All-optical analog-to-digital converter based on cascade multimode interferometer

Abstract

The invention discloses an all-optical analog-to-digital converter based on a cascade multimode interferometer, and relates to the technical field of all-optical analog-to-digital conversion, N CSS-MMI modules are configured in parallel, and the CSS-MMI modules comprise an MMI1 and an MMI2; the MMI1 receives the signal sub-beam and the reference sub-beam, converts double-path input light into three-path output light, and generates a fixed phase difference; three paths of light output by the MMI1 are input to the MMI2, the MMI2 realizes odd channel self-imaging through stepping width adjustment, and light intensity distribution related to phase difference is formed at K output ports; k output ports of the CSS-MMI module are respectively connected with a photoelectric detector, an optical signal is converted into a current signal, the current signal is converted into a voltage signal through an amplifier, the voltage signal is compared with a preset threshold value, and a binary signal is output; and the decoder receives binary signals of all channels, integrates N * K channel data through logical operation, and generates a multi-bit digital code.

Description

Technical Field

[0001] This invention relates to the field of all-optical analog-to-digital conversion technology, specifically an all-optical analog-to-digital converter based on a cascaded multimode interferometer. Background Technology

[0002] As optical communication speeds evolve towards 100Gbps and above, electrical analog-to-digital converters (ADCs) are limited by the bandwidth bottleneck of electronic devices (such as the difficulty in breaking through 100GHz clock frequency), making it impossible to meet the real-time quantization requirements of ultra-high-speed optical signals. Traditional electrical ADCs suffer from high power consumption, low sampling rate, and limited quantization accuracy when processing terahertz (THz) level optical signals, becoming a key "bandwidth bottleneck" in optical communication systems.

[0003] All-optical ADCs directly convert optical signals into digital signals using photonic devices, which can overcome the limitations of electrical bandwidth. However, they still lack multi-module parallel phase bias design, making it difficult to improve quantization accuracy through misaligned coding. The width adjustment and phase difference generation of MMI have not formed a precise mathematical model, and the relationship between light intensity distribution and phase mapping is ambiguous. The voltage threshold and hysteresis control after photoelectric conversion are not deeply coordinated with the optical coding state, which can easily lead to misjudgment and affect the effective number of bits. Summary of the Invention

[0004] The purpose of this invention is to provide an all-optical analog-to-digital converter based on a cascaded multimode interferometer to solve the problems mentioned in the prior art.

[0005] To achieve the above objectives, the present invention provides the following technical solution: an all-optical analog-to-digital converter based on a cascaded multimode interferometer. The input light includes a signal light and a reference light; the signal light and the reference light are split into N paths by a 1×N beam splitter, where N is a positive integer, generating a signal sub-beam and a reference sub-beam; N CSS-MMI modules are configured in parallel. The CSS-MMI modules include MMI1 and MMI2. MMI1 receives the signal sub-beam and the reference sub-beam, converts the dual-path input light into three-path output, and generates a fixed phase difference. The three-path light output from MMI1 is input to MMI2. MMI2 achieves odd-channel self-imaging through step-width adjustment, forming a light intensity distribution related to the phase difference at K output ports, where K is a positive integer. The N CSS-MMI modules operate independently, outputting a total of N×K channel signals; the K output ports of the CSS-MMI modules are respectively connected to photodetectors, converting optical signals into current signals, which are then amplified into voltage signals, compared with a preset threshold, and outputting binary signals. The decoder receives binary signals from all channels, integrates the N×K channel data through logical operations, and generates a multi-bit digital code.

[0006] According to the above scheme, the reference sub-beams are respectively reference sub-beams R1, R2, ..., R N ; in reference sub-beams R2 to R N In the middle, an electro-optic phase shifter is set up to apply a fixed phase shift φ to the reference sub-beam. n =π / (NK), where n=2, 3, ..., N; where n represents the index of the beam and K represents the number of output ports of a single CSS-MMI module.

[0007] According to the above scheme, the multimode interference region of MMI1 adopts a rectangular waveguide structure, and the length and width of the multimode interference region of MMI1 satisfy the self-image condition, as shown in the following formula: ; Where L1 represents the length of the multimode interference region of MMI1; L c1 This is expressed as the coupling length of MMI1; The coupling length of MMI1 is given by the following formula: ; Among them, L c1 The coupling length of MMI1 is represented by n; eff λ represents the effective refractive index of the waveguide, which is the proportion by which light is slowed down relative to the speed in a vacuum when propagating in the waveguide; W1 represents the width of the multimode interference region of MMI1; and λ represents the wavelength of the input light.

[0008] According to the above scheme, the MMI1 converts the signal light and reference light into three single-mode outputs with a specific phase difference. The transmission matrix of the MMI1 is as follows: ; Where M1 represents the output of MMI1; j is the imaginary unit, representing a 90° phase delay; The signal light and reference light are injected from the two input ports of the MMI1, respectively; after entering the MMI1, the signal light forms a self-image E with 100% power output at the second port in the middle through multimode interference. s After the reference light enters the MMI1, it forms a self-image E with 50% power output at the first and third ports on both sides through multimode interference. p1 'and E p2 '; The three output light fields satisfy the phase relationship: ∠E p1 '-∠E s =0, ∠Ep2 '-∠E s =π / 2; where ∠E p1 ' represents the phase of the output optical field at the first port; ∠E s ' represents the phase of the output optical field at the second port; ∠E p2 ' represents the phase of the output optical field at the third port.

[0009] According to the above scheme, the length of the MMI2 multimode interference region is L2, and the coupling length of the MMI2 is L. c2 It satisfies the self-mapping condition, and the formula is as follows: ; Where K represents the number of output ports; The coupling length of the MMI2 is L c2 , the formula is as follows: ; L c2 The coupling length of MMI1 is represented by n; eff Wi represents the effective refractive index of the waveguide, which is the proportion by which light is slowed down relative to the speed in a vacuum when propagating in the waveguide; W2 represents the width of the multimode interference region of MMI2; λ represents the wavelength of the input light. The width W2 of the MMI2 multimode interference region and the width W1 of the MMI1 multimode interference region are adjusted in a stepwise manner, as shown in the following formula: W2 = W1 + (K-1)ΔW; Where ΔW represents the width adjustment step size; The formula for the width adjustment step size is as follows: ΔW=λ / 2n eff ; Where λ represents the wavelength of the input light; n eff It is expressed as the effective refractive index of the waveguide.

[0010] According to the above scheme, the self-image E output by MMI1 s ', located at the center position W2 / 2 in the MMI2; the self-image E output by the MMI1 p1 ', located at (K+2) / 2K in MMI2; the self-image E output by MMI1 p2 ', located at (K-2) / 2K in the MMI2.

[0011] According to the above scheme, after multimode interference, the relationship between the light intensity distribution and phase difference at the K output ports is as follows: ; Among them, I i Represented as light intensity distribution; The phase difference between the signal light and the reference light is represented by ; i represents the index of the output port.

[0012] According to the above scheme, each CSS-MMI module's K output ports are connected to an independent photodetector array. The photodetectors are PIN photodiodes, and their response wavelength range covers the input light wave. The current signal output by the photodetector is converted into a voltage signal by an amplifier; the gain of the amplifier is given by the following formula: ; Where G represents the amplifier gain; V th Represented by the preset threshold voltage; r represents the responsivity of the photodetector; P min This is expressed as the minimum detectable optical power; The threshold voltage is given by the following formula: V th =(V max +V min ) / 2; Among them, V th Represented as threshold voltage; V max This represents the output voltage at the maximum optical power of the corresponding output port; V min This represents the output voltage at the minimum optical power of the corresponding output port; Each voltage signal is compared with a preset threshold voltage by a comparator, and a binary signal is output. Each output channel generates a 1-bit binary signal, and N CSS-MMI modules output a total of N×K bits of parallel digital signal.

[0013] According to the above scheme, the binary signal includes: When the output voltage V out ≥V th +V hys When the output voltage V is 1, the logic is 1; when the output voltage V is 1, the logic is 1. out ≤V th -V hys When V is active, output logic 0; when V is active, output logic 0. th -V hys <V out <V th +V hys At that time, maintain the previous state; where V hys This is represented as hysteresis voltage.

[0014] According to the above scheme, each CSS-MMI module outputs a K-bit binary signal, and the N modules achieve phase interval misalignment through phase offset, wherein the reference light phase offset of the nth module is φ. n=(n-1)π / (NK), n=1,2,…,N; phase offset φ of N modules n By sequentially increasing π / (NK), the coding range of each module is offset by π / (NK) relative to the previous module, and the total coding range eventually covers 2π. The total number of encoded states satisfies the formula: ; Where, N bin The total number of codes is represented by N; N represents the number of corresponding phase offset states, with each CSS-MMI module corresponding to one phase offset state; 2 represents that each channel outputs two logics, 0 and 1; K represents the number of output channels. The total number of encoded states corresponds to the phase step size, as shown in the following formula: ; Where Δθ represents the phase step size corresponding to the total number of encoded states; 2π represents the signal light phase range; The effective number of bits is obtained based on the total number of encoded states, using the following formula: ; Where, N eff Represented as the number of significant digits, This indicates rounding down.

[0015] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention employs N-module parallel configuration and phase bias to achieve fine phase resolution, with an effective number of bits exceeding 5 bits, significantly improving analog-to-digital conversion accuracy; 2. This invention adopts a cascaded MMI design, which significantly reduces the chip area and achieves higher integration. 3. This invention achieves configurable precision of 3 to 8 bits by adjusting the values ​​of N and K, adapting to different application requirements. It not only has higher precision but also stronger adaptability. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the structure of an all-optical analog-to-digital converter based on a cascaded multimode interferometer according to the present invention; Figure 2 This is a schematic diagram of the MMI1 structure of an all-optical analog-to-digital converter based on a cascaded multimode interferometer according to the present invention; Figure 3 This is a schematic diagram of the MMI1 structure of an all-optical analog-to-digital converter based on a cascaded multimode interferometer according to the present invention; Figure 4 This is a schematic diagram of the CSS-MMI structure of an all-optical analog-to-digital converter based on a cascaded multimode interferometer according to the present invention; Figure 5This is a schematic diagram of the structure of a K=5 all-optical analog-to-digital converter based on a cascaded multimode interferometer according to the present invention. Detailed Implementation

[0017] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0018] Example: Figure 1-Figure 5 As shown, the present invention provides a technical solution, an all-optical analog-to-digital converter based on a cascaded multimode interferometer, including an input signal light (100), a reference light (101), a 1×N beam splitter (200), a CSS-MMI module (400), ..., a CSS-MMI module (40(N-1)), an electro-optic phase shifter (300), ..., an electro-optic phase shifter (30(N-1)), a photodetector (500), ..., a photodetector (50(N-1)), an amplifier (600), ..., an amplifier (60(N-1)), a comparator (700), ..., a comparator (70(N-1)), and a decoder (8); A 1×N beam splitter (200) divides the signal light (100) into N paths, where N is a positive integer, generating signal sub-beams; a 1×N beam splitter (201) divides the reference light (101) into N paths, where N is a positive integer, generating reference sub-beams; the reference sub-beams are reference sub-beams R1, R2, ..., R N ; in reference sub-beams R2 to R N In the middle, electro-optic phase shifters (300), ..., electro-optic phase shifters (30(N-1)) are respectively set to apply a fixed phase shift φ to the reference sub-beam. n =π / (NK), where n=2, 3, ..., N; where n represents the index of the beam and K represents the number of output ports of a single CSS-MMI module.

[0019] The CSS-MMI module (400) receives one signal sub-beam and one reference sub-beam, converts the dual input light into three outputs, and generates a fixed phase difference; and achieves odd channel self-imaging through step width adjustment, forming a light intensity distribution related to the phase difference at K output ports, where K is a positive integer; CSS-MMI modules (400), ..., CSS-MMI modules (40(N-1)) are connected to photodetectors (500), ..., photodetectors (50(N-1)) respectively, and the response wavelength range covers the input light wave; Photodetectors (500), ..., and photodetector (50(N-1)) are respectively connected to amplifiers (600), ..., and amplifier (60(N-1)) and comparators (700), ..., and comparator (70(N-1)); the current signal output by the photodetector is converted into a voltage signal by the amplifier; the gain of the amplifier is given by the following formula: ; Where G represents the amplifier gain; V th Represented by the preset threshold voltage; r represents the responsivity of the photodetector; P min This is expressed as the minimum detectable optical power; Specifically, the threshold voltage is calculated using the following formula: V th =(V max +V min ) / 2; Among them, V th Represented as threshold voltage; V max This represents the output voltage at the maximum optical power of the corresponding output port; V min This represents the output voltage at the minimum optical power of the corresponding output port; Each voltage signal is compared with a preset threshold voltage by a comparator, and a binary signal is output. Specifically, binary signals include: When the output voltage V out ≥V th +V hys When the output voltage V is 1, the logic is 1; when the output voltage V is 1, the logic is 1. out ≤V th -V hys When V is active, output logic 0; when V is active, output logic 0. th -V hys <V out <V th +V hys At that time, maintain the previous state; where V hys Represented as hysteresis voltage; Each output channel generates a 1-bit binary signal, and N CSS-MMI modules output a total of N×K bits of parallel digital signal; Furthermore, each CSS-MMI module outputs a K-bit binary signal, and the N modules achieve phase misalignment through phase offset, where the reference light phase offset of the nth module is φ. n =(n-1)π / (NK), n=1,2,…,N; phase offset φ of N modules n By sequentially increasing π / (NK), the coding range of each module is offset by π / (NK) relative to the previous module, and the total coding range eventually covers 2π. The total number of encoded states satisfies the formula: ; Where, N bin The total number of codes is represented by N; N represents the number of corresponding phase offset states, with each CSS-MMI module corresponding to one phase offset state; 2 represents that each channel outputs two logics, 0 and 1; K represents the number of output channels. The total number of encoded states corresponds to the phase step size, as shown in the following formula: ; Where Δθ represents the phase step size corresponding to the total number of encoded states; 2π represents the signal light phase range; The effective number of bits is obtained based on the total number of encoded states, using the following formula: ; Where, N eff Represented as the number of significant digits, This indicates rounding down.

[0020] This invention provides another technical solution, an MMI1 based on a cascaded multimode interferometer and an all-optical analog-to-digital converter, such as... Figure 2 As shown, the MMI1 includes an input signal light (100), an input reference light (101), an MMI1 multimode interference region (2), a first output port (22), a second output port (21), and a third output port (20). Specifically, the multimode interference region of MMI1 adopts a rectangular waveguide structure, and the length and width of the multimode interference region of MMI1 satisfy the self-image condition, as shown in the following formula: ; Where L1 represents the length of the multimode interference region of MMI1; L c1 This is expressed as the coupling length of MMI1; The coupling length of MMI1 is given by the following formula: ; Among them, L c1 The coupling length of MMI1 is represented by n; eff λ represents the effective refractive index of the waveguide, which is the proportion by which light is slowed down relative to the speed in a vacuum when propagating in the waveguide; W1 represents the width of the multimode interference region of MMI1; and λ represents the wavelength of the input light.

[0021] MMI1 converts the signal light (100) and reference light (101) into three single-mode outputs with a specific phase difference. The transmission matrix of MMI1 is given by the following formula: ; Where M1 represents the output of MMI1; j is the imaginary unit, representing a 90° phase delay; The signal light (100) and the reference light (101) are injected from the two input ports of the MMI1, respectively; After the signal light (100) enters MMI1, it forms a self-image E with 100% power output at the second output port (21) in the middle through the multimode interference effect. s After the reference light enters the MMI1, it forms a self-image E with 50% power output at the first output port (22) and the third output port (20) on both sides through multimode interference effect. p1 'and E p2 '; Furthermore, the three output light fields satisfy the phase relationship: ∠E p1 '-∠E s =0, ∠E p2 '-∠E s =π / 2; where ∠E p1 ' represents the phase of the output optical field at the first port; ∠E s ' represents the phase of the output optical field at the second port; ∠E p2 ' represents the phase of the output optical field at the third port.

[0022] This invention provides another technical solution, an MMI2 based on a cascaded multimode interferometer and an all-optical analog-to-digital converter, such as... Figure 3 As shown, the MMI2 includes an input port (100), an input port (101), an input port (102), an MMI2 multimode interference region (2), an output port (30), ..., an output port (3(K-1)). The length of the multimode interference region of MMI2 is L2, and the coupling length of MMI2 is L. c2 It satisfies the self-mapping condition, and the formula is as follows: ; Where K represents the number of output ports; The coupling length of the MMI2 is L c2 , the formula is as follows: ; L c2 The coupling length of MMI1 is represented by n; eff Wi represents the effective refractive index of the waveguide, which is the proportion by which light is slowed down relative to the speed in a vacuum when propagating in the waveguide; W2 represents the width of the multimode interference region of MMI2; λ represents the wavelength of the input light. Furthermore, the width W2 of the MMI2 multimode interference region and the width W1 of the MMI1 multimode interference region are adjusted in a stepwise manner, as shown in the following formula: W2 = W1 + (K-1)ΔW; Where ΔW represents the width adjustment step size; The formula for the width adjustment step size is as follows: ΔW=λ / 2n eff ; Where λ represents the wavelength of the input light; n eff It is expressed as the effective refractive index of the waveguide.

[0023] Furthermore, the self-image E output by the MMI1 s ', located at the center position W2 / 2 in the MMI2; the self-image E output by the MMI1 p1 ', located at (K+2) / 2K in MMI2; the self-image E output by MMI1 p2 ', located at (K-2) / 2K in the MMI2.

[0024] Furthermore, after multimode interference, the relationship between the light intensity distribution and phase difference at the K output ports is as follows: ; Among them, I i Represented as light intensity distribution; The phase difference between the signal light and the reference light is represented by ; i represents the index of the output port.

[0025] This invention provides another technical solution: a K=5 all-optical analog-to-digital converter; like Figure 5 As shown, the K=5 all-optical analog-to-digital converter includes: input signal light (100), input reference light (101), MMI1 (2), MMI (3), output port (400), output port (401), output port (402), output port (403), output port (404), photodetector (500), photodetector (501), photodetector (502), photodetector (503), photodetector (504), amplifier (600), amplifier (601), amplifier (602), amplifier (603), amplifier (604), comparator (700), comparator (701), comparator (702), comparator (703), comparator (704), and decoder (8); Design an analog-to-digital converter with K=5 based on SOI planar waveguide technology; Number of parallel modules: N=2 (2 CSS-MMI modules in parallel); Number of output ports per module: K=5 (5 output channels per module); Operating wavelength: λ=1550nm (communication band); Waveguide effective refractive index: n eff =3.4 (SOI waveguide); MMI1 multimode interference region: width W1 = 4 μm; The coupling length L of MMI1 C1 , the formula is as follows: ; Among them, L c1 The coupling length of MMI1 is represented by n; eff λ represents the effective refractive index of the waveguide, which is the proportion by which light is slowed down relative to the speed in a vacuum when propagating in the waveguide; W1 represents the width of the multimode interference region of MMI1; λ represents the wavelength of the input light. The coupling length L of MMI1 C1 ≈56.6μm; Actual length L1=L C1 =56.6μm; The width W2 of the MMI2 multimode interference region is adjusted in a stepwise manner relative to the width W1 of the MMI1 multimode interference region, as shown in the following formula: W2 = W1 + (K-1)ΔW; Where ΔW represents the width adjustment step size; The formula for the width adjustment step size is as follows: ΔW=λ / 2n eff ; Where λ represents the wavelength of the input light; n eff Expressed as the effective refractive index of the waveguide; Width adjustment step ΔW = 228nm; Input width W2 = 4.91μm; The coupling length of the MMI2 is L c2 , the formula is as follows: ; L c2 The coupling length of MMI1 is represented by n; eff Wi represents the effective refractive index of the waveguide, which is the proportion by which light is slowed down relative to the speed in a vacuum when propagating in the waveguide; W2 represents the width of the multimode interference region of MMI2; λ represents the wavelength of the input light. The coupling length of MMI2 is L c2 =84.9μm; Actual length L2=34μm; Total number of encoded states and number of significant bits: N bin =N×2×K=2×2×5=20; Δθ=2π / N bin =π / 10; N eff=⌊log2(20)⌋=⌊4.32⌋=4bit.

[0026] This invention provides another technical solution: three CSS-MMI modules, each outputting a 6-bit binary signal, and a method for calculating the total number of effective bits in the encoding; Each CSS-MMI module outputs a 6-bit binary signal. The three modules achieve phase misalignment through phase offset, where the reference light phase offset of the nth module is φ. n =(n-1)π / (NK), n=1, 2, 3; Phase offset φ of the 3 modules n By sequentially increasing π / (NK), the coding range of each module is offset by π / (NK) relative to the previous module, and the total coding range eventually covers 2π. The total number of encoded states satisfies the formula: ; Where, N bin The total number of codes is represented by N; N represents the number of corresponding phase offset states, with each CSS-MMI module corresponding to one phase offset state; 2 represents that each channel outputs two logics, 0 and 1; K represents the number of output channels. N bin =3×2×6=36; The total number of encoded states corresponds to the phase step size, as shown in the following formula: ; Where Δθ represents the phase step size corresponding to the total number of encoded states; 2π represents the signal light phase range; The effective number of bits is obtained based on the total number of encoded states, using the following formula: ; Where, N eff Represented as the number of significant digits, This is represented as rounding down; N eff =log2(36)≈5.17; Three CSS-MMI modules are obtained, each of which outputs a 6-bit binary signal, for a total of approximately 5 effective bits in the encoding.

[0027] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

Claims

1. An all-optical analog-to-digital converter based on a cascaded multimode interferometer, characterized in that: The input light includes a signal light and a reference light; the signal light and the reference light are split into N paths by a 1×N beam splitter, where N is a positive integer, generating a signal sub-beam and a reference sub-beam; N CSS-MMI modules are configured in parallel. The CSS-MMI modules include MMI1 and MMI2. MMI1 receives the signal sub-beam and the reference sub-beam, converts the dual-path input light into three-path output, and generates a fixed phase difference. The three-path light output from MMI1 is input to MMI2. MMI2 achieves odd-channel self-imaging through step-width adjustment, forming a light intensity distribution related to the phase difference at K output ports, where K is a positive integer. The N CSS-MMI modules operate independently, outputting a total of N×K channel signals; the K output ports of the CSS-MMI modules are respectively connected to photodetectors, converting optical signals into current signals, which are then amplified into voltage signals, compared with a preset threshold, and outputting binary signals. The decoder receives binary signals from all channels, integrates the N×K channel data through logical operations, and generates a multi-bit digital code.

2. The all-optical analog-to-digital converter based on a cascaded multimode interferometer according to claim 1, characterized in that: The reference sub-beams are respectively reference sub-beams R1, R2, ..., R N ; in reference sub-beams R2 to R N In the middle, an electro-optic phase shifter is set up to apply a fixed phase shift φ to the reference sub-beam. n =π / (NK), where n=2, 3, ..., N; where n represents the index of the beam and K represents the number of output ports of a single CSS-MMI module.

3. The all-optical analog-to-digital converter based on a cascaded multimode interferometer according to claim 1, characterized in that: The multimode interference region of MMI1 adopts a rectangular waveguide structure. The length and width of the multimode interference region of MMI1 satisfy the self-image condition, as shown in the following formula: ； Where L1 represents the length of the multimode interference region of MMI1; L c1 This is represented as the coupling length of MMI1.

4. The all-optical analog-to-digital converter based on a cascaded multimode interferometer according to claim 1, characterized in that: The MMI1 converts the signal light and reference light into three single-mode outputs with a specific phase difference. The transmission matrix of the MMI1 is given by the following formula: ； Where M1 represents the output of MMI1; j is the imaginary unit, representing a 90° phase delay; The signal light and reference light are injected from the two input ports of the MMI1, respectively; after entering the MMI1, the signal light forms a self-image E with 100% power output at the second port in the middle through multimode interference. s After the reference light enters the MMI1, it forms a self-image E with 50% power output at the first and third ports on both sides through multimode interference. p1 'and E p2 '.

5. The all-optical analog-to-digital converter based on a cascaded multimode interferometer according to claim 1, characterized in that: The length of the MMI2 multimode interference region is L2, and the coupling length of the MMI2 is L. c2 It satisfies the self-mapping condition, and the formula is as follows: ； Where K represents the number of output ports; The width W2 of the MMI2 multimode interference region and the width W1 of the MMI1 multimode interference region are adjusted in a stepwise manner.

6. The all-optical analog-to-digital converter based on a cascaded multimode interferometer according to claim 1, characterized in that: The self-image E output by MMI1 s ', located at the center position W2 / 2 in the MMI2; the self-image E output by the MMI1 p1 ', located at (K+2) / 2K in MMI2; the self-image E output by MMI1 p2 ', located at (K-2) / 2K in the MMI2.

7. The all-optical analog-to-digital converter based on a cascaded multimode interferometer according to claim 6, characterized in that: After multimode interference, the relationship between the light intensity distribution and phase difference at the K output ports is as follows: ； Among them, I i Represented as light intensity distribution; The phase difference between the signal light and the reference light is represented by ; i represents the index of the output port.

8. The all-optical analog-to-digital converter based on a cascaded multimode interferometer according to claim 1, characterized in that: Each CSS-MMI module has K output ports connected to an independent photodetector array. The photodetectors are PIN photodiodes with a response wavelength range covering the input light wave. The current signal output by the photodetector is converted into a voltage signal by an amplifier; the gain of the amplifier is given by the following formula: ； Where G represents the amplifier gain; V th Represented by the preset threshold voltage; r represents the responsivity of the photodetector; P min This is expressed as the minimum detectable optical power; Each voltage signal is compared with a preset threshold voltage by a comparator, and a binary signal is output. Each output channel generates a 1-bit binary signal, and N CSS-MMI modules output a total of N×K bits of parallel digital signal.

9. The all-optical analog-to-digital converter based on a cascaded multimode interferometer according to claim 8, characterized in that: The binary signal includes: When the output voltage V out ≥V th +V hys When the output voltage V is 1, the logic is 1; when the output voltage V is 1, the logic is 1. out ≤V th -V hys When V is active, output logic 0; when V is active, output logic 0. th -V hys <V out <V th +V hys At that time, maintain the previous state; where V hys This is represented as hysteresis voltage.

10. An all-optical analog-to-digital converter based on a cascaded multimode interferometer according to claim 1, characterized in that: Each CSS-MMI module outputs a K-bit binary signal. The N modules achieve phase misalignment through phase offset, where the reference light phase offset of the nth module is φ. n =(n-1)π / (NK), n=1,2,…,N; phase offset φ of N modules n By sequentially increasing π / (NK), the coding range of each module is offset by π / (NK) relative to the previous module, and the total coding range eventually covers 2π. The total number of encoded states satisfies the formula: ； Where, N bin The total number of codes is represented by N; N represents the number of corresponding phase offset states, with each CSS-MMI module corresponding to one phase offset state; 2 represents that each channel outputs two logics, 0 and 1; K represents the number of output channels. The total number of encoded states corresponds to the phase step size, as shown in the following formula: ； Where Δθ represents the phase step size corresponding to the total number of encoded states; 2π represents the signal light phase range; The effective number of bits is obtained based on the total number of encoded states, using the following formula: ； Where, N eff Represented as the number of significant digits, This indicates rounding down.

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