An optical vector network analyzer based on direct detection and method thereof

Abstract

The application discloses a kind of optical vector network analyzers based on direct detection and method thereof. Including continuous light source, electro-optic modulation module, arbitrary waveform generator, device under test and signal processing module;Continuous light source is arranged on the side of electro-optic modulation module with interval, and device under test and signal processing module are sequentially arranged with interval on the other side, and arbitrary waveform generator is electrically connected to electro-optic modulation module;The optical signal output by continuous light source and the multi-carrier microwave signal output by arbitrary waveform generator are input into electro-optic modulation module together, and modulated optical signal is obtained;After modulated optical signal is output from electro-optic modulation module, it is input into signal processing module by device under test and the frequency response information of device under test is obtained by processing.The application can realize the direct detection of the frequency response of the optical device under test, and is expected to be applied in coherent photon measurement, dynamic spectrum analysis, optical instrument measurement and other fields.

Description

Technical Field

[0001] This invention belongs to the field of microwave photonics technology, specifically relating to a direct detection-based optical vector network analyzer and its method. Background Technology

[0002] In fields such as optical sensing, high-Q optical microcavity characterization, and optical communication device analysis, high-precision measurement of the spectral and vector characteristics (amplitude and phase) of optical signals is a core requirement. However, existing related technologies have long suffered from bottlenecks that make it difficult to balance resolution, response speed (or dynamic range), and measurement bandwidth.

[0003] In the field of optical spectrum measurement, although some commercially available traditional optical spectrum analyzers can achieve a resolution of 0.001 nm, they rely on mechanical scanning, requiring scanning times of 0.01 s to 2 s, resulting in slow response speeds that cannot meet the real-time monitoring needs of dynamic processes. Tunable laser spectroscopy theoretically offers sub-millisecond response and 1 fm-level resolution, but in practice, the introduction of intensity noise, 2 pm wavelength drift, and linewidth broadening due to current injection tuning leads to decreased accuracy. Traditional optical frequency combs are mostly generated through optical methods, resulting in large comb line spacing, which is only suitable for discrete spectral line measurement and cannot directly sample continuous spectra at high resolution. To address these issues, a research proposal suggests a scheme based on digital signal processing to generate ultrafine optical frequency combs (UFOFCs): the user-defined 0 / 1 data sequence is converted into an electrical waveform via inverse fast Fourier transform, driving an electro-optic modulator to modulate a narrow-linewidth continuous-wave laser to generate a UFOFC, and then coherent detection is used to synchronously capture the amplitude and phase of the optical frequency comb, followed by fast Fourier transform to reconstruct the full spectrum. This solution achieves a resolution of 0.01 pm and a response time of 0.7 ms, which is four orders of magnitude faster and two orders of magnitude faster in terms of resolution compared to traditional technologies. It breaks through the bottleneck of "high resolution and fast response cannot be achieved at the same time". However, the measurement bandwidth is only 10 GHz, and expansion requires complex spectrum splicing. Furthermore, the dynamic range is not optimized, making it difficult to meet the requirements of broadband measurement.

[0004] In the field of optical vector analysis (OVA), interferometric OVA, while boasting THz-level bandwidth and a large dynamic range, has a resolution of only 200 MHz, making it unsuitable for finely characterizing narrow-bandwidth devices (such as high-Q microcavities with an 11.4 kHz bandwidth). Optical channel estimation OVA achieves a resolution of 0.732 MHz, but its dynamic range is only 25 dB and its bandwidth is 250 GHz, making it difficult to balance multiple performance aspects. OVA based on optical single-sideband modulation theoretically achieves sub-Hz resolution, but the high-order sideband interference generated by modulation leads to increased errors and a dynamic range ≤60 dB. Furthermore, its bandwidth is limited to 105 GHz due to device limitations, failing to meet the requirements for broadband measurements. Another study proposed an OVA scheme based on an asymmetric optical probe signal generator (ASG) and receiver (ASR): the ASG splits a single optical frequency comb line into two paths, one path is frequency-shifted by an acousto-optic modulator, and the other path is used by a Mach-Zehnder modulator to generate a carrier-suppressed double-sideband signal, which is then combined into an asymmetric probe signal; the ASR uses dual photodetectors and coherent electrical receivers to filter out high-order sideband interference based on frequency differences, and combines multiple comb lines to extend the bandwidth. This scheme achieves a resolution of 334 Hz ​​(2.67 attoseconds at 1550 nm), a dynamic range of >90 dB, and a bandwidth of 1.075 THz, solving the problem of multiple performance coexistence in traditional OVAs. However, the technical architecture is complex, requiring the integration of an optical frequency comb mode selection module, an electrical vector network analyzer, and a multi-channel signal processing unit, resulting in high equipment costs and cumbersome operation, which is not conducive to low-cost and miniaturized promotion.

[0005] Both of the above improvement methods involve the carrier and sideband taking different paths, which requires ensuring that the system is in an environment with minimal interference, thus increasing the system complexity. Summary of the Invention

[0006] In view of the above-mentioned shortcomings in the existing technology, the present invention provides a light vector network analyzer and method based on direct detection.

[0007] To achieve the above-mentioned objectives, the present invention adopts the following technical solution: II. A Direct Detection-Based Optical Vector Network Analyzer: The system includes a continuous light source, an electro-optic modulation module, an arbitrary waveform generator, a device under test (DUT), and a signal processing module. One end of the electro-optic modulation module is connected to the continuous light source, and the other end is sequentially connected to the DUT and the signal processing module. The electro-optic modulation module is electrically connected to the arbitrary waveform generator. The continuous light source, electro-optic modulation module, DUT, and signal processing module are arranged at intervals along the light propagation direction. The optical signal output from the continuous light source and the multi-carrier microwave signal output from the arbitrary waveform generator are input together into the electro-optic modulation module. The electro-optic modulation module uses the multi-carrier microwave signal from the waveform generator to modulate the optical signal from the continuous light source, obtaining a modulated optical signal. After the modulated optical signal is output from the electro-optic modulation module, it is input to the signal processing module via the DUT for processing to obtain the frequency response information of the DUT.

[0008] The device under test is specifically an optical device made of optical fiber, waveguide, or free light, such as a micro-ring coupler.

[0009] The electro-optic modulation module adopts a dual parallel Mach-Zehnder modulator, which includes a first sub-modulator, a second sub-modulator, and an electro-optic modulation output sub-module. The first and second sub-modulators are arranged in parallel to each other, and the line in which the first and second sub-modulators are located is perpendicular to the direction of light propagation. A continuous light source is provided at a distance in front of the input end of the dual parallel Mach-Zehnder modulator. The input ends of the first and second sub-modulators are connected to the input end of the dual parallel Mach-Zehnder modulator. The output ends of the first and second sub-modulators are connected to the input end of the electro-optic modulation output sub-module. The output end of the electro-optic modulation output sub-module is used as the output end of the dual parallel Mach-Zehnder modulator and then used for optical pairing of the test device. The optical signal output from the continuous light source is split into two paths at the input end of the electro-optic modulation module and then input to the first sub-modulator and the second sub-modulator, respectively. The multi-carrier microwave signal output from the arbitrary waveform generator is input to the first sub-modulator to modulate its optical signal. The optical signal output from the first sub-modulator after being modulated by the multi-carrier microwave signal and the unmodulated optical signal output from the second sub-modulator are input together into the electro-optic modulation output sub-module to complete the interference processing and then input to the device under test.

[0010] The signal processing module includes a photodetector, an analog-to-digital converter (ADC), and a digital signal processor (DSP). A device under test (DUT) is spaced apart on one side of the photodetector, and an ADC and DSP are sequentially spaced apart on the other side. The electro-optic modulation module, DUT, and photodetector are sequentially spaced apart along the light propagation direction. The photodetector, ADC, and DSP are sequentially electrically connected. The modulated optical signal is output to the electro-optic modulation module, passes through the DUT, and is then input to the photodetector to be converted into an electrical signal. The electrical signal is then input to the DSP after passing through the ADC.

[0011] II. Optical Vector Detection Method Based on Direct Detection Optical Vector Network Analyzer: S1, Optical signal modulation: The continuous light source outputs the original optical signal and inputs it into the electro-optic modulation module. The arbitrary waveform generator generates a multi-carrier microwave signal and inputs it into the electro-optic modulation module to modulate the optical signal. The electro-optic modulation module outputs the modulated optical signal. S2. Frequency response calculation: The modulated optical signal is detected by the device under test to obtain an output optical signal. The output optical signal is input into a photodetector to obtain an output electrical signal. The output electrical signal is sequentially processed by an analog-to-digital converter and a digital signal processor to calculate the spectrum of the electrical signal. S3. The original optical carrier light signal output by the continuous light source is directly input into the device under test according to step S2 without being modulated by the electro-optic modulation module to obtain the output light signal, which is used as the carrier response result. S4. Repeat steps S1 to S2 above to make the arbitrary waveform generator output different multi-carrier microwave signals for four different measurements. By only four repeated measurements, and combining the carrier response results obtained in step S3, a simultaneous equation is established to obtain the frequency response information C of the device under test.

[0012] Specifically, a continuous light source outputs a narrow-linewidth continuous optical signal, which is then input to an electro-optic modulation module. An arbitrary waveform generator generates a multi-carrier microwave signal, which is also input to the electro-optic modulation module to modulate the continuous optical signal. The modulated optical signal output from the electro-optic modulation module passes through the device under test (DUT), completing the detection process. The output optical signal then passes through a photodetector, converting the optical signal into an electrical signal, resulting in an output electrical signal. Next, an analog-to-digital converter (ADC) acquires the electrical signal, transmits it to a digital signal processor (DSP), and calculates the frequency response of the electrical signal, thereby further analyzing the frequency response of the DUT.

[0013] In step S1, when the electro-optic modulation module is working, the first DC bias point in the first sub-modulator is adjusted to the minimum bias point, the second DC bias point in the second sub-modulator is appropriately biased while retaining sufficient optical carrier power, and the third DC bias point in the electro-optic modulation output sub-module is adjusted to the maximum point, so that the optical signal at the output end of the electro-optic modulation module, i.e., the electro-optic modulation output sub-module of the dual parallel Mach-Zehnder modulator, is a combination of optical carrier and multiple optical sidebands.

[0014] In the dual parallel Mach-Zehnder modulator, the first sub-modulator, the second sub-modulator, and the electro-optic modulation output sub-module are each provided with a DC bias point. The first sub-modulator is provided with a first DC bias point, the second sub-modulator is provided with a second DC bias point, and the electro-optic modulation output sub-module is provided with a third DC bias point.

[0015] The DC bias point is a voltage signal applied to the DC bias electrode of the device. It changes the refractive index of the waveguide inside the device through the electro-optic effect, thereby precisely adjusting the phase of the optical signal passing through the device.

[0016] In step S2, the modulated optical signal passes through the device under test to obtain an output optical signal, and the carrier, positive frequency sideband and negative frequency sideband of the output optical signal carry the frequency response information of the device under test.

[0017] The position and spacing of the multi-carrier microwave signals generated by the arbitrary waveform generator 3 can be flexibly adjusted according to the frequency response test results to achieve more precise frequency response measurements. The optical carrier response of the device under test 4 needs to be measured without modulating the microwave signal.

[0018] The digital signal processor is clock-synchronized with the arbitrary waveform generator so that the digital signal processor 7 can set an anti-distortion training sequence.

[0019] In step S2, the electrical signal acquired by the analog-to-digital converter includes multiple frequency components, which are one or more combinations of the following: DC component, odd-order frequency components after the positive frequency sideband beats with the same carrier, odd-order frequency components after the negative frequency sideband beats with the same carrier, and even-order frequency components after the positive and negative frequency sidebands beat with each other.

[0020] In step S2, when the digital signal processor calculates the frequency response of the electrical signal, the even-numbered frequency channels of the digital signal processor are turned off, and only the frequency components of the odd-numbered channels are processed. This is to filter out frequency components in the electrical signal acquired by the analog-to-digital converter that interfere with the calculation of the frequency response.

[0021] Specifically, the even-frequency channels of the digital signal processor are turned off, so the even-frequency components resulting from the interleaving of the positive and negative sidebands are ignored. Additionally, the DC component in the frequency composition is a subcarrier interleaving interference term, and the noise it generates falls on the even-frequency channels. Again, because the even-frequency channels of the system are turned off, this type of noise is reduced.

[0022] When the optical carrier frequency response is known, the frequency components are filtered to leave odd-order frequency components. The unknowns in the odd-order frequency components include the frequency response information of the positive and negative sidebands of the device under test. Each frequency response contains two mutually orthogonal frequency response components. The complete frequency response information of the device under test requires at least four measurements and simultaneous equations to solve.

[0023] In step S4, steps S1 to S2 are repeated so that the arbitrary waveform generator outputs multi-carrier microwave signals with different intensities and phases for four different measurements.

[0024] In step S4, the following formula is established based on I, c0, s obtained from the four measurements. - s + The parameter x is obtained by substituting s0 into the equation and calculating backwards. + x - y + With y - : I=|E| 2 =(s0c0) 2 +(s - c - ) 2 +(s + c + ) 2 +s0c0s + c + +s0c0s - c - +s - c - s + c + E=S×C T =(s - c - , s0c0, s + c + ) C=(c - , c0, c + ) S=(s - , s0, s + ) c + =x+ +iy + c - =x - +iy - Where I is the spectrum of the output electrical signal obtained by photoelectric conversion of the output optical signal spectrum through the photodetector; E is the spectrum of the output optical signal obtained after the modulated optical signal passes through the device under test; s0 represents the spectral parameters of the unmodulated optical carrier output by the second sub-modulator (it is the spectrum of the output optical carrier of the second sub-modulator, not the carrier response. The second sub-modulator does not modulate the optical carrier, retaining a portion of the optical carrier), s + With s - These represent the positive and negative frequency sidebands of the modulated optical signal, respectively. + c - Here, c0 represents the frequency response information of the positive and negative sidebands of the device under test (DUT), respectively. c0 represents the carrier response result of the optical carrier emitted from the continuous light source passing directly through the DUT without processing, i.e., the result of step S3; x + y + These represent the frequency response information c. + Two orthogonal components, x - y - These represent the frequency response information c. - Two orthogonal components, i representing the imaginary unit, T representing the matrix transpose, c + c - Both are complex numbers. S represents the spectrum of the modulated optical signal, and C represents the frequency response information of the device under test.

[0025] Finally, based on the frequency response information of the positive and negative sidebands of the device under test (DUT) and the carrier response result obtained in step S3, the complete frequency response information C of the DUT is obtained, C=(c - , c0, c + ).

[0026] Compared with the prior art, the beneficial effects of this invention are: (1) The present invention closes the even-order frequency channels, thereby filtering out subcarrier inter-interference noise falling on the even-order frequency channels.

[0027] (2) In this invention, the carrier and the sideband follow the same path, which effectively reduces the system complexity.

[0028] (3) The present invention sets up an anti-distortion training sequence, which can effectively reduce measurement error. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the structure of a direct-detection-based optical vector network analyzer according to an embodiment of the present invention; Figure 2 This is a spectrum diagram of the detection process according to an embodiment of the present invention, wherein A is a spectrum diagram of the continuous optical signal at the second sub-modulator of the electro-optic modulation module; B is a spectrum diagram of the modulated spectrum output by the first sub-modulator of the electro-optic modulation module; C is a spectrum diagram of the modulated optical signal output by the electro-optic modulation module; D is a spectrum diagram of the continuous light passing directly through the device under test without any modulation operation; E is a spectrum diagram of the optical signal output by the electro-optic modulation module passing through the device under test; and F is a spectrum diagram of the electrical signal output by the photodetector containing the frequency response information of the device under test.

[0030] In the figure: 1. Continuous light source, 2. Electro-optic modulation module, 2a. First sub-modulator of electro-optic modulation module, 2b. Second sub-modulator of electro-optic modulation module, 3. Arbitrary waveform generator, 4. Device under test, 5. Photodetector, 6. Analog-to-digital converter, 7. Digital signal processor. Detailed Implementation

[0031] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0032] To more clearly illustrate the embodiments of the present invention, specific implementation methods will be described below with reference to the accompanying drawings. Obviously, the drawings described below are merely some embodiments of the present invention. For those skilled in the art, other drawings and other implementation methods can be obtained based on these drawings without any creative effort.

[0033] like Figure 1 As shown, the specific implementation includes a continuous light source 1, an electro-optic modulation module 2, an arbitrary waveform generator 3, a device under test (DUT) 4, and a signal processing module. One end of the electro-optic modulation module 2 is spaced apart from the continuous light source 1, and the other end is sequentially spaced apart from the DUT 4 and the signal processing module. The electro-optic modulation module 2 is electrically connected to the arbitrary waveform generator 3. The continuous light source 1, the electro-optic modulation module 2, the DUT 4, and the signal processing module are sequentially spaced apart along the light propagation direction. The narrow-linewidth continuous optical signal output from the continuous light source 1 and the multi-carrier microwave signal output from the arbitrary waveform generator 3 are input together into the electro-optic modulation module 2. The electro-optic modulation module 2 uses the multi-carrier microwave signal from the waveform generator 3 to modulate the narrow-linewidth continuous optical signal from the continuous light source 1 to obtain a modulated optical signal. After the modulated optical signal is output from the electro-optic modulation module 2, it is input into the signal processing module via the DUT 4 for processing to obtain the frequency response information of the DUT 4.

[0034] The electro-optic modulation module 2 adopts a dual parallel Mach-Zehnder modulator. The dual parallel Mach-Zehnder modulator contains a first sub-modulator 2a in the upper branch, a second sub-modulator 2b in the lower branch, and an electro-optic modulation output sub-module located at the final output end. The first sub-modulator 2a and the second sub-modulator 2b are arranged in parallel to each other, and the line containing the first sub-modulator 2a and the second sub-modulator 2b is perpendicular to the direction of light propagation. A continuous light source 1 is arranged at intervals in front of the input end of the dual parallel Mach-Zehnder modulator. The input ends of the first sub-modulator 2a and the second sub-modulator 2b are connected to the input end of the dual parallel Mach-Zehnder modulator. The output ends of the first sub-modulator 2a and the second sub-modulator 2b are connected to the input end of the electro-optic modulation output sub-module. The output end of the electro-optic modulation output sub-module is used as the output end of the dual parallel Mach-Zehnder modulator and then used for optical pairing with the test device 4.

[0035] The electro-optic modulation output submodule can be an output optical combiner, such as a Mach-Zehnder interferometer. The electro-optic modulation output submodule is used to superimpose and interfere the optical signals output by the first sub-modulator 2a and the second sub-modulator 2b and output them to the device under test 4. In this way, the first sub-modulator 2a and the second sub-modulator 2b can be connected to the electro-optic modulation output submodule through optical waveguides.

[0036] The optical signal output from the continuous light source 1 is split into two paths at the input of the electro-optic modulation module 2 and then input to the first sub-modulator 2a and the second sub-modulator 2b respectively. The multi-carrier microwave signal output from the arbitrary waveform generator 3 is input to the first sub-modulator 2a to modulate its optical signal. The optical signal output from the first sub-modulator 2a after being modulated by the multi-carrier microwave signal and the unmodulated optical signal output from the second sub-modulator 2b are input together into the electro-optic modulation output sub-module to complete the interference processing and then input to the device under test 4.

[0037] Specifically, the continuous optical signal output from the continuous light source 1 is split into two paths at the input of the electro-optic modulation module 2 and then input to the first sub-modulator 2a and the second sub-modulator 2b respectively. The first sub-modulator 2a in the upper branch is electrically connected to and receives the multi-carrier microwave signal output from the arbitrary waveform generator 3 to modulate the continuous optical signal in the first sub-modulator 2a. The second sub-modulator 2b only receives the optical signal output from the continuous light source 1. After the optical signal modulated by the multi-carrier microwave signal is output from the first sub-modulator 2a, it and the unmodulated optical signal output from the second sub-modulator 2b are interfered together in the electro-optic modulation output sub-module and then input to the device under test 4.

[0038] The first sub-modulator 2a receives a multi-carrier microwave signal from the arbitrary waveform generator 3 and modulates its optical signal. The second sub-modulator 2b in the lower branch allows the optical signal to pass directly without modulation. The signals output from the two sub-modulators are interfered in the electro-optic modulation output submodule and then input to the device under test.

[0039] The signal processing module includes a photodetector 5, an analog-to-digital converter 6, and a digital signal processor 7. The device under test 4 is arranged at intervals on one side of the photodetector 5, and the analog-to-digital converter 6 and the digital signal processor 7 are arranged at intervals on the other side. The electro-optic modulation module 2, the device under test 4, and the photodetector 5 are arranged at intervals along the light propagation direction. The photodetector 5, the analog-to-digital converter 6, and the digital signal processor 7 are electrically connected in sequence. After the modulated optical signal is output to the electro-optic modulation module 2, it is input into the photodetector 5 through the device under test 4 and converted into an electrical signal. The electrical signal is then input into the digital signal processor 7 through the analog-to-digital converter 6.

[0040] This invention belongs to the field of microwave photonics technology. An arbitrary waveform generator produces a multi-carrier microwave signal, which is input to the first sub-modulator of the upper branch of an electro-optic modulation module to modulate the optical signal from a continuous light source. Simultaneously, in the lower branch, the optical signal output from the continuous light source directly passes through the second sub-modulator of the electro-optic modulation module and interferes with the modulated optical signal output from the first sub-modulator. The system is based on a direct-detection optical vector network analyzer, where the optical signal output from the electro-optic modulation module undergoes direct photoelectric conversion and analog-to-digital conversion after passing through the device under test (DUT). At the subsequent digital signal processor, the system performs simultaneous equations based on the frequency responses of the four acquired electrical signals, ultimately analytically obtaining the frequency response of the DUT. This invention enables direct detection of the frequency response of optical devices under test and is expected to be applied in fields such as coherent photonics measurement, dynamic spectrum analysis, and optical instrument measurement.

[0041] Example 1: like Figure 1 As shown, the optical vector network analyzer of this embodiment employs microwave photonics direct detection technology to measure the frequency response of the device under test (DUT). The system includes: a continuous light source 1, a first sub-modulator 2a of the electro-optic modulation module, a second sub-modulator 2b of the electro-optic modulation module, an arbitrary waveform generator 3, the DUT 4, a photodetector 5, an analog-to-digital converter 6, and a digital signal processor 7. Specifically, the electro-optic modulation module uses a dual parallel Mach-Zehnder modulator. A specific implementation method of an optical vector network analyzer based on direct detection includes the following steps: The continuous light source 1 outputs a narrow-linewidth continuous optical signal and inputs it into the upper and lower branches of the electro-optic modulation module 2. The arbitrary waveform generator 3 generates a multi-carrier microwave signal and inputs it into the first sub-modulator 2a of the electro-optic modulation module to modulate the continuous optical signal in the upper branch. Simultaneously, the second sub-modulator 2b of the electro-optic modulation module does not modulate the signal, allowing the continuous optical signal in the lower branch to pass directly and interfere with the modulated optical signal in the upper branch. The modulated optical signal output by the electro-optic modulation module 2 passes through the device under test 4, completing the detection process. Subsequently, the optical signal carrying the frequency response information of the signal under test passes through the photodetector 5, converting the optical signal into an electrical signal. Immediately afterwards, the analog-to-digital converter 6 acquires the electrical signal, transmits it to the digital signal processor 7, calculates the frequency response of the electrical signal, and further analyzes the frequency response of the device under test.

[0042] The working principle of the optical vector network analyzer based on direct detection provided by this invention is as follows: The continuous light source 1 generates narrow-linewidth continuous light, which is then input into the dual-parallel Mach-Zehnder modulator. In the upper branch of the modulator, the arbitrary waveform generator 3 generates a multi-carrier microwave signal, which is input into the first sub-modulator 2a of the dual-parallel Mach-Zehnder modulator 2. Carrier-suppressed double-sideband modulation is employed. A schematic diagram of the modulated signal spectrum is shown below. Figure 2 As shown in B, the spectrum consists of positive frequency sidebands s. + With negative frequency sidebands s - Composition, expression writing: s + =Σ j=1 N s j s - =Σ j=1 N s -j Where N is the number of subcarriers, j is the subcarrier number in the positive frequency sideband, -j is the subcarrier number in the negative frequency sideband, and s j Let s be the j-th subcarrier in the positive frequency sideband. -j It is the j-th subcarrier in the negative frequency sideband.

[0043] As can be seen from the above formula, both the positive frequency sideband and the negative frequency sideband are composed of N subcarriers, and N is the same as the number of microwave signal carriers output by the arbitrary waveform generator 3.

[0044] In the lower branch of the dual parallel Mach-Zehnder modulator, the optical carrier is not modulated and is directly output from the second sub-modulator. Its spectrum diagram is shown below. Figure 2As shown in Figure A, the optical carrier at this point is represented by S0. The optical signals from the upper and lower branches interfere at the output of the dual parallel Mach-Zehnder modulator, and its output is a modulated optical signal, the spectrum of which is shown in the schematic diagram below. Figure 2 As shown in C.

[0045] The spectrum of the modulated optical signal output from the dual parallel Mach-Zehnder modulator is S( Figure 2 The frequency response information of the device under test is C, as shown in the following expression: C=(c - , c0, c + ) S=(s - , s0, s + ) Where s0 represents the unmodulated optical carrier output by the second sub-modulator 2b, and s0 is the combined optical carrier spectrum output by 2b and the spectrum output by 2a. Figure 2 The spectrum of C is then passed through the device under test 4 together; + For the frequency response information of the positive sideband of the device under test, c - This represents the frequency response information of the negative frequency sideband of the device under test (DUT). c0 represents the carrier response result after the optical carrier emitted by continuous light source 1 passes directly through DUT 4 without processing. The spectral diagram of the carrier response result is shown below. Figure 2 As shown in D.

[0046] When the modulated optical signal output from the electro-optic modulation module 2 passes through the device under test 4, the output optical signal is obtained. The spectrum E of the output optical signal is expressed as: E=S×C T =(s - c - , s0c0, s + c + ) Where E is the spectrum of the output optical signal obtained after the modulated optical signal passes through the device under test 4. T represents matrix transpose; As shown in the above equation, the positive frequency sideband, negative frequency sideband, and carrier of the optical signal at this time all carry the frequency response information of the device under test 4. The spectrum diagram is as follows. Figure 2 As shown in E.

[0047] Subsequently, the output optical signal is input to photodetector 5 to complete photoelectric conversion, resulting in an output electrical signal. The spectrum expression of the output electrical signal is shown below: I=|E| 2 =(s0c0) 2 +(s - c - ) 2 +(s + c +) 2 +s0c0s + c + +s0c0s - c - +s - c - s + c + Where I is the spectrum of the output electrical signal obtained by photoelectric conversion of the output optical signal spectrum through photodetector 5.

[0048] As shown in the above formula, the frequency spectrum of the electrical signal output by photodetector 5 includes the following frequency components: At DC, there are inter-beat terms between subcarriers of the same order; at odd orders, there are sidebands after each subcarrier beats with the optical carrier; at even orders, there are inter-beat terms between subcarriers of different orders. The electrical spectrum diagrams for each frequency component are shown below. Figure 2 As shown in F.

[0049] Subsequently, the output electrical signal undergoes analog-to-digital conversion at analog-to-digital converter 6. In the subsequent digital signal processor 7, even-order channels are shut down, meaning the back-end processing focuses only on the frequency components of odd-order channels. Simultaneously, because noise generated by the DC term falls within even-order channels, this noise is also suppressed by shutting down the even-order channels.

[0050] Based on the preceding explanation, the carrier response result c0 is obtained by directly passing the optical carrier emitted by the continuous light source 1 through the device under test 4. Furthermore, c... + and c - The orthogonal forms of the frequency response information expressions are respectively set as follows: c + =x + +iy + c - =x - +iy - Where, x + y + They represent c respectively + Two orthogonal components, x - y - They represent c respectively - The two orthogonal components, i, represent the imaginary unit.

[0051] As can be seen from the above equation, this simultaneous equation has four unknowns, namely x. + x - y + With y -As unknowns, the intensity and phase of the multi-carrier microwave signal output by the arbitrary waveform generator (3) are obtained by performing only 4 measurements and solving the equations. + With c - The value of . Finally, combined with the known values ​​of I, c0, and s. - s + By performing reverse calculations on s0, the complete frequency response information C of the device under test can be obtained.

[0052] For other structures and principles, please refer to Example 1.

[0053] It should be noted that the above embodiments can be freely combined as needed. The above description is only a detailed explanation of the preferred embodiments and principles of the present invention. For those skilled in the art, there will be changes in the specific implementation methods based on the ideas provided by the present invention, and these changes should also be considered within the scope of protection of the present invention.

Claims

1. A direct-detection-based optical vector network analyzer, characterized in that, The system includes a continuous light source (1), an electro-optic modulation module (2), an arbitrary waveform generator (3), a device under test (DUT) (4), and a signal processing module. One end of the electro-optic modulation module (2) is provided with a continuous light source (1), and the other end is provided with the DUT (4) and the signal processing module in sequence. The electro-optic modulation module (2) is electrically connected to the arbitrary waveform generator (3). The continuous light source (1), the electro-optic modulation module (2), the DUT (4), and the signal processing module are arranged at intervals along the light propagation direction. The optical signal output from the continuous light source (1) and the multi-carrier microwave signal output from the arbitrary waveform generator (3) are input into the electro-optic modulation module (2). The electro-optic modulation module (2) uses the multi-carrier microwave signal from the waveform generator (3) to modulate the optical signal from the continuous light source (1) to obtain a modulated optical signal. After the modulated optical signal is output from the electro-optic modulation module (2), it is input into the signal processing module through the DUT (4) to obtain the frequency response information of the DUT (4).

2. The optical vector network analyzer based on direct detection according to claim 1, characterized in that, The electro-optic modulation module (2) adopts a dual parallel Mach-Zehnder modulator, which is provided with a first sub-modulator (2a), a second sub-modulator (2b) and an electro-optic modulation output sub-module. The first sub-modulator (2a) and the second sub-modulator (2b) are arranged in parallel to each other. The line between the first sub-modulator (2a) and the second sub-modulator (2b) is perpendicular to the direction of light propagation. A continuous light source (1) is provided in front of the input end of the dual parallel Mach-Zehnder modulator. The input ends of the first sub-modulator (2a) and the second sub-modulator (2b) are connected to the input end of the dual parallel Mach-Zehnder modulator. The output ends of the first sub-modulator (2a) and the second sub-modulator (2b) are connected to the input end of the electro-optic modulation output sub-module. The output end of the electro-optic modulation output sub-module is used as the output end of the dual parallel Mach-Zehnder modulator and then used for optical connection to the test device (4). The optical signal output by the continuous light source (1) is divided into two paths at the input end of the electro-optic modulation module (2) and then input to the first sub-modulator (2a) and the second sub-modulator (2b) respectively. The multi-carrier microwave signal output by the arbitrary waveform generator (3) is input to the first sub-modulator (2a) to modulate its optical signal. The optical signal output by the first sub-modulator (2a) after being modulated by the multi-carrier microwave signal and the unmodulated optical signal output by the second sub-modulator (2b) are input together into the electro-optic modulation output sub-module to complete the interference processing and then input to the device under test (4).

3. The optical vector network analyzer based on direct detection according to claim 1, characterized in that, The signal processing module includes a photodetector (5), an analog-to-digital converter (6), and a digital signal processor (7). The photodetector (5) has a device under test (4) spaced apart on one side and an analog-to-digital converter (6) and a digital signal processor (7) spaced apart on the other side. The electro-optic modulation module (2), the device under test (4), and the photodetector (5) are spaced apart along the direction of light propagation. The photodetector (5), the analog-to-digital converter (6), and the digital signal processor (7) are electrically connected in sequence. After the modulated optical signal is output to the electro-optic modulation module (2), it is input into the photodetector (5) after passing through the device under test (4) and converted into an electrical signal. The electrical signal is then input into the digital signal processor (7) after passing through the analog-to-digital converter (6).

4. The optical vector detection method of an optical vector network analyzer based on direct detection as described in any one of claims 1-3, characterized in that, S1, Optical signal modulation: The continuous light source (1) outputs the original optical signal and inputs it into the electro-optic modulation module (2). The arbitrary waveform generator (3) generates a multi-carrier microwave signal and inputs it into the electro-optic modulation module (2) to modulate the optical signal. The electro-optic modulation module (2) outputs the modulated optical signal. S2, Frequency response calculation: The modulated optical signal is detected by the device under test (4) to obtain an output optical signal. The output optical signal is input into the photodetector (5) to obtain an output electrical signal. The output electrical signal is sequentially processed by the analog-to-digital converter (6) and the digital signal processor (7) to obtain the spectrum of the electrical signal. S3. The original light signal output by the continuous light source (1) is directly input to the device under test (4) according to step S2 without being modulated by the electro-optic modulation module (2) to obtain the output light signal as the carrier response result. S4. Repeat steps S1 to S2. After only 4 repeated measurements, and combining the carrier response results obtained in step S3, establish a simultaneous equation to obtain the frequency response information C of the device under test (4).

5. The optical vector detection method of an optical vector network analyzer based on direct detection according to claim 4, characterized in that, In step S2, the modulated optical signal passes through the device under test (4) to obtain an output optical signal, and the output optical signal carries the frequency response information of the device under test (4).

6. The optical vector detection method of an optical vector network analyzer based on direct detection according to claim 4, characterized in that, In step S2, the electrical signal acquired by the analog-to-digital converter (6) includes multiple frequency components, which are one or more combinations of the following: DC component, odd-order frequency component after the positive frequency sideband beats with the same carrier, odd-order frequency component after the negative frequency sideband beats with the same carrier, and even-order frequency component after the positive and negative frequency sideband beats with each other.

7. The optical vector detection method of an optical vector network analyzer based on direct detection according to claim 4, characterized in that, In step S2, when the digital signal processor (7) calculates the frequency response of the electrical signal, the even-numbered frequency channels of the digital signal processor (7) are turned off, and only the frequency components of the odd-numbered channels are processed, in order to filter out the frequency components in the electrical signal collected by the analog-to-digital converter (6) that interfere with the calculation of the frequency response.

8. The optical vector detection method of an optical vector network analyzer based on direct detection according to claim 4, characterized in that, In step S4, the above steps S1 to S2 are repeated so that the arbitrary waveform generator (3) outputs multi-carrier microwave signals with different intensities and phases for four different measurements.

9. The optical vector detection method of an optical vector network analyzer based on direct detection according to claim 4, characterized in that, In step S4, the following formula is established based on I, c0, s obtained from four measurements. - s + The parameter x is obtained by substituting s0 into the equation and calculating backwards. + x - y + With y - : I=|E| 2 =(s0c0) 2 +(s - c - ) 2 +(s + c + ) 2 +s0c0s + c + +s0c0s - c - +s - c - s + c + c + =x + +iy + c - =x - +iy - Where I is the spectrum of the output electrical signal; E is the spectrum of the output optical signal; s0 represents the spectral parameters of the unmodulated optical carrier output by the second sub-modulator (2b), s + With s - These represent the positive and negative frequency sidebands of the modulated optical signal, respectively. + c - The values ​​represent the frequency response information of the positive and negative sidebands of the device under test (4), respectively. c0 represents the carrier response result of the optical carrier emitted by the continuous light source (1) passing directly through the device under test (4) without processing; x + y + These represent the frequency response information c. + Two orthogonal components, x - y - These represent the frequency response information c. - , where i represents the imaginary unit; Finally, based on the frequency response information of the positive and negative frequency sidebands of the device under test (4) and the carrier response result obtained in step S3, the complete frequency response information C of the device under test is obtained, C=(c - , c0, c + ).

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