A bandpass / bandstop dual-output integrated microwave photonic filter

Abstract

The application discloses a band-pass / band-stop dual-output integrated microwave photon filter, which comprises a thin film lithium niobate chip, the thin film lithium niobate chip comprises a first optical waveguide, a first optical coupler, a second optical waveguide and a third optical waveguide, a second optical coupler, a first phase shift waveguide and a second phase shift waveguide, a row wave electrode group, a third optical coupler, a fourth optical waveguide, a first ring resonant cavity, a second ring resonant cavity, a fifth optical waveguide and a fourth optical coupler and a sixth optical waveguide. The application integrates a Mach-Zehnder modulator, a micro-ring resonator, an optical coupler and other basic devices on the thin film lithium niobate chip. The application has a simple structure, and can simultaneously realize complementary band-pass filtering and band-stop filtering through a small number of basic unit devices such as the micro-ring resonator and the optical coupler. The structure except the laser and the detector is integrated on the chip, so that the system power consumption, cost and complexity are reduced, and the system stability is improved.

Description

Technical Field

[0001] This invention relates to the field of microwave photonics, and more specifically to a bandpass / bandstop dual-output integrated microwave photonic filter. Background Technology

[0002] With rapid social and economic development, the demand for information is exponentially increasing, and information flow is growing at an exponential rate. Traditional microwave technology is gradually revealing its bottlenecks in terms of speed and bandwidth, making it difficult to meet the ever-growing communication needs. In contrast, optical communication, with its advantages of high frequency, large bandwidth, low loss, and resistance to electromagnetic interference, has become an ideal solution to this challenge. Furthermore, optical devices, due to their small size and lightweight characteristics, can effectively overcome the limitations of traditional electronic technologies, demonstrating enormous development potential.

[0003] Against this backdrop, microwave photonics (MWP), as a product of the fusion of microwave and photonic technologies, has become an important interdisciplinary field. Microwave photonics primarily studies the interaction between microwave signals and photons, generating, processing, controlling, and transmitting microwave signals through optical means. This technology can transfer microwave signals to the optical frequency domain, fully utilizing the advantages of light—its large bandwidth, low loss, and resistance to electromagnetic interference—while retaining the wide coverage, portability, and high flexibility of microwaves. Therefore, microwave photonics has broad application prospects in radar, wireless communication, sensing, imaging, and instrumentation.

[0004] Microwave photonic filters, as one of the popular research areas in microwave photonics, load electrical signals onto light waves through electro-optic modulation and process these signals using photonic devices. While realizing the functions of traditional filters, they have significant advantages such as low loss, high bandwidth, resistance to electromagnetic interference, tunability, and reconfigurability, and can meet the increasingly stringent performance requirements of modern communication systems for filters.

[0005] The main advantage of multi-output filters over single-output filters lies in their ability to generate multiple output signals from a single input signal. This capability allows multi-output filters to perform signal multiplexing and selection within a single device, significantly improving the system's functional density and flexibility. Furthermore, multi-output filters reduce the need for multiple individual filters, lowering system complexity and cost, and reducing physical space requirements. By implementing multiple outputs in a single device, the system can process signals more efficiently, improving overall performance and resource utilization. Therefore, the implementation of multi-output microwave photonic filters is of great significance for improving system efficiency and reducing system cost and complexity.

[0006] In recent years, the rapid development of photonic integrated circuit (PIC) technology has further propelled the advancement of integrated microwave photonics (IMWP). PIC-based IMWP filters achieve significant reductions in size, weight, and power consumption, while enhancing system stability, by integrating key optical components onto a chip-level platform. Compared to traditional fiber-optic based MWP filters, IMWP filters, with their centimeter-scale photonic chips, exhibit superior performance and broader application potential. Summary of the Invention

[0007] The purpose of this invention is to provide a bandpass / bandstop dual-output integrated microwave photonic filter based on a thin-film lithium niobate platform, with the two outputs having complementary bandpass and bandstop responses.

[0008] A bandpass / bandstop dual-output integrated microwave photonic filter includes: a thin-film lithium niobate chip, wherein the thin-film lithium niobate chip comprises:

[0009] The first optical waveguide used for transmitting optical signals;

[0010] A first optical coupler connected to the output terminal of the first optical waveguide;

[0011] The second and third optical waveguides are connected to the first optical coupler;

[0012] The second optical coupler is connected to the second optical waveguide;

[0013] The first phase-shifting waveguide and the second phase-shifting waveguide are connected to the second optical coupler;

[0014] Traveling wave electrode group used to modulate optical signals in the first phase-shifting waveguide and the second phase-shifting waveguide;

[0015] A third optical coupler connected to the first phase-shifting waveguide and the second phase-shifting waveguide;

[0016] The fourth optical waveguide is connected to the third optical coupler;

[0017] The first annular resonant cavity is coupled to the fourth optical waveguide;

[0018] The second annular resonant cavity is coupled to the fourth optical waveguide;

[0019] A fifth optical waveguide coupled to the first annular resonant cavity;

[0020] A fourth optical coupler connected to the output terminals of the third and fifth optical waveguides;

[0021] The sixth optical waveguide is connected to the fourth optical coupler.

[0022] The second optical waveguide, the second optical coupler, the first phase-shifting waveguide, the second phase-shifting waveguide, the first traveling-wave electrode group, the third optical coupler, and the fourth optical waveguide constitute an electro-optic modulator.

[0023] The thin-film lithium niobate chip has a film thickness of 350–450 nm.

[0024] The thin-film lithium niobate chip is based on an X-cut thin-film lithium niobate platform, comprising a silicon substrate, a SiO2 buried oxide layer disposed on the silicon substrate, and a lithium niobate thin film (400 nm thick) disposed on the SiO2 buried oxide layer. Light propagates along the y-direction, and the electric field is directed in the z-direction. All waveguides used are ridge waveguides.

[0025] The first annular resonant cavity is racetrack-shaped with a waveguide width of 4 μm. It includes two 600 μm long straight waveguide modulation arm regions on both sides and a 180-degree Euler-bent waveguide connecting the straight waveguides. The 180-degree Euler-bent waveguide is composed of two identical 90-degree Euler bends, with a maximum bending radius of 4000 μm and a minimum bending radius of 100 μm. The total circumference of the first annular resonant cavity is 1813 μm. The annular resonant cavity waveguide is made of lithium niobate material, with a convex cross-section and a waveguide height of 400 nm, of which the height of the top protrusion is 200 nm. The coupling length between the cascaded waveguide and the micro-ring waveguide is 550 μm, and the gap is 500 nm.

[0026] The second annular resonant cavity is racetrack-shaped with a waveguide width of 3.6 μm. It includes two 588 μm long straight waveguide modulation arm regions on both sides and a 180-degree Euler-bent waveguide connecting the straight waveguides. The 180-degree Euler-bent waveguide is composed of two identical 90-degree Euler bends, with a maximum bending radius of 4000 μm and a minimum bending radius of 100 μm. The total circumference of the first annular resonant cavity is 1789 μm. This annular resonant cavity waveguide is made of lithium niobate material, with a convex cross-section and a waveguide height of 400 nm, of which the height of the top convex part is 200 nm. The coupling length between the cascaded waveguide and the micro-ring waveguide is 550 μm, and the gap is 500 nm.

[0027] The input terminal of the thin-film lithium niobate chip is connected to a laser.

[0028] The output terminal of the thin-film lithium niobate chip is connected to a photodetector.

[0029] This invention is based on a thin-film lithium niobate (LNOI) platform. The chip input is connected to a laser to input an optical carrier. An on-chip opto-modulator converts the electrical signal to an optical signal. On-chip micro-rings, couplers, and other basic components handle the optical signal processing. The chip output is connected to a photodetector to recover the signal back to an electrical signal. This results in a dual-output integrated microwave photonic filter with complementary bandpass / bandstop responses, reducing the need for multiple single-output filters and lowering system complexity and cost. Utilizing PIC technology to integrate the microwave photonic filter reduces system weight, power consumption, and size, making this system widely applicable in various communication and electronic devices.

[0030] Compared with the prior art, the present invention has the following advantages:

[0031] I. This invention innovatively proposes a novel dual-output microwave photonic filter structure, with the two outputs being band-stop and band-pass filters respectively, and their responses being complementary. Currently, there are few inventions that realize multi-output filters using microwave photonics, and this invention fills this gap.

[0032] Second, integrating devices other than lasers and photodetectors onto the chip offers advantages such as low power consumption, low cost, and high stability.

[0033] Third, LN material has a high electro-optic coefficient and excellent electro-optic effect. Therefore, the modulator can operate at a lower driving voltage, which reduces power consumption and the impact of thermal effects on device performance, thereby improving system efficiency and stability.

[0034] Fourth, the present invention has a simple structure, requiring only one Mach-Zehnder electro-optic modulator and two micro-rings to achieve dual-output filtering function. Attached Figure Description

[0035] Figure 1 This is a schematic diagram of the dual-output integrated microwave photonic filter structure in this invention;

[0036] Figure 2 This is a schematic diagram of the dual-output integrated microwave photonic filter in this invention;

[0037] Figure 3 The figure shows the simulation results of the dual-output integrated microwave photonic filter in this invention. Figure 3 (a) is the spectrum of the signal after passing through the modulator; Figure 3 (b) is the spectrum of the signal after being filtered by two micro-rings; Figure 3 (c) is the spectrum of the output of the drop end of the first micro-ring resonator and the optical carrier superimposed; Figure 3 (d) shows the first output result of the microwave photonic filter, which has band-stop filtering characteristics; Figure 3 (e) is the second output result of the microwave photonic filter, which has bandpass filtering characteristics. Detailed Implementation

[0038] like Figure 1 As shown, a bandpass / bandstop dual-output integrated microwave photonic filter based on a thin-film lithium niobate platform includes: a thin-film lithium niobate chip; a 1550nm wavelength tunable laser 19; a first photodetector 20 and a second photodetector 21 connected to the chip's output. The thin-film lithium niobate chip includes: a first optical waveguide 1 for transmitting optical signals; a first optical coupler 2 connected to the output of the first optical waveguide 1; a second optical waveguide 3 and a third optical waveguide 4 connected to the first optical coupler 2; a second optical coupler 5 connected to the second optical waveguide 3; a traveling-wave electrode group 6 for modulating optical signals within a first phase-shifting waveguide 7 and a second phase-shifting waveguide 8; the first phase-shifting waveguide 7 and the second phase-shifting waveguide 8 connected to the second optical coupler 5; a third optical coupler 9 connected to the phase-shifting waveguide; and a fourth optical waveguide connected to the third optical coupler 9. 10; a first annular resonant cavity 11 coupled to the fourth optical waveguide 10; a fifth optical waveguide 12 coupled to the first annular resonant cavity 11; a fourth optical coupler 13 connected to the output terminals of the third optical waveguide 4 and the fifth optical waveguide 12; a sixth optical waveguide 14 connected to the fourth optical coupler 13; a second annular resonant cavity 15 connected to the output terminal of the fourth optical waveguide 10; a SiO2 buried oxide layer 17 disposed on the silicon substrate 18; and a lithium niobate thin film 16 (400 nm thick) disposed on the SiO2 buried oxide layer 17.

[0039] The thin-film lithium niobate chip is based on an X-cut thin-film lithium niobate platform. The lithium niobate film is 400 nm thick, and light propagates along the y-direction while the electric field is directed along the z-direction. All waveguides used are ridge waveguides.

[0040] The first annular resonant cavity is racetrack-shaped with a waveguide width of 4 μm. It includes two 600 μm long straight waveguide modulation arm regions on both sides and a 180-degree Euler-bent waveguide connecting the straight waveguides. The 180-degree Euler-bent waveguide is composed of two identical 90-degree Euler bends, with a maximum bending radius of 4000 μm and a minimum bending radius of 100 μm. The total circumference of the first annular resonant cavity is 1813 μm. The annular resonant cavity waveguide is made of lithium niobate material, with a convex cross-section and a waveguide height of 400 nm, of which the height of the top protrusion is 200 nm. The coupling length between the cascaded waveguide and the micro-ring waveguide is 550 μm, and the gap is 500 nm.

[0041] The second annular resonant cavity is racetrack-shaped with a waveguide width of 3.6 μm. It includes two 588 μm long straight waveguide modulation arm regions on both sides and a 180-degree Euler-bent waveguide connecting the straight waveguides. The 180-degree Euler-bent waveguide is composed of two identical 90-degree Euler bends, with a maximum bending radius of 4000 μm and a minimum bending radius of 100 μm. The total circumference of the first annular resonant cavity is 1789 μm. This annular resonant cavity waveguide is made of lithium niobate material, with a convex cross-section and a waveguide height of 400 nm, of which the height of the top convex part is 200 nm. The coupling length between the cascaded waveguide and the micro-ring waveguide is 550 μm, and the gap is 500 nm.

[0042] This invention is based on a thin-film lithium niobate (LNOI) platform. The chip input terminal is connected to a laser to input an optical carrier. An on-chip opto-modulator realizes the conversion of electrical signals to optical signals. On-chip micro-rings, couplers and other basic device structures realize optical signal processing. The chip output terminal is connected to a photodetector to restore the signal to an electrical signal.

[0043] Figure 2 This is a schematic diagram illustrating the principle of the dual-output integrated microwave photonic filter in this invention. The laser output frequency is ω. c The light reaches the chip and is split into two parts by a 1×2 MMI. The first part is input to the modulator as an optical carrier. The light with frequency ω in Figure (1) is... RF The electrical signal is input into the Mach-Zehnder modulator, and the modulated optical signal is shown in Figure (2), which has three frequency components, namely ω c -ω RF ω c ω c +ω RF These correspond to the lower sideband, optical carrier, and upper sideband, respectively. The upper and lower sidebands have the same amplitude and the same phase relative to the optical carrier.

[0044] The modulated signal passes through an add-drop micro-ring filter. The resonant peak of the first ring resonator is aligned to the upper sideband of the signal. The output at the through end is shown in Figure (3), which is the optical signal remaining after filtering out the resonant frequency. The output at the drop end is shown in Figure (4), which is the optical signal at the resonant frequency.

[0045] At the through end of the first ring resonator, a portion of the upper sideband signal, having been filtered out, is transmitted to the second ring resonator. The resonant peak of the second ring resonator is aligned with the lower sideband, and the frequency difference between the resonant peaks of the two ring resonators and the optical carrier is equal. After the second filtering, the spectrum is shown in Figure (5). The optical signal is input into the photodetector and recovered as an electrical signal, the spectrum of which is shown in Figure (6). At this point, there is no electrical signal at the frequency difference between the resonant peak and the optical carrier, exhibiting band-stop filtering characteristics.

[0046] At the drop end of the first ring resonator, the output optical signal is superimposed with the output of another part of the laser through a 2×1 MMI. The spectrum of the superimposed optical signals is shown in Figure (7). The optical signal is then subjected to beat frequency detection by a photodetector to recover the electrical signal. The spectrum of the electrical signal is shown in Figure (8). Since only the electrical signal at the difference between the resonant peak and the optical carrier frequency exists at this time, it exhibits bandpass filtering characteristics.

[0047] A simulation model was built using Ansys Lumerical INTERCONNECT software to verify the working principle of the microwave photonic filter. In the model, the electrical input of the microwave photonic filter is a broadband signal, the wavelength of the laser input is 193.101 THz, and the signal after modulation is as follows: Figure 3 As shown in (a), the resonant peak frequency of the first micro-ring resonator is 193.127 THz, and the resonant peak frequency of the second micro-ring resonator is 193.075 THz, both with a frequency difference of 26 GHz from the optical carrier signal. The modulated optical signal is filtered by the two micro-ring resonators to remove some of the upper and lower sidebands, and its spectrum is as follows. Figure 3 As shown in (b). The signal output after this optical signal passes through the photodetector is as follows: Figure 3 As shown in (d), it exhibits band-stop filtering characteristics, with a center frequency of 26 GHz, a bandwidth of 1 GHz, and a rejection ratio of 14 dBm.

[0048] In this invention, after the optical signal passes through the first micro-ring resonant cavity, the spectrum resulting from the superposition of the signal output from the drop end and the optical signal output from the laser is as follows: Figure 3 As shown in (c). The output of the signal after detection by the photodetector is as follows. Figure 3 As shown in (e), it exhibits bandpass filtering characteristics with a center frequency of 26 GHz, a bandwidth of 1 GHz, and a rejection ratio of 15 dBm.

Claims

1. A bandpass / bandstop dual output integrated microwave photonic filter comprising: A thin film lithium niobate chip, characterized in that the thin film lithium niobate chip comprises: a first optical waveguide for transmitting an optical signal; a first optical coupler connected to an output end of the first optical waveguide; a second optical waveguide and a third optical waveguide connected to the first optical coupler; a second optical coupler connected to the second optical waveguide; a first phase shift waveguide and a second phase shift waveguide connected to the second optical coupler; a set of traveling wave electrodes for modulating the optical signal in the first phase shift waveguide and the second phase shift waveguide; a third optical coupler connected to the first phase shift waveguide and the second phase shift waveguide; a fourth optical waveguide connected to the third optical coupler; a first ring resonator cavity coupled to the fourth optical waveguide; a second ring resonator cavity coupled to the fourth optical waveguide; a fifth optical waveguide coupled to the first ring resonator cavity; a fourth optical coupler connected to an output end of the third optical waveguide and an output end of the fifth optical waveguide; a sixth optical waveguide connected to the fourth optical coupler.

2. The bandpass / bandstop dual-output integrated microwave photonic filter of claim 1, comprising: A thin film lithium niobate chip, characterized in that the thin film lithium niobate chip has a film thickness of 350-450 nm.

3. The bandpass / band-reject dual-output integrated microwave photonic filter of claim 1, comprising: A thin film lithium niobate chip, characterized in that a laser is connected to an input end of the thin film lithium niobate chip.

4. The bandpass / band-reject dual-output integrated microwave photonic filter of claim 1, comprising: A thin film lithium niobate chip, characterized in that a photodetector is connected to an output end of the thin film lithium niobate chip.

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