Optical switch comprising a plurality of ring resonators

Abstract

The present invention relates to optical switches comprising multiple ring resonators, structures for optical switches and methods of forming such structures are disclosed. The structures include a Mach-Zehnder interferometer comprising a first arm, a second arm, a first waveguide core segment coupled with the first arm, and a second waveguide core segment coupled with the second arm. The structures also include a first ring resonator and a second ring resonator. The first ring resonator is located between the first waveguide core segment and the second ring resonator, and the second ring resonator is located between the second waveguide core segment and the first ring resonator.

Description

Technical Field

[0001] This disclosure relates to photonic chips, and more specifically, to the structure of optical switches and methods for forming them. Background Technology

[0002] Photonic chips are used in a variety of applications and systems, including but not limited to data communication systems and data computing systems. A photonic chip contains a photonic integrated circuit composed of photonic components such as modulators, polarizers, and couplers, which are used to manipulate light received from a light source such as an optical fiber or laser.

[0003] Optical switches are common photonic components in photonic integrated circuits. A Mach-Zehnder interferometer serves as a fundamental device for optical switches. An optical coupler distributes input light into a pair of arms of the Mach-Zehnder interferometer. A phase difference is introduced between the light propagating in the different arms, providing a pair of different switched conditions. These arms converge at a downstream optical coupler, where the light is combined. In one switched condition, the phase difference after propagation through the two arms is an odd multiple of π (pi), and the combined light exits from one output port of the output coupler. In the other switched condition, the phase difference after propagation through the two arms is an even multiple of π, and the combined light exits from the other output port of the output coupler.

[0004] Traditional optical switches based on Mach-Zehnder interferometers may suffer from high insertion loss, which is unacceptable in some applications or systems. Furthermore, traditional optical switches based on Mach-Zehnder interferometers may also face problems such as low extinction ratio and excessive footprint.

[0005] There is an urgent need for improved structures for optical switches and methods for forming such structures. Summary of the Invention

[0006] In one embodiment of the present invention, a structure for an optical switch is provided. The structure includes a Mach-Zehnder interferometer comprising a first arm, a second arm, a first waveguide core segment coupled to the first arm, and a second waveguide core segment coupled to the second arm. The structure also includes a first ring resonator and a second ring resonator. The first ring resonator is located between the first waveguide core segment and the second ring resonator, and the second ring resonator is located between the second waveguide core segment and the first ring resonator.

[0007] In one embodiment of the present invention, a method for forming a structure for an optical switch is provided. The method includes forming a Mach-Zehnder interferometer comprising a first arm, a second arm, a first waveguide core segment coupled to the first arm, and a second waveguide core segment coupled to the second arm. The structure further includes forming a first ring resonator and forming a second ring resonator. The first ring resonator is located between the first waveguide core segment and the second ring resonator, and the second ring resonator is located between the second waveguide core segment and the first ring resonator. Attached Figure Description

[0008] The accompanying drawings, which are incorporated in and form a part of this specification, illustrate various embodiments of the invention. These drawings, taken in conjunction with the foregoing general description of the invention and the following detailed description of the embodiments, aid in understanding the embodiments of the invention. In the drawings, the same reference numerals refer to the same features in the various views.

[0009] Figure 1 This is a top view of the structure in the initial manufacturing stage of the processing method in an embodiment of the present invention.

[0010] Figure 2 For along Figure 1 A sectional view along line 2-2.

[0011] Figure 2A For along Figure 1 A sectional view along line 2A-2A.

[0012] Figure 3 , Figure 3A In order to be in Figure 1 , Figure 2 , Figure 2A The subsequent processing method is a structural cross-sectional view of the manufacturing stage.

[0013] Figure 4 This is a top view of the structure in an alternative embodiment of the present invention.

[0014] Figure 5 This is a schematic diagram of the structure in an embodiment of the present invention. Detailed Implementation

[0015] Reference Figure 1 , Figure 2 , Figure 2AAccording to an embodiment of the present invention, a structure 10 for an optical switch includes a waveguide core 12, a waveguide core 14, a phase shifter 24 constituting a Mach-Zehnder interferometer, a ring resonator 16, a ring resonator 18 cascaded with the ring resonator 16, a ring resonator 20, and a ring resonator 22 cascaded with the ring resonator 20. The waveguide cores 12, 14, the phase shifter 24, and the ring resonators 16, 18, 20, and 22 are all located on and cover a dielectric layer 25 and a semiconductor substrate 26. In one embodiment, the dielectric layer 25 may be made of a dielectric material, such as an oxide (e.g., silicon dioxide), and the semiconductor substrate 26 may be made of a semiconductor material, such as single-crystal silicon. In one embodiment, the dielectric layer 25 may be a buried oxide layer on a silicon-on-insulator substrate. The dielectric layer 25 provides a low-index cladding to optically isolate the waveguide cores 12, 14, ring resonators 16, 18, 20, 22, and phase shifter 24 from the semiconductor substrate 26.

[0016] Waveguide cores 12 and 14 are paired to structurally constitute a Mach-Zehnder interferometer. The wiring of waveguide cores 12 and 14 includes adjacent segments of directional coupler 36 and directional coupler 38 representing the Mach-Zehnder interferometer. Waveguide core 12 includes an arm 40 of the Mach-Zehnder interferometer located between directional couplers 36 and 38, and waveguide core 14 includes an arm 42 of the Mach-Zehnder interferometer located between directional couplers 36 and 38. The Mach-Zehnder interferometer also includes a segment 28 of waveguide core 12 coupled to a segment of waveguide core 12 participating in directional coupler 38. The Mach-Zehnder interferometer also includes a segment 30 of waveguide core 14 (coupled to a segment of waveguide core 14 participating in directional coupler 36), a segment 32 of arm 42 included in waveguide core 14, and a segment 34 of arm 42 included in waveguide core 14.

[0017] Arm 40 couples to both the segment of waveguide core 12 participating in directional coupler 36 and the segment of waveguide core 12 participating in directional coupler 38. Arm 42 couples to both the segment of waveguide core 14 participating in directional coupler 36 and the segment of waveguide core 14 participating in directional coupler 38. Arms 40 and 42 are arranged along the length of waveguide cores 12 and 14 between directional couplers 36 and 38. Directional coupler 36 has a coupling length along which the participating segments of waveguide cores 12 and 14 have a spacing that allows optical coupling. Similarly, directional coupler 38 has a coupling length along which the participating segments of waveguide cores 12 and 14 have a spacing that allows optical coupling. In alternative embodiments, directional couplers 36 and 38 can be replaced with other types of optical couplers, such as multi-mode interference couplers.

[0018] Segment 28 of waveguide core 12 is coupled to a segment of waveguide core 12 participating in directional coupler 38 via a bend. Segment 30 of waveguide core 14 is coupled to a segment of waveguide core 14 participating in directional coupler 36 via a bend. Segment 32 of arm 42 included in waveguide core 14 is coupled to a segment of waveguide core 14 participating in directional coupler 36 via a bend, and the segment of waveguide core 14 participating in directional coupler 36 is arranged along the length of waveguide core 14 between segments 30 and 32. Segment 32 of arm 42 included in waveguide core 14 is coupled to segment 34 of arm 42 included in waveguide core 14 via segment 33 of arm 42. Segment 34 of arm 42 included in waveguide core 14 is coupled to a segment of waveguide core 14 participating in directional coupler 38 via a bend.

[0019] Along the direction of light propagation in waveguide core 12, the length of segment 28 of waveguide core 12 is a portion of the total length of waveguide core 12. Along the direction of light propagation in waveguide core 14, the lengths of segments 30, 32, and 34 of waveguide core 14 are each a portion of the total length of waveguide core 14. In one embodiment, the lengths of segments 30, 32, and 34 may be equal. In one embodiment, segment 28 may have a length, and the lengths of segments 30, 32, and 34 may be equal to the length of segment 28. In one embodiment, the length of segment 28 and the respective lengths of segments 30, 32, and 34 can effectively introduce a phase shift of half π (i.e., π / 2), and the difference between the optical path length in waveguide core 14 and the optical path length in waveguide core 12 can be equal to π (i.e., pi).

[0020] Phase shifter 24 is coupled to a segment of arm 40 included in waveguide core 12, the segment being arranged along the length of waveguide core 12 between directional couplers 36 and directional couplers 38. In one embodiment, phase shifter 24 may be a thermo-optic phase shifter, comprising resistance heating elements 41, 43 disposed on opposite sides of the segment of arm 40 of waveguide core 12 and coupled to the segment of arm 40 of waveguide core 12 via slab layer 45. Under the control of a variable electrical signal, the resistance heating elements 41, 43 of phase shifter 24 generate heat through Joule heating, and the generated heat is transferred from the resistance heating elements 41, 43 to the coupled segment of arm 40 of waveguide core 12 via thermal conduction in slab layer 45. The transferred heat causes a localized temperature increase in the coupled segment of waveguide core 12. The localized temperature variations experienced by the coupling segment of arm 40 of waveguide core 12 can effectively alter the refractive index of its constituent materials through a thermo-optic effect, thereby changing the phase of light propagating in the coupling segment of arm 40 of waveguide core 12. In one embodiment, phase shifter 24 can be operated to provide a phase shift equal to zero (i.e., 0) or an integer multiple of π, or a phase shift equal to half a π (i.e., π / 2) or a half-integer multiple of π. The phase shift generated by phase shifter 24 can cancel the phase shift introduced by segments 28, 30, 32, 34, thereby providing a total phase shift modulated between integer multiples of π or half-integer multiples of π. In alternative embodiments, phase shifter 24 can be replaced by an electro-optic phase shifter, a lithium niobate-based phase shifter, a barium titanate-based phase shifter, a polymer-based phase shifter, a two-dimensional material-based phase shifter, or a microelectromechanical system-based phase shifter.

[0021] Ring resonator 16 includes a closed-shape waveguide core 17 and a heater 44 disposed on the inner periphery of the waveguide core 17. Ring resonator 18 includes a closed-shape waveguide core 19 and a heater 46 disposed on the inner periphery of the waveguide core 19. Mach-Zehnder interferometer includes a segment 48 of waveguide core 12, which is coupled to a segment of waveguide core 12 participating in directional coupler 36. Mach-Zehnder interferometer includes a segment 50 of waveguide core 14, which is coupled to a segment of waveguide core 14 participating in directional coupler 36. Ring resonators 16 and 18 are laterally disposed between segment 48 of waveguide core 12 and segment 50 of waveguide core 14. Heater 44 is configured to provide heat to waveguide core 17 to achieve resonant tuning of ring resonator 16, while heater 46 is configured to provide heat to waveguide core 19 to achieve resonant tuning of ring resonator 18.

[0022] Ring resonator 20 includes a closed-shape waveguide core 21 and a heater 52 disposed on the inner periphery of the waveguide core 21. Ring resonator 22 includes a closed-shape waveguide core 23 and a heater 54 disposed on the inner periphery of the waveguide core 23. Mach-Zehnder interferometer includes a segment 56 of waveguide core 12 coupled to a segment of waveguide core 12 participating in directional coupler 38. Mach-Zehnder interferometer includes a segment 58 of waveguide core 14 coupled to a segment of waveguide core 14 participating in directional coupler 38. Ring resonators 20 and 22 are laterally disposed between segment 56 of waveguide core 12 and segment 58 of waveguide core 14. Heater 52 is configured to provide heat to waveguide core 21 to achieve resonant tuning of ring resonator 20, while heater 54 is configured to provide heat to waveguide core 23 to achieve resonant tuning of ring resonator 22.

[0023] Sections 48 and 50 of waveguide cores 12 and 14, and sections 56 and 58 of waveguide cores 12 and 14, can be connected to other photonic components of the photonic integrated circuit. In one embodiment, sections 48 and 50 of waveguide cores 12 and 14 can be configured as input ports for receiving light from an upstream photonic component, while sections 56 and 58 of waveguide cores 12 and 14 can be configured as output ports for outputting light to a downstream photonic component. In an alternative embodiment, sections 56 and 58 of waveguide cores 12 and 14 can be configured as input ports of structure 10, while sections 48 and 50 of waveguide cores 12 and 14 can be configured as output ports of structure 10. Light received through the input ports can be modulated and output as modulated light from the output ports of structure 10, thereby guiding it to the downstream photonic component.

[0024] In one embodiment, waveguide cores 12, 14, and 17, 19, 21, 23 may be made of a material with a refractive index greater than that of silicon dioxide. In one embodiment, waveguide cores 12, 14, 17, 19, 21, 23 may be made of a semiconductor material, such as monocrystalline silicon, amorphous silicon, or polycrystalline silicon. In an alternative embodiment, waveguide cores 12, 14, 17, 19, 21, 23 may be made of a dielectric material, such as silicon nitride, silicon oxynitride, or aluminum nitride. In an alternative embodiment, other materials (such as III-V compound semiconductors) may also be used to form waveguide cores 12, 14, 17, 19, 21, 23.

[0025] In one embodiment, waveguide cores 12, 14 and 17, 19, 21, 23 can be formed by patterning layers of their constituent materials using photolithography and etching processes. In one embodiment, an etching mask can be formed over the layer using photolithography, and then the unmasked sections of the layer can be etched and removed using etching. In one embodiment, waveguide cores 12, 14 and 17, 19, 21, 23 can be formed by patterning single-crystal silicon in a device layer of a silicon-on-insulator substrate. In one embodiment, waveguide cores 12, 14 and 17, 19, 21, 23 can be formed by patterning a deposited layer of their constituent materials.

[0026] Reference Figure 3 , Figure 3A (where the same reference numerals refer to) Figure 1 , Figure 2 , Figure 2A (The same characteristics as in the previous stage) can be used to form a back-end-of-line stack 60 covering waveguide cores 12, 14 and ring resonators 16, 18, 20, 22 in subsequent manufacturing stages. The back-end-of-line stack 60 may include a stack of multiple dielectric layers, each of which is made of a dielectric material, such as an oxide of silicon (e.g., silicon dioxide), a nitride of silicon (e.g., silicon nitride), tetraethyl orthosilicate silicon dioxide, or fluorinated tetraethyl orthosilicate silicon dioxide.

[0027] Ring resonators 16 and 18 are optically cascaded with directional coupler 36 coupled to a Mach-Zehnder interferometer and may be positioned near segments 48 and 50 of the Mach-Zehnder interferometer. Ring resonators 20 and 22 are similarly cascaded with the optical path of directional coupler 38 coupled to a Mach-Zehnder interferometer, and in an alternative embodiment, may be positioned near segments 56 and 58 of the Mach-Zehnder interferometer. In one embodiment, segments 48 and 50 may represent input ports of the Mach-Zehnder interferometer, and segments 56 and 58 may represent output ports of the Mach-Zehnder interferometer. In one embodiment, segment 30 in the optical path may introduce a half-π (π / 2) phase difference in the light entering the directional coupler 36 through waveguide core 14. Additional π (π) phase difference may be introduced in arm 42 of the Mach-Zehnder interferometer by segments 32 and 34. In one embodiment, segment 30 in the optical path introduces a phase difference of half a π (π / 2) into the light entering the directional coupler 36. In another embodiment, segment 28 in the optical path introduces a phase difference of half a π (π / 2) into the light exiting the directional coupler 38 through the waveguide core 12.

[0028] Structure 10 represents a broadband optical switch characterized by the absence of a free spectral range. Compared to conventional optical switches based on Mach-Zehnder interferometers, the optical switch implemented with Structure 10 has lower power consumption. The optical switch implemented with Structure 10 also features a compact footprint, smaller than that of conventional optical switches, and operates at lower power. The parameters of ring resonators 16 and 18, as well as ring resonators 20 and 22, can be optimized to achieve both minimal insertion loss and high crosstalk rejection during operation.

[0029] Reference Figure 4 (where the same reference numerals refer to) Figure 1 (The same features as in the original text), and according to an alternative embodiment, the Mach-Zehnder interferometer may include a waveguide core crossing 62 where waveguide cores 12 and 14 intersect. Segments 30 and 50 are coupled to directional couplers 36 and arm 42 via waveguide core crossing 62. Segment 48 is coupled to directional couplers 36 and arm 40 via waveguide core crossing 62. Light entering from the input port represented by segment 50 receives the phase delay introduced by segment 30, then crosses with waveguide core 12 at waveguide core crossing 62, and is routed through a series of bends to the segment in waveguide core 14 that participates in directional coupler 36.

[0030] Reference Figure 5Furthermore, according to an alternative embodiment, multiple instances of structure 10 can be aggregated to form an optical circuit 64 for switching applications. For example, multiple instances of structure 10 can be used to implement optical path switching between inputs 0-7 and outputs 0'-7'. A representative optical path switching between inputs 0-7 and outputs 0'-7' is shown by a single-headed arrow.

[0031] Multiple instances of structure 10 provide broadband, low-loss, and low-crosstalk optical switching units that can be used to construct a switching matrix, represented by optical circuit 64. In alternative embodiments, multiple instances of structure 10 can also be used to construct a switching matrix with an architecture different from that of optical circuit 64.

[0032] The methods described above are used to manufacture integrated circuit chips. The manufactured integrated circuit chips can be distributed by the manufacturer in the form of bare wafers (e.g., a single wafer containing multiple unpackaged chips), bare dies, or packages. The chips can be integrated as part of intermediate or final products with other chips, discrete circuit elements, and / or other signal processing devices. The final product can be any product containing integrated circuit chips, such as a computer product with a central processing unit or a smartphone.

[0033] Terms used herein with approximate language such as “about,” “approximately,” or “basically” should not be limited to the specified precise values ​​or conditions. In embodiments, approximate language may indicate a range of ±10% relative to the stated value or condition.

[0034] The terms "vertical" and "horizontal" used in this document are for illustrative purposes only and are not intended to be limiting; their purpose is to establish a reference frame. "Horizontal" as used herein is defined as a direction or plane parallel to the conventional plane of the semiconductor substrate, regardless of its actual three-dimensional orientation. "Vertical" and "normal" refer to directions or planes perpendicular to the horizontal plane within the aforementioned reference frame. "Transverse" refers to a direction within the horizontal plane within the aforementioned reference frame.

[0035] If a feature is "connected" or "coupled" to another feature, it may be a direct connection or coupling to that other feature, or there may be one or more intermediate features. If no intermediate features exist, the feature is "directly connected" or "directly coupled" to the other feature. If at least one intermediate feature exists, the feature is "indirectly connected" or "indirectly coupled" to the other feature. A feature "on" or "in contact" with another feature may be directly on or in direct contact with that other feature, or there may be one or more intermediate features. If no intermediate features exist, the feature may be directly "on" or in direct contact with the other feature. If at least one intermediate feature exists, the feature may be "indirectly" on or indirectly in contact with the other feature. If a feature is located above another feature, the feature is said to "cover" the other feature. If a feature extends above another feature and covers a portion of it, these different features are said to "overlap".

[0036] The above descriptions of the various embodiments of the present invention are merely illustrative and are not intended to be exhaustive or limited to the disclosed embodiments. For those skilled in the art, various modifications and variations can be made without departing from the scope and spirit of the embodiments. The terminology used herein is chosen to best explain the principles, practical applications, or technical improvements to existing market technologies, or to enable those skilled in the art to understand the embodiments disclosed herein.

Claims

1. A structure for an optical switch, characterized in that, The structure includes: The Mach-Zehnder interferometer includes a first arm, a second arm, a first waveguide core segment coupled to the first arm, and a second waveguide core segment coupled to the second arm; The first ring resonator; and Second ring resonator; The first ring resonator is located between the first waveguide core section and the second ring resonator, and the second ring resonator is located between the second waveguide core section and the first ring resonator.

2. The structure according to claim 1, characterized in that, The Mach-Zehnder interferometer includes a first optical coupler, a first waveguide core segment coupled to a first arm via the first optical coupler, and a second waveguide core segment coupled to a second arm via the first optical coupler.

3. The structure according to claim 2, characterized in that, The Mach-Zehnder interferometer includes a third waveguide core segment and a fourth waveguide core segment located in the first arm, the third waveguide core segment being configured to generate a first half-π phase delay, and the fourth waveguide core segment being configured to generate a second half-π phase delay.

4. The structure according to claim 3, characterized in that, The Mach-Zehnder interferometer includes a fifth waveguide core segment located between the first waveguide core segment and the first optical coupler, and the fifth waveguide core segment is configured to generate a third half-π phase delay.

5. The structure according to claim 2, characterized in that, The first optical coupler is a first directional coupler.

6. The structure according to claim 2, characterized in that, The Mach-Zehnder interferometer includes a second optical coupler, the first arm is coupled to the second optical coupler, the second arm is coupled to the second optical coupler, and the first arm and the second arm extend from the first optical coupler to the second optical coupler.

7. The structure according to claim 6, characterized in that, The Mach-Zehnder interferometer includes a third waveguide core segment coupled to the first arm via the second optical coupler, and a fourth waveguide core segment coupled to the second arm via the second optical coupler.

8. The structure according to claim 7, characterized in that, Also includes: Third ring resonator; as well as Fourth ring resonator; The third ring resonator is located between the third waveguide core section and the fourth ring resonator, and the fourth ring resonator is located between the fourth waveguide core section and the third ring resonator.

9. The structure according to claim 6, characterized in that, The second optical coupler is a second directional coupler.

10. The structure according to claim 2, characterized in that, The first optical coupler is located between the first arm and the first waveguide core segment, and the first optical coupler is located between the first arm and the second waveguide core segment.

11. The structure according to claim 2, characterized in that, The first waveguide core segment and the second waveguide core segment are configured to input light into the Mach-Zehnder interferometer.

12. The structure according to claim 1, characterized in that, The Mach-Zehnder interferometer includes a third waveguide core segment and a fourth waveguide core segment located in the first arm, the third waveguide core segment being configured to generate a first half-π phase delay, and the fourth waveguide core segment being configured to generate a second half-π phase delay.

13. The structure according to claim 12, characterized in that, The Mach-Zehnder interferometer includes an optical coupler and a fifth waveguide core segment located between the first waveguide core segment and the optical coupler. The first waveguide core segment is coupled to the first arm via the optical coupler, the second waveguide core segment is coupled to the second arm via the optical coupler, and the fifth waveguide core segment is configured to generate a third half-π phase delay.

14. The structure according to claim 13, characterized in that, Also includes: A phase shifter coupled to the second arm.

15. The structure according to claim 1, characterized in that, Also includes: A phase shifter coupled to the second arm.

16. The structure according to claim 15, characterized in that, The phase shifter includes a resistance heating element.

17. The structure according to claim 1, characterized in that, The Mach-Zehnder interferometer includes a waveguide core crossover point, and the first waveguide core segment is coupled to the first arm through the waveguide core crossover point.

18. The structure according to claim 17, characterized in that, The second waveguide core segment is coupled to the second arm through the waveguide core intersection.

19. The structure according to claim 1, characterized in that, The first arm, the second arm, the first waveguide core segment, and the second waveguide core segment are made of monocrystalline silicon.

20. A method for forming a structure for an optical switch, characterized in that, The method includes: A Mach-Zehnder interferometer is formed, the Mach-Zehnder interferometer including a first arm, a second arm, a first waveguide core section coupled to the first arm, and a second waveguide core section coupled to the second arm; Forming the first ring resonator; and Form a second ring resonator; The first ring resonator is located between the first waveguide core section and the second ring resonator, and the second ring resonator is located between the second waveguide core section and the first ring resonator.

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