BENT TAPER AND POLARIZATION ROTATOR
A bent taper is provided that includes one or more waveguide bends, at least one of which has a tapering waveguide width along at least a portion thereof. In one embodiment, the bent taper is an S-shaped bent taper that is configured as a TE0-TE1 mode convertor. Such a bent taper can be combined with a linear bi-layer taper configured as a TM0-TE1 mode converter to form a TM0-TE0 polarization rotator.
This application is a continuation-in-part of and claims priority to U.S. patent application Ser. No. 14/754,105, filed Jun. 29, 2015, which is hereby incorporated by reference herein in its entirety.
FIELD OF THE INVENTIONThe present invention relates to optical waveguide components including a taper. More particularly, the present invention relates to optical waveguide components including a bent taper.
BACKGROUND OF THE INVENTIONIn the field of integrated optics, conventional linear tapers are used for various purposes, such as adiabatic mode-size conversion, edge coupling, and mode conversion. For example, linear bi-layer tapers configured as TM0-TE1 mode converters are described in D. Dai and J. E. Bowers, Opt. Express 19, 10940 (2011), and in W. D. Sacher, T. Barwicz, B. J. F. Taylor, and J. K. S. Poon, Opt. Express 22, 3777 (2014), each of which is hereby incorporated by reference herein in its entirety. On the other hand, when waveguide bending is desired, single-mode waveguide bends are conventionally used to avoid multimode mixing.
There is a need for improved tapers for use in optical waveguide components, for example, with lower loss, lower back-reflection, higher optical bandwidth, and/or other improvements.
SUMMARY OF THE INVENTIONAccordingly, one aspect of the present invention relates to an optical waveguide component comprising: a bent taper having a first port and a second port, the bent taper comprising a first waveguide bend proximate to the first port, the first waveguide bend tapered along at least a portion thereof proximate to the first port, the tapered portion having a waveguide width that tapers towards the first port.
The foregoing and other objects, aspects, features, and advantages of the invention will become more apparent from the following description and from the claims.
The objects and features of the present invention can be better understood with reference to the drawings described below, and the claims. The drawings are not necessarily to scale, emphasis instead generally being placed upon illustrating the principles of the present invention. In the drawings, like numerals are used to indicate like parts throughout the various views.
We describe herein a bent taper that can be included in an optical waveguide component, such as a polarization rotator. The bent taper includes one or more waveguide bends, at least one of which has a tapering waveguide width along at least a portion thereof. The bent taper may be S-shaped, L-shaped, or may have some other bent shape.
Typically, the bent taper has a first port, i.e., a first end, and a second port, i.e., a second end, and includes a first waveguide bend proximate to the first port. The first waveguide bend is tapered along at least a portion thereof proximate to the first port, and the tapered portion has a waveguide width that tapers towards the first port. The waveguide width of the tapered portion may taper symmetrically or asymmetrically with respect to a center arc of the first waveguide bend, at a substantially constant rate or at a varying rate.
Also typically, the bent taper is a multimode bent taper that transitions from single-mode at the first port to multimode at the second port. Accordingly, the waveguide width of the tapered portion typically tapers from a multimode waveguide width to a single-mode waveguide width. By controlling the geometry of the bent taper, the multimode region of the bent taper can be used to provide a variety of functions.
In some embodiments, the bent taper is configured as a mode converter. In the field of integrated optics, mode converters can be used to realize polarization-diversified photonic integrated circuits (PICs). In some embodiments, the bent taper is configured for use in a polarization rotator, which may form part of a polarization controller or a polarization-diversified PIC, such as a transceiver, for example. Some embodiments of the bent taper can be used in multiplexing applications such as mode-division multiplexing (MDM), wavelength-division multiplexing (WDM), polarization-division multiplexing (PDM), or combinations thereof.
In some embodiments, the first waveguide bend 110 and the second waveguide bend 120 are circular waveguide bends that typically have a substantially same center radius of curvature R0. In such embodiments, the S-bend of the bent taper 100 may be defined by three parameters: the center radius of curvature R0 measured to a center arc of each waveguide bend, a lateral offset dy measured as a lateral distance between the centers of the first port 102 and the second port 104, and a waveguide width (Ui+Di) that varies along at least a portion of the S-bend. It should be noted that the first port 102 and the second port 104 may also be offset in angle.
The bent taper 100 may be configured as a mode converter. Typically, the bent taper 100 is configured to provide mode conversion between a fundamental transverse electric (TE0) mode and an intermediate mode, e.g., a higher-order transverse electric (TE) mode. In some embodiments, the bent taper 100 is configured as a TE0-TE1 mode converter that provides mode conversion between a TE0 mode and a first-order transverse electric (TE1) mode. For example, when used to provide TE0-to-TE1 mode conversion, the bent taper 100 is configured to receive a TE0 mode via the first port 102, which serves as an input port, to convert the TE0 mode to a TE1 mode, and to provide the TE1 mode via the second port 104, which serves as an output port.
TE modes are defined as those with an electric field parallel to the chip plane, and transverse magnetic (TM) modes are defined as those with a magnetic field parallel to the chip plane. In some instances, the TE and TM modes are quasi-TE and quasi-TM modes.
The bent taper 100 may be designed by decomposing the S-bend into a plurality of segments of equal angular measure d0, optimizing the waveguide widths at the segment boundaries, and interpolating the waveguide width between the segment boundaries to make the transitions smooth. In other embodiments, segments of different angular measures may be used, for example. The waveguide width is defined relative to the center arcs described by the center radius of curvature R0. The center arcs divide the S-bend into a first side, referred to as the up side, and a second side, referred to as the down side. Asymmetric waveguide widths may be used to increase the optimization freedom. In other embodiments, symmetric waveguide widths may be used. A particle swarm optimization (PSO) may be used during a finite-difference time-domain (FDTD) simulation to determine an optimized geometry for the bent taper 100.
In the embodiment illustrated in
A bent taper 100 configured as a TE0-TE1 mode convertor with ultra-high efficiency was realized by only varying the waveguide widths (U2+D2) and (U3+D3). The waveguide width (U1+D1) at the narrow first port 102 was set to a standard width of a single-mode waveguide. In this embodiment, the waveguide width of the first three segments, i.e., the tapered portion 111, tapers towards the first port 102 and is asymmetric with respect to the center arc of the first waveguide bend 110. The waveguide width of the last five segments, i.e., the non-tapered portion, is substantially constant at a waveguide wide of the second port 104. When the lateral offset dy was set to 1.2 μm, a center radius of curvature R0 of about 8.5 μm was found after optimization. The device length of the bent taper 100 was only about 6.3 μm. Typically, the bent taper 100 has a device length of less than about 10 μm.
A bent taper, such as the S-shaped bent taper 100 of
A linear bi-layer taper can be used as the mode-conversion element in the polarization rotator.
The bi-layer taper 400 may be configured as a mode converter. Typically, the bi-layer taper 400 is configured to provide mode conversion between a TM0 mode and an intermediate mode. In some embodiments, the bi-layer taper 400 is configured as a TM0-TE1 that provides mode conversion between a TM0 mode and a TE1 mode. For example, when used to provide TM0-to-TE1 mode conversion, the bi-layer taper 400 is configured to receive a TM0 mode via the input port 402, to convert the TM0 mode to a TE1 mode, and to provide the TE1 mode via the output port 404.
The bi-layer taper 400 may be designed by decomposing each layer 410 or 420 into a plurality of layer segments of equal length, optimizing the layer widths at the segment boundaries, and interpolating the waveguide width between the segment boundaries to make the transitions smooth. In other embodiments, layer segments of different lengths may be used, for example. A PSO may be used during an FDTD simulation to determine an optimized geometry for the bi-layer taper 400.
In the embodiment illustrated in
A bi-layer taper, such as the bi-layer taper 400 of
When the polarization rotator receives a TM0 mode as an input signal, via the input port of the bi-layer taper, at the left side of
Two TM0-TE0 polarization rotators can be cascaded to form an on-chip polarizer. Typically, the polarizer is a TM0-pass polarizer that is configured to pass substantially only TM0-mode light.
In various embodiments, the devices described herein may be configured to operate in one or more of the wavelength ranges described in Table I.
In various embodiments, the devices described herein may be fabricated using any suitable material system. Typically, the devices are fabricated using an SOI material system. Alternatively, the devices could be fabricated using a silica-on-silicon material system, a silicon nitride material system, a silicon oxynitride material system, or a III-V material system, for example. The optical waveguide components of the devices are typically formed as ridge waveguides or rib waveguides.
Although the theoretical description given herein is thought to be correct, the operation of the devices described and claimed herein does not depend upon the accuracy or validity of the theoretical description. That is, later theoretical developments that may explain the observed results on a basis different from the theory presented herein will not detract from the inventions described herein.
Any material, or portion thereof, that is said to be incorporated by reference herein, but which conflicts with existing definitions, statements, or other disclosure material explicitly set forth herein is only incorporated to the extent that no conflict arises between that incorporated material and the present disclosure material. In the event of a conflict, the conflict is to be resolved in favor of the present disclosure as the preferred disclosure.
The present disclosure is not to be limited in scope by the specific embodiments described herein. Indeed, other various embodiments of and modifications to the present disclosure, in addition to those described herein, will be apparent to those of ordinary skill in the art from the foregoing description and accompanying drawings. Thus, such other embodiments and modifications are intended to fall within the scope of the present disclosure. Further, although the present disclosure has been described herein in the context of a particular implementation in a particular environment for a particular purpose, those of ordinary skill in the art will recognize that its usefulness is not limited thereto and that the present disclosure may be beneficially implemented in any number of environments for any number of purposes.
Claims
1-22. (canceled)
23. A waveguide test structure comprising:
- a substrate;
- a pair of waveguide mode converters supported by the substrate, the pair of waveguide mode converters comprising: a first waveguide mode converter supported by the substrate and configured for converting between a first optical mode and a second optical mode, the first waveguide mode converter comprising a first port configured for coupling the first optical mode, and a second port configured for coupling the second optical mode; and, a second waveguide mode converter supported by the substrate and configured for converting between the first optical mode and the second optical mode, the first waveguide mode converter comprising a first port configured for coupling the first optical mode, and a second port configured for coupling the second optical mode;
- wherein the second port of the first waveguide mode converter is optically coupled to the second port of the second waveguide mode converter so that the first waveguide mode converter and the second waveguide mode converter are optically connected in series.
24. The waveguide test structure of claim 23 further comprising a first test port optically coupled to the first port of the first waveguide mode converter, and a second test port optically coupled to the first port of the second waveguide mode converter.
25. The waveguide test structure of claim 24 wherein at least one of the first test port or the second test port comprises a vertical coupler.
26. The waveguide test structure of claim 23 wherein the first optical mode is a TE mode, the second optical mode is a TM mode.
27. The waveguide test structure of claim 23 wherein the first optical mode is a fundamental TE mode and the second optical mode is a higher-order TE mode.
28. A wafer comprising two or more instances of the pair of waveguide mode converters of claim 23 optically connected in series between a first test port and a second test port.
29. The waveguide test structure of claim 23 wherein the first waveguide mode converter comprises a bent waveguide taper.
30. The waveguide test structure of claim 29 wherein the bent waveguide taper comprises two bent waveguide segments of opposite curvature.
31. The waveguide test structure of claim 30 wherein the two bent waveguide segments comprise a first bent waveguide segment and a second bent waveguide segment optically connected in series, and wherein the first bent waveguide segment increases in width in a direction toward the second bent waveguide segment.
32. The waveguide test structure of claim 29 wherein the bent waveguide taper is configured to convert a fundamental TE mode to a higher-order TE mode.
33. The waveguide test structure of claim 32 wherein the first waveguide mode converter further comprises a TE to TM mode converter configured to convert the higher-order TE mode to the fundamental TE mode.
34. The waveguide test structure of claim 32 wherein the TE to TM mode converter comprises a bilayer taper.
35. The waveguide test structure of claim 23 wherein the first waveguide mode converter comprises a bent waveguide taper.
36. The waveguide test structure of claim 23 wherein each of the first waveguide mode converter and the second waveguide mode converter comprises a bent waveguide taper.
37. The waveguide test structure of claim 36 wherein each of the bent waveguide tapers comprises two bent waveguide segments of opposite curvature.
38. The waveguide test structure of claim 37 wherein the two bent waveguide segments comprise a first bent waveguide segment and a second bent waveguide segment optically connected in series, and wherein the first bent waveguide segment increases in width in a direction toward the second bent waveguide segment.
39. The waveguide test structure of claim 36 wherein each of the bent waveguide tapers is configured to convert a fundamental TE mode to a higher-order TE mode.
40. The waveguide test structure of claim 39 wherein each of the first waveguide mode converter and the second waveguide mode converter further comprises a TE to TM mode converter configured to convert the higher-order TE mode to the fundamental TE mode.
41. The waveguide test structure of claim 40 wherein the TE to TM mode converter comprises a bilayer taper.
42. A wafer comprising:
- one or more waveguide test structures, the one or more waveguide test structures comprising:
- a first test port;
- a second test port; and,
- a waveguide mode converter optically connected between the first test port and the second test port, the waveguide mode converter configured for converting between a first optical mode and a second optical mode;
- wherein each of the first test port and the second test port is configured to preferentially couple in the waveguide mode converter or out of the waveguide mode converter the same one of the first optical mode or the second optical mode.
Type: Application
Filed: Mar 19, 2019
Publication Date: Jul 11, 2019
Inventors: Yangjin Ma (Brooklyn, NY), Michael J. Hochberg (New York, NY)
Application Number: 16/357,381