An ultra-narrow-band optical filter with adjustable wavelength and controllable bandwidth and its control method

Abstract

The present invention discloses an ultra-narrowband optical filter with adjustable wavelength and controllable bandwidth and a control method thereof. A bottom dielectric flat film, a microcavity, a middle dielectric flat film, a dielectric grating and a top dielectric flat film are sequentially laid on a substrate metal film; by adjusting the angle of the incident light and changing the refractive index of the material in the microcavity, the range adjustment of the output wavelength of the ultra-narrowband optical filter can be achieved; by adjusting the thickness of the dielectric flat plate, the microcavity and the dielectric grating structure parameters, the bandwidth of the ultra-narrowband optical filter can be controlled. The present invention combines a multi-layer dielectric flat plate with a single-layer dielectric grating to provide an ultra-narrowband filter structure for optical filtering and a method for controlling bandwidth and wavelength. Compared with existing narrowband filters, the bandwidth reaches 8.51e‑5nm, and has the characteristics of wide-range tunable filtering band and controllable bandwidth.

Description

Technical Field

[0001] The present invention relates to a filter structure composed of a multi-layer waveguide and a single-layer grating, and in particular to an ultra-narrowband optical filter with adjustable wavelength and controllable bandwidth and a control method thereof, which can realize multi-band tunable and bandwidth-controllable ultra-narrowband filtering applications, and belongs to the field of waveguide optics technology. Background Art

[0002] Ultra-narrowband filters play a vital role in a variety of applications such as lidar, optical satellite communications, gas detection, and multispectral imaging. Traditional narrowband filters generally use two dielectric materials with a large difference in refractive index, which are alternately deposited on a substrate and use the interference effect generated by the thin film structure to achieve filtering. Once the material and number of layers of the structure are determined, the filtering band is also determined. Therefore, this method can only achieve single-band filtering, and the production cycle is long, the process requirements are rigorous, and the cost is also high. The number of thin films contained in the narrowband filter designed based on the guided mode resonance effect is generally no more than five layers, the structure is simple, and the production is easy. It has excellent characteristics such as high peak reflectivity (transmittance), low bypass band reflection, narrow band and controllable bandwidth.

[0003] Before the present invention was made, in 1992, Magnusson et al. first proposed to design an optical filter using the guided-mode resonance effect of a grating-waveguide structure, and pointed out that such an optical filter can be used as a basic optical element and widely used in various optical systems (see reference: SS Wang, and R. Magnusson, "Theory and applications of guided-mode resonance filters," Applied Optics 32, 2606-2613 (1993).). In recent years, the design and research of narrowband guided-mode resonance filters have received increasing attention and have been reported. Li et al. studied a large-range tunable guided-mode resonance filter based on dielectric grating in the visible light band. The operating wavelength can be tuned in the range of 491nm to 690nm by changing the incident angle, and the minimum filtering bandwidth can reach 0.0012nm (see reference: C. Li, K. Zhang, Y. Zhang, Y. Cheng, and W. Kong, "Large-rangewavelength tunable guided-mode resonance filter based on dielectric grating,"Optics Communications 437, 271-275 (2019).). Zheng et al. studied a structure composed of a single-layer grating and a gradient refractive index substrate, realizing the design of a bandstop filter with both ultra-narrow linewidth and angle-insensitive characteristics, with a maximum bandwidth of 1.1nm (see reference: G. Zheng, X. Zou, L. Xu, and J. Wang, "Singlelayer narrow bandwidth angle-insensitive guided-mode resonance bandstop filters," Optik 130, 19-23 (2017).). According to existing reports, research on narrowband filters still faces some problems and challenges: the filtering bandwidth is difficult to be ultra-narrowband (the filtering bandwidth is below the MHz level); the central wavelength of the filter is difficult to tune over a large range; the central frequency of the filter is difficult to remain stable for a long time, etc. Summary of the invention

[0004] In view of the shortcomings of existing filters in that the filtering bandwidth is difficult to be ultra-narrowband and the filtering center is difficult to tune over a large range, the present invention provides an ultra-narrowband filter structure with tunable wavelength and controllable bandwidth based on the principle of guided mode resonance and a control method thereof, which can not only realize ultra-narrowband filtering of a single band (ultra-narrowband filtering generally refers to filtering bandwidth below the MHz level), but also realize multi-band adjustable filtering by changing the incident angle or other structural parameters, and the filtering bandwidth has a certain degree of controllability.

[0005] In order to achieve the above-mentioned purpose of the invention, the technical solution adopted by the present invention provides an ultra-narrowband optical filter with adjustable wavelength and controllable bandwidth, which includes a single-layer dielectric grating and a multi-layer dielectric planar waveguide structure, and a bottom dielectric planar film, a microcavity, a middle dielectric planar film, a dielectric grating and a top dielectric planar film are sequentially covered on a substrate metal film; the thickness of the bottom dielectric planar film is 400nm~500nm, the thickness of the middle dielectric planar film is 450nm~500nm, and the thickness of the top dielectric planar film is 100nm~200nm; the thickness of the microcavity is 900nm~1050nm, and the microcavity is filled with gas or liquid; the dielectric grating has a period of 1498nm~1501nm, a slit width of 900nm~1060nm, and a thickness of 100nm~250nm.

[0006] The ultra-narrowband optical filter with adjustable wavelength and controllable bandwidth described in the present invention has a refractive index of 1-1.0005 for the material filled with gas in its microcavity and a refractive index of 1.3-1.35 for the material filled with liquid in its microcavity.

[0007] The technical solution of the present invention also includes a wavelength and bandwidth control method of an ultra-narrowband optical filter as described above, and the wavelength control method is as follows:

[0008] (1) Adjust the wavelength by adjusting the angle of incident light

[0009] When the incident light is TE polarized and the incident angle is in the range of -3º to 3º, the wavelength bandwidth of the spectrum with absorption response is 3.57e-4nm to 8.51e-5nm; when the incident light is TM polarized and the incident angle is in the range of -30º to 30º, the wavelength bandwidth of the spectrum with absorption response is 0.023nm to 0.11nm.

[0010] (2) Adjusting the wavelength by changing the refractive index of the material in the microcavity

[0011] (a) Under the condition of TE polarization of the incident light, when the refractive index of the material in the microcavity is in the gas refractive index range of 1 to 1.0005, the wavelength bandwidth range is 8.51e-5nm to 8.57e-5nm; when the refractive index of the material in the microcavity is in the liquid refractive index range of 1.3 to 1.35, the resonance wavelength redshifts from 1556.1976nm to 1557.6167nm as the refractive index of the material in the microcavity increases;

[0012] (b) Under the condition of TM polarization of the incident light, when the refractive index of the material in the microcavity is within the gas refractive index range of 1 to 1.0005, the resonance wavelength red-shifts from 2150.514nm to 2150.718nm as the refractive index of the material in the microcavity increases, and its bandwidth value remains unchanged at 0.023nm; when the refractive index of the material in the microcavity is within the liquid refractive index range of 1.3 to 1.35, the resonance wavelength red-shifts from 2411.628nm to 2434.611nm as the refractive index of the material in the microcavity increases;

[0013] (3) First, method (1) is used to adjust the wavelength over a large range by changing the angle of the incident light, and then method (2) is used to adjust the wavelength over a small range by changing the refractive index of the material in the microcavity, thereby making the adjustment result more accurate.

[0014] The bandwidth control method is as follows:

[0015] (1) Under the condition of TM polarization of the incident light, an optical filter with a bandwidth ranging from 4.14e-5nm to 6.68e-4nm is obtained by designing the thickness of the dielectric slab, microcavity and dielectric grating structure parameters;

[0016] (2) When the incident light is TM polarized, an optical filter with a bandwidth range of 0.01 nm to 0.04 nm is obtained by designing the thickness of the dielectric slab, microcavity, and dielectric grating structure parameters.

[0017] The present invention is based on the principle of guided mode resonance of waveguide gratings, and the guided mode resonance effect is essentially an abnormal diffraction phenomenon in a sub-wavelength grating structure, which means that when a certain high-order evanescent wave generated by the grating matches the leakage mode supported by the waveguide grating structure, this leakage mode will be strongly coupled with the external propagating light wave, resulting in redistribution of light wave energy. Due to the periodic modulation of the grating, the coupled energy will be completely reflected or transmitted, so a sharp reflection peak or transmission peak appears at the resonant wavelength. This is the basic principle of guided mode resonance. Based on the principle of guided mode resonance of waveguide gratings, according to the Helmholtz equation and the boundary conditions of the electromagnetic field, the waveguide equation of the ultra-narrowband filter structure provided by the present invention is obtained as shown in formula (1):

[0018] (1)

[0019] Where d1, d2, d4, d6, d3, and d5 are the thicknesses of the substrate metal film, the bottom, middle, and top dielectric flat films, the microcavity, and the dielectric grating, respectively; m is the number of guided modes allowed to propagate in the structure; ε is the dielectric constant of the material; β is the propagation constant; k0 is the wave number in free space and k0=2π / λ; γ, δ, and T are parameters defined to simplify the formulas. The relationships between them and the above variables are shown in equations (2) to (5):

[0020] (2)

[0021] (3)

[0022] (4)

[0023] (5)

[0024] According to equations (1) to (5), the propagation modes supported by the ultra-narrowband filter structure provided by the present invention and the position where each mode resonates can be obtained. The reflection (or transmission) diffraction efficiency under different polarization conditions can be obtained using rigorous coupled wave analysis theory. The propagation constant β in equation (2) is a complex number. The imaginary part of the propagation constant represents the leakage of the waveguide, which determines not only the propagation length of the mode, but also the bandwidth of the resonance. The resonance linewidth is defined as follows (6):

[0025] (6)

[0026] in, represents the imaginary part of the propagation constant β, represents the resonance wavelength, Represents the period of the dielectric grating.

[0027] The ultra-narrowband filter with tunable wavelength and controllable bandwidth provided by the present invention includes a substrate metal film, a multilayer dielectric flat film, a single-layer dielectric grating and a microcavity. It is based on the principle of guided mode resonance. In order to achieve narrowband filtering, a grating structure is added to the structure. According to the strict coupled wave theory and waveguide equation, the propagation mode allowed by the ultra-narrowband filter structure provided by the present invention can be calculated to optimize the structural parameters. Without changing the structural parameters, a large range of tuning of the working band can be achieved by changing the incident angle, and the controllable bandwidth is reflected in the linear relationship between the spectral bandwidth and different structural parameters. In addition, since the ultra-narrowband filter structure provided by the present invention contains a microcavity structure, gas or liquid materials with different refractive indices are filled in the microcavity, so that the tuning of a small range of working bands can be achieved and the bandwidth is also controllable.

[0028] Compared with the prior art, the present invention has the following significant features:

[0029] 1. The present invention combines a multi-layer dielectric plate and a single-layer dielectric grating to provide an ultra-narrowband filter structure for optical filtering. Compared with existing narrowband filters, the filter band can be tuned over a wide range, the filter bandwidth reaches 8.51e-5nm (converted to a frequency of 106KHz), and the bandwidth is controllable.

[0030] 2. The ultra-narrowband filter structure provided by the present invention can not only realize ultra-narrowband filtering in a large range by changing the incident angle, but also realize ultra-narrowband filtering in a small range by changing the refractive index of the filling material in the microcavity. The filtering bandwidth varies linearly with the refractive index and is controllable. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is a schematic diagram of the planar structure of an ultra-narrowband filter with tunable wavelength and controllable bandwidth provided by an embodiment of the present invention;

[0032] Figure 2 is a spectrum diagram of the ultra-narrowband filter structure provided by an embodiment of the present invention under different polarized light incident conditions;

[0033] Figure 3 is a graph showing the relationship between the incident angle and the resonance wavelength obtained when TM polarized light is incident on the ultra-narrowband filter structure provided in this embodiment;

[0034] Figure 4 is a graph showing the relationship between the incident angle and the resonance peak bandwidth obtained when TM polarized light is incident on the ultra-narrowband filter structure provided in this embodiment;

[0035] Figure 5 is a graph showing the relationship between the incident angle and the resonance wavelength of the ultra-narrowband filter structure provided in this embodiment when TE polarized light is incident;

[0036] Figure 6 is a graph showing the relationship between the incident angle and the resonance peak bandwidth of the ultra-narrowband filter structure provided in this embodiment when TE polarized light is incident;

[0037] Figure 7 is a relationship diagram of the change of the resonant wavelength obtained by the ultra-narrowband filter structure provided by this embodiment under the condition of TM polarized light incident and the change of the refractive index of the material in the microcavity;

[0038] Figure 8 is a graph showing the relationship between the resonance peak bandwidth obtained by the ultra-narrowband filter structure provided in this embodiment under the condition of TM polarized light incidence and the refractive index of the material in the microcavity;

[0039] Fig. 9 is a relationship diagram of the change of the resonant wavelength obtained by the ultra-narrowband filter structure provided by this embodiment under the condition of TM polarized light incident and the change of the refractive index of the material in the microcavity;

[0040] Fig.10 is a graph showing the relationship between the resonance peak bandwidth obtained by the ultra-narrowband filter structure provided in this embodiment under the condition of TM polarized light incidence and the refractive index of the material in the microcavity;

[0041] Fig.11 is a relationship diagram of the change of the resonant wavelength obtained by the ultra-narrowband filter structure provided by this embodiment under the condition of TE polarized light incident and the change of the refractive index of the material in the microcavity;

[0042] Fig.12 is a graph showing the relationship between the resonance peak bandwidth obtained by the ultra-narrowband filter structure provided in this embodiment when TE polarized light is incident and the refractive index of the material in the microcavity;

[0043] Fig.13 is a relationship diagram of the change of the resonant wavelength obtained by the ultra-narrowband filter structure provided by this embodiment under the condition of TE polarized light incident and the change of the refractive index of the material in the microcavity;

[0044] Fig.14 is a graph showing the relationship between the resonance peak bandwidth obtained by the ultra-narrowband filter structure provided in this embodiment when TE polarized light is incident and the refractive index of the material in the microcavity;

[0045] Fig.15 is a graph showing the relationship between the thickness of the underlying dielectric plate and the bandwidth of the ultra-narrowband filter structure provided by an embodiment of the present invention when TE polarized light is incident;

[0046] Fig.16 is a graph showing the relationship between the thickness and bandwidth of the microcavity obtained when the ultra-narrowband filter structure provided by an embodiment of the present invention is incident on TE polarized light;

[0047] Fig.17 is a graph showing the relationship between the thickness of the dielectric plate and the bandwidth obtained when TE polarized light is incident on the ultra-narrowband filter structure provided by an embodiment of the present invention;

[0048] Fig.18 is a graph showing the relationship between the thickness and bandwidth of a single-layer dielectric grating obtained when TE polarized light is incident on the ultra-narrowband filter structure provided by an embodiment of the present invention;

[0049] Fig.19 is a relationship diagram between the slit width and bandwidth of a single-layer dielectric grating obtained when TE polarized light is incident on the ultra-narrowband filter structure provided by an embodiment of the present invention;

[0050] Fig. 20is a relationship diagram between the period and bandwidth of a single-layer dielectric grating obtained when TE polarized light is incident on the ultra-narrowband filter structure provided by an embodiment of the present invention;

[0051] In the figure, 1. substrate metal film; 2. bottom dielectric flat film; 3. microcavity; 4. middle dielectric flat film; 5. dielectric grating; 6. top dielectric flat film; 7. incident light. DETAILED DESCRIPTION

[0052] The technical solution of the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments.

[0053] Example 1

[0054] See attached Figure 1 , which is a schematic diagram of the planar structure of the bandwidth-controllable and wavelength-adjustable ultra-narrowband optical filter provided in this embodiment. It is a single-layer dielectric grating and a multi-layer dielectric planar waveguide structure. In this embodiment, a three-layer dielectric planar film is used. The specific structure is: a bottom dielectric planar film 2, a microcavity 3, a middle dielectric planar film 4, a single-layer dielectric grating 5 and a top dielectric planar film 6 are sequentially laid on a substrate metal film 1; and an incident light 7 is incident on the surface of the structure from the top of the structure.

[0055] In this embodiment, the substrate metal film 1 is Au with a thickness of 120nm; the bottom dielectric flat film 2 is a ZrO film with a thickness of 450nm; the thickness of the microcavity 3 is 930nm, and the material in the microcavity can be selected from gases or liquids with different refractive indices. In this embodiment, a vacuum state is adopted, that is, the refractive index is 1; the thickness of the middle dielectric flat film 4 is 460nm, and the refractive index of the selected material film is 2.33; the material of the grating 5 is composed of SiO2 and MgF2, the thickness of the grating is 180nm, and the unit period of the grating is 1500nm; the top dielectric flat film 6 is SiO2 with a thickness of 150nm.

[0056] See attached Figure 2 , is the absorption spectrum diagram of the ultra-narrowband filter structure provided in this embodiment obtained under different polarized light incident conditions, and the incident light is incident under two polarization conditions, TE and TM. Figure 2 It can be seen that when the incident light is TE polarized, an ultra-narrow resonance peak is excited at 1550nm with a bandwidth of 8.51e-5nm (i.e. 106KHz); when the incident light is TM polarized, a resonance peak is excited at 2277nm with a bandwidth of 0.068nm.

[0057] See attached Figure 3, is a graph showing the relationship between the incident angle and the resonant wavelength of the ultra-narrowband filter structure provided in this embodiment when TM polarized light is incident. In the figure, curves 1, 2, 3 and 4 represent incident angles θ of θ=0º, θ=1º, θ=2º, and θ=3º, respectively. It can be seen from the figure that as the incident angle increases, the resonant wavelength redshifts. For every 1° increase in the incident angle, the resonant wavelength redshifts 18nm, and the absorbance of the resonance peak remains above 93%.

[0058] See attached Figure 4 , is a graph showing the relationship between the incident angle and the resonance peak bandwidth of the ultra-narrowband filter structure provided in this embodiment under the condition of TM polarized light incident. It can be seen from the graph that the bandwidth gradually increases with the increase of the incident angle.

[0059] See attached Figure 5 , is a graph showing the relationship between the incident angle and the resonant wavelength obtained under the condition of TE polarized light incident on the ultra-narrowband filter structure provided in this embodiment. In the figure, curves 1, 2, 3 and 4 represent incident angles θ of θ=0º, θ=1º, θ=2º, and θ=3º, respectively. It can be seen from the figure that as the incident angle increases, the resonant wavelength blue-shifts. For every 1° increase in the incident angle, the resonant wavelength blue-shifts by 11nm, but the absorbance decreases as the incident angle increases.

[0060] See attached Figure 6 , is a relationship diagram between the incident angle and the resonance peak bandwidth of the ultra-narrowband filter structure provided in this embodiment under the condition of TE polarized light incident. It can be seen from the figure that the bandwidth also increases with the increase of the incident angle.

[0061] Example 2

[0062] According to the filter plane structure and component parameters provided in Example 1, this example only changes the filling material in the microcavity to prepare a series of filters, and the specific parameters are as follows:

[0063] (1) Gas materials with different refractive indices are selected to be filled in the microcavity, and the refractive indices are 1, 1.0001, 1.0002, 1.0003, 1.0004 and 1.0005 respectively.

[0064] (2) Liquid materials with different refractive indices are selected in the microcavity, and the refractive indices are 1.30, 1.31, 1.32, 1.33, 1.34 and 1.35, respectively.

[0065] See attached Figure 7, which is a relationship diagram of the resonance wavelength obtained by the ultra-narrowband filter structure provided in this embodiment under the condition of TM polarized light incidence as the refractive index of the material in the microcavity changes. When the refractive index of the material in the microcavity is a material within the gas refractive index range, the resonance wavelength redshifts from 2150.514nm to 2150.718nm as the refractive index of the material in the microcavity increases, and the redshift amount is 0.204nm. In the figure, curves 1, 2, 3, 4, 5 and 6 represent refractive indices of 1, 1.0001, 1.0002, 1.0003, 1.0004 and 1.0005, respectively.

[0066] See attached Figure 8 , which is a graph showing the relationship between the resonance peak bandwidth obtained under the TM polarized light incident condition and the refractive index of the material in the microcavity of the ultra-narrowband filter structure provided in this embodiment. It can be seen from the graph that the bandwidth of the resonance peak remains unchanged, and its value is 0.023nm.

[0067] See attached Fig. 9 , which is a relationship diagram of the resonance wavelength obtained by the ultra-narrowband filter structure provided by this embodiment under the condition of TM polarized light incidence as the refractive index of the material in the microcavity changes. When the refractive index of the material in the microcavity is a material within the refractive index range of the liquid, the resonance wavelength redshifts as the refractive index of the material in the microcavity increases, from 2411.628nm to 2434.611nm, and the redshift amount is 22.983nm. In the figure, curves 1, 2, 3, 4, 5 and 6 represent refractive indices of 1.30, 1.31, 1.32, 1.33, 1.34, and 1.35, respectively.

[0068] See attached Fig.10 , is a graph showing the relationship between the resonance peak bandwidth obtained under the TM polarized light incident condition and the refractive index of the material in the microcavity of the ultra-narrowband filter structure provided in this embodiment. It can be seen from the graph that the resonance peak bandwidth increases with the increase of the refractive index of the material in the microcavity.

[0069] See attached Fig.11 , is a relationship diagram of the resonance wavelength obtained by the ultra-narrowband filter structure provided in this embodiment under the condition of TE polarized light incidence as the refractive index of the material in the microcavity changes. When the refractive index of the material in the microcavity is a material within the gas refractive index range, the resonance wavelength redshifts as the refractive index of the material in the microcavity increases, from 1550nm to 1550.00724nm, and the redshift amount is 0.00724nm. In the figure, curves 1, 2, 3, 4, 5 and 6 represent refractive indices of 1, 1.0001, 1.0002, 1.0003, 1.0004 and 1.0005, respectively.

[0070] See attached Fig.12, is a graph showing the relationship between the resonance peak bandwidth obtained under the TE polarized light incident condition and the refractive index of the material in the microcavity of the ultra-narrowband filter structure provided in this embodiment. It can be seen from the graph that the resonance peak bandwidth increases with the increase of the refractive index of the material in the microcavity.

[0071] See attached Fig.13 , is a relationship diagram of the resonance wavelength obtained by the ultra-narrowband filter structure provided in this embodiment under the condition of TE polarized light incidence as the refractive index of the material in the microcavity changes. When the refractive index of the material in the microcavity is a material within the gas refractive index range, the resonance wavelength redshifts as the refractive index of the material in the microcavity increases, from 1556.1976nm to 1557.6167nm, and the redshift amount is 1.4191nm. In the figure, curves 1, 2, 3, 4, 5 and 6 represent refractive indices of 1, 1.0001, 1.0002, 1.0003, 1.0004 and 1.0005, respectively.

[0072] See attached Fig.14 , is a graph showing the relationship between the resonance peak bandwidth obtained under the TE polarized light incident condition and the refractive index of the material in the microcavity of the ultra-narrowband filter structure provided in this embodiment. It can be seen from the graph that the resonance peak bandwidth increases with the increase of the refractive index of the material in the microcavity.

[0073] Example 3

[0074] According to the filter plane structure and component parameters provided in Example 1, the thickness of the dielectric flat film and the microcavity are changed respectively in this embodiment to prepare a series of filters. The specific parameters are as follows:

[0075] (1) The thickness parameters of the bottom dielectric slab are 440nm, 450nm, 460nm, 470nm, 480nm and 490nm respectively.

[0076] See attached Fig.15 , is a graph showing the relationship between the thickness of the bottom dielectric slab and the bandwidth of the ultra-narrowband filter structure provided in this embodiment under the condition of TE polarized light incidence. As can be seen from the graph, the bandwidth of the resonance peak increases with the increase in the thickness of the bottom dielectric slab film.

[0077] (2) The thickness parameters of the microcavity are 910nm, 920nm, 930nm, 940nm, 950nm, 960nm and 970nm respectively.

[0078] See attached Fig.16 , is a graph showing the relationship between the thickness and bandwidth of the microcavity obtained under the TE polarized light incident condition for the ultra-narrowband filter structure provided in this embodiment. As can be seen from the graph, the bandwidth of the resonance peak increases with the increase of the microcavity thickness.

[0079] (3) The thickness parameters of the middle-layer dielectric flat film are 456nm, 458nm, 460nm, 462nm and 464nm respectively.

[0080] See attached Fig.17 , is a graph showing the relationship between the thickness of the middle dielectric flat film and the bandwidth of the ultra-narrowband filter structure provided in this embodiment under the condition of TE polarized light incidence. As can be seen from the graph, the bandwidth of the resonance peak increases with the increase in the thickness of the middle dielectric flat film.

[0081] Example 4

[0082] According to the filter plane structure and component parameters provided in Example 1, the thickness, slit width, and periodic structure of the grating are changed in this embodiment to prepare a series of filters. The specific parameters are as follows:

[0083] (1) The thickness parameters of the grating are 160 nm, 170 nm, 180 nm, 190 nm and 200 nm respectively.

[0084] See attached Fig.18 , is a relationship diagram between the thickness of the dielectric grating and the bandwidth obtained under the TE polarized light incident condition for the ultra-narrowband filter structure provided in this embodiment. As can be seen from the figure, the bandwidth of the resonance peak increases with the increase of the dielectric grating thickness.

[0085] (2) The slit width parameters of the grating are 940nm, 960nm, 980nm, 1000nm and 1020nm respectively.

[0086] See attached Fig.19 , is a relationship diagram between the slit width and bandwidth of the dielectric grating obtained under the TE polarized light incident condition of the ultra-narrowband filter structure provided in this embodiment. As can be seen from the figure, the bandwidth of the resonance peak increases with the increase of the slit width of the dielectric grating.

[0087] (3) The periodic parameters of the gratings are 1498 nm, 1499 nm, 1500 nm, 1501 nm and 1502 nm respectively.

[0088] See attached Fig. 20 , is a relationship diagram between the period and bandwidth of the dielectric grating obtained by the ultra-narrowband filter structure provided in this embodiment under the condition of TE polarized light incidence. As can be seen from the figure, the bandwidth of the resonance peak decreases as the period of the dielectric grating increases.

[0089] Example 5

[0090] Press Attach Figure 1According to the filter structure provided and the component parameters provided in Example 1, according to the thickness of the bottom dielectric plate 2, microcavity 3, middle dielectric plate 4, dielectric grating 5, and top dielectric plate 6 (the corresponding components in Table 1 are [2], [3], [4], [5], and [6]) and the period and slit width parameters of the dielectric grating 5 provided in Table 1, a series of ultra-narrowband filters are obtained. The relationship between the various parameters and the bandwidth under TM polarization conditions is shown in Table 1.

[0091] Table 1

[0092] .

[0093] It can be seen from the results given in Examples 1 to 5 of the present invention that the ultra-narrowband wavelength-tunable optical filter provided by the present invention can achieve controllable bandwidth through structural design (thickness of the dielectric plate and the microcavity, thickness, period and slit width of the grating and other parameters). Under TE polarization, the bandwidth is adjustable between 4.14e-5nm and 6.68e-4nm; under TM polarization, the bandwidth is adjustable between 0.01nm and 0.04nm.

[0094] The ultra-narrowband wavelength-tunable optical filter provided by the present invention can adjust the wavelength by the following method:

[0095] (1) By adjusting the angle of the incident light, a wide range of wavelength adjustment is achieved; when the incident light is TE polarized, the incident angle is in the range of -3° to 3°, and the wavelength bandwidth of the spectrum with absorption response is 3.57e-4nm to 8.51e-5nm. Using the structure provided in Example 1, the wavelength shifts by 11nm for every 1° change in the incident angle; when the incident light is TM polarized, the incident angle is in the range of -30° to 30°, and the wavelength bandwidth of the spectrum with absorption response is 0.023nm to 0.11nm, and the wavelength shifts by 18nm for every 1° change in the incident angle; as the absolute value of the angle increases, the bandwidth gradually increases.

[0096] (2) By changing the refractive index of the material in the microcavity, the wavelength can be adjusted in a small range. Using the structure provided in Example 1, under the condition of TE polarization of the incident light, when the refractive index of the material in the microcavity is within the gas refractive index range (1-1.0005), the resonance wavelength redshifts from 1550 nm to 1550.00724 nm with an increase in the refractive index of the material in the microcavity, with a redshift of 0.00724 nm, and the bandwidth varies in the range of 8.51e-5 nm to 8.57e-5 nm; when the refractive index of the material in the microcavity is within the liquid refractive index range (1.3-1.35), the resonance wavelength redshifts from 1556.1976 nm to 1557.6167 nm with an redshift of 1.4191 nm, and its bandwidth increases with the increase in the refractive index of the material in the microcavity. In the case of TM polarization, when the refractive index of the material in the microcavity is within the gas refractive index range (1-1.0005), the resonance wavelength redshifts from 2150.514nm to 2150.718nm with an amount of 0.204nm, and its bandwidth remains unchanged at 0.023nm. When the refractive index of the material in the microcavity is within the liquid refractive index range (1.3-1.35), the resonance wavelength redshifts from 2411.628nm to 2434.611nm with an amount of 22.983nm, and its bandwidth increases with the increase of the refractive index of the material in the microcavity.

[0097] (3) Combining the above two methods, firstly changing the angle of the incident light to achieve a large range of wavelength adjustment, and then changing the refractive index of the material in the microcavity to achieve a small range of adjustment, so that the adjustment result is more precise.

Claims

1. A wavelength control method for an ultra-narrowband optical filter with adjustable wavelength and controllable bandwidth, characterized in that: The wavelength-adjustable and bandwidth-controllable ultra-narrowband optical filter comprises a single-layer dielectric grating and a multi-layer dielectric planar waveguide structure, wherein a bottom dielectric planar film (2), a microcavity (3), a middle dielectric planar film (4), a dielectric grating (5) and a top dielectric planar film (6) are sequentially laid on a substrate metal film (1); the bottom dielectric planar film has a thickness of 400nm to 500nm, the middle dielectric planar film has a thickness of 450nm to 500nm, and the top dielectric planar film has a thickness of 100nm to 200nm; the microcavity has a thickness of 900nm to 1050nm, and is filled with gas or liquid; the dielectric grating has a period of 1498nm to 1501nm, a slit width of 900nm to 1060nm, and a thickness of 100nm to 250nm; and the wavelength control method is as follows: (1) Adjust the wavelength by adjusting the angle of incident light When the incident light is TE polarized, the incident angle is in the range of -3º to 3º, and the wavelength bandwidth of the spectrum with absorption response is 3.57e-4nm to 8.51e-5nm; when the incident light is TM polarized, the incident angle is in the range of -30º to 30º, and the wavelength bandwidth of the spectrum with absorption response is 0.023nm to 0.11nm; (2) Adjusting the wavelength by changing the refractive index of the material in the microcavity (a) Under the condition of TE polarization of the incident light, when the refractive index of the material in the microcavity is in the gas refractive index range of 1 to 1.0005, the wavelength bandwidth range is 8.51e-5nm to 8.57e-5nm; when the refractive index of the material in the microcavity is in the liquid refractive index range of 1.3 to 1.35, the resonance wavelength redshifts from 1556.1976nm to 1557.6167nm as the refractive index of the material in the microcavity increases; (b) Under the condition of TM polarization of the incident light, when the refractive index of the material in the microcavity is within the gas refractive index range of 1 to 1.0005, the resonance wavelength red-shifts from 2150.514nm to 2150.718nm as the refractive index of the material in the microcavity increases, and its bandwidth value remains unchanged at 0.023nm; when the refractive index of the material in the microcavity is within the liquid refractive index range of 1.3 to 1.35, the resonance wavelength red-shifts from 2411.628nm to 2434.611nm as the refractive index of the material in the microcavity increases; (3) First, method (1) is used to adjust the wavelength over a large range by changing the angle of the incident light, and then method (2) is used to adjust the wavelength over a small range by changing the refractive index of the material in the microcavity, thereby making the adjustment result more accurate.

2. A bandwidth control method for an ultra-narrowband optical filter with adjustable wavelength and controllable bandwidth, characterized in that: The wavelength-adjustable and bandwidth-controllable ultra-narrowband optical filter comprises a single-layer dielectric grating and a multi-layer dielectric planar waveguide structure, wherein a bottom dielectric planar film (2), a microcavity (3), a middle dielectric planar film (4), a dielectric grating (5) and a top dielectric planar film (6) are sequentially laid on a substrate metal film (1); the bottom dielectric planar film has a thickness of 400nm to 500nm, the middle dielectric planar film has a thickness of 450nm to 500nm, and the top dielectric planar film has a thickness of 100nm to 200nm; the microcavity has a thickness of 900nm to 1050nm, and is filled with gas or liquid; the dielectric grating has a period of 1498nm to 1501nm, a slit width of 900nm to 1060nm, and a thickness of 100nm to 250nm; and the bandwidth control method is as follows: (a) When the incident light is TE polarized, an optical filter with a bandwidth ranging from 4.14e-5nm to 6.68e-4nm is obtained by designing the thickness of the dielectric slab, microcavity, and dielectric grating structure parameters; (b) When the incident light is TM polarized, an optical filter with a bandwidth range of 0.01nm to 0.04nm is obtained by designing the thickness of the dielectric slab, microcavity and dielectric grating structure parameters.

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