Filtering structure, wavelength division multiplexing structure and optical chip
By pre-filtering the broadband optical signal through the folded interference output structure and the all-pass microring resonator in the filtering structure, the channel crosstalk problem of the wavelength division multiplexer is solved, and lower channel crosstalk and more compact optical chip design are achieved.
Patent Information
- Application Number
- CN202510733615.3
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-06-03
- Publication Date
- 2025-09-19
Smart Images
Figure CN120669354A_ABST
Abstract
Description
Technical Field
[0001] The present application relates to the field of optical communication technology, and in particular to a filtering structure, a wavelength division multiplexing structure and an optical chip. Background Art
[0002] Wavelength division multiplexers (WDMs), as important lightwave multiplexing devices, have been widely used in optical communications. Furthermore, due to their compact size, compatible manufacturing processes, and high integration, WDMs have been applied on multiple semiconductor material platforms with high refractive index contrast, such as silicon-on-insulator (SOI), silicon nitride (Si3N4), and indium phosphide (InP).
[0003] However, in nanowire waveguides with high-refractive-index cores on semiconductor platforms, deviations in waveguide dimensions caused by existing process conditions can easily lead to significant phase errors. WDMs are highly sensitive to phase errors, and increasing phase errors can lead to increased channel crosstalk, making it difficult to achieve satisfactory channel crosstalk characteristics at the WDM output. Therefore, before a broadband optical signal is input into the WDM, how to retain the optical signal with the same wavelength as the output center wavelength of each channel of the WDM, while suppressing the optical signal with a different wavelength from the output center wavelength of each channel, thereby reducing the channel crosstalk problem of the WDM, has become an urgent problem to be solved. Summary of the Invention
[0004] In order to overcome the above-mentioned defects, the present application is proposed to solve or at least partially solve the technical problem of how to pre-filter the broadband optical signal before inputting it into the wavelength division multiplexer, thereby reducing the channel crosstalk of the wavelength division multiplexer.
[0005] In a first aspect, the present application provides a filtering structure comprising a directional coupler, a microring, a delay line, a first reflector, and a second reflector; The directional coupler includes a first waveguide and a second waveguide, wherein the first end of the first waveguide is the input end of the filtering structure, and the second end of the first waveguide is connected to the delay line and the first reflector in sequence; the first end of the second waveguide is the output end of the filtering structure, and the second end of the second waveguide is connected to the second reflector; The directional coupler, the delay line, the first reflector and the second reflector form a folded interferometer output structure; The microring is located on one side of the first waveguide and forms an all-through microring resonator with the first waveguide.
[0006] In one technical solution of the above-mentioned filtering structure, the directional coupler is a bent directional coupler; wherein: The first waveguide includes a first straight waveguide, a first curved waveguide, and a third straight waveguide connected in sequence, wherein a first end of the first straight waveguide not connected to the first curved waveguide constitutes a first end of the first waveguide, and a second end of the third straight waveguide not connected to the first curved waveguide constitutes a second end of the first waveguide; The second waveguide includes a second straight waveguide, a second curved waveguide, and a fourth straight waveguide connected in sequence. The first end of the second straight waveguide not connected to the second curved waveguide constitutes the first end of the second waveguide, and the second end of the fourth straight waveguide not connected to the second curved waveguide constitutes the second end of the second waveguide.
[0007] In one technical solution of the above filtering structure, when the first end of the first waveguide is the input end of the optical signal, the directional coupler is configured such that: the amplitude and phase of the first output optical signal and the second output optical signal are the same; The first output optical signal is an optical signal output from the second end of the first waveguide, and the second output optical signal is an optical signal output from the second end of the second waveguide.
[0008] In a technical solution of the above-mentioned filtering structure, the first reflector and the second reflector are both annular reflectors.
[0009] In one technical solution of the above-mentioned filtering structure, the delay line is configured as follows: after the optical signal with the set central wavelength passes through the delay line, the phase difference of the optical signals at both ends of the delay line is π / 4+2nπ, where n is an integer greater than or equal to 0.
[0010] In one technical solution of the above-mentioned filtering structure, the free spectrum range of the folded interferometer output structure is equal to the free spectrum range of the all-pass microring resonator.
[0011] In one technical solution of the above-mentioned filtering structure, the resonant wavelength of the folded interference output structure is consistent with the resonant wavelength of the all-pass microring resonator.
[0012] In a technical solution of the above-mentioned filtering structure, the filtering structure further includes: a first phase shifter corresponding to the all-pass microring resonator, such as a heating electrode.
[0013] In a technical solution of the above-mentioned filtering structure, the filtering structure further includes: a second phase shifter corresponding to the delay line, such as a heating electrode.
[0014] In a second aspect, the present application provides a wavelength division multiplexing structure, which includes a wavelength division multiplexer and a filtering structure according to any one of the above technical solutions; The output end of the filter structure is connected to the input end of the wavelength division multiplexer. The wavelength division multiplexer has multiple output channels and outputs the optical signals of multiple set wavelengths output from the filter structure from the corresponding output channels.
[0015] In one technical solution of the above-mentioned wavelength division multiplexing structure, the resonant wavelength of the folded interference output structure in the filter structure is consistent with the output center wavelength of each output channel of the wavelength division multiplexer.
[0016] In one technical solution of the above-mentioned wavelength division multiplexing structure, the resonant wavelength of the all-pass microring resonator in the filtering structure is consistent with the output center wavelength of each output channel of the wavelength division multiplexer.
[0017] In a technical solution of the above-mentioned wavelength division multiplexing structure, the free spectral range of the folded interference output structure in the filtering structure is equal to the channel spacing of the output channels of the wavelength division multiplexer.
[0018] In one technical solution of the above-mentioned wavelength division multiplexing structure, the free spectral range of the all-pass microring resonator in the filtering structure is equal to the channel spacing of the output channels of the wavelength division multiplexer.
[0019] In a third aspect, the present application provides an optical chip, comprising: The filtering structure according to any one of the above technical solutions; A wavelength division multiplexing structure according to any of the above technical solutions.
[0020] One or more of the above-mentioned technical solutions of the present application have at least one or more of the following beneficial effects: multiple resonance filtering is performed on the target wavelength (the output center wavelength of each output channel of the wavelength division multiplexer) by jointly using the folded interference output structure and the all-pass microring resonator, thereby retaining the target wavelength, greatly suppressing the potential level of non-target wavelengths, and realizing pre-filtering of the target wavelength; then the pre-filtered optical signal is used as the input of the wavelength division multiplexer, thereby reducing the crosstalk problem between the output channels of the wavelength division multiplexing structure. BRIEF DESCRIPTION OF THE DRAWINGS
[0021] The disclosure of this application will become more easily understood with reference to the accompanying drawings. Those skilled in the art will readily understand that these drawings are for illustrative purposes only and are not intended to limit the scope of protection of this application.
[0022] Figure 1 is a schematic diagram of a filtering structure according to an embodiment of the present application.
[0023] Figure 2 It is a schematic diagram of optical signal transmission in a filtering structure according to an embodiment of the present application.
[0024] Figure 3 is a schematic diagram of the position of the heating electrode according to an embodiment of the present application.
[0025] Figure 4 is a schematic diagram of a wavelength division multiplexing structure according to an embodiment of the present application.
[0026] Figure 5 According to one embodiment of the present application Figure 3 (a) Schematic diagram of the cross-sectional structure of the heating electrode and micro-ring along the AA' direction.
[0027] Figure 6 According to one embodiment of the present application, Figure 1 The comparison chart of the optical simulation results of two wavelength division multiplexing structures of the filtering structure shown. DETAILED DESCRIPTION
[0028] Some embodiments of the present application are described below with reference to the accompanying drawings. Those skilled in the art should understand that these embodiments are only used to explain the technical principles of the present application and are not intended to limit the scope of protection of the present application.
[0029] It should be noted that, in the description of this application, the terms "upper", "lower", "left", "right", "inside", "outside" and the like indicating directions or positional relationships are based on the directions or positional relationships shown in the accompanying drawings. This is merely for the convenience of description and does not indicate or imply that the device, structure or component must have a specific orientation, be constructed and operated in a specific orientation. Therefore, it cannot be understood as a limitation on this application. In addition, the terms "first" and "second" are used for descriptive purposes only and cannot be understood as indicating or implying relative importance. The term "A and / or B" represents all possible combinations of A and B, such as just A, just B, or A and B. The term "at least one A or B" or "at least one of A and B" has a similar meaning to "A and / or B" and may include just A, just B, or A and B. The singular terms "one" and "this" may also include plural forms.
[0030] Read First Figure 1 , Figure 1 (a) is an overall schematic diagram of a filtering structure according to an embodiment of the present application, Figure 1 (b) is a schematic diagram of the bent directional coupler in the filtering structure. Figure 1 (c) is a schematic diagram of an all-pass microring resonator in a filtering structure. The filtering structure of the embodiment of the present application includes a directional coupler, a microring 200 , a delay line 300 , a first reflector 410 and a second reflector 420 .
[0031] In the embodiment of the present application, the directional coupler is a bent directional coupler 100 having four ports. The bent directional coupler 100 includes a first waveguide and a second waveguide.
[0032] The first waveguide includes a first straight waveguide 111, a first curved waveguide 112, and a third straight waveguide 113, each of which has a first end and a second end. The first end of the first straight waveguide 111 constitutes the first end of the first waveguide (port 1 of the curved directional coupler 100); the first end of the first waveguide also constitutes the input end of the filtering structure; the second end of the first straight waveguide 111 is connected to the first end of the first curved waveguide 112, and the second end of the first curved waveguide 112 is connected to the first end of the third straight waveguide 113; the second end of the third straight waveguide 113 constitutes the second end of the first waveguide (port 2 of the curved directional coupler 100).
[0033] The second end of the first waveguide is sequentially connected to the delay line 300 and the first reflector 410. Specifically, the second end of the first waveguide is connected to the first end of the delay line 300, and the second end of the delay line 300 is connected to the input and output common end of the first reflector 410.
[0034] The second waveguide includes a second straight waveguide 121, a second curved waveguide 122, and a fourth straight waveguide 123, each of which has a first end and a second end. The first end of the second straight waveguide 121 constitutes the first end of the second waveguide (port 4 of the curved directional coupler 100) and the output end of the filtering structure. The second end of the second straight waveguide 121 is connected to the first end of the second curved waveguide 122, and the second end of the second curved waveguide 122 is connected to the first end of the fourth straight waveguide 123. The second end of the fourth straight waveguide 123 constitutes the second end of the second waveguide (port 3 of the curved directional coupler 100). The second end of the second waveguide is connected to the common input and output end of the second reflector 420.
[0035] In other embodiments, the first curved waveguide 112 and the second curved waveguide 122 may be replaced with straight waveguides. In this case, the directional coupler is a straight waveguide directional coupler.
[0036] It should be noted that compared with straight waveguide directional couplers, bent directional couplers have the advantages of good process stability, high bandwidth, and uniform splitting ratio, which can further improve the filtering effect of the filtering structure.
[0037] exist Figure 1 In the filtering structure shown, the bent directional coupler 100, the delay line 300, the first reflector 410 and the second reflector 420 together form a folded interferometer output structure.
[0038] The microring located on one side of the first waveguide and the first waveguide form an all-pass microring resonator. Figure 1As shown in FIG. 5( c ), for the curved directional coupler 100 , the microring 200 located inside the bending radius of the first curved waveguide 112 and the first curved waveguide 112 form an all-through microring resonator 210 . The first end of the first curved waveguide 112 is port 5 , and the second end of the first curved waveguide 112 is port 6 .
[0039] Continue reading Figure 2 , Figure 2 is a schematic diagram of optical signal transmission in a filter structure according to an embodiment of the present application, combined with Figure 2 The design and working principle of the filter structure of this application are described, wherein Figure 2 The numbers 11, 12, ..., 17, 21, 22, 31, etc. are used to distinguish optical signals at different positions in the filtering structure.
[0040] In the embodiment of the present application, the design requirements of the filtering structure are: retaining a group of optical signals of set wavelengths in the broadband optical signal, while suppressing optical signals of non-set wavelengths.
[0041] As an example, the group of optical signals that the filter structure expects to output is: wavelengths are set to λ1, λ2, ..., λ m , m≥2, where the wavelength interval between any two adjacent optical signals is △λ, and the set center wavelength of the group of optical signals is the median of the wavelengths of all the optical signals in the group (when the number of wavelengths of the optical signal is even, any one of the two middle wavelengths is selected), or it can also be any wavelength value in the group of optical signals.
[0042] Periodically, including λ1,λ2,...,λ m A broadband optical signal (optical signal 11) is input into the curved directional coupler 100 from port 1. While propagating along the first waveguide, optical signal 11 enters the all-pass microring resonator 210 from port 5 (port 5 is the input end of the all-pass microring resonator). After being resonated and filtered by the all-pass microring resonator 210, optical signal 12 continues to propagate along the first bending waveguide to port 6 (port 6 is the through end of the all-pass microring resonator).
[0043] With respect to the broad spectrum optical signal (optical signal 11), the wavelengths of the optical signal 12 after resonant filtering are λ1, λ2, ..., λ m The optical signals of are retained instead of λ1,λ2,...,λ m The potential levels of other wavelength optical signals are greatly suppressed.
[0044] In order to suppress optical signals of non-set wavelengths, the microring 200 can be designed according to the design requirements of the filter structure (setting the center wavelength and wavelength interval), and the resonant wavelengths of the all-pass microring resonator 210 are set to λ1, λ2, ..., λ m, the free spectral range (FSR) is set to △λ.
[0045] In an embodiment of the present application, when the first end of the first waveguide serves as the input end of the optical signal of the directional coupler, the bent directional coupler 100 is configured such that port 2 outputs a first output optical signal (optical signal 13), and port 3 outputs a second output optical signal (optical signal 21), and the phase and amplitude of optical signal 13 and optical signal 21 are the same.
[0046] It should be noted that the amplitudes of the optical signal 13 and the optical signal 21 may be the same or different. The smaller the amplitude difference between the two, the better the filtering effect is.
[0047] Optical signal 13 enters delay line 300 from the first end and outputs optical signal 14 from the second end of delay line 300. The phase difference between optical signal 13 and optical signal 14 is π / 4+2nπ (equal amplitudes), where n is an integer greater than or equal to 0, i.e., n is a natural number. As an example, the phase difference between optical signal 13 and optical signal 14 is π / 4.
[0048] It should be noted that this application is intended to illustrate the operating principles of filtering and wavelength division multiplexing structures, and therefore optical signals can be considered to be transmitted losslessly in each waveguide. Furthermore, terms such as "equal," "same," and "unchanged" in this application may refer to two values being equal or approximately equal. For example, the ratio of the difference between two values to their average is within a predetermined percentage range. For example, the percentage may be set to 10%, or other values.
[0049] The optical signal 14 enters the first reflector 410 , which reflects and outputs a first reflected optical signal 15 . The first reflected optical signal 15 has the same amplitude as the optical signal 14 , and the phase difference is Φ1 , where Φ1 is the phase delay generated by the first reflector 410 .
[0050] The first reflected light signal 15 enters the delay line 300 from the second end and outputs the first reflected light signal 16 from the first end of the delay line 300. The phase difference between the first reflected light signal 15 and the first reflected light signal 16 is π / 4 (the amplitudes are equal).
[0051] The length of the delay line 300 can be designed according to the set center wavelength of the aforementioned group of optical signals, that is, the delay line 300 is designed to achieve a phase difference of π / 4 between the optical signals at both ends of the delay line 300 after the optical signal with the set center wavelength passes through the delay line 300.
[0052] At this time, the phase of the optical signal 13 is subtracted from the phase of the first reflected optical signal 16 , and the phase difference between the two is π / 2+Φ1 (the amplitudes are equal).
[0053] The optical signal 21 directly enters the second reflector 420 , which reflects and outputs a second reflected optical signal 22 . The second reflected optical signal 22 has the same amplitude as the optical signal 21 , and the phase difference is Φ2 , where Φ2 is the phase delay generated by the second reflector 420 .
[0054] In this embodiment of the present application, the second reflector 420 and the first reflector 410 have the same structural dimensions and are both simple annular reflectors. In this case, Φ1 equals Φ2. Accordingly, the phase difference between the second reflected light signal 22 and the first reflected light signal 16 is π / 2 (equal amplitudes).
[0055] In other embodiments, the second reflector 420 and the first reflector 410 may also employ an Echelle Grating structure, and the relationship between Φ1 and Φ2 may be Φ1 = 2nπ + Φ2, where n is an integer greater than or equal to 0. Without departing from the principles of the present application, these modified or replaced technical solutions shall fall within the scope of protection of the present application.
[0056] The first reflected light signal 16 and the second reflected light signal 22 are input into the bent directional coupler 100 through port 2 and port 3 respectively.
[0057] During the transmission process of the first reflected light signal 16 along the first waveguide to the port 1, the first reflected light signal 16 enters the all-pass microring resonator 210 from the port 6 (the port 6 is the input end of the all-pass microring resonator at this time), and the first reflected light signal 17 (with wavelengths of λ1, λ2, ..., λ m The optical signals of non-λ1,λ2,...,λ m The potential levels of optical signals of other wavelengths are suppressed again) continue to be transmitted along the first bending waveguide to port 5 (at this time port 5 is the through end of the all-pass microring resonator), and the first reflected light signal 17 has the same phase as the first reflected light signal 16.
[0058] According to the transmission model of the directional coupler, when the field intensities of the two optical signals input to port 3 and port 2 are the same and the phase difference is π / 2, no optical signal can be output from port 1, and the field intensity of the optical signal output from port 4 is the sum of the field intensities of the two optical signals from port 3 and port 2.
[0059] Therefore, the first reflected light signal 16 (17) and the second reflected light signal 22 are interfered and enhanced in the bent directional coupler 100, and an optical signal 31 is output from the output end of the filter structure (port 4 of the bent directional coupler 100), and a set of set wavelengths λ1, λ2, ..., λ that meet the design requirements of the filter structure are obtained. m of the optical signal 31.
[0060] It should be noted that the folded interference output structure composed of the directional coupler 100, the delay line 300, the first reflector 410 and the second reflector 420 also needs to be designed according to the design requirements of the filtering structure, that is, the folded interference output structure needs to be designed according to the set center wavelength, and the free spectrum range of the folded interference output structure should also correspond to the wavelength interval.
[0061] Since the free spectrum range of the folded interferometer output structure is mainly determined by the delay line 300 , the requirements of the phase difference (π / 4) and the free spectrum range (Δλ) must be met simultaneously when designing the delay line 300 .
[0062] In the embodiment of the present application, the free spectrum ranges of the folded interferometer output structure and the all-pass microring resonator 210 are the same as the wavelength interval required by the filter structure. At this time, the resonant wavelengths of the folded interferometer output structure and the all-pass microring resonator 210 are the same as the set wavelengths λ1, λ2, ..., λ required by the filter structure. m The filtering output effect of the filtering structure is the best.
[0063] In other embodiments, the free spectrum range of the all-pass microring resonator 210 can be designed to be the same as the wavelength interval (Δλ) required by the filter structure, and the free spectrum range of the folded interferometer output structure can be designed to be (Δλ / 2 k ), K≥1.
[0064] Accordingly, the resonant wavelength of the all-pass microring resonator 210 is consistent with the design requirements of the filter structure (the wavelengths are λ1, λ2, ..., λ m The resonant wavelength of the folded interferometer output structure will include λ1,λ2,...,λ m In this case, the filtering structure of the present application can still achieve the design requirements of the filtering structure, but the filtering effect will be inferior to the design in which the free spectrum range is equal to the wavelength interval.
[0065] In another embodiment, Figure 1 The illustrated filtering structure further includes heating electrodes corresponding to the all-pass microring resonator 210 and / or the delay line 300 .
[0066] As an example, Figure 3As shown in (a), a curved first heating electrode 201 is provided at the corresponding position of the microring 200 in the all-through microring resonator 210; Figure 3 As shown in (b), a rectangular second heating electrode 301 is provided at the position corresponding to the delay line 300.
[0067] In other embodiments, those skilled in the art may also adjust the heating electrode according to actual conditions, for example, setting a rectangular heating electrode in the coupling region formed by the microring 200 and the first waveguide, or setting two identical curved heating electrodes at symmetrical positions of the microring 200.
[0068] By adjusting the voltage applied by the heating electrode, the resonant wavelength of the all-pass microring resonator 210 and / or the folded interferometer output structure is tuned so that the resonant wavelength shifts within a preset range, thereby compensating for the impact of process manufacturing errors on the resonant wavelength of the all-pass microring resonator 210 and / or the folded interferometer output structure. Of course, in addition to using heating electrodes, other types of phase shifters can also be used as long as they can achieve the above purpose.
[0069] Furthermore, this application also provides a wavelength division multiplexing structure. Figure 4 , Figure 4 FIG1 is a schematic diagram of a wavelength division multiplexing structure according to an embodiment of the present application. The wavelength division multiplexing structure of the present application includes the filtering structure and the wavelength division multiplexer 500 described in the above embodiment.
[0070] The output end of the filtering structure (the first end of the second straight waveguide 121) is connected to the input end of the wavelength division multiplexer 500. The wavelength division multiplexer 500 has multiple output channels and outputs multiple optical signals of set wavelengths output from the filtering structure from corresponding output channels.
[0071] In the embodiment of the present application, the optical signal 31 (wavelengths λ1, λ2, ..., λ m The wavelength division multiplexer 500 is configured to include n output channels (n≤m), wherein the output center wavelengths of the n output channels are respectively aligned with some or all of λ1, λ2, ..., λ m Corresponding.
[0072] The channel spacing between adjacent output channels of wavelength division multiplexer 500 is equal to the free spectral range of the folded interferometer output structure in the filter structure and the all-pass microring resonator 210, both being Δλ. Accordingly, the resonant wavelengths of the folded interferometer output structure in the filter structure and the all-pass microring resonator 210 coincide with each other, fully or partially including the center wavelength of each output channel of wavelength division multiplexer 500. In this case, the wavelength division multiplexing structure achieves minimal channel crosstalk.
[0073] In other embodiments, the free spectrum range of the all-pass microring resonator 210 can be designed to be the same as the channel spacing (Δλ) of the wavelength division multiplexer 500, and the free spectrum range of the folded interferometer output structure can be designed to be (Δλ / 2 k ), K ≥ 1, the resonant wavelength of the folded interferometer output structure will include the output center wavelength of each output channel of the wavelength division multiplexer 500. In this case, compared with a design in which each free spectral range and channel spacing are equal, the filtering effect of the filter structure will be weakened, and accordingly, the channel crosstalk of the wavelength division multiplexing structure will be increased. However, the channel crosstalk of the wavelength division multiplexing structure can still be effectively reduced.
[0074] It should be noted that Figure 1 The filter structure shown and Figure 4 The components in the wavelength division multiplexing structure shown (first waveguide, second waveguide, delay line 300, first reflector 410, second reflector 420, wavelength division multiplexer 500, etc.) can be connected through curved waveguides and / or straight waveguides.
[0075] As an example, the second end of the delay line 300 and the first reflector 410 are connected through a curved waveguide and a straight waveguide; and the second end of the second waveguide and the second reflector 420 are connected through a straight waveguide.
[0076] It should be noted that this application does not limit the implementation method of the wavelength division multiplexer 500. As an example, the wavelength division multiplexer is implemented using methods such as arrayed waveguide gratings, Mach-Zehnder interferometers (MZI), and microring resonator arrays.
[0077] In this application, the design of the microring resonator, the calculation of the radius of the microring in the microring resonator, etc. are all well-known technologies in the art and are not limited in this application.
[0078] As an example, the central resonant wavelength of the all-pass microring resonator 210 can be determined based on the median of the output central wavelengths of each output channel of the wavelength division multiplexing structure; and the free spectral range of the all-pass microring resonator 210 can be determined based on the channel spacing (Δλ) of the output channels of the wavelength division multiplexing structure.
[0079] After determining the central resonant wavelength and free spectrum range of the all-pass microring resonator 210, the following formula is used: c =mλ、 The values of the radius of the microring 200 and other related parameters are calculated using the formula, where λ is the central resonant wavelength, R is the radius of the microring, and n c is the effective refractive index of the curved waveguide, n g is the group refractive index of the curved waveguide, and m is a positive integer.
[0080] Similarly, the implementation methods of specific components such as directional couplers, annular reflectors, and waveguides are all well-known technologies in the art and are not limited in this application. As an example, a three-dimensional finite-difference time-domain method can be used for design and implementation.
[0081] For the delay line 300 in the folded interferometer output structure, the delay line length (ΔL) needs to satisfy the phase difference As an example, first, according to the phase difference, set the formula between the central wavelength and the delay line length. Calculate a set of candidate delay line lengths that can meet the phase difference, where λ is the set center wavelength, n eff is the effective refractive index of the waveguide, n is an integer greater than or equal to 0, in the embodiment of the present application,
[0082] Then, according to the free spectrum range, set the relationship between the central wavelength and the delay line length At the same time, a suitable delay line length is determined by combining the above set of candidate delay line lengths, where n g is the group refractive index of the waveguide.
[0083] It should be noted that the phase difference π / 4 described in this application is not a single phase value, but can also be a set of phase values 2nπ + π / 4, where n is an integer greater than or equal to 0. Any phase difference in this set of phase values is equivalent to a phase difference of π / 4. Accordingly, when the phase difference between optical signal 13 and optical signal 14 is 2nπ + π / 4, the phase difference between second reflected optical signal 22 and first reflected optical signal 16 is 2nπ + π / 2.
[0084] Likewise, the same phase mentioned in this application may indicate that the phase values of the two optical signals are equal, or may indicate that the phase difference between the two optical signals is 2nπ.
[0085] Furthermore, the above-mentioned filtering structure or wavelength division multiplexing structure can be realized through semiconductor technology. For this purpose, the present application also provides an optical chip, which is prepared based on an SOI substrate.
[0086] The SOI substrate consists of a silicon-based substrate, a buried oxide layer (silicon dioxide), and a top silicon layer. Figure 1 The filter structure shown or Figure 4 The waveguides and other structures in the wavelength division multiplexing structure shown are all created by patterning the top silicon layer. A dielectric layer, typically silicon dioxide, is placed over the top silicon layer to fill the gaps between and cover the various components of the filter structure or wavelength division multiplexing structure.
[0087] Continue reading Figure 5 , Figure 5 for Figure 3 (a) is a schematic diagram of the cross-sectional structure of the heating electrode and microring along the AA' direction, including a silicon-based substrate 710, a buried oxide layer 720, a microring 730 formed by patterning the top silicon layer, and a dielectric layer 740 covering the buried oxide layer 720 and the microring 730, wherein the buried oxide layer 720 and the dielectric layer 740 serve as the lower cladding and upper cladding of the microring 730, respectively.
[0088] The heating electrode 750 is disposed on the dielectric layer 740 and corresponds to the position of the microring 730. The interlayer dielectric layer 760 covers the heating electrode 750 and the dielectric layer 740. The heating electrode 750 can be made of TiN. The heating electrode 750 includes a first open end and a second open end disposed opposite each other.
[0089] A first contact hole and a second contact hole are provided in the interlayer dielectric layer 760, exposing a first open end and a second open end, respectively. A first metal plug 771 and a second metal plug 772 are provided in the first contact hole and the second contact hole, respectively. A metal wiring layer is provided on the interlayer dielectric layer 760, and the metal wiring layer includes a first metal layer 781 and a second metal layer 782. The first metal layer 781 is electrically connected to the first open end of the heater electrode 750 via the first metal plug 771, and the second metal layer 782 is electrically connected to the second open end of the heater electrode 750 via the second metal plug 772.
[0090] In a specific embodiment of the present application, the thickness of the silicon-based substrate of the SOI is 500 μm, the thickness of the buried oxide layer is 8 μm, and the thickness of the top silicon layer is 220 nm.
[0091] based on Figure 1 The filter structure shown or Figure 4 In the actual fabrication process of the wavelength division multiplexing structure shown, the waveguide core structure is fabricated by photolithography and etching (patterning) the top silicon layer of the SOI wafer. After cleaning, SiO2 is deposited as the dielectric layer (upper cladding) using PECVD. To achieve a smooth upper surface, the upper cladding layer can also be planarized using chemical mechanical polishing (CMP).
[0092] As a specific example, Figure 4 The wavelength division multiplexer 500 in the wavelength division multiplexing structure shown adopts a 3-channel structure, and the channel center wavelengths of the output channels are respectively: 1546.8nm, 1550nm and 1553.2nm, and the channel spacing Δλ between two adjacent output channels is 3.2nm. At this time, the center wavelength of the wavelength division multiplexer 500 can be taken as the median of the center wavelengths of each channel, that is, the center wavelength of the wavelength division multiplexer 500 is 1550nm (set center wavelength).
[0093] According to the central wavelength and channel spacing of the wavelength division multiplexer 500, the central wavelength (central resonant wavelength) and free spectrum range corresponding to the resonant wavelength of the folded interference output structure in the filtering structure and the all-pass microring resonator 210 can be determined.
[0094] Specifically, the set center wavelength corresponding to the resonant wavelength of the folded interference output structure and the all-pass microring resonator 210 is equal to the output center wavelength of the wavelength division multiplexer 500, that is, λ = 1550nm; the free spectrum range of the folded interference output structure and the all-pass microring resonator 210 is equal to the channel spacing of the wavelength division multiplexer 500, that is, △λ = 3.2nm.
[0095] The specifications of the main components of the wavelength division multiplexing structure are as follows: the radius of the microring 200 is 32 μm. The first curved waveguide 112 and the second curved waveguide 122 in the curved directional coupler 100 are both Euler bends with a minimum bend radius of 100 μm. The coupling gaps between the microring and the first curved waveguide, and between the first curved waveguide and the second curved waveguide, are both 0.2 μm. The waveguide length of the delay line 300 is 86 μm. The cross-sectional dimensions of all transmission waveguides (including straight waveguides, curved waveguides, and delay line waveguides) are 500 nm x 220 nm. The wavelength division multiplexing structure also includes an input waveguide 600 located at the edge of the optical chip. Its input end is configured as an end coupler with a tip size of 0.2 μm.
[0096] A broadband optical signal (optical signal 11) with a wavelength range of 1500 nm to 1600 nm enters the wavelength division multiplexing structure from the input waveguide 600 (the input waveguide 600 can be regarded as a filtering structure or a part of the wavelength division multiplexing structure).
[0097] During the transmission of the optical signal 11 from port 1 to port 2 of the bent directional coupler 100, resonant filtering is performed in the all-pass microring resonator 210. The amplitudes of a group of optical signals including 1546.8 nm, 1500 nm, and 1503.2 nm (the wavelength interval of this group of optical signals is 3.2 nm) remain unchanged, and the potential levels of other wavelengths are greatly suppressed.
[0098] After resonant filtering, optical signal 12 continues to propagate along first curved waveguide 112 toward port 2. At ports 2 and 3 of curved directional coupler 100, it is split into two paths, optical signal 13 and optical signal 21, with identical amplitude and phase. Optical signal 13 then passes through delay line 300 and reaches annular reflector 410. The optical signal reflected and output by annular reflector 410 passes through delay line 300 again, yielding first reflected optical signal 16. Optical signal 21 directly reaches annular reflector 420, where it is reflected and output, yielding second reflected optical signal 22.
[0099] At this time, the amplitudes of the second reflected light signal 22 and the first reflected light signal 16 are the same, and the phase difference between the second reflected light signal 22 and the first reflected light signal 16 is π / 2.
[0100] The first reflected light signal 16 and the second reflected light signal 22 enter the bent directional coupler 100 from port 2 and port 3, respectively. During transmission toward port 1, the first reflected light signal 16 undergoes resonant filtering again in the all-pass microring resonator 210 to produce the first reflected light signal 17 (the other wavelengths of optical signals, such as the non-resonant wavelengths of 1546.8 nm, 1500 nm, and 1503.2 nm, are suppressed again).
[0101] The first reflected light signal 17 (16) and the second reflected light signal 22 interfere and enhance in the bent directional coupler 100, and the light signal 31 is output from the port 4. At this time, the field intensity of the light signal 31 is the sum of the field intensities of the first reflected light signal 17 (16) and the second reflected light signal 22.
[0102] The optical signal 31 output by the filtering structure enters the wavelength division multiplexer 500 , and the three output channels of the wavelength division multiplexer 500 output optical signals of 1546.8 nm, 1500 nm, and 1503.2 nm respectively.
[0103] Figure 6 (a) is a broadband optical signal with a wavelength range of 1500nm-1600nm, directly input Figure 4 Optical simulation diagram of the wavelength division multiplexer 500 in FIG. Figure 6 (b) is a broad spectrum optical signal with a wavelength range of 1500nm-1600nm, which is input through the input waveguide 600 Figure 4 The optical simulation diagram of the wavelength division multiplexing structure shown in the figure. Figure 6 (a) and Figure 6 (b) It can be seen that Figure 4 The channel crosstalk and noise floor of the wavelength division multiplexing structure shown are significantly reduced.
[0104] In other embodiments, the optical chip of the present application can also be prepared based on other semiconductor material platforms such as SiN, InP, etc. As an example, the thickness of the silicon substrate of the optical chip based on SiN material is 500 μm, the thickness of the silicon dioxide layer is 8 μm, and the thickness of the top silicon nitride layer is 400 nm.
[0105] When the aforementioned three-channel wavelength division multiplexing structure (channel center wavelengths are 1546.8nm, 1550nm and 1553.2nm, and the channel spacing is 3.2nm) is based on a waveguide made of SIN material, the specifications of the main components of the wavelength division multiplexing structure are as follows: the radius of the microring 200 is 50μm, the bending radius of the first curved waveguide 112 and the second curved waveguide 122 in the curved directional coupler 100 are both 200μm Euler bends, the coupling gap is 0.4μm, the waveguide length of the delay line 300 is 156μm, and the cross-sectional dimensions of all transmission waveguides (including straight waveguides, curved waveguides, delay line waveguides, etc.) are all 1μm×0.4μm.
[0106] As can be seen from the above embodiments, the filtering structure of the present application mainly includes two functional units: a folded interference output structure and an all-pass microring resonator. During the periodic transmission of wide-spectrum optical signals, the folded interference output structure and the all-pass microring resonator jointly perform multiple resonance filtering and interference enhancement on the target wavelength (the output center wavelength of each output channel of the wavelength division multiplexer), thereby retaining the target wavelength and greatly suppressing the potential level of non-target wavelengths, thereby achieving pre-filtering of the target wavelength; the pre-filtered optical signal is then used as the input of the wavelength division multiplexer, reducing the channel crosstalk of the wavelength division multiplexing structure.
[0107] It should be noted that the interference output structure in this application is called a "folded" interference output structure because, by introducing a ring reflector, a set of directional couplers and an all-pass microring resonator can realize the functions of two sets of directional couplers and all-pass microring resonators, thereby halving the component size of the optical chip, that is, the structure is "folded"; accordingly, bidirectional transmission of optical signals is realized in a set of directional couplers and all-pass microring resonators, and the optical signal realizes two pre-filtering of the target wavelength during the bidirectional transmission process, that is, the optical path and filtering are "folded". Through the above-mentioned folded interference output structure design, while realizing pre-filtering and reducing the crosstalk problem between the output channels of the wavelength division multiplexing structure, it also makes the structure of the filtering structure / wavelength division multiplexing structure simpler and more compact, reducing the design and process difficulty of the optical chip.
[0108] Thus far, the technical solution of the present application has been described in conjunction with an embodiment shown in the accompanying drawings. However, it is readily understood by those skilled in the art that the scope of protection of the present application is obviously not limited to these specific embodiments. Without departing from the principles of the present application, those skilled in the art may make equivalent changes or substitutions to the relevant technical features, and the technical solutions after such changes or substitutions will fall within the scope of protection of the present application.
Claims
1. A filtering structure, characterized in that: It includes a directional coupler (100), a micro-ring (200), a delay line (300), a first reflector (410) and a second reflector (420); The directional coupler (100) comprises a first waveguide and a second waveguide, wherein the first end of the first waveguide is the input end of the filtering structure, and the second end of the first waveguide is connected to the delay line (300) and the first reflector (410) in sequence; the first end of the second waveguide is the output end of the filtering structure; and the second end of the second waveguide is connected to the second reflector (420); The directional coupler (100), the delay line (300), the first reflector (410) and the second reflector (420) form a folded interference output structure; The microring (200) is located on one side of the first waveguide and forms an all-through microring resonator with the first waveguide.
2. The filtering structure according to claim 1, characterized in that The directional coupler (100) is a bent directional coupler, wherein: The first waveguide comprises a first straight waveguide (111), a first curved waveguide (112), and a third straight waveguide (113) connected in sequence, wherein the first end of the first straight waveguide (111) not connected to the first curved waveguide (112) constitutes the first end of the first waveguide, and the second end of the third straight waveguide (113) not connected to the first curved waveguide (112) constitutes the second end of the first waveguide; The second waveguide comprises a second straight waveguide (121), a second curved waveguide (122), and a fourth straight waveguide (123) connected in sequence, wherein the first end of the second straight waveguide (121) not connected to the second curved waveguide (122) constitutes the first end of the second waveguide, and the second end of the fourth straight waveguide (123) not connected to the second curved waveguide (122) constitutes the second end of the second waveguide.
3. The filtering structure according to claim 1 or 2, characterized in that: When the first end of the first waveguide serves as the input end of the optical signal, the directional coupler (100) is configured such that the amplitude and phase of the first output optical signal and the second output optical signal are the same; The first output optical signal is an optical signal output from the second end of the first waveguide, and the second output optical signal is an optical signal output from the second end of the second waveguide.
4. The filtering structure according to claim 1, characterized in that The first reflector (410) and the second reflector (420) are both annular reflectors.
5. The filtering structure according to claim 1, characterized in that The delay line (300) is configured such that after an optical signal with a set central wavelength passes through the delay line (300), a phase difference between the optical signals at both ends of the delay line (300) is π / 4+2nπ, where n is an integer greater than or equal to 0.
6. The filtering structure according to any one of claims 1 to 5, characterized in that: The free spectrum range of the folded interferometer output structure is equal to the free spectrum range of the all-pass microring resonator (210); and / or, The resonant wavelength of the folded interference output structure is consistent with the resonant wavelength of the all-pass microring resonator (210).
7. The filtering structure according to any one of claims 1 to 5, characterized in that: The filtering structure further includes: a first phase shifter corresponding to the all-pass microring resonator (210); and / or, A second phase shifter corresponding to the delay line (300).
8. A wavelength division multiplexing structure, characterized in that: Comprising a wavelength division multiplexer (500) and the filtering structure according to any one of claims 1 to 7; The output end of the filter structure is connected to the input end of the wavelength division multiplexer (500), and the wavelength division multiplexer (500) has multiple output channels, and outputs multiple optical signals of set wavelengths output from the filter structure from corresponding output channels.
9. The wavelength division multiplexing structure according to claim 8, characterized in that: The resonant wavelength of the folded interference output structure in the filtering structure is consistent with the output center wavelength of each output channel of the wavelength division multiplexer (500); and / or, The resonant wavelength of the all-pass micro-ring resonator (210) in the filtering structure is consistent with the output center wavelength of each output channel of the wavelength division multiplexer (500); and / or, The free spectral range of the folded interference output structure in the filtering structure is equal to the channel spacing of the output channels of the wavelength division multiplexer (500); and / or, The free spectral range of the all-pass micro-ring resonator (210) in the filtering structure is equal to the channel spacing of the output channels of the wavelength division multiplexer (500).
10. An optical chip, characterized in that: The optical chip comprises the filter structure according to any one of claims 1 to 7; or The optical chip includes the wavelength division multiplexing structure according to any one of claims 8 or 9.