Modulator, optical module, and communication device

Abstract

Provided in the embodiments of the present application are a modulator, an optical module, and a communication device, so as to improve the linearity of a modulator for modulating optical signals. The modulator comprises an optical splitter, an optical combiner, a first modulation arm, a second modulation arm, a modulation electrode, a first micro-ring and a second micro-ring, wherein an input end of the optical splitter is connected to a light source, and two output ends of the optical splitter are connected to an input end of the first modulation arm and an input end of the second modulation arm, respectively; an output end of the first modulation arm and an output end of the second modulation arm are connected to two input ends of the optical combiner, respectively; the modulation electrode comprises a signal electrode, a first ground electrode and a second ground electrode; a first straight waveguide of the first micro-ring is coupled to the first modulation arm, and a second straight waveguide of the first micro-ring is arranged between the signal electrode and the first ground electrode; and a first straight waveguide of the second micro-ring is coupled to the second modulation arm, and a second straight waveguide of the second micro-ring is arranged between the signal electrode and the second ground electrode.

Description

Modulator, optical module and communication equipment

[0001] This application claims priority to the Chinese patent application filed with the State Intellectual Property Office on August 30, 2023, with application number 202311113122.7 and application name “A modulator, optical module and communication equipment”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present application relates to the field of communication technology, and in particular to a modulator, an optical module and a communication device. Background Art

[0003] Analog radio-over-fiber (ROF) technology can move components like the digital intermediate frequency (IF) signal from the headend to the motherboard, reducing headend power consumption and size. It is expected to become a key technology for next-generation wireless communications. Analog ROF technology transmits analog RF signals, placing high demands on the modulator's transmission bandwidth and linearity.

[0004] Summary of the Invention

[0005] Embodiments of the present application provide a modulator, an optical module, and a communication device for improving the linearity of an optical signal modulated by the modulator.

[0006] In a first aspect, an embodiment of the present application provides a modulator, which includes: an optical splitter, an optical combiner, a first modulation arm, a second modulation arm, a modulation electrode, a first microring and a second microring; the input end of the optical splitter is connected to a light source, the first output end of the optical splitter is connected to the input end of the first modulation arm, and the second output end of the optical splitter is connected to the input end of the second modulation arm; the output end of the first modulation arm is connected to the first input end of the optical combiner, and the output end of the second modulation arm is connected to the second input end of the optical combiner; the modulation electrode includes a signal electrode, a first ground electrode and a second ground electrode, the first microring includes a first straight waveguide and a second straight waveguide, and the second microring includes a first straight waveguide and a second straight waveguide; the first straight waveguide of the first microring is coupled to the first modulation arm, and the second straight waveguide of the first microring is arranged between the signal electrode and the first ground electrode; the first straight waveguide of the second microring is coupled to the second modulation arm, and the second straight waveguide of the second microring is arranged between the signal electrode and the second ground electrode.

[0007] The modulator provided by the embodiment of the present application adopts a dual-microring assisted Mach-Zehnder modulator structure, and the dual-arm microrings are modulated by the same group of modulation electrodes. A set of electrodes can be used to apply electric fields of exactly the same size and opposite directions to the dual-arm microrings, forming a push-pull structure. The push-pull structure can ensure the elimination or suppression of second-order (and other even-order) distortion. The third-order distortion can be eliminated or suppressed by adjusting the coupling coefficient between the microring and the main modulator. Compared with modulation structures such as dual MZM series-parallel, the insertion loss is smaller and the coupling efficiency is higher. At the same time, the two microrings of the modulator provided by the embodiment of the present application are modulated by the same group of modulation electrodes, and the modulation of the dual microrings can be achieved by one RF signal, which can simplify the modulation structure and ensure the consistency of the RF signals of the dual microrings. The modulation efficiency is higher. Compared with the microring-assisted modulator in which both arm microrings are controlled by electrodes, the microrings of the dual arms of the modulator provided by the embodiment of the present application are modulated by the same modulation electrode, and the phase control stability is better.

[0008] In one possible implementation, the first modulation arm is coupled to the first straight waveguide of the first microring to form a first coupler and a second coupler. The first coupler and the second coupler may be multimode interference couplers. The first coupler, the second coupler, the portion of the first modulation arm between them, and the portion of the first straight waveguide of the first microring together constitute a 2×2 optical beam splitter with an adjustable splitting ratio. By adjusting the phase of the first modulation arm between the first coupler and the second coupler or the phase of the first microring, the coupling coefficient and transmission coefficient between the first microring and the first modulation arm can be adjusted. By adjusting the coupling coefficient and transmission coefficient between the first microring and the first modulation arm, the third-order intermodulation can be eliminated or suppressed.

[0009] In one possible implementation, the modulator further includes a first thermal tuning electrode disposed in the portion of the first straight waveguide of the first microring located between the first coupler and the second coupler. By disposing the first thermal tuning electrode in the portion of the first straight waveguide of the first microring located between the first coupler and the second coupler, the first thermal tuning electrode can heat the first modulator arm. Upon heating, the refractive index of the first modulator arm changes, thereby altering the phase of the optical signal transmitted by the first modulator arm. This can thereby adjust the splitting ratio of the 2×2 optical beam splitter and the transmission coefficient and coupling coefficient of the first microring.

[0010] In one possible implementation, the modulator further includes a first thermal tuning electrode, which is disposed in the portion of the first modulator arm located between the first coupler and the second coupler. The first thermal tuning electrode can be disposed on the first microring between the first coupler and the second coupler, or on the first modulator arm between the first coupler and the second coupler. By disposing the first thermal tuning electrode in the portion of the first modulator arm located between the first coupler and the second coupler, the first thermal tuning electrode can heat the first modulator arm. Upon heating, the refractive index of the first modulator arm changes, thereby altering the phase of the optical signal transmitted by the first modulator arm, thereby adjusting the splitting ratio of the 2×2 optical beam splitter and adjusting the transmission coefficient and coupling coefficient of the first microring.

[0011] In one possible implementation, the second modulation arm couples with the first straight waveguide of the second microring to form a third coupler and a fourth coupler. The upper and lower arms of the modulator provided in this embodiment of the application are symmetrically structured. The first modulation arm couples with the first microring, and the second modulation arm couples with the second microring. Modulation signals of equal magnitude and opposite directions are applied to the microrings, forming a push-pull structure that can offset or suppress second-order and other even-order distortion.

[0012] In a possible implementation, the modulator further includes a second thermal tuning electrode, and the second thermal tuning electrode is disposed at a portion of the first straight waveguide of the second microring located between the third coupler and the fourth coupler.

[0013] In a possible implementation, the modulator further includes a second thermal tuning electrode, and the second thermal tuning electrode is disposed at a portion of the second modulation arm between the third coupler and the fourth coupler.

[0014] In one possible implementation, the modulator further includes a third thermal adjustment electrode, which is arranged in a portion of the first modulation arm between the optical splitter and the first coupler, or in a portion of the first modulation arm between the second coupler and the optical combiner.

[0015] The third thermal adjustment electrode can heat the waveguide of the first modulation arm to adjust the refractive index of the first modulation arm, thereby changing the phase of the optical signal transmitted by the first modulation arm and adjusting the working point of the modulator.

[0016] In a possible implementation, the modulator further includes a third thermal adjustment electrode, which is arranged in the portion of the first modulation arm between the optical splitter and the third coupler, or the third thermal adjustment electrode is arranged in the portion of the second modulation arm between the fourth coupler and the optical combiner.

[0017] The third thermal modulation electrode can be arranged in the first modulation arm or in the second modulation arm, and the effects of both are the same.

[0018] In one possible implementation, the modulation electrode includes a signal input part, a modulation part, and a signal output part, wherein the modulation part is located in the same layer as the first microring and the second microring; the signal input part and the signal output part are located in the upper layer of the first microring and the second microring.

[0019] In one possible implementation, the first modulation arm, the second modulation arm, the first microring, and the second microring are lithium niobate waveguides. Lithium niobate waveguides have excellent electro-optical properties, and their refractive index changes linearly when an electric field is applied, thereby improving modulation accuracy.

[0020] In a second aspect, an embodiment of the present application further provides an optical module, comprising a light source and a modulator provided by any implementation method of the aforementioned first aspect, wherein the light source is used to generate a light beam and transmit the light beam to the modulator; the modulator is used to modulate the light beam to obtain a modulated optical signal.

[0021] In a third aspect, an embodiment of the present application further provides a communication device, comprising a circuit board and an optical module as provided in the second aspect, wherein the optical module is arranged on the circuit board.

[0022] For the description of the technical principles and technical effects of the second and third aspects, please refer to the relevant description of the first aspect and will not be repeated here. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] FIG1 is a schematic diagram of a communication system provided in an embodiment of the present application;

[0024] FIG2 is a schematic diagram of another communication system provided in an embodiment of the present application;

[0025] FIG3 is a schematic diagram of a direct-adjusted RoF provided in an embodiment of the present application;

[0026] FIG4 is a schematic diagram of an external RoF provided in an embodiment of the present application;

[0027] FIG5 is a schematic diagram of a Mach-Zehnder modulator provided in an embodiment of the present application;

[0028] FIG6 is a schematic diagram of the spectrum distribution of intermodulation distortion components and harmonic distortion components provided by an embodiment of the present application;

[0029] FIG7 is a schematic diagram of a parallel Mach-Zehnder modulator provided in an embodiment of the present application;

[0030] FIG8 is a schematic diagram of a main signal and a third-order intermodulation distortion signal provided by an embodiment of the present application;

[0031] FIG9 is a schematic diagram of a microring structure provided in an embodiment of the present application;

[0032] FIG10 is a schematic diagram of a dual microring-assisted Mach-Zehnder modulator provided in an embodiment of the present application;

[0033] FIG11 is a schematic structural diagram of a modulator provided in an embodiment of the present application;

[0034] FIG12 is a schematic diagram of an MMI provided in an embodiment of the present application;

[0035] FIG13 is a schematic diagram of the coupling between the first modulation arm and the first micro-ring provided in an embodiment of the present application;

[0036] FIG14 is another schematic diagram of the coupling between the first modulation arm and the first micro-ring provided in an embodiment of the present application;

[0037] FIG15 is another schematic diagram of the coupling between the first modulation arm and the first micro-ring provided in an embodiment of the present application;

[0038] FIG16 is another schematic diagram of the coupling between the first modulation arm and the first micro-ring provided in an embodiment of the present application;

[0039] FIG17 is a schematic diagram of the coupling between the second modulation arm and the second micro-ring provided in an embodiment of the present application;

[0040] FIG18 is another schematic diagram of the structure of a modulator provided in an embodiment of the present application;

[0041] FIG19 is a schematic diagram of a modulation electrode provided in an embodiment of the present application;

[0042] FIG20 is a schematic diagram of a modulation curve of a modulator provided in an embodiment of the present application;

[0043] FIG21 is a schematic diagram of an optical module provided in an embodiment of the present application. DETAILED DESCRIPTION

[0044] The technical solutions in the embodiments of the present application will be described below in conjunction with the drawings in the embodiments of the present application. In the present application, "at least one" refers to one or more, and "more" refers to two or more. "And / or" describes the association relationship of associated objects, indicating that there may be three relationships. For example, A and / or B can represent: the existence of A alone, the existence of A and B at the same time, and the existence of B alone, where A and B can be singular or plural. "At least one of the following items (individuals)" or similar expressions refers to any combination of these items, including any combination of single items (individuals) or plural items (individuals). For example, at least one of a, b or c can represent: a, b, c, a and b, a and c, b and c or a, b and c, where a, b and c can be single or multiple.

[0045] The embodiments of this application use terms such as "first" and "second" to distinguish objects with similar names, functions, or effects. Those skilled in the art will understand that terms such as "first" and "second" do not limit the quantity or order of execution. The term "coupled" is used to indicate an electrical connection, including direct connection via wires or connectors or indirect connection via other devices. Therefore, "coupling" should be considered a broadly defined electronic communication connection.

[0046] It should be noted that, in this application, words such as "exemplary" or "for example" are used to indicate examples, illustrations, or descriptions. Any embodiment or design described in this application as "exemplary" or "for example" should not be construed as being preferred or advantageous over other embodiments or designs. Rather, the use of words such as "exemplary" or "for example" is intended to present the relevant concepts in a concrete manner.

[0047] An extensible pico base station, also known as a distributed pico base station, is composed of a base band unit (BBU), a remote radio unit hub (RHUB) and a remote radio unit (RRU). RHUB is called a mother end, and RRU is called a head end. Figure 1 shows a schematic diagram of a communication system provided by an embodiment of the present application, including an RHUB and an RRU, wherein the RHUB and the RRU are connected by an optical fiber, the optical fiber is used to transmit digital signals, and the RRU includes a conversion circuit for converting digital signals into analog signals, which are then transmitted through an antenna for users to use. However, with the development of technology, according to statistics, the power consumption of base stations in the 5G era will be several times higher than that in the 4G era. At the same time, for high-frequency scenarios, the bandwidth demand is greater, and the signal quality requirements are getting higher and higher, which leads to an increase in the power consumption and volume of the head end. Analog radio-over-fiber (RoF) technology can move parts such as the digital intermediate frequency from the head end to the mother end, transmit analog signals with high quality, and reduce the power consumption and volume of the head end. It is expected to become a key technology for the next generation of wireless communications.

[0048] RoF is an emerging wireless access technology that combines fiber optic and wireless communications, responding to the demand for high-speed, high-capacity wireless communications. It modulates radio frequency signals into optical signals for transmission. It offers advantages such as long transmission distance, interference resistance, high capacity, and low distortion, and is widely used in mobile communications, satellite communications, remote sensing, and telemetry.

[0049] Figure 2 shows a schematic diagram of another communication system provided in an embodiment of the present application, including an RHUB and an RRU, wherein analog signals are transmitted between the RHUB and the RRU via an analog RoF. Compared with the optical fiber used to transmit digital signals in the communication system shown in Figure 1, the advantage of the solution shown in Figure 2 is that analog signals are transmitted between the RHUB and the RRU via the analog RoF. In this way, a complex digital processing module is no longer required in the RRU, thereby reducing the size and power consumption of the RRU.

[0050] Analog RoF technology transmits analog RF signals, placing high demands on the modulator's transmission bandwidth and linearity. A RoF typically consists of three components: an optical transmitter, an optical fiber, and an optical receiver. A semiconductor laser modulates the RF signal onto an optical carrier at the optical transmitter, which is then transmitted via the optical fiber to the optical receiver. The receiver then demodulates the signal and recovers the original RF signal. Based on the modulation method used for the electrical signal, links can be categorized into two types: direct modulation links and external modulation links.

[0051] Referring to Figure 3, the working principle of the direct modulation link is to load the radio frequency (RF) signal directly onto the laser at the transmitting end. The optical carrier emitted by the laser is modulated by the RF signal to achieve the conversion of the electrical signal into an optical signal. The modulated optical signal is transmitted through the optical fiber to the photodetector at the receiving end, where the photodetector performs photoelectric conversion on it and recovers the electrical signal.

[0052] While direct modulation links are simple, economical, and easy to implement, they suffer from a high noise figure, severely impacting system sensitivity. External modulation links, with their low nonlinear distortion and high modulation rate, complement these shortcomings, and as a result, have been widely researched and applied.

[0053] The difference between an external modulation link and a direct modulation link lies in the way the RF signal is modulated. In an external modulation link, the RF signal is loaded onto a modulator along with an optical signal to convert the electrical signal into an optical signal. Figure 4 shows an external modulation link. An external modulation link primarily consists of three components: a laser, a modulator, and a photodetector. At the transmitter, the modulator modulates the RF signal onto an optical signal emitted by the laser and then transmits it. The modulated optical signal is then transmitted via optical fiber to the photodetector at the receiver, where it undergoes photoelectric conversion to recover the electrical signal. The nonlinearity generated by the modulator in an external modulation link significantly impacts system nonlinearity and is a key focus of research on system nonlinearity.

[0054] The modulator provided in the embodiments of this application can also be referred to as an electro-optic modulator, which refers to a modulator made by utilizing the electro-optic effect of certain electro-optic crystals, such as lithium niobate (LiNbO3). The electro-optic effect is that when a voltage is applied to an electro-optic crystal, the refractive index of the crystal changes, causing the phase of light passing through the crystal to change, thereby modulating the phase, amplitude, intensity, and polarization state of the optical signal.

[0055] Lithium niobate crystal electro-optical modulators offer high bandwidth and a wide transmission wavelength, making them suitable for high-speed signal modulation. However, their drawbacks are bulk and high material cost. Thin-film lithium niobate is achieved by forming lithium niobate into thin sheets, reducing its half-wave voltage, miniaturizing it, and integrating it on-chip, hoping to achieve the same modulation effect as bulk lithium niobate modulators. Thin-film lithium niobate is typically fabricated into a Mach-Zehnder modulator (MZM). A typical MZM structure is shown in FIG5 , and includes an optical splitter, an optical combiner, and two parallel modulator arms (waveguides) disposed between the optical splitter and the optical combiner. Input light is split equally into two paths by the optical splitter, transmitted through symmetrical upper and lower arms, and then output after interference and superposition at the optical combiner. The upper and lower arm waveguides are constructed of electro-optical materials, such as the aforementioned lithium niobate crystal. Therefore, when a modulating electric field is applied to the upper and / or lower arms via electrodes, the refractive index of the lithium niobate waveguide changes linearly under the action of the applied electric field, causing the two optical signals to produce corresponding phase changes. Consequently, the two optical signals transmitted through the upper and lower arms are combined by the optical combiner, whereupon the optical fields interfere and superpose. This phase change is converted into an intensity change, causing the intensity of the output optical signal to vary with the applied electric field.

[0056] Assume that the expression of the modulator input optical signal is:

[0057] Among them, E in (t) is the intensity of the incident light, E0 is the amplitude of the incident light, and ω0 is the frequency of the incident light. After passing through the optical splitter, it is divided into two beams of equal power, E1(t) and E2(t). The expression is:

[0058] The optical signal after modulation of the arm without electrodes is:

[0059] The optical signal after modulation of one arm of the loaded electrode is:

[0060] in, They are the inherent phase changes produced by the two beams of light being modulated by the two arms when no voltage is applied to the electrodes. It indicates the phase change caused by the modulation of an optical signal on an electrode after the electrode is loaded with a modulation signal.

[0061] After passing through the optical combiner, the two beams are combined into one beam. The output optical signal at this time is:

[0062] The above formula can be rewritten as:

[0063] At this time, the output optical power of the modulator can be expressed as:

[0064] In the above formula, I0=E0 2 , It is the inherent phase difference between the two arms of the modulator, which only determines the initial phase of the modulator modulation curve. V π is the half-wave voltage of the modulator, π is defined as the electric field voltage required when the modulated optical carrier phase shifts, V b is the voltage applied to the electrode.

[0065] Typically, the electrodes of a Mach-Zehnder modulator are loaded with two voltages: one is a radio frequency signal, represented by V(t), and the other is a DC voltage, represented by V DC A DC voltage can be used to modify the refractive index of the two arms in the modulator, which will introduce a fixed phase shift in each arm.

[0066] Let V b =V DC +V(t), the output optical power of the modulator can be expressed as:

[0067] As can be seen from the above formula, the modulation curve of the Mach-Zehnder modulator is similar to a trigonometric function curve and is nonlinear. That is, the relationship between the output optical power and the input RF signal is nonlinear.

[0068] For nonlinear systems, signals will be distorted when passing through the nonlinear system. This is mainly reflected in the generation of new frequency components when a single frequency passes through the system. If the generated new frequency components are close to the frequency of the original signal, it is difficult for the filter to filter them out, resulting in interference when the original signal is restored at the receiving end, affecting system performance.

[0069] Taking the Mach-Zehnder modulator as an example, the expression of the power of the output signal of the Mach-Zehnder modulator is:

[0070] For the convenience of calculation, let

[0071] The above formula can be rewritten as:

[0072] make The above formula can be rewritten as:

[0073] When the input is a single tone signal, that is, V(t) = v0cosωt, let At this time, the output optical power of the modulator is:

[0074] In order to analyze the frequency components contained in the output light field, the above formula is expanded into the form of Bessel function:

[0075] J0, J1, J2, etc. are zero-order, first-order, and second-order Bessel functions, respectively. n is a positive integer 1, 2, 3...m is the modulation index. It can be seen that when the input signal is a single-tone signal, only multiple frequencies xω of frequency ω appear. x is a natural number 0, 1, 2, 3...When is the DC component, when x is 1, it is the DC component, when x is 1, it is the fundamental frequency component, when n is 2, 3..., the frequency component xω is called the harmonic component (harmonic distortion, HD) of the signal, the order of the harmonic component is x, cos2ωt is the second harmonic component HD2, cos3ωt is the third harmonic component HD3...

[0076] It can be seen from the above formula that the coefficients of the even-order harmonic components include Therefore, it is only necessary to make The coefficient can be set to 0 to eliminate the even-order harmonic components.

[0077] In practical applications, the modulated signal is often not just a single frequency signal, so it is necessary to analyze the nonlinear distortion of the Mach-Zehnder modulator output in the case of multi-tone signal modulation.

[0078] When the input is a dual-tone signal, that is, V(t) = v1sinω1t + v2sinω2t, let At this time, the output optical power of the modulator is:

[0079] For example, it is convenient to calculate Continuing to expand the above formula into the form of Bessel function, we can get:

[0080] As can be seen from the above formula: In addition to the DC component, fundamental frequency component, and harmonic component nω (where n is a natural number 0, 1, 2, 3...) of the signal, the modulator output also includes various combinations of two frequencies pω1+qω2, where p, q = ±1, ±2, ±3... These frequency components are called intermodulation distortion (IMD) components of the signal. The order of the intermodulation distortion components is |p|+|q|, where p, q = ±1, ±2, ±3... For example, 2ω1-ω2 and 2ω2-ω1 are called third-order intermodulation distortion IMD3. As shown in Table 1:

[0081] Table 1

[0082] Figure 6 shows the spectral distribution of intermodulation distortion and harmonic distortion components, which clearly illustrates the relationship between the various components. Due to the nonlinearity of the modulator, additional nonlinear distortion signals are generated, primarily consisting of second-order harmonic distortion and third-order intermodulation distortion. As can be seen from the figure, the RF signals to be recovered are the fundamental signals ω1 and ω2. Second-order harmonic distortion corresponds to the higher-order distortion signals with frequency components 2ω1 and 2ω2 in the figure. Although second-order harmonic distortion has relatively high energy, its frequency components are far from the fundamental signal and can be directly filtered. Third-order intermodulation distortion (2ω1-ω2 and 2ω2-ω1), while weaker than second-order harmonic distortion, is closest to the fundamental signal, making it difficult to filter directly through post-processing. Therefore, to improve modulator linearity, it is necessary to eliminate or suppress the effects of third-order intermodulation distortion.

[0083] Linearization technology primarily aims to cancel or suppress intermodulation distortion generated by the input signal. There are two main approaches to linearization. One is electrical-domain linearization, or linearization of the electrical signal itself. This involves compensating for inherent nonlinearity in the electrical signal. However, electrical-domain linearization has certain limitations, such as limited bandwidth. Therefore, optical-domain linearization is often employed. Optical-domain linearization manipulates the properties of light and offers greater bandwidth and stability than electrical-domain linearization. Common implementations include push-pull architectures, series-parallel Mach-Zehnder modulators, and micro-ring-assisted approaches.

[0084] The push-pull structure is a type of linearization structure, that is, voltages of equal magnitude and opposite direction are applied to the upper and lower arms. For example, the upper arm of the Mach-Zehnder modulator is modulated by v1, and the lower arm of the Mach-Zehnder modulator is modulated by v2. V1 and v2 are equal in magnitude and opposite in direction, which can make the bias point or operating point of the Mach-Zehnder modulator be At the position of , even-order harmonic distortion can be eliminated.

[0085] Figure 7 shows another linearization approach, employing a parallel Mach-Zehnder modulator (DPMZM) modulation structure, also known as a dual-parallel Mach-Zehnder modulator (DPMZM). The DPMZM modulation structure comprises three Mach-Zehnder modulators (MZM1, MZM2, and MZM3), with MZM1 and MZM2 located in the upper and lower arms of MZM3, respectively. V1 and V2 are the modulation voltages for MZM1 and MZM2, respectively, while V3 is the modulation voltage for MZM3. After entering the DPMZM modulation structure, the lightwave is split into an upper and lower path in the first Y-branch waveguide of MZM3. The upper path is modulated by MZM1, while the lower path is modulated by MZM2. The modulation voltage V3 of MZM3 then introduces a new phase difference between the two output paths. Finally, the two paths are coupled out through the second Y-branch waveguide. In actual use, different modulation effects can be achieved by reasonably setting the modulation voltage and the power distribution ratio of the upper and lower MZMs.

[0086] For example, one of MZM1 and MZM2 can be used as the main modulator, and the other as the auxiliary modulator. Input light is split unequally to the main and auxiliary modulators. The main modulator has a stronger input light intensity, while the auxiliary modulator has a lower light intensity. By adjusting the splitting ratio of the light split to the main and auxiliary modulators, as well as the operating points of the main and auxiliary modulators, the third-order intermodulation distortion (3OMD) output by the main modulator and the auxiliary modulator are made equal in magnitude but opposite in direction. By adjusting the operating point of MZM3, the modulated signals output by MZM1 and MZM2 are coherently canceled, thereby canceling or suppressing the third-order intermodulation.

[0087] DPMZM adjusts the electro-optical modulation transmission curve by adjusting the operating point and the splitting ratio of the two parallel MZMs to achieve the effect of canceling intermodulation terms other than the main signal. However, because odd-order Bessel functions have the same coefficient, when third-order intermodulation is suppressed, the main signal is also suppressed. A similar relationship can be seen in Figure 8, which shows that when the third-order signal is suppressed, the main signal also suffers significant loss. At the same time, due to the thin-film lithium niobate modulator, each additional coupling will increase the insertion loss, resulting in a high insertion loss in the DPMZM structure.

[0088] In addition to the linearization schemes described above, the linearity of the Mach-Zehnder modulator can also be improved with the assistance of a microring. A microring is a type of optical resonator. The common structure of a microring resonator is shown in Figure 9 below. It is usually composed of a straight waveguide and a ring waveguide. When the input light in the straight waveguide passes through the intermediate coupling region, part of the light is coupled into the ring waveguide, while part of the light remains in the straight waveguide. After propagating a circumference, the light coupled into the ring waveguide returns to the coupling region, where part of the light is again coupled into the straight waveguide, while part of the light remains in the ring waveguide, and this cycle repeats. The modulation curve of the microring is also nonlinear. Therefore, the nonlinearity of the microring modulation curve can be used to cancel the nonlinearity of the modulation curve of the Mach-Zehnder modulator, offsetting some of the intermodulation distortion.

[0089] Referring to FIG10 , FIG10 shows a push-pull dual-arm micro-ring assisted Mach-Zehnder modulator. A micro-ring is coupled to the upper and lower arms of the Mach-Zehnder modulator respectively. The same modulation voltage is applied to the upper and lower micro-rings. The signal intermodulation nonlinearity generated by the micro-ring is canceled by the nonlinearity generated by the Mach-Zehnder modulator, thereby realizing the linearization of the transfer function in the optical domain.

[0090] The obvious shortcoming of the push-pull dual-arm microring-assisted Mach-Zehnder modulator is that both microrings need to add modulation signals, which reduces the main signal and leads to relatively low overall gain. In addition, the modulation function is obviously more sensitive to phase. At the same time, both microrings need to add modulation signals, and consistency is difficult to ensure. Therefore, the dual microring structure also requires relatively high control accuracy of the modulator.

[0091] In order to improve the above-mentioned problems, an embodiment of the present application provides a new type of modulator, which uses a push-pull dual-arm micro-ring assisted Mach-Zehnder modulator, wherein the push-pull structure ensures the suppression or cancellation of the second-order intermodulation, and the suppression or cancellation of the third-order intermodulation mainly relies on the micro-ring structure. By adjusting the coupling ratio between the micro-ring and the main modulation arm, the optimal linearization region is obtained to ensure the linearization of the entire transmission function. In addition, the two micro-rings can share the same electrode for modulation, the consistency of the modulation signal can be guaranteed, and the overall control structure is simplified.

[0092] Referring to FIG. 11 , FIG11 shows a modulator 100 provided in an embodiment of the present application, including: an optical splitter 110 , an optical combiner 120 , a first modulation arm 130 , a second modulation arm 140 , a first microring 150 , a second microring 160 and a modulation electrode 170 . The optical splitter 110 is a one-to-two splitter, and the optical combiner 120 is a two-in-one combiner. The input end of the optical splitter 110 is connected to a light source, the first output end of the optical splitter 110 is connected to the first modulator arm 130, and the second output end of the optical splitter 110 is connected to the input end of the second modulator arm 140. The output end of the first modulator arm 130 is connected to the first input end of the optical combiner 120, and the output end of the second modulator arm 140 is connected to the second input end of the optical combiner 120. After passing through the optical splitter 110, the input light is evenly divided into two paths and enters the first modulator arm 130 and the second modulator arm 140 respectively. The light transmitted by the first modulator arm 130 and the second modulator arm 140 are combined when passing through the optical combiner 120 to form a Mach-Zehnder modulator structure. The first microring 150 is a racetrack-type microring, including a first straight waveguide 151 and a second straight waveguide 152. The second microring 160 is also a racetrack-type microring, including a first straight waveguide 161 and a second straight waveguide 162. The first microring 150 and the second microring 160 are modulated using the same group of modulation electrodes 170. For example, the modulation electrode 170 includes a signal electrode 171, a first ground electrode 172, and a second ground electrode 173. The first straight waveguide 151 of the first microring 150 is coupled to the first modulation arm 130, and the second straight waveguide of the first microring 150 is arranged between the signal electrode 171 and the first ground electrode 172. The first straight waveguide 161 of the second microring 160 is coupled to the second modulation arm 140, and the second straight waveguide 162 of the second microring 160 is arranged between the signal electrode 171 and the second ground electrode 173.

[0093] In the modulator 100 provided in the embodiment of the present application, the optical splitter 110, the first modulation arm 130, the second modulation arm 140 and the optical combiner 120 constitute a Mach-Zehnder modulator structure. In order to distinguish it from other modulation structures of the modulator 100 provided in this embodiment, the formed Mach-Zehnder modulator structure is referred to as a main modulator; the main modulator is assisted by a double microring, wherein the first straight waveguide 151 of the first microring 150 is coupled to the upper arm of the main modulator, and the first straight waveguide 161 of the second microring 160 is coupled to the lower arm of the main modulator. The first microring 150 and the second microring 160 are modulated by the same group of modulation electrodes 170, and the modulation electrodes 170 include a signal electrode 171, a first ground electrode 172 and a second ground electrode 173, wherein the second straight waveguide 152 of the first microring 150 is arranged on the signal electrode 171. 171 and the first ground electrode 172, and the second straight waveguide 162 of the second microring 160 is set in the gap between the signal electrode 171 and the second ground electrode 173. In this way, electric fields of exactly the same magnitude and opposite directions can be applied to the first microring 150 and the second microring 160, forming a push-pull structure. A group of modulation electrodes 170 simultaneously and reversely control the refractive index of the straight waveguides in the upper and lower groups of microring tracks to achieve electro-optical modulation function. The push-pull structure can ensure the elimination or suppression of second-order (and other even-order) distortion. The third-order distortion can be canceled or suppressed by adjusting the coupling coefficient between the microring and the main modulator. Compared with modulation structures such as dual MZM series and parallel, the insertion loss of the microring structure is close to that of a single MZM, so the insertion loss is smaller than that of modulation structures such as dual MZM series and parallel, and the coupling efficiency is higher. At the same time, the two micro-rings of the modulator 100 provided in the embodiment of the present application are modulated by the same set of modulation electrodes 170, and the dual micro-rings can be modulated by a single RF signal, which can simplify the modulation structure while ensuring the consistency of the RF signals of the dual micro-rings, resulting in higher modulation efficiency. Compared with a micro-ring-assisted modulator in which both micro-rings in both arms are controlled by electrodes separately, the micro-rings in both arms of the modulator 100 provided in the embodiment of the present application are modulated by the same modulation electrode 170, and the phase control stability is better.

[0094] Illustratively, the first modulation arm 130 , the second modulation arm 140 , the first microring 150 , and the second microring 160 may be made of lithium niobate waveguide, or may be made of other materials having similar electro-optical effects.

[0095] The modulation structures of the upper arm and the lower arm of the modulator 100 provided in the embodiment of the present application are symmetrical. Here, the first modulation arm 130 is first introduced as an example. For example, the modulator 100 provided in the embodiment of the present application eliminates even-order distortion through a push-pull structure, but the third-order distortion requires adjusting the coupling coefficient of the micro-ring to achieve cancellation or suppression.

[0096] In one possible implementation, the first straight waveguide 151 of the first microring 150 is coupled to the first modulator arm 130 to form a first coupler 101 and a second coupler 102. The two coupling nodes, the first coupler 101 and the second coupler 102, divide the first modulator arm 130 into three parts: a first part 130a, a second part 130b, and a third part 130c. The first part 130a of the first modulator arm 130 is located between the optical splitter 110 and the first coupler 101; the second part 130b of the first modulator arm 130 is located between the first coupler 101 and the second coupler 102; and the third part 130c of the first modulator arm 130 is located between the second coupler 102 and the optical combiner 120.

[0097] Similarly, the two coupling nodes of the first coupler 101 and the second coupler 102 also divide the first straight waveguide 151 of the first microring 150 into three parts: a first part 151a, a second part 151b, and a third part 151c, wherein the second part 151b of the first straight waveguide 151 of the first microring 150 is located between the first coupler 101 and the second coupler 102.

[0098] For example, the coupler provided in the embodiments of the present application can be a multi-mode interferometer (MMI). As shown in FIG12 , the MMI can be designed as an MxN structure, i.e., M input ports and N output ports. Common MMI structures include 1x2, 2x2, and 1x4. FIG12 shows a 2×2 MMI.

[0099] In one possible implementation, referring to FIG. 13 , the first coupler 101 includes a first end 101a, a second end 101b, a third end 101c, and a fourth end 101d; the second coupler 102 includes a first end 102a, a second end 102b, a third end 102c, and a fourth end 102d.

[0100] The first end 101a of the first coupler 101 is connected to the first part 130a of the first modulation arm 130, and the second end 101b of the first coupler 101 is connected to the first part 151a of the first straight waveguide 151 of the first microring 150; the third end 101c of the first coupler 101 is connected to the first end 102a of the second coupler 102 through the second part 130b of the first modulation arm 130, the fourth end 101d of the first coupler 101 is connected to the second end 102b of the second coupler 102 through the second part 151b of the first straight waveguide 151, the third end 102c of the second coupler 102 is connected to the third part 130c of the first modulation arm 130, and the fourth end 102d of the second coupler 102 is connected to the third part 151c of the first straight waveguide 151.

[0101] The first coupler 101, the second coupler 102, the second portion 130b of the first modulator arm 130, and the second portion 151b of the first straight waveguide 151 of the first microring 150 together constitute a 2×2 optical beam splitter 103, or can be considered as a sub-stage MZM structure. The first microring 150 is coupled to the first modulator arm 130 through this 2×2 optical beam splitter 103. By adjusting the coupling coefficient and transmission coefficient between the first microring 150 and the first modulator arm 130, the splitting ratio between the first modulator arm 130 and the first microring 150 can be adjusted. Under an appropriate transmission coefficient, a good effect of suppressing third-order intermodulation can be achieved.

[0102] Exemplarily, the embodiment of the present application further includes a first thermal adjustment electrode 104 for adjusting the coupling coefficient k and the transmission coefficient τ between the first micro-ring 150 and the first modulation arm 130, so that the energy conservation law is satisfied without considering the loss: τ 2 +k 2 =1, τ is the transmission coefficient or power transmission coefficient of the microring, which represents the energy directly passed through, that is, the proportion of the light beam from the first part 130a of the first modulator arm 130 directly passing through the 2×2 optical beam splitter 103 to the third part 130c of the first modulator arm 130; k is the coupling coefficient, which represents the proportion of light from the first part 130a of the first modulator arm 130 coupled to the third part 151c of the first straight waveguide 151 through the 2×2 optical beam splitter 103.

[0103] In one possible implementation, referring to FIG. 14 , the first thermal tuning electrode 104 can be disposed in the portion of the first straight waveguide 151 of the first microring 150 located between the first coupler 101 and the second coupler 102. That is, the first thermal tuning electrode 104 can be disposed in the second portion 151b of the first straight waveguide 151. The first thermal tuning electrode 104 can heat the second portion 151b of the first straight waveguide 151. After heating, the refractive index of the second portion 151b of the first straight waveguide 151 changes, thereby changing the phase of the optical signal transmitted by the second portion 151b of the first straight waveguide 151. This can thereby adjust the splitting ratio of the 2×2 optical beam splitter 103 and adjust the transmission coefficient and coupling coefficient between the first microring 150 and the first modulation arm 130.

[0104] In another possible implementation, referring to FIG. 15 , the first thermal tuning electrode 104 can be disposed in a portion of the first modulation arm 130 between the first coupler 101 and the second coupler 102. That is, the first thermal tuning electrode 104 can be disposed in the second portion 130 b of the first modulation arm 130. The first thermal tuning electrode 104 can heat the second portion 130 b of the first modulation arm 130. After heating, the refractive index of the second portion 130 b of the first modulation arm 130 changes, thereby changing the phase of the optical signal transmitted by the second portion 130 b of the first modulation arm 130. This can thereby adjust the splitting ratio of the 2×2 optical beam splitter 103 and the transmission coefficient and coupling coefficient between the first microring 150 and the first modulation arm 130.

[0105] In the above example, the first modulation arm 130 (i.e., the second portion 130b of the first modulation arm 130) between the first coupler 101 and the second coupler 102 and the first microring 150 (i.e., the second portion 151b of the first straight waveguide 151 of the first microring 150) between the first coupler 101 and the second coupler 102 are asymmetric, and the waveguide lengths of the two are different. However, in some other possible implementations, with reference to FIG16 , the second portion 130b of the first modulation arm 130 and the second portion 151b of the first straight waveguide 151 of the first microring 150 may also be symmetrical structures, that is, the lengths of the first modulation arm 130 between the first coupler 101 and the second coupler 102 and the first microring 150 between the first coupler 101 and the second coupler 102 are the same.

[0106] The structures of the upper arm and the lower arm of the modulator 100 are symmetrical. The first microring 150 is coupled to the first modulation arm 130, and correspondingly, the second microring 160 is coupled to the second modulation arm 140. The structures of the second modulation arm 140 and the second microring 160 are similar to the structures of the first modulation arm 130 and the first microring 150. Therefore, the embodiments of the present application are only briefly introduced.

[0107] 11 and 17 , the second modulation arm 140 is coupled to the first straight waveguide 161 of the second microring 160 to form a third coupler 105 and a fourth coupler 106 .

[0108] The two coupling nodes, the third coupler 105 and the fourth coupler 106, divide the second modulator arm 140 into three parts: a first part 140a, a second part 140b, and a third part 140c. The first part 140a of the second modulator arm 140 is located between the optical beam splitter and the third coupler 105; the second part 140b of the second modulator arm 140 is located between the third coupler 105 and the fourth coupler 106; and the third part 140c of the second modulator arm 140 is located between the fourth coupler 106 and the optical combiner 120. Similarly, the two coupling nodes, the third coupler 105 and the fourth coupler 106, divide the first straight waveguide 161 of the second microring 160 into three parts: a first part 161a, a second part 161b, and a third part 161c. The second part 161b of the first straight waveguide 161 of the second microring 160 is located between the third coupler 105 and the fourth coupler 106.

[0109] The first end 105a of the third coupler 105 is connected to the first part 140a of the second modulation arm 140, and the second end 105b of the third coupler 105 is connected to the first part 161a of the first straight waveguide 161 of the second microring 160; the third end 105c of the third coupler 105 is connected to the first end 106a of the fourth coupler 106 through the second part 140b of the second modulation arm 140, the fourth end 105d of the third coupler 105 is connected to the second end 106b of the fourth coupler 106 through the second part 161b of the first straight waveguide 161, the third end 106c of the fourth coupler 106 is connected to the third part 140c of the second modulation arm 140, and the fourth end 106d of the fourth coupler 106 is connected to the third part 161c of the first straight waveguide 161.

[0110] The third coupler 105, the fourth coupler 106, the second portion 140b of the second modulator arm 140, and the second portion 161b of the first straight waveguide 161 of the second microring 160 together form a 2×2 optical beam splitter 107, or can be considered as a sub-stage MZM structure. The second microring 160 is coupled to the second modulator arm 140 via this 2×2 optical beam splitter 107. By adjusting the splitting ratio of the 2×2 optical beam splitter 107, the transmission coefficient and coupling coefficient between the second microring 160 and the second modulator arm 140 can be adjusted. When the transmission coefficient and coupling coefficient are appropriate, the third-order intermodulation can be suppressed.

[0111] Accordingly, the modulator 100 provided in the embodiment of the present application further includes a second thermal tuning electrode 108. In one possible implementation, referring to FIG. 17 , the second thermal tuning electrode 108 can be disposed in the portion of the first straight waveguide 161 of the second microring 160 between the third coupler 105 and the fourth coupler 106. That is, the second thermal tuning electrode 108 can be disposed in the second portion 161b of the first straight waveguide 161. The second thermal tuning electrode 108 can heat the second portion 161b of the first straight waveguide 161. After heating, the refractive index of the second portion 161b of the first straight waveguide 161 changes, thereby changing the phase of the optical signal transmitted by the second portion 161b of the first straight waveguide 161. This can thereby adjust the splitting ratio of the 2×2 optical beam splitter 107 and adjust the transmission coefficient and coupling coefficient between the second microring 160 and the second modulator arm 140.

[0112] In another possible implementation, the second thermal tuning electrode 108 can be disposed in a portion of the second modulation arm 140 between the third coupler 105 and the fourth coupler 106. That is, the second thermal tuning electrode 108 can be disposed in the second portion 140 b of the second modulation arm 140. The second thermal tuning electrode 108 can heat the second portion 140 b of the second modulation arm 140. After heating, the refractive index of the second portion 140 b of the second modulation arm 140 changes, thereby changing the phase of the optical signal transmitted by the second portion 140 b of the second modulation arm 140. This can thereby adjust the splitting ratio of the 2×2 optical beam splitter 107 and adjust the transmission coefficient and coupling coefficient between the second microring 160 and the second modulation arm 140.

[0113] In the above example, the second modulation arm 140 (i.e., the second portion 140b of the second modulation arm 140) between the third coupler 105 and the fourth coupler 106 and the second microring 160 (i.e., the second portion 161b of the first straight waveguide 161 of the second microring 160) between the third coupler 105 and the fourth coupler 106 are asymmetric, and their waveguide lengths are different. However, in some other possible implementations, the second portion 140b of the second modulation arm 140 and the second portion 161b of the first straight waveguide 161 of the second microring 160 may also be symmetrical structures, that is, the lengths of the second modulation arm 140 between the third coupler 105 and the fourth coupler 106 and the second microring 160 between the third coupler 105 and the fourth coupler 106 are the same.

[0114] Although the modulator 100 provided in the embodiment of the present application adopts a symmetrical structure, the first modulator arm 130 and the second modulator arm 140 have the same length and a symmetrical structure, due to process reasons, it cannot be guaranteed that the phase of the same light after passing through the first modulator arm 130 and the second modulator arm 140 is exactly the same. There may be an inherent phase difference, so the operating point of the main modulator also needs to be adjusted.

[0115] Exemplarily, the modulator 100 further includes a third thermal tuning electrode 109. The third thermal tuning electrode 109 can be disposed in the first modulation arm 130, for example, in the first portion 130a or the third portion 130c of the first modulation arm 130. The third thermal tuning electrode 109 can heat the waveguide of the first modulation arm 130 and adjust the refractive index of the first modulation arm 130, thereby changing the phase of the optical signal transmitted by the first modulation arm 130 and adjusting the operating point of the modulator 100.

[0116] In another possible implementation, for example, referring to FIG. 18 , the third thermal tuning electrode 109 may be disposed in the second modulation arm 140, for example, in the first portion 140a or the third portion 140c of the second modulation arm 140. The third thermal tuning electrode 109 may heat the waveguide of the second modulation arm 140 to adjust the refractive index of the second modulation arm 140, thereby changing the phase of the optical signal transmitted by the second modulation arm 140 and adjusting the operating point of the modulator 100.

[0117] The modulator 100 provided in the embodiment of the present application adopts a dual-microring-assisted Mach-Zehnder modulator. The upper arm and the lower arm of the Mach-Zehnder modulator are respectively coupled with a microring. For example, the first microring 150 is coupled with the first modulation arm 130, and the second microring 160 is coupled with the second modulation arm 140. The first microring 150 and the second microring 160 are modulated by the same set of modulation electrodes 170.

[0118] Continuing with Figure 18, modulation electrode 170 includes a signal electrode 171, a first ground electrode 172, and a second ground electrode 173. First ground electrode 172, signal electrode 171, and second ground electrode 173 are arranged sequentially, without contact, and in the same orientation as the upper and lower arms of the main modulator. Modulation electrode 170 can be used to modulate the microrings. For example, electric fields of equal magnitude and opposite directions are applied to first microring 150 and second microring 160, thereby changing the refractive index of first microring 150 and second microring 160 and modulating the RF signal onto the optical signal.

[0119] Exemplarily, the modulation electrode 170 is arranged between the first modulation arm 130 and the second modulation arm 140, and the first ground electrode 172, the signal electrode 171 and the second ground electrode 173 are arranged in sequence, or it can be considered that the first ground electrode 172 and the second ground electrode 173 are respectively located on both sides of the signal electrode 171, the second straight waveguide 152 of the first microring 150 is arranged between the signal electrode 171 and the first ground electrode 172, and the second straight waveguide 162 of the second microring 160 is arranged between the signal electrode 171 and the second ground electrode 173. In this way, the second straight waveguide 152 of the first microring 150 is arranged between the signal electrode 171 and the second ground electrode 173. The first ground electrode 172 applies an electric field; the second straight waveguide 162 of the second microring 160 is set in the electric field applied by the signal electrode 171 and the second ground electrode 173, wherein the signal electrode 171 is used to connect the radio frequency signal, the first ground electrode 172 and the second ground electrode 173 are grounded, and the first microring 150 and the second microring 160 are modulated by the same group of modulation electrodes 170, and electric fields of the same magnitude and opposite directions can be applied to the first microring 150 and the second microring 160, which simplifies the modulation structure of the first microring 150 and the second microring 160, and can ensure the consistency of the radio frequency signals of the two microrings, thereby improving the control accuracy.

[0120] Referring to Figures 18 and 19 , the modulation electrode 170 can be divided into a signal input portion 170A, a modulation portion 170B, and a signal output portion 170C, which are connected in sequence. The signal input portion 170A is used to input signals, the modulation portion 170B is used to modulate the first microring 150 and the second microring 160, and the signal output portion 170C is used to output signals. To ensure effective modulation, the modulation portion 170B can be located on the same layer as the waveguides of the modulator 100 (e.g., the first modulation arm 130, the second modulation arm 140, the first microring 150, and the second microring 160). The signal input part 170A and the signal output part 170C can be located on the upper layer of the waveguide. In addition, the signal input part 170A and the signal output part 170C of the modulation electrode 170 need to be provided with an interface to access or output signals. Therefore, in order to save space, the signal input part 170A and the signal output part 170C of the modulation electrode 170 can be set on the same side of the modulator 100, rather than across different sides of the modulator 100.

[0121] In addition, in the above example, the modulator 100 provided in the embodiment of the present application adopts a traveling wave electrode. In some other possible implementations, a lumped electrode may also be adopted.

[0122] In some other possible implementations, the optical splitter 110 and the optical combiner 120 provided in the embodiments of the present application may adopt a multimode interference coupler (eg, a 1*2 multimode interference coupler), a Y-shaped structure, and the like.

[0123] The dual microring-assisted modulator provided in the embodiment of the present application uses two microrings to assist the first modulation arm 130 and the second modulation arm 140 respectively. The structure is symmetrical and has a response to the optical wavelength similar to that of a traditional single Mach-Zehnder modulator, and similar insertion loss. It has the advantage of low insertion loss like a single Mach-Zehnder modulator. At the same time, compared with a single microring-assisted modulator, due to its good symmetry, it is relatively insensitive to the optical wavelength response. In addition, since the microring structure has no 3dB loss at the operating point, the microring size is similar to that of the Mach-Zehnder modulator, there is no re-coupling with the optical fiber, and the coupling path is similar to that of the Mach-Zehnder modulator. Compared with the series-parallel Mach-Zehnder modulator, the coupling efficiency is high. In addition, the dual microring-assisted modulator provided in the embodiment of the present application uses a set of modulation electrodes 170 to simultaneously control the two microrings, which has high modulation efficiency and good phase control stability compared with a microring-assisted modulator in which both arms are controlled by electrodes.

[0124] Combined with Figure 20, Figure 20 shows a schematic diagram of the relationship between the output curve and the transmission coefficient of the modulator provided in an embodiment of the present application, wherein the output curve of the conventional MZM shows obvious nonlinearity. Combined with Figure 20, it can be seen that by adjusting the transmission coefficient, the output of the modulator can be made approximately linear under appropriate transmission coefficient conditions.

[0125] In one possible implementation, the output function of the modulator provided in the embodiment of the present application can be expressed as the following formula:

[0126] In the above formula, I in is the input light, I out is the output light, τ is the transmission coefficient, θ is the single cycle modulation phase of the micro-ring, and I out Taking the third-order derivative at θ = 0, we can get:

[0127] Let the third order be 0, and the transmission coefficient and coupling coefficient can be obtained as:

[0128] Therefore, the transmission coefficient of the microring is adjusted to be 2 When =0.25, the third-order intermodulation can be offset or suppressed, and the linearity of the modulator output signal can be improved.

[0129] Based on the modulator provided in the aforementioned example, referring to FIG. 21 , an embodiment of the present application further provides an optical module 20, comprising a light source 210 and a modulator 220. The modulator 220 may be the modulator 100 provided in the aforementioned example. The light source 210 is configured to generate a light beam and transmit the light beam to the modulator 220. The modulator 220 is configured to modulate the light beam to obtain a modulated optical signal. For example, the light beam may be modulated according to a radio frequency signal. In one possible implementation, the light source 210 may be a semiconductor laser.

[0130] An embodiment of the present application also provides a communication device. For example, the communication device can be an RHUB or RRU as provided in the aforementioned example, or it can also be any communication device that needs to transmit an analog signal. The communication device includes a circuit board and an optical module as provided in the aforementioned example. The optical module can use a radio frequency signal to modulate an optical signal and transmit the analog signal through an optical fiber.

[0131] The above description is merely a specific embodiment of the present application, but the scope of protection of the present application is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in this application should be included in the scope of protection of this application. Therefore, the scope of protection of this application should be based on the scope of protection of the claims.

Claims

1. A modulator, characterized in that: The modulator comprises: An optical splitter, an optical combiner, a first modulation arm, a second modulation arm, a modulation electrode, a first micro-ring and a second micro-ring; The input end of the optical splitter is connected to a light source, the first output end of the optical splitter is connected to the input end of the first modulation arm, and the second output end of the optical splitter is connected to the input end of the second modulation arm; The output end of the first modulation arm is connected to the first input end of the optical combiner, and the output end of the second modulation arm is connected to the second input end of the optical combiner; The modulation electrode includes a signal electrode, a first ground electrode and a second ground electrode, the first microring includes a first straight waveguide and a second straight waveguide, and the second microring includes a first straight waveguide and a second straight waveguide; The first straight waveguide of the first microring is coupled to the first modulation arm, and the second straight waveguide of the first microring is arranged between the signal electrode and the first ground electrode; The first straight waveguide of the second microring is coupled to the second modulation arm, and the second straight waveguide of the second microring is arranged between the signal electrode and the second ground electrode.

2. The modulator according to claim 1, characterized in that The first modulation arm is coupled to the first straight waveguide of the first micro-ring to form a first coupler and a second coupler.

3. The modulator according to claim 2, characterized in that The modulator further includes a first thermal tuning electrode, which is disposed at a portion of the first straight waveguide of the first microring between the first coupler and the second coupler.

4. The modulator according to claim 2, characterized in that The modulator further includes a first thermal tuning electrode, which is disposed at a portion of the first modulation arm between the first coupler and the second coupler.

5. The modulator according to any one of claims 1 to 4, characterized in that: The second modulation arm is coupled to the first straight waveguide of the second micro-ring to form a third coupler and a fourth coupler.

6. The modulator according to claim 5, characterized in that The modulator further includes a second thermal tuning electrode, which is disposed at a portion of the first straight waveguide of the second microring between the third coupler and the fourth coupler.

7. The modulator according to claim 5, characterized in that The modulator further includes a second thermal tuning electrode, which is disposed at a portion of the second modulation arm between the third coupler and the fourth coupler.

8. The modulator according to any one of claims 2 to 7, characterized in that: The modulator further comprises a third thermal tuning electrode, which is arranged at a portion of the first modulation arm between the optical splitter and the first coupler, or the third thermal tuning electrode is arranged at a portion of the first modulation arm between the second coupler and the optical combiner.

9. The modulator according to any one of claims 1 to 7, characterized in that: The modulator further comprises a third thermal tuning electrode, which is arranged at a portion of the first modulation arm between the optical splitter and the third coupler, or the third thermal tuning electrode is arranged at a portion of the second modulation arm between the fourth coupler and the optical combiner.

10. The modulator according to any one of claims 1 to 9, characterized in that: The modulation electrode includes a signal input part, a modulation part and a signal output part, wherein the modulation part is located in the same layer as the first microring and the second microring; the signal input part and the signal output part are located in the upper layer of the first microring and the second microring.

11. The modulator according to any one of claims 1 to 10, characterized in that: The first modulation arm, the second modulation arm, the first microring, and the second microring are lithium niobate waveguides.

12. An optical module, characterized in that: A device comprising a light source and a modulator as claimed in any one of claims 1 to 11, wherein the light source is used to generate a light beam and transmit the light beam to the modulator; The modulator is used to modulate the light beam to obtain a modulated light signal.

13. A communication device, characterized in that: It comprises a circuit board and the optical module as claimed in claim 12, wherein the optical module is arranged on the circuit board.

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