An optical filter with integrated grating-assisted reverse coupler

Abstract

The present invention provides an optical filter with an integrated grating-assisted reverse coupler, comprising: an input optical waveguide connected to a first input curved grating-assisted reverse coupler of a first microring optical filter of a first-stage integrated grating-assisted reverse coupler in a microring filter unit, for inputting an optical signal to be processed; the microring filter unit, comprising a first microring optical filter of the first-stage integrated grating-assisted reverse coupler, a second microring optical filter of the second-stage integrated grating-assisted reverse coupler, and a third-stage reverse coupler, for filtering the optical signal; an intermediate optical waveguide unit, comprising a first intermediate optical waveguide, a second intermediate optical waveguide, and a third intermediate optical waveguide, for transmitting the optical signal in the microring filter unit; and an output optical waveguide connected to a straight output periodic corrugated waveguide of the third-stage reverse coupler, for outputting the processed optical signal.

Description

Technical Field

[0001] The present disclosure relates to the field of optical fiber communication technology, and more specifically, to an optical filter with an integrated grating-assisted reverse coupler. Background Art

[0002] The emergence of wavelength division multiplexing (WDM) technology and erbium doped fiber amplifier (EDFA) has made breakthrough progress in optical communication, and the rate of optical fiber transmission network has been continuously improved. Optical filters use optical methods and optical components to realize the filtering function of optical signals in signal processing in the field of communication technology. Compared with traditional electronic technology, optical components have flexible and wide bandwidth characteristics and can directly filter high-frequency broadband microwave signals. It is of great significance in the advanced applications of broadband access, quantum communication, lidar and astronomical systems.

[0003] The ability to select the target frequency band is an important indicator of optical filters used in microwave photon signal processing, which requires optical filters to have high roll-off rate and relatively narrow passband bandwidth. The smaller the proportion of the passband bandwidth in a free spectral range (FSR), the stronger the selectivity. Optical filter devices based on integrated photonics are convenient for large-scale integration, and can achieve large-scale and low-cost mass production by using mature semiconductor process processing platforms. Common narrow-bandwidth, high-roll-off rate optical filters often use structures such as Bragg fiber grating (FBG), Mach-Zehnder (MZ), and microring resonator (MRR). However, the above solutions have problems such as high loss, large volume, high cost, poor stability, and difficulty in adjustment and control. At the same time, traditional filters are limited by limited FSR, which leads to an upper limit on their ability to select the target frequency band. Summary of the invention

[0004] In view of this, an embodiment of the present disclosure provides an optical filter with an integrated grating-assisted reverse coupler.

[0005] One aspect of an embodiment of the present disclosure provides an optical filter with an integrated grating-assisted reverse coupler, comprising:

[0006] An input optical waveguide is connected to a first input curved grating-assisted reverse coupler of a first micro-ring optical filter of a first-stage integrated grating-assisted reverse coupler in a micro-ring filter unit, and is used for inputting an optical signal to be processed;

[0007] A micro-ring filter unit, comprising a first micro-ring optical filter of a first-stage integrated grating-assisted reverse coupler, a second micro-ring optical filter of a second-stage integrated grating-assisted reverse coupler, and a third-stage reverse coupler, for filtering the above optical signal;

[0008] An intermediate optical waveguide unit, comprising a first intermediate optical waveguide, a second intermediate optical waveguide and a third intermediate optical waveguide, for transmitting an optical signal in the micro-ring filter unit;

[0009] The first input curved grating assisted reverse coupler is connected to the second input curved grating assisted reverse coupler of the second micro-ring optical filter through the first intermediate optical waveguide, the first output curved grating assisted reverse coupler of the first micro-ring optical filter is connected to the second output curved grating assisted reverse coupler of the second micro-ring optical filter through the second intermediate optical waveguide, the straight input periodic corrugated waveguide of the third-stage reverse coupler is connected to the second input curved grating assisted reverse coupler through the third intermediate optical waveguide; the output optical waveguide is connected to the straight output periodic corrugated waveguide of the third-stage reverse coupler, and is used to output the processed optical signal.

[0010] According to an embodiment of the present disclosure, the first micro-ring optical filter of the first-stage integrated grating-assisted reverse coupler and the second micro-ring optical filter of the second-stage integrated grating-assisted reverse coupler both include: an input curved grating-assisted reverse coupler; an output curved grating-assisted reverse coupler; and a connecting curved waveguide disposed between the input curved grating-assisted reverse coupler and the output curved grating-assisted reverse coupler so as to connect the input curved grating-assisted reverse coupler and the output curved grating-assisted reverse coupler into a complete circular structure.

[0011] According to an embodiment of the present disclosure, the above-mentioned input curved grating assisted reverse coupler and the above-mentioned output curved grating assisted reverse coupler both include: a curved bus periodic corrugated waveguide and a curved micro-ring periodic corrugated waveguide.

[0012] According to the embodiments of the present disclosure, the corrugation shapes of the curved bus periodic corrugation waveguide and the curved microring periodic corrugation waveguide include: rectangular, sinusoidal and trapezoidal; the waveguide thickness, corrugation period, duty cycle, number of periods and bending radius of the curved bus periodic corrugation waveguide and the curved microring periodic corrugation waveguide are the same; the average waveguide width and corrugation depth of the curved microring periodic corrugation waveguide are greater than those of the curved bus periodic corrugation waveguide, so as to reduce the forward cross-coupling coefficient of the input curved grating assisted reverse coupler and the output curved grating assisted reverse coupler; the inner wall of the curved bus periodic corrugation waveguide and the inner wall of the curved microring periodic corrugation waveguide meet the phase matching condition, so as to increase the coupling coefficient between the forward mode and the reverse mode in the waveguide; the inner wall and the outer wall of the same waveguide in the curved bus periodic corrugation waveguide and the curved microring periodic corrugation waveguide meet the phase mismatch condition, so as to suppress the Bragg reflection in the waveguide.

[0013] According to an embodiment of the present disclosure, the first input curved grating assisted reverse coupler is connected to the second input curved grating assisted reverse coupler of the second micro-ring optical filter through a first intermediate optical waveguide, including: the curved bus periodic corrugated waveguide of the first input curved grating assisted reverse coupler is connected to the curved bus periodic corrugated waveguide of the second input curved grating assisted reverse coupler of the second micro-ring optical filter through the first intermediate optical waveguide;

[0014] The first output curved grating assisted reverse coupler of the first micro-ring optical filter is connected to the second output curved grating assisted reverse coupler of the second micro-ring optical filter through a second intermediate optical waveguide, comprising: the curved bus periodic corrugated waveguide of the first output curved grating assisted reverse coupler of the first micro-ring optical filter is connected to the curved bus periodic corrugated waveguide of the second output curved grating assisted reverse coupler of the second micro-ring optical filter through a second intermediate optical waveguide;

[0015] The straight input periodic corrugated waveguide of the third-stage reverse coupler is connected to the second input curved grating assisted reverse coupler through a third intermediate optical waveguide, including: the straight input periodic corrugated waveguide of the third-stage reverse coupler is connected to the curved bus periodic corrugated waveguide of the second input curved grating assisted reverse coupler through a third intermediate optical waveguide.

[0016] According to the embodiments of the present disclosure, the corrugation shapes of the direct-input periodic corrugation waveguide and the direct-output periodic corrugation waveguide include: rectangular, sinusoidal and trapezoidal; the waveguide thickness, corrugation period, duty cycle and number of periods of the direct-input periodic corrugation waveguide and the direct-output periodic corrugation waveguide are the same; the average waveguide width and corrugation depth of the direct-input periodic corrugation waveguide are smaller than those of the direct-output periodic corrugation waveguide, so as to reduce the forward cross-coupling coefficient of the reverse coupler; the inner walls of the two waveguides in the reverse coupler composed of the direct-input periodic corrugation waveguide and the direct-output periodic corrugation waveguide satisfy the phase matching condition, so as to increase the coupling coefficient between the forward mode and the reverse mode in the waveguide; the inner wall and the outer wall of the same waveguide in the reverse coupler composed of the direct-input periodic corrugation waveguide and the direct-output periodic corrugation waveguide satisfy the phase mismatch condition, so as to suppress the Bragg reflection in the waveguide.

[0017] According to an embodiment of the present disclosure, the average waveguide width of the straight output periodic corrugated waveguide of the third-stage reverse coupler is the same as the average waveguide width of the curved micro-ring periodic corrugated waveguide of the first micro-ring optical filter and the second micro-ring optical filter; the average waveguide width of the straight input periodic corrugated waveguide of the third-stage reverse coupler is the same as the average waveguide width of the curved bus periodic corrugated waveguide of the first micro-ring optical filter and the second micro-ring optical filter; the third-stage reverse coupler has the same waveguide thickness, waveguide spacing, corrugation period, duty cycle, and number of periods as the first micro-ring optical filter and the second micro-ring optical filter.

[0018] According to an embodiment of the present disclosure, the length difference between the second intermediate optical waveguide and the first intermediate optical waveguide is an integer multiple of the circumference of the micro-ring.

[0019] According to an embodiment of the present disclosure, the micro-ring filtering unit is also used to determine that the center wavelengths of the filtering curves of the first micro-ring optical filter, the second micro-ring optical filter and the third-stage reverse coupler are independently tuned when tuning the center wavelength of the optical filter of the integrated grating-assisted reverse coupler; wherein the first micro-ring optical filter, the second micro-ring optical filter and the third-stage reverse coupler are tuned using thermo-optical effect or electro-optical effect.

[0020] According to the embodiments of the present disclosure, because the optical filter of the integrated grating-assisted reverse coupler is connected by using a two-stage integrated grating-assisted reverse coupler micro-ring optical filter and then input into the reverse coupler to achieve filtering of broadband optical signals, while achieving narrow bandwidth and high roll-off rate filtering, it also has the technical effects of simple structure, low loss, low difficulty in adjustment and control, and no free spectral range. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The above and other objects, features and advantages of the present disclosure will become more apparent through the following description of the embodiments of the present disclosure with reference to the accompanying drawings, in which:

[0022] Figure 1 A schematic diagram of the structure of an optical filter with integrated grating-assisted reverse coupler according to an embodiment of the present disclosure is shown;

[0023] Figure 2 The schematic diagram of the structure of a first micro-ring optical filter of a first-stage integrated grating-assisted reverse coupler and a second micro-ring optical filter of a second-stage integrated grating-assisted reverse coupler of an optical filter of an integrated grating-assisted reverse coupler according to an embodiment of the present disclosure is shown;

[0024] Figure 3 A schematic diagram schematically shows the composition structure of an input curved grating-assisted reverse coupler and an output curved grating-assisted reverse coupler of an optical filter with an integrated grating-assisted reverse coupler according to an embodiment of the present disclosure;

[0025] Figure 4 A filtering spectrum diagram of a micro-ring optical filter with a single integrated grating-assisted reverse coupler of an optical filter with an integrated grating-assisted reverse coupler according to an embodiment of the present disclosure is schematically shown;

[0026] Figure 5 A schematic diagram of filtering spectrum of two micro-ring optical filters with integrated grating-assisted reverse couplers of an optical filter with integrated grating-assisted reverse couplers according to an embodiment of the present disclosure is shown;

[0027] Figure 6 A schematic diagram of the structure of a third-stage reverse coupler of an optical filter integrated with a grating-assisted reverse coupler according to an embodiment of the present disclosure is shown;

[0028] Figure 7 A filtering spectrum diagram of a third-stage reverse coupler of an optical filter integrated with a grating-assisted reverse coupler according to an embodiment of the present disclosure is schematically shown;

[0029] Figure 8 The filtering spectrum diagram of an optical filter integrated with a grating-assisted reverse coupler according to an embodiment of the present disclosure is schematically shown.

[0030] Description of Reference Numerals

[0031] 110 Input optical waveguide

[0032] 120 micro-ring optical filter units

[0033] 121The first micro-ring optical filter with integrated grating-assisted reverse coupler

[0034] 122 The second micro-ring optical filter with second-stage integrated grating-assisted reverse coupler

[0035] 123 Third stage reverse coupler

[0036] 130 intermediate optical waveguide unit

[0037] 131 first intermediate optical waveguide

[0038] 132 Second intermediate optical waveguide

[0039] 133 Third intermediate optical waveguide

[0040] 140 Output optical waveguide

[0041] 1211 Input Bent Grating Assisted Back Coupler

[0042] 1212 output bent grating assisted reverse coupler

[0043] 1213 Connecting curved waveguides

[0044] 12111 curved bus periodic corrugated waveguide

[0045] 12112Bent Microring Periodic Corrugated Waveguide

[0046] 1231 Direct Input Periodic Corrugated Waveguide

[0047] 1232 Direct Output Periodic Corrugated Waveguide DETAILED DESCRIPTION

[0048] The present disclosure is further described in detail below in conjunction with the accompanying drawings and embodiments. It is understood that the specific embodiments described herein are only used to explain the present disclosure, rather than to limit the present disclosure, and the various features recorded in the embodiments can be combined to form multiple optional solutions. It should also be noted that, for ease of description, only parts related to the present disclosure are shown in the accompanying drawings, rather than all structures.

[0049] The terms used herein are only for describing specific embodiments and are not intended to limit the present disclosure. The terms "comprise", "include", etc. used herein indicate the existence of the features, steps, operations and / or components, but do not exclude the existence or addition of one or more other features, steps, operations or components.

[0050] All terms (including technical and scientific terms) used herein have the meanings commonly understood by those skilled in the art, unless otherwise defined. It should be noted that the terms used herein should be interpreted as having a meaning consistent with the context of this specification, and should not be interpreted in an idealized or overly rigid manner.

[0051] In the case of using expressions such as "at least one of A, B, and C, etc.", it should generally be interpreted in accordance with the meaning of the expression generally understood by those skilled in the art (for example, "a system having at least one of A, B, and C" should include but is not limited to a system having A alone, B alone, C alone, A and B, A and C, B and C, and / or A, B, C, etc.). In the case of using expressions such as "at least one of A, B, or C, etc.", it should generally be interpreted in accordance with the meaning of the expression generally understood by those skilled in the art (for example, "a system having at least one of A, B, or C" should include but is not limited to a system having A alone, B alone, C alone, A and B, A and C, B and C, and / or A, B, C, etc.).

[0052] Since common narrow bandwidth, high roll-off rate optical filters often use Bragg fiber gratings, Mach-Zehnder, microring resonators and other structures, they have problems such as high loss, large size, high cost, poor stability, and difficulty in adjustment and control, and are restricted by limited FSR, their ability to select the target frequency band has an upper limit.

[0053] In view of this, an embodiment of the present disclosure provides an optical filter with an integrated grating-assisted reverse coupler, comprising: an input optical waveguide connected to a first input curved grating-assisted reverse coupler of a first microring optical filter of a first-stage integrated grating-assisted reverse coupler in a microring filter unit, for inputting an optical signal to be processed; the microring filter unit, comprising a first microring optical filter of the first-stage integrated grating-assisted reverse coupler, a second microring optical filter of the second-stage integrated grating-assisted reverse coupler, and a third-stage reverse coupler, for filtering the optical signal; an intermediate optical waveguide unit, comprising a first intermediate optical waveguide, a second intermediate optical waveguide, and a third intermediate optical waveguide, for filtering the optical signal; The invention is used for transmitting the optical signal in the micro-ring filter unit; wherein the first input curved grating auxiliary reverse coupler is connected with the second input curved grating auxiliary reverse coupler of the second micro-ring optical filter through the first intermediate optical waveguide, the first output curved grating auxiliary reverse coupler of the first micro-ring optical filter is connected with the second output curved grating auxiliary reverse coupler of the second micro-ring optical filter through the second intermediate optical waveguide, the straight input periodic corrugated waveguide of the third-stage reverse coupler is connected with the second input curved grating auxiliary reverse coupler through the third intermediate optical waveguide; the output optical waveguide is connected with the straight output periodic corrugated waveguide of the third-stage reverse coupler, and is used for outputting the processed optical signal.

[0054] Figure 1 The schematic diagram shows the structure of an optical filter with integrated grating-assisted reverse coupler according to an embodiment of the present disclosure.

[0055] like Figure 1As shown, the optical filter includes an input optical waveguide 110 , a micro-ring filter unit 120 , an intermediate optical waveguide unit 130 and an output optical waveguide 140 .

[0056] The input optical waveguide 110 is connected to the first input curved grating-assisted reverse coupler of the first microring optical filter 121 of the first-stage integrated grating-assisted reverse coupler in the microring filter unit 120 , and is used to input the optical signal to be processed.

[0057] The micro-ring filter unit 120 includes a first micro-ring optical filter 121 of a first-stage integrated grating-assisted reverse coupler, a second micro-ring optical filter 122 of a second-stage integrated grating-assisted reverse coupler, and a third-stage reverse coupler 123, and is used to filter the optical signal.

[0058] The intermediate optical waveguide unit 130 includes a first intermediate optical waveguide 131, a second intermediate optical waveguide 132 and a third intermediate optical waveguide 133, and is used to transmit the optical signal in the microring filter unit; wherein the first input curved grating auxiliary reverse coupler is connected to the second input curved grating auxiliary reverse coupler of the second microring optical filter 122 through the first intermediate optical waveguide 131, the first output curved grating auxiliary reverse coupler of the first microring optical filter 121 is connected to the second output curved grating auxiliary reverse coupler of the second microring optical filter 122 through the second intermediate optical waveguide 132, and the straight input periodic corrugated waveguide of the third-stage reverse coupler 123 is connected to the second input curved grating auxiliary reverse coupler through the third intermediate optical waveguide 133.

[0059] The output optical waveguide 140 is connected to the straight output periodic corrugated waveguide of the third-stage reverse coupler 123 and is used to output the processed optical signal.

[0060] According to an embodiment of the present disclosure, the bending radius of the first micro-ring optical filter of the first-stage integrated grating-assisted reverse coupler and the second micro-ring optical filter of the second-stage integrated grating-assisted reverse coupler are the same.

[0061] According to an embodiment of the present disclosure, the average waveguide width of the straight output periodic corrugated waveguide of the third-stage reverse coupler is the same as the average waveguide width of the curved micro-ring periodic corrugated waveguide of the first micro-ring optical filter and the second micro-ring optical filter; the average waveguide width of the straight input periodic corrugated waveguide of the third-stage reverse coupler is the same as the average waveguide width of the curved bus periodic corrugated waveguide of the first micro-ring optical filter and the second micro-ring optical filter; the third-stage reverse coupler has the same waveguide thickness, waveguide spacing, corrugation period, duty cycle, and number of periods as the first micro-ring optical filter and the second micro-ring optical filter.

[0062] According to an embodiment of the present disclosure, the length difference between the second intermediate optical waveguide and the first intermediate optical waveguide is an integer multiple of the circumference of the micro-ring.

[0063] According to an embodiment of the present disclosure, the micro-ring refers to a circular structure composed of a curved bus periodic corrugated waveguide and two connecting curved waveguides of an input curved grating-assisted reverse coupler and an output curved grating-assisted reverse coupler of each micro-ring optical filter with integrated grating-assisted reverse coupler. The micro-ring optical filter with integrated grating-assisted reverse coupler includes a first micro-ring optical filter with a first-stage integrated grating-assisted reverse coupler and a second micro-ring optical filter with a second-stage integrated grating-assisted reverse coupler.

[0064] According to an embodiment of the present disclosure, the length difference between the second intermediate optical waveguide and the first intermediate optical waveguide is set to an integer multiple of the circumference of the microring, so that the phases of the filtering curves of the first microring optical filter 121 of the first-stage integrated grating-assisted reverse coupler and the second microring optical filter 122 of the second-stage integrated grating-assisted reverse coupler will not shift or will only shift by an integer multiple of 2π.

[0065] According to an embodiment of the present disclosure, a first broadband optical signal transmitted in an input optical waveguide is first filtered at a first micro-ring optical filter of a first-stage integrated grating-assisted reverse coupler to obtain a second optical signal; then, the second optical signal is input into a second micro-ring optical filter of a second-stage integrated grating-assisted reverse coupler through a first intermediate optical waveguide and a second intermediate optical waveguide to obtain a third optical signal; then, the third optical signal is combined through a third intermediate optical waveguide and then input into a third-stage reverse coupler to filter out a depression in a spectrum of the third optical signal and its narrow peak to obtain a fourth optical signal; finally, the fourth optical signal is output through an output optical waveguide.

[0066] According to the embodiments of the present disclosure, the first micro-ring optical filter 121 of the first-stage integrated grating-assisted reverse coupler and the second micro-ring optical filter 122 of the second-stage integrated grating-assisted reverse coupler are used to perform the same filtering process twice, and the result of the superposition of the two filtering processes produces an electromagnetically induced transparent (EIT) spectrum, which doubles the extinction ratio of the filtering curve and improves the roll-off rate of the spectrum line.

[0067] According to the embodiments of the present disclosure, because the optical filter of the integrated grating-assisted reverse coupler in the present disclosure is connected by a two-stage integrated grating-assisted reverse coupler micro-ring optical filter and then input into the reverse coupler to achieve filtering of broadband optical signals, while achieving narrow bandwidth and high roll-off rate filtering, it also has the technical effects of simple structure, low loss, small size, low difficulty in adjustment and control, and no free spectral range.

[0068] Figure 2The structure diagram of a first micro-ring optical filter of a first-stage integrated grating-assisted reverse coupler and a second micro-ring optical filter of a second-stage integrated grating-assisted reverse coupler of an optical filter with an integrated grating-assisted reverse coupler according to an embodiment of the present disclosure is schematically shown.

[0069] like Figure 2 As shown, the first micro-ring optical filter of the first-stage integrated grating-assisted reverse coupler and the second micro-ring optical filter of the second-stage integrated grating-assisted reverse coupler both include 1211 - 1213 .

[0070] According to an embodiment of the present disclosure, a first micro-ring optical filter of a first-stage integrated grating-assisted reverse coupler and a second micro-ring optical filter of a second-stage integrated grating-assisted reverse coupler both include:

[0071] Input bent grating assisted reverse coupler 1211;

[0072] Output bent grating assisted reverse coupler 1212;

[0073] The connecting curved waveguide 1213 is disposed between the input curved grating assisted reverse coupler and the output curved grating assisted reverse coupler so as to connect the input curved grating assisted reverse coupler and the output curved grating assisted reverse coupler into a complete circular structure.

[0074] According to an embodiment of the present disclosure, a first micro-ring optical filter of a first-stage integrated grating-assisted reverse coupler includes: a first input curved grating-assisted reverse coupler, a first output curved grating-assisted reverse coupler, and two first connected curved waveguides; a second micro-ring optical filter of a second-stage integrated grating-assisted reverse coupler includes: a second input curved grating-assisted reverse coupler, a second output curved grating-assisted reverse coupler, and two second connected curved waveguides.

[0075] According to an embodiment of the present disclosure, the first micro-ring optical filter of the first-stage integrated grating-assisted reverse coupler and the second micro-ring optical filter of the second-stage integrated grating-assisted reverse coupler both include four ports, namely: a first port, a second port, a third port and a fourth port. The ports can be divided into an input port, a through port, an upload port and a download port according to the input port of the optical signal, wherein when the first port is the input port, the second port is the through port, the third port is the upload port and the fourth port is the download port; when the fourth port is the input port, the first port is the download port, the second port is the upload port and the third port is the through port; when the third port is the input port, the first port is the upload port, the second port is the download port and the fourth port is the through port.

[0076] According to an embodiment of the present disclosure, after a broadband optical signal enters the input end of the microring optical filter of each integrated grating-assisted reverse coupler, the band that satisfies the Bragg reflection condition will be reversely coupled into the microring optical filter of the integrated grating-assisted reverse coupler, and then coupled to the download end, while the band that does not satisfy the Bragg reflection condition will not be coupled into the microring optical filter of the integrated grating-assisted reverse coupler.

[0077] According to an embodiment of the present disclosure, the Bragg reflection condition is as follows:

[0078] λ0 = Λ[n eff,B (λ0) + n eff,R (λ0)](one)

[0079] where λ0 is the central wavelength of filtering, Λ is the grating period, n eff,B and n eff,R are the effective refractive indices of the curved bus periodic corrugated waveguide and the curved microring periodic corrugated waveguide respectively, and are both functions of the wavelength λ. When the Bragg reflection condition is satisfied, only the light wave or band near the central wavelength λ0 can be coupled from one periodic corrugated waveguide in the reverse coupler to another periodic corrugated waveguide, and the remaining light wave or band will directly pass through the same input periodic corrugated waveguide, thus realizing filtering.

[0080] According to an embodiment of the present disclosure, the first port of the first microring optical filter of the first-stage integrated grating-assisted reverse coupler is connected to the input optical waveguide, the second port is connected to the first intermediate optical waveguide, and the fourth port is connected to the second intermediate optical waveguide. The first microring optical filter of the second-stage integrated grating-assisted reverse coupler is connected to the first intermediate optical waveguide, the second port is connected to the third intermediate optical waveguide, and the third port is connected to the second intermediate optical waveguide.

[0081] According to an embodiment of the present disclosure, the filtering process of the first microring optical filter of the first-stage integrated grating-assisted reverse coupler includes: the optical signal to be processed is input through the first port of the first microring optical filter of the first-stage integrated grating-assisted reverse coupler. After a part of the optical signal is filtered by the first input curved grating-assisted reverse coupler, it is output from the second port to obtain the second direct-through optical signal; another part of the optical signal is coupled to the fourth port to obtain the second download optical signal. The filtering process of the second microring optical filter of the second-stage integrated grating-assisted reverse coupler includes: the second direct-through optical signal is input through the first port of the second microring optical filter of the second-stage integrated grating-assisted reverse coupler via the first intermediate optical waveguide, and the third direct-through optical signal is obtained after direct-through filtering at the second port; the second download optical signal is input through the third port of the second microring optical filter of the second-stage integrated grating-assisted reverse coupler via the second intermediate optical waveguide, and the third download optical signal is obtained after download filtering at the second port.

[0082] Figure 3 A schematic diagram schematically shows the composition structure of an input curved grating-assisted reverse coupler and an output curved grating-assisted reverse coupler of an optical filter with an integrated grating-assisted reverse coupler according to an embodiment of the present disclosure.

[0083] like Figure 3 The input curved grating assisted reverse coupler and the output curved grating assisted reverse coupler both include: a curved bus periodic corrugated waveguide 12111 and a curved micro-ring periodic corrugated waveguide 12112 .

[0084] According to an embodiment of the present disclosure, the input curved grating assisted reverse coupler and the output curved grating assisted reverse coupler both include: a curved bus periodic corrugated waveguide 12111 and a curved micro-ring periodic corrugated waveguide 12112 .

[0085] According to an embodiment of the present disclosure, the curved bus periodic corrugated waveguide of the first input curved grating assisted reverse coupler is connected to the curved bus periodic corrugated waveguide of the second input curved grating assisted reverse coupler of the second micro-ring optical filter through a first intermediate optical waveguide; the curved bus periodic corrugated waveguide of the first output curved grating assisted reverse coupler of the first micro-ring optical filter is connected to the curved bus periodic corrugated waveguide of the second output curved grating assisted reverse coupler of the second micro-ring optical filter through a second intermediate optical waveguide; the straight input periodic corrugated waveguide of the third-stage reverse coupler is connected to the curved bus periodic corrugated waveguide of the second input curved grating assisted reverse coupler through a third intermediate optical waveguide.

[0086] According to an embodiment of the present disclosure, the waveguide width of the connected curved waveguide is the same as the average waveguide width and bending radius of the curved micro-ring periodic corrugation waveguide; the connected curved waveguide and the curved micro-ring periodic corrugation waveguide are connected to form a centrally symmetrical circle.

[0087] According to an embodiment of the present disclosure, the curved bus periodic corrugated waveguide 12111 is located at the upper position of the input or output curved grating assisted reverse coupler, and each optical signal will first pass through the curved bus periodic corrugated waveguide 12111 when entering the input or output curved grating assisted reverse coupler; the curved microring periodic corrugated waveguide 12112 is located at the lower position of the input or output curved grating assisted reverse coupler, and the curved bus periodic corrugated waveguide of the input and output curved grating assisted reverse coupler and the two connecting curved waveguides 1213 form a microring, that is, its structure is circular.

[0088] According to the embodiments of the present disclosure, the corrugation shapes of the curved bus periodic corrugation waveguide and the curved microring periodic corrugation waveguide include: rectangular, sinusoidal and trapezoidal; the waveguide thickness, corrugation period, duty cycle, number of periods and bending radius of the curved bus periodic corrugation waveguide and the curved microring periodic corrugation waveguide are the same; the average waveguide width and corrugation depth of the curved microring periodic corrugation waveguide are greater than those of the curved bus periodic corrugation waveguide, so as to reduce the forward cross-coupling coefficient of the input curved grating assisted reverse coupler and the output curved grating assisted reverse coupler; the inner wall of the curved bus periodic corrugation waveguide and the inner wall of the curved microring periodic corrugation waveguide meet the phase matching condition, so as to increase the coupling coefficient between the forward mode and the reverse mode in the waveguide; the inner wall and the outer wall of the same waveguide in the curved bus periodic corrugation waveguide and the curved microring periodic corrugation waveguide meet the phase mismatch condition, so as to suppress the Bragg reflection in the waveguide.

[0089] According to an embodiment of the present disclosure, the above phase mismatch condition is based on the coupling coefficient formula as follows:

[0090]

[0091] Where κ0 is the coupling coefficient when there is no mismatch, ΔL is the offset of the gratings on both sides of the same waveguide, Λ is the grating period, and ΔL / Λ is used to measure the alignment of the gratings on both sides of the same waveguide. When the phase mismatch is satisfied, At this time, κ=0, so it is called phase mismatch.

[0092] According to the embodiments of the present disclosure, when the phase mismatch condition is met, destructive interference will occur between the Bragg gratings on the left and right sides of the periodic corrugated waveguide. At this time, there will be almost no reflection when the optical signal is transmitted in the periodic corrugated waveguide.

[0093] According to the embodiment of the present disclosure, the above phase matching condition means that the coupling coefficient between the forward mode and the reverse mode of the inner wall of the curved bus periodic corrugated waveguide and the curved microring periodic corrugated waveguide is the smallest, that is, according to the coupling coefficient formula (II), when the phase matching is satisfied, At this time, κ=κ0, which is also the maximum value of κ, so it is called phase matching.

[0094] According to the embodiments of the present disclosure, in the parameter setting of the curved bus periodic corrugated waveguide and the curved microring periodic corrugated waveguide, the first microring optical filter of the first-stage integrated grating-assisted reverse coupler and the second microring optical filter of the second-stage integrated grating-assisted reverse coupler are exactly the same, in order to ensure that the two have completely consistent parameters, ensure that the two optical filters have the same filtering curve shape and Bragg reflection center wavelength, and the length difference between the first intermediate waveguide and the second intermediate waveguide is an integer multiple of the circumference of the microring, so that the optical signal to be processed undergoes two completely identical filtering processes at the through end and the download end, respectively, thereby generating an EIT spectrum, so that the extinction ratio of the filtering curve is increased by two times, and the roll-off rate of the spectrum line is improved at the same time.

[0095] Figure 4 A filtering spectrum diagram of a micro-ring optical filter with a single integrated grating-assisted reverse coupler of an optical filter with an integrated grating-assisted reverse coupler according to an embodiment of the present disclosure is schematically shown; Figure 5 The filtering spectrum diagram of two micro-ring optical filters with integrated grating-assisted reverse couplers of an optical filter with integrated grating-assisted reverse coupler according to an embodiment of the present disclosure is schematically shown.

[0096] like Figure 4 and Figure 5 As shown, by comparing the filtering of the micro-ring optical filter using one integrated grating-assisted reverse coupler and the filtering of the micro-ring optical filter using two integrated grating-assisted reverse couplers, it can be seen that Figure 5 As shown, the micro-ring optical filter using two integrated grating-assisted reverse couplers produces an EIT spectrum, in which the filtered spectrum has a narrow peak located in the groove, and its spectral line diagram has the advantages of narrower bandwidth and higher roll-off rate.

[0097] Figure 6 The schematic diagram of the structure of the third-stage reverse coupler of an optical filter integrating a grating-assisted reverse coupler according to an embodiment of the present disclosure is shown.

[0098] like Figure 6 As shown, the third-stage reverse coupler includes a straight input periodic corrugated waveguide 1231 and a straight output periodic corrugated waveguide 1232 .

[0099] According to the embodiments of the present disclosure, the corrugation shapes of the direct input periodic corrugation waveguide 1231 and the direct output periodic corrugation waveguide 1232 include: rectangular, sinusoidal and trapezoidal; the waveguide thickness, corrugation period, duty cycle and number of periods of the direct input periodic corrugation waveguide 1231 and the direct output periodic corrugation waveguide 1232 are the same; the average waveguide width and corrugation depth of the direct input periodic corrugation waveguide 1231 are smaller than those of the direct output periodic corrugation waveguide 1232, so as to reduce reverse coupling. The forward cross-coupling coefficient of the device is increased; the inner walls of the two waveguides in the reverse coupler composed of the direct input periodic corrugated waveguide 1231 and the direct output periodic corrugated waveguide 1232 meet the phase matching condition, which is used to increase the coupling coefficient between the forward mode and the reverse mode in the waveguide; the inner wall and the outer wall of the same waveguide in the reverse coupler composed of the direct input periodic corrugated waveguide 1231 and the direct output periodic corrugated waveguide 1232 meet the phase mismatch condition, which is used to suppress the Bragg reflection in the waveguide.

[0100] According to an embodiment of the present disclosure, the optical signal input into the direct input periodic corrugation waveguide 1231 is filtered, and the band that meets the Bragg reflection condition will be downloaded from the fourth port of the direct output periodic corrugation waveguide 1232 through the third-stage reverse coupler, while the band that does not meet the Bragg reflection condition will be retained at the second port of the direct input periodic corrugation waveguide 1231.

[0101] According to the embodiments of the present disclosure, the parameters of the direct input periodic corrugated waveguide 1231 and the direct output periodic corrugated waveguide 1232 are specifically set, which is conducive to ensuring that the third-stage reverse coupler filters out the notches in the optical signal spectrum and its narrow peaks.

[0102] Figure 7 The filtering spectrum diagram of the third-stage reverse coupler of an optical filter integrating a grating-assisted reverse coupler according to an embodiment of the present disclosure is schematically shown.

[0103] like Figure 7 As shown in the filtering spectrum diagram of the download end and the through end of the third-stage reverse coupler, it can be seen that the central wavelength of the third-stage reverse coupler is exactly the same as the first micro-ring optical filter of the first-stage integrated grating-assisted reverse coupler and the second micro-ring optical filter of the second-stage integrated grating-assisted reverse coupler. Therefore, the depression in the spectrum and its narrow peak can be filtered out without changing the waveform of the third optical signal.

[0104] According to an embodiment of the present disclosure, the micro-ring filtering unit is also used to determine that the center wavelengths of the filtering curves of the first micro-ring optical filter, the second micro-ring optical filter and the third-stage reverse coupler are independently tuned when tuning the center wavelength of the optical filter of the integrated grating-assisted reverse coupler; wherein the first micro-ring optical filter, the second micro-ring optical filter and the third-stage reverse coupler are tuned using thermo-optical effect or electro-optical effect.

[0105] According to the embodiments of the present disclosure, the first micro-ring optical filter of the first-stage integrated grating-assisted reverse coupler, the second micro-ring optical filter of the second-stage integrated grating-assisted reverse coupler, and the third-stage reverse coupler can be tuned independently, so that the tuning of the central wavelength of the optical filter of the integrated grating-assisted reverse coupler can be realized, and the central wavelengths of the filtering spectral lines of the two micro-ring optical filters can be tuned separately to achieve adjustable bandwidth, that is, different degrees of alignment of the central wavelengths between the two micro-ring filters will result in different thicknesses of the synthesized peaks, thereby achieving the adjustment of the bandwidth.

[0106] According to an embodiment of the present disclosure, an optical filter integrated with a grating-assisted reverse coupler may be an optical element.

[0107] Figure 8 The filtering spectrum diagram of an optical filter integrated with a grating-assisted reverse coupler according to an embodiment of the present disclosure is schematically shown.

[0108] According to an embodiment of the present disclosure, a first broadband optical signal transmitted in an input optical waveguide first enters a first micro-ring optical filter of a first-stage integrated grating-assisted reverse coupler for filtering, wherein the signal is divided into two optical paths, an input end and a download end, for filtering, to obtain a second through-end optical signal and a second download end optical signal; then, the second through-end optical signal and the second download end optical signal are input into a second micro-ring optical filter of a second-stage integrated grating-assisted reverse coupler, wherein the signal is also divided into two optical paths, an input end and a download end, for filtering, to obtain a third through-end optical signal and a third download end optical signal; then, the third through-end optical signal and the third download end optical signal are combined in a third intermediate optical waveguide and then input into a third-stage reverse coupler to obtain a fourth optical signal; and the fourth optical signal is output through an output optical waveguide, wherein, as Figure 8 (c) shows the overall filtering spectrum of the optical filter with integrated grating-assisted reverse coupler; Figure 8 (a) is a combined filtering curve diagram of a first micro-ring optical filter of a first-stage integrated grating-assisted reverse coupler and a second micro-ring optical filter of a second-stage integrated grating-assisted reverse coupler; Figure 8 (b) is the filtering curve diagram of the third-stage reverse coupler.

[0109] According to the embodiments of the present disclosure, Figure 8As shown in (c), the filtered optical signal output by the output optical waveguide has the advantages of no FSR, low loss, narrow bandwidth, and high roll-off rate. Among them, the advantage of no FSR enables the optical filter to have a strong target frequency band selection capability.

[0110] The embodiments of the present disclosure are described above. However, these embodiments are only for illustrative purposes and are not intended to limit the scope of the present disclosure. Although the embodiments are described above separately, this does not mean that the measures in the various embodiments cannot be used in combination to advantage. The scope of the present disclosure is defined by the attached claims and their equivalents. Without departing from the scope of the present disclosure, those skilled in the art may make a variety of substitutions and modifications, which should all fall within the scope of the present disclosure.

Claims

1. An optical filter with integrated grating-assisted reverse coupler, include: An input optical waveguide is connected to a first input curved grating-assisted reverse coupler of a first micro-ring optical filter of a first-stage integrated grating-assisted reverse coupler in a micro-ring filter unit, and is used for inputting an optical signal to be processed; A micro-ring filter unit, comprising a first micro-ring optical filter of a first-stage integrated grating-assisted reverse coupler, a second micro-ring optical filter of a second-stage integrated grating-assisted reverse coupler, and a third-stage reverse coupler, for filtering the optical signal; An intermediate optical waveguide unit, comprising a first intermediate optical waveguide, a second intermediate optical waveguide and a third intermediate optical waveguide, for transmitting an optical signal in the micro-ring filter unit; wherein the first input curved grating assisted reverse coupler is connected to the second input curved grating assisted reverse coupler of the second micro-ring optical filter through the first intermediate optical waveguide, the first output curved grating assisted reverse coupler of the first micro-ring optical filter is connected to the second output curved grating assisted reverse coupler of the second micro-ring optical filter through the second intermediate optical waveguide, and the straight input periodic corrugated waveguide of the third-stage reverse coupler is connected to the second input curved grating assisted reverse coupler through the third intermediate optical waveguide; The output optical waveguide is connected to the straight output periodic corrugated waveguide of the third-stage reverse coupler and is used to output the processed optical signal.

2. The optical filter with integrated grating-assisted backcoupler according to claim 1, in, The first micro-ring optical filter of the first-stage integrated grating-assisted reverse coupler and the second micro-ring optical filter of the second-stage integrated grating-assisted reverse coupler both include: Input bent grating assisted backcoupler; Output bent grating assisted backcoupler; A connecting curved waveguide is disposed between the input curved grating assisted reverse coupler and the output curved grating assisted reverse coupler so as to connect the input curved grating assisted reverse coupler and the output curved grating assisted reverse coupler into a complete circular structure.

3. The optical filter with integrated grating-assisted backcoupler according to claim 2, in, The input curved grating assisted reverse coupler and the output curved grating assisted reverse coupler both include: a curved bus periodic corrugated waveguide and a curved micro-ring periodic corrugated waveguide.

4. The optical filter with integrated grating-assisted backcoupler according to claim 3, in, The corrugation shapes of the curved bus periodic corrugation waveguide and the curved micro-ring periodic corrugation waveguide include: rectangular, sinusoidal and trapezoidal; The waveguide thickness, corrugation period, duty cycle, number of periods and bending radius of the curved bus periodic corrugated waveguide and the curved micro-ring periodic corrugated waveguide are all the same; The average waveguide width and the corrugation depth of the curved micro-ring periodic corrugation waveguide are both greater than those of the curved bus periodic corrugation waveguide, so as to reduce the forward cross-coupling coefficient of the input curved grating assisted reverse coupler and the output curved grating assisted reverse coupler; The inner wall of the curved bus periodic corrugated waveguide and the inner wall of the curved micro-ring periodic corrugated waveguide meet a phase matching condition so as to increase the coupling coefficient between the forward mode and the reverse mode in the waveguide; The inner wall and the outer wall of the same waveguide in the curved bus periodic corrugated waveguide and the curved micro-ring periodic corrugated waveguide meet a phase mismatch condition so as to suppress Bragg reflection in the waveguide.

5. The optical filter with integrated grating-assisted backcoupler according to claim 3, in, The first input curved grating assisted reverse coupler is connected to the second input curved grating assisted reverse coupler of the second micro-ring optical filter through the first intermediate optical waveguide, comprising: The curved bus periodic corrugated waveguide of the first input curved grating assisted reverse coupler is connected to the curved bus periodic corrugated waveguide of the second input curved grating assisted reverse coupler of the second micro-ring optical filter through the first intermediate optical waveguide; The first output curved grating assisted reverse coupler of the first micro-ring optical filter is connected to the second output curved grating assisted reverse coupler of the second micro-ring optical filter through the second intermediate optical waveguide, comprising: The curved bus periodic corrugated waveguide of the first output curved grating assisted reverse coupler of the first micro-ring optical filter is connected to the curved bus periodic corrugated waveguide of the second output curved grating assisted reverse coupler of the second micro-ring optical filter through the second intermediate optical waveguide; The straight input periodic corrugated waveguide of the third-stage reverse coupler is connected to the second input curved grating auxiliary reverse coupler through the third intermediate optical waveguide, comprising: The straight input periodic corrugated waveguide of the third-stage reverse coupler is connected to the curved bus periodic corrugated waveguide of the second input curved grating-assisted reverse coupler through the third intermediate optical waveguide.

6. The optical filter with integrated grating-assisted backcoupler according to claim 3, in, The waveguide width of the connecting curved waveguide is the same as the average waveguide width and bending radius of the curved micro-ring periodic corrugated waveguide; The connecting curved waveguide and the curved micro-ring periodic corrugated waveguide are connected to form a centrally symmetrical circle.

7. The optical filter with integrated grating-assisted backcoupler according to claim 1, in, The corrugation shapes of the straight input periodic corrugation waveguide and the straight output periodic corrugation waveguide include: rectangular, sinusoidal and trapezoidal; The waveguide thickness, corrugation period, duty cycle and number of periods of the direct input periodic corrugation waveguide and the direct output periodic corrugation waveguide are all the same; The average waveguide width and corrugation depth of the direct input periodic corrugation waveguide are smaller than those of the direct output periodic corrugation waveguide, so as to reduce the forward cross-coupling coefficient of the reverse coupler; The inner walls of the two waveguides in the reverse coupler composed of the direct input periodic corrugated waveguide and the direct output periodic corrugated waveguide meet the phase matching condition, so as to increase the coupling coefficient between the forward mode and the reverse mode in the waveguide; The inner wall and outer wall of the same waveguide in the reverse coupler composed of the straight-input periodic corrugated waveguide and the straight-output periodic corrugated waveguide meet the phase mismatch condition, so as to suppress the Bragg reflection in the waveguide.

8. The optical filter with integrated grating-assisted backcoupler according to claim 1, in, The average waveguide width of the straight output periodic corrugated waveguide of the third-stage reverse coupler is the same as the average waveguide width of the curved micro-ring periodic corrugated waveguides of the first micro-ring optical filter and the second micro-ring optical filter; The average waveguide width of the straight input periodic corrugated waveguide of the third-stage reverse coupler is the same as the average waveguide width of the curved bus periodic corrugated waveguide of the first micro-ring optical filter and the second micro-ring optical filter; The third-stage reverse coupler has the same waveguide thickness, waveguide spacing, corrugation period, duty cycle, and number of periods as the first micro-ring optical filter and the second micro-ring optical filter.

9. The optical filter with integrated grating-assisted backcoupler according to claim 1, in, The length difference between the second intermediate optical waveguide and the first intermediate optical waveguide is an integer multiple of the circumference of the micro-ring.

10. The optical filter of the integrated grating-assisted reverse coupler according to claim 1, wherein the micro-ring filtering unit is further used to determine to independently tune the center wavelengths of the filtering curves of the first micro-ring optical filter, the second micro-ring optical filter and the third-stage reverse coupler when tuning the center wavelength of the optical filter of the integrated grating-assisted reverse coupler; in, The first micro-ring optical filter, the second micro-ring optical filter and the third-stage reverse coupler are tuned by utilizing thermo-optic effect or electro-optic effect.

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