Narrow band filter with optical communication module

Abstract

The present application relates to the field of optical communication technology, provide a kind of narrow-band filter and optical communication module.Narrow-band filter includes interference film and diffraction grating;Interference film includes high refractive index film layer and low refractive index film layer of alternative laminated arrangement, the total thickness of interference film is d;Diffraction grating is arranged on the surface of interference film, diffraction grating has grating period p, grating ridge width w And grating thickness h;Wherein, the structural parameters of narrow-band filter satisfy the following relationship:0.65≤h / d≤0.80 or 1.37≤h / d≤1.53, and 0.6≤w / p≤0.66.The present application realizes narrow-band filtering by combining interference and diffraction under specific parameters, in predetermined waveband range, any target waveband has narrow transmission bandwidth and stable center wavelength, size can be controlled in micrometer level, preparation flexibility is strong, has higher manufacturing tolerance, improves the robustness of large-scale manufacturing.

Description

Technical Field

[0001] This invention relates to the field of optical communication technology, and in particular to a narrowband filter and an optical communication module. Background Technology

[0002] With the exponential growth in data transmission demand and the computing power of large AI models, new technical requirements have been put forward for the high integration and ultra-low latency of filtering devices in optical communication, increasingly leading to high-performance, integrable devices.

[0003] Currently, the main technical solutions for achieving narrowband filtering include dielectric film interference filters, Fabry-Perot etalons, and volume Bragg gratings. Dielectric film interference filters are typically composed of dozens of thin film layers stacked together, or a dozen layers of dielectric and metal films stacked together. To improve the narrowband filtering effect, narrowband filter devices require high precision in fabrication and installation. However, an excessive number of film layers leads to significant cumulative errors in film thickness. This not only results in a large film thickness for the narrowband filter device but also affects the target wavelength due to thickness errors, making it impossible to lock onto the target wavelength and ensuring effective narrowband filtering within the target band. Volume Bragg gratings are typically large in size and, in some applications, require high device thickness, which is not conducive to miniaturization and integration. Furthermore, achieving extremely narrow bandwidth solely through volume Bragg gratings often requires extremely high refractive index modulation depths, making fabrication processes difficult.

[0004] To combine the advantages of both, the applicant integrated a diffraction grating onto the surface of the interference thin film, utilizing the interference thin film to provide the main reflection / transmission characteristics and the diffraction grating to provide additional dispersion and frequency selection mechanisms to achieve narrowband filtering. However, in practical applications, this hybrid structure of interference thin film and diffraction grating faces significant technical challenges, mainly manifested in the following ways: (1) The center wavelength shift problem: the resonance condition of the interference film and the Bragg condition of the diffraction grating differ in physical mechanism. When the two are coupled, due to the complex interaction between the phase delay introduced by the interference film and the effective refractive index of the grating, the actual filtering center wavelength often deviates from the theoretical design value; (2) Existing technologies lack precise control over the synergistic relationship between the thickness of the interference film and the geometric parameters of the grating, which makes it difficult to ensure high filtering efficiency and low side crosstalk while achieving narrowband. (3) It is difficult to maintain the above-mentioned optical performance stability at the micrometer scale.

[0005] In summary, there is an urgent need to provide a narrowband filter and optical communication module that can simultaneously achieve extremely narrow bandwidth and high center wavelength accuracy, which would facilitate the monolithic integration of small-sized narrowband filters. Summary of the Invention

[0006] This invention aims to solve the technical problems existing in related technologies. To this end, this invention provides a narrowband filter that can achieve precise narrowband filtering at a micrometer-scale, ensuring the narrowband filtering effect within the target band and facilitating the monolithic integration of small-sized narrowband filters.

[0007] The present invention also provides an optical communication module.

[0008] In a first aspect, the present invention provides a narrowband filter, comprising: An interference thin film includes alternating layers of high-refractive-index and low-refractive-index films, the total thickness of the interference thin film being d; A diffraction grating is disposed on the surface of the interference film, and the diffraction grating has a grating period p, a grating ridge width w, and a grating thickness h; The structural parameters of the narrowband filter satisfy the following relationship: 0.65≤h / d≤0.80 or 1.37≤h / d≤1.53, and 0.6≤w / p≤0.66.

[0009] According to the present invention, a narrowband filter is provided that, under the condition that 0.65≤h / d≤0.80, 0.86μm≤h+d≤0.95μm.

[0010] According to the present invention, a narrowband filter is provided that, under the condition that 1.37≤h / d≤1.53, 1.24μm≤h+d≤1.33μm.

[0011] According to the present invention, a narrowband filter is provided with 0.843μm≤p≤0.8655μm.

[0012] According to the present invention, the narrowband filter has an efficiency of not less than 99.7% at the center wavelength of the target band and an efficiency of not more than 15% in the sideband regions on both sides of the main passband.

[0013] According to a narrowband filter provided by the present invention, the wavelength range of the target band is 1530nm to 1565nm.

[0014] According to a narrowband filter provided by the present invention, the narrowband filter further includes a substrate, an interference film disposed on the substrate, and a diffraction grating disposed on the side of the interference film opposite to the substrate.

[0015] According to a narrowband filter provided by the present invention, the material of the high refractive index film includes any one of niobium pentoxide, titanium dioxide, tantalum pentoxide, hafnium dioxide, and zirconium dioxide; And / or, the material of the low refractive index film is silicon dioxide; And / or, the total number of the high refractive index film layer and the low refractive index film layer is 2-30 layers; And / or, the material of the diffraction grating is silicon nitride.

[0016] According to a narrowband filter provided by the present invention, the thickness of the high refractive index film is λ0 / (4n1), and the thickness of the low refractive index film is λ0 / (4n2). Wherein, λ0 is the center wavelength of the target band, n1 is the refractive index of the high refractive index film, and n2 is the refractive index of the low refractive index film.

[0017] In a second aspect, the present invention also provides an optical communication module including a narrowband filter as described above.

[0018] The narrowband filter and optical communication module provided by this invention, by integrating a diffraction grating on the surface of an interference film and employing a vertically stacked interference film-diffraction grating structure, eliminates the large optical components and complex optical paths required by traditional filters. Light undergoes multi-beam interference when passing through the interference film, and simultaneously couples with the surface diffraction grating. This invention discovers that, under the conditions of 0.65≤h / d≤0.80 or 1.37≤h / d≤1.53, and 0.6≤w / p≤0.66, the phase modulation introduced by the grating achieves optimal phase matching with the multi-beam interference effect of the interference film, resulting in a narrow transmission bandwidth and a stable center wavelength within any target band in a predetermined wavelength range.

[0019] Compared to traditional methods that require thicker film layers, this invention achieves critical coupling using a specific thickness ratio. It can achieve the same or even better narrowband performance as thick films with a thinner total thickness, and it eliminates the need to accumulate phase difference by extending the grating interaction length. This allows filtering to be completed within an extremely short axial or lateral dimension, which enables the overall feature size of the filter to be controlled at the micrometer level. This greatly eliminates the need for large optical components required by traditional filters, perfectly matching the micrometer-level process nodes of photonic integrated circuits, and is conducive to high-density, monolithic integration.

[0020] Compared to existing large-size thin-film filter devices (e.g., with a thickness exceeding 10 μm), this invention achieves narrowband filtering by combining interference and diffraction under specific parameters. The structure of this invention is simple, consisting only of multiple dielectric films and diffraction gratings. It does not require complex optical path alignment and can flexibly adjust the filtering performance to meet the needs of different wavebands. Furthermore, the entire narrowband filter has a simple structure, high fabrication flexibility, high manufacturing tolerance, and improved robustness for large-scale manufacturing. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0022] Figure 1 This is a three-dimensional structural diagram of the narrowband filter provided by the present invention.

[0023] Figure 2 This is a schematic diagram of the main structure of the narrowband filter provided by the present invention.

[0024] Figure 3 This is a simulation diagram of the C-band 1550nm narrowband effect that meets the parameter conditions of Example 1 provided by the present invention.

[0025] Figure 4 This is a simulation diagram of the C-band 1550nm narrowband effect that meets the parameter conditions of Embodiment 2 provided by the present invention.

[0026] Figure 5 This is a simulation diagram of the C-band 1550nm narrowband effect that meets the parameter conditions of Example 3 provided by the present invention.

[0027] Figure 6 This is a simulation diagram of the C-band 1550nm narrowband effect that meets the parameter conditions of Example 4 provided by the present invention.

[0028] Figure 7 This is a simulation diagram of the C-band 1550nm narrowband effect that meets the parameter conditions of Example 5 provided by the present invention.

[0029] Figure 8 This is a simulation diagram of the C-band 1550nm narrowband effect that meets the parameter conditions of Example 6 provided by the present invention.

[0030] Figure 9 This is a simulation diagram of the C-band 1550nm narrowband effect that meets the parameter conditions of Example 7 provided by the present invention.

[0031] Figure 10 This is a simulation diagram of the C-band 1530nm narrowband effect that meets the parameter conditions of Example 8 provided by the present invention.

[0032] Figure 11 This is a simulation diagram of the C-band 1530nm narrowband effect that meets the parameter conditions of Example 9 provided by the present invention.

[0033] Figure 12 This is a simulation diagram of the C-band 1530nm narrowband effect that meets the parameter conditions of Example 10 provided by the present invention.

[0034] Figure 13 This is a simulation diagram of the C-band 1530nm narrowband effect that meets the parameter conditions of Example 11 provided by the present invention.

[0035] Figure 14 This is a simulation diagram of the C-band 1530nm narrowband effect that meets the parameter conditions of Example 12 provided by the present invention.

[0036] Figure 15 This is a simulation diagram of the C-band 1530nm narrowband effect that meets the parameter conditions of Example 13 provided by the present invention.

[0037] Figure 16 This is a simulation diagram of the C-band 1530nm narrowband effect that meets the parameter conditions of Example 14 provided by the present invention.

[0038] Figure 17 This is a simulation diagram of the C-band 1565nm narrowband effect that meets the parameter conditions of Example 15 provided by the present invention.

[0039] Figure 18 This is a simulation diagram of the C-band 1565nm narrowband effect that meets the parameter conditions of Example 16 provided by the present invention.

[0040] Figure 19 This is a simulation diagram of the C-band 1565nm narrowband effect that meets the parameter conditions of Example 17 provided by the present invention.

[0041] Figure 20 This is a simulation diagram of the C-band 1565nm narrowband effect that meets the parameter conditions of Example 18 provided by the present invention.

[0042] Figure 21 This is a simulation diagram of the C-band 1565nm narrowband effect that meets the parameter conditions of Example 19 provided by the present invention.

[0043] Figure 22 This is a simulation diagram of the C-band 1550nm narrowband effect that meets the parameter conditions of Comparative Example 1, provided by the present invention.

[0044] Figure 23 This is a simulation diagram of the C-band 1550nm narrowband effect that meets the parameter conditions of Comparative Example 2, provided by the present invention.

[0045] Figure label: 1. Interference thin film; 101. High refractive index film; 102. Low refractive index film; 2. Diffraction grating; 3. Substrate. Detailed Implementation

[0046] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0047] The following is combined with Figures 1-23 The narrowband filter and optical communication module provided by the present invention will be described in detail through specific embodiments and application scenarios.

[0048] In the first aspect, such as Figure 1 and Figure 2 As shown, an embodiment of the present invention provides a narrowband filter, including an interference thin film 1 and a diffraction grating 2; The interference thin film 1 includes a high refractive index film layer 101 and a low refractive index film layer 102, which are stacked and arranged alternately in sequence; a diffraction grating 2 is disposed on the surface of the interference thin film 1. Under the conditions that 0.65≤h / d≤0.80 or 1.37≤h / d≤1.53 and 0.6≤w / p≤0.66, the narrowband filter achieves narrowband filtering within the target band; where d is the thickness of the interference film 1, h is the thickness of the diffraction grating 2, p is the grating period of the diffraction grating 2, and w is the grating ridge width of the diffraction grating 2.

[0049] It is understandable that, for the interference thin film 1, magnetron sputtering or vapor deposition can be used to alternately deposit the high refractive index film 101 and the low refractive index film 102 to ensure the compactness of the bonding between the high refractive index film 101 and the low refractive index film 102.

[0050] The high refractive index film 101 and the low refractive index film 102 are arranged according to Figure 1 The schematic Z-axis stacking configuration shows that the refractive index of the high refractive index film 101 is greater than the refractive index of the low refractive index film 102. For example, the refractive index of the high refractive index film 101 is greater than 2, and the refractive index of the low refractive index film 102 is less than 2.

[0051] It should be noted that, based on the alternating arrangement of high refractive index film 101 and low refractive index film 102, a combined structure formed by a Fabry-Perot resonant cavity and two high reflective mirrors on both sides can be constructed. This combined structure allows light to be reflected and coherently superimposed multiple times within the film stack, thereby allowing only light in a very narrow band to pass through, while other bands are suppressed.

[0052] The diffraction grating 2 is stacked on the upper surface of the interference film 1 along the Z-axis direction. The diffraction grating 2 is used to diffract specific incident light, which can come from the interference film 1 or from the external environment, without specific limitation.

[0053] It should be noted that the diffraction grating 2 is usually used to diffract light based on the diffraction equation to ensure that the output diffracted by the diffraction grating meets the requirements of narrowband filtering, thereby ensuring that the entire narrowband filter achieves narrowband filtering within the target band.

[0054] The diffraction equation can be: p (sin θ i +sin θ m )=mλ0; where p is the grating period, θ i Angle of incidence θ m λ is the m-th order diffraction angle, and λ0 is the center wavelength of the target band.

[0055] For example, such as Figure 2 As shown, the diffraction grating 2 is a one-dimensional grating, which includes multiple gratings arranged at equal intervals on the surface of the interference film 1.

[0056] Specifically, multiple grid lines Figure 1 The grids shown are arranged at equal intervals along the X-axis, with each grid extending along the Y-axis. The width of each grid along the X-axis is the grating ridge width *w*, and the spacing between the same side of any two adjacent grids along the X-axis is the grating period *p*. It should be noted that the Y-axis is perpendicular to both the X-axis and Z-axis. Figure 1 It is not specifically shown in the text.

[0057] The narrowband filter shown in this invention achieves synergistic enhancement of interference and diffraction effects by integrating a diffraction grating 2 on the surface of the interference film 1. The light first passes through the interference film 1, which is composed of alternating high-refractive-index film layers 101 and low-refractive-index film layers 102. The spectrum is initially shaped and high-transmittance of the predetermined wavelength band is achieved by utilizing the multi-beam interference principle. Subsequently, the light is diffracted by the diffraction grating 2. The wavelength is finely selected by utilizing the dispersion characteristics of the grating. This hybrid mechanism of "interference + diffraction" enables the two to produce a phase synergistic effect at the target wavelength.

[0058] The narrowband filter provided by this invention operates through the coupling effect of the interference film and the diffraction grating. It discovers and utilizes the synergistic effect of the ratio of the interference film thickness d to the grating depth h, and the ratio of the grating ridge width w to the grating period p on the filtering performance. This invention finds that, in particular, when 0.65≤h / d≤0.80 or 1.37≤h / d≤1.53, and 0.6≤w / p≤0.66, the phase modulation introduced by the grating and the multi-beam interference effect of the interference film achieve the optimal phase matching state. Thus, while ensuring the narrowband filtering effect, the center wavelength shift can be significantly suppressed within any target wavelength range within the predetermined band, achieving precise locking of the target wavelength.

[0059] Research has found that when 0.65≤h / d≤0.80 or 1.37≤h / d≤1.53, a narrow transmission bandwidth at the target wavelength can be effectively controlled. When 0.6≤w / p≤0.66, the center wavelength shift can be effectively controlled, ensuring the presence of a center wavelength. Ultimately, this achieves a narrow transmission bandwidth and a stable center wavelength for the narrowband filter at the target wavelength.

[0060] The research suggests that the optimal phase matching between the phase modulation introduced by the grating and the multi-beam interference effect of the interferometer film is achieved when h / d is within this range, resulting in extremely high precision and a very narrow bandwidth. The narrow and steep transmission spectrum means that external interference (such as slight fluctuations in the light source wavelength) is less likely to escape the passband, thus exhibiting a more stable wavelength locking effect at the system level. This ensures an extremely narrow bandwidth and high sideband suppression, allowing the filter to maintain excellent frequency selectivity even under complex environmental interference.

[0061] Studies have found that when h / d is outside this range, sideband suppression is insufficient, resulting in a wider effective bandwidth. This may be because when the h / d ratio is small, longer wavelengths of light may be more likely to pass through the diffraction grating, thus improving the efficiency of the sideband portion with a larger target wavelength. When the h / d ratio is large, the diffraction grating improves the efficiency of all sideband portions, with a greater improvement in the efficiency of the sideband portion with a smaller target wavelength. This can easily lead to a decrease in the signal-to-noise ratio of the narrowband filter.

[0062] The ratio of h to d can be 0.65, 0.73, 0.80, 1.37, 1.40, 1.53, or other suitable values, without any specific limitation.

[0063] Furthermore, a slight mismatch may exist between the Fabry-Perot resonant wavelength of the interferometer film and the Bragg diffraction wavelength of the grating. This mismatch can cause the actual filter center wavelength to shift relative to the theoretical target wavelength. When 0.6 ≤ w / p ≤ 0.66, the effective refractive index distribution of the grating may produce a nonlinear phase compensation effect. This effect precisely cancels out the phase error introduced by thickness fluctuations or refractive index changes in the interferometer film. Therefore, within this range, the filter center wavelength can achieve zero or minimal shift.

[0064] Studies have found that when the ratio of the grating ridge width *w* to the grating period *p* is outside this range, the center wavelength cannot be stabilized. This may be because the dominant wavelength of the grating diffraction shifts to shorter wavelengths, thus deviating from the target narrowband (target wavelength range), causing the actual wavelength of the filter device (the center wavelength of the narrowband) to deviate from the target wavelength. Conversely, when the ratio of the grating ridge width *w* to the grating period *p* is too large, the dominant wavelength of the grating diffraction shifts to longer wavelengths, also deviating from the target narrowband (target wavelength range), similarly causing the actual wavelength of the filter device to deviate from the target wavelength. Experiments have shown that satisfying the relationship 0.6 ≤ *w / p* ≤ 0.66 provides excellent narrowband performance at any wavelength within the predetermined wavelength range, indicating strong robustness in grating fabrication.

[0065] The ratio of w to p can be 0.6, 0.648, 0.66, or other suitable values, without any specific limitation.

[0066] Therefore, under the conditions of 0.65≤h / d≤0.80 or 1.37≤h / d≤1.53, and 0.6≤w / p≤0.66, the narrowband filter can achieve accurate narrowband filtering at a small scale of 1μm, ensuring good narrowband filtering effect in the target band, which is conducive to realizing monolithic integration of small-sized narrowband filters.

[0067] In particular, compared with existing large-size thin-film filter devices (e.g., with a thickness exceeding 10 μm), since this application uses a combination of interference and diffraction to achieve narrowband filtering, while taking into account the small-scale integration of the narrowband filter, the narrowband filtering can be adjusted by adjusting the structure of the interference thin film 1 and the diffraction grating 2 respectively. The entire narrowband filter has a simple structure, strong fabrication flexibility, high manufacturing tolerance, and improved robustness for large-scale manufacturing.

[0068] Compared to traditional methods that require thicker film layers, this invention achieves critical coupling using a specific thickness ratio. It can achieve the same or even better narrowband performance as thick films with a thinner total thickness, and it eliminates the need to accumulate phase difference by extending the grating interaction length. This allows filtering to be completed within an extremely short axial or lateral dimension, which enables the overall feature size of the filter to be controlled at the micrometer level. This greatly eliminates the need for large optical components required by traditional filters, perfectly matching the micrometer-level process nodes of photonic integrated circuits, and is conducive to high-density, monolithic integration.

[0069] In some embodiments, the total number of high-refractive-index film layer 101 and low-refractive-index film layer 102 can be set to 2-30 layers; for example, the total number of layers can be 2-10 layers.

[0070] like Figure 1 As shown, in Figure 1 In the illustrated narrowband filter, the total number of layers is four, including the high-refractive-index film 101 and the low-refractive-index film 102. Two layers of each film are provided. This design ensures that the entire narrowband filter system contains five layers. This number of layers is a significant advantage compared to traditional thin-film filters with dozens of layers stacked on top of each other. Furthermore, the high-refractive-index film 101 and the low-refractive-index film 102 can be made of two different materials, making the structure of the entire narrowband filter simpler, the cost lower, the manufacturing process more streamlined, and the error accumulation less, thereby improving the robustness of large-scale manufacturing.

[0071] In some embodiments, such as Figure 1 and Figure 2 As shown, the narrowband filter also includes a substrate 3, an interference film 1 disposed on the substrate 3, and a diffraction grating 2 disposed on the side of the interference film 1 facing away from the substrate 3.

[0072] It is understandable that when fabricating a narrowband filter, magnetron sputtering or vapor deposition can be used to alternately deposit a high-refractive-index film 101 and a low-refractive-index film 102 on the substrate 3 to prepare an interference film 1. Then, a substrate layer is deposited on the surface of the interference film 1, and the substrate layer is processed by photolithography and etching to form a diffraction grating 2 on the surface of the interference film 1.

[0073] The substrate 3 can be a glass substrate with a refractive index of 1.6-2.0.

[0074] In some embodiments, the high refractive index film 101 is made of any one of niobium pentoxide, titanium dioxide, tantalum pentoxide, hafnium dioxide, and zirconium dioxide; and / or, the low refractive index film 102 is made of silicon dioxide; and / or, the diffraction grating 2 is made of silicon nitride.

[0075] It should be noted that the refractive index of niobium pentoxide is 2.3, the refractive index of titanium dioxide is 2.3-2.4, the refractive index of tantalum pentoxide is 2.1, the refractive index of hafnium dioxide is 2.0-2.15, the refractive index of zirconium dioxide is 2.05, the refractive index of silicon dioxide is 1.44, and the refractive index of silicon nitride is 1.97-2.2.

[0076] Specifically, the high-refractive-index film 101 is made of niobium pentoxide, the low-refractive-index film 102 is made of silicon dioxide, and the diffraction grating 2 is made of silicon nitride.

[0077] It should be noted that the material of the diffraction grating 2 can also be any of niobium pentoxide, titanium dioxide, tantalum pentoxide, hafnium dioxide and zirconium dioxide. However, since silicon nitride is easier to process and can ensure product yield, silicon nitride is selected as the material of the diffraction grating 2 shown in this embodiment.

[0078] In some embodiments, such as Figure 2 As shown, under the condition that 0.65≤h / d≤0.80, 0.86μm≤h+d≤0.95μm.

[0079] It is understandable that although this application uses a combination of interference and diffraction to achieve narrowband filtering, when the thickness h of the diffraction grating is less than the thickness d of the interference film, the interference film can be set with relatively more layers. The interference film has a strong pre-selection effect on light interference. At this time, the diffraction grating is mainly responsible for locking the narrowband filtering of the target band. Thus, the total thickness corresponding to h and d can be set to be smaller, thereby reducing the total thickness of the narrowband filter layers. This is beneficial for the large-scale fabrication and monolithic integration of the narrowband filter at the 1μm scale.

[0080] In this embodiment, by limiting the total thickness corresponding to h and d to the range of 0.86-0.95 μm, the efficiency of the sideband portion can be minimized as much as possible, so as to ensure the narrowband filtering effect of the narrowband filter in the target band.

[0081] The total thickness corresponding to h and d can be 0.86μm, 0.908μm, 0.95μm, or other suitable values, without any specific limitation.

[0082] In some embodiments, such as Figure 2 As shown, under the condition that 1.37≤h / d≤1.53, 1.24μm≤h+d<≤1.33μm.

[0083] Understandably, when the thickness h of the diffraction grating is greater than the thickness d of the interference film, the interference film can have relatively fewer layers, weakening the interference preselection effect of the interference film on light. The diffraction grating then needs a larger thickness to ensure both target wavelength locking and narrowband filtering performance. In this case, the total thickness corresponding to h and d can be set relatively large. By limiting the total thickness corresponding to h and d to the range of 1.24-1.33 μm, which is larger than the aforementioned range of 0.86-0.95 μm, it is still possible to ensure that the total thickness of the filter film is controlled within 1.5 μm. Furthermore, the increased film thickness enhances the narrowband filtering effect of the narrowband filter in the target wavelength band and helps improve the signal-to-noise ratio of the narrowband filter.

[0084] The total thickness corresponding to h and d can be 1.24μm, 1.30μm, 1.33μm, or other suitable values, without any specific limitation.

[0085] In some embodiments, the thickness of the high-refractive-index film is λ0 / (4n1), and the thickness of the low-refractive-index film is λ0 / (4n2); where λ0 is the center wavelength of the target band, n1 is the refractive index of the high-refractive-index film, and n2 is the refractive index of the low-refractive-index film.

[0086] It is understandable that, due to the surface integration of diffraction gratings on the interference film, and the fact that the interference film is set with alternating high-refractive-index and low-refractive-index layers, by setting the thickness of the high-refractive-index layer to λ0 / (4n1) and the thickness of the low-refractive-index layer to λ0 / (4n2), the entire interference film is stacked sequentially according to a quarter of the optical thickness to produce thin-film interference of light. This ensures that, near λ0, the echoes reflected multiple times from the high- and low-refractive-index interfaces are superimposed in phase, while when deviating from λ0, the echoes from adjacent layers are phase-destructive and suppressed, thus forming a basic transmission window for interference pre-selection of light. The light output from the interference film is then angle-wavelength locked by the diffraction equation of the diffraction grating, ensuring that the entire narrowband filter accurately achieves narrowband filtering at the 1μm scale.

[0087] In some embodiments, for the diffraction grating 2, 0.843μm≤p≤0.8655μm.

[0088] Understandably, according to the diffraction equation of diffraction grating 2, the grating period p can lock the center wavelength λ0 of the target band output by the diffraction grating. For example, when p = 0.8558 μm, the center wavelength λ0 of the target band is 1550 nm; when p = 0.843 μm, the center wavelength λ0 of the target band is 1530 nm; and when p = 0.8655 μm, the center wavelength λ0 of the target band is 1565 nm. Therefore, by limiting p to 0.843-0.8655 μm, this application can ensure that the wavelength range of the target band is 1530 nm to 1565 nm. This wavelength range covers the C-band. Since the C-band is the most classic and commonly used low-loss window in optical fiber communication, this application can perform optical fiber communication based on light filtered by a narrowband filter.

[0089] Experimental studies have shown that by adjusting the grating period p, the center wavelength λ0 of the target band output by the diffraction grating can be locked. Within the entire C-band, when 0.65≤h / d≤0.80 or 1.37≤h / d≤1.53 and 0.6≤w / p≤0.66 are satisfied, any target band has a narrow transmission bandwidth and a stable center wavelength.

[0090] In some embodiments, the narrowband filter shown in this application has an efficiency of not less than 99.7% at the center wavelength of the target band, and an efficiency of not more than 15% in the sideband regions on both sides of the main passband. The main passband is the spectral range of the target band centered on the target center wavelength, and the sidebands are the unwanted transmission regions on both sides of the main passband.

[0091] Referring to Table 1 below, the solutions of the above embodiments will be specifically described through specific examples.

[0092] Table 1:

[0093] Figure 3 This is a simulation diagram of the C-band 1550nm narrowband effect under the parameter conditions of Embodiment 1 of the present invention. Figure 3 It can be seen that when the grating period p = 0.8558 μm, w / p = 0.648, h / d = 0.73, and h+d = 0.908 μm are satisfied, Figure 3 The center wavelength of the narrow band is located at 1550nm, and the efficiency (light transmittance) at the center wavelength is greater than 99.7%, while the efficiency (light transmittance) of the side band is mainly less than 3%.

[0094] Figure 4 This is a simulation diagram of the C-band 1550nm narrowband effect under the parameter conditions of Embodiment 2 of the present invention. Figure 4It can be seen that when the grating period p = 0.8558 μm, w / p = 0.648, h / d = 0.65, and h+d = 0.86 μm are satisfied, Figure 4 The center wavelength of the narrow band portion is located at 1550nm, meaning that the narrow band effect and the target wavelength are still maintained, and the efficiency (light transmittance) at the center wavelength is greater than 99.7%. Since the values ​​of (h / d) and (h+d) in Example 2 are close to the lower limit of the corresponding range of these two relationships, compared with Example 1, the grating diffraction of Example 2 is more conducive to the transmission of the long-wavelength portion. Therefore, the efficiency of the sideband portion with a larger target wavelength is improved (the efficiency is about 10%), while the efficiency of the sideband portion with a smaller target wavelength remains at around 3%.

[0095] Figure 5 This is a simulation diagram of the C-band 1550nm narrowband effect under the parameter conditions of Embodiment 3 of the present invention. Figure 5 It can be seen that when the grating period p = 0.8558 μm, w / p = 0.648, h / d = 1.37, and h+d = 1.24 μm are satisfied, Figure 5 The center wavelength of the narrow band portion is located at 1550nm, meaning that the narrow band effect and the target wavelength are still maintained, and the efficiency (light transmittance) at the center wavelength is greater than 99.7%. Since the values ​​of (h / d) and (h+d) in Example 3 are close to the lower limit of the corresponding range of these two relationships, compared with Example 1, the grating diffraction of Example 3 is more conducive to the transmission of the long-wavelength portion. Therefore, the efficiency of the sideband portion with a larger target wavelength is improved (the efficiency is about 10%), while the efficiency of the sideband portion with a smaller target wavelength remains at around 3%.

[0096] Figure 6 This is a simulation diagram of the C-band 1550nm narrowband effect under the parameter conditions of Embodiment 4 of the present invention. Figure 6 It can be seen that when the grating period p = 0.8558 μm, w / p = 0.648, h / d = 0.8, and h+d = 0.95 μm, Figure 6 The center wavelength of the narrowband portion is located at 1550nm, meaning that the narrowband effect and the target wavelength are still maintained, and the efficiency (light transmittance) at the center wavelength is greater than 99.7%. Since the values ​​of (h / d) and (h+d) in Example 4 are close to the upper limit of the corresponding range of these two relationships, compared with Example 1, the efficiency of all sideband portions except the narrowband portion in Example 4 is improved, especially the efficiency of the sideband portion smaller than the target wavelength is improved more (approximately 15%), and the efficiency of the sideband portion larger than the target wavelength is approximately between 8% and 10%.

[0097] Figure 7This is a simulation diagram of the C-band 1550nm narrowband effect under the parameter conditions of Embodiment 5 of the present invention. Figure 7 It can be seen that when the grating period p = 0.8558 μm, w / p = 0.648, h / d = 1.53, and h+d = 1.33 μm, Figure 7 The center wavelength of the narrowband portion is located at 1550nm, meaning that the narrowband effect and the target wavelength are still maintained, and the efficiency (light transmittance) at the center wavelength is greater than 99.7%. Since the values ​​of (h / d) and (h+d) in Example 5 are close to the upper limit of the corresponding range of these two relationships, compared with Example 1, the efficiency of all sideband portions except the narrowband portion in Example 5 is improved, especially the efficiency of the sideband portion smaller than the target wavelength is improved more (approximately 15%), and the efficiency of the sideband portion larger than the target wavelength is approximately between 8% and 10%.

[0098] Figure 8 This is a simulation diagram of the C-band 1550nm narrowband effect under the parameter conditions of Embodiment 6 of the present invention. Figure 8 It can be seen that when the grating period p=0.8558μm, w / p=0.60, h / d=0.73, and h+d=0.908μm are satisfied, the narrowband filtering effect of Example 6 is comparable to that of Example 1. The efficiency of the sideband portion is suppressed to a low level of 3%. However, since the value of (w / p) is close to the lower limit of the range corresponding to this relationship, the actual wavelength of the narrowband filter is slightly shifted below the target wavelength (1550nm).

[0099] Figure 9 This is a simulation diagram of the C-band 1550nm narrowband effect under the parameter conditions of Embodiment 7 of the present invention. Figure 9 It can be seen that when the grating period p=0.8558μm, w / p=0.66, h / d=0.73, and h+d=0.908μm are satisfied, the narrowband filtering effect of Example 7 is comparable to that of Example 1. The efficiency of the sideband portion is suppressed to a low level of 3%. However, since the value of (w / p) is close to the upper limit of the range corresponding to this relationship, the actual wavelength of the narrowband filter is slightly shifted towards the target wavelength (1550nm).

[0100] Figure 10 This is a simulation diagram of the C-band 1530nm narrowband effect under the parameter conditions of Embodiment 8 of the present invention. Figure 10 It can be seen that when the grating period p = 0.843 μm, w / p = 0.648, h / d = 0.73, and h+d = 0.908 μm are satisfied, Figure 10 The center wavelength of the mid-narrow band is located at 1530nm, and the efficiency (light transmittance) at the center wavelength is greater than 99.7%, while the efficiency (light transmittance) of the side band is mainly less than 3%.

[0101] Figure 11 This is a simulation diagram of the C-band 1530nm narrowband effect under the parameter conditions of Embodiment 9 of the present invention. Figure 11 It can be seen that when the grating period p = 0.843 μm, w / p = 0.648, h / d = 0.65, and h+d = 0.86 μm are satisfied, Figure 11 The center wavelength of the narrow band portion is located at 1530nm, meaning that the narrow band effect and the target wavelength are still maintained, and the efficiency (light transmittance) at the center wavelength is greater than 99.7%. Since the values ​​of (h / d) and (h+d) in Example 9 are close to the lower limit of the corresponding range of these two relationships, compared with Example 8, the grating diffraction of Example 9 is more conducive to the transmission of the long-wavelength portion. Therefore, the efficiency of the sideband portion with a larger target wavelength is improved (the efficiency is about 10%), while the efficiency of the sideband portion with a smaller target wavelength remains at around 3%.

[0102] Figure 12 This is a simulation diagram of the C-band 1530nm narrowband effect under the parameter conditions of Embodiment 10 of the present invention. Figure 12 It can be seen that when the grating period p = 0.843 μm, w / p = 0.648, h / d = 1.37, and h+d = 1.24 μm are satisfied, Figure 12 The center wavelength of the narrow band portion is located at 1530nm, meaning that the narrow band effect and the target wavelength are still maintained, and the efficiency (light transmittance) at the center wavelength is greater than 99.7%. Since the values ​​of (h / d) and (h+d) in Example 10 are close to the lower limit of the corresponding range of these two relationships, compared with Example 8, the grating diffraction of Example 10 is more conducive to the transmission of the long-wavelength portion. Therefore, the efficiency of the sideband portion with a larger target wavelength is improved (the efficiency is about 10%), while the efficiency of the sideband portion with a larger target wavelength remains at around 3%.

[0103] Figure 13 This is a simulation diagram of the C-band 1530nm narrowband effect under the parameter conditions of Embodiment 11 of the present invention. Figure 13 It can be seen that when the grating period p = 0.843 μm, w / p = 0.648, h / d = 0.8, and h+d = 0.95 μm, Figure 13The center wavelength of the narrowband portion is located at 1530nm, meaning that the narrowband effect and the target wavelength are still maintained, and the efficiency (light transmittance) at the center wavelength is greater than 99.7%. Since the values ​​of (h / d) and (h+d) in Example 11 are close to the upper limit of the corresponding range of these two relationships, compared with Example 8, the efficiency of all sideband portions in Example 11 except for the narrowband portion is improved. The efficiency of the sideband portion smaller than the target wavelength is about 15%, and the efficiency of the sideband portion larger than the target wavelength is about 8%-10%.

[0104] Figure 14 This is a simulation diagram of the C-band 1530nm narrowband effect under the parameter conditions of Embodiment 12 of the present invention. Figure 14 It can be seen that when the grating period p = 0.843 μm, w / p = 0.648, h / d = 1.53, and h+d = 1.33 μm, Figure 14 The center wavelength of the narrowband portion is located at 1530nm, meaning that the narrowband effect and the target wavelength are still maintained, and the efficiency (light transmittance) at the center wavelength is greater than 99.7%. Since the values ​​of (h / d) and (h+d) in Example 12 are close to the upper limit of the corresponding range of these two relationships, compared with Example 8, the efficiency of all sideband portions except the narrowband portion in Example 12 is improved. The efficiency of the sideband portion smaller than the target wavelength is about 15%, and the efficiency of the sideband portion larger than the target wavelength is about 8%-10%.

[0105] Figure 15 This is a simulation diagram of the C-band 1530nm narrowband effect under the parameter conditions of Embodiment 13 of the present invention. Figure 13 It can be seen that when the grating period p=0.843μm, w / p=0.60, h / d=0.73, and h+d=0.908μm are satisfied, the narrowband filtering effect of Example 13 is comparable to that of Example 8. The efficiency of the sideband portion is suppressed to a low level of 3%. However, since the value of (w / p) is close to the lower limit of the range corresponding to this relationship, the actual wavelength of the narrowband filter is slightly shifted towards the target wavelength (1530nm) below.

[0106] Figure 16 This is a simulation diagram of the C-band 1530nm narrowband effect under the parameter conditions of Embodiment 14 of the present invention. Figure 16It can be seen that when the grating period p=0.843μm, w / p=0.66, h / d=0.73, and h+d=0.908μm are satisfied, the narrowband filtering effect of Example 14 is comparable to that of Example 8. The efficiency of the sideband portion is suppressed to a low level of 3%. However, since the value of (w / p) is close to the upper limit of the range corresponding to this relationship, the actual wavelength of the narrowband filter is slightly shifted towards the target wavelength (1530nm).

[0107] Figure 17 This is a simulation diagram of the C-band 1565nm narrowband effect under the parameter conditions of Embodiment 15 of the present invention. Figure 17 It can be seen that when the grating period p = 0.8655 μm, w / p = 0.648, h / d = 0.73, and h+d = 0.908 μm are satisfied, Figure 17 The center wavelength of the narrow band is 1565nm, and the efficiency (light transmittance) at the center wavelength is greater than 99.7%, while the efficiency (light transmittance) of the side band is mainly less than 3%.

[0108] Figure 18 This is a simulation diagram of the C-band 1565nm narrowband effect under the parameter conditions of Embodiment 16 of the present invention. Figure 18 It can be seen that when the grating period p = 0.8655 μm, w / p = 0.648, h / d = 0.65, and h+d = 0.86 μm are satisfied, Figure 18 The center wavelength of the narrowband portion is located at 1565 nm, meaning the narrowband effect and the target wavelength are still maintained, with an efficiency (light transmittance) greater than 99.7% at the center wavelength. Since the values ​​of (h / d) and (h+d) in Example 16 are close to the lower limit of the corresponding ranges of these two relationships, compared to Example 15, the grating diffraction in Example 16 is more favorable for the transmission of longer wavelengths. Therefore, the efficiency of the sideband portion, which is larger than the target wavelength, is improved (by approximately 10%), while the efficiency of the sideband portion, which is smaller than the target wavelength, remains around 3%. However, since the wavelength of the narrowband portion in Example 16 is located at the maximum position of the C-band at 1565 nm, the increase in efficiency of the sideband portion to the right of the target wavelength does not have an adverse effect.

[0109] Figure 19 This is a simulation diagram of the C-band 1565nm narrowband effect under the parameter conditions of Embodiment 17 of the present invention. Figure 19 It can be seen that when the grating period p = 0.8655 μm, w / p = 0.648, h / d = 1.37, and h+d = 1.24 μm are satisfied, Figure 19The center wavelength of the narrowband portion is located at 1565 nm, meaning the narrowband effect and the target wavelength are still maintained, with an efficiency (light transmittance) greater than 99.7% at the center wavelength. Since the values ​​of (h / d) and (h+d) in Example 17 are close to the lower limit of the corresponding ranges of these two relationships, compared to Example 15, the grating diffraction in Example 17 favors the transmission of the longer wavelength portion. Therefore, the efficiency of the sideband portion, which is larger than the target wavelength, is improved (by approximately 10%), while the efficiency of the sideband portion, which is smaller than the target wavelength, remains around 3%. However, since the wavelength of the narrowband portion in Example 17 is located at the maximum position of the C-band at 1565 nm, the increase in efficiency of the sideband portion to the right of the target wavelength does not have an adverse effect.

[0110] Figure 20 This is a simulation diagram of the C-band 1565nm narrowband effect under the parameter conditions of Embodiment 18 of the present invention. Figure 20 It can be seen that when the grating period p=0.8655μm, w / p=0.60, h / d=0.73, and h+d=0.908μm are satisfied, the narrowband filtering effect of Example 18 is comparable to that of Example 15. The efficiency of the sideband portion is suppressed to a low level of 3%. However, since the value of (w / p) is close to the lower limit of the range corresponding to this relationship, the actual wavelength of the narrowband filter is slightly shifted towards the target wavelength (1565nm) below.

[0111] Figure 21 This is a simulation diagram of the C-band 1565nm narrowband effect under the parameter conditions of Embodiment 19 of the present invention. Figure 21 It can be seen that when the grating period p=0.8655μm, w / p=0.66, h / d=0.73, and h+d=0.908μm are satisfied, the narrowband filtering effect of Example 19 is comparable to that of Example 15. The efficiency of the sideband portion is suppressed to a low level of 3%. However, since the value of (w / p) is close to the upper limit of the range corresponding to this relationship, the actual wavelength of the narrowband filter is slightly shifted towards the target wavelength (1565nm).

[0112] Figure 22 This is a simulation diagram of the C-band 1550nm narrowband effect under the parameter conditions of Comparative Example 1 of the present invention. Figure 22It can be seen that when the grating period p=0.8558μm, w / p=0.648, h / d=0.57, and h+d=0.86μm are satisfied, compared with the waveform diagram of Example 2 (h / d=0.65), since the value of (h / d) (0.57) in Comparative Example 1 is lower than the lower limit of the corresponding range (0.65) of this relationship, the efficiency of the sideband portion with a larger target wavelength increases significantly (more than 25%). This will cause serious interference to the target wavelength of 1550nm, resulting in the signal-to-noise ratio of the narrowband filter being far inferior to the filtering effect of the parameter range shown in this invention.

[0113] Figure 23 This is a simulation diagram of the C-band 1550nm narrowband effect under the parameter conditions of Comparative Example 2 of the present invention. Figure 23 It can be seen that when the grating period p=0.8558μm, w / p=0.648, h / d=1.62, and h+d=1.33μm are satisfied, compared with the waveform diagram of Example 5 (h / d=1.53), since the value of (h / d) (1.62) in Comparative Example 2 is higher than the upper limit of the corresponding range of this relationship (1.53), the efficiency of all sidebands in Comparative Example 2 except for the narrowband part is improved. In particular, the efficiency of the sideband part with a smaller wavelength than the target wavelength is improved even more (the efficiency reaches 30%). The efficiency of this part is equivalent to twice the efficiency of the corresponding band in Example 5, which leads to a significant reduction in the filtering effect of the narrowband filter.

[0114] As can be seen from the above, the narrowband filter of the present invention has the following beneficial effects: (1) The narrowband filter of the present invention optimizes the design of the thickness d of the interference film, the thickness h of the diffraction grating, the grating period p and the grating ridge width w of the diffraction grating, and achieves a good narrowband filtering effect at the micrometer scale. That is, it can maintain the narrowband filtering efficiency at the target wavelength while avoiding the sideband efficiency being increased too much and affecting the final signal-to-noise ratio. It is also beneficial for small-sized monolithic integration. (2) The narrowband filter of the present invention has a simple structure, few film layers and few types of film materials, strong robustness, and is suitable for large-scale fabrication; (3) The overall film thickness of the narrowband filter of the present invention is less than 1.5 μm, and it can be directly integrated on the device, for example, it is suitable for direct fabrication on the CPO substrate of the optical communication module; (4) The narrowband filter of the present invention has excellent performance throughout the C-band, can easily and accurately lock the working wavelength, and is simple and convenient to install and use.

[0115] In a second aspect, the present invention also provides an optical communication module including a narrowband filter as described above.

[0116] It is understood that since the optical communication module includes a narrowband filter, and the specific structure of the narrowband filter is as described in the above embodiments, the optical communication module of this embodiment includes all the technical solutions of the above embodiments. Therefore, it has at least all the beneficial effects achieved by all the technical solutions of the above embodiments, which will not be elaborated further.

[0117] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A narrowband filter, characterized in that, include: An interference thin film includes alternating layers of high-refractive-index and low-refractive-index films, the total thickness of the interference thin film being d; A diffraction grating is disposed on the surface of the interference film, and the diffraction grating has a grating period p, a grating ridge width w, and a grating thickness h; The structural parameters of the narrowband filter satisfy the following relationship: 0.65≤h / d≤0.80 or 1.37≤h / d≤1.53, and 0.6≤w / p≤0.

66.

2. The narrowband filter according to claim 1, characterized in that, Under the condition that 0.65≤h / d≤0.80, 0.86μm≤h+d≤0.95μm.

3. The narrowband filter according to claim 1, characterized in that, Under the condition that 1.37≤h / d≤1.53, 1.24μm≤h+d≤1.33μm.

4. The narrowband filter according to claim 1, characterized in that, 0.843μm≤p≤0.8655μm.

5. The narrowband filter according to any one of claims 1 to 4, characterized in that, The narrowband filter has an efficiency of not less than 99.7% at the center wavelength of the target band and an efficiency of not more than 15% in the sideband regions on both sides of the main passband.

6. The narrowband filter according to claim 5, characterized in that, The target band has a wavelength range of 1530nm to 1565nm.

7. The narrowband filter according to any one of claims 1 to 4, characterized in that, The narrowband filter further includes a substrate, the interference film is disposed on the substrate, and the diffraction grating is disposed on the side of the interference film opposite to the substrate.

8. The narrowband filter according to any one of claims 1 to 4, characterized in that, The material of the high refractive index film includes any one of niobium pentoxide, titanium dioxide, tantalum pentoxide, hafnium dioxide, and zirconium dioxide; And / or, the material of the low refractive index film is silicon dioxide; And / or, the total number of the high refractive index film layer and the low refractive index film layer is 2-30 layers; And / or, the material of the diffraction grating is silicon nitride.

9. The narrowband filter according to claim 1, characterized in that, The thickness of the high refractive index film is λ0 / (4n1), and the thickness of the low refractive index film is λ0 / (4n2). Wherein, λ0 is the center wavelength of the narrow band of the target band, n1 is the refractive index of the high refractive index film, and n2 is the refractive index of the low refractive index film.

10. An optical communication module, characterized in that, Includes the narrowband filter as described in any one of claims 1 to 9.

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