High-order mode filter and preparation method thereof

Abstract

The invention provides a high-order mode filter and a preparation method thereof. The high-order mode filter comprises a substrate, a flat plate groove, a first stray light absorption region and a reflection region, wherein the substrate comprises a base, an insulating layer and a semiconductor top layer which are arranged in sequence; the flat plate grooves are arranged in the semiconductor top layer at intervals, and a ridge waveguide is formed between every two adjacent flat plate grooves; the first stray light absorption areas are distributed in the semiconductor top layer on the two sides of the ridge waveguide and are used for absorbing stray light in incident light; the reflection areas are arranged in the flat plate grooves in the two sides of the ridge waveguide, an inclination angle is formed between the length direction of the reflection areas and the light propagation direction in the ridge waveguide, the inclination angle is smaller than 90 degrees, and the reflection areas are used for reflecting light emitted from the outer sides of the reflection areas to the ridge waveguide. The stray light reflected by the side wall of the flat plate groove can be blocked to a great extent, the stray light is prevented from entering the waveguide again, and attenuation of stray light is greatly increased.

Description

Technical Field

[0001] The invention belongs to the technical field of integrated optical device design and manufacturing, and in particular relates to a high-order mode filter and a preparation method thereof. Background Art

[0002] In today's optical communication and photonic integration fields, as technology develops towards higher performance and smaller size, photonic integrated chips (PICs) play a core role. Photonic integrated chips are designed to integrate multiple optical functional devices on a single chip to achieve complex and efficient optical signal processing.

[0003] In the process of optical signal transmission, waveguide, as the transmission channel of optical signals, will inevitably introduce high-order mode optical signals. The existence of these high-order mode optical signals has many adverse effects on the performance of optical devices on photonic integrated chips. On the one hand, high-order mode optical signals will cause obvious fluctuations in the transmission light spectrum, which will reduce the spectral purity of the optical signal and make it difficult to meet some application scenarios with strict requirements on spectral accuracy, such as high-resolution spectral analysis and precision optical sensing. On the other hand, more critically, the interference of high-order mode optical signals will cause unstable output power. In practical applications such as optical communication links and optical sensing systems, stable output power is a basic requirement to ensure the reliable operation of the system. Unstable power output may cause serious consequences such as signal misjudgment and communication interruption.

[0004] To solve this problem, high-order mode filters (HOMF) came into being. Its core function is to accurately eliminate high-order mode optical signals from the waveguide, thereby ensuring that the optical devices on the photonic integrated chip can work in a relatively stable light environment and minimize the fluctuations in the transmitted light spectrum and stable output power. However, the traditional high-order mode filters in the prior art have significant defects. After a large number of experiments and feedback from practical applications, traditional high-order mode filters can only provide a very limited attenuation capability of 20dB / mm. This means that when facing complex photonic integrated chip applications with extremely high power stability requirements, such a low attenuation level is far from meeting the power stability specification requirements set by the system. For example, in some optical sensing devices with high precision requirements, even a slight change in the optical signal may cause deviations in the detection results, and traditional high-order mode filters are difficult to effectively filter out the power fluctuations caused by high-order mode optical signals, which greatly limits the detection accuracy and reliability improvement of such equipment. Similarly, in the optical transmitting and receiving modules of long-distance optical communications, the accumulated high-order mode interference is easily caused by insufficient attenuation of traditional filters, which can easily cause signal degradation and reduce communication quality. In summary, in order to meet the growing demand for high-performance photonic integrated chip applications, it is necessary to develop a high-order mode filter with higher attenuation performance.

[0005] It should be noted that the above introduction to the technical background is only for the convenience of providing a clear and complete description of the technical solutions of the present application and for the convenience of understanding by those skilled in the art. It cannot be considered that the above technical solutions are well known to those skilled in the art simply because they are described in the background technology section of the present application. Summary of the invention

[0006] In view of the above-mentioned shortcomings of the prior art, an object of the present invention is to provide a high-order mode filter and a preparation method thereof, so as to solve the problem of insufficient attenuation performance of the high-order mode filter in the prior art.

[0007] To achieve the above-mentioned purpose and other related purposes, the present invention provides a high-order mode filter, which includes: a substrate, including a base, an insulating layer and a semiconductor top layer arranged in sequence; a plate groove, which is arranged at intervals in the semiconductor top layer, and a ridge waveguide is formed between two adjacent plate grooves; a first stray light absorption region, which is distributed in the semiconductor top layer on both sides of the ridge waveguide and is used to absorb stray light in the incident light; a reflection region, which is arranged in the plate grooves on both sides of the ridge waveguide, and the length direction of the reflection region has an inclination angle with the light propagation direction in the ridge waveguide, and the inclination angle is less than 90 degrees, and is used to reflect the light incident from the outside of the reflection region to the ridge waveguide.

[0008] Optionally, the reflection area is configured as a reflection groove, the reflection groove is configured in the slab grooves on both sides of the ridge waveguide, and the reflection groove extends from the bottom surface of the slab groove to the inside of the substrate.

[0009] Optionally, the depth of the reflective groove is greater than or equal to the depth of the first stray light absorption region, and the depth of the reflective groove is less than or equal to the thickness of the semiconductor top layer.

[0010] Optionally, the filler of the reflective groove includes one of air and silicon dioxide.

[0011] Optionally, the high-order mode filter includes a plurality of reflection regions, and the plurality of reflection regions are configured to be arranged at intervals along a light propagation direction in the ridge waveguide.

[0012] Optionally, the inclination angles corresponding to the multiple reflection areas are equal.

[0013] Optionally, the ratio of the projection length of the reflection area in the width direction of the slab groove to the width of the slab groove is 0.5-1.

[0014] Optionally, the inclination angle is 20 degrees to 85 degrees.

[0015] Optionally, the width of the plate groove is 10 micrometers to 50 micrometers, and the width of the first stray light absorption area is 15 micrometers to 60 micrometers.

[0016] Optionally, the high-order mode filter further includes a second stray light absorption region, the second stray light absorption region is arranged in the first stray light absorption region, and the doping concentration of the second stray light absorption region is greater than the doping concentration of the first stray light absorption region.

[0017] Optionally, the dopants of the first stray light absorption region and the second stray light absorption region include one of boron, arsenic, boron difluoride, phosphorus and antimony, and the doping concentration of the first stray light absorption region is 1×10 18 / cm 3 ~5×10 19 / cm 3 , the doping concentration of the second stray light absorption region is 5×10 18 / cm 3 ~1×10 20 / cm 3 .

[0018] The present invention also provides a photonic integrated chip, which includes a high-order mode filter according to any one of the above solutions.

[0019] The present invention also provides a method for preparing a high-order mode filter, the preparation method comprising: providing a substrate, the substrate comprising a base, an insulating layer and a semiconductor top layer arranged in sequence; forming a first stray light absorption region arranged at intervals in the semiconductor top layer, for absorbing stray light in incident light; etching a planar groove arranged at intervals in the semiconductor top layer, forming a ridge waveguide between two adjacent planar grooves, the ridge waveguide being located between two adjacent first stray light absorption regions; forming a reflection region in the planar grooves on both sides of the ridge waveguide, the length direction of the reflection region having an inclination angle with the light propagation direction in the ridge waveguide, the inclination angle being less than 90 degrees, for reflecting light incident from the outside of the reflection region toward the ridge waveguide.

[0020] Optionally, forming a reflective area in the slab grooves on both sides of the ridge waveguide includes: defining the reflective area pattern by a photolithography process; etching the semiconductor top layer based on the reflective area pattern to form reflective grooves in the slab grooves on both sides of the ridge waveguide, the reflective grooves extending from the bottom surface of the slab groove to the inside of the substrate, and the depth of the reflective grooves is less than or equal to the thickness of the semiconductor top layer.

[0021] Optionally, there are multiple reflection area patterns defined by the photolithography process, and the multiple reflection area patterns are configured to be arranged at intervals along the light propagation direction in the ridge waveguide. The semiconductor top layer is etched based on the reflection area patterns to form multiple reflection grooves in the flat plate grooves on both sides of the ridge waveguide.

[0022] Optionally, the inclination angles corresponding to the multiple reflective grooves are equal.

[0023] Optionally, the preparation method further comprises the step of: filling silicon dioxide in the reflective groove.

[0024] Optionally, the ratio of the projection length of the reflective groove in the width direction of the slab groove to the width of the slab groove is 0.5-1.

[0025] Optionally, the inclination angle is 20 degrees to 85 degrees.

[0026] Optionally, the width of the plate groove is 10 micrometers to 50 micrometers, and the width of the first stray light absorption area is 15 micrometers to 60 micrometers.

[0027] Optionally, a second stray light absorption region is formed in the first stray light absorption region by an ion implantation process, the doping concentration of the second stray light absorption region is greater than the doping concentration of the first stray light absorption region, the dopants of the first stray light absorption region and the second stray light absorption region include one of boron, arsenic, boron difluoride, phosphorus and antimony, and the doping concentration of the first stray light absorption region is 1×10 18 / cm 3 ~5×10 19 / cm 3 , the doping concentration of the second stray light absorption region is 5×10 18 / cm 3 ~1×10 20 / cm 3 .

[0028] As described above, the high-order mode filter and the preparation method thereof of the present invention have the following beneficial effects:

[0029] The present invention designs reflection areas on both sides of the ridge waveguide, and the length direction of the reflection area has an inclined angle with the light propagation direction in the ridge waveguide. The reflection area can reflect the light incident from the outside of the reflection area toward the ridge waveguide, especially can block the stray light reflected by the side wall of the flat groove to a great extent, and prevent the stray light from re-entering the waveguide.

[0030] The present invention can further increase the absorption of stray light by designing a highly doped second stray light absorption region in the plate groove region, thereby greatly increasing the attenuation of stray light.

[0031] The high-order mode filter of the present invention is crucial to reducing the harmful effects of high-order modes in complex photonic circuits. The design of the reflective zone of the present invention effectively eliminates the downstream propagation of high-order modes and avoids the interaction between high-order modes and fundamental modes, so that the wavelength and temperature of the integrated photonic chip have better power stability. The attenuation of the high-order mode filter of the present invention is greater than 40dB / mm, which is two orders of magnitude higher than the traditional filter design, so that the integrated photonic chip has a higher signal-to-noise ratio, thereby greatly improving the sensitivity of the integrated photonic chip.

[0032] The high-order mode filter of the present invention is compatible with traditional process flows and can be combined with a doping process to achieve further attenuation, and has a good application basis and a wide range of applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The included drawings are used to provide a further understanding of the embodiments of the present application, which constitute a part of the specification, are used to illustrate the implementation of the present application, and together with the text description, explain the principles of the present application. Obviously, the drawings described below are only some embodiments of the present application.

[0034] Figure 1 to Figure 4 It is a schematic structural diagram showing each step of the method for preparing a high-order mode filter according to an embodiment of the present invention, Figure 1 to Figure 4 The diagrams include a top view (above) and a cross-sectional view at A-A', wherein: Figure 3 It is a schematic diagram showing the structure of a high-order mode filter provided with a reflection area according to an embodiment of the present invention, Figure 4 Shown is a schematic structural diagram of a high-order mode filter provided with a reflection region and a high-concentration stray light absorption region according to an embodiment of the present invention.

[0035] Figure 5 A schematic diagram of the optical signal path for a conventional high-order mode filter structure is shown.

[0036] Figure 6 Shown is a schematic diagram of an optical signal path of a high-order mode filter structure according to an embodiment of the present invention.

[0037] Component number description

[0038] 101 Base

[0039] 102 insulation layer

[0040] 103 semiconductor top

[0041] 104 first stray light absorption area

[0042] 105 flat plate groove

[0043] 106 Ridge Waveguide

[0044] 107 Reflection groove

[0045] 108 Second stray light absorption area

[0046] 201 light signal

[0047] 202 reflected light DETAILED DESCRIPTION

[0048] The following describes the embodiments of the present invention through specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention.

[0049] It should be emphasized that the term “include / comprises” when used herein refers to the presence of features, integers, steps or components, but does not exclude the presence or addition of one or more other features, integers, steps or components.

[0050] Features described and / or illustrated with respect to one embodiment may be used in the same or similar manner in one or more other embodiments, combined with features in other embodiments, or substituted for features in other embodiments.

[0051] For example, when describing the embodiments of the present invention in detail, for the sake of convenience, the cross-sectional view showing the device structure will not be partially enlarged according to the general scale, and the schematic view is only an example, which should not limit the scope of protection of the present invention. In addition, in actual production, the three-dimensional space dimensions of length, width and depth should be included.

[0052] For ease of description, spatially relative terms such as "under", "below", "below", "below", "above", "on", etc. may be used herein to describe the relationship of one element or feature shown in the drawings to other elements or features. It will be understood that these spatially relative terms are intended to encompass other orientations of the device in use or operation in addition to the orientation depicted in the drawings. In addition, when a layer is referred to as being "between" two layers, it can be the only layer between the two layers, or one or more intervening layers may also be present.

[0053] In the context of the present application, a structure in which a first feature is described as being "above" a second feature may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features are formed between the first and second features, such that the first and second features may not be in direct contact.

[0054] It should be noted that the illustrations provided in this embodiment are only used to illustrate the basic concept of the present invention in a schematic manner, and therefore the illustrations only show components related to the present invention rather than being drawn according to the number, shape and size of components in actual implementation. In actual implementation, the type, quantity and proportion of each component may be changed arbitrarily, and the component layout may also be more complicated.

[0055] like Figure 3 As shown, Figure 3Including a top view structure diagram of a high-order mode filter (upper figure) and a cross-sectional structure diagram at AA (lower figure), this embodiment provides a high-order mode filter, the high-order mode filter includes: a substrate, a planar groove 105, a first stray light absorption region 104 and a reflection region.

[0056] like Figure 3 As shown, the substrate may include a base 101 , an insulating layer 102 and a semiconductor top layer 103 which are arranged in sequence.

[0057] In one embodiment, the substrate 101 may be a silicon substrate, a germanium substrate, a silicon germanium substrate, a silicon carbide substrate, etc., the insulating layer 102 may be an appropriate dielectric layer, such as a silicon dioxide layer, and the semiconductor top layer 103 may be a silicon top layer. The thickness of the silicon top layer may be 2.5 microns to 5 microns, etc., and may be specifically 3 microns.

[0058] like Figure 3 As shown, the slab trenches 105 are arranged at intervals in the semiconductor top layer 103 , and a ridge waveguide 106 is formed between two adjacent slab trenches 105 .

[0059] In one embodiment, the width z of the slab groove 105 can be 10 microns to 50 microns, and the depth of the slab groove 105 can be 1.1 microns to 1.3 microns. The depth of the slab groove 105 can be set according to the required thickness of the ridge waveguide 106, and is not limited to the examples listed here. The shape of the slab groove 105 can be adjusted according to the required shape of the ridge waveguide 106. For example, when the ridge waveguide 106 is a rectangular waveguide, the slab groove 105 can be set as a rectangular groove so that a rectangular waveguide is constructed between adjacent slab grooves 105; and when the ridge waveguide 106 is tapered, the slab groove 105 can be set as a trapezoid so that a tapered waveguide is constructed between adjacent slab grooves 105.

[0060] like Figure 3 As shown, the first stray light absorption regions 104 are spaced apart in the semiconductor top layer 103 on both sides of the ridge waveguide 106 for absorbing stray light in the incident light. The first stray light absorption regions 104 may be continuously distributed or discontinuously distributed in the extension direction of the ridge waveguide 106. In the present embodiment, the first stray light absorption regions 104 are arranged to be continuously distributed in the extension direction of the ridge waveguide 106.

[0061] In one embodiment, the dopant of the first stray light absorption region 104 includes one of boron, arsenic, boron difluoride, phosphorus and antimony. The specific dopant may depend on design requirements, such as the wavelength of light to be absorbed.

[0062] Specifically, the size of the pattern of the first stray light absorption region 104 can be adjusted according to the width of the slab groove 105 of the ridge waveguide 106 used. For a slab groove 105 with a width between 10 μm and 50 μm, the width of the first stray light absorption region 104 can be between 15 μm and 60 μm, and the depth of the first stray light absorption region 104 can be between 2.5 μm and 3 μm. In this embodiment, the doping concentration of the first stray light absorption region is 1×10 18 / cm 3 ~5×10 19 / cm 3 .

[0063] like Figure 3 As shown, the reflection area is arranged in the plate groove 105 on both sides of the ridge waveguide 106, and the length direction of the reflection area has an inclination angle with the light propagation direction in the ridge waveguide 106, and the inclination angle θ is less than 90 degrees, which is used to reflect the light incident from the outside of the reflection area to the ridge waveguide 106. In one embodiment, the inclination angle θ is 20 degrees to 85 degrees, and preferably can be 30 degrees.

[0064] In one embodiment, the reflection area is set as a reflection groove 107, which is set in the plate groove 105 on both sides of the ridge waveguide 106, and the reflection groove 107 extends from the bottom surface of the plate groove 105 to the inside of the substrate. The depth of the reflection groove 107 is less than or equal to the thickness of the semiconductor top layer 103 to avoid damage to the insulating layer 102. For example, the depth of the reflection groove 107 can be between 2.5 microns and 3 microns. The ratio of the projection length of the reflection area in the width direction of the plate groove 105 to the width of the plate groove 105 is 0.5 to 1, that is, the width of the reflection groove 107 can be designed to cover most of the width of the plate groove 105 as much as possible to increase its probability of reflecting stray light. For a plate groove 105 with a width between 10 microns and 50 microns, the actual length of the reflection groove 107 can be between 10 microns and 100 microns. The width of the reflection groove 107 can be between 3 microns and 10 microns. Since there is a large difference in refractive index between the semiconductor top layer 103 on one side of the reflective groove 107 and the filler (such as air or silicon dioxide) in the emission groove, on the one hand, when the stray light or high-order mode from the outside is irradiated or emitted from the outer wall of the plate groove 105 to the reflective groove 107, the stray light or high-order mode will be reflected on the side wall of the reflective groove 107, thereby preventing the stray light or high-order mode from entering the ridge waveguide 106, thereby greatly improving the attenuation of the stray light or high-order mode. On the other hand, when the stray light or high-order mode moves out of the waveguide and irradiates the inner side of the reflective groove 107, it can be reflected multiple times on the side walls of the adjacent reflective grooves 107, and finally moves out to the outer side of the reflective groove 107, further improving the attenuation of the stray light or high-order mode.

[0065] In one embodiment, the reflective groove 107 may be a rectangular groove, an inverted trapezoidal groove, a U-shaped groove, a V-shaped groove, etc., and may be set according to design requirements or process requirements, and is not limited to the examples listed here.

[0066] In one embodiment, the filler of the reflective groove 107 includes one of air and silicon dioxide. The refractive index of air and silicon dioxide is relatively low, which can effectively increase the total reflection probability of the sidewall of the reflective groove 107, thereby increasing the reflectivity of the reflective groove 107 to stray light or high-order modes. Of course, the filler can also be other low-refractive-index dielectric materials, and is not limited to the examples listed here.

[0067] In one embodiment, the high-order mode filter includes a plurality of reflection regions, and the plurality of reflection regions are configured to be arranged at intervals along the light propagation direction in the ridge waveguide 106. The tilt angles θ corresponding to the plurality of reflection regions may be equal, that is, the length directions of the plurality of reflection regions are parallel to each other, which simplifies the design and manufacturing process while ensuring the reflection probability of the plurality of reflection regions for stray light or high-order modes. Alternatively, the tilt angles θ corresponding to the plurality of reflection regions are configured to gradually decrease along the light propagation direction in the ridge waveguide 106, so as to increase the reflection probability of subsequent reflection regions for stray light or high-order modes from the outside. Of course, in other examples, the tilt angle θ rule of the plurality of reflection regions may be designed according to actual conditions, and is not limited to the examples listed here.

[0068] like Figure 4 As shown, the high-order mode filter may further include a second stray light absorption region 108 , which is disposed in the first stray light absorption region 104 , and the doping concentration of the second stray light absorption region 108 is greater than the doping concentration of the first stray light absorption region 104 .

[0069] In one embodiment, the second stray light absorption region 108 is arranged to surround the inner and outer sides of the reflection region, so as to facilitate the subsequent absorption of stray light incident or reflected from the inner and outer sides of the reflection region.

[0070] In one embodiment, the dopant of the second stray light absorption region 108 includes one of boron, arsenic, boron difluoride, phosphorus and antimony.

[0071] The absorption of stray light increases exponentially with the doping concentration. The higher the doping concentration, the more significant the suppression effect on stray light. However, when the doping concentration is higher than the threshold of about 5×1018 / cm 3 When the doping concentration is 5×10 , the stray light absorption begins to deviate from the exponential relationship. The reason is that the doping concentration causes the refractive index perturbation of the semiconductor top layer 103, which causes the stray light to be reflected back into the waveguide. In one embodiment, the doping concentration of the second stray light absorption region is 5×10 18 / cm3 ~1×10 20 / cm 3 , so that the second stray light absorption zone 108 has a strong absorption of the stray light and / or the high-order mode entering its region. In general, even if the second stray light absorption zone 108 and the first stray light absorption zone 104 have a certain reflection at their interface due to the difference in refractive index, however, since the actual difference in refractive index between the second stray light absorption zone 108 and the first stray light absorption zone 104 is not too large, the probability of total reflection at the interface is small, and therefore, most of the stray light or high-order mode can still enter the second stray light absorption zone 108 and be absorbed by the second stray light absorption zone 108. The depth of the second stray light absorption zone 108 can be set to be less than half or less than one-third of the depth of the first stray light absorption zone 104, etc., and can be set according to actual design requirements. In some embodiments, a concentration gradient zone or a concentration gradient zone may be provided between the second stray light absorption zone 108 and the first stray light absorption zone 104, and the doping concentration of the concentration gradient zone or the concentration gradient zone may gradually increase from the first stray light absorption zone 104 toward the second stray light absorption zone 108, thereby avoiding further increase of stray light and high-order modes entering the second stray light absorption zone 108 from the first stray light absorption zone 104.

[0072] This embodiment also provides a photon integrated chip, which includes the high-order mode filter of the above embodiment. The photon integrated chip may also include other optical components, such as a photodetector, an avalanche photodiode, an optical waveguide, an optical beam splitter, an optical input / output coupler, an optical resonator, etc. The photon integrated chip may also include other optical components, which are not limited to the examples listed here.

[0073] like Figure 1 to Figure 3 As shown, this embodiment also provides a method for preparing a high-order mode filter, the preparation method comprising:

[0074] like Figure 1 As shown, firstly, step 1) is performed to provide a substrate, wherein the substrate comprises a base 101 , an insulating layer 102 and a semiconductor top layer 103 which are arranged in sequence.

[0075] In one embodiment, the substrate 101 may be a silicon substrate, a germanium substrate, a silicon germanium substrate, a silicon carbide substrate, etc., the insulating layer 102 may be an appropriate dielectric layer, such as a silicon dioxide layer, and the semiconductor top layer 103 may be a silicon top layer. The thickness of the silicon top layer may be 2.5 microns to 5 microns, etc., and may be specifically 3 microns.

[0076] like Figure 1 As shown, step 2) is then performed to form first stray light absorption regions 104 arranged at intervals in the semiconductor top layer 103 to absorb stray light in the incident light.

[0077] In one embodiment, forming the first stray light absorption regions 104 arranged in intervals includes:

[0078] The photoresist layer is spun onto the substrate and patterned using a photolithography process to remove the photoresist areas that require stray light doping, and then dopants (such as boron, arsenic, boron difluoride, phosphorus and antimony, etc.) are implanted into the substrate, followed by high-temperature annealing to diffuse the dopants from the implanted areas into the semiconductor top layer 103, so that the final profile almost reaches the insulating layer 102 below.

[0079] Specifically, the size of the pattern of the first stray light absorption region 104 can be adjusted according to the width of the slab groove 105 of the ridge waveguide 106 used. For a slab groove 105 with a width z between 10 μm and 50 μm, the width x of the first stray light absorption region 104 can be between 15 μm and 60 μm, and the depth y of the first stray light absorption region 104 can be between 2.5 μm and 3 μm. In this embodiment, the doping concentration of the first stray light absorption region is 1×10 18 / cm 3 ~5×10 19 / cm 3 .

[0080] like Figure 2 As shown, step 3) is then performed to etch spaced apart planar grooves 105 in the semiconductor top layer 103 , a ridge waveguide 106 is formed between two adjacent planar grooves 105 , and the ridge waveguide 106 is located between two adjacent first stray light absorption regions 104 .

[0081] In one embodiment, etching the spaced apart planar grooves 105 in the semiconductor top layer 103 includes:

[0082] Spinning the photoresist layer onto the substrate and patterning it using a photolithography process to define an etching area of ​​the plate groove 105;

[0083] The plate trench 105 is etched in the semiconductor top layer 103 by anisotropic dry etching.

[0084] In one embodiment, the width z of the slab groove 105 can be 10 microns to 50 microns, and the depth of the slab groove 105 can be 1.1 microns to 1.3 microns. The depth of the slab groove 105 can be set according to the required thickness of the ridge waveguide 106, and is not limited to the examples listed here. The shape of the slab groove 105 can be adjusted according to the required shape of the ridge waveguide 106. For example, when the ridge waveguide 106 is a rectangular waveguide, the slab groove 105 can be set as a rectangular groove so that a rectangular waveguide is constructed between adjacent slab grooves 105; and when the ridge waveguide 106 is tapered, the slab groove 105 can be set as a trapezoid so that a tapered waveguide is constructed between adjacent slab grooves 105.

[0085] like Figure 3 Then, step 4) is performed to form a reflection area in the slab grooves 105 on both sides of the ridge waveguide 106. The length direction of the reflection area has an inclination angle θ with the light propagation direction in the ridge waveguide 106. The inclination angle θ is less than 90 degrees, and is used to reflect the light incident from the outside of the reflection area to the ridge waveguide 106. In one embodiment, the inclination angle θ is 20 degrees to 85 degrees, and preferably can be 30 degrees.

[0086] In one embodiment, forming a reflection region in the slab groove 105 on both sides of the ridge waveguide 106 includes:

[0087] Defining the pattern of the reflective area by photolithography;

[0088] The semiconductor top layer 103 is etched based on the reflection area pattern to form reflection grooves 107 in the slab grooves 105 on both sides of the ridge waveguide 106. The reflection grooves 107 extend from the bottom surface of the slab grooves 105 to the inside of the substrate. The depth of the reflection grooves 107 is greater than or equal to the depth of the first stray light absorption area 104, and the depth of the reflection grooves 107 is less than or equal to the thickness of the semiconductor top layer 103.

[0089] In one embodiment, there are multiple reflection area patterns defined by the photolithography process, and the multiple reflection area patterns are configured to be arranged at intervals along the light propagation direction in the ridge waveguide 106. The semiconductor top layer 103 is etched based on the reflection area patterns to form multiple reflection grooves 107 in the plate grooves 105 on both sides of the ridge waveguide 106. The tilt angles θ corresponding to the multiple reflection areas can be equal, that is, the length directions of the multiple reflection areas are parallel to each other, while ensuring the reflection probability of the multiple reflection areas for stray light or high-order modes, simplifying the design and manufacturing process. Alternatively, the tilt angles θ corresponding to the multiple reflection areas are configured to gradually decrease along the light propagation direction in the ridge waveguide 106, so as to increase the reflection probability of the subsequent reflection areas for stray light or high-order modes from the outside. Of course, in other examples, the tilt angle θ rule of the multiple reflection areas can be designed according to actual conditions, and is not limited to the examples listed here.

[0090] The depth of the reflective groove 107 is less than or equal to the thickness of the semiconductor top layer 103 to avoid damage to the insulating layer 102. For example, the depth of the reflective groove 107 can be between 2.5 microns and 3 microns. The ratio of the projection length of the reflective area in the width direction of the flat groove 105 to the width of the flat groove 105 is 0.5 to 1, that is, the width of the reflective groove 107 can be designed to cover most of the flat groove 105 width as much as possible to increase its probability of reflecting stray light. For a flat groove 105 with a width between 10 microns and 50 microns, the actual length of the reflective groove 107 can be between 10 microns and 100 microns. The width of the reflective groove 107 can be between 3 microns and 10 microns. Since there is a large difference in refractive index between the semiconductor top layer 103 on one side of the reflective groove 107 and the filler (such as air or silicon dioxide) in the emission groove, on the one hand, when the stray light or high-order mode from the outside is irradiated or emitted from the outer wall of the plate groove 105 to the reflective groove 107, the stray light or high-order mode will be reflected on the side wall of the reflective groove 107, thereby preventing the stray light or high-order mode from entering the ridge waveguide 106, thereby greatly improving the attenuation of the stray light or high-order mode. On the other hand, when the stray light or high-order mode moves out of the waveguide and irradiates the inner side of the reflective groove 107, it can be reflected multiple times on the side walls of the adjacent reflective grooves 107, and finally moves out to the outer side of the reflective groove 107, further improving the attenuation of the stray light or high-order mode.

[0091] In one embodiment, the reflective groove 107 may be a rectangular groove, an inverted trapezoidal groove, a U-shaped groove, a V-shaped groove, etc., and may be set according to design requirements or process requirements, and is not limited to the examples listed here.

[0092] In one embodiment, the preparation method further includes the step of: filling silicon dioxide in the reflective groove 107. Specifically, when silicon dioxide is filled in the reflective groove 107, it can be deposited simultaneously with the upper cladding layer (silicon dioxide layer) of the ridge waveguide in the subsequent process to save process steps. Of course, the reflective groove 107 can also be kept as air through other processes (such as controlling deposition conditions or filling a sacrificial layer, etc.) to ensure a lower refractive index inside the reflective groove 107.

[0093] like Figure 4 As shown, the preparation method may further include: forming a second stray light absorption region 108 in the first stray light absorption region 104 through an ion implantation process, the doping concentration of the second stray light absorption region 108 is greater than the doping concentration of the first stray light absorption region 104, and the dopants of the first stray light absorption region 104 and the second stray light absorption region 108 include one of boron, arsenic, boron difluoride, phosphorus and antimony.

[0094] The absorption of stray light increases exponentially with the doping concentration. The higher the doping concentration, the more significant the suppression effect on stray light. However, when the doping concentration is higher than the threshold of about 5×1018 / cm 3 When the doping concentration is 5×10 , the stray light absorption begins to deviate from the exponential relationship. The reason is that the doping concentration causes the refractive index perturbation of the semiconductor top layer 103, which causes the stray light to be reflected back into the waveguide. In one embodiment, the doping concentration of the second stray light absorption region is 5×10 18 / cm 3 ~1×10 20 / cm 3 , so that the second stray light absorption zone 108 has a strong absorption of the stray light and / or the high-order mode entering its region. In general, even if the second stray light absorption zone 108 and the first stray light absorption zone 104 have a certain reflection at their interface due to the difference in refractive index, however, since the actual difference in refractive index between the second stray light absorption zone 108 and the first stray light absorption zone 104 is not too large, the probability of total reflection at the interface is small, and therefore, most of the stray light or high-order mode can still enter the second stray light absorption zone 108 and be absorbed by the second stray light absorption zone 108. The depth of the second stray light absorption zone 108 can be set to be less than half or less than one-third of the depth of the first stray light absorption zone 104, etc., and can be set according to actual design requirements. In some embodiments, a concentration gradient zone or a concentration gradient zone may be provided between the second stray light absorption zone 108 and the first stray light absorption zone 104, and the doping concentration of the concentration gradient zone or the concentration gradient zone may gradually increase from the first stray light absorption zone 104 toward the second stray light absorption zone 108, thereby avoiding further increase of stray light and high-order modes entering the second stray light absorption zone 108 from the first stray light absorption zone 104.

[0095] In one embodiment, the second stray light absorption region 108 is arranged to surround the inner and outer sides of the reflection region, so as to facilitate the subsequent absorption of stray light incident or reflected from the inner and outer sides of the reflection region.

[0096] Figure 5 It shows a top view and a cross-sectional view of an existing high-order mode filter structure. After entering the ridge waveguide 106, the optical signal 201 (such as a TE10 optical signal) is moved out of the ridge waveguide 106 due to the diffraction effect. However, part of the optical signal 201 is reflected by the side wall of the slab groove 105 and the reflected light re-enters the ridge waveguide 106. Figure 6The top view and cross-sectional view of the high-order mode filter structure of the embodiment of the present invention are shown. After entering the ridge waveguide 106, the optical signal 201 (such as the TE10 optical signal) is moved out of the ridge waveguide 106 due to the diffraction effect. However, the reflected light 202 after part of the optical signal 201 is reflected by the side wall of the slab groove 105 is reflected again by the reflection area to the outside of the ridge waveguide 106, and the reflection area effectively prevents the TE10 optical signal from re-entering the ridge waveguide 106. Furthermore, after multiple reflections, a part of the reflected light 202 is directly moved out of the slab groove 105, and the other part is repeatedly absorbed by the first stray light absorption area 104 and the second stray light absorption area 108, thereby greatly improving the attenuation of the optical signal.

[0097] As described above, the high-order mode filter and the preparation method thereof of the present invention have the following beneficial effects:

[0098] The present invention designs reflection areas on both sides of the ridge waveguide, and the length direction of the reflection area has an inclined angle with the light propagation direction in the ridge waveguide. The reflection area can reflect the light incident from the outside of the reflection area toward the ridge waveguide, especially can block the stray light reflected by the side wall of the flat groove to a great extent, and prevent the stray light from re-entering the waveguide.

[0099] The present invention can further increase the absorption of stray light by designing a highly doped second stray light absorption region in the plate groove region, thereby greatly increasing the attenuation of stray light.

[0100] The high-order mode filter of the present invention is crucial to reducing the harmful effects of high-order modes in complex photonic circuits. The design of the reflective zone of the present invention effectively eliminates the downstream propagation of high-order modes and avoids the interaction between high-order modes and fundamental modes, so that the wavelength and temperature of the integrated photonic chip have better power stability. The attenuation of the high-order mode filter of the present invention is greater than 40dB / mm, which is two orders of magnitude higher than the traditional filter design, so that the integrated photonic chip has a higher signal-to-noise ratio, thereby greatly improving the sensitivity of the integrated photonic chip.

[0101] The high-order mode filter of the present invention is compatible with traditional process flows and can be combined with a doping process to achieve further attenuation, and has a good application basis and a wide range of applications.

[0102] Therefore, the present invention effectively overcomes various shortcomings in the prior art and has high industrial utilization value.

[0103] The above embodiments are merely illustrative of the principles and effects of the present invention, and are not intended to limit the present invention. Anyone familiar with the art may 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 a person of ordinary skill in the art without departing from the spirit and technical concept disclosed by the present invention shall still be covered by the claims of the present invention.

Claims

1. A high-order mode filter, characterized in that: The high-order mode filter comprises: A substrate, comprising a base, an insulating layer and a semiconductor top layer arranged in sequence; Planar grooves are arranged at intervals in the semiconductor top layer, and a ridge waveguide is formed between two adjacent planar grooves; A first stray light absorption region, distributed in the semiconductor top layer on both sides of the ridge waveguide, for absorbing stray light in the incident light; A reflection zone, wherein the reflection zone is arranged in the planar grooves on both sides of the ridge waveguide, and the length direction of the reflection zone has an inclination angle with the light propagation direction in the ridge waveguide, and the inclination angle is less than 90 degrees, and is used to reflect the light incident from the outside of the reflection zone toward the ridge waveguide.

2. The high-order mode filter according to claim 1, characterized in that: The reflection area is configured as a reflection groove, the reflection groove is configured in the slab grooves on both sides of the ridge waveguide, the reflection groove extends from the bottom surface of the slab groove to the inside of the substrate, and the depth of the reflection groove is less than or equal to the thickness of the semiconductor top layer.

3. The high-order mode filter according to claim 2, characterized in that: The filler of the reflective groove includes one of air and silicon dioxide.

4. The high-order mode filter according to claim 1, characterized in that: The high-order mode filter includes a plurality of the reflection regions, and the plurality of the reflection regions are configured to be arranged at intervals along a light propagation direction in the ridge waveguide.

5. The high-order mode filter according to claim 4, characterized in that: The inclination angles corresponding to the plurality of reflection areas are equal.

6. The high-order mode filter according to claim 1, characterized in that: The ratio of the projection length of the reflection area in the width direction of the plate groove to the width of the plate groove is 0.5-1.

7. The high-order mode filter according to claim 1, characterized in that: The inclination angle is 20 degrees to 85 degrees.

8. The high-order mode filter according to claim 1, characterized in that: The width of the plate groove is 10 micrometers to 50 micrometers, and the width of the first stray light absorption area is 15 micrometers to 60 micrometers.

9. The high-order mode filter according to claim 1, characterized in that: The high-order mode filter further includes a second stray light absorption region, which is disposed in the first stray light absorption region, and the doping concentration of the second stray light absorption region is greater than the doping concentration of the first stray light absorption region.

10. The high-order mode filter according to claim 9, characterized in that: The dopants of the first stray light absorption region and the second stray light absorption region include one of boron, arsenic, boron difluoride, phosphorus and antimony, and the doping concentration of the first stray light absorption region is 1×10 18 / cm 3 ~5×10 19 / cm 3 , the doping concentration of the second stray light absorption region is 5×10 18 / cm 3 ~1×10 20 / cm 3 .

11. A photonic integrated chip, characterized in that: The photonic integrated chip comprises the high-order mode filter as claimed in any one of claims 1 to 10.

12. A method for preparing a high-order mode filter, characterized in that: The preparation method comprises: Providing a substrate, the substrate comprising a base, an insulating layer and a semiconductor top layer arranged in sequence; forming first stray light absorption regions arranged at intervals in the semiconductor top layer for absorbing stray light in incident light; Etching spaced apart planar grooves in the semiconductor top layer, forming a ridge waveguide between two adjacent planar grooves, and the ridge waveguide is located between two adjacent first stray light absorption regions; A reflection zone is formed in the plate grooves on both sides of the ridge waveguide, and the length direction of the reflection zone has an inclination angle with the light propagation direction in the ridge waveguide, and the inclination angle is less than 90 degrees, which is used to reflect the light incident from the outside of the reflection zone to the ridge waveguide.

13. The method for preparing a high-order mode filter according to claim 12, characterized in that: Forming a reflection area in the slab grooves on both sides of the ridge waveguide comprises: Defining the pattern of the reflective area by photolithography; The semiconductor top layer is etched based on the reflection area pattern to form reflection grooves in the slab grooves on both sides of the ridge waveguide, wherein the reflection grooves extend from the bottom surface of the slab grooves to the inside of the substrate, and the depth of the reflection grooves is less than or equal to the thickness of the semiconductor top layer.

14. The method for preparing a high-order mode filter according to claim 13, characterized in that: There are multiple reflection area patterns defined by the photolithography process, and the multiple reflection area patterns are configured to be arranged at intervals along the light propagation direction in the ridge waveguide. The semiconductor top layer is etched based on the reflection area patterns to form multiple reflection grooves in the flat plate grooves on both sides of the ridge waveguide.

15. The method for preparing a high-order mode filter according to claim 14, characterized in that: The inclination angles corresponding to the plurality of reflective grooves are equal.

16. The method for preparing a high-order mode filter according to claim 13, characterized in that: The preparation method further comprises the step of: filling silicon dioxide in the reflective groove.

17. The method for preparing a high-order mode filter according to claim 13, characterized in that: The ratio of the projection length of the reflective groove in the width direction of the flat groove to the width of the flat groove is 0.5-1.

18. The method for preparing a high-order mode filter according to claim 12, characterized in that: The inclination angle is 20 degrees to 85 degrees.

19. The method for preparing a high-order mode filter according to claim 12, characterized in that: The width of the plate groove is 10 micrometers to 50 micrometers, and the width of the first stray light absorption area is 15 micrometers to 60 micrometers.

20. The method for preparing a high-order mode filter according to claim 12, characterized in that: A second stray light absorption region is formed in the first stray light absorption region by an ion implantation process, wherein the doping concentration of the second stray light absorption region is greater than the doping concentration of the first stray light absorption region, and the dopants of the first stray light absorption region and the second stray light absorption region include one of boron, arsenic, boron difluoride, phosphorus and antimony, and the doping concentration of the first stray light absorption region is 1×10 18 / cm 3 ~5×10 19 / cm 3 , the doping concentration of the second stray light absorption region is 5×10 18 / cm 3 ~1×10 20 / cm 3 .

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