A tm mode short pass filter

Abstract

The application provides a TM mode short-pass filter, which realizes smooth energy transmission of TM mode in a passband by adopting a three-section variable-width waveguide region and an adiabatic gradual change structure design, obtains high cutoff depth while ensuring low passband insertion loss, ensures adiabatic transmission of an optical field, and significantly improves passband flatness; by adjusting the width of the second waveguide, linear tuning of the cutoff wavelength in a super-wide range can be realized, covering multiple communication wavebands. In addition, by integrating heating electrodes on both sides of the waveguide region, the refractive index of the waveguide region is adjusted by using the thermo-optic effect, and fine adjustment of the cutoff wavelength is realized. The application has a simple structure and excellent thermal tuning performance, and has outstanding technical advantages in applications such as on-chip pumped light stripping and noise filtering.

Description

Technical Field

[0001] This invention relates to the field of integrated photonics technology, and in particular to a TM mode short-pass filter. Background Technology

[0002] With the rapid development of integrated photonics technology, the requirements for precise control of spectral characteristics in on-chip optical information processing systems are becoming increasingly stringent. As a core passive integrated photonic device, the short-pass filter's core function is to allow short-wavelength optical signals to pass through while suppressing long-wavelength optical signals. It is crucial in pump light stripping, noise filtering, and band selection in multi-wavelength systems. Its performance directly determines the signal quality and system stability of high-performance photonic integrated chips (PICs), and is a key factor restricting the upgrade of photonic integrated systems.

[0003] Currently, most filters are fabricated based on top-layer silicon on SOI (silicon-on-insulator) substrates. However, filters based on top-layer silicon materials are no longer suitable for the core requirements of high frequency, wide bandwidth, and high sensitivity. Furthermore, the complex structural design, small fabrication tolerance, and high mass production difficulty of filters hinder industrialization. Most filters are designed for TE (Transverse Electric Mode), with a lack of research on TM (Transverse Magnetic Mode) broadband filtering. In pursuit of extremely high cutoff depth, insertion loss or flatness in the passband is often sacrificed. Simultaneously, the cutoff wavelength of traditional filters is fixed after fabrication and cannot be flexibly adjusted, limiting the applicability of devices in variable system environments. Summary of the Invention

[0004] In view of the shortcomings of the prior art described above, the purpose of this invention is to provide a TM mode short-pass filter to solve the problems of high filter loss and limited cutoff wavelength adjustment in the prior art.

[0005] To achieve the above and other related objectives, the present invention provides a TM mode short-pass filter, the TM mode short-pass filter comprising at least:

[0006] A waveguide region includes a first waveguide, a second waveguide, and a third waveguide that are sequentially contacted along the optical transmission direction. The second waveguide is located between the first waveguide and the third waveguide. In the direction perpendicular to the optical transmission direction, the width of the second waveguide is defined as W1. The first waveguide and the third waveguide are both trapezoidal structures. The ends of the first waveguide and the third waveguide that are closer to the second waveguide have the same width as the second waveguide. The ends of the first waveguide and the third waveguide that are farther from the second waveguide have the same width. The width of the ends of the first waveguide and the third waveguide that are farther from the second waveguide is greater than the width of the ends that are closer to the second waveguide.

[0007] A heating electrode is disposed on the side of the second waveguide, and the heating electrodes are symmetrically disposed on both sides of the second waveguide. The distance between the heating electrode and the second waveguide is greater than 1 μm.

[0008] Preferably, the waveguide region is made of lithium niobate or silicon nitride.

[0009] Preferably, when the waveguide region is made of lithium niobate, the waveguide region is a ridge waveguide structure; when the waveguide region is made of silicon nitride, the waveguide region is a strip waveguide structure.

[0010] Preferably, the cross-sectional shape of the second waveguide includes one of trapezoidal, rectangular, and square shapes.

[0011] Preferably, the height of the waveguide region ranges from 200nm to 800nm; along the optical transmission direction, the lengths of the first waveguide and the third waveguide both range from 30μm to 200μm.

[0012] Preferably, the angle between the sidewall and the bottom surface of the second waveguide is in the range of 60° to 90°.

[0013] Preferably, the second waveguide and the heating electrode have the same length along the light transmission direction; the heating electrode is made of one of gold, platinum, and titanium.

[0014] Preferably, in the TM mode short-pass filter, the lower cladding of the waveguide region is made of silicon dioxide, and the upper cladding is made of air.

[0015] Preferably, the second waveguide achieves the filtering of long-wavelength signals through mode cutoff effect. When the TM mode is transmitted in the waveguide, the distribution law of the effective refractive index of the TM mode is changed by adjusting the width W1. The cutoff depth and cutoff slope of the filter stopband are adjusted by changing the length of the second waveguide along the optical transmission direction.

[0016] As described above, the TM mode short-pass filter of the present invention has the following beneficial effects:

[0017] 1. This invention employs a three-segment variable-width waveguide design. This non-resonant structure significantly reduces the reliance on high-precision electron beam lithography (EBL) and deep ultraviolet (DUV) lithography processes, effectively improving the fabrication yield and uniformity of the device. The designed TM mode short-pass filter has a simple structure and high process tolerance, making it highly practical.

[0018] 2. The present invention adopts an adiabatic gradient structure, which can realize smooth energy transmission in the passband of TM mode. It has the advantages of low insertion loss and high passband flatness, ensuring high-fidelity transmission of optical signals and meeting the application requirements of future ultra-low loss integrated photonic chips.

[0019] 3. By adjusting the width W1 of the second waveguide, this invention can achieve extremely deep optical signal suppression within the stopband, thereby filtering out long-wavelength noise and pump light interference. Simultaneously, it allows for linear tuning of the cutoff wavelength over an ultra-wide range, covering multiple core communication bands such as O, C, and L.

[0020] 4. This invention integrates heating electrodes in the waveguide region and utilizes the thermo-optical effect of the heating electrodes to change the refractive index of the waveguide region, thereby achieving fine adjustment of the cutoff wavelength.

[0021] 5. The TM-mode integrated photonic short-pass filter described in this invention possesses excellent universality and mode specificity. Based on a lithium niobate or silicon nitride waveguide platform and combined with an optimized waveguide structure, the TM-mode integrated photonic short-pass filter achieves superior filtering characteristics through mode cutoff effects. It exhibits excellent optical transmission performance and a high extinction ratio. Attached Figure Description

[0022] Figure 1 The diagram shown is a schematic representation of the waveguide region in an embodiment of the present invention.

[0023] Figure 2 The diagram shown is a structural schematic of a TM mode short-pass filter according to Embodiment 1 of the present invention.

[0024] Figure 3 The image shows S21 transmission spectrum diagrams of second waveguides of different sizes in Embodiment 1 of the present invention.

[0025] Figure 4 The image shown is a magnified view of the transmission spectrum of the TM mode short-pass filter in the C-band in Embodiment 1 of the present invention.

[0026] Figure 5 The image shows transmission spectrum diagrams at different operating temperatures in Embodiment 1 of the present invention.

[0027] Figure 6 The diagram shown is a structural schematic of a TM mode short-pass filter according to Embodiment 2 of the present invention.

[0028] Figure 7 The image shows S21 transmission spectrum diagrams of second waveguides of different sizes in Embodiment 2 of the present invention.

[0029] Figure 8 The image shown is a magnified view of the transmission spectrum of the TM mode short-pass filter in the C-band in Embodiment 2 of the present invention.

[0030] Figure 9 The image shows transmission spectrum diagrams at different operating temperatures in Embodiment 2 of the present invention.

[0031] Component designation explanation

[0032] 100 waveguide region 110 First Waveguide 120 Second waveguide 130 Third waveguide 200 heating electrodes 300 substrate Detailed Implementation

[0033] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0034] Please see Figures 1 to 9 It should be noted that the illustrations provided in this embodiment are only schematic representations of the basic concept of the present invention. Therefore, the illustrations only show the components related to the present invention and are not drawn according to the actual number, shape and size of the components in the actual implementation. In the actual implementation, the form, quantity and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex.

[0035] In the TM mode short-pass filter of the present invention, the length of the waveguide region 100 is defined as along the optical transmission direction, the width is defined as along the direction perpendicular to the optical transmission in the top view plane, and the height is defined as along the direction perpendicular to the optical transmission on the cross section.

[0036] like Figure 1 and Figure 2 As shown, an embodiment of the present invention provides a TM mode short-pass filter, the TM mode short-pass filter comprising at least:

[0037] Waveguide region 100 includes a first waveguide 110, a second waveguide 120, and a third waveguide 130 that are sequentially contacted along the optical transmission direction. The second waveguide 120 is located between the first waveguide 110 and the third waveguide 130. In the direction perpendicular to the optical transmission direction, the width of the second waveguide 120 is defined as W1. The first waveguide 110 and the third waveguide 130 are both trapezoidal structures. The ends of the first waveguide 110 and the third waveguide 130 closest to the second waveguide 120 have the same width as the second waveguide 120. The ends of the first waveguide 110 and the third waveguide 130 furthest from the second waveguide 120 have the same width. The widths of the ends of the first waveguide 110 and the third waveguide 130 furthest from the second waveguide 120 are both greater than the widths of the ends closest to the second waveguide 120.

[0038] A heating electrode 200 is disposed on the side of the second waveguide 120. The heating electrodes 200 are symmetrically disposed on both sides of the second waveguide 120, and the distance between the heating electrode 200 and the second waveguide 120 is greater than 1 μm.

[0039] Specifically, the length of the second waveguide 120 is L1, the length of the first waveguide 110 is L2, and the length of the third waveguide 130 is L3. The end of the first waveguide 110 furthest from the second waveguide 120 is the widest point of the first waveguide 110, with a size of W2. The end of the third waveguide 130 furthest from the second waveguide 120 is the widest point of the third waveguide 130, with a size of W3. Both W2 and W3 are greater than W1.

[0040] In this embodiment, as Figure 1 As shown, the length of the first waveguide 110 is equal to the length of the third waveguide 130, and the length of both the first waveguide 110 and the third waveguide 130 is L2. The widths of the ends of the first waveguide 110 and the third waveguide 130 away from the second waveguide 120 are the same, and the widths of the ends of the first waveguide 110 and the third waveguide 130 away from the second waveguide 120 are both W2, where W1 is less than W2.

[0041] It should be noted that W2 and W3 are not limited here, and the specific settings depend on the required connecting elements.

[0042] As an example, the material of the waveguide region 100 may include lithium niobate or silicon nitride, but is not limited to these.

[0043] Specifically, lithium niobate and silicon nitride possess excellent modulation performance and a wide optical transparency window, which can effectively reduce optical transmission loss and improve the modulation efficiency and operating bandwidth of the device.

[0044] As an example, when the material of the waveguide region 100 is lithium niobate, the waveguide region 100 is a ridge waveguide structure; when the material of the waveguide region 100 is silicon nitride, the waveguide region 100 is a strip waveguide structure.

[0045] As an example, the height H1 of the waveguide region 100 ranges from 200nm to 800nm, such as 200nm, 300nm, 400nm, 500nm, 600nm, 700nm, 800nm, etc.

[0046] Specifically, when the material of the waveguide region 100 is lithium niobate, the height H1 of the waveguide region 100 is preferably in the range of 200nm~400nm; when the material of the waveguide region 100 is silicon nitride, the height H1 of the waveguide region 100 is preferably in the range of 600nm~800nm.

[0047] As an example, the lengths of the first waveguide 110 and the third waveguide 130 range from 30μm to 200μm, such as 30μm, 50μm, 100μm, 150μm, 200μm, etc.

[0048] Specifically, the lengths of the first waveguide 110 and the third waveguide 130 are set based on the difference between the width of the widest point of each end of the first waveguide 110 and the third waveguide 130 furthest from the second waveguide 120 and the width W1 of the second waveguide 120. The greater the difference between the width of the widest point of the corresponding ends of the first waveguide 110 and the third waveguide 130 and the width W1 of the second waveguide 120, the longer the lengths of the first waveguide 110 and the third waveguide 130 are set, to ensure stable and low-loss signal transmission in the waveguide region 100.

[0049] As an example, the angle α between the sidewall and bottom surface of the second waveguide 120 ranges from 60° to 90°.

[0050] Specifically, the angle between the sidewall and bottom surface of the second waveguide 120 (i.e., the sidewall tilt angle α) is set within the range of 60° to 90°. This ensures the structural stability and transmission performance of the second waveguide 120, while also guaranteeing the feasibility of the process and effectively avoiding problems such as decreased TM mode transmission efficiency due to an excessively small tilt angle. When the material of the waveguide region 100 is lithium niobate, the angle α between the sidewall and bottom surface of the second waveguide 120 ranges from 60° to 70°; when the material of the waveguide region 100 is silicon nitride, the angle α between the sidewall and bottom surface of the second waveguide 120 ranges from 80° to 90°.

[0051] As an example, specifically, the heating electrode 200 is used to heat the second waveguide 120, adjust the refractive index of the second waveguide 120 through the thermo-optic effect, thereby changing the transmission spectrum characteristics of the device, and finally achieving high-precision and fine-tuning of the cutoff wavelength.

[0052] As an example, the heating electrodes 200 are symmetrically arranged on both sides of the second waveguide 120.

[0053] Specifically, the heating electrodes 200 are mirror-symmetrically distributed on both sides of the second waveguide 120 in its width direction, with the central axis of the second waveguide 120 as the axis of symmetry. This ensures that the heating effect on the second waveguide 120 is uniformly distributed along its width direction, thereby maintaining a consistent temperature in the waveguide region 100 along its width. This enables uniform control of the refractive index of the waveguide region 100, effectively avoiding problems such as refractive index deviation and inaccurate cutoff wavelength adjustment caused by unilateral heating, thus ensuring the accuracy of the device in cutoff wavelength control and the stability of transmission.

[0054] As an example, the distance between the heating electrode 200 and the second waveguide 120 is greater than 1 μm.

[0055] Specifically, the distance between the heating electrode 200 and the second waveguide 120 is set to be greater than 1 μm, which can effectively avoid the absorption effect of the heating electrode 200 on the transmitted signal in the waveguide region 100, avoid additional propagation loss in the waveguide region 100 due to the absorption of the heating electrode 200, ensure the transmission efficiency of the signal in the waveguide region 100, and ensure the stability and reliability of the transmission performance during the fine adjustment of the device cutoff wavelength.

[0056] As an example, the second waveguide 120 and the heating electrode 200 have the same length, but the length of the heating electrode 200 may be longer or shorter than that of the second waveguide 120.

[0057] As an example, the material of the heating electrode 200 includes, but is not limited to, gold, platinum, and titanium.

[0058] As an example, the TM mode short-pass filter also includes a substrate 300.

[0059] As an example, the substrate 300 may include silicon oxide, but is not limited thereto. In this embodiment, the substrate 300 is preferably silicon oxide.

[0060] As an example, in the TM mode short-pass filter, the lower cladding of the waveguide region 100 is made of silicon dioxide, and the upper cladding is made of air.

[0061] Specifically, the TM mode short-pass filter is disposed on the surface of the substrate 300, which may include silicon dioxide. The waveguide region 100 is located in the middle of the silicon dioxide, and no covering layer is disposed above the waveguide region 100, which is directly exposed to the air. This forms a cladding of the waveguide region 100 with a high refractive index difference, thereby enhancing the ability to confine the TM mode and maintaining the efficient transmission of the waveguide region 100. Furthermore, it simplifies the device fabrication process, reduces process complexity and cost, and avoids interference from the covering layer on the transmission of the waveguide region 100, ensuring the working performance of the TM mode short-pass filter.

[0062] As an example, the second waveguide 120 achieves the filtering of long-wavelength signals through the mode cutoff effect. When the TM mode is transmitted in the waveguide, the distribution law of the effective refractive index of the TM mode is changed by adjusting the width W1. The cutoff depth and cutoff slope of the filter stopband are adjusted by changing the length of the second waveguide 120 along the light transmission direction.

[0063] Specifically, the second waveguide 120 is used to filter out long-wavelength signals through mode cutoff effect, and the effective refractive index n of the TM mode propagating in the waveguide is... eff Depending on the waveguide geometry and the operating wavelength λ, the dispersion relation n is satisfied. eff =f(W1,λ). For a given waveguide structure, as the operating wavelength λ increases, n eff It decreases accordingly; when n eff Reduce to a refractive index n close to that of the substrate 300 sub When n meets the cutoff condition: eff (W1,λ)≈n sub When the cutoff condition is met, the corresponding wavelength is the cutoff wavelength λ. c Because n eff The waveguide width W1 is extremely sensitive; therefore, during device fabrication, the size of W1 can be changed to alter the value of n. eff The distribution pattern is determined to achieve the cutoff wavelength λ. c The design is preset within a range of several hundred nanometers; at the same time, by increasing the length L1 of the second waveguide 120 by design, a greater cutoff depth and a steeper cutoff slope can be achieved for the stopband, thereby improving the filtering performance of long-wavelength signals.

[0064] Example 1

[0065] The structure provided in this embodiment is based on the TM mode short-pass filter described above. Its related structural composition, connection relationships, material selection, and basic working principle can be found in the detailed descriptions of the corresponding sections above, and will not be repeated here. This embodiment uses a lithium niobate short-pass filter as an example.

[0066] In this embodiment, the TM mode short-pass filter is fabricated based on a Z-cut lithium niobate platform. Figure 1 and Figure 2 As shown, the waveguide region 100 has a ridge waveguide structure, and the bottom of the waveguide region 100 also has unetched lithium niobate with a height of H2. The second waveguide 120 has a width of W1 and a length of L1. The first waveguide 110 and the third waveguide 130 have a linearly tapered trapezoidal structure. The width of the end of the first waveguide 110 and the third waveguide 130 away from the second waveguide 120 is W2, where W1 is less than W2. The heating electrode 200 is symmetrically deposited on both sides of the second waveguide 120, and the heating electrode 200 is located on the surface of the unetched lithium niobate.

[0067] Specifically, the height H1 of the lithium niobate waveguide region ranges from 200 nm to 400 nm, and the height H2 of the unetched lithium niobate ranges from 0 nm to 400 nm. The sidewall tilt angle α of the lithium niobate waveguide region ranges from 60° to 70°.

[0068] In this embodiment, the height H1 of the lithium niobate waveguide region 100 is preferably 300 nm, and the sidewall tilt angle α of the lithium niobate waveguide region 100 is preferably 65°.

[0069] It should be noted that the height H2 of the unetched lithium niobate is set according to actual needs and is not limited here.

[0070] In this embodiment, a lithium niobate short-pass filter is disposed on the surface of a silicon dioxide substrate 300, with the top of the lithium niobate short-pass filter exposed to air, thereby forming a waveguide region 100 cladding with a high refractive index difference to enhance the confinement capability of TM modes and maintain the efficient transmission of the waveguide region 100.

[0071] In this embodiment, simulation results are as follows: Figure 3 As shown, by adjusting the ridge width W1 of the second waveguide 120 to between 1.2 μm and 1.7 μm, the waveguide region 100 can produce different short-pass cutoff effects for TM polarized light in the 1.2 μm to 1.8 μm band. In this way, the short-pass cutoff wavelength can be controlled by adjusting the width W1 of the second waveguide 120.

[0072] In this embodiment, the narrowest part of the gradient portion of the first waveguide 110 and the third waveguide 130 is aligned with the ridge width W1 of the second waveguide 120, and the widest part W2 is set according to the access element to ensure that the optical field can be transmitted in the form of the fundamental mode with low loss within this segment, avoiding light scattering loss caused by abrupt changes in waveguide width, and further improving the signal transmission efficiency and filtering performance of the TM mode short-pass filter.

[0073] In this embodiment, the length L1 of the second waveguide 120 is further set to 1800 μm, which is sufficient to ensure that long-wavelength components are sufficiently attenuated in the cutoff section, thereby increasing the cutoff depth. The lengths L2 of the first waveguide 110 and the third waveguide 130 are both 100 μm, which conforms to the adiabatic gradient criterion and can effectively suppress inter-mode crosstalk.

[0074] In this embodiment, the lithium niobate short-pass filter designed covers the O, C, and L bands, with corresponding widths W1 of 1.2 μm, 1.5 μm, and 1.6 μm for the second waveguide 120, respectively. It exhibits outstanding overall performance in the C band, such as... Figure 4 As shown, the passband insertion loss is as low as 0.03 dB, the flatness is better than 0.05 dB, the cutoff depth is more than 20 dB, and a cutoff slope of 0.1983 dB / nm is achieved.

[0075] In this embodiment, to achieve dynamic and precise wavelength coverage, the heating electrode 200 is a Ti electrode. The Ti electrode is 1 μm away from the edge of the second waveguide 120; this spacing effectively avoids additional absorption losses introduced by the metal layer. The Ti electrode has a height of 200 nm, and the cutoff wavelength can be finely adjusted by the thermo-optical effect generated by applying voltage. Figure 5 As shown, under temperature control of 300K~600K, the 3dB wavelength shift range is 1582nm~1599nm, and the average thermal tuning efficiency is 5.4nm / 100K.

[0076] Example 2

[0077] The structure provided in this embodiment is based on the TM mode short-pass filter described above. Its related structural composition, connection relationships, material selection, and basic working principle can be found in the detailed descriptions of the corresponding sections above, and will not be repeated here. This embodiment uses a silicon nitride short-pass filter as an example.

[0078] In this embodiment, the TM mode short-pass filter is fabricated based on a silicon nitride platform. For example... Figure 1 and Figure 6 As shown, the waveguide region 100 adopts a strip waveguide structure. The width of the second waveguide 120 is W1, and the length is L1. The first waveguide 110 and the third waveguide 130 have a linearly tapered trapezoidal structure. The width of the end of the first waveguide 110 and the third waveguide 130 away from the second waveguide 120 is W2, where W1 is less than W2. The heating electrodes 200 are symmetrically deposited on both sides of the second waveguide 120. In this embodiment, the structural division along the light transmission direction is consistent with that in Embodiment 1, but the size parameters are optimized for the difference in material refractive index.

[0079] Specifically, the height H1 of the silicon nitride waveguide region 100 ranges from 600 nm to 800 nm, and the sidewall tilt angle α of the silicon nitride waveguide region 100 ranges from 80° to 90°.

[0080] In this embodiment, the height H1 of the silicon nitride waveguide region is preferably 700 nm, and the sidewall tilt angle of the silicon nitride waveguide region is preferably 85°.

[0081] In this embodiment, a silicon nitride short-pass filter is disposed on the surface of the silicon dioxide substrate 300, with the top of the silicon nitride short-pass filter exposed to air, thereby forming a cladding of the waveguide region 100 with a high refractive index difference to enhance the confinement capability of the TM mode and maintain the efficient transmission of the waveguide region 100. The heating electrode 200 is also located on the surface of the silicon dioxide substrate 300.

[0082] In this embodiment, simulation results are as follows: Figure 7As shown, by adjusting the width W1 of the second waveguide 120 to between 0.3 μm and 0.7 μm, different short-pass cutoff effects can be generated for TM polarized light in the 1.2 μm to 2.0 μm band corresponding to the waveguide region 100; thus, the short-pass cutoff wavelength can be controlled by adjusting the width W1 of the second waveguide 120.

[0083] In this embodiment, the narrowest part of the gradient portion of the first waveguide 110 and the third waveguide 130 is aligned with the ridge width W1 of the second waveguide 120, and the widest part W2 is set according to the access element; to ensure that the optical field can be transmitted in the form of the fundamental mode with low loss within this segment, avoid light scattering loss caused by abrupt changes in waveguide width, and further improve the signal transmission efficiency and filtering performance of the TM mode short-pass filter.

[0084] In this embodiment, the length L1 of the second waveguide 120 is 200 μm, which is sufficient to ensure that long-wavelength components are sufficiently attenuated in the cutoff section, thereby increasing the cutoff depth. The length L2 of the first waveguide 110 and the third waveguide 130 is 150 μm, which conforms to the adiabatic gradient criterion and can effectively suppress inter-mode crosstalk.

[0085] In this embodiment, the silicon nitride short-pass filter designed in this embodiment covers the O, C, and L bands. Among them, it exhibits superior performance in the C band. In the C band, the width W1 of the second waveguide 120 is 0.45μm. Figure 8 As shown, the passband insertion loss is only 0.04dB, the passband flatness is 0.06dB, the maximum cutoff depth is close to 70dB, and the cutoff slope is 0.4090dB / nm.

[0086] In this embodiment, the heating electrode 200 is a Ti electrode, and the structural parameters of the heating electrode 200 are the same as in Embodiment 1. Figure 9 As stated, under temperature control of 300K~600K, the 3dB wavelength shift range is 1577nm~1592nm, and the average thermal regulation efficiency is 5.0nm / 100K.

[0087] In summary, this invention provides a TM mode short-pass filter. By employing a three-segment variable-width waveguide region and an adiabatic gradient structure design, it achieves smooth energy transmission in the TM mode within the passband, ensuring low passband insertion loss while achieving a high cutoff depth, guaranteeing adiabatic optical field transmission, and significantly improving passband flatness. By adjusting the width of the second waveguide, linear tuning of the cutoff wavelength can be achieved over an ultra-wide range, covering multiple communication bands. Furthermore, by integrating heating electrodes on both sides of the waveguide region, the refractive index of the waveguide region is controlled using the thermo-optic effect, enabling fine adjustment of the cutoff wavelength. This invention has a simple structure and excellent thermal tuning performance, exhibiting significant technical advantages in applications such as on-chip pump light stripping and noise filtering. Therefore, this invention effectively overcomes the various shortcomings of existing technologies and has high industrial applicability.

[0088] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A TM mode short-pass filter, characterized in that, The TM mode short-pass filter includes at least: A waveguide region includes a first waveguide, a second waveguide, and a third waveguide that are sequentially contacted along the optical transmission direction. The second waveguide is located between the first waveguide and the third waveguide. In the direction perpendicular to the optical transmission direction, the width of the second waveguide is defined as W1. The first waveguide and the third waveguide are both trapezoidal structures. The ends of the first waveguide and the third waveguide that are closer to the second waveguide have the same width as the second waveguide. The ends of the first waveguide and the third waveguide that are farther from the second waveguide have the same width. The width of the ends of the first waveguide and the third waveguide that are farther from the second waveguide is greater than the width of the ends that are closer to the second waveguide. The waveguide region is made of lithium niobate or silicon nitride. When the waveguide region is made of lithium niobate, it is a ridge waveguide structure, wherein the ridge bottom width W1 of the second waveguide is 1.2 mm to 1.7 mm. When the waveguide region is made of silicon nitride, it is a strip waveguide structure, wherein the width W1 of the second waveguide is 0.3 mm to 0.7 mm. A heating electrode is disposed on the side of the second waveguide. The heating electrodes are symmetrically disposed on both sides of the second waveguide, and the distance between the heating electrode and the second waveguide is greater than 1 mm.

2. The TM mode short-pass filter according to claim 1, characterized in that: The cross-sectional shape of the second waveguide includes one of trapezoidal, rectangular, or square shapes.

3. The TM mode short-pass filter according to claim 1, characterized in that: The height of the waveguide region ranges from 200nm to 800nm; along the optical transmission direction, the lengths of the first waveguide and the third waveguide both range from 30mm to 200mm.

4. The TM mode short-pass filter according to claim 1, characterized in that: The angle between the sidewall and bottom surface of the second waveguide ranges from 60° to 90°.

5. The TM mode short-pass filter according to claim 1, characterized in that: Along the direction of light transmission, the second waveguide and the heating electrode have the same length; the heating electrode is made of one of gold, platinum, and titanium.

6. The TM mode short-pass filter according to claim 1, characterized in that: In the TM mode short-pass filter, the lower cladding of the waveguide region is made of silicon dioxide, and the upper cladding is made of air.

7. The TM mode short-pass filter according to claim 1, characterized in that: The second waveguide filters out long-wavelength signals through mode cutoff effect. When the TM mode is transmitted in the waveguide, the distribution law of the effective refractive index of the TM mode is changed by adjusting the width W1. The cutoff depth and cutoff slope of the filter stopband are adjusted by changing the length of the second waveguide along the optical transmission direction.

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