Patent Application
20170212307
The present disclosure relates generally to optical telecommunications and, more particularly, to optical couplers for interfacing optical fibers with photonic integrated circuits.
A photonic integrated circuit (PIC) built on silicon-on-insulator (SOI) platform is very compact and exhibits a high level of functional integration. This technology promises advantages in terms of speed, compactness and low cost. To implement the SOI photonic chip, a large quantity of optical signals must be transmitted into and out of the chip. Surface grating couplers (SCG) on the silicon chip interface with optical fibers to perform input/output functions. A surface grating coupler (SGC) is designed and fabricated on the silicon chip to couple light from the optical fiber to the PIC chip, or in reverse. The SGC transmits the incident optical beam at an angle to the chip surface. The SGC comprises a diffraction grating and a waveguide in the plane of the chip. The grating diffracts the incident beam into the waveguide. The SGC can also work in reverse as an optical output coupler. As the incident angle affects significantly the first mode diffraction, a high coupling efficiency can only be achieved by assiduously preserving the precision of the incident angle. Hence, the precise packaging of the optical fiber and PIC is required. However, this task is challenging because the optical fiber must be packaged vertically (or close to vertically) with respect to the chip plane, depending on the incident angle of the light beam. In most cases, silica fiber is used for fiber-to-chip packaging. The silica fiber is positioned vertically, or close to vertically, relative to the PIC chip. The fiber is bent or curved to permit the tail to extend out of the packaging. However, silica fiber has little tolerance to bending. Its bending radius is limited by optical loss and mechanical durability. Because of its large bending radius, silica fiber requires a large space to bend 90 degrees. Furthermore, silica fiber is easily broken during or after the packaging process. Use of silica fiber therefore limits the coupling quality, compactness and cost.
An improved optical coupler is therefore 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 coupler, such as a silicon grating coupler, that has one or more plastic optical fibers bent over a curved mechanical support. The plastic optical fiber has a significantly smaller bend radius than silica fibers, thus enabling more compact packaging. The plastic optical fiber is also more resistant to thermal strain at the joint of fiber to silicon chip because the adhesive used to adhere the plastic optical fiber to the photonic integrated circuit is a polymer glue having a thermal expansion coefficient identical, or at least very similar, to that of the plastic optical fiber.
One inventive aspect of the disclosure is an optical coupler that has a plastic optical fiber and a curved support member for mechanically supporting the plastic optical fiber at a predetermined bend radius. The plastic optical fiber can be made of perfluorinated polymer which is a category of low-loss optical polymer. The plastic optical fiber can be curved at a bend radius of less than 10 mm (0.4 inches). The plastic optical fiber may be packaged as part of a ribbon of fibers or a two-dimensional array of fibers. This optical coupler is compact and more resistant to thermal strain.
Another inventive aspect of the disclosure is a method of coupling an optical fiber to a photonic integrated circuit. The method entails bending a plastic optical fiber over a curved support member that mechanically supports the plastic optical fiber at a predetermined bend radius and adhering the plastic optical fiber to the photonic integrated circuit.
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 illustrated by way of example in
In the embodiment depicted by way of example in
In the embodiment depicted by way of example in
The optical coupler 10 is shown interfaced or coupled to a photonic integrated circuit (PIC) 30. As illustrated in this particular example, the optical coupler 10 is coupled to a grating 32 such as, for example, a silicon grating coupler (SCG). The SCG in the figure is connected to an optical waveguide 34.
In the embodiment depicted in
The plastic optical fibers 12 of the ribbon 14 along with support member 18 and support structures 20, 22 adhere to the PIC 30 by a polymer glue (i.e. polymer adhesive such as a thermally curable or UV curable epoxy, a polymer-based bond material, etc.) that has a same or similar thermal expansion coefficient as the plastic optical fibers 12 to thereby minimize or lessen thermally induced strain. The support structures 20, 22 may be a single support structure in another embodiment.
In the embodiments depicted in
In other embodiments, the plastic optical fiber 12 could be designed in various mode sizes by tailoring the core/cladding index contrast ratio in order to maximize the efficiency of the grating coupler 32.
In the embodiment illustrated by way of example in
Another inventive aspect disclosed herein is a method of coupling an optical fiber to a photonic integrated circuit. The method entails bending a plastic optical fiber, e.g. the POF 12, over a curved support member, e.g. the curved support member 18, that mechanically supports the plastic optical fiber at a predetermined bend radius and adhering the plastic optical fiber to the photonic integrated circuit. In one implementation, adhering the plastic optical fiber to the photonic integrated circuit entails using a polymer glue that has a same thermal expansion coefficient as the plastic optical fiber to thereby minimize thermally induced strain. In one implementation, bending the plastic optical fiber entails bending the plastic optical fiber to a bend radius of less than 10 mm (0.4 inches). In one implementation, the method is used to couple the plastic optical fiber at a predetermined angled with a silicon grating coupler. This method enables compact packaging of fiber-to-PIC couplings. As noted above, plastic optical fiber provides significant advantages over silica fiber in terms of bending radius. The bend radius of a plastic optical fiber is usually one order of magnitude better than that of silica fiber. The larger tolerance for bending not only enables more compact packaging but also means that the plastic optical fiber is less susceptible to thermal strain and fatigue than silica fiber. Furthermore, plastic optical fiber is less susceptible to crosstalk than silica fiber.
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”, “entailing” and “containing”, or verb tense variants thereof, 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.
