A tunable optical filter based on a slot-waveguide micro-ring resonator

Abstract

The application discloses a tunable optical filter based on a slot waveguide micro-ring resonator, which comprises an insulating silicon substrate and a slot waveguide micro-ring resonator, and the slot waveguide micro-ring resonator is composed of two straight slot waveguides and a slot waveguide micro-ring; the straight slot waveguide is composed of two high-refractive-index medium silicon (Si) layers and an intermediate low-refractive-index silicon dioxide (SiO2) layer which are vertically stacked; the slot waveguide micro-ring is composed of seven layers of electrode metal gold (Au) ring, high-refractive-index medium silicon (Si) ring, hafnium dioxide (HfO2) ring, EO polymer ring, hafnium dioxide (HfO2) ring, high-refractive-index medium silicon (Si) ring and electrode metal gold (Au) ring which are stacked from top to bottom in sequence and symmetrical; the upper and lower electrode metal layers are respectively connected with positive and negative electrodes. The application has the advantages of low power consumption, high light confinement and tunability.

Description

Technical Field

[0001] This invention relates to the fields of micro-nano optics and optical network-on-a-chip (ONA) technology, and specifically to a tunable optical filter based on a slot waveguide microring resonator. Background Technology

[0002] Optical interconnect-on-chip (OIC) networks transmit data using waveguides, offering advantages such as higher bandwidth, lower latency, and a better signal-to-noise ratio. An OIC network consists of six main components: a light source, a router, an optical modulator, an electro-optical conversion driver, a photonic interconnect network, and a photodetector. Optical filters are primarily used for demultiplexing the light waves passing through the photonic interconnect network.

[0003] Optical filters are a crucial component of silicon photonics, and are essential devices for demultiplexing in optical networks-on-a-chip (ONCs). Demultiplexing is a key technology in current optical interconnect ONCs for processing optical information, primarily used to select multiplexed signals. Demultiplexing can also significantly increase the bandwidth density of interconnects, effectively solving key challenges in electrical interconnect technology. This function can be achieved through tunable filters.

[0004] A slot waveguide is a micro / nanostructure composed of two high-refractive-index dielectric strips and a low-refractive-index gap between them. Due to the dielectric discontinuity, the TM optical mode tends to be highly concentrated between the two high-refractive-index dielectric strips. This structure utilizes the discontinuity of the transverse electric field at the waveguide boundary to confine most of the light energy to the subwavelength-level intermediate low-refractive-index layer, thus breaking the diffraction limit in the transverse direction of the waveguide. Simultaneously, the intermediate layer of the slot waveguide can be filled with different materials, greatly enriching the selection range of waveguide materials and significantly improving efficiency, thereby achieving different functions. Slot waveguides not only enable the design of small-sized photonic devices but are also all-dielectric waveguides, facilitating waveguide integration.

[0005] Silicon's relatively weak free carrier dispersion limits its overall modulation performance and requires high power consumption. Recently, electro-optic polymers (EO polymers) have shown great promise as a silicon alternative because they can change their refractive index under applied voltage while maintaining negligible optical losses.

[0006]

[0007] In the formula, Δn E0 For the change in refractive index of EO polymer, n E0 r is the refractive index of the EO polymer. 33 denoted as the photoelectric coefficient of the EO polymer, expressed in pm / v, where V is the applied voltage and d is the distance between the electrodes.

[0008] The most significant characteristic of light propagation in a microring waveguide is the resonance effect. Light enters from the incident port, and when it reaches the coupling region, coupling occurs. The light couples from the straight waveguide into the microring, resonates within the microring, and couples back into the straight waveguide, outputting at either the through port or the download port. Specifically, when the phase difference in the propagation of light in the ring waveguide is an integer multiple of 2π, the light forms a steady-state mode in the microring and is output from the through port or download port. When the phase difference in the propagation of light in the ring waveguide is an odd multiple of π, the optical signal undergoes coherent destructive propagation; a small amount of light couples, while most of the light continues to propagate in the original straight waveguide. Therefore, the fundamental function of the microring is to achieve wavelength separation.

[0009] Because microrings possess resonant characteristics, wavelength-selective filtering can be achieved using this property. When an optical signal resonates within the microring, the wavelength that can stably exist and transmit is the resonant wavelength. According to optical coherence theory, the following conditions must be met at this time:

[0010] 2πRn eff =mλ (2)

[0011] In the formula, R is the radius of the toroidal silicon waveguide; n eff λ is the effective refractive index of the waveguide, m is the resonant order of the circular silicon waveguide, which is a set constant integer determined by the circumference of the circular silicon waveguide. In other words, the value on the left side of the equation must be equal to m times the wavelength, which is a constant; λ is the wavelength of the light wave.

[0012] By combining slot waveguides and microrings, a multi-layered slot waveguide microring is obtained. Electrodes are placed on the upper and lower sides of the slot waveguide microring. By applying an external electric field, the refractive index of the EO polymer can be changed, thereby adjusting the position of the resonance peak and realizing a tunable filtering function. Summary of the Invention

[0013] This invention provides a tunable optical filter based on a slot waveguide microring resonator.

[0014] This invention is achieved through the following technical solution:

[0015] A tunable optical filter based on a slot waveguide microring resonator includes an insulating silicon substrate and a slot waveguide microring resonator. The slot waveguide microring resonator consists of two straight slot waveguides and one slot waveguide microring. The two straight slot waveguides are arranged laterally and are parallel to each other. The microring slot waveguide is located between the two straight slot waveguides. The left end of the upper straight slot waveguide forms the optical input terminal of the filter, the right end of the upper straight slot waveguide is the optical output terminal OUT1, the left end of the lower straight slot waveguide is another output terminal OUT2, and the right end of the lower straight slot waveguide is suspended.

[0016] In the above scheme, the insulating silicon substrate consists of a lower silicon substrate and an upper silicon dioxide substrate. The straight slot waveguide is composed of two high-refractive-index dielectric silicon (Si) layers and a middle low-refractive-index silicon dioxide (SiO2) layer stacked vertically. The slot waveguide microring is composed of seven layers stacked vertically from top to bottom: an electrode metal gold (Au) ring, a high-refractive-index dielectric silicon (Si) ring, a hafnium dioxide (HfO2) ring, an EO polymer ring, a hafnium dioxide (HfO2) ring, a high-refractive-index dielectric silicon (Si) ring, and an electrode metal gold (Au) ring. The upper and lower electrode metal layers are respectively connected to the positive and negative electrodes.

[0017] In the above scheme, the two high-refractive-index dielectric silicon (Si) layers of the straight slot waveguide are symmetrical.

[0018] In the above scheme, the upper and lower straight slot waveguides are identical and placed symmetrically.

[0019] In the above scheme, two hafnium dioxide (HfO2) rings serve as carrier barriers to reduce leakage current and improve the polarization efficiency of the electro-optic polymer.

[0020] In the above scheme, the optical output terminal OUT1 functions as a band-stop filter, and the optical output terminal OUT2 functions as a band-pass filter.

[0021] In the above scheme, the EO polymer ring material is polymer AJ404.

[0022] In the above scheme, the resonance equation that the circular silicon waveguide must satisfy is: 2πRn eff =mλ

[0023] In the formula, R is the radius of the toroidal silicon waveguide; n eff denoted as the effective refractive index of the waveguide, and m as the resonant order of the circular silicon waveguide. The resonant order is a set constant integer, which is determined by the circumference of the circular silicon waveguide. In other words, the value on the left side of the equation must be equal to m times the wavelength, which is a constant.

[0024] Compared with the prior art, the present invention has the following characteristics:

[0025] 1. A completely independent design was developed for a tunable optical filter structure based on a slot waveguide microring resonator, which combines the slot waveguide and the microring to achieve optical filtering function.

[0026] 2. Based on the micro-ring of electro-optic material, the refractive index of the electro-optic material can be changed by an electric field to change the position of the resonance peak, thereby realizing the tunable filtering function.

[0027] 3. The structure combining slot waveguide and microring features high optical confinement and low loss.

[0028] 4. Although the design flexibility of the straight slot waveguide multilayer structure is limited, the manufacturing process of this multilayer structure is more direct, the process is simpler, and the transmission loss is also lower.

[0029] 5. Multiple tunable optical filters based on slot waveguide microring resonators can be connected in series and superimposed to form a multi-channel filter. For example... Figure 10 As shown. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of a three-dimensional structure of a tunable optical filter based on a slot waveguide microring resonator.

[0031] Figure 2 This is a schematic diagram of the three-dimensional structure of the upper and lower straight slot waveguides.

[0032] Figure 3 This is a schematic diagram of the three-dimensional structure of the slot waveguide microring.

[0033] Figure 4 This is a top view of a tunable optical filter based on a slot waveguide microring resonator.

[0034] Figure 5 This is a front view of a tunable optical filter based on a slot waveguide microring resonator.

[0035] Figure 6 This is a side view of a tunable optical filter based on a slot waveguide microring resonator.

[0036] Figure 7 This is a schematic diagram of the cross-sectional structure of a tunable optical filter based on a slot waveguide microring resonator.

[0037] Figure 8 This is a schematic diagram of the cross-sectional structure of the upper and lower straight slot waveguides.

[0038] Figure 9 This is a schematic diagram of the cross-sectional structure of the slot waveguide microring.

[0039] Figure 10 This is a schematic diagram of a series connection of multiple tunable optical filters based on slot waveguide microring resonators.

[0040] Labels in the diagram: 1: Silicon (Si) substrate; 2: Silicon dioxide (SiO2) substrate; 3: Upper straight slot waveguide; 4: Lower straight slot waveguide; 5: Slot waveguide microring resonator;

[0041] 3-1: Upper high-refractive-index dielectric silicon (Si) layer of the slot waveguide; 3-2: Middle low-refractive-index silicon dioxide (SiO2) layer of the slot waveguide; 3-3: Lower high-refractive-index dielectric silicon (Si) layer of the slot waveguide; 4-1: Upper high-refractive-index dielectric silicon (Si) layer of the slot waveguide; 4-2: Middle low-refractive-index silicon dioxide (SiO2) layer of the slot waveguide; 4-3: Lower high-refractive-index dielectric silicon (Si) layer of the slot waveguide;

[0042] The microring resonator, from top to bottom, consists of: 5-1: upper metal electrode gold (Au) layer; 5-2: high refractive index dielectric silicon (Si) layer; 5-3: barrier hafnium dioxide (HfO2) layer; 5-4: EO polymer layer; 5-5: barrier hafnium dioxide (HfO2) layer; 5-6: high refractive index dielectric silicon (Si) layer; 5-7: lower metal electrode gold (Au) layer.

[0043] L: Length of the upper and lower straight slot waveguides; R: Outer radius of the slot waveguide microring; r: Inner radius of the slot waveguide microring; H1: Thickness of silicon substrate 1; H2: Thickness of silicon dioxide substrate 2; w: Width of the straight slot waveguide; gap: Coupling distance between the upper and lower straight slot waveguides and the microring; h1: Thickness of the high refractive index dielectric silicon layer of the straight slot waveguide; h2: Thickness of the low refractive index silicon dioxide layer in the middle of the straight slot waveguide; he: Thickness of the gold layer of the microring metal electrode; ho: Thickness of the hafnium dioxide barrier layer; hs: Thickness of the high refractive index dielectric silicon layer of the microring; h EO The thickness of the microring EO polymer layer; Detailed Implementation

[0044] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific examples.

[0045] like Figure 1 As shown, a tunable optical filter based on a slot waveguide microring resonator is disclosed. The filter consists of an insulating silicon substrate and a slot waveguide microring resonator. In this example, the insulating silicon substrate is composed of a lower silicon substrate with a thickness of H1 = 10 μm and an upper silicon dioxide substrate with a thickness of H2 = 3 μm.

[0046] The straight slot waveguide has two sections, 3 and 4. The left end of the upper straight slot waveguide 3 forms the optical input terminal IN of the filter, and the right end of the upper straight slot waveguide 3 is the optical output terminal OUT1. The left end of the lower straight slot waveguide 4 is another output terminal OUT2, and the right end of the lower straight slot waveguide 4 is suspended. The two straight slot waveguides are identical and symmetrically placed, each with a length L = 5 μm. They are composed of two high-refractive-index dielectric silicon (Si) layers and an intermediate low-refractive-index silicon dioxide (SiO2) layer stacked vertically. The two high-refractive-index dielectric layers and the intermediate low-refractive-index layer of the straight slot waveguide are all elongated strips, and the widths of the high-refractive-index dielectric layer and the intermediate low-refractive-index layer are the same, both w = 400 nm. In this example, the high-refractive-index dielectric layer is a silicon (Si) layer with a thickness h1 = 300 nm, and the intermediate low-refractive-index layer is a silicon dioxide (SiO2) layer with a thickness h2 = 100 nm. A schematic diagram of the three-dimensional structure is shown below. Figure 2 As shown, the cross-sectional structural diagram is as follows: Figure 8 As shown.

[0047] The slot waveguide microring consists of a square-section ring composed of seven parts: an upper metal electrode gold (Au) layer 5-1, a high-refractive-index dielectric silicon (Si) layer 5-2, a barrier hafnium dioxide (HfO2) layer 5-3, an EO polymer layer 5-4, another barrier hafnium dioxide (HfO2) layer 5-5, another high-refractive-index dielectric silicon (Si) layer 5-6, and a lower metal electrode gold (Au) layer 5-7, exhibiting a symmetrical structure. Each part has the same inner and outer radii and width. In this example, the outer radius of each layer is R = 2.2 μm, the inner radius is r = 1.8 μm, and the width is w = 400 nm. The thickness of the metal electrode layer is he = 10 nm, the thickness of the high-refractive-index dielectric silicon layer is hs = 280 nm, the thickness of the barrier hafnium dioxide layer is ho = 10 nm, and the thickness of the EO polymer layer is h. EO =100nm, 3D structure diagram as shown Figure 3 As shown in the figure, the cross-sectional structure of the slot waveguide microring resonator is schematically illustrated. Figure 9 As shown.

[0048] In this example, the lengths of both the upper and lower straight waveguides are L = 5 μm; the distance between the upper and lower straight waveguides and the micro-ring is gap = 50 nm, as shown below. Figure 6 As shown.

[0049] In this example, the refractive index of silicon (Si) is 3.475, the refractive index of silicon dioxide (SiO2) is 1.44, the refractive index of air is 1, the refractive index of the EO polymer without voltage is 1.69, the refractive index of hafnium dioxide (HfO2) is 1.98, and the refractive index of the gold (Au) metal electrode layer is 10.35+0.19i.

[0050] The barrier layer of the slot waveguide microring is made of hafnium dioxide (HfO2). Hafnium dioxide is a commonly used dielectric material with a high DC dielectric constant k = 25. A layer of hafnium dioxide (HfO2) dielectric material is used to isolate the EO polymer layer from the silicon (Si) layer so that it can act as a carrier barrier to reduce leakage current and improve the polarization efficiency of the electro-optic polymer when an electric field is applied to the metal.

[0051] In this embodiment, the tunable optical filter based on a slot waveguide microring resonator is based on a vertical multilayer structure. First, the microring and waveguide geometry are patterned on a substrate using photolithography and etching. Then, the sample is doped by ion implantation, and the bottom contacts are defined through a metal evaporation and lift-off process. Next, an EO polymer is spin-coated as the dielectric layer for the microrings; the thickness of this layer can be controlled using different spin-coating formulations, supplemented by a reverse etching process. Before coating with noble metals, a thin layer of low-conductivity insulating material can be deposited to reduce leakage current. Before device operation, a high electric field should be applied through the defined contacts to effectively polarize the polymer.

[0052] By controlling the bias voltage applied to the electrode layer to apply a voltage to the EO polymer layer in the microring, the refractive index of the EO polymer changes, thereby causing the resonance peak of the microring to shift, thus achieving the function of tunable filtering.

[0053] Due to the thermo-optical (TO) coefficient of silicon, microrings remain highly sensitive to fluctuations in ambient temperature. Because the positive TO coefficient of silicon rings is 1.8 × 10⁻⁴ / ℃, the resonance of silicon rings exhibits a strong temperature-dependent wavelength shift (TDWS). This problem can be addressed in two ways: one is by using an active thermal controller in the integrated device to reduce TDWS, which may lead to further power consumption issues; the other is by using a polymer with a negative TO coefficient, the opposite of silicon's positive coefficient, which can reduce TDWS to almost zero.

[0054] In summary, this filter can control the transmission wavelength of light through a bias voltage, thus achieving the function of an optical filter. This structure can also be used for switching, modulation, and other on-chip resonator-based functions.

[0055] It should be noted that although the embodiments described above are illustrative, they are not intended to limit the invention. Therefore, the invention is not limited to the specific embodiments described above. Any other embodiments obtained by those skilled in the art under the guidance of this invention without departing from its principles are considered to be within the protection scope of this invention.

Claims

1. A tunable optical filter based on a slot waveguide microring resonator, the tunable optical filter is composed of five parts: a silicon substrate (1), a silicon dioxide substrate (2), two straight slot waveguides (3) and (4), and a slot waveguide microring (5); the silicon substrate (1) is a 10 μm high silicon (Si) layer, and the silicon dioxide substrate (2) is a 3 μm high silicon dioxide (SiO2) layer; The upper straight slot waveguide (3) and (4) have their left ends forming the optical input terminal IN of the filter and their right ends forming the optical output terminal OUT1. The lower straight slot waveguide (4) has its left ends forming another output terminal OUT2 and its right ends suspended. The two straight slot waveguides are identical and symmetrically placed. The straight slot waveguide (3) is composed of two 300nm thick high refractive index dielectric silicon (Si) layers (3-1) and (3-3) and a 100nm thick intermediate low refractive index silicon dioxide (SiO2) layer (3-2) stacked vertically. The intermediate low refractive index silicon dioxide layer is located between the two high refractive index dielectric silicon layers. The two high refractive index dielectric layers and the intermediate low refractive index layer of the straight slot waveguide are all long strips. The widths of the high refractive index dielectric layer and the intermediate low refractive index layer are the same, both being 400nm. The slot waveguide microring (5) is a square-shaped ring composed of seven parts. From top to bottom, they are: a 10nm thick upper metal electrode gold (Au) layer (5-1), a 280nm thick high refractive index dielectric silicon (Si) layer (5-2), a 10nm thick barrier hafnium dioxide (HfO2) layer (5-3), a 100nm thick EO polymer layer (5-4), a 10nm thick barrier hafnium dioxide (HfO2) layer (5-5), a 280nm thick high refractive index dielectric silicon (Si) layer (5-6), and a 10nm thick lower metal electrode gold (Au) layer (5-7), forming a symmetrical structure. The inner and outer radii of each part are the same, which are 180nm and 220nm respectively, and the width is 400nm. The lengths of both the upper and lower straight waveguides are L=5um; the distance between the upper and lower straight waveguides and the microring is gap=50nm; The refractive index of silicon (Si) material is 3.475, the refractive index of silicon dioxide (SiO2) material is 1.44, the refractive index of EO polymer without voltage is 1.69, the refractive index of hafnium dioxide (HfO2) material is 1.98, and the refractive index of gold (Au) metal electrode layer material is 10.35+0.19i.

2. The tunable optical filter based on a slot waveguide microring resonator according to claim 1, characterized in that, The EO polymer layer (5-4) of the slot waveguide microring (5) can be replaced with other EO polymer materials.

3. A tunable optical filter based on a slot waveguide microring resonator according to claim 1, characterized in that, The barrier layer of the slot waveguide microring (5) can be replaced with other suitable low-conductivity insulating materials.

4. A tunable optical filter based on a slot waveguide microring resonator according to claim 1, characterized in that, The optical output terminal OUT1 functions as a band-stop filter, and the optical output terminal OUT2 functions as a band-pass filter.

5. A tunable optical filter based on a slot waveguide microring resonator according to claim 1, characterized in that, By connecting the optical input terminals IN of multiple filters in series with the optical output terminal OUT1 of the previous stage, multi-channel tunable filtering can be achieved.

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