Patent Application
20170097470
The present disclosure generally relates to fiber optics and, more particularly, optical coupling adaptors for coupling optical signals between an optical fiber and a photonic integrated circuit (PIC) chip.
A photonic integrated circuit (PIC) based on a silicon-on-insulator (SOI) platform is highly compact and exhibits a high level of functional integration due to its high index contrast. As such, PIC chips on an SOI platform provide advantages of speed, compactness and a low cost per bit for optical communication.
The silicon waveguide cross-section of a PIC chip is usually on a sub-micron scale. To implement the SOI chip in an optical data transmission network, the photonic integrated circuit (PIC) must be connected with optical fibers to enable the optical signal to transmit on/off the chip. However, coupling optical fibers with a PIC chip is challenging because of a number of factors.
Firstly, to increase the PIC functional capability and capacity, a large number of optical fibers usually must be connected to the small PIC chip. A large number of edge couplers is required at the edge of the PIC chip. The pitch of the edge coupler is very small, for example 20 μm, in order to accommodate more couplers in the limited space of the PIC edge. However, the diameter of the fiber is usually 250 μm. This pitch mismatch is illustrated in
Secondly, the mode field dimension (MFD) of optical fiber is about 10 μm for most commercial fibers. For coupling the fiber optical mode into a sub-micron photonic waveguide, e.g. a silicon waveguide whose dimension is usually 500 nm×220 mn, there is a huge mismatch between them as shown in
Thirdly, in a chip-to-fiber packaging process directly connecting the fiber to the chip by a fiber array, fiber-waveguide alignment is challenging. Furthermore, the aligned fiber might shift post packaging from its original packaged position when environmental parameters such as temperature and/or humidity change.
Addressing these factors makes conventional fiber-to-chip packaging processes very time-consuming and costly. Accordingly, a novel optical coupling adaptor and method of coupling a PIC chip to an optical fiber are highly desirable.
The following presents a simplified summary of some aspects or embodiments of the invention in order to provide a basic understanding of the invention. This summary is not an extensive overview of the invention. It is not intended to identify key or critical elements of the invention or to delineate the scope of the invention. Its sole purpose is to present some embodiments of the invention in a simplified form as a prelude to the more detailed description that is presented later.
The present specification discloses an optical coupling adaptor that efficiently couples optical signals between a photonic integrated circuit (PIC) chip and an optical fiber, or array of fibers, that have different pitches. In other words, the optical coupling adaptor acts as an edge coupling device that effectively expands the narrow waveguide mode of the PIC to a wide fiber mode, enabling efficient (low-loss) coupling of the PIC chip with optical fiber.
One inventive aspect of the disclosure is an optical coupling adaptor for connecting optically a photonic integrated circuit (PIC) chip with an optical fiber. The optical coupling adaptor includes a first section having a base layer of cladding, a plurality of ridge waveguides formed on the base layer and separated by cladding, and a top layer of cladding over the ridge waveguides. The optical coupling adaptor includes a second section having a base layer of cladding and a plurality of trenches, wherein the trenches abut the ridge waveguides to form continuous waveguides that transmit and confine an enlarged optical mode of inverted taper waveguides of the PIC chip. The second section connects to the first section and wherein a height of the second section is smaller than a height of the first section.
Another inventive aspect of the disclosure is a chip-adaptor assembly that includes a photonic integrated circuit (PIC) chip having a plurality of inverted taper waveguides having an enlarged optical mode and an optical coupling adaptor. The adaptor has a first section having a plurality of ridge waveguides between layers of cladding and also separated laterally by cladding and a second section abutting the first section, the second section having a plurality of trenches each filled with an optical polymer that once cured has a refractive index that matches that of the ridge waveguides. The optical coupling adaptor is adhered to the PIC chip using the optical polymer as an adhesive such that the optical polymer in the trenches once cured form polymer waveguides that confine the enlarged mode of the inverted taper waveguides.
Yet another inventive aspect of the disclosure is a method of connecting an optical coupling adaptor to a photonic integrated circuit (PIC) chip. The method entails providing a photonic integrated circuit (PIC) chip having a plurality of inverted taper waveguides having an enlarged optical mode, providing an optical coupling adaptor having a first section having a plurality of ridge waveguides between layers of cladding and also separated laterally by cladding and having a second section abutting the first section, the second section having a plurality of trenches, filling the plurality of trenches with an optical polymer, mating the optical coupling adaptor with the PIC chip, and curing the optical polymer to adhere the optical coupling adaptor to the PIC chip to furthermore cause the optical polymer once cured to exhibit a refractive index that matches that of the ridge waveguides to form polymer waveguides that confine the enlarged mode of the inverted taper waveguides.
These and other features of the disclosure will become more apparent from the description in which reference is made to the following appended drawings.
The following detailed description contains, for the purposes of explanation, numerous specific embodiments, implementations, examples and details in order to provide a thorough understanding of the invention. It is apparent, however, that the embodiments may be practiced without these specific details or with an equivalent arrangement. In other instances, some well-known structures and devices are shown in block diagram form in order to avoid unnecessarily obscuring the embodiments of the invention. The description should in no way be limited to the illustrative implementations, drawings, and techniques illustrated below, including the exemplary-designs and implementations illustrated and described herein, but may be modified within the scope of the appended claims along with their full scope of equivalents.
In the embodiment shown by way of example in
In the embodiment depicted in
As depicted by way of example in
As illustrated by way of example in
On the PIC chip 40, the inverted edge coupler is designed without a top silica cladding. A small amount of the optical polymer liquid or solution 50 is dropped, deposited or otherwise placed on the surface of the taper waveguide region before the adaptor 10 and PIC chip 40 are attached. The polymer material 50 is the same material as, or has the same refractive index as, that of the ridge waveguide in the first section 20 of the optical coupling adaptor 10. After the polymer liquid 50 is deposited, the optical coupling adaptor 10 is flipped over inverted) and mated with the PIC chip 40 such that the trenches of the optical coupling adaptor 10 align with and overlap the inverted taper waveguides of the NC chip 40. The adapter is pressed gently onto the PlC chip, thereby causing the curable polymer solution 50 to fill the trenches 34. The curable optical polymer is then cured thermally or optically (e.g., with ultraviolet light). After having cured the optical polymer within the trenches, the optical coupling adaptor 10 and the PIC chip 40 are tightly stacked and bonded to one another. The polymer in the trench acts as the waveguide which effectively confines and transmits the optical mode enlarged by the inverted silicon taper waveguide. Furthermore, no further adhesive is required to bond the optical coupling adaptor to the PIC chip because the optical polymer 50 plays the dual roles of both optical waveguide material and adhesive. In addition to confining the enlarged mode, the adaptor has the effect of vertically increasing the waveguide height (as measured from the chip plane).
The PIC chip 40 is usually designed with inverted taper waveguides as edge couplers. The effective index of the waveguide decreases as the taper narrows. Accordingly, the optical mode in the taper waveguide is enlarged. At the tip, the optical mode matches that of the optical fiber. Without the polymer-filled trenches, the enlarged optical mode of the inverted taper waveguide would be weakly confined due to the lack of proper confinement structure. A large amount of light would be lost by light scattering in the plane of the waveguide. With the chip adaptor disclosed herein, the new waveguide created by the optical polymer 50 in the trenches 34 acts as the waveguide that confines and transmits the enlarged optical mode from the inverted taper waveguide through the polymer-filled trenches to the end of the chip adaptor where the optical fibers are connected. This enables the PIC chip to couple light to the optical fibers with a substantially lower coupling loss.
In the first section 20 of the adaptor chip 10, one end of the ridge waveguide 24 connects to the end of the respective trench 34. In other words, the ridge waveguides are aligned and abut (adjoin) the respective polymer-filled trenches to together constitute a continuous waveguide when the adaptor stacks on the PIC chip. The continuous waveguide exhibits a lower coupling loss compared with traditional edge coupling that directly connects to fiber or that uses an interposer as a pitch reducer/mode convertor between fiber and chip.
As shown by way of example in
Soft lithography may be used to fabricate the chip adaptor 10 since it is useful for making polymer waveguide devices. As shown in
Alternatively, for a silica-based optical coupling adaptor, planar lightwave circuit (PLC) technology (e.g. silica-on-silicon) can be used cost-effectively for design and fabrication. Reactive ion etching could also be used for fabrication.
For the embodiments disclosed herein, the optical coupling adaptor 10 creates waveguides able to confine the mode enlarged by the inverted the taper waveguide. This significantly reduces the inverted taper edge coupler toss. The optical coupling adaptor 10 can be designed with different sizes and geometries. The size and geometry of the ridges and trenches of the optical coupling adaptor 10 can be designed to match the characteristics of the inverted taper waveguides and the pitch of the fiber optic array. Although a PIC chip with silicon waveguides is described herein, it will be appreciated that the adaptor may be used with other PIC chips having waveguides made of other semiconductor materials, e.g. Group III-IV-V materials.
The chip-adaptor assembly 100 of
The optical coupling adaptor disclosed herein could be used to couple any suitable photonic integrated circuit chip to one or more optical fibers for the purposes of transmitting and/or receiving optical signals to and from the one or more optical fibers. The adaptor can provide fiber-to-PIC coupling for a variety of optical telecommunication technologies including, but not limited to, metro optical core networks, wireless aggregation networks or Cloud Radio Access Networks (C-RAN), data center transceivers, data center core switching networks, coherent optical transceivers in metro and long-haul networks.
It is to be understood that the singular forms “a”, “an” and “the” include plural referents unless the context clearly dictates otherwise, Thus, for example, reference to “a device” includes reference to one or more of such devices, i.e. that there is at least one device. The terms “comprising”, “having”, “including” and “containing” are to be construed as open-ended terms (i.e., meaning “including, but not limited to,”) unless otherwise noted. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of examples or exemplary language (e.g. “such as”) is intended merely to better illustrate or describe embodiments of the invention and is not intended to limit the scope of the invention unless otherwise claimed.
While several embodiments have been provided in the present disclosure, it should be understood that the disclosed systems and methods might be embodied in many other specific forms without departing from the scope of the present disclosure. The present examples are to be considered as illustrative and not restrictive, and the intention is not to be limited to the details given herein. For example, the various elements or components may be combined or integrated in another system or certain features may be omitted, or not implemented.
In addition, techniques, systems, subsystems, and methods described and illustrated in the various embodiments as discrete or separate may be combined or integrated with other systems, modules, techniques, or methods without departing from the scope of the present disclosure. Other items shown or discussed as coupled or directly coupled or communicating with each other may be indirectly coupled or communicating through some interface, device, or intermediate component whether electrically, mechanically, or otherwise. Other examples of changes, substitutions, and alterations are ascertainable by one skilled in the art and could be made without departing from the inventive concept(s) disclosed herein.
