阅读说明：本技术 用于具有不同模尺寸的波导之间的耦合的光学模变换器 (Optical mode converter for coupling between waveguides having different mode sizes ) 是由 王志仁 马薇 陈逸轩 陈玉雅 洪伟 于 2019-06-20 设计创作，主要内容包括：本发明示出一种用于不同模尺寸的光子集成电路(PIC)与光纤之间的耦合的光学模变换器。光学模变换器包括波导组件,波导组件包括单波导结构、多层波导结构和过渡波导结构。单波导结构包括单波导。单波导的第一端的尺寸和传播常数类似于光子集成电路(PIC)的波导。此外,多层波导结构包括多层波导。另外,在过渡结构处形成过渡波导结构。过渡波导结构允许光学模在单波导结构与多层波导结构之间过渡。多层波导结构被配置成用于耦合过渡波导结构与光纤之间的光,并且单波导结构被配置成用于耦合PIC与过渡波导结构之间的光。(An optical mode converter for coupling between Photonic Integrated Circuits (PICs) of different mode sizes and optical fibers is shown. The optical mode converter includes a waveguide assembly including a single waveguide structure, a multilayer waveguide structure, and a transition waveguide structure. The single waveguide structure includes a single waveguide. The dimensions and propagation constant of the first end of the single waveguide are similar to those of a Photonic Integrated Circuit (PIC). Further, the multilayer waveguide structure includes a multilayer waveguide. In addition, a transition waveguide structure is formed at the transition structure. The transition waveguide structure allows an optical mode to transition between the single waveguide structure and the multilayer waveguide structure. The multilayer waveguide structure is configured to couple light between the transition waveguide structure and the optical fiber, and the single waveguide structure is configured to couple light between the PIC and the transition waveguide structure.)

1. An optical mode converter for coupling between Photonic Integrated Circuits (PICs) of different mode sizes and one of an optical fiber, a Planar Lightwave Circuit (PLC) and a laser diode, the optical mode converter comprising:

a waveguide assembly, the waveguide assembly comprising:

a single waveguide structure having a single waveguide, wherein a first end of the single waveguide has dimensions and a propagation constant similar to a waveguide of a Photonic Integrated Circuit (PIC);

a multilayer waveguide structure having a multilayer waveguide;

a transition waveguide structure having a first inverted taper, wherein the transition waveguide structure allows an optical mode to transition between the single waveguide structure and the multilayer waveguide structure, wherein the first inverted taper is located approximately at a center of the multilayer waveguide structure, wherein the multilayer waveguide structure is configured to couple light between the transition waveguide structure and an optical fiber, and wherein the single waveguide structure is configured to couple the light between the Photonic Integrated Circuit (PIC) and the transition waveguide structure.

2. The optical mode converter of claim 1, wherein the waveguide axis of the single waveguide structure is located approximately at the center of the multilayer waveguide structure.

3. The optical mode converter of claim 1, wherein for the multilayer waveguide structure, the multilayer waveguide is made of a dielectric material embedded in a material having a relatively low dielectric constant.

4. The optical mode converter of claim 1, wherein the optical modules of the waveguides of each layer of the multilayer waveguide structure together form a larger optical supermode that matches the optical mode size and propagation constant of the optical fiber.

5. The optical mode converter of claim 1, wherein the thickness and shape of each layer of the multilayer waveguide is different.

6. The optical mode converter of claim 1, wherein the optical mode converter is fabricated in the Photonic Integrated Circuit (PIC).

7. The optical mode converter of claim 1, wherein the structure of the transition waveguide structure is dependent on the number of layers of the multilayer waveguide.

8. The optical mode converter of claim 7, wherein the single waveguide of the single waveguide structure is connected to the first inverse taper of the transition waveguide structure,

wherein the first inverse taper extends toward the multilayer waveguide structure and is surrounded by extensions of the layers of the multilayer waveguide structure,

wherein a cross-sectional area of the first inverse taper decreases as the multilayer waveguide structure is approached,

wherein the optical mode size increases as the cross-sectional area of the first inverse taper decreases,

and wherein light in the first inverted cone having an expanded optical mode is coupled to the multilayer structure via evanescent field coupling and forms a large area optical mode when propagating in the multilayer waveguide structure.

9. The optical mode converter of claim 8, wherein when the number of layers in the multilayer waveguide structure is odd, a layer surrounding a center of the optical mode is placed below or above the first inverse taper.

10. The optical mode converter of claim 7, wherein the first inverted taper in the transition waveguide structure is positioned around the middle of an extension from multiple layers of the multilayer waveguide structure when the number of layers in the multilayer waveguide structure is even.

11. The optical mode transformer of claim 7 wherein each layer of the multilayer waveguide structure has one or more waveguides on the same vertical level, wherein an extension of the one or more waveguides at each layer connects to a second inverted taper in the transition waveguide structure.

12. The optical mode converter of claim 9, wherein a waveguide in the transition waveguide structure is in direct contact with a single waveguide of the single waveguide structure and a layer in the multilayer waveguide structure surrounding a center of the optical mode when the single waveguide of the single waveguide structure has a same vertical position and a same height of the layer in the multilayer waveguide structure surrounding the center of the optical mode.

13. The optical mode converter of claim 12, wherein the waveguides in the transition waveguide structure are tapered waveguides with one end having the same area as the single waveguides of the single waveguide structure and expanding in width towards the layers in the multilayer waveguide structure around the center of the optical mode until matching the width/area of the layers around the center.

14. The optical mode converter of claim 13, wherein when the single waveguide of the single waveguide structure has the same vertical position of the layer around the center of the optical mode in an odd number of layers of the multilayer waveguide structure and a waveguide height of the single waveguide is greater than the layer around the center of the multilayer waveguide structure, one portion of the single waveguide is connected to the tapered waveguide in the transition waveguide structure and another portion of the single waveguide due to the additional height is connected to the first inverse taper inserted on the tapered waveguide, the first inverse taper expanding to match and connect the layer around the center of the optical mode in the multilayer waveguide structure.

15. The optical mode transformer of claim 11 wherein two or more layers of the multilayer waveguide structure extend and are connected to a second inverted taper in the transition waveguide structure, and wherein the second inverted taper corresponding to the two or more layers are different in size.

16. The optical mode converter of claim 1 wherein the materials of the layers of the multilayer waveguide structure are different, wherein the materials of the layers of the multilayer waveguide structure are different from the materials of the waveguides in the single layer waveguide structure.

Technical Field

The present application relates to optical modules including integrated photonic devices, and more particularly to the connection of optical fibers to integrated photonic components.

Background

The rapidly evolving cloud computing and artificial intelligence applications are pushing the internet technology to construct powerful data centers. To date, building a large data center is more cost effective and less complex than building multiple medium-sized data centers to expand processing capacity. However, in order to transmit massive data at ultra high speed, a server node/rack in a data center requires a high transmission bandwidth. Traditionally, the interconnection is implemented using copper cables and electrical transceivers for sending and receiving data in the form of electrical signals. This electrolytic solution is very bulky and has a transmission distance of less than 20 meters (m) at a data rate of 10 gigabits per second (Gbps).

Optical fiber networks have replaced copper-based networks for many years due to the obvious advantages of optical solutions in terms of more space saving at 10Gbps and longer transmission distances up to 300 m. Conventional optical transceivers in a data center are primarily multimode fiber (MMF). Typical multimode fiber links have data rates of 10 megabits per second (Mbps) to 10Gbps only over link lengths up to 600 m. However, it is quite common that today the node interconnections of Mega data centers easily exceed distances of 500m to 2 km. As a result, there is a great need for single mode transceivers for single mode fiber transmission between connected nodes. Conventional single-mode transceivers are constructed from many high-cost discrete optical components. They take up a large space and require costly assembly processes and maintenance.

With the advent of silicon photonics (SiPh) technology, the potential for low cost and small footprint solutions for large scale implementations of interconnects beyond 500m to 2km has increased. The SiPh technology employs the state-of-the-art Complementary Metal Oxide Semiconductor (CMOS) casting process to fabricate Photonic Integrated Circuit (PIC) devices with most of the optical components integrated onto a single silicon chip. However, the optical mode size (spot size of light in the waveguide) of the input/output (I/O) port of a SiPh chip (also known as a Si PIC) is on the order of 1 μm, while Single Mode Fiber (SMF) is on the order of 10 μm. This large difference in mode size causes large optical power losses in the butt-coupling (head-to-head coupling between the Si PIC I/O port and the SMF). The optical power loss of conventional coupling methods from the PIC to fiber optics, PLC (conventional glass-based planar lightwave circuits) and edge-emitting laser diodes is quite high (greater than 50%).

The main reason is that the optical mode size of the waveguides in the PIC is much smaller than that of optical fibers, PLCs and laser diodes. Conventional coupling methods use discrete free-space optics, such as micro-sized lenses, to transform the mode size. This high cost approach is not a viable solution to this problem. Unless this coupling problem is solved, the SiPh technique will not be a solution for bulk implementation of SMF interconnects.

Disclosure of Invention

The summary is provided in part to introduce concepts related to optical mode converters for coupling between waveguides having different mode sizes. This summary is not intended to identify essential features of the claimed subject matter, nor is it intended for use in determining or limiting the scope of the claimed subject matter.

In one embodiment, an optical mode converter for coupling between a Photonic Integrated Circuit (PIC) of different mode sizes and one of an optical fiber, a Planar Lightwave Circuit (PLC), and a laser diode is shown. The optical mode converter includes a waveguide assembly including a single waveguide structure, a multilayer waveguide structure, and a transition waveguide structure. The single waveguide structure includes a single waveguide. The dimensions and propagation constant of the first end of the single waveguide are similar to those of a Photonic Integrated Circuit (PIC). Further, the multilayer waveguide structure includes a multilayer waveguide. In addition, a transition waveguide structure is formed at the transition structure. The transition waveguide structure allows an optical mode to transition between the single waveguide structure and the multilayer waveguide structure, wherein the waveguide axis of the single waveguide structure is located approximately at the center of the multilayer waveguide structure. Further, the multilayer waveguide structure is configured to couple light between the transition waveguide structure and the optical fiber, and wherein the single waveguide structure is configured to couple light between the PIC and the transition waveguide structure.

Drawings

The detailed description is described with reference to the accompanying drawings. In the figures, the left-most digit(s) of a reference number identifies the figure in which the reference number first appears. The same numbers are used throughout the drawings to reference like features and components.

Fig. 1 shows a schematic side view of an optical mode transformer according to an embodiment of the invention.

Fig. 2 shows a schematic cross-sectional view of an optical mode transformer according to an embodiment of the invention.

Fig. 3a and 3b show side and top views of variants of an optical mode transformer according to embodiments of the invention.

Fig. 4a and 4b illustrate an overlap between reverse tapers formed at a single waveguide structure and a multilayer waveguide structure in an optical mode converter according to an embodiment of the present invention.

Fig. 5a and 5b illustrate a change in length of an inverse taper formed at a multilayer waveguide structure according to an embodiment of the present invention.

FIG. 6 shows a side view of an optical mode converter with an even number of layers at a multilayer waveguide structure according to an embodiment of the invention.

Fig. 7a and 7b show top views of two waveguides in each layer of a multilayer waveguide structure according to an embodiment of the invention.

FIG. 8 illustrates a tapered waveguide connecting a single layer waveguide and an intermediate layer of a multilayer waveguide structure according to an embodiment of the invention.

Fig. 9a and 9b show top views of tapered waveguides connecting a single layer waveguide and an intermediate layer in a multilayer waveguide structure, according to an embodiment of the invention.

Fig. 10a and 10b show front and top views of an overlap between a tapered waveguide and an inverted taper at a transition waveguide structure according to an embodiment of the invention.

FIG. 11 illustrates a top view of an overlap between a tapered waveguide and an inverted taper at a transition waveguide structure, according to an embodiment of the invention.

Detailed Description

Reference throughout the specification to "various embodiments," "some embodiments," "one embodiment," or "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, appearances of the phrases "in various embodiments," "in some embodiments," "in one embodiment," or "in an embodiment" in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.

The present application is directed to reducing optical power coupling losses between a Photonic Integrated Circuit (PIC) and an optical fiber by transforming the optical mode size without significant power losses. The present application also simplifies the assembly process from free-space optical coupling to conventional Planar Lightwave Circuit (PLC) assembly processes. In other words, the present application aims to minimize the optical power loss of coupling between the PIC and the fiber and to simplify the assembly process to a conventional PLC assembly process.

In one embodiment, an optical mode transformer for coupling between waveguides having different mode sizes is disclosed. The mode converter may be configured for coupling between the PIC and a single mode fiber. The optical mode converter is preferably fabricated in a PIC device for optical mode conversion between the PIC and a single mode optical fiber. The PIC device may be a silicon photonic device. The optical mode converter may contain three sections of the waveguide assembly. A schematic side view of an optical mode transformer 100 is shown in fig. 1. However, FIG. 2 shows a cross-sectional side view of an optical mode transformer 100 according to an embodiment of the invention.

The optical mode converter 100 includes a waveguide assembly having three regions/portions, namely a single waveguide structure 102, a multilayer waveguide structure 104, and a transition waveguide structure 106. It has to be noted that these three parts are merely illustrative of the different functional areas of the optical mode converter 100 and that there are no physical boundaries between all three parts. The three portions may be a single element. In one embodiment, single waveguide structure 102 includes a single waveguide 108 having a first end and a second end. The first end of the single waveguide 108 in the single waveguide structure 102 has similar dimensions and propagation constants as the PIC waveguide. The single waveguide 108 is surrounded by a layer of low index material 120. The single waveguide structure 102 couples light between the single waveguide 108 and the transition structure. The transition structure is a structure formed between single waveguide structure 102 and multilayer waveguide structure 104, and is referred to hereinafter as transition waveguide structure 106.

In one embodiment, multilayer waveguide structure 104 includes multilayer waveguide 118. The layers of multilayer waveguide 118 are formed of a high dielectric constant dielectric material and are embedded in a material having a relatively low dielectric constant. Multilayer waveguide 118 may be formed from multiple layers of high index material. It must be noted that single waveguide 108 and multilayer waveguide 118 are both separated by a layer of low index material 120 as represented in fig. 1. In addition, the optical mode of each layer structure in the combined multilayer waveguide 118 forms a larger optical supermode that matches the optical mode size and propagation constant of the optical fiber 116, glass-based PLC, etc. The thickness of each layer in multilayer waveguide 118 may be the same or different. The shape of the layers in multilayer waveguide 118 may be the same or different. The material of each layer of multilayer waveguide 118 may be the same or different. The layers of the multilayer waveguide structure 104 and the material of the single waveguide 108 may be the same or different.

In one embodiment, transition waveguide structure 106 is a waveguide structure that is present at the transition structure and allows an optical mode to transition between single waveguide structure 102 and multilayer waveguide structure 104. In one embodiment, the waveguide axis of the single waveguide structure 102 surrounds the middle of the multilayer waveguide structure 104. It must be noted, however, that there are a number of options for transition waveguide structure 106. Transition waveguide structure 106 is essentially a region where single waveguide 108 and multilayer waveguide 118 extend and overlap each other, where transition waveguide structure 106 serves as a coupling region/transition structure. The structure and size of the overlapping portions of single waveguide 108 and multilayer waveguide 118 at transition waveguide structure 106 may vary for different applications. Fig. 3-11 illustrate some examples of variations in the structure and size of the overlapping portions of single waveguide 108 and multilayer waveguide 118 at transition waveguide structure 106, but are not limited thereto.

Fig. 3a and 3b show side and top views of an optical mode transformer 100 with a single waveguide 108 in a single waveguide structure 102 connected to a dielectric structure represented as an inverted taper 1 present in a transition waveguide structure 106. The inverse taper 1 extends towards the multilayer waveguide structure 104 and is surrounded by the extension of the layers of the multilayer waveguide structure 104, wherein a first inverse taper (hereinafter referred to as inverse taper 1) is located substantially at the center of the multilayer waveguide structure 104. The cross-sectional area of the inverse taper 1 decreases as it approaches the multilayer waveguide structure 104. The optical mode size increases as the cross-sectional area of the inverse taper 1 decreases. Light in the inverted cone 1 with an expanded optical mode is coupled to the multilayer waveguide 118 via evanescent field coupling and forms a large area optical mode when propagating in the multilayer waveguide structure 104.

In one embodiment, if there are an odd number of layers in the multilayer waveguide structure 104, the layers around the center of the optical mode are placed under or over the inverted taper 1 such that the inverted taper 1 vertically overlaps with at least one layer of the multilayer waveguide structure 104 in the transition waveguide structure 106. In one embodiment, the inverse taper 1 and at least one layer of the multilayer waveguide structure 104 may not be in direct contact with each other and may be separated by a thin layer of lower index material 120.

Referring now to fig. 4a and 4b, the multilayer waveguide 118 in the multilayer waveguide structure 104 extends into the transition waveguide structure 106 as a second inverted taper (hereinafter referred to as inverted taper 2). This inverted taper 2 extends towards the single waveguide structure 102 and then surrounds the inverted taper 1 from the single waveguide structure 102 in the transition waveguide structure 106. In one embodiment, the width or cross-sectional area of the inverted taper 2 from the multilayer waveguide structure 104 decreases as it approaches the single waveguide structure 102 in the transition waveguide structure 106.

In one embodiment, each of the inverted tapers 2 of the multilayer waveguide structure 104 may not necessarily have the same shape. Notably, two or more layers of the multilayer waveguide structure 104 extend and connect to the inverted taper 2 in the transition waveguide structure 106, where the dimensions of the inverted tapers 2 corresponding to the two or more layers are different. Fig. 5a and 5b illustrate a change in the shape of the reverse taper 2 formed at multiple layers of the multilayer waveguide 118. As represented in fig. 5a and 5b, the inverse taper 2-1 associated with the top layer in the multilayer waveguide 118 has a different shape/size than the inverse taper 2-2 associated with the middle layer in the multilayer waveguide 118. The inverted taper 2-1 and the inverted taper 2-2 terminate at different locations in the transition waveguide structure 106. In such a supermode structure, the optical mode size decreases as the width or cross-sectional area of the waveguide device decreases. Light in the inverted taper 2 from the multilayer waveguide structure couples to the inverted taper 1 from the single waveguide structure via evanescent field coupling and forms a small area optical mode when propagating in the single waveguide structure 102.

In one embodiment, the number of layers in the multilayer waveguide structure 104 may be an even number. Fig. 6 shows an even number of layers in multilayer waveguide 118 of multilayer waveguide structure 104. If an even number of layers are present, the inverted taper 1 in the transition waveguide structure 106 may be placed around the middle of the extension of the multilayer waveguide 118 of the multilayer waveguide structure 104 such that the inverted taper 1 is located near the center of the optical mode converter, as shown in the cross-sectional view of the optical mode converter of FIG. 6.

In one embodiment, each layer of the multilayer waveguide structure 104 is not limited to having one single waveguide. The multilayer waveguide structure 104 may be comprised of multiple waveguides along the waveguide axis at the same vertical level. The number of waveguides at each layer may be even. Fig. 7a shows a top view of an optical mode transformer 100 having two waveguides in each layer of a multilayer waveguide structure 104. Fig. 7b shows another variation of the multilayer waveguide structure 104, where waveguides at the same vertical level connect/extend to the inverse taper 2 in the transition waveguide structure 106.

Further, if the situation is: where the number of layers in multilayer waveguide 118 is odd and the number of waveguides at each layer is even, the waveguides of single waveguide structure 102 have the same vertical position of the layers at the center of multilayer waveguide 118.

In one embodiment, the waveguides in transition waveguide structure 106 may be in direct contact with the waveguides in multilayer waveguide structure 118 and single waveguide 108. As represented in fig. 8, tapered waveguide 802 at transition waveguide structure 106 is in direct contact with single waveguide 108 of single waveguide structure 102 and the intermediate layers in multilayer waveguide structure 104. It must be noted that the tapered waveguide 802, the single waveguide 108 and the intermediate layers of the multilayer waveguide structure 104 are coplanar and in this case have the same height.

FIG. 9a shows a top view of a tapered waveguide 802 connecting a single waveguide 108 and an intermediate layer in a multilayer waveguide structure 104. As represented in fig. 9a, tapered waveguide 802 of transition waveguide structure 106 is a tapered structure of single waveguide structure 102, one end of which has the same area as single waveguide 108 and expands in width towards the waveguiding layers in multilayer waveguide structure 104 around the center of the optical mode until it matches the width/area of the waveguide at the center of multilayer waveguide structure 104. Fig. 9b shows another variation in which the remaining waveguide layers from the multilayer waveguide structure 104 are connected to the inverted taper 2 in the transition waveguide structure 106.

In one embodiment, the single waveguides 108 of the single waveguide structure 102 may have the same vertical position of the layers surrounding the center of the optical mode in the odd number of layers of the multilayer waveguide structure 104, but their waveguide heights may not match. In this case, a portion of the single waveguide 108 at the single waveguide structure 102 may be connected to the tapered waveguide 802 in the transition waveguide structure 106, and another portion of the single waveguide 108 resulting from the additional height is connected to the inverted taper 1 inserted on the tapered waveguide 108, the inverted taper 1 expanding to match and connect the waveguide layers in the multilayer waveguide structure 104 around the center of the optical mode for better optical mode conversion, as shown in fig. 10a and 10 b.

Fig. 11 shows another variation of the multilayer waveguide structure 104 of fig. 10, wherein the remaining waveguide layers from the multilayer waveguide structure 104 are connected to the inverted taper 2 in the transition waveguide structure 106.

Although embodiments of an optical mode converter for coupling between a Photonic Integrated Circuit (PIC) and an optical fiber have been described in language specific to structural features, it is to be understood that the appended claims are not necessarily limited to these specific features. Rather, these specific features are disclosed as examples of embodiments of optical mode converters for coupling between Photonic Integrated Circuits (PICs) of different mode sizes and optical fibers.