers 122, 124 of the second waveguide 120 does not affect the lateral footprint of the adiabatic splitter 100. The tapering and translating of the second layer 124 of the second waveguide 120 facilitates a symmetric photonic structure at the output 106 of the adiabatic splitter 100, which enables a desired 50:50 split of optical signals.
With reference now to
As shown in
At the second longitudinal cross section X2 (or Z=50% L), the first TE mode signal TE1 is shown still traversing through the first layer 112 of the first waveguide 110, and the second TE mode signal TE2 is shown still traversing through the first and second layers 122, 124 of the second waveguide 120. Although the first and second waveguides 110, 120 have approached one another, the refractive indexes of the first and second waveguides 110, 120 have largely prevented light scatter between the first and second waveguides 110, 120. Accordingly, the light intensities of the optical signals at the second longitudinal cross section X2 are largely undiminished compared to their respective light intensities at the first longitudinal cross section X1.
At the third longitudinal cross section X3 (or Z=100% L), after undergoing optical coupling between the first and second waveguides 110, 120, the first TE mode signal TE1 is shown split 50:50 between the first layer 112 of the first waveguide 110 and the first layer 122 of the second waveguide 120. The first TE mode signal TE1 does not traverse through the second layer 124 of the second waveguide 120 at the third longitudinal cross section X3, enabling the 50:50 split at the output 106 or outlet ports 116, 128 of the adiabatic splitter 100. Further, the second TE mode signal TE2 is shown split 50:50 between the first layer 112 of the first waveguide 110 and the first layer 122 of the second waveguide 120. Like the first TE mode signal TE1, the second TE mode signal TE2 does not traverse through the second layer 124 of the second waveguide 120 at the third longitudinal cross section X3, enabling the 50:50 split at the output 106 or outlet ports 116, 128 of the adiabatic splitter 100.
Accordingly, the adiabatic splitter 100 outputs the first TE mode signal TE1 50:50 between the first waveguide 110 and the second waveguide 120 and the second TE mode signal TE2 50:50 between the first waveguide 110 and the second waveguide 120 as shown in
With reference now to
In the first stage S1, the first waveguide 110 and the second waveguide 120 approach one another, e.g., as they extend along the longitudinal direction Z from the input plane P1 to the first region plane P2. The first layer 122 and the second layer 124 of the second waveguide 120 are in a stacked arrangement (i.e., the first and second layers 122, 124 are vertically stacked) and have a same width. The first layer 112 of the first waveguide 110 inverse tapers along the first stage S1, e.g., as the first layer 112 extends along the longitudinal direction Z.
In the second stage S2, the second layer 124 of the second waveguide 120 tapers in width, e.g., as the second layer 124 extends along the longitudinal direction Z from the first region plane P2 to the crossover plane P3. In this example embodiment, the second layer 124 tapers in a non-linear manner and translates toward a center of the crossover adiabatic splitter 102. The second layer 124 crosses the inner edge 132 of the first layer 122 and is positioned laterally between the first layer 122 of the second waveguide 120 and the first layer 112 of the first waveguide 110, e.g., at the crossover plane P3. The width of the first layer 122 of the second waveguide 120 remains constant or substantially constant along the second stage S2. Moreover, the first waveguide 110 and the first layer 122 of the second waveguide 120 can have a constant or substantially constant lateral edge-to-edge separation along the second stage S2. A width of the first layer 112 of the first waveguide 110 can remain substantially constant along the second stage S2.
In the third stage S3, and particularly at the crossover plane P3, the second layer 124 switches from tapering to inverse tapering to increase in width. The second layer 124 inverse tapers in a non-linear manner and translates to track with the first layer 112 of the first waveguide 110. The second layer 124 can inverse taper and translate so as to be positioned, at least in part, in a stacked arrangement with the first layer 112 of the first waveguide 110. Specifically, the second layer 124 crosses an inner edge 136 of the first layer 112 of the first waveguide 110 and inverse tapers to eventually match the width of the first layer 112 of the first waveguide 110 (eventually matching in width at the second region plane P4). In this regard, the second layer 124 essentially becomes a part of the first waveguide 110 in the second region R2. Consequently, in the third stage S3, the first waveguide 110 becomes a bilayer waveguide while the second waveguide 120 becomes a single layer waveguide. Moreover, the first layer 122 of the second waveguide 120 and the first layer 112 of the first waveguide 110 can have a constant or substantially constant lateral edge-to-edge separation along the third stage S3. A width of the first layer 122 of the second waveguide 120 can remain substantially constant along the third stage S3.
In the fourth stage S4, the first waveguide 110 and the second waveguide 120 diverge from one another, e.g., as they extend along the longitudinal direction Z from the second region plane P4 to the output plane P5. The first layer 112 and the second layer 124, which is now effectively a part of the first waveguide 110, have a same width, which can be fixed, and can traverse through the fourth stage S4 in the vertically stacked arrangement commenced in the third stage S3. The first layer 122 of the second waveguide 120 inverse tapers along the fourth stage S4, e.g., as the first layer 122 extends along the longitudinal direction Z. For the depicted embodiment of
The crossover adiabatic splitter 102 of
In some embodiments, the first and second optical signals SG1, SG2 can be first and second TE mode signals, respectively. Accordingly, in such embodiments, the first TE mode signal can be input into the inlet port of the first waveguide 110 and the second TE mode signal can be input into the inlet port of the second waveguide 120. The crossover adiabatic splitter 102 can cross the signals so that the first TE mode signal can be output from the outlet port of the second waveguide 120 and the second TE mode signal can be output from the outlet port of the first waveguide 110.
In other embodiments, the first and second optical signals SG1, SG2 can be TE mode signal and a transverse magnetic (TM) mode signal, respectively. Accordingly, in such embodiments, the TE mode signal can be input into the inlet port of the first waveguide 110 and the TM mode signal can be input into the inlet port of the second waveguide 120. The crossover adiabatic splitter 102 can cross the signals so that the TE mode signal can be output from the outlet port of the second waveguide 120 and the TM mode signal can be output from the outlet port of the first waveguide 110. Such an embodiment advantageously provides for low loss.
With reference now to
For the illustrated embodiment of
In the second stage S2 of the first region R1, the first arm 124-1 of the second layer 124 translates away from the center of the crossover adiabatic splitter 103, or rather, so that the first arm 124-1 of the second layer 124 translates toward a side. Specifically, in the second stage S2, the first arm 124-1 of the second layer 124 translates so that, at the crossover plane P3, the first arm 124-1 of the second layer 124 is positioned laterally outward of the outer edge 134 of the first layer 122 of the second waveguide 120. In some embodiments, at the crossover plane P3, the first arm 124-1 of the second layer 124 is spaced a lateral distance D2 that is equal to or greater than the width of the first layer 122 at the crossover plane P3.
In the third stage S3 of the second region R2, the second arm 124-2 of the second layer 124 is positioned at a side of the crossover adiabatic splitter 103 at the crossover plane P3, or more specifically, the side of the crossover adiabatic splitter 103 opposite the side to which the first arm 124-1 of the second layer 124 is positioned at the crossover plane P3. At the crossover plane P3, the second arm 124-2 is positioned laterally outward of an outer edge 138 of the first layer 112 of the first waveguide 110. In some embodiments, at the crossover plane P3, the second arm 124-2 of the second layer 124 is spaced a lateral distance D3 that is equal to or greater than the width of the first layer 112 at the crossover plane P3. From its position at the crossover plane P3, the second arm 124-2 of the second layer 124 inverse tapers in a non-linear manner and translates laterally inward toward the first layer 112 of the first waveguide 110. Specifically, the second arm 124-2 of the second layer 124 translates to cross the outer edge 138 of the first layer 112 of the first waveguide 110 and inverse tapers to eventually match the width of the first layer 112 of the first waveguide 110 (eventually matching in width at the second region plane P4). The arrangement of the first arm 124-1 and the second arm 124-2 advantageously remove or greatly reduce the risk of scattering, particularly at the crossover plane P3. Also, such an arrangement can be useful where a minimum manufacturable tip width (or arm width) is relatively large.
Although the inventive aspects were described herein with reference to an adiabatic splitter having a single layer waveguide and a bilayer waveguide, the inventive aspects of the present disclosure are applicable to adiabatic splitters having at least two waveguides, wherein one waveguide has at least one more layer than the other waveguide. Further, although the inventive aspects were described herein with reference to a 2×2 adiabatic splitter, the inventive aspects of the present disclosure are applicable to adiabatic splitters having more than two waveguides, such as adiabatic splitters with four waveguides. In addition, although the inventive aspects were described herein with reference to an adiabatic splitter configured with a 50:50 split ratio, the inventive aspects of the present disclosure are applicable to adiabatic splitters having other split ratios.
In the current disclosure, reference is made to various embodiments. However, the scope of the present disclosure is not limited to specific described embodiments. Instead, any combination of the described features and elements, whether related to different embodiments or not, is contemplated to implement and practice contemplated embodiments. Additionally, when elements of the embodiments are described in the form of “at least one of A and B,” or “at least one of A or B,” it will be understood that embodiments including element A exclusively, including element B exclusively, and including element A and B are each contemplated. Furthermore, although some embodiments disclosed herein may achieve advantages over other possible solutions or over the prior art, whether or not a particular advantage is achieved by a given embodiment is not limiting of the scope of the present disclosure. Thus, the aspects, features, embodiments and advantages disclosed herein are merely illustrative and are not considered elements or limitations of the appended claims except where explicitly recited in a claim(s). Likewise, reference to “the invention” shall not be construed as a generalization of any inventive subject matter disclosed herein and shall not be considered to be an element or limitation of the appended claims except where explicitly recited in a claim(s).
In view of the foregoing, the scope of the present disclosure is determined by the claims that follow.
