CN112379485B - Integrated optical filter structure with ultra-large free spectral range - Google Patents

Abstract

The invention discloses an integrated optical filter structure with an ultra-large free spectral range. The structure includes a side-coupling waveguide composed of an incident waveguide, a curved waveguide and an outgoing waveguide connected in sequence, and a left Bragg waveguide grating, a tapered gradient type, and a left Bragg waveguide grating connected in sequence. Waveguide grating, reverse taper gradient waveguide grating, right Bragg waveguide grating. And the vertical line of the lowest point of the curved waveguide passes through the connection point of the tapered tapered gradient waveguide grating and the reverse tapered tapered tapered waveguide grating. All the waveguide gratings have the same period, and the band gap of the Bragg waveguide grating is less than twice the free spectral range of the F‑P resonator, and the resonant wavelength of the F‑P resonator is close to the middle of the forbidden band of the Bragg waveguide grating. The invention combines the waveguide coupler, the Bragg waveguide grating and the F-P resonant cavity, and utilizes the limited band gap of the Bragg grating and the large free spectral range of the F-P resonant cavity to realize the excitation of the single longitudinal mode in the whole spectral range, thereby realizing the single longitudinal mode excitation of the whole spectral range. Channel signal filtering.

Description

An integrated optical filter structure with a very large free spectral range

technical field

The invention relates to the field of optical filters, in particular to an integrated optical filter structure with a super large free spectral range.

Background technique

In today's communication networks and computing systems, the growing demand for high-rate data drives the development of low-cost, high-speed optical links. In optical interconnection, various advanced multiplexing technologies, such as wavelength division multiplexing, polarization multiplexing and mode multiplexing, have been successively used to improve the optical communication capacity. Among them, wavelength division multiplexing using different wavelengths in a shared physical channel is one of the most popular technologies in optical interconnection in recent decades. Such a photonic link based on wavelength division multiplexing technology needs to have a large number of wavelength channels. Therefore, in the operation of filter wavelengths used in wavelength division multiplexing-based optical interconnects, multiple filters are cascaded to achieve multiplexing of multiple wavelength channels. A larger free spectral range means that more independent wavelength channels can be supported without interfering with each other. Using the principle of reversibility of the optical path, the filter with a large free spectral range can realize the download of the input spectrum, so that the wide-spectrum signal analysis can be realized.

On the other hand, in recent years, driven by the needs of IoT scenarios, optical sensors have been widely used in medical, oil and gas, electric power, military industry, urban construction, food safety and geological exploration, which has spawned a market of hundreds of millions. In order to realize multi-site and multi-parameter sensing, distributed sensing using wavelength division multiplexing technology is one of the key technologies for building a sensor network. Distributed light detection technology can simultaneously obtain the spatial distribution and time-dependent information of the measured field. Using a filter with a large free spectral range can effectively increase the number of independent sensors on a single sensing link, enabling simultaneous sensing of more sites and parameters.

At present, there are many schemes to realize the large free spectral range filter. Microring resonators can achieve a large free spectral range by selecting an ultra-small radius, and at the same time have a compact volume, but the free spectral range is difficult to exceed 100 nm, which limits its application. To achieve extended free spectral range in microring resonators, Vernier effect or two-point coupled multi-string coupled microrings have been used, but this scheme is sensitive to actual device size changes, has small process tolerances, and usually requires thermal tuning Perform microring resonance peak alignment. Cascading inverse couplers on a single ring can also achieve a wide free spectral range, but in order to obtain a narrow forbidden band width in this scheme, the groove width of the Bragg waveguide grating in the inverse coupler is required to be extremely small, and the process is difficult. , which is not conducive to industrial production, and this solution still requires alignment of the main peak of the Bragg waveguide grating with the resonant peak of the microring, and the process tolerance is small. An ideal integrated filter should have a large free spectral range, a high rejection ratio, and a large process tolerance to avoid precise wavelength alignment.

SUMMARY OF THE INVENTION

In view of the deficiencies of the prior art, the present invention proposes an integrated optical filter structure with a large free spectral range, which can realize single-channel signal filtering in a wide spectral range or even a full spectral range.

The object of the present invention is achieved through the following technical solutions:

An integrated optical filter structure with an ultra-large free spectral range, comprising an incident waveguide, an outgoing waveguide, a curved waveguide, a left Bragg waveguide grating, a right Bragg waveguide grating, a tapered tapered waveguide grating, and a reverse tapered tapered waveguide grating, where:

The incident waveguide, the curved waveguide and the outgoing waveguide are connected in sequence to form an edge-coupling waveguide;

The left Bragg waveguide grating, the tapered tapered waveguide grating, the reverse tapered tapered waveguide grating, and the right Bragg waveguide grating are connected in sequence, and the left Bragg waveguide grating is coaxial with the right Bragg waveguide grating ;

The vertical line of the lowest point of the curved waveguide passes through the connection point of the tapered tapered waveguide grating and the reverse tapered tapered waveguide grating;

The incident waveguide, the curved waveguide, the outgoing waveguide, the left Bragg waveguide grating, the tapered tapered waveguide grating, the reverse tapered tapered waveguide grating, and the right Bragg waveguide grating are all single-mode waveguides;

The left Bragg waveguide grating, the tapered tapered waveguide grating, the reverse tapered tapered waveguide grating, and the right Bragg waveguide grating are all periodic structures, and the periods of the four are equal;

The left Bragg waveguide grating and the right Bragg waveguide grating form an F-P resonant cavity;

The curved waveguide and the F-P resonator form a side-coupled F-P resonator;

The larger value of the forbidden band width of the left Bragg waveguide grating and the right Bragg waveguide grating is Δλ _sb , and the free spectral range FSR _FP of the FP cavity, then the two satisfy the following relationship:

Δλ _sb < 2FSR _FP

And the resonance wavelength of the F-P resonant cavity is close to the middle of the forbidden band of the left Bragg waveguide grating and the right Bragg waveguide grating.

Further, the filter structure is a left-right symmetrical structure, and Δλ _sb < FSR _FP .

Further, the filter structure also includes a single-mode waveguide located between the tapered tapered waveguide grating and the reverse tapered tapered waveguide grating, and the lowest point tangent of the curved waveguide is parallel to the single-mode waveguide and has a gap. , forming a side-coupling waveguide structure; and the vertical line from the lowest point of the curved waveguide to the single-mode waveguide passes through the midpoint of the single-mode waveguide.

Further, the calculation formula of the free spectral range FSR _FP of the FP cavity is as follows:

Wherein, L _pd is the penetration depth of the left Bragg waveguide grating and the right Bragg waveguide grating, L _t is the length of the tapered tapered waveguide grating and the reverse tapered tapered waveguide grating, and n _g1 represents the single-mode waveguide , n _g2 represents the group refractive index of the left Bragg waveguide grating and the right Bragg waveguide grating, n _g3 represents the group refractive index of the tapered tapered waveguide grating and the reverse tapered tapered waveguide grating ; n _eff,w and n _eff,n are the effective refractive indices of the left Bragg waveguide grating and the right Bragg waveguide grating which change periodically; λ is the working wavelength of the filter structure.

The beneficial effects of the present invention are as follows:

The integrated optical filter structure of the ultra-large free spectral range of the present invention can simultaneously realize operation in the ultra-large free spectral range, sub-nanometer optical bandwidth and large process tolerance. That is to say, more independent wavelength channels can be supported without interfering with each other. This has great application value in the field of optical communication and distributed sensing.

Description of drawings

1 is a schematic diagram of a filter structure with a super large free spectral range according to Embodiment 1 of the present invention;

Fig. 2 is the working principle diagram of the filter of the ultra-large free spectral range of the first embodiment of the present invention;

3 is a schematic diagram of the transmittance of the filter in the first embodiment in the wavelength range of 1400-1620 nm;

FIG. 4 is a schematic diagram of the simulated electric field distribution at 1400, 1521, 1522, and 1620 nm of the filter of the first embodiment, wherein the white arrows indicate the direction of the injected light.

5 is a schematic diagram of a filter structure with a super large free spectral range according to Embodiment 3 of the present invention;

6 is a schematic diagram of a filter structure with a super large free spectral range according to Embodiment 5 of the present invention;

FIG. 7 is a waveguide cross-sectional view of the Bragg waveguide grating 104 on the left side of FIG. 6;

8 is a schematic diagram of a filter structure with a super large free spectral range according to Embodiment 6 of the present invention;

FIG. 9 is a waveguide cross-sectional view of the Bragg waveguide grating 104 on the left side of FIG. 8;

10 is a schematic diagram of a filter structure with a super large free spectral range according to Embodiment 7 of the present invention;

In the first to seventh embodiments, 101 is the incident waveguide, 102 is the outgoing waveguide, 103 is the curved waveguide, 104 is the left Bragg waveguide grating, 105 is the right Bragg waveguide grating, 106 is the tapered gradient waveguide grating, and 107 is the inverted waveguide grating. The tapered gradient waveguide grating, 108 is a single-mode waveguide, 201 is a waveguide core layer, 202 is a waveguide cladding layer, 203 is an etched waveguide cladding layer, 301 is a waveguide core layer, 302 is a waveguide cladding layer, 303 is Nanopillars.

Detailed ways

The filter structure of the present invention with a large free spectral range will be described in more detail below with reference to the schematic diagram, wherein the schematic diagram represents a preferred embodiment of the present invention, and it should be understood that those skilled in the art can modify the present invention described herein, and still achieve Advantageous effects of the present invention. Therefore, the following description should be construed as widely known to those skilled in the art and not as a limitation of the present invention.

In the description of the present invention, it should be noted that, for orientation words, such as the terms "center", "horizontal", "longitudinal", "length", "width", "thickness", "upper", "lower" , "Front", "Back", "Left", "Right", "Vertical", "Horizontal", "Top", "Bottom", "Inside", "Outside", "Clockwise", "Counterclockwise" ” etc. indicating the orientation and positional relationship are based on the orientation or positional relationship shown in the accompanying drawings, which are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation or a specific orientation. The structure and operation should not be construed as limiting the specific protection scope of the present invention.

The invention is described in more detail by way of example in the following paragraphs with reference to the accompanying drawings. The advantages and features of the present invention will become more apparent from the following description. It should be noted that, the accompanying drawings are all in a very simplified form and in inaccurate scales, and are only used to facilitate and clearly assist the purpose of explaining the embodiments of the present invention.

As shown in FIG. 1 , the filter structure of the present invention with a large free spectral range includes an incident waveguide 101 , an exit waveguide 102 , a curved waveguide 103 , a left Bragg waveguide grating 104 , a right Bragg waveguide grating 105 , and a tapered tapered waveguide. grating 106, reverse taper gradient waveguide grating 107 and single-mode waveguide 108;

The incident waveguide 101, the curved waveguide 103 and the outgoing waveguide 102 are connected in sequence to form an edge-coupling waveguide;

The left Bragg waveguide grating 104 , the tapered tapered waveguide grating 106 , the single-mode waveguide 108 , the reverse tapered tapered waveguide grating 107 , and the right Bragg waveguide grating 105 are connected in sequence, and the left Bragg waveguide grating 104 It is coaxial with the right Bragg waveguide grating; a single-mode waveguide 108 exists between the left Bragg waveguide grating 104 and the right Bragg waveguide grating 105 to form an F-P resonant cavity; the lowest point tangent of the curved waveguide 103 is connected to the single-mode waveguide 108 Parallel and there is a gap to form a side-coupling waveguide structure; the length of the single-mode waveguide 108 can be zero. The vertical line from the lowest point of the curved waveguide 103 to the single-mode waveguide 108 passes through the midpoint of the single-mode waveguide 108; the curved waveguide 103 and the F-P resonator form a side-coupled F-P resonator.

In addition, the incident waveguide 101 , the curved waveguide 103 , the outgoing waveguide 102 , the left Bragg waveguide grating 104 , the tapered tapered waveguide grating 106 , the reverse tapered tapered waveguide grating 107 , and the right Bragg waveguide grating 105 are all single-mode waveguides. , and the left Bragg waveguide grating 104 , the tapered tapered waveguide grating 106 , the reverse tapered tapered waveguide grating 107 , and the right Bragg waveguide grating 105 are all periodic structures with equal periods.

Specifically, when the filter is in use, laser light is injected into the incident waveguide 101 of the filter, and the laser light is coupled into the FP resonator through the curved waveguide 103 . The non-resonant wavelength is coupled from the FP resonator into the outgoing waveguide 102, and the resonant wavelength is coupled into the FP resonator and intensifies until the input power, out-coupling power, and cavity loss power reach a dynamic balance, and the optical image is bound by the cavity, There is no way to couple from the FP resonator to the exit waveguide 102, enabling filtering of specific wavelengths of light. By introducing the tapered tapered waveguide grating 106 and the reverse tapered tapered waveguide grating 107 between the left Bragg grating 104 and the right Bragg grating 105, the left Bragg grating 104, the right Bragg grating 105 and the single-mode waveguide are lowered 108 mode mismatch, thereby reducing intracavity losses, suppressing sideband jitter and increasing the quality factor of the resonator. The single-mode waveguide 108 connects the tapered tapered waveguide grating 106 and the reverse tapered tapered waveguide grating 107 . The free spectral range of the FP resonator can be regulated by controlling the number of periods of the tapered tapered waveguide grating 106 and the reverse tapered tapered waveguide grating 107 and the length of the single-mode waveguide 108 . As shown in FIG. 2 , the number of periods of the tapered tapered waveguide grating 106 and the reverse tapered tapered waveguide grating 107 and the length of the single-mode waveguide 108 (the length of the single-mode waveguide 108 can be zero) are selected as small as possible, so that the left The band gap of the side Bragg waveguide grating 104 and the right Bragg waveguide grating 105 is less than twice the free spectral range of the FP resonator cavity, so that the excitation of a single longitudinal mode can be realized, thereby realizing a single peak or a single valley in the full spectral range. Filter for spectral range. Among them, Δλ _sb represents the forbidden band bandwidth of the Bragg waveguide grating, and FSR _FP is the free spectral range of the FP cavity, and the two satisfy the following relationship:

Δλ _sb <2FSR _FP ;

And the resonance wavelength of the F-P resonant cavity is close to the middle of the forbidden band of the left Bragg waveguide grating (104) and the right Bragg waveguide grating (105).

Among them, the calculation formula of FSR _FP is as follows:

Wherein, L _pd is the penetration depth of the left Bragg waveguide grating 104 and the right Bragg waveguide grating 105 , Lt is the length of the tapered tapered waveguide grating 106 and the reverse tapered tapered waveguide grating 107 , and n _g1 represents The group refractive index of the single-mode waveguide 108, n _g2 represents the group refractive index of the left Bragg waveguide grating 104 and the right Bragg waveguide grating 105, n _g3 represents the tapered waveguide grating 106, the reverse tapered tapered The group refractive index of the waveguide grating 107; n _{eff, w} and n _{eff, n} are the effective refractive indices of the left Bragg waveguide grating 104 and the right Bragg waveguide grating 105 that change periodically; λ is the working wavelength of the filter structure.

Several embodiments of the filter structure of the present invention are given below.

Example 1

An integrated ultra-large free spectral range filter was fabricated based on a 220 nm silicon-on-insulator platform. The width of the incident waveguide 101 , the outgoing waveguide 102 , the curved waveguide 103 and the single-mode waveguide 108 is 500 nm, the waveguide is a ridge waveguide, the etching depth (waveguide height) is 150 nm, and the bending radius of the curved waveguide is 20 μm. The left Bragg waveguide grating 104 and the right Bragg waveguide grating 105 are formed by periodically alternating wide waveguides and narrow waveguides. The width of the wide waveguide is 500 nm, the width of the narrow waveguide is 300 nm, the number of periods is 150, and the period is 317 nm. The tapered gradient waveguide grating 106 is formed by periodically alternating wide waveguides and narrow waveguides. The width of the wide waveguide is 500nm, and the width is unchanged. The tapered gradient waveguide grating 107 is formed by periodically alternating wide waveguides and narrow waveguides. The width of the wide waveguide is 500nm, and the width is unchanged. The width of the narrow waveguide changes linearly from 500nm to 300nm, the number of periods is 5, and the period is 317nm; The mode waveguide 108 has a length of zero, and the gap between the curved waveguide 103 and the single mode waveguide 108 is 250 nm.

In this embodiment, when the filter is in use, the swept-frequency continuous laser is injected into the incident waveguide 101 of the filter, and the laser is coupled into the F-P resonator through the side-coupling waveguide structure. The resonant wavelength of 1521 nm has been oscillating in the resonator and cannot be coupled from the resonator to the exit waveguide 102, and the non-resonant wavelengths (except 1521 nm) are coupled from the F-P resonator into the exit waveguide 102, so as to realize the filtering of the 1521 nm wavelength laser.

Figure 3 shows the spectral transmission diagram of the filter of Example 1. It can be seen from the figure that in the ultra-large wavelength range of 220 nm, only a deep depression can be seen at 1521 nm, while it is flat at the non-resonant wavelength. the response to. Figure 4 shows the electric field distribution of the whole structure at operating wavelengths of 1400, 1521, 1522 and 1620 nm. For light with out-of-band wavelengths of 1400 and 1620 nm, the filter is considered a conventional dual-waveguide coupler. Therefore, the light cannot be enhanced in the F-P cavity, but is coupled into the Bragg grating on the right. For wavelengths within the stopband of 1522 nm but not at resonance, light is coupled into the cavity, then reflected by the Bragg grating, and finally transmitted to the thru port. For the resonant wavelength of 1521 nm, light is coupled into the cavity, enhancing the power in the cavity until a dynamic balance is achieved between coupled power, outcoupling power, and loss power. Therefore, the light appears to be trapped inside the cavity, with little power coupled into the thru port.

Embodiment 2

The difference between the second embodiment and the first embodiment is only that the ridge waveguide in the first embodiment is changed into a strip waveguide.

Embodiment 3

The difference between the third embodiment and the first embodiment is only that the left Bragg waveguide grating 104 , the right Bragg waveguide grating 105 , the tapered tapered waveguide grating 106 and the reverse tapered tapered waveguide grating 107 in the first embodiment are changed. The scheme of alternating wide waveguides and narrow waveguides is changed to the scheme of etching small holes in the waveguide. As shown in FIG. 5 , the left Bragg waveguide grating 104 and the right Bragg waveguide grating 105 are both formed by a common single mode waveguide and a perforated single mode waveguide periodically alternately; the tapered gradient waveguide grating 106 is composed of a single mode waveguide and a punched single mode waveguide The single-mode waveguides of the holes are periodically alternated, the width of the single-mode waveguides remains unchanged, and the radius of the circular holes gradually decreases; the reverse taper gradient waveguide grating 107 is composed of the single-mode waveguides and the perforated single-mode waveguides periodically alternated. The width of the single-mode waveguide remains unchanged, and the radius of the circular hole gradually increases.

Embodiment 4

The difference between the fourth embodiment and the third embodiment is only that the left Bragg waveguide grating 104, the right Bragg waveguide grating 105, the tapered tapered waveguide grating 106 and the reverse tapered tapered waveguide grating 107 in the third embodiment are replaced. The round holes of this kind are replaced with non-circular holes, such as rectangular holes, square holes, oval holes, etc.

Embodiment 5

The difference between the fifth embodiment and the first embodiment is only that the left Bragg waveguide grating 104 , the right Bragg waveguide grating 105 , the tapered tapered waveguide grating 106 and the reverse tapered tapered waveguide grating 107 in the first embodiment are replaced. The scheme of alternating wide and narrow waveguides is changed to the scheme of etching the waveguide cladding. As shown in FIG. 6, the left Bragg waveguide grating 104, the right Bragg waveguide grating 105, the tapered tapered waveguide grating 106 and the reverse tapered tapered waveguide grating 107 are all made of ordinary single-mode waveguides and periodically etched packages. layer composition. FIG. 7 is a cross-sectional view of the waveguide of the Bragg waveguide grating 104 on the left side of FIG. 6 . 201 is the waveguide core layer, 202 is the waveguide cladding layer, and 203 is the etched waveguide cladding layer.

Embodiment 6

The difference between the sixth embodiment and the fifth embodiment is only that the left Bragg waveguide grating 104, the right Bragg waveguide grating 105, the tapered tapered waveguide grating 106 and the reverse tapered tapered waveguide grating 107 of the fifth embodiment are replaced by The scheme for etching the waveguide cladding is changed to etching nanopillars next to the waveguide. As shown in FIG. 8 , the left Bragg waveguide grating 104 , the right Bragg waveguide grating 105 , the tapered tapered waveguide grating 106 and the reverse tapered tapered waveguide grating 107 are all made of ordinary single-mode waveguides and periodically etched nanometers. Column composition. FIG. 9 is a cross-sectional view of the waveguide of the Bragg waveguide grating 104 on the left side of FIG. 8 . 601 is a waveguide core layer, 302 is a waveguide cladding layer, and 303 is a nanocolumn. The nanopillars 303 can be rectangular, square, cylindrical, or elliptical.

Embodiment 7

The difference between the seventh embodiment and the first embodiment is only that the left Bragg waveguide grating 104 , the right Bragg waveguide grating 105 , the tapered tapered waveguide grating 106 and the reverse tapered tapered waveguide grating 107 of the first embodiment are combined with each other. The single-mode waveguide 108 is changed from an ordinary waveguide to a slit waveguide, as shown in FIG. 10 .

In addition, for those of ordinary skill in the art, without departing from the principles of the present invention, several improvements and modifications can also be made, and other integrated optical platforms, such as silicon-on-insulator platforms, inorganic chalcogenide glass platforms, can be used. , titanium oxide platform, silicon nitride platform, lithium niobate platform on insulating layer and indium phosphide platform, etc.; using different optical working bands, such as ultraviolet band, visible light band, near-infrared waveguide, mid-infrared waveguide and far Infrared band, etc.

To sum up, in this embodiment, the proposed filter structure with a large free spectral range, the present invention combines a waveguide coupler, a Bragg waveguide grating and an F-P resonant cavity, and utilizes the limited band gap of the Bragg grating and the large F-P resonant cavity. The characteristics of the free spectral range, controlling the cavity length of the F-P resonator so that the band gap of the Bragg waveguide grating is less than twice the free spectral range of the F-P resonator cavity, so that the excitation of a single longitudinal mode can be achieved, thereby realizing a single peak in the full spectral range. Or a single-valley filter with a very large free spectral range.

Those of ordinary skill in the art can understand that the above are only preferred examples of the invention and are not intended to limit the invention. Although the invention has been described in detail with reference to the foregoing examples, those skilled in the art can still understand the Modifications are made to the technical solutions described in the foregoing examples, or equivalent replacements are made to some of the technical features. All modifications and equivalent replacements made within the spirit and principle of the invention shall be included within the protection scope of the invention.

Claims (3)

1. An integrated optical filter structure with a super large free spectral range, characterized in that it comprises an incident waveguide (101), an exit waveguide (102), a curved waveguide (103), a left Bragg waveguide grating (104), a right Bragg waveguide grating (105), tapered tapered waveguide grating (106), reverse tapered tapered waveguide grating (107), wherein: The incident waveguide (101), the curved waveguide (103) and the outgoing waveguide (102) are connected in sequence to form an edge-coupling waveguide; The left Bragg waveguide grating (104), the tapered tapered waveguide grating (106), the reverse tapered tapered waveguide grating (107), and the right Bragg waveguide grating (105) are connected in sequence, and the left Bragg The waveguide grating (104) is coaxial with the right Bragg waveguide grating; The vertical line of the lowest point of the curved waveguide (103) passes through the connection point of the tapered tapered waveguide grating (106) and the reverse tapered tapered waveguide grating (107); The incident waveguide (101), the curved waveguide (103), the outgoing waveguide (102), the left Bragg waveguide grating (104), the tapered tapered waveguide grating (106), and the reverse tapered tapered waveguide grating (107) , the Bragg waveguide grating (105) on the right side is a single-mode waveguide; The left Bragg waveguide grating (104), the tapered tapered waveguide grating (106), the reverse tapered tapered waveguide grating (107), and the right Bragg waveguide grating (105) are all periodic structures, and the four period is equal; The left Bragg waveguide grating (104) and the right Bragg waveguide grating (105) form an F-P resonant cavity; The curved waveguide (103) and the F-P resonator form a side-coupled F-P resonator; The larger value of the forbidden band width of the left Bragg waveguide grating (104) and the right Bragg waveguide grating (105) is Δλ _sb , and the free spectral range FSR _FP of the FP cavity, then the two satisfy the following relationship: Δλ _sb < 2FSR _FP and the resonance wavelength of the F-P resonant cavity is close to the middle of the forbidden band of the left Bragg waveguide grating (104) and the right Bragg waveguide grating (105); The calculation formula of the free spectral range FSR _FP of the FP cavity is as follows:

Wherein, L _pd is the penetration depth of the left Bragg waveguide grating (104) and the right Bragg waveguide grating (105), and L _t is the tapered tapered waveguide grating (106) and the reverse tapered tapered waveguide grating The length of (107), n _g1 represents the group refractive index of the single-mode waveguide (108), n _g2 represents the group refractive index of the left Bragg waveguide grating (104) and the right Bragg waveguide grating (105), and n _g3 represents Group refractive indices of the tapered tapered waveguide grating (106) and the reverse tapered tapered waveguide grating (107); n _eff,w and n _eff,n are the left Bragg waveguide grating (104), the right Bragg The effective refractive index of the waveguide grating (105) varies periodically; λ is the working wavelength of the filter structure. 2 . The integrated optical filter structure with a large free spectral range according to claim 1 , wherein the filter structure is a left-right symmetric structure, and Δλ _sb < FSR _FP . 3 . 3. The integrated optical filter structure with ultra-large free spectral range according to claim 1 or 2, characterized in that the filter structure further comprises a tapered tapered waveguide grating (106), a reverse tapered tapered waveguide A single-mode waveguide (108) between the gratings (107), the lowest point tangent of the curved waveguide (103) is parallel to the single-mode waveguide (108) and there is a gap, forming a side-coupling waveguide structure; and the curved The vertical line from the lowest point of the waveguide (103) to the single-mode waveguide (108) passes through the midpoint of the single-mode waveguide (108)

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