An anticoupler based on a thin-film lithium niobate platform

Abstract

This invention belongs to the field of wavelength division multiplexing optical communication technology, specifically relating to a reverse coupler based on a thin-film lithium niobate platform. The reverse coupler includes: a lithium niobate-on-insulator substrate, a first waveguide, a second waveguide, and a coupling region. The first and second waveguides are disposed in the device layer of the lithium niobate-on-insulator substrate. The first and second waveguides are arranged in parallel along the light propagation direction within the coupling region. A periodic grating perturbation structure is disposed on the first and / or second waveguides. This reverse coupler utilizes the grating perturbation structure to ensure that the modes of the two waveguides satisfy the phase matching condition. The optical signal input to one waveguide is reverse-coupled to the falling port of the other waveguide. Utilizing the large photoelectric coefficient of lithium niobate material, this reverse coupler can tune its spectrum under specific conditions by applying a voltage.

Description

Technical Field

[0001] This invention belongs to the field of wavelength division multiplexing optical communication technology, and specifically relates to a reverse coupler based on a thin-film lithium niobate platform. Background Technology

[0002] With the rapid development of optical communication and on-chip optical interconnect technologies, the demand for high-performance, wide-bandwidth, low-crosstalk optical filtering and wavelength division multiplexing devices in photonic integrated circuits is increasing. The lithium niobate-on-insulator platform, due to its intrinsically low propagation loss (down to 0.05–0.1 dB / cm) and excellent electro-optic effect (electro-optic coefficient r33 approximately 30 pm / V), has become an important candidate platform for next-generation photonic integration.

[0003] Currently, research on the lithium niobate platform mainly focuses on high-speed electro-optic modulators, while research on high-performance passive optical filters and wavelength division multiplexing (WDM) devices is relatively limited. While traditional microring resonator structures offer the advantage of compact size, their free spectral range is typically limited by the cavity length, generally less than 10 nm, and their passband bandwidth is usually less than 1 nm, making it difficult to meet the requirements of high-bandwidth, multi-channel WDM systems. In the silicon-on-insulator (SiI) platform, Bragg-type optical filters and multiplexers based on reverse coupling have been extensively studied, achieving free spectral ranges greater than 100 nm, passband bandwidths from several nanometers to tens of nanometers, and excellent channel isolation. However, directly transplanting these structures to the lithium niobate platform faces significant challenges. On the one hand, lithium niobate materials exhibit significant anisotropy, with its refractive index tensor varying with crystal orientation; on the other hand, the refractive index contrast of lithium niobate waveguides is significantly lower than that of silicon-based platforms (approximately one-fifth of that of silicon platforms), resulting in weakened mode confinement and easier excitation of higher-order transverse modes. The aforementioned factors make traditional reverse-coupled structures prone to multimode coupling and self-reflection on the lithium niobate platform, thereby introducing large spectral crosstalk, reducing the channel isolation of the filter and affecting the free spectral range and the performance of adjacent channels.

[0004] Therefore, it is necessary to design a specially optimized structure to address the material anisotropy and low refractive index contrast of the lithium niobate platform. This structure aims to suppress higher-order mode coupling, reduce spectral crosstalk, and achieve a high-performance passive optical filter and multiplexer with a large free spectral range, wide passband bandwidth, and high channel isolation. Furthermore, the excellent electro-optic effect of lithium niobate material allows for tunable spectrum in this device. Summary of the Invention

[0005] To address the issues of limited free spectral range and severe multimode crosstalk in existing passive optical filters based on lithium niobate platforms, this invention provides a reverse coupler based on a thin-film lithium niobate platform. The aim is to provide a lithium niobate reverse coupler device with high sidelobe suppression ratio, no free spectral limitation, and support for electrical tunability, suitable for on-chip wavelength division multiplexing and spectral shaping.

[0006] To achieve the above objectives, the present invention provides the following solution: A reverse coupler based on a thin-film lithium niobate platform, the reverse coupler comprising: a lithium niobate on insulator substrate, a first waveguide, a second waveguide, and a coupling region; The first waveguide and the second waveguide are disposed on the lithium niobate substrate on the insulator; The first waveguide and the second waveguide are arranged in parallel along the direction of light propagation within the coupling region; A periodic grating perturbation structure is provided on the first waveguide and / or the second waveguide.

[0007] Preferably, the lithium niobate substrate on the insulator is an X-cut thin-film lithium niobate; the first waveguide and the second waveguide are ridge waveguides or partially etched waveguides disposed in the thin-film lithium niobate.

[0008] Preferably, the widths of the first waveguide and the second waveguide are different.

[0009] Preferably, there is a phase difference between the grating perturbation structures on the outer and inner sides of the first and second waveguides to suppress Bragg back reflection within the waveguides.

[0010] Preferably, the grating perturbation structure adopts an apodized design, and by modulating the perturbation depth and duty cycle of the grating, the coupling strength between the grating and the waveguide is non-uniformly distributed along the light propagation direction.

[0011] Preferably, a tapered waveguide is connected at the descent port of the second waveguide, so that the width of the second waveguide gradually decreases.

[0012] Preferably, an electrode structure is disposed near the coupling region, and an electric field is introduced in the thin-film lithium niobate by applying a voltage between the electrode structures to change the effective refractive index of the waveguide, thereby adjusting the center operating wavelength and / or passband position of the reverse coupler.

[0013] Preferably, the reverse coupler is used in a tunable optical filter.

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention proposes a reverse coupler based on a thin-film lithium niobate platform. The reverse coupler includes a through waveguide and a down waveguide fabricated on a thin-film lithium niobate film. The two waveguides are asymmetrically parallel, and the sidewalls of the waveguides are provided with periodic Bragg grating perturbation structures. The grating perturbation structure ensures that the modes of the two waveguides satisfy the phase-matching condition, and the optical signal from the input waveguide is reverse-coupled to the down waveguide port of the other waveguide. Utilizing the large photoelectric coefficient of lithium niobate, this reverse coupler can be spectrally tuned by applying a voltage under specific conditions. The reverse coupler based on the thin-film lithium niobate platform proposed in this invention has an unrestricted free spectral range, can achieve designable passband characteristics over a wide wavelength range, and also features high sidelobe suppression, high channel isolation, and good manufacturing tolerance. Attached Figure Description

[0015] To more clearly illustrate the technical solution of the present invention, the drawings used in the embodiments are briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0016] Figure 1 The schematic diagram of the reverse coupler on the thin-film lithium niobate platform provided in Example 1 includes a thin-film lithium niobate layer, a buried oxide layer and an upper cladding layer disposed on a substrate, wherein a waveguide structure is formed in the thin-film lithium niobate layer.

[0017] Figure 2 This is a schematic diagram of a thin-film lithium niobate platform wavelength-tunable device with electrodes provided in Example 1.

[0018] Figure 3 This is a schematic diagram of a structure provided in Example 1, in which n reverse coupler units are sequentially set up for wavelength division multiplexing or demultiplexing.

[0019] Figure 4 It is based on the relationship between the effective refractive index of the upper and lower waveguides of the reverse coupler on the lithium niobate platform provided in Example 1 and the waveguide width.

[0020] Figure 5 This is a schematic diagram of the spectral response of a reverse coupler on a preferred thin-film lithium niobate platform provided in Example 2 of the present invention.

[0021] Figure 6 This is a schematic diagram of the spectral response of a preferred device with tunable spectral response on a thin-film lithium niobate platform provided in Example 3 of the present invention. Figure 7 This is a schematic diagram of the spectral response of a four-channel wave decomposition and multiplexing on a preferred thin-film lithium niobate platform provided in Example 4 of the present invention.

[0022] Figure 8 This is a schematic diagram of the structure of a preferred thin-film lithium niobate platform provided in Example 5 of the present invention, which combines a power distribution device such as an MMI and a device such as an optical switch with selectable bandwidth for spectral processing.

[0023] Among them, 1-buried oxide layer; 2-planar layer; 3-etched layer; 4-cladding layer; 5-first waveguide; 6-second waveguide; 7-coupling region; 8-tapered waveguide; 9-electrode structure; 10-main waveguide; 11-input waveguide; 12-power distribution unit; 13-optical switch unit. Detailed Implementation

[0024] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0026] To better illustrate this embodiment, the components in the accompanying drawings may be enlarged or reduced, and do not represent the actual device dimensions. It is understandable that some well-known structures and their descriptions may be omitted in the drawings for those skilled in the art.

[0027] Example 1 The present invention provides a reverse coupler based on a thin-film lithium niobate platform, comprising: a lithium niobate on insulator substrate, a first waveguide 5, a second waveguide 6, and a coupling region 7; The first waveguide 5 and the second waveguide 6 are disposed in the device layer of the lithium niobate substrate on the insulator. The device layer is located above the buried oxide layer 1 and is composed of a planar layer 2 and an etched layer 3. The first waveguide 5 and the second waveguide 6 are arranged in parallel along the direction of light propagation within the coupling region 7; A periodic grating perturbation structure is set on the first waveguide 5 and / or the second waveguide 6, that is, a periodic grating perturbation structure is introduced on at least one waveguide to achieve reverse mode coupling.

[0028] Specifically: The lithium niobate substrate on the insulator is an X-cut thin-film lithium niobate; the first waveguide 5 and the second waveguide 6 are ridge waveguides or partially etched waveguides disposed in the thin-film lithium niobate. By selecting the width parameters of the two waveguides, the phase matching wavelength between the fundamental mode and the higher-order modes is deviated from the operating band of the reverse coupler, thereby reducing higher-order mode crosstalk.

[0029] Furthermore, in this embodiment, the widths of the first waveguide 5 and the second waveguide 6 are different from each other to disrupt the directional coupling condition between the two waveguides, so that at the predetermined center operating wavelength, only the forward propagation fundamental mode in the first waveguide 5 and the backward propagation fundamental mode in the second waveguide 6 satisfy the Bragg phase matching condition and undergo reverse coupling, thereby suppressing the coupling between the fundamental mode and higher-order modes.

[0030] This invention suppresses unwanted directional coupling and higher-order mode coupling through asymmetric waveguide structure design. Specifically, the width of the first waveguide 5 is W1, and the width of the second waveguide 6 is W2, where there is a significant width difference between W1 and W2. This allows only the fundamental mode that satisfies the Bragg phase-matching condition to undergo reverse coupling, while higher-order modes are effectively suppressed due to phase mismatch.

[0031] Furthermore, in this embodiment, a phase difference exists between the grating perturbation structures of the outer and inner sidewalls of the first waveguide 5 and the second waveguide 6, which is used to suppress Bragg back reflection within the waveguides. This phase difference Δφ is achieved by a relative position offset ΔL between the grating perturbation structures of the outer and inner sidewalls in the light propagation direction, where Δφ = 2πΔL / Λ, and Λ is the grating period. This is used to modulate the interference characteristics of Bragg scattering, thereby suppressing back reflection within the waveguides.

[0032] Furthermore, in this embodiment, the grating perturbation structure adopts an apodized design. By modulating the perturbation depth and duty cycle of the grating, the coupling strength between the grating and the waveguide is non-uniformly distributed along the light propagation direction to suppress spectral sidelobes.

[0033] Within the coupling region 7, the grating has a period Λ, and the grating period satisfies the Bragg phase-matching condition for reverse coupling with the propagation constants of the fundamental modes in the first waveguide 5 and the second waveguide 6. The grating can be rectangular, trapezoidal, or sinusoidal modulated, and its perturbation depth and duty cycle are designed within a predetermined range to ensure the expected coupling strength. To further reduce spectral sidelobes, this invention introduces a certain apodization design into the grating perturbation structure, making the grating coupling strength non-uniformly distributed along the propagation direction, thereby significantly improving the sidelobe suppression ratio and improving the spectral morphology. This apodization design is achieved by changing at least one parameter of the grating's duty cycle, perturbation depth, and waveguide width along the light propagation direction using modulation methods including but not limited to Gaussian modulation, cosine modulation, and exponential modulation. This causes the coupling strength of the grating perturbation structure to gradually change along the propagation direction according to a preset function controlled by the modulation method, thereby significantly improving the sidelobe suppression ratio and improving the spectral morphology.

[0034] Furthermore, in this embodiment, a tapered waveguide 8 is connected at the descent port of the second waveguide 6, so that the width of the second waveguide 6 gradually decreases.

[0035] At the descent port of the second waveguide 6, in order to suppress unnecessary higher-order modes, a tapered waveguide structure—a tapered waveguide 8—is introduced, which gradually reduces the width of the second waveguide 6 from W2 to W3, thereby gradually leaking unnecessary higher-order modes into the cladding 4 and suppressing crosstalk of higher-order modes.

[0036] Furthermore, in this embodiment, an electrode structure 9 is provided near the coupling region 7. By applying a voltage between the electrode structures 9, an electric field is introduced into the thin-film lithium niobate to change the effective refractive index of the waveguide, thereby adjusting the center operating wavelength and / or passband position of the reverse coupler.

[0037] The present invention sets an electrode structure 9 near the coupling region 7, and by introducing a transverse or longitudinal electric field in the thin film lithium niobate, the effective refractive index of the waveguide is adjusted by utilizing the electro-optic effect of the lithium niobate material, thereby realizing the continuous adjustment of the center wavelength and / or passband bandwidth of the reverse coupler.

[0038] Furthermore, in this embodiment, the reverse coupler is used for a tunable optical filter.

[0039] Specifically, the tunable optical filter can be a wavelength division multiplexing or demultiplexing device based on lithium niobate on an insulator, including: An input bus waveguide is used to transmit optical signals containing multiple wavelength components; Multiple grating-assisted reverse coupler units are cascaded sequentially along the light propagation direction of the input bus waveguide, wherein each reverse coupler unit is the reverse coupler described above. In this configuration, the grating period and / or waveguide effective refractive index of different reverse coupler units are configured to correspond to different center operating wavelengths, so that each reverse coupler unit sequentially couples optical signals of different wavelengths from the input bus waveguide to the corresponding output port, thereby realizing coarse wavelength division multiplexing or demultiplexing functions with high isolation and low crosstalk.

[0040] Among them, at least some of the reverse coupler units include electrode structures 9, and by applying independently or in groups controlled voltages to different reverse coupler units, the wavelength division multiplexing or demultiplexing device can be dynamically adjustable or reconfigurable.

[0041] The tunable optical filter can also be a selective bandwidth spectral processing device based on lithium niobate on an insulator, including: An input waveguide 11 is used to receive an optical signal containing at least one wavelength component; The power distribution unit 12, which is optically connected to the input waveguide 11, is used to distribute the optical signal to multiple parallel branch waveguides. Optical switch unit 13 is installed in each branch waveguide; Multiple grating-assisted reverse coupler units (the aforementioned reverse couplers) are respectively set in each branch waveguide. The grating-assisted reverse coupler units in different branch waveguides have different spectral response characteristics, preferably with different passband bandwidths. By controlling the conduction state of the optical switch unit 13, the optical signal is selectively guided to the grating-assisted reverse coupler unit in the corresponding branch waveguide, thereby achieving selection of the output optical signal bandwidth. At least some of the reverse coupler units include electrode structures 9, and the center wavelength can be adjusted by applying independently or in groups controlled voltages to different reverse coupler units.

[0042] In summary, the reverse coupler based on the thin-film lithium niobate platform proposed in this invention has an unrestricted free spectral range, can achieve designable passband characteristics over a wide wavelength range, and also features high sidelobe suppression, high channel isolation, and good manufacturing tolerance.

[0043] Example 2 like Figure 1 As shown, this example illustrates a reverse coupler structure built on a lithium niobate-on-insulator wafer, comprising: Oxygen layer 1; A ridge-shaped lithium niobate waveguide structure consisting of a flat plate layer 2 and an etched layer 3 on the buried oxide layer 1; The cladding 4 covering the buried oxygen layer 1; First waveguide 5 and second waveguide 6 are composed of thin-film lithium niobate; The coupling region 7 formed by the grating; Tapered waveguide 8 connected to the descent port.

[0044] The buried oxide layer 1, the flat plate layer 2, and the etched layer 3 constitute the lithium niobate substrate on the insulator, and the disturbance caused by the grating is the grating disturbance structure.

[0045] The depth of the etched layer 3 and the thickness of the planar layer 2 are selected to ensure that the waveguide supports mode propagation within the target operating band. In some embodiments, the depth of the etched layer 3 and the thickness of the planar layer 2 are on the same order of magnitude.

[0046] The reverse coupler consists of a first waveguide 5 and a second waveguide 6. The first waveguide 5 serves as a through waveguide, and the second waveguide 6 serves as a down waveguide. The two waveguides are arranged in parallel within a predetermined coupling region 7. The first waveguide 5 and the second waveguide 6 have different waveguide widths, and the width difference is designed to disrupt the directional coupling condition and suppress higher-order mode coupling.

[0047] The center wavelength of the reverse coupling is determined by the phase-matching condition: λc = Λ(n1 + n2), where λc is the center wavelength of the reverse coupling (i.e., the Bragg wavelength), Λ is the grating period, and n1 and n2 are the effective refractive indices of the forward-propagating target mode in the first waveguide 5 and the backward-propagating target mode in the second waveguide 6, respectively. Within the coupling region 7, periodic grating perturbations are formed on the relatively inner sidewalls of the first waveguide 5 and / or the second waveguide 6 to achieve reverse-mode coupling that satisfies the Bragg phase-matching condition. The grating can be sinusoidal, rectangular, or a combination thereof, with a period on the sub-micrometer scale to adapt to the reverse coupling conditions of the communication band.

[0048] To suppress spectral sidelobes, the modulation intensity of the grating in the coupling region 7 is non-uniformly distributed along the propagation direction. In some embodiments, the modulation intensity follows a Gaussian function, a cosine function, or other continuously varying functions, thereby reducing sidelobe amplitude and improving passband spectral flatness.

[0049] To suppress unwanted higher-order modes, a tapered waveguide 8 with a gradually decreasing width is introduced at the descent port of the second waveguide 6. The width of the tapered waveguide 8 gradually decreases from W2 to W3, thereby gradually leaking unwanted higher-order modes into the cladding 4 and suppressing crosstalk of higher-order modes.

[0050] Furthermore, based on the lithium niobate reverse coupler structure described above, an electro-optic modulation structure is introduced to achieve tunable spectral response of the device. For example... Figure 2 As shown, the reverse coupler is formed on a thin-film lithium niobate substrate. The first waveguide 5 and the second waveguide 6 are arranged in parallel within the coupling region 7, and periodic grating structures are formed on their opposing inner sidewalls. An electrode structure 9 is disposed above or below the coupling region 7, and the electrode is electrically isolated from the first waveguide 5 and the second waveguide 6 by a dielectric isolation layer.

[0051] In some embodiments, the electrode structure 9 includes at least one pair of modulation electrodes extending along the waveguide propagation direction and covering the coupling region 7. The electrode structure 9 may be positioned above, beside, or in combination with the waveguide to generate transverse or longitudinal electric field components in the thin-film lithium niobate. The dielectric isolation layer may comprise silicon dioxide or other insulating materials, the thickness of which is selected to reduce optical absorption losses introduced by the metal electrodes while ensuring the electric field effectively acts on the waveguide region.

[0052] When a voltage is applied between the electrodes, the effective refractive index of the thin-film lithium niobate changes due to the electro-optic effect, thereby causing a change in the propagation constants in the first waveguide 5 and the second waveguide 6, and thus altering the Bragg phase matching condition of the reverse coupler. By adjusting the amplitude and / or polarity of the applied voltage, continuous tuning of the center operating wavelength and / or passband position of the reverse coupler can be achieved.

[0053] In some embodiments, the electrode structure 9 is designed with a non-perfectly symmetrical distribution to enhance the effective electro-optic coefficient and improve tuning efficiency. Compared with thermal tuning-based methods, the electro-optic tuning mechanism described in this embodiment has the advantages of fast response speed, low power consumption, and no introduction of significant thermal crosstalk.

[0054] Furthermore, based on the above structure, a wavelength division multiplexing (WDM) device based on n cascaded reverse couplers is provided for constructing a lithium niobate reverse coupler structure to achieve WDM multiplexing or demultiplexing of multi-channel optical signals. Each reverse coupler unit is arranged sequentially along the propagation direction of the main waveguide 10, so that different wavelength channels are separated in spatial order.

[0055] like Figure 3 As shown, the wavelength division multiplexing device includes a main waveguide 10, which has an input end and a direct output end for transmitting composite optical signals containing multiple wavelength components. Along the propagation direction of the main waveguide 10, n reverse coupler units are sequentially arranged. Each reverse coupler unit includes a descending waveguide arranged parallel to the main waveguide 10, and forms a periodic grating structure within the corresponding coupling region 7.

[0056] In some implementations, the grating periods and / or waveguide parameters of different anticoupler units are designed to be different from each other, so that each anticoupler unit corresponds to a different center operating wavelength, thereby achieving selective coupling to channels of different wavelengths. When the composite optical signal enters from the input port of the main waveguide 10, each anticoupler unit sequentially couples the optical signal that satisfies its Bragg phase matching condition from the main waveguide 10 to the corresponding falling waveguide, and outputs it through different output ports.

[0057] In some implementations, a predetermined spacing is maintained between each anticoupler unit along the main waveguide 10 to reduce optical crosstalk between adjacent coupling units and reduce reflection superposition effects. The anticoupler units can employ the same or different coupling lengths, grating modulation intensities, and apodized distributions to meet design requirements for different channel bandwidths and isolation levels.

[0058] In a further embodiment, at least some of the reverse coupler units can be combined with the electrode structure 9 described above. By applying a voltage to adjust the center operating wavelength of the corresponding reverse coupler unit, dynamic tuning of the channel wavelength or channel selection function can be achieved. By controlling the electrodes of different reverse coupler units independently or in groups, a reconfigurable wavelength division multiplexing or demultiplexing system can be constructed.

[0059] According to Example 1, the effective refractive index of the upper and lower waveguides of the reverse coupler on the lithium niobate platform varies with the waveguide width as follows: Figure 4 As shown.

[0060] Example 3 like Figure 5 The diagram illustrates the spectral response of the cascaded reverse coupler wavelength division multiplexing device of the present invention under a preferred embodiment. Results show that, in this specific embodiment, the device exhibits excellent spectral performance within the communication band. Under specific design parameters, the reverse coupler can achieve a passband bandwidth on the order of nanometers and has a sidelobe suppression ratio greater than 30 dB, while maintaining a low insertion loss. The reverse coupler of this embodiment achieves high sidelobe suppression ratio and low insertion loss within the target operating band, and its spectral response is not limited by a free spectral range over a wide wavelength range, making it suitable for broadband or multi-channel wavelength division multiplexing applications.

[0061] It should be understood that the above performance indicators are only used to illustrate the feasibility and superiority of the present invention and do not constitute a limitation on the scope of protection of the present invention. By adjusting design parameters such as waveguide size, grating parameters, and coupling length, the spectral performance of the reverse coupler described in this invention can be adjusted within a wide range. Preferably, in some specific embodiments, the above parameters can be further limited to specific numerical ranges to achieve optimized design for specific communication bands.

[0062] Example 4 like Figure 6 The diagram illustrates the spectral response of the tunable device according to a preferred embodiment of the present invention. When no voltage is applied, the reverse coupler achieves reverse coupling at a predetermined center wavelength. When a voltage is applied between the electrode structures 9, the effective refractive index of the waveguide changes due to the electro-optic effect in the thin-film lithium niobate, thereby altering the phase-matching condition of the reverse coupling and causing a shift in the center operating wavelength of the reverse coupler.

[0063] The results show that, in this preferred embodiment, the tuning magnitude of the center operating wavelength can reach the sub-nanometer level. Within a reasonable voltage range, the center operating wavelength can be continuously and controllably tuned, and the passband shape and sidelobe suppression characteristics of the device remain essentially unchanged, indicating that the structure described in this invention is suitable for channel alignment and dynamic reconstruction in wavelength division multiplexing systems.

[0064] Example 5 like Figure 7 The diagram shown illustrates the spectral response of the cascaded reverse coupler wavelength demultiplexing device of the present invention in a preferred embodiment. This spectrum corresponds to a four-channel demultiplexing structure, where different reverse coupler units correspond to different center operating wavelengths. Figure 7 As can be seen, when a composite optical signal containing multiple wavelength components is input from the main waveguide 10, each reverse coupler unit can selectively couple the optical signal within the corresponding wavelength range to different falling waveguide ports, thereby realizing the demultiplexing of multi-channel optical signals. Each output channel exhibits good passband characteristics within its corresponding operating band and maintains high isolation from adjacent channels, and is not limited by the free spectral range, making it suitable for on-chip optical interconnects and reconfigurable optical communication systems.

[0065] It should be understood that, Figure 7 The spectral response shown is only for illustrating the technical effects of the present invention. By adjusting the grating parameters, waveguide structure, or cascade number of the reverse coupler unit, the number of channels, channel spacing, and operating band of the wave demultiplexing device described in the present invention can be adjusted accordingly.

[0066] Example 6 like Figure 8 As shown, this embodiment provides a spectrum processing device with selectable bandwidth, which includes an input waveguide 11, a power distribution unit 12, an optical switch unit 13, and multiple reverse coupler branches.

[0067] The power distribution unit 12 is disposed after the input waveguide 11 and is used to distribute the input optical signal to multiple parallel branch waveguides. In one embodiment, the power distribution unit 12 may be a multimode interference coupler (MMI) with a Y-branch, but is not limited thereto.

[0068] Each branch waveguide is provided with an optical switch unit 13 and a reverse coupler unit. The reverse coupler units in different branches have different spectral response characteristics. Preferably, the reverse coupler units have different passband bandwidths.

[0069] By controlling the conduction state of the optical switch unit 13, the input optical signal can be selectively guided to the anti-coupler unit in the corresponding branch, thereby achieving selection of the output optical signal bandwidth. The unselected branch is in a cutoff or bypass state to avoid interference with the optical signal.

[0070] In a preferred embodiment, the reverse coupler unit is any of the grating-assisted reverse couplers described in the foregoing embodiments, and different bandwidth spectral filtering can be achieved by changing the grating length, apodization method, coupling spacing, and / or waveguide parameters. The number of branches of the reverse coupler can be flexibly configured according to system design requirements.

[0071] Furthermore, at least some of the reverse coupler units include electrode structures 9, which enable the adjustment of the center wavelength of the different bandwidths by applying independently or in groups controlled voltages to different reverse coupler units.

[0072] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made to the technical solutions of the present invention by those skilled in the art without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A reverse coupler based on a thin-film lithium niobate platform, characterized in that, The reverse coupler includes: a lithium niobate on an insulator substrate, a first waveguide, a second waveguide, and a coupling region; The first waveguide and the second waveguide are disposed on the lithium niobate substrate on the insulator; The first waveguide and the second waveguide are arranged in parallel along the direction of light propagation within the coupling region; A periodic grating perturbation structure is provided on the first waveguide and / or the second waveguide.

2. The reverse coupler according to claim 1, characterized in that, The lithium niobate substrate on the insulator is an X-cut thin-film lithium niobate; the first waveguide and the second waveguide are ridge waveguides or partially etched waveguides disposed in the thin-film lithium niobate.

3. The reverse coupler according to claim 1, characterized in that, The widths of the first waveguide and the second waveguide are different.

4. The reverse coupler according to claim 1, characterized in that, There is a phase difference between the grating perturbation structures on the outer and inner sides of the first and second waveguides, which is used to suppress Bragg back reflection within the waveguides.

5. The reverse coupler according to claim 1, characterized in that, The grating perturbation structure adopts an apodized design. By modulating the perturbation depth and duty cycle of the grating, the coupling strength between the grating and the waveguide is non-uniformly distributed along the light propagation direction.

6. The reverse coupler according to claim 1, characterized in that, At the descent port of the second waveguide, a tapered waveguide is connected to make the width of the second waveguide gradually decrease.

7. The reverse coupler according to claim 1, characterized in that, An electrode structure is disposed near the coupling region. By applying a voltage between the electrode structures, an electric field is introduced into the thin-film lithium niobate to change the effective refractive index of the waveguide, thereby adjusting the center operating wavelength and / or passband position of the reverse coupler.

8. The reverse coupler according to any one of claims 1-7, characterized in that, The reverse coupler is used in a tunable optical filter.

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