Thin-film lithium niobate electro-optical modulator

Abstract

The invention discloses a thin-film lithium niobate electro-optical modulator which comprises a Mach-Zehnder structure formed by thin-film lithium niobate optical waveguides, the Mach-Zehnder structure comprises a beam splitter section, a plurality of electro-optical modulation sections and a crossed waveguide section, and the beam splitter section, the plurality of electro-optical modulation sections and the crossed waveguide section form a series connection structure. The modulation arms of the adjacent electro-optical modulation sections are in cross connection through the cross waveguide sections; the beam splitter section is connected with the first electro-optical modulation section, and the beam combiner section is connected with the last electro-optical modulation section; each electro-optical modulation section is provided with a modulation electrode used for modulating the phase of optical signals passing through the two sets of modulation arms in the corresponding electro-optical modulation section, the polarities of electric signals generated by the modulation electrodes of the adjacent electro-optical modulation sections are opposite, and the time when the modulation electrodes generate the electric signals is synchronous with the time when the optical signals enter the corresponding electro-optical modulation sections. According to the invention, the requirements of higher bandwidth and smaller half-wave voltage are met, and meanwhile, the method has the advantage of lower process difficulty and longer modulation distance.

Description

Technical Field

[0001] The invention relates to the field of electro-optic modulators, in particular to a thin-film lithium niobate electro-optic modulator. Background Art

[0002] Electro-optic modulators use linear optical effect, electro-absorption effect or plasma dispersion effect to modulate the intensity of optical signals. Thin-film lithium niobate electro-optic modulators use linear optical effect to achieve efficient electro-optic modulation. Compared with existing integrated silicon modulators, integrated lithium niobate electro-optic modulators have the unique advantage of changing the modal refractive index through electro-optic effect rather than silicon plasma dispersion effect. Therefore, the response time of thin-film lithium niobate electro-optic modulators to modulated signals (on femtosecond time scale) is much shorter than that of silicon modulators (on nanosecond time scale), thus achieving ultra-high-speed modulation.

[0003] In recent years, thin-film lithium niobate electro-optic modulators have attracted widespread attention due to their excellent performance. In 2018, Cheng Wang et al. from Harvard University fabricated a lumped electrode microring modulator and MZ modulator on LNOI, where the electrode length of the MZ modulator was 2 mm, the half-wave voltage was 9 V, and the 3 dB bandwidth was 15 GHz (Wang C, Zhang M, Stern B, et al. Nanophotonic lithium niobate electro-optic modulators [J]. Optics Express, 2018, 26 (2): 1547-1555.). In the same year, the team also produced an MZ modulator with a traveling wave electrode, in which the half-wave voltage of the device with a modulation electrode length of 20 mm was only 1.4 V, which could be directly driven by a CMOS chip, and the 3dB bandwidth reached 45 GHz. This work set off a research boom in LNOI modulators (Wang C, Zhang M, Chen X, et al. Integrated lithium niobate electro-optic modulators operating at CMOS-compatible voltages [J]. Nature, 2018, 562, 101-104.). In 2021, Prashanta Kharel et al. of HyperLight applied T-type track electrodes to design LNOI modulators on quartz substrates, with a half-wave voltage of 1.3 V and an estimated bandwidth of 175 GHz (Kharel P, Reimer C, Luke K, et al. Breaking voltage-bandwidth limits in integrated lithium niobate modulators using micro-structured electrodes [J]. 2021, 8 (3): 357-363.). However, in the current high-speed optical communication field, the bandwidth of the above modulators cannot fully meet the transmission rate requirements of big data. In view of this situation, it is necessary to design electro-optical modulators with higher bandwidth and lower half-wave voltage to achieve higher data transmission rates and lower power loss.

[0004] In the Chinese patent "A thin-film lithium niobate electro-optic modulator based on differential drive and push-pull" with the prior art application number CN202211280207.X, differential drive and push-pull structure are combined for the first time on the thin-film lithium niobate platform. By introducing a periodic electrode with a specific structure, the modulation length is halved, and the bandwidth performance is improved. However, the electro-optic modulator of this patent has the following problems: First, the patent uses a periodic structure electrode with a specific structure and a positive and negative electrode to modulate the optical signal passing through the Mach-Zehnder structure formed by the thin-film lithium niobate optical waveguide. The manufacturing precision of the periodic structure electrode with this specific structure is high and the process is difficult. Secondly, the periodic structure electrode with a specific structure used in the patent is difficult to bend. Therefore, if long-distance signal modulation is to be achieved, the periodic structure electrode, the positive electrode, and the negative electrode are all required to be flat and unfolded in one line, and the length of the periodic structure electrode, the positive electrode, and the negative electrode needs to be designed to be very long, that is, the electro-optic modulator of this patent needs to be made very long when realizing long-distance signal modulation, and the long electrode length will also lead to the problem of increased microwave loss. Summary of the invention

[0005] The present invention provides a thin film lithium niobate electro-optic modulator to solve the problems of the prior art Chinese patent "A thin film lithium niobate electro-optic modulator based on differential drive and push-pull" with application number CN202211280207.X, which is difficult to manufacture and requires a longer length to be designed when performing long-distance signal modulation.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is:

[0007] A thin-film lithium niobate electro-optic modulator, comprising a Mach-Zehnder structure formed by a thin-film lithium niobate optical waveguide, wherein the Mach-Zehnder structure comprises a beam splitter section, N electro-optic modulation sections, N-1 cross-waveguide sections, and a beam combiner section, wherein N is greater than or equal to 2, each electro-optic modulation section comprises two groups of modulation arms, the N electro-optic modulation sections and the N-1 cross-waveguide sections form a series structure, and the modulation arms of adjacent electro-optic modulation sections in the series structure are cross-connected through the cross-waveguide section;

[0008] The beam splitter section is connected to the two groups of modulation arms of the first electro-optical modulation section in the series structure as an optical signal input end, and the beam combiner section is connected to the two groups of modulation arms of the last electro-optical modulation section in the series structure as an optical signal output end; the input optical signal enters the beam splitter section and is divided into two beams, and then passes through the two groups of modulation arms of the first electro-optical modulation section one by one, and passes through the other electro-optical modulation sections and the cross waveguide section in sequence, and finally outputs from the two groups of modulation arms of the last electro-optical modulation section to the beam combiner section for beam combining interference, wherein the cross waveguide section makes the optical signals output by the two groups of modulation arms of the previous electro-optical modulation section in the corresponding adjacent electro-optical modulation section cross and enter the two groups of modulation arms of the next electro-optical modulation section;

[0009] Each electro-optical modulation segment is respectively configured with a modulation electrode, which generates an electrical signal to modulate the phase of the optical signal passing through the two groups of modulation arms in the corresponding electro-optical modulation segment. The electrical signals generated by the modulation electrodes of adjacent electro-optical modulation segments in the series structure have opposite polarities when modulated. The time when the modulation electrodes configured in each electro-optical modulation segment generate the electrical signal is synchronized with the time when the optical signal enters the two groups of modulation arms of the corresponding electro-optical modulation segment.

[0010] Furthermore, it also includes an electrical signal source, which directly outputs electrical signals to the modulation electrodes configured in the first electro-optical modulation segment in the series structure, thereby causing the modulation electrodes configured in the first electro-optical modulation segment to generate electrical signals for modulation, and the time when the electrical signal source outputs electrical signals to the modulation electrodes configured in the first electro-optical modulation segment in the series structure is synchronized with the time when the two optical signals output by the beam splitter segment enter the two groups of modulation arms of the first electro-optical modulation segment;

[0011] The electrical signal source outputs electrical signals to the modulation electrodes configured in each other electro-optical modulation segment through the delay module. The delay module synchronizes the time when the electrical signal source outputs the electrical signal to each other modulation electrode with the time when the optical signal enters the two groups of modulation arms of the corresponding electro-optical modulation segment.

[0012] Furthermore, the delay module is an electromagnetic delay line.

[0013] Furthermore, the modulation electrode is a GSG electrode, and the signal electrode in the GSG electrode and one of the ground electrodes cooperate to phase modulate the optical signals passing through a group of modulation arms of the corresponding electro-optical modulation segment, and the signal electrode in the GSG electrode and another ground electrode cooperate to phase modulate the optical signals passing through another group of modulation arms of the corresponding electro-optical modulation segment.

[0014] Furthermore, the overall shape of each electro-optical modulation segment is U-shaped.

[0015] Furthermore, it also includes a substrate, a buried oxide layer arranged on the substrate, a lithium niobate layer arranged on the buried oxide layer, and a cladding layer arranged on the lithium niobate layer. The Mach-Zehnder structure formed by the thin-film lithium niobate optical waveguide is etched on the lithium niobate layer, and the Mach-Zehnder structure formed by the thin-film lithium niobate optical waveguide is coated by the cladding layer.

[0016] Furthermore, the modulation electrode is arranged on the cladding.

[0017] Furthermore, the material of the cladding is silicon dioxide.

[0018] In the present invention, the electro-optical modulation channel of the Mach-Zehnder structure is a segmented structure, that is, the Mach-Zehnder structure has N electro-optical modulation segments, and each electro-optical modulation segment is separately configured with a modulation electrode. The modulation electrodes configured in adjacent electro-optical modulation segments output electrical signals with opposite polarities, that is, if one modulation electrode in the modulation electrodes configured in adjacent electro-optical modulation segments outputs a positive voltage, the other modulation electrode outputs a negative voltage. In addition, the modulation arms of adjacent electro-optical modulation segments are cross-connected through cross-waveguide segments.

[0019] Therefore, the present invention innovatively adopts a segmented continuous relay modulation method, by which each modulation electrode separately phase-modulates the optical signal of the corresponding electro-optical modulation segment in the Mach-Zehnder structure, and uses a cross-waveguide segment to make the optical signals output by the two modulation arms of the previous electro-optical modulation segment in the adjacent electro-optical modulation segment cross and enter the two modulation arms of the next electro-optical modulation segment, and then cooperates with the modulation method of different polarities of the electrical signals generated by the modulation electrodes corresponding to the adjacent electro-optical modulation segments, so that each modulation electrode can relay continuous modulation, thereby ensuring that the phase modulation amount of each optical signal output by the beam splitter segment is continuously superimposed in the segmented continuous relay modulation process, and the phase modulation amount of the adjacent electro-optical modulation segments will not be cancelled.

[0020] Finally, the two optical signals output by the beam splitter section are phase modulated by continuous superposition and then enter the beam combiner section for beam combining interference. During interference, the intensities of the two phase-modulated optical signals are superimposed. Therefore, compared with the unsplit input optical signal entering the beam splitter section, the modulation of the optical signal intensity is finally achieved.

[0021] Furthermore, taking into account the different times at which the optical signal enters each electro-optical modulation segment, the present invention adopts a delay module to delay the time at which the modulation electrode corresponding to each of the remaining electro-optical modulation segments after the first electro-optical modulation segment generates an electrical signal, so as to ensure that the time at which the modulation electrode corresponding to each electro-optical modulation segment generates an electrical signal is synchronized with the time of the optical signal entering the corresponding electro-optical modulation segment.

[0022] Since the present invention adopts segmented continuous relay modulation to perform phase modulation of optical signals, the length of each modulation electrode only needs to match the length of the corresponding electro-optical modulation segment, and the modulation electrode length does not need to be designed to be very long, thereby significantly reducing microwave losses.

[0023] Furthermore, since the present invention uses segmented continuous relay modulation to perform phase modulation of optical signals, in the Mach-Zehnder structure formed by the thin-film lithium niobate optical waveguide in the present invention, the shape of each electro-optic modulation segment can be designed to be U-shaped. When the Mach-Zehnder structure thus formed is a multi-channel curved shape, it can have a longer modulation distance, and the overall length of the entire electro-optic modulator does not need to be designed to be very long. Therefore, long-distance modulation can be achieved on the basis of ensuring that the overall length of the electro-optic modulator is not too long.

[0024] At the same time, since the cross-transmission of optical signals of adjacent electro-optical modulation segments is achieved through cross-waveguides in the present invention, and the modulation electrodes corresponding to adjacent electro-optical modulation segments generate different polarities of electrical signals, continuous superposition phase modulation can be achieved. Therefore, the modulation electrodes in the present invention do not require a special structure, and the modulation electrodes can be commonly used electrodes such as GSG electrodes. Therefore, the overall manufacturing process of the present invention is not difficult, and the manufacturing difficulty will not be increased due to the need to manufacture modulation electrodes of special shapes.

[0025] In summary, when the present invention modulates optical signals, it has the advantage of less process difficulty while meeting the requirements of higher bandwidth and smaller half-wave voltage. Moreover, since a curved waveguide can be formed, a longer modulation distance can be achieved without having to design a longer overall length. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a top view of the overall structure of an embodiment of the present invention.

[0027] Figure 2 It is a front view of the overall structure of an embodiment of the present invention.

[0028] Figure 3 1 is a top view of a Mach-Zehnder structure in an embodiment of the present invention. DETAILED DESCRIPTION

[0029] In order to enable those skilled in the art to better understand the solutions of the present invention, the following will describe the implementation methods of the present invention in detail in conjunction with the accompanying drawings and embodiments, so that the implementation process of how the present invention applies technical means to solve technical problems and achieve corresponding technical effects can be fully understood and implemented accordingly. The embodiments of the present invention and the various features in the embodiments can be combined with each other without conflict, and the technical solutions formed are all within the protection scope of the present invention.

[0030] Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0031] It should be noted that the terms "include" and "have" in the specification and claims of the present invention and the above drawings and any modifications thereof are intended to cover non-exclusive inclusions.

[0032] like Figure 1 , Figure 2 , Figure 3As shown, this embodiment discloses a thin-film lithium niobate electro-optic modulator, including a substrate 1, a buried oxide layer 2 is provided on the substrate 1, a lithium niobate layer 3 is provided on the buried oxide layer 2, a Mach-Zehnder structure formed by a thin-film lithium niobate optical waveguide 4 is provided on the lithium niobate layer 3, and a cladding 5 is further provided on the lithium niobate layer 3, and a Mach-Zehnder structure is formed by the cladding 5 covering the thin-film lithium niobate optical waveguide 4.

[0033] In this embodiment, the material of the substrate 1 is silicon, lithium niobate, quartz, or air, with a thickness of 200um-1000um. The material of the buried oxide layer is silicon dioxide, with a thickness of 1-6um. The material of the cladding 5 is silicon dioxide, with a thickness of 0.1-2um. The cladding 5 made of silicon dioxide can reduce microwave loss and optical loss, and is conducive to the deposition of metal electrodes in terms of process.

[0034] In this embodiment, Figure 3 As shown, the Mach-Zehnder structure formed by the thin-film lithium niobate optical waveguide 4 includes a 1×2 beam splitter segment 10, N electro-optical modulation segments 11, N-1 cross waveguide segments 6, and a 2×1 beam combiner segment 12, where N≥2. Each electro-optical modulation segment 11 includes a first group of modulation arms A1 and a second group of modulation arms A2, and the overall shape of each electro-optical modulation segment 11 is U-shaped, that is, the shape of each group of modulation arms in each electro-optical modulation segment 11 is a U-shape including two straight line segments and a curved segment connecting one end of the two straight line segments, wherein Figure 1 , Figure 3 As shown, the second group of modulation arms A2 in each electro-optical modulation segment 11 is located in the U-shape of the first group of modulation arms A1. A series structure is formed by connecting N electro-optical modulation segments 11 and N-1 cross waveguide segments 6 in series. In addition, in this embodiment, each electro-optical modulation segment 11 is separately configured with a modulation electrode 8.

[0035] In the specific series structure, a cross waveguide section 6 is arranged between every two adjacent electro-optical modulation sections 11. In the series structure, the output ends of the two groups of modulation arms A1 and A2 of the first electro-optical modulation section 11 are connected to the input ends of the two waveguide channels of the first cross waveguide section 6, the output end of the waveguide channel corresponding to the first group of modulation arms A1 of the first electro-optical modulation section in the first cross waveguide section 6 is connected to the input end of the second group of modulation arms A2 of the second electro-optical modulation section, and the output end of the waveguide channel corresponding to the second group of modulation arms A2 of the first electro-optical modulation section in the first cross waveguide section 6 is connected to the input end of the first group of modulation arms A1 of the second electro-optical modulation section, that is, the two groups of modulation arms A1 and A2 of the first electro-optical modulation section 11 are cross-connected with the two groups of modulation arms A1 and A2 of the second electro-optical modulation section in the first cross waveguide section 6.

[0036] Similarly, the first group of modulation arms A1 of the second electro-optical modulation segment is connected to the second group of modulation arms A2 of the third electro-optical modulation segment through the second cross-waveguide segment, and the second group of modulation arms A2 of the second electro-optical modulation segment is connected to the first group of modulation arms A1 of the third electro-optical modulation segment through the second cross-waveguide segment.

[0037] By analogy, the first group of modulation arms A1 of the N-1th electro-optical modulation segment is connected to the second group of modulation arms A2 of the N-1th electro-optical modulation segment through the N-1th cross-waveguide segment, and the second group of modulation arms A2 of the N-1th electro-optical modulation segment is connected to the first group of modulation arms A1 of the N-1th electro-optical modulation segment through the N-1th cross-waveguide segment. Thus, in the Mach-Zehnder structure of this embodiment, the modulation arms of adjacent electro-optical modulation segments are cross-connected through the cross-waveguide segment, thereby forming a plurality of electro-optical modulation segments in a series structure.

[0038] The Mach-Zehnder structure includes a 1×2 beam splitter section 10 as an optical signal input end, which is connected to the input ends of the two groups of modulation arms A1 and A2 of the first electro-optical modulation section in the series structure. The 2×1 beam combiner section 12 is connected to the output ends of the two groups of modulation arms A1 and A2 of the last electro-optical modulation section in the series structure as an optical signal output end, thereby forming a complete optical signal modulation channel.

[0039] In the optical signal modulation channel, the input optical signal enters the 1×2 beam splitter section 10 and is evenly divided into two beams, and then passes through the two groups of modulation arms A1 and A2 of the first electro-optical modulation section 11 one by one. Then, the optical signal output by the first group of modulation arms A1 of the first electro-optical modulation section 11 enters the second group of modulation arms A2 of the second electro-optical modulation section through the first cross-waveguide section 6, and the optical signal output by the second group of modulation arms A2 of the first electro-optical modulation section 11 enters the first group of modulation arms A1 of the second electro-optical modulation section through the first cross-waveguide section 6. Similarly, the optical signal output by the first group of modulation arms A1 of the second electro-optical modulation section enters the second group of modulation arms A2 of the third electro-optical modulation section through the second cross-waveguide section, and the optical signal output by the second group of modulation arms A2 of the second electro-optical modulation section enters the first group of modulation arms A1 of the third electro-optical modulation section through the second cross-waveguide section.

[0040] By analogy, the optical signal output by the first group of modulation arms A1 of the N-1th electro-optical modulation segment enters the second group of modulation arms A2 of the N-1th electro-optical modulation segment through the N-1th cross waveguide segment, and the optical signal output by the second group of modulation arms A2 of the N-1th electro-optical modulation segment enters the first group of modulation arms A1 of the N-1th electro-optical modulation segment through the N-1th cross waveguide segment. Thus, in the Mach-Zehnder structure of this embodiment, the optical signals output by the two groups of modulation arms A1 and A2 of the previous electro-optical modulation segment in the corresponding adjacent electro-optical modulation segments cross and enter the two groups of modulation arms of the next electro-optical modulation segment through the cross waveguide segment.

[0041] The optical signals output by the two groups of modulation arms A1 and A2 in the Nth electro-optical modulation section finally enter the 2×1 beam combiner section 12 for beam combining interference.

[0042] In the Mach-Zehnder structure formed by the thin-film lithium niobate optical waveguide 4 of this embodiment, since each electro-optic modulation segment 11 is U-shaped, the ultimately formed Mach-Zehnder structure is a multi-channel curved shape, which can achieve a longer modulation length.

[0043] In this embodiment, each modulation electrode 8 generates an electrical signal to modulate the phase of the optical signal passing through the two groups of modulation arms A1 and A2 of the corresponding electro-optical modulation segment 11. The electrical signals generated by the modulation electrodes 8 of adjacent electro-optical modulation segments in the series structure have opposite polarities when modulating, that is, in adjacent electro-optical modulation segments, when the electrical signal generated by the modulation electrode corresponding to one electro-optical modulation segment is a positive voltage, the electrical signal generated by the modulation electrode corresponding to the other electro-optical modulation segment is a negative voltage.

[0044] In this embodiment, each modulation electrode 8 adopts a GSG electrode, and the GSG electrode includes a signal electrode 8.1 and two ground electrodes 8.2 and 8.3. Among them, the signal electrode 8.1 is used to connect to an electrical signal source to generate a positive voltage or a negative voltage. The position of the signal electrode 8.1 corresponds to the area between the two groups of modulation arms A1 and A2 in the corresponding electro-optical modulation segment 11, and the shape of the signal electrode 8.1 matches the shape of the corresponding electro-optical modulation segment 11. In this embodiment, the shape of the electro-optical modulation segment 11 is U-shaped, so the shape of the signal electrode 8.1 is the same U-shaped, that is, the shape of the signal electrode 8.1 is composed of two straight line segments and a curved segment connecting one end of the two straight line segments. The position of the first ground electrode 8.2 corresponds to the U-shaped outer side of the first group of modulation arms A1 in the corresponding electro-optical modulation segment 11, and the signal electrode 8.1 and the first ground electrode 8.2 cooperate to modulate the phase of the optical signal passing through the first group of modulation arms A1. The position of the second ground electrode 8.3 corresponds to the U-shape of the second group of modulation arms A2 in the corresponding electro-optical modulation section 11. The signal electrode 8.1 and the second ground electrode 8.3 cooperate to modulate the phase of the optical signal passing through the second group of modulation arms A2.

[0045] The signal electrode 8.1 cooperates with the two ground electrodes 8.2 and 8.3 to achieve phase modulation of the optical signals passing through the two groups of modulation arms A1 and A2 of the electro-optical modulation section 11. That is, the signal electrode 8.1 cooperates with the first ground electrode 8.2 to achieve phase modulation of the optical signals passing through the first group of modulation arms A1 of the corresponding electro-optical modulation section 11; the signal electrode 8.1 cooperates with the second ground electrode 8.3 to achieve phase modulation of the optical signals passing through the second group of modulation arms A2 of the corresponding electro-optical modulation section 11.

[0046] The following takes the two optical signals output by the 1×2 beam splitter segment 10 with the initial phase angles of θ as an example, and combines the modulation electrode 8 using the GSG electrode of the present embodiment, the cross transmission mode of the adjacent electro-optical modulation segments 11, and the modulation mode in which the polarity of the electrical signal generated when the modulation electrodes 8 of the adjacent electro-optical modulation segments are modulated is opposite, to illustrate the process of implementing the segmented continuous relay phase superposition modulation in the present embodiment:

[0047] The phase angles of the optical signals of the two groups of modulation arms A1 and A2 entering the first electro-optic modulation segment 11 are both θ, and the signal electrode 8.1 in the GSG electrode corresponding to the first electro-optic modulation segment 11 generates a positive voltage. The signal electrode 8.1 in the GSG electrode corresponding to the first electro-optic modulation segment 11 cooperates with the first ground electrode 8.2, and the positive voltage signal is used to modulate the phase angle of the optical signal passing through the first group of modulation arms A1 of the first electro-optic modulation segment to θ+Δθ, where Δθ is the phase angle modulation variation. The signal electrode 8.1 in the GSG electrode corresponding to the first electro-optic modulation segment 11 cooperates with the second ground electrode 8.3, and the positive voltage signal is used to modulate the phase angle of the optical signal passing through the second group of modulation arms A2 of the first electro-optic modulation segment 11 to θ-Δθ. In this embodiment, since lithium niobate is a trigonal 3m point group, n1=n2=n o , n3=n e , where n1 and n2 are the refractive indices in the short axis direction of the refractive index ellipsoid, n3 is the refractive index in the long axis direction of the refractive index ellipsoid, and n o is the refractive index value of normal light, n e is the extraordinary refractive index value. Due to the electro-optic effect, that is, the change in the refractive index of the medium due to the change in the electric field, it can be expressed as n = n0 + aE + bE 2 +…, where a is the Pockels coefficient, b is the Kerr coefficient, and E is the electric field strength. When an electric field is applied to lithium niobate in the z-axis direction, its refractive index changes and can be expressed as, n x =n o -n o 3 r 33 Ez / 2,n y =n o +n o 3 r 33 Ez / 2,n z =n e , where n x is the refractive index in the x direction of the refractive index ellipsoid, n y is the refractive index in the y direction of the refractive index ellipsoid, n z is the refractive index in the z direction of the refractive index ellipsoid, r 33is the electro-optic coefficient matrix component, and Ez is the electric field intensity in the z direction. When the refractive index of lithium niobate changes, the optical path changes. If the refractive index increases, the optical path increases and the phase angle increases; if the refractive index decreases, the optical path decreases and the phase angle decreases. In the GSG electrode corresponding to the first electro-optic modulation segment 11, since when a positive voltage is applied to the signal electrode 8.1, the electric field direction of the first group of modulation arms A1 in the first electro-optic modulation segment 11 is from the signal electrode 8.1 to the first ground electrode 8.2, and the electric field direction of the second group of modulation arms A2 in the first electro-optic modulation segment 11 is from the signal electrode 8.1 to the second ground electrode 8.3, when the phase angle of the first group of modulation arms A1 in the first electro-optic modulation segment is modulated to θ+Δθ, the optical signal phase angle of the second group of modulation arms A2 in the first electro-optic modulation segment is modulated to θ-Δθ.

[0048] The optical signal with a phase of θ+Δθ output by the first group of modulation arms A1 in the first electro-optical modulation segment 11 enters the second group of modulation arms A2 in the second electro-optical modulation segment through the first cross waveguide segment 6. The optical signal with a phase of θ-Δθ output by the second group of modulation arms A2 in the first electro-optical modulation segment 11 enters the first group of modulation arms A1 in the second electro-optical modulation segment through the first cross waveguide segment 6.

[0049] In the second electro-optical modulation segment, since the signal electrode 8.1 in the GSG electrode corresponding to the second electro-optical modulation segment generates a negative voltage, and the phase angle of the optical signal entering the first group of modulation arms A1 of the second electro-optical modulation segment is θ-Δθ, and the phase angle of the optical signal entering the second group of modulation arms A2 of the second electro-optical modulation segment is θ+Δθ, the phase angle of the optical signal with a phase of θ-Δθ passing through the first group of modulation arms A1 of the second electro-optical modulation segment is modulated to θ-2Δθ by using a negative voltage signal through the cooperation of the signal electrode 8.1 in the GSG electrode corresponding to the second electro-optical modulation segment and the first ground electrode 8.2. The phase angle of the optical signal with a phase of θ+Δθ passing through the second group of modulation arms A2 of the second electro-optical modulation segment is modulated to θ+2Δθ by using a negative voltage signal through the cooperation of the signal electrode 8.1 in the GSG electrode corresponding to the second electro-optical modulation segment and the second ground electrode 8.3. In the GSG electrode corresponding to the second electro-optical modulation segment, when a negative voltage is applied to the signal electrode 8.1, the electric field direction of the first group of modulation arms A1 of the second electro-optical modulation segment is from the first ground electrode 8.2 to the signal electrode 8.1, and the electric field direction of the second group of modulation arms A2 of the second electro-optical modulation segment is from the second ground electrode 8.3 to the signal electrode 8.1. Therefore, when the phase angle of the first group of modulation arms A1 of the second electro-optical modulation segment is modulated to θ-2Δθ, the optical signal phase angle of the second group of modulation arms A2 of the second electro-optical modulation segment is modulated to θ+2Δθ.

[0050] The optical signal with a phase of θ-2Δθ output by the first group of modulation arms A1 in the second electro-optical modulation segment enters the second group of modulation arms A2 in the third electro-optical modulation segment through the second cross-waveguide segment. The optical signal with a phase of θ+2Δθ output by the second group of modulation arms A2 in the second electro-optical modulation segment enters the first group of modulation arms A1 in the third electro-optical modulation segment through the second cross-waveguide segment.

[0051] In the third electro-optical modulation segment, since the signal electrode 8.1 in the GSG electrode corresponding to the third electro-optical modulation segment generates a positive voltage, and the phase angle of the optical signal entering the first group of modulation arms A1 of the third electro-optical modulation segment is θ+2Δθ, and the phase angle of the optical signal entering the second group of modulation arms A2 of the third electro-optical modulation segment is θ-2Δθ, the signal electrode 8.1 in the GSG electrode corresponding to the third electro-optical modulation segment cooperates with the first ground electrode 8.2, and the phase angle of the optical signal with a phase of θ+2Δθ passing through the first group of modulation arms A1 of the third electro-optical modulation segment is modulated to θ+3Δθ by using a positive voltage signal. The signal electrode 8.1 in the GSG electrode corresponding to the third electro-optical modulation segment cooperates with the second ground electrode 8.3, and the phase angle of the optical signal with a phase of θ-2Δθ passing through the second group of modulation arms A2 of the third electro-optical modulation segment is modulated to θ-3Δθ by using a positive voltage signal. In the GSG electrode corresponding to the third electro-optical modulation segment, when a positive voltage is applied to the signal electrode 8.1, the electric field direction of the first group of modulation arms A1 of the third electro-optical modulation segment is from the signal electrode 8.1 to the first ground electrode 8.2, and the electric field direction of the second group of modulation arms A2 of the third electro-optical modulation segment is from the signal electrode 8.1 to the second ground electrode 8.3. Therefore, when the phase angle of the first group of modulation arms A1 of the third electro-optical modulation segment is modulated to θ+3Δθ, the optical signal phase angle of the second group of modulation arms A2 of the third electro-optical modulation segment is modulated to θ-3Δθ.

[0052] By analogy, the signal electrode 8.1 in the GSG electrode corresponding to the Nth electro-optical modulation segment cooperates with the first ground electrode 8.2, and the phase angle of the optical signal with a phase of θ+(N-1)Δθ passing through the first group of modulation arms A1 of the Nth electro-optical modulation segment is modulated to θ+NΔθ by using a voltage signal of a corresponding polarity. The signal electrode 8.1 in the GSG electrode corresponding to the Nth electro-optical modulation segment cooperates with the second ground electrode 8.3, and the phase angle of the optical signal with a phase of θ-(N-1)Δθ passing through the second group of modulation arms A2 of the Nth electro-optical modulation segment is modulated to θ-NΔθ by using a voltage signal of a corresponding polarity.

[0053] Finally, the optical signals with phase angles of θ+NΔθ and θ-NΔθ output by the two groups of modulation arms A1 and A2 of the Nth electro-optical modulation segment respectively enter the 2×1 combiner segment 12 for beam combining interference. Since the phase angles of the two optical signals are continuously superimposed and modulated, the intensities of the two optical signals after the phase angles are modulated are superimposed during interference, so that the intensity of the combined light beam formed is changed compared to the input optical signal entering the 1×2 beam splitter segment 10, thereby realizing the modulation of the optical signal intensity.

[0054] In this embodiment, each modulation electrode 8 is integrally arranged on the cladding 5. The cladding 5 made of silicon dioxide can reduce microwave loss and optical loss, and is conducive to the deposition of metal electrodes in terms of process. Therefore, when the modulation electrode 8 is a GSG electrode, the signal electrode 8.1 is located directly above the area between the two groups of modulation arms A1 and A2 in the corresponding electro-optical modulation segment 11, the first ground electrode 8.2 is located directly above the outer side of the first group of modulation arms A1 in the corresponding electro-optical modulation segment 11, and the second ground electrode 8.3 is located directly above the U-shaped inner area of ​​the second group of modulation arms A2 in the corresponding electro-optical modulation segment 11.

[0055] It should be noted that the modulation electrode 8 using the GSG electrode in this embodiment can be arranged not only on the cladding 5, but also in other ways, such as being directly arranged on the lithium niobate layer 3, as long as the signal electrode 8.1 in the modulation electrode 8 cooperates with each ground electrode, the optical signals passing through the two groups of modulation arms A1 and A2 can be modulated in the straight line section corresponding to the electro-optical modulation section 11. Therefore, the technical solutions using this embodiment and other ways of arranging the GSG electrode should also be regarded as falling within the protection scope of the present invention.

[0056] At the same time, although the modulation electrode 8 in this embodiment is described using the GSG electrode as an example, it should not be regarded as the modulation electrode 8 in this embodiment being limited to the use of the GSG electrode. Technical solutions that apply this embodiment and use other types of modulation electrodes that can achieve the modulation function of this embodiment should also be regarded as falling within the scope of protection of the present invention.

[0057] Furthermore, although the present embodiment is described using the example of each electro-optical modulation segment 11 being in a U-shape, it should be pointed out that when each electro-optical modulation segment 11 is in other shapes, such as a straight line or an S-shape, the above-mentioned electro-optical modulation process of the present embodiment is still valid. Therefore, the technical solutions applying the present embodiment and adopting electro-optical modulation segments 11 in other shapes should also be deemed to fall within the scope of protection of the present invention.

[0058] This embodiment also includes an electrical signal source 7, which is a device that can output multiple positive and negative voltage signals, such as a DSP. Different voltage output ends of the electrical signal source 7 are connected to the modulation electrodes 8 configured for each electro-optical modulation segment 11 in a one-to-one correspondence. When the modulation electrode 8 is a GSG electrode, the voltage output end of the electrical signal source 7 is connected to the signal electrode 8.1 in the modulation electrode 8 configured for each electro-optical modulation segment.

[0059] Taking into account that the time when the optical signal enters each electro-optical modulation segment 11 is different, that is, after the optical signal enters the two groups of modulation arms of the N-1th electro-optical modulation segment, it needs to pass through the two groups of modulation arms of the N-1th electro-optical modulation segment, and then cross through the N-1th cross waveguide segment to enter the two groups of modulation arms of the Nth electro-optical modulation segment. A time difference is generated in this process, which makes the time when the optical signal enters the two groups of modulation arms of the Nth electro-optical modulation segment slower than the time when the optical signal enters the two groups of modulation arms of the N-1th electro-optical modulation segment, so that the time when the optical signal enters each electro-optical modulation segment is different.

[0060] Therefore, in order to ensure accurate modulation of the optical signal, appropriate measures need to be taken to ensure that the time when the optical signal enters each electro-optical modulation segment 11 is synchronized with the time when the modulation electrode 8 corresponding to each electro-optical modulation segment 11 generates the electrical signal.

[0061] In this embodiment, for the first electro-optical modulation segment 11, the electric signal source 7 is directly connected to the modulation electrode 8 configured in the first electro-optical modulation segment 11. It is only necessary to control the time when the corresponding voltage output terminal of the electric signal source 7 outputs the electric signal to the modulation electrode 8 configured in the first electro-optical modulation segment 11 through the internal program of the electric signal source 7, and synchronize it with the time when the two light beams output by the 1×2 beam splitter segment 10 enter the two groups of modulation arms A1 and A2 of the first electro-optical modulation segment 11. At this time, the electric signal source 7 outputs the electric signal to the modulation electrode 8 configured in the first electro-optical modulation segment 11, so that the modulation electrode 8 configured in the first electro-optical modulation segment 11 generates the electric signal for modulation, and modulates the light signal passing through the two modulation arms A1 and A2 of the first electro-optical modulation segment 11.

[0062] For the modulation electrodes configured in each of the remaining electro-optical modulation segments except the first electro-optical modulation segment 11, the corresponding voltage output end of the electric signal source 7 is connected to the corresponding electrodes configured in each of the remaining electro-optical modulation segments through a delay module. The corresponding voltage output end of the electric signal source 7 outputs an electric signal to the corresponding modulation electrode configured in each of the remaining electro-optical modulation segments through the delay module, and the time when the electric signal source outputs the electric signal to each of the remaining modulation electrodes is synchronized with the time when the optical signal enters the two groups of modulation arms of the corresponding electro-optical modulation segment through the delay module.

[0063] Taking the example that each electro-optical modulation segment 11 has the same length and each cross-waveguide segment 6 has the same length, let the total time length of the optical signal passing through each electro-optical modulation segment 11 and the cross-waveguide segment 6 connected to its output end be t, and let the time for the electrical signal source 7 to output the electrical signal to the modulation electrode 8 configured for the first electro-optical modulation segment 11 (that is, the time for the two beams of optical signals output by the 1×2 beam splitter segment 10 to enter the two groups of modulation arms A1 and A2 of the first electro-optical modulation segment 11) be t0. The time it takes for the two optical signals to cross through the two groups of modulation arms of the first electro-optical modulation segment and enter the two groups of modulation arms of the second electro-optical modulation segment is t+t0, the time it takes for the optical signals output by the two groups of modulation arms of the second electro-optical modulation segment to cross and enter the two groups of modulation arms of the third electro-optical modulation segment is t+2×t0, the time it takes for the optical signals output by the two groups of modulation arms of the third electro-optical modulation segment to cross and enter the two groups of modulation arms of the fourth electro-optical modulation segment is t+3×t0, and so on. The time it takes for the optical signals output by the two groups of modulation arms of the N-1th electro-optical modulation segment to cross and enter the two groups of modulation arms of the Nth electro-optical modulation segment is t+(N-1)×t0.

[0064] At this time, the delay module corresponding to the modulation electrode configured in the second electro-optical modulation segment makes the time for the electrical signal output by the electrical signal source 7 to the modulation electrode configured in the second electro-optical modulation segment t+t0, that is, through the delay module corresponding to the modulation electrode configured in the second electro-optical modulation segment, the time for the electrical signal output by the electrical signal source 7 to the modulation electrode configured in the second electro-optical modulation segment is delayed by t0 relative to the time for the electrical signal output by the electrical signal source 7 to the modulation electrode configured in the first electro-optical modulation segment, so that the time for the modulation electrode configured in the second electro-optical modulation segment to generate the electrical signal can be synchronized with the time when the optical signal enters the second electro-optical modulation segment.

[0065] Similarly, through the delay module corresponding to the modulation electrode configured in the third electro-optical modulation segment, the time of the electrical signal output by the electrical signal source 7 to the modulation electrode configured in the third electro-optical modulation segment is delayed by 2×t0 relative to the time of the electrical signal output by the electrical signal source 7 to the modulation electrode configured in the first electro-optical modulation segment. This can achieve synchronization between the time when the modulation electrode configured in the third electro-optical modulation segment generates the electrical signal and the time when the optical signal enters the third electro-optical modulation segment.

[0066] By analogy, through the delay module corresponding to the modulation electrode configured in the Nth electro-optical modulation segment, the time of the electrical signal output by the electrical signal source 7 to the modulation electrode configured in the Nth electro-optical modulation segment is delayed by (N-1)×t0 relative to the time of the electrical signal output by the electrical signal source 7 to the modulation electrode configured in the first electro-optical modulation segment. This can achieve synchronization between the time when the modulation electrode configured in the Nth electro-optical modulation segment generates the electrical signal and the time when the optical signal enters the Nth electro-optical modulation segment.

[0067] It should be noted that, although the present embodiment is described by taking the example that each electro-optical modulation segment 11 has the same length and each cross waveguide segment 6 has the same length, in actual application, even if the lengths of the electro-optical modulation segments and the cross waveguide segments are different, it is only necessary to calculate the time for the optical signal to pass through each electro-optical modulation segment and the cross waveguide segment connected to its output end according to the corresponding lengths, and the above-mentioned synchronous modulation process of the present embodiment can still be realized. Therefore, the technical solution of applying the present embodiment and using electro-optical modulation segments and cross waveguide segments of different lengths should still be regarded as falling within the scope of protection of the present invention.

[0068] In this embodiment, the delay module may use an electromagnetic delay line. The electromagnetic delay line determines the signal delay time according to the propagation speed of the electromagnetic wave and the delay distance, and may be a coaxial cable, etc. The electromagnetic delay line material is a nickel-chromium alloy, a copper-aluminum material, a titanium material, etc., that is, a material with a small temperature change is selected to be wound and stretched to achieve time delay. Using an electromagnetic delay line as a delay module to achieve electrical signal delay belongs to the prior art and will not be described in detail here.

[0069] The preferred embodiments of the present invention are described in detail above in conjunction with the accompanying drawings. The embodiments described in the present invention are merely descriptions of the preferred embodiments of the present invention, and do not limit the concept and scope of the present invention. The various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction, and such combinations should also be regarded as the contents disclosed in the present disclosure as long as they do not violate the concept of the present invention. In order to avoid unnecessary repetition, the present invention will not further describe various possible combinations.

[0070] The present invention is not limited to the specific details of the above-mentioned embodiments. Within the technical concept of the present invention and without departing from the design concept of the present invention, various modifications and improvements made to the technical solution of the present invention by technical personnel in this field should fall within the protection scope of the present invention. The technical contents for which protection is sought in the present invention have been fully recorded in the claims.

Claims

1. A thin film lithium niobate electro-optic modulator, characterized in that: A Mach-Zehnder structure formed by a thin-film lithium niobate optical waveguide, wherein the Mach-Zehnder structure comprises a beam splitter section, N electro-optical modulation sections, N-1 cross-waveguide sections, and a beam combiner section, where N is greater than or equal to 2, each electro-optical modulation section comprises two groups of modulation arms, the N electro-optical modulation sections and the N-1 cross-waveguide sections form a series structure, and the modulation arms of adjacent electro-optical modulation sections in the series structure are cross-connected through the cross-waveguide sections; The beam splitter section is connected to the two groups of modulation arms of the first electro-optical modulation section in the series structure as an optical signal input end, and the beam combiner section is connected to the two groups of modulation arms of the last electro-optical modulation section in the series structure as an optical signal output end; the input optical signal enters the beam splitter section and is divided into two beams, and then passes through the two groups of modulation arms of the first electro-optical modulation section one by one, and passes through the other electro-optical modulation sections and the cross waveguide section in sequence, and finally outputs from the two groups of modulation arms of the last electro-optical modulation section to the beam combiner section for beam combining interference, wherein the cross waveguide section makes the optical signals output by the two groups of modulation arms of the previous electro-optical modulation section in the corresponding adjacent electro-optical modulation section cross and enter the two groups of modulation arms of the next electro-optical modulation section; Each electro-optical modulation segment is respectively configured with a modulation electrode, which generates an electrical signal to modulate the phase of the optical signal passing through the two groups of modulation arms in the corresponding electro-optical modulation segment. The electrical signals generated by the modulation electrodes of adjacent electro-optical modulation segments in the series structure have opposite polarities when modulated. The time when the modulation electrodes configured in each electro-optical modulation segment generate the electrical signal is synchronized with the time when the optical signal enters the two groups of modulation arms of the corresponding electro-optical modulation segment.

2. A thin film lithium niobate electro-optic modulator according to claim 1, characterized in that: It also includes an electric signal source, which directly outputs an electric signal to a modulation electrode configured in the first electro-optical modulation segment in the series structure, thereby causing the modulation electrode configured in the first electro-optical modulation segment to generate an electric signal for modulation, and the time when the electric signal source outputs the electric signal to the modulation electrode configured in the first electro-optical modulation segment in the series structure is synchronized with the time when the two light beams output by the beam splitter segment enter the two groups of modulation arms of the first electro-optical modulation segment; The electrical signal source outputs electrical signals to the modulation electrodes configured in each other electro-optical modulation segment through the delay module. The delay module synchronizes the time when the electrical signal source outputs the electrical signal to each other modulation electrode with the time when the optical signal enters the two groups of modulation arms of the corresponding electro-optical modulation segment.

3. A thin film lithium niobate electro-optic modulator according to claim 2, characterized in that: The delay module is an electromagnetic delay line.

4. The thin film lithium niobate electro-optic modulator according to claim 1, characterized in that: The modulation electrode is a GSG electrode, and the signal electrode in the GSG electrode and one of the ground electrodes cooperate to phase modulate the optical signals passing through a group of modulation arms of the corresponding electro-optical modulation segment, and the signal electrode in the GSG electrode and another ground electrode cooperate to phase modulate the optical signals passing through another group of modulation arms of the corresponding electro-optical modulation segment.

5. The thin film lithium niobate electro-optic modulator according to claim 1, characterized in that: The overall shape of each electro-optical modulation segment is U-shaped.

6. A thin film lithium niobate electro-optic modulator according to any one of claims 1 to 5, characterized in that: It also includes a substrate, a buried oxide layer arranged on the substrate, a lithium niobate layer arranged on the buried oxide layer, and a cladding layer arranged on the lithium niobate layer. The Mach-Zehnder structure formed by the thin-film lithium niobate optical waveguide is etched on the lithium niobate layer, and the Mach-Zehnder structure formed by the thin-film lithium niobate optical waveguide is coated by the cladding layer.

7. A thin film lithium niobate electro-optic modulator according to claim 6, characterized in that: The modulation electrode is arranged on the cladding.

8. The thin film lithium niobate electro-optic modulator according to claim 7, characterized in that: The material of the cladding layer is silicon dioxide.

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