Photonic integrated circuit device and method of forming same

Abstract

Embodiments of the invention relate to photonic integrated circuit devices and methods of forming the same. A photonic integrated circuit device has an asymmetric double ring resonator. The asymmetric double ring resonator includes a first ring having a first effective length and a second ring having a second effective length different from the first effective length. The first effective length and the second effective length are close to an integer multiple of the third effective length. The third effective length is within about one magnitude or order of magnitude of the first effective length and the second effective length. The asymmetric double-ring resonator has a free spectral range corresponding to a single-ring resonator having a third effective length, but is less sensitive to manufacturing process variations than a single-ring resonator having a third effective length.

Description

Technical Field

[0001] Embodiments of the present application relate to photonic integrated circuit devices and methods of forming the same. Background Art

[0002] Photonic integrated circuit (PIC) devices are widely used in communications and are increasingly used in sensing and computing. PIC devices can operate at higher speeds than electronic integrated circuit (IC) devices. PICs consist of two or more optical devices coupled to form a circuit. Examples of optical devices include waveguides, splitters, multiplexers, filters, modulators, sensors, and converters. PIC devices can interface with ICs using lasers, photodiodes, and other devices to provide additional functionality. As with ICs, there is a constant demand for higher component density in PIC devices. Summary of the Invention

[0003] According to one aspect of an embodiment of the present application, a photonic integrated circuit device is provided, comprising: a substrate; a first waveguide located above the substrate; a second waveguide located above the substrate; and a multi-ring resonator comprising a first ring having a first effective length and a second ring having a second effective length, wherein the multi-ring resonator is coupled between the first waveguide and the second waveguide and has a larger free spectral range than a single-ring resonator having the first effective length or having the second effective length.

[0004] According to another aspect of an embodiment of the present application, a photonic integrated circuit device is provided, comprising: a substrate; a first waveguide located above the substrate; a first ring, wherein the first ring has a first effective length; and a second ring, wherein the second ring has a second effective length and is optically coupled between the first waveguide and the first ring; wherein the first effective length is a first integer multiple of a third effective length; the second effective length is a second integer multiple of the third effective length; the first integer multiple is different from the second integer multiple; and the first integer multiple and the second integer multiple are integers greater than 1.

[0005] According to another aspect of an embodiment of the present application, a method for forming a photonic integrated circuit device is provided, comprising: providing a substrate; and forming a multi-ring resonator, a first waveguide, and a second waveguide above the substrate, wherein the multi-ring resonator comprises a first ring and a second ring, the first ring having a first effective length, the second ring having a second effective length, the free spectral range of the multi-ring resonator being greater than that of a single-ring resonator having the first effective length or a single-ring resonator having the second effective length, the first ring being coupled to the first waveguide, and the second ring being coupled to the second waveguide. BRIEF DESCRIPTION OF THE DRAWINGS

[0006] Various aspects of the present disclosure will be best understood from the following detailed description when read in conjunction with the accompanying drawings. It should be emphasized that, in accordance with standard practice in the industry, various components are not drawn to scale and are used for illustrative purposes only. In fact, the dimensions of various components may be arbitrarily increased or decreased for clarity of discussion.

[0007] Figure 1 A plan view of a PIC device with an asymmetric multi-ring resonator according to an embodiment of the present disclosure is shown.

[0008] Figure 2A-2C Shown according to various embodiments Figure 1 Cross-sectional view of a PIC device.

[0009] Figure 3-Figure 10 A plan view of a PIC device with an asymmetric multi-ring resonator according to various embodiments of the present disclosure is shown.

[0010] Figures 11A-13B are pairs of plan and cross-sectional views of a PIC device with an asymmetric multi-ring resonator according to various embodiments of the present disclosure.

[0011] Figure 14-16 A plan view of a PIC device with an asymmetric multi-ring resonator according to various embodiments of the present disclosure is shown.

[0012] Figures 17-20 is a series of cross-sectional views illustrating some embodiments of methods of forming a PIC device having an asymmetric multi-ring resonator.

[0013] Figure 21 Flowcharts are provided illustrating some embodiments of methods of forming a PIC device having an asymmetric multi-ring resonator. DETAILED DESCRIPTION

[0014] The following disclosure provides many different embodiments or examples for implementing the different features of the present disclosure. Specific embodiments or examples of components and arrangements are described below to simplify the present disclosure. Of course, these are merely examples and are not intended to be limiting. For example, in the following description, forming a first component above or on a second component may include an embodiment in which the first component and the second component are directly in contact with each other, and may also include an embodiment in which an additional component may be formed between the first component and the second component so that the first component and the second component may not be in direct contact. In addition, the present disclosure may repeat reference numbers and / or letters in various examples. This repetition is for the purpose of simplicity and clarity and does not itself indicate the relationship between the various embodiments and / or configurations discussed.

[0015] Furthermore, for ease of description, spacing terms such as "below," "beneath," "lower," "above," "upper," etc., may be used herein to describe the relationship of one element or component to another element or component as illustrated in the figures. Spacing terms are intended to encompass different orientations of the device in use or during operation in addition to the orientations depicted in the figures. The device may be otherwise oriented (rotated 90 degrees or at other orientations), and spacing descriptors used herein should be interpreted accordingly.

[0016] Wavelength division multiplexing (WDM) is commonly used for communications over optical fiber. WDM increases bandwidth by allowing a single optical fiber to carry multiple signals simultaneously. PIC devices that receive or transmit multiplexed signals widely use ring resonators. Ring resonators have the property of selectively transmitting signals with a wavelength corresponding to their primary resonant mode and attenuating or blocking signals of other wavelengths. The primary resonant mode is the wavelength of light for which the optical path length of the loop around the ring (the effective length of the ring) is roughly an integer multiple of the wavelength. The primary wavelengths have a periodic interval called the free spectral range (FSR). The FSR in the frequency domain is given by the following formula:

[0017]

[0018] Where c is the speed of light, L eff is the effective length of the loop around the ring. The effective length is the circumference of the ring multiplied by the group index. The group index is the ratio of the speed of light in a vacuum to the speed of light in the ring. The group index is similar to the refractive index, but takes into account dispersion and other effects that depend on the ring geometry.

[0019] The bandwidth of a WDM system is proportional to the number of available channels within one FSR interval. There is a minimum acceptable channel spacing, so the number of available channels is proportional to the FSR. By using eff Smaller rings can improve FSR, but as the rings get smaller, their sensitivity to manufacturing process variations increases, so manufacturing process variations become a limiting factor.

[0020] One aspect of the present disclosure is a PIC having an asymmetric dual-ring resonator, the resonator including a first ring having a first effective length and a second ring having a second effective length. The first effective length and the second effective length are different from each other and are selected so that the dual-ring resonator has a larger FSR than a ring resonator having either the first effective length or the second effective length. It has been found that if the first and second effective lengths are close to an integer multiple (greater than 1) of a third effective length corresponding to a larger FSR, and the third effective length is within about one order of magnitude or magnitude of the first and second effective lengths, then the sensitivity to manufacturing process variations is sufficiently low that a larger FSR can be achieved.

[0021] The concept of the asymmetric dual ring resonator described above can be extended to a multi-ring resonator with three or more rings coupled in series. In some embodiments, the third ring has the same effective length as the first or second ring. This configuration combines the advantages of a symmetric dual ring resonator (such as improved filtering) with the advantages of an asymmetric dual ring resonator. In some embodiments, the effective length of the third ring is also a near integer multiple of the third effective length, but is different from both the first and second effective lengths. By using three or more rings with effective lengths, each having an effective length that is a different near integer multiple of a smaller effective length, a larger FSR can be achieved.

[0022] In some embodiments, in a heterogeneous multi-ring resonator, the radial thickness of the first ring is different from that of the second ring. The radial thickness affects the group index. In an asymmetric multi-ring resonator, varying the radial thickness provides a method for fine-tuning the effective length without having to change the distance between the first and second rings, the distance between the multi-ring resonator and the input and output waveguides, or repositioning the waveguides or rings. The width variation can be limited so that the multi-ring resonator supports only one optical mode. The first ring can be coupled to the first waveguide, and the second ring can be coupled to the second waveguide. The first waveguide and the second waveguide are the input waveguide and the output waveguide.

[0023] In some embodiments, the spacing between the first and second rings in the asymmetric multi-ring resonator is greater than the spacing between the first ring and the first waveguide. It has been found that asymmetric multi-ring resonators benefit from high coupling coefficients with the input and output waveguides, but making the coupling coefficients between the rings too large degrades the Q factor.

[0024] In some embodiments, the first ring or more than one ring in an asymmetric multi-ring resonator is non-circular. In some embodiments, the non-circular ring has a lower radius of curvature in the region where it couples with another PIC device, such as a waveguide. The reduced curvature can be used to increase the coupling coefficient. Alternatively, the reduced curvature can be used to achieve a given coupling coefficient that is less sensitive to manufacturing process variations. In some embodiments, the waveguide is curved to match the curvature of the ring in its coupling region. In some embodiments, the non-circular ring provides a more compact layout than an equivalent PIC with circular rings. The rings can be made non-circular to a certain extent without affecting the free spectral range.

[0025] In some embodiments, the input and output waveguides are located in a first optical layer at a first height above the substrate, and the asymmetric multi-ring resonator is located in a second optical layer at a second height above the substrate. The spacing between the layers can then be used to precisely control the spacing between the asymmetric multi-ring resonator and the input and output waveguides.

[0026] In some embodiments, the first ring is located in a first optical device layer at a first height above the substrate, and the second ring is located in a second optical device layer at a second height above the substrate. The first device layer and the second device layer can be made of different optical materials, such that the first ring and the second ring have different compositions. In some embodiments, one of the optical materials is a nonlinear optical material, such that the multi-ring resonator can provide a nonlinear optical effect.

[0027] Figure 1 A plan view of a PIC device 100 including an asymmetric dual-ring resonator 111A is shown. Asymmetric dual-ring resonator 111A includes a first ring 103A optically coupled to a second ring 107A. First ring 103A is optically coupled to first waveguide 101, and second ring 107A is optically coupled to second waveguide 109. First waveguide 101 and second waveguide 109 provide input and output waveguides for asymmetric dual-ring resonator 111A. First waveguide 101, first ring 103A, second ring 107A, and second waveguide 109 are composed of optical material and are surrounded by cladding 105.

[0028] The first ring 103A has a first radius R1 and a first effective length L eff1 The second ring 107A has a second radius R2 and a second effective length L eff2 The first effective length L eff1 Different from the second effective length L eff2 The first ring 103A and the second ring 107A are circular and have equal radial widths, so that the difference in effective length is proportional to the difference in radius.

[0029] The first effective length Leff1 and the second effective length L eff2 is predetermined so that the FSR of the asymmetric dual ring resonator 111A is greater than that of the asymmetric dual ring resonator 111A having the first effective length L eff1 Or the second effective length L eff2 The FSR of the single ring resonator 111A is the FSR of the asymmetric dual ring resonator 111A with a first effective length L eff1 The first integer multiple of the FSR of the single ring resonator and has a second effective length L eff2 A second integer multiple of the FSR of the single ring resonator, wherein the first integer and the second integer are small integers greater than 1.

[0030] The FSR can be determined by plotting the signal transmission efficiency as a function of wavelength. The plot will show peaks in transmission efficiency. The highest peaks are resonant modes. The wavelength spacing between resonant modes is a measure of the FSR. f ) and FSR in wavelength domain (FSR Δλ ) are as follows:

[0031]

[0032] therefore

[0033]

[0034] Between the highest peaks of the resonant modes, lower peaks can be observed. These lower peaks are side modes. In order for a heterogeneous multi-ring resonator to be effective, the transmission loss in the resonant mode must be acceptable, and there must be a sufficient difference between the resonant mode and the side modes. As the ratio of the effective length of the ring to its lowest common denominator increases, the difference between the resonant mode and the side modes decreases.

[0035] In a first embodiment, R1 is twice R0 and R2 is three times R0, where R0 is the radius of a single-ring resonator with the same FSR as asymmetric dual-ring resonator 111A. An example of this embodiment is one in which R1 is 6 μm, R2 is 9 μm, and first and second rings 103A, 107A, have the same group index. The FSR of asymmetric dual-ring resonator 111A will be the same as that of a single-ring resonator with a radius of 3 μm, which is twice the FSR of a single-ring resonator with a radius of 6 μm. For this example, signals with wavelengths corresponding to the resonant mode may have an intensity drop ranging from approximately -1 dB to approximately -3 dB. In contrast, signals with wavelengths corresponding to the side mode may exhibit an intensity drop of -18 dB or greater. The transmission efficiency of signals at or near the side mode wavelength is more than an order of magnitude lower than the transmission efficiency of signals at or near the resonant mode wavelength. These differences are large enough to provide effective filtering for all signals except the resonant mode signals.

[0036] In the second embodiment, R1 is three times R0, and R2 is four times R0. The side mode intensity is slightly greater than that of the first embodiment, but the transmission efficiency for signals at or near the resonant mode wavelength is likely to be more than an order of magnitude lower. If R1 is the same in both the first and second embodiments, the second embodiment provides a 50% greater FSR than the first embodiment.

[0037] In the third embodiment, R1 is six times R0, and R2 is seven times R0. Signals at wavelengths corresponding to the resonant mode can be similar to the previous embodiments, with an intensity drop in the range of approximately -1 dB to approximately -3 dB. Side mode intensity will show a significant increase compared to the first and second embodiments, but will likely remain at approximately 14 dB or less, and still be more than an order of magnitude less efficient than transmission of signals at or near the resonant mode wavelength. If R1 is the same in both the first and third embodiments, the third embodiment provides a 200% greater FSR than the first embodiment.

[0038] In a fourth embodiment, R1 is twelve times greater than R0, and R2 is thirteen times greater than R0. Assuming that the first ring 103A and the second ring 107A have the same group index, an example of this embodiment is where R1 is 6 μm and R2 is 6.5 μm. For this embodiment, the transmission loss of the side mode intensity may be only approximately -9 dB, which is within an order of magnitude of the signal transmission loss at the resonant mode wavelength. For some applications, the difference in transmission efficiency between the intended resonant mode and the intended side mode may be too small. If the intended resonant mode is sufficiently distinct from the side mode, this embodiment provides a 500% increase in FSR compared to the first embodiment and an 1100% increase in FSR compared to the single-ring resonator with R1. However, if the intended resonant mode is not sufficiently distinct from the side mode, the FSR does not increase compared to the single-ring resonator with R1.

[0039] These examples work if the resonant mode peaks are well enough defined and sufficiently distinct from the side modes. eff1 and L eff2 Must be close to L eff3 In this context, "close" usually means within 1 / 10 of 1%. eff3 It can be defined as L eff1 The first integer fraction of L. eff2 It should be L eff3 is a close integer multiple of eff2 With L eff3 When the deviation from the exact integer multiple of L reaches about 1 / 10 of 1%, the transmission efficiency at the resonant mode wavelength begins to decrease significantly, and the resonant mode peak begins to split into two peaks. eff2 Keep at m*L eff3 The asymmetric dual-ring resonator achieves a higher FSR than a single ring, where L eff3 It's L eff1 / n, m and n are small integers, each greater than 1, and have no common divisor greater than 1. In some embodiments, m and n are 12 or less. In some embodiments, m and n are 10 or less. In some embodiments, m and n are 7 or less. In some embodiments, m and n are 4 or less. The smaller m and n are, the more L eff2 The closer to L eff3 The greater the integer multiple of , the better the performance of the asymmetric dual-ring resonator 111A.

[0040] Back to Figure 1, the first ring 103A is separated from the first waveguide 101 by a distance d1. In some embodiments, d1 is in a range of about 50 nm to about 300 nm. In some embodiments, the coupling coefficient (κ squared) between the first ring 103A and the first waveguide 101 is in a range of about 0.25% to about 30%. In some embodiments, the coupling coefficient between the first ring 103A and the first waveguide 101 is at least about 2%. These comments also apply to the relationship between the second ring 107A and the second waveguide 109.

[0041] The first ring 103A and the second ring 107A are separated by a distance d2. Distance d2 is greater than d1. In some embodiments, d2 is in a range from approximately 100 nm to approximately 350 nm. In some embodiments, d2 is at least approximately twice d1. In some embodiments, the coupling coefficient between the first ring 103A and the second ring 107A is in a range from approximately 0.05% to approximately 2.5%. In some embodiments, the coupling coefficient between the first ring 103A and the second ring 107A is in a range from approximately 0.05% to approximately 1%. If the coupling coefficient is too low, transmission efficiency may be insufficient. If the coupling coefficient is too high, the Q factor may decrease, the resonance peak may split, and other undesirable effects may occur. In some embodiments, the coupling coefficient between the first ring 103A and the second ring 107A is approximately half or less than half of the coupling coefficient between the first ring 103A and the first waveguide 101. In some embodiments, the coupling coefficient between the first ring 103A and the second ring 107A is approximately 10% or less of the coupling coefficient between the first ring 103A and the first waveguide 101.

[0042] Figure 2A Shown with Figure 1 The embodiment of the PIC device 100 corresponds to the cross-sectional view 200A. Figure 2A As shown, the first waveguide 101, the first ring 103A, the second ring 107A, and the second waveguide 109 have rectangular cross-sections and may all be located within the optics layer 201 above the substrate 203. Providing the first ring 103A and the second ring 107A with rectangular cross-sections may make their group indices more predictable.

[0043] Figure 2B Shown with Figure 1 FIG20B is a cross-sectional view corresponding to another embodiment of the PIC device 100. In this embodiment, the first waveguide 101, the first ring 103A, the second ring 107A, and the second waveguide 109 have sidewalls 205 that taper at an angle θ. The taper angle θ may be caused by a relatively low energy etching process or other etching conditions, and may be different from the embodiment of the PIC device 100. Figure 2ACompared to the process for providing vertical sidewalls shown in cross-sectional view 200A, these etching conditions result in less vertical and more isotropic etching. The lower energy process can be a more repeatable process. In some embodiments, angle θ is about 3° or greater. In some embodiments, angle θ is about 10° or greater.

[0044] Figure 2C Shown with Figure 1 FIG200C is a cross-sectional view corresponding to another embodiment of the PIC device 100. In this embodiment, the first waveguide 101, the first ring 103A, the second ring 107A, and the second waveguide 109 have sidewalls 205 with curved lower surfaces 207. The curved lower surface 207 may be a result of a lower energy etching process or other etching conditions (e.g., for providing a desired effect). Figure 2A These processes or conditions may result in another artifact of more isotropic etching compared to the process that produces the rectangular cross-section shown in the cross-sectional view 200A. The conditions that produce the curved lower surface 207 may be more repeatable than the conditions that result in the rectangular cross-section and may therefore be useful for fine-tuning the effective lengths of the first and second rings 103A, 107A.

[0045] Figure 3 FIG shows a plan view of a PIC device 300 including an asymmetric dual ring resonator 111B. The asymmetric dual ring resonator 111B includes a first ring 103B optically coupled to a second ring 107B. The asymmetric dual ring resonator 111B is similar to FIG. 1 except that the first ring 103B and the second ring 107B are non-circular. Figure 1 For example, the first ring 103B and the second ring 107B may be elliptical.

[0046] Figure 4 FIG shows a plan view of a PIC device 400 including an asymmetric dual ring resonator 111C. The asymmetric dual ring resonator 111C is similar to Figure 3 The asymmetric dual ring resonator 111B is shown, except that the first ring 103B and the second ring 107B are oriented with their long axes parallel to the first waveguide 101 and the second waveguide 109. This configuration allows the first waveguide 101 and the second waveguide 109 to be placed closer together.

[0047] The first ring 103B has an increased radius of curvature in the region 501 where it couples with the first waveguide 101. The radius of curvature is increased relative to some other locations along the perimeter of the first ring 103B, such as region 507, and is also increased compared to a circular ring of the same effective length. This increased radius of curvature can be used to increase the coupling coefficient between the first ring 103B and the first waveguide 101. Even if the distance d1 is increased so that the coupling coefficient is Figure 1Similar to the first ring 103A, the increased radius of curvature in region 501 also reduces the sensitivity of the coupling coefficient to manufacturing process variations. The second ring 107B may also have an increased radius of curvature in region 505 coupled to the second waveguide 109.

[0048] The first and second rings 103B, 107B may also have an increased radius of curvature in the region 503 where they are coupled to each other. As previously discussed, it is desirable to maintain the degree of coupling between the first and second rings 103B, 107B within a limited range. Increasing the radius of curvature within the region 503 provides a given degree of coupling with a greater distance d2 between the first and second rings 103B, 107B and makes the coupling coefficient less sensitive to manufacturing process variations.

[0049] Figure 5 FIG. 5 shows a plan view of a PIC device 500 including an asymmetric dual ring resonator 111D including a first ring 103D and a second ring 107D. The asymmetric dual ring resonator 111D is similar to Figure 4 The asymmetric dual ring resonator 111C is shown in FIG. 1 , except that the first ring 103D and the second ring 107D become linear (with infinite radius of curvature) and are parallel to their coupling partners in regions 501 and 505 coupled to the first waveguide 101 and the second waveguide 109, respectively, and in region 503 where they couple to each other. The advantages of these structures are similar to those of FIG. Figure 4 The advantages of the asymmetric dual-ring resonator 111C are similar.

[0050] Figure 6 A plan view of a PIC device 600 is shown, which includes an asymmetric dual-ring resonator 111A coupled between a first waveguide 101A and a second waveguide 109A. In region 501 where the first waveguide 101A is coupled to the first ring 103A, the first waveguide 101A has a curvature parallel to that of the first ring 103A. Similarly, in region 505 where the second waveguide 109A is coupled to the second ring 107A, the second waveguide 109A has a curvature parallel to that of the second ring 107A. Distance d1 can remain constant within these regions of parallel curvature. This structure provides an alternative approach to providing high coupling coefficients between the first ring 103A and the first waveguide 101A, and between the second ring 107A and the second waveguide 109A.

[0051] Figure 7A plan view of a PIC device 700 including an asymmetric dual-ring resonator 111J is shown. Asymmetric dual-ring resonator 111J includes a circular first ring 103A and a noncircular second ring 107D. First ring 103A is coupled to first waveguide 101A in region 501. In region 501, the curvature of first waveguide 101A matches that of first ring 103A. Second ring 107D is coupled to second waveguide 109 in region 505. In region 505, second ring 107D becomes linear and parallel to second waveguide 109. Because second ring 107D has a greater effective length than first ring 103A, it is easier to deviate from a circular shape without affecting resonance.

[0052] Figure 8 FIG. 8 is a plan view of a PIC device 800 including an asymmetric dual ring resonator 111E coupled between a first waveguide 101 and a second waveguide 109. Figure 1 The asymmetric dual ring resonator 111A differs in that the first ring 103A is offset with respect to the shortest path between the first waveguide 101 and the second ring 107A.

[0053] Figure 9 FIG. 1 shows a plan view of a PIC device 900 including an asymmetric dual ring resonator 111F coupled between a first waveguide 101 and a second waveguide 109. Figure 8 The difference between the asymmetric dual ring resonator 111E and the asymmetric dual ring resonator 111F is that the asymmetric dual ring resonator 111F includes a first ring 103F having a modified first radius R1′ and a modified first effective length L1. eff1 ', the first effective length L eff1 'Greater than the first effective length L of the first ring 103A eff1 (See Figure 8 ). Figure 8 and Figure 9 The comparison shows the advantage of the offset arrangement: the first effective length L of the first ring 103A can be adjusted while maintaining the distances d1 and d2. eff1 , without changing the position of the first waveguide 101, the second waveguide 109 or the second ring 107A. This may help to fine-tune the first effective length L eff1 and the second effective length L eff2 The relationship between the first effective length L and the second effective length L makes the FSR of the asymmetric dual ring resonator 111F greater than that of the first effective length L eff1 Or the second effective length L eff2 The FSR of a single ring resonator. The first effective length L eff1 Fine-tuning can also be used to improve the Q factor.

[0054] Figure 10 FIG. 1 shows a plan view of a PIC device 1000 including an asymmetric dual ring resonator 111G. Figure 8 The difference between the asymmetric dual ring resonator 111E and the asymmetric dual ring resonator 111G is that the asymmetric dual ring resonator 111G includes a first ring 103G, and the radial thickness t2 of the first ring 103G is greater than the radial thickness t1 of the first ring 103A (see FIG. Figure 8 ) or the radial thickness of the second ring 107A. Adjust the radial thickness t2 by changing the group index to the first effective length L eff1 Change to the modified first effective length L eff1 ', and provides another method to fine-tune the first effective length L eff1 , while maintaining the distances d1 and d2, and without changing the positions of the first waveguide 101, the second waveguide 109, or the second ring 107A.

[0055] In some embodiments, the radial thickness t1 and the radial thickness t2 are both in the range of about 300 nm to about 500 nm, thereby limiting the transmission to one optical mode and avoiding optical losses. Variations within this range may be sufficient for fine-tuning. For example, adjusting the radial thickness of a silicon (Si) ring with a radius of 5 μm from 370 nm to 470 nm can change the group index from about 4.16 to about 4.10, thereby changing the effective length by 1.4%. Figure 4 As shown, even a 0.05% change in effective length can have a significant effect.

[0056] In some embodiments, by changing the inner radius R I While maintaining the outer radius R O The radius of the ring resonator is the inner radius R I and outer radius R O If the outer radius R is maintained O By reducing the inner radius R I To increase the radial thickness t1, the modified first effective length L can be adjusted without changing the position or location of the first ring 103G. eff1 '.

[0057] Figure 11A shows a plan view of a PIC device 1100, Figure 11B FIG. 1 shows a cross-sectional view of a PIC device 1100 including an asymmetric dual ring resonator 111A. Figure 1The PIC device 100 differs in that the asymmetric dual-ring resonator 111A is located in the first device layer 1101, while the first waveguide 101 and the second waveguide 109, which provide the input and output waveguides for the asymmetric dual-ring resonator 111A, are located in the second device layer 1103. This configuration has the advantage that the distance d1 and the associated coupling coefficient can be precisely controlled based on the thickness of the cladding layer 105 between the first device layer 1101 and the second device layer 1103.

[0058] Figure 12A shows a plan view of a PIC device 1200, Figure 12B FIG1 shows a cross-sectional view of a PIC device 1200, which includes an asymmetric dual-ring resonator 111H. Figure 11A and Figure 11B The asymmetric dual-ring resonator 111A in the PIC device 1100 differs in that the asymmetric dual-ring resonator 111H has the first ring 103A and the second ring 107A in different device layers. Distance d1 is determined by the thickness of the cladding layer 105 between the first device layer 1101 and the second device layer 1103. By varying the lateral offset d3 between the first and second rings 103A, 107A, the distance d2 between the first and second rings 103A, 107A can be independently adjusted. Distance d2 changes more slowly relative to the lateral offset d3 than when the first and second rings 103A, 107A are in different device layers, making distance d2 less sensitive to manufacturing process variations.

[0059] Figure 13A shows a plan view of a PIC device 1300, Figure 13B FIG. 1 shows a cross-sectional view of a PIC device 1300 including an asymmetric dual-ring resonator 111I. Figure 12A and Figure 12B The asymmetric dual ring resonator 111H is different from the asymmetric dual ring resonator 111I in that it has a first ring 103E. The first ring 103E is located in a separate device layer from the first waveguide 101, the second waveguide 109, and the second ring 107A. This structure allows the first ring 103E to have a different composition than the first waveguide 101, the second waveguide 109, and the second ring 107A. Providing a different composition for the first ring 103E provides a method for making L eff1 Relative to L eff2 If the optical components in the first device layer 1101 are made of an optical material with a lower refractive index than the optical components in the second device layer 1103, the first effective length L can be made larger without physically reducing the size of the first ring 103E. eff1This structure can also be used to provide the first ring 103E as a nonlinear optical material.

[0060] Figure 14 FIG. 1 shows a plan view of a PIC device 1400 including an asymmetric multi-ring resonator 111K. The asymmetric multi-ring resonator 111K includes a first radius R1 and an effective length L1. eff1 The first ring 103A has a second radius R2 and a second effective length L eff2 The second ring 107A and the second ring 107A having a third radius R3 and a third effective length Leff3 The first radius R1, the second radius R2 and the third radius R3 are different from each other, so that the first effective length L eff1 , the second effective length L eff2 and the third effective length L eff3 different.

[0061] In some embodiments, the first effective length L eff1 , the second effective length L eff2 and the third effective length L eff3 have a greatest common divisor that is less than the first effective length L eff1 , the second effective length L eff2 and the third effective length L eff3 Any one of, and less than the first effective length L eff1 , the second effective length L eff2 and the third effective length L eff3 The greatest common divisor of any pair in . For example, L eff1 , L eff2 and L eff3 The ratio can be close to 6:10:15, so their greatest common divisor is L eff1 In this example, the FSR is six times greater than that achieved using only the smallest of the three rings. The same FSR can be achieved using a dual-ring resonator with a ratio of almost 6:7. Replacing the size 7 ring with two larger rings (size 10 and size 15) reduces sensitivity to manufacturing tolerances and improves the distinction between the resonant peak and the side modes.

[0062] In some embodiments, the first effective length L eff1 , the second effective length L eff2 and the third effective length L eff3 have a greatest common divisor that is less than the first effective length L eff1 , the second effective length L eff2 and the third effective length L eff3 Any one of them, but not less than the greatest common divisor of two of the three rings. For example, L eff1, L eff2 and L eff3 The ratio may be close to 2:3:5, so their greatest common divisor is L eff1 In this embodiment, the third ring can provide additional wavelength filtering and can improve the distinction between the resonant peak and the side modes.

[0063] Figure 15 A plan view of a PIC device 1500 including an asymmetric multi-ring resonator 111L is shown. The asymmetric multi-ring resonator 111L includes two of the first rings 103A and one of the second rings 107A. The use of two rings having a first effective length and another ring having a second effective length combines the benefits of a heterogeneous dual-ring resonator (smaller FSR) with the benefits of a symmetric dual-ring resonator (e.g., improved filtering).

[0064] Figure 16 FIG. 1 shows a plan view of a PIC device 1600 including an asymmetric multi-ring resonator 111M. The asymmetric multi-ring resonator 111L includes one of the first rings 103A and two of the second rings 107A. Figure 15 The asymmetric multi-ring resonator 111L is smaller in the same size, providing a more compact design. Figure 16 The asymmetric multi-ring resonator 111M has the same larger size and can reduce sensitivity to manufacturing tolerances.

[0065] Figures 17-20 is a cross-sectional view illustrating a process according to the present disclosure. Figures 17-20

[0014] Although various embodiments are described with reference to a method, it should be understood that Figures 17-20 The structure shown in is not limited to this method, but can be independent of this method. Figures 17-20 is described as a series of actions. In other embodiments, the order of these actions may be changed. Figures 17-20 A particular set of actions is shown and described, but some may be omitted in other embodiments. Additionally, actions not shown and / or described may be included in other embodiments.

[0066] like Figure 17As shown in cross-sectional view 1700 of FIG, the method may begin by providing a substrate 203 having a cladding layer 105 and a first optical material layer 1701. The substrate 203 having the cladding layer 105 and the first optical material layer 1701 may be provided by a semiconductor-on-insulator (SOI) substrate, or the cladding layer 105 and the first optical material layer 1701 may be deposited on the substrate 203. The substrate 203 may be, for example, an SOI substrate, a bulk semiconductor substrate, a silicon-on-sapphire substrate, or any other suitable substrate type. The semiconductor may be silicon (Si), a III-V semiconductor, or some other binary semiconductor (e.g., GaAs), a ternary semiconductor (e.g., AlGaAs), or a higher-order semiconductor. The cladding layer 105 may be silicon dioxide (SiO2), or some other cladding material. The first optical material layer 1701 may be silicon (Si), silicon nitride (SiN), or some other optical material. In some embodiments, the thickness of the first optical material layer 1701 ranges from approximately 100 nm to approximately 1000 nm. In some embodiments, the thickness of the first optical material layer 1701 is in a range from about 300 nm to about 500 nm.

[0067] like Figure 18 As shown in the cross-sectional view 1800 of FIG. 1 , a mask 1801 can be formed and used to pattern the second device layer 1103 from the first optical material layer 1701. The patterning can form the first waveguide 101, the second ring 107A, and the second waveguide 109. Alternatively, the second device layer 1103 can be formed by a damascene process.

[0068] like Figure 19 As shown in the cross-sectional view 1900, the additional layer 1901 of the cladding 105 and the second optical material layer 1903 can be deposited on Figure 18 1800 . Optionally, before depositing the second portion of the additional layer 1901, the first portion of the additional layer 1901 is deposited and planarized onto the second device layer 1103. This planarization process facilitates precise control of the thickness of the cladding layer 105 between the second device layer 1103 and the second optical material layer 1903. The additional layer 1901 and the second optical material layer 1903 of the cladding layer 105 can be deposited by chemical vapor deposition (CVD), physical vapor deposition, atomic layer deposition (ALD), or any other suitable process. The second optical material layer 1903 can have the same composition as the first optical material layer 1701, or can have a different composition.

[0069] In some embodiments, at least one of the first optical material layer 1701 and the second optical material layer 1903 is a conventional optical material layer. In some embodiments, at least one of the first optical material layer 1701 and the second optical material layer 1903 is a nonlinear optical material layer. As used herein, a nonlinear optical material is a material having a non-centrosymmetric crystal structure. Compared to conventional optical materials, nonlinear optical materials have a non-zero second-order nonlinear magnetic susceptibility and exhibit the Pockels effect. The Pockels effect results in a change in the refractive index that is linearly related to the applied electric field strength. In some embodiments, the nonlinear optical material has a refractive index of at least about 10 -24 As / V 2 The second-order nonlinear magnetic susceptibility of the nonlinear optical material is 1. The nonlinear optical material can provide or enhance the nonlinear optical effect in the PIC. Examples of nonlinear optical effects that can be provided or enhanced include parametric down-conversion (frequency doubling), sum frequency generation, optical parametric generation, optical parametric amplification, optical parametric oscillation, optical rectification, etc. Examples of nonlinear optical materials with these properties include aluminum nitride (AlN), lithium niobate (LiNbO3), silicon carbide (SiC), indium phosphide (InP), gallium arsenide (GaAs), aluminum gallium arsenide (AlGaAs), etc. In some embodiments, the nonlinear optical material is aluminum nitride (AlN), etc. AlN is particularly suitable for CMOS compatible processing and can be used to provide various nonlinear optical effects.

[0070] like Figure 20 As shown in the cross-sectional view 2000 of FIG. 1 , a mask 2001 may be formed and used to pattern the first device layer 1101 from the second optical material layer 1903. The patterning may form the first ring 103E. Alternatively, the first device layer 1101 may be formed by a damascene process. Additional cladding layers may be deposited to form Figure 11A and Figure 11B The PIC device 1100 or some other PIC device.

[0071] In addition to the optical devices shown, the PIC device according to the present disclosure may also include optical devices. The optical device can be any device that transmits, receives, propagates, generates, modifies or detects an optical signal, any device that converts an optical signal into an electrical signal or any device that converts an electrical signal into an optical signal. Examples of optical devices that transmit, receive, propagate, generate, modify or detect an optical signal include waveguides, splitters, multiplexers, filters, modulators (such as phase shifters, PiN modulators or electro-absorption modulators), sensors, converters (such as Mach-Zehnder interferometers), amplifiers, edge couplers, grating couplers, ring resonators, etc. Examples of optical devices that convert an electrical signal into an optical signal include laser diodes, light-emitting diodes, etc. Examples of optical devices that convert an optical signal into an electrical signal include photodetectors, etc.

[0072] Figure 21 A flow chart of a process 2100 that can be used to form a PIC device according to the present disclosure is shown. Figure 21 The process 2100 is shown and described herein as a series of actions or events, but it should be understood that the order of these actions or events shown should not be construed as limiting. For example, some actions may occur in a different order and / or concurrently with other actions or events shown and / or not shown herein. Furthermore, not all shown actions are required to implement one or more aspects or embodiments described herein, and one or more of the actions described herein may be performed in one or more separate actions and / or stages.

[0073] Process 2100 may begin with act 2101 by forming a PIC device including an asymmetric dual ring resonator. Figures 13A-20 An example is provided by cross-sectional views 1300-2000 of Asymmetric dual ring resonators can be located in a single device layer or can have rings in two different device layers.

[0074] Act 2103 determines whether the FSR and Q factor of the asymmetric dual ring resonator are within the design specifications. This may involve measuring the drop in transmitted intensity as a function of wavelength. This determination may include factors such as whether the resonant mode has a single peak or a double peak, and whether the side modes are sufficiently distinct from the desired resonant mode. If the FSR and Q factor are within the design specifications, the process 2100 continues with the fabrication of additional devices having the same asymmetric dual ring resonator layout. If the FSR or Q factor is not within the design specifications, the process 2100 continues with act 2105 to modify the device layout to change the L eff1 (or L eff2 ). In some embodiments, the modification includes adjusting R1 or otherwise enlarging or shrinking one of the rings. Figure 8 and Figure 9 Examples of such adjustments are provided by PIC devices 800 and 900 in

[0044] In some embodiments, the modification includes adjusting the radial thickness of one of the rings. Figure 8 and Figure 10 PIC devices 800 and 1000 in FIG. 8 provide examples of such adjustments.

[0075] Some aspects of the present disclosure relate to a photonic integrated circuit device comprising: a substrate; a first waveguide located above the substrate; a second waveguide located above the substrate; and a multi-ring resonator. The multi-ring resonator comprises a first ring having a first effective length and a second ring having a second effective length. The multi-ring resonator is coupled between the first waveguide and the second waveguide and has a larger free spectral range than a single-ring resonator having the first effective length or having the second effective length. In some embodiments, the larger free spectral range is within an order of magnitude of the free spectral region of the single-ring resonator having the first effective length or the second effective length. In some embodiments, the multi-ring resonator has a main resonant mode separated by the free spectral range and a side resonant mode within the free spectral range, and the intensity of the side resonant mode is at least one order of magnitude lower than the intensity of the main resonant mode. In some embodiments, the first effective length and the second effective length are sufficiently close to integer multiples of the third effective length so that the main resonant mode has a single peak.

[0076] In some embodiments, the first ring has a different radial thickness than the second ring. In some embodiments, the multi-ring resonator supports only one optical mode. In some embodiments, the first spacing between the first ring and the second ring is greater than the second spacing between the first ring and the first waveguide, and greater than the third spacing between the second ring and the second waveguide. In some embodiments, the first ring has a non-circular perimeter. In some embodiments, the first ring has a coupling region, wherein the first ring has a first radius of curvature; the first ring has a non-coupling region, which is different from the coupling region, wherein the first ring has a second radius of curvature; and the first radius of curvature is greater than the second radius of curvature. In some embodiments, the first waveguide and the second waveguide have a first height above the substrate, the first ring has a second height above the substrate, and the first height is different from the second height. In some embodiments, the first ring has a first height above the substrate, the second ring has a second height above the substrate, the first height is different from the second height, and the first ring and the second ring have different compositions. In some embodiments, the first waveguide has a coupling region with the first ring, and the first waveguide is curved in the coupling region. In some embodiments, the first ring is offset relative to the alignment between the first waveguide and the second ring. In some embodiments, the multi-ring resonator further includes a third ring having a first effective length. In some embodiments, the multi-ring resonator further includes a third ring having a third effective length, wherein the third effective length is different from the first effective length and the second effective length.

[0077] Some aspects of the present disclosure relate to a photonic integrated circuit device comprising: a substrate; a first waveguide positioned above the substrate; a first ring, wherein the first ring has a first effective length; and a second ring, wherein the second ring has a second effective length and is optically coupled between the first waveguide and the first ring; wherein the first effective length is a first integer multiple of a third effective length; the second effective length is a second integer multiple of the third effective length; and the first integer multiple is different from the second integer multiple. The first integer multiple and the second integer multiple are integers greater than 1. In some embodiments, the first integer multiple and the second integer multiple are in a range from 2 to 12. In some embodiments, the first integer multiple and the second integer multiple are both 10 or less. In some embodiments, the first integer multiple and the second integer multiple are both 7 or less. In some embodiments, the first integer multiple and the second integer multiple are both 4 or less. In some embodiments, the first integer multiple and the second integer multiple are 2 and 3.

[0078] In some embodiments, the radial thickness of the first ring is different from the thickness of the first waveguide. In some embodiments, the first ring supports only one optical mode. In some embodiments, a first coupling coefficient between the first ring and the first waveguide is greater than a second coupling coefficient between the first ring and the second ring. In some embodiments, in a region where the first waveguide couples to the first ring, the first waveguide has a curvature parallel to the first ring.

[0079] Some aspects of the present disclosure relate to a method for forming a photonic integrated circuit device, the method comprising providing a substrate and forming a multi-ring resonator, a first waveguide, and a second waveguide over the substrate. The multi-ring resonator comprises a first ring and a second ring. The first ring has a first effective length, and the second ring has a second effective length. The multi-ring resonator has a free spectral range greater than that of a single ring resonator having the first effective length or a single ring resonator having the second effective length. The first ring can be coupled to the first waveguide, and the second ring can be coupled to the second waveguide. In some embodiments, the method further comprises forming a first optical device layer and forming a second optical device layer. Forming the first optical device layer creates the first ring, and forming the second optical device layer creates the second ring. The first ring and the second ring can have different compositions.

[0080] In some embodiments, the first ring and the second ring are formed according to a layout, and the method includes modifying the layout to adjust the first effective length or the second effective length. In some embodiments, the adjustment includes changing a thickness of the first ring or the second ring.

[0081] The features of several embodiments are summarized above so that those skilled in the art can better understand the various aspects of the present disclosure. Those skilled in the art will appreciate that they can easily use the present disclosure as a basis for designing or modifying other processes and structures for achieving the same purpose and / or achieving the same advantages of the embodiments introduced herein. Those skilled in the art will also appreciate that such equivalent structures do not depart from the spirit and scope of the present disclosure, and that they can make various changes, substitutions, and modifications in the present disclosure without departing from the spirit and scope of the present disclosure.

Claims

1. A photonic integrated circuit device, comprising: substrate; a first waveguide located above the substrate; a second waveguide located above the substrate; as well as A multi-ring resonator includes a first ring having a first effective length and a second ring having a second effective length, wherein the multi-ring resonator is coupled between the first waveguide and the second waveguide and has a larger free spectral range than a single-ring resonator having the first effective length or having the second effective length.

2. The photonic integrated circuit device according to claim 1, wherein: The larger free spectral range is within an order of magnitude of a free spectral region of a single ring resonator having the first effective length or the second effective length.

3. The photonic integrated circuit device according to claim 1, wherein: The multi-ring resonator has a main resonant mode separated by a free spectral range and a side resonant mode in the free spectral range, and an intensity of the side resonant mode is at least one order of magnitude lower than an intensity of the main resonant mode.

4. The photonic integrated circuit device according to claim 3, wherein: The first effective length and the second effective length are sufficiently close to an integer multiple of the third effective length so that the main resonant mode has a single peak.

5. The photonic integrated circuit device according to claim 1, wherein: The first ring has a different radial thickness than the second ring.

6. The photonic integrated circuit device according to claim 5, wherein: The multi-ring resonator supports only one optical mode.

7. The photonic integrated circuit device according to claim 1, wherein: A first spacing between the first ring and the second ring is greater than a second spacing between the first ring and the first waveguide, and greater than a third spacing between the second ring and the second waveguide.

8. The photonic integrated circuit device according to claim 1, wherein: The first ring has a non-circular perimeter.

9. A photonic integrated circuit device comprising: substrate; a first waveguide located above the substrate; a first loop, wherein the first loop has a first effective length; and a second ring, wherein the second ring has a second effective length and is optically coupled between the first waveguide and the first ring; wherein the first effective length is a first integer multiple of the third effective length; The second effective length is a second integer multiple of the third effective length; The first integer multiple is different from the second integer multiple; and The first integer multiple and the second integer multiple are integers greater than 1.

10. A method of forming a photonic integrated circuit device, comprising: providing a substrate; as well as A multi-ring resonator, a first waveguide, and a second waveguide are formed over the substrate, wherein the multi-ring resonator includes a first ring and a second ring, the first ring has a first effective length, the second ring has a second effective length, the free spectral range of the multi-ring resonator is greater than that of a single ring resonator having the first effective length or a single ring resonator having the second effective length, the first ring is coupled to the first waveguide, and the second ring is coupled to the second waveguide.

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