Modulator, optical module and communication equipment

Abstract

The embodiment of the invention provides a modulator, an optical module and communication equipment, which are used for improving the linearity of an optical signal modulated by the modulator. 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 with a light source, and two output ends of the optical splitter are respectively connected with the input end of the first modulation arm and the input end of the second modulation arm; the output end of the first modulation arm and the output end of the second modulation arm are respectively connected with two input ends of the optical combiner; 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 with 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; the first straight waveguide of the second micro-ring is coupled with the second modulation arm, and the second straight waveguide of the second micro-ring is arranged between the signal electrode and the second ground electrode.

Description

Technical Field

[0001] 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

[0002] Analog radio-over-fiber (ROF) technology can move digital intermediate frequency and other parts from the head end to the mother end, reducing the power consumption and volume of the head end, and is expected to become a key technology for the next generation of wireless communications. Analog ROF technology transmits analog RF signals and has high requirements for the transmission bandwidth and linearity of the modulator. Summary of the invention

[0003] Embodiments of the present application provide a modulator, an optical module, and a communication device to improve the linearity of an optical signal modulated by the modulator.

[0004] In the 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.

[0005] The modulator provided in the embodiment of the present application adopts a dual-micro-ring assisted Mach-Zehnder modulator structure, and the dual-arm micro-rings are modulated by the same group of modulation electrodes. A set of electrodes can be used to apply an electric field of exactly the same size and opposite direction to the dual-arm micro-rings, forming a push-pull structure. The push-pull structure can ensure the elimination or suppression of the second-order (and other even-order) distortion. The third-order distortion can be eliminated or suppressed by adjusting the coupling coefficient between the micro-ring and the main modulator. Compared with the modulation structure such as the dual MZM series-parallel connection, the insertion loss is smaller and the coupling efficiency is higher. At the same time, the two micro-rings of the modulator provided in the embodiment of the present application are modulated by the same group of modulation electrodes, and the modulation of the dual micro-rings can be achieved by one radio frequency signal, which can simplify the modulation structure, and at the same time ensure the consistency of the radio frequency signals of the dual micro-rings, and the modulation efficiency is higher. Compared with the micro-ring assisted modulator in which the dual-arm micro-rings are respectively controlled by electrodes, the micro-rings of the dual arms of the modulator provided in the embodiment of the present application are modulated by the same modulation electrode, and the phase control stability is better.

[0006] In a possible implementation, the first modulation arm is coupled with 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, and the first coupler, the second coupler, and the portion of the first modulation arm therebetween, 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, transmission coefficient, etc. between the first microring and the first modulation arm may be adjusted, and by adjusting the coupling coefficient, transmission coefficient, etc. between the first microring and the first modulation arm, the third-order intermodulation amount may be eliminated or suppressed.

[0007] In a possible implementation, the modulator further includes a first thermal adjustment electrode, which is arranged at a portion of the first straight waveguide of the first microring between the first coupler and the second coupler. By arranging the first thermal adjustment electrode at a portion of the first straight waveguide of the first microring between the first coupler and the second coupler, the first thermal adjustment electrode can heat the first modulation arm, and after heating, the refractive index of the first modulation arm will change, so that the phase of the optical signal transmitted by the first modulation arm can be changed, thereby adjusting the splitting ratio of the 2×2 optical beam splitter and adjusting the transmission coefficient and coupling coefficient of the first microring.

[0008] In a possible implementation, the modulator further includes a first thermal adjustment electrode, which is arranged at a portion of the first modulation arm between the first coupler and the second coupler. The first thermal adjustment electrode can be arranged on the first micro-ring between the first coupler and the second coupler, or can be arranged on the first modulation arm between the first coupler and the second coupler. By arranging the first thermal adjustment electrode on the portion of the first modulation arm between the first coupler and the second coupler, the first thermal adjustment electrode can heat the first modulation arm, and after heating, the refractive index of the first modulation arm will change, so that the phase of the optical signal transmitted by the first modulation arm can be changed, so that the splitting ratio of the 2×2 optical beam splitter can be adjusted, and the transmission coefficient and coupling coefficient of the first micro-ring can be adjusted.

[0009] In a possible implementation, the second modulation arm is coupled with the first straight waveguide of the second micro-ring to form a third coupler and a fourth coupler. The upper and lower arms of the modulator provided in the embodiment of the present application have symmetrical structures, the first modulation arm is coupled with the first micro-ring, the second modulation arm is coupled with the second micro-ring, and modulation signals of the same magnitude and opposite directions are applied to the micro-ring to form a push-pull structure, which can offset or suppress second-order and other even-order distortions.

[0010] 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.

[0011] 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.

[0012] In a possible implementation, the modulator further includes a third thermal tuning electrode, which is disposed at a portion of the first modulation arm between the optical splitter and the first coupler, or at a portion of the first modulation arm between the second coupler and the optical combiner.

[0013] 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.

[0014] In a possible implementation, the modulator further includes a third thermal tuning electrode, which is disposed at a portion of the first modulation arm between the optical splitter and the third coupler, or at a portion of the second modulation arm between the fourth coupler and the optical combiner.

[0015] The third heat modulation electrode can be arranged in the first modulation arm, or can also be arranged in the second modulation arm, and the effects of both are the same.

[0016] In a possible implementation, the modulation electrode includes a signal input part, a modulation part and a signal output part, wherein the modulation part and the first microring and the second microring are located in the same layer; the signal input part and the signal output part are located in the upper layer of the first microring and the second microring.

[0017] In a possible implementation, the first modulation arm, the second modulation arm, the first microring, and the second microring are lithium niobate waveguides. The lithium niobate waveguide has good electro-optical properties, and its refractive index changes linearly when an electric field is applied thereto, thereby improving modulation accuracy.

[0018] 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 first aspect, wherein the light source is used to generate a light beam and transmit the light beam to the modulator; and the modulator is used to modulate the light beam to obtain a modulated light signal.

[0019] In a third aspect, an embodiment of the present application further provides a communication device, including a circuit board and an optical module as provided in the second aspect, wherein the optical module is arranged on the circuit board.

[0020] For the description of the technical principles and technical effects of the second and third aspects, reference may be made to the relevant description of the first aspect and will not be repeated here. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 A schematic diagram of a communication system provided in an embodiment of the present application;

[0022] Figure 2 A schematic diagram of another communication system provided in an embodiment of the present application;

[0023] Figure 3 A schematic diagram of a direct adjustment RoF provided in an embodiment of the present application;

[0024] Figure 4 A schematic diagram of an external RoF provided in an embodiment of the present application;

[0025] Figure 5 A schematic diagram of a Mach-Zehnder modulator provided in an embodiment of the present application;

[0026] Figure 6 A schematic diagram of the spectrum distribution of the intermodulation distortion component and the harmonic distortion component provided in the embodiment of the present application;

[0027] Figure 7 A schematic diagram of a parallel Mach-Zehnder modulator provided in an embodiment of the present application;

[0028] Figure 8 A schematic diagram of a main signal and a third-order intermodulation distortion signal provided in an embodiment of the present application;

[0029] Fig. 9 A schematic diagram of a micro-ring structure provided in an embodiment of the present application;

[0030] Fig.10 A schematic diagram of a dual micro-ring assisted Mach-Zehnder modulator provided in an embodiment of the present application;

[0031] Fig.11 A schematic diagram of the structure of a modulator provided in an embodiment of the present application;

[0032] Fig.12 A schematic diagram of the MMI provided in an embodiment of the present application;

[0033] Fig.13 A schematic diagram of coupling between a first modulation arm and a first micro-ring provided in an embodiment of the present application;

[0034] Fig.14 Another schematic diagram of coupling between the first modulation arm and the first micro-ring provided in an embodiment of the present application;

[0035] Fig.15Another schematic diagram of coupling between the first modulation arm and the first micro-ring provided in an embodiment of the present application;

[0036] Fig.16 Another schematic diagram of coupling between the first modulation arm and the first micro-ring provided in an embodiment of the present application;

[0037] Fig.17 A schematic diagram of coupling between a second modulation arm and a second micro-ring provided in an embodiment of the present application;

[0038] Fig.18 Another structural schematic diagram of a modulator provided in an embodiment of the present application;

[0039] Fig.19 A schematic diagram of a modulation electrode provided in an embodiment of the present application;

[0040] Fig. 20 A schematic diagram of a modulation curve of a modulator provided in an embodiment of the present application;

[0041] Fig.21 A schematic diagram of an optical module provided in an embodiment of the present application. DETAILED DESCRIPTION

[0042] 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 "plurality" refers to two or more. "And / or" describes the association relationship of associated objects, indicating that three relationships may exist. 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" or its similar expressions refers to any combination of these items, including any combination of single or plural items. 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.

[0043] The embodiments of the present application use words such as "first" and "second" to distinguish objects with similar names, functions or effects. Those skilled in the art will understand that words such as "first" and "second" do not limit the quantity and execution order. The term "coupled" is used to indicate electrical connection, including direct connection through wires or connection terminals or indirect connection through other devices. Therefore, "coupled" should be regarded as a broad electronic communication connection.

[0044] 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 as "exemplary" or "for example" in this application should not be interpreted as being more preferred or more advantageous than other embodiments or designs. Specifically, the use of words such as "exemplary" or "for example" is intended to present related concepts in a specific way.

[0045] The scalable pico base station, also known as a distributed pico base station, consists of a base band unit (BBU), a remote radio unit hub (RHUB) and a remote radio unit (RRU). The RHUB is called the mother end and the RRU is called the head end. Figure 1 A schematic diagram of a communication system provided by an embodiment of the present application is shown, including RHUB and RRU, wherein RHUB and RRU are connected by optical fiber, optical fiber is used to transmit digital signals, and RRU includes a conversion circuit for converting digital signals into analog signals, which are then transmitted through antennas 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 and other 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 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, which is expected to become a key technology for the next generation of wireless communications.

[0046] RoF is a new wireless access technology that combines optical fiber communication and wireless communication and has been developed to meet the needs of high-speed and large-capacity wireless communication. It modulates radio frequency electrical signals into optical signals for transmission. It has the advantages of long transmission distance, anti-interference, large capacity, and low distortion. It is widely used in mobile communications, satellite communications, remote sensing and telemetry, etc.

[0047] Figure 2 A schematic diagram of another communication system provided by an embodiment of the present application is shown, including an RHUB and an RRU, wherein an analog signal is transmitted between the RHUB and the RRU via an analog RoF. Figure 1 The optical fiber used in the communication system shown transmits digital signals. Figure 2 The advantage of the solution shown is that analog signals are transmitted between the RHUB and the RRU through the analog RoF, so that a complex digital processing module is no longer required in the RRU, thereby reducing the size and power consumption of the RRU.

[0048] The analog ROF technology transmits analog RF signals, which has high requirements on the transmission bandwidth and linearity of the modulator. ROF usually consists of three parts: optical transmitter, optical fiber and optical receiver. The semiconductor laser modulates the RF signal onto the optical carrier at the optical transmitter, which is transmitted to the optical receiver via the optical fiber. The optical receiver recovers the original RF signal through demodulation. According to the different modulation methods of the electrical signal, there are two types of links: direct modulation link and external modulation link.

[0049] See also Figure 3 The working principle of the direct modulation link is to load the radio frequency signal (RF) directly onto the laser at the transmitting end. The optical carrier emitted by the laser is modulated by the radio frequency signal to realize the conversion of electrical signal to optical signal. The modulated optical signal is transmitted through the optical fiber to the photodetector at the receiving end. The photodetector performs photoelectric conversion on it to restore the electrical signal.

[0050] Although the direct modulation link is simple, economical and easy to implement, the noise coefficient of the link is large, which seriously affects the sensitivity of the system. The external modulation link has the characteristics of small nonlinear distortion and high modulation rate, which just makes up for the shortcomings of the direct modulation link. Therefore, this modulation method has been widely studied and applied.

[0051] The difference between external modulation links and direct modulation links lies in the way the RF signal is modulated. In an external modulation link, the RF signal is loaded onto the modulator together with the optical signal to achieve the conversion from electrical signal to optical signal. Figure 4 As shown. The external modulation link mainly consists of three parts: laser, modulator and photodetector. At the transmitting end, the RF signal is modulated by the modulator onto the optical signal emitted by the laser and then sent. The modulated optical signal is transmitted through the optical fiber to the photodetector at the receiving end, where the photodetector performs photoelectric conversion to restore the electrical signal. The nonlinearity generated by the modulator in the external modulation link has a greater impact on the nonlinearity of the system and is also the focus of the study of system nonlinearity problems.

[0052] The modulator provided in the embodiment of the present application may also be referred to as an electro-optic modulator, which refers to a modulator that utilizes certain electro-optic crystals, such as lithium niobate crystals (LiNbO 3 ) is a modulator made by the electro-optic effect. The electro-optic effect means that when voltage is applied to the electro-optic crystal, the refractive index of the electro-optic crystal will change, causing the phase of the light passing through the crystal to change, thereby modulating the phase, amplitude, intensity and polarization state of the optical signal.

[0053] Among them, lithium niobate crystal electro-optic modulators have a large bandwidth and a wide transmitted light band, and can be used for high-speed modulation of signals. However, their disadvantages are large size and high material cost. Thin-film lithium niobate is made into thin sheets, reduces its half-wave voltage, reduces its size, and integrates it on-chip in the hope of achieving the same modulation effect as bulk lithium niobate modulators. Thin-film lithium niobate is usually made into a Mach-Zehnder modulator (MZM). The typical Mach-Zehnder modulator structure is as follows: Figure 5 As shown, it includes an optical splitter, an optical combiner, and two parallel modulation arms (waveguides) arranged between the optical splitter and the optical combiner. The input light is evenly divided into two paths by the optical splitter, transmitted through the symmetrical upper arm and lower arm, and then output after interference superposition at the optical combiner. The upper arm and lower arm waveguides are made of electro-optical materials, such as the above-mentioned lithium niobate crystal. Therefore, when the upper arm and / or the lower arm apply a modulated electric field through the electrode, the refractive index of the lithium niobate waveguide will change linearly under the action of the external electric field, thereby causing the two optical signals to produce corresponding phase changes. Therefore, the two optical signals transmitted through the upper and lower arms are combined by the optical combiner, and the optical fields are interfered and superimposed. The phase change will be converted into intensity change, so that the light intensity of the output optical signal changes with the change of the external electric field.

[0054] Assume that the expression of the modulator input optical signal is:

[0055]

[0056] Among them, E in (t) is the intensity of the incident light, E 0 is the amplitude of the incident light, ω 0 is the frequency of the incident light. After passing through the optical splitter, it is divided into two beams of equal power, upper and lower beams E 1 (t) and E 2 (t), the expression is:

[0057]

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

[0059]

[0060] The optical signal after modulation of one arm of the loaded electrode is:

[0061]

[0062] in, They are the inherent phase changes of the two beams after being modulated by the two arms without applying voltage to the electrodes. It indicates the phase change of an optical signal provided with an electrode after being modulated after the electrode is loaded with a modulation signal.

[0063] After passing through the optical combiner, the two beams are combined into one beam, and the output optical signal at this time is:

[0064]

[0065] The above formula can be rewritten as:

[0066]

[0067] At this time, the output optical power of the modulator can be expressed as:

[0068]

[0069] In the above formula, I 0 =E 0 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.

[0070] Usually, the electrodes of the Mach-Zehnder modulator are usually loaded with two voltages, one is the RF signal, represented by V(t), and the other is the 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.

[0071] Let V b =V DC +V(t), the output optical power of the modulator can be expressed as:

[0072]

[0073] It can be seen from the above formula that 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.

[0074] 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.

[0075] Taking the Mach-Zehnder modulator as an example, the expression of the power of the output signal of the Mach-Zehnder modulator is:

[0076]

[0077] For the convenience of calculation, let

[0078] The above formula can be rewritten as:

[0079]

[0080] make The above formula can be rewritten as:

[0081]

[0082] When the input is a single tone signal, that is, V(t) = v 0 cosωt, let At this time, the output optical power of the modulator is:

[0083]

[0084] In order to analyze the frequency components contained in the output light field, the above formula is expanded into the form of Bessel function:

[0085]

[0086] J 0 , J 1 , J 2 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 the multiple frequencies xω of the frequency ω appear. x is a natural number 0, 1, 2, 3...when is a DC component, when x is 1, it is a DC component, when x is 1, it is a 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, cos2xω is the second harmonic component HD2, cos3ωt is the third harmonic component HD3...

[0087] 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 even-order harmonic components.

[0088] 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.

[0089] When the input is a dual-tone signal, that is, V(t) = v 1 sinω 1 t+v 2sinω 2 t, let At this time, the output optical power of the modulator is:

[0090]

[0091] For example, it is convenient to calculate, so Continue to expand the above formula into the form of Bessel function, we can get:

[0092]

[0093] It can be seen from the above formula that the output of the modulator contains not only the DC component, fundamental frequency component, harmonic component nω (where n is a natural number 0, 1, 2, 3...) of the signal, but also various combinations of two frequencies pω 1 +qω 2 , 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|, p, q = ±1, ±2, ±3... For example, 2ω 1 -ω 2 , 2ω 2 -ω 1 It is called third-order intermodulation distortion IMD3. As shown in Table 1:

[0094]

[0095] Table 1

[0096] Figure 6 The spectral distribution of intermodulation distortion components and harmonic distortion components, from which the relationship between the components can be intuitively seen. Due to the nonlinearity of the modulator, additional nonlinear distortion signals will be generated. These distortion signals mainly include second-order harmonic distortion and third-order intermodulation distortion. As can be seen from the figure, the RF signal we want to recover is the baseband signal ω 1 ,ω 2 , where the second harmonic distortion corresponds to the frequency component in the figure as 2ω 1 and 2ω 2 Although the second-order harmonic distortion energy is relatively strong, the frequency component is far away from the baseband signal and can be directly filtered through the filter. 1 -ω 2 , 2ω 2 -ω 1 Although their energy is relatively weaker than the second-order harmonic distortion, they are closest to the baseband signal and are therefore difficult to filter directly by adding a filter later. Therefore, in order to improve the linearity of the modulator, it is necessary to eliminate or suppress the influence of the third-order intermodulation distortion.

[0097] The main content of linearization technology is to cancel or suppress the intermodulation distortion generated by the input signal. There are two main types of linearization technology. One type of linearization technology is electrical domain linearization, or the linearization of the electrical signal itself, which is to compensate for the nonlinearity of the electrical signal itself. However, the electrical domain linearization method has certain limitations, such as small bandwidth. Therefore, in most cases, optical domain linearization technology is often used. Optical domain linearization technology regulates the characteristics of light. Compared with the electrical domain linearization method, it has a large bandwidth and strong stability. The general implementation methods include push-pull structure, series-parallel Mach-Zehnder modulator, micro-ring assistance, etc.

[0098] The push-pull structure is a type of linearization structure, that is, equal voltages in opposite directions are applied to the upper and lower arms. 1 Modulate the upper arm of the Mach-Zehnder modulator using v 2 Modulate the lower arm of the Mach-Zehnder modulator, v 1 With v 2 The magnitude is equal and the direction is opposite, which can make the bias point or operating point of the Mach-Zehnder modulator At the position of , even-order harmonic distortion can be eliminated.

[0099] Figure 7 Another linearization method is shown, which uses the modulation structure of a parallel Mach-Zehnder modulator, also known as a dual-parallel Mach-Zehnder modulator (DPMZM). The modulation structure of the parallel Mach-Zehnder modulator includes three Mach-Zehnder modulators MZM1, MZM2 and MZM3, where MZM1 and MZM2 are located in the upper and lower arms of MZM3 respectively. V1 and V2 are the modulation voltages of MZM1 and MZM2 respectively, and V3 is the modulation voltage of MZM3. After the light wave enters the modulation structure of the parallel Mach-Zehnder modulator, it is divided into an upper path and a lower path in the first Y-type branch waveguide of MZM3. The upper path light is modulated by MZM1, and the lower path light is modulated by MZM2. After that, the two output lights will each introduce a new phase difference due to the modulation voltage V3 of MZM3, and finally the two lights are coupled and output in the second Y-type 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.

[0100] For example, one of MZM1 and MZM2 can be used as the main modulator, and the other can be used as the auxiliary modulator. The input light is split into two modulators, the main modulator has a strong input light, and the auxiliary modulator has a small light intensity. By adjusting the splitting ratio of the main modulator and the auxiliary modulator, and adjusting the working points of the main modulator and the auxiliary modulator, the third-order intermodulation distortion output by the main modulator and the third-order intermodulation distortion output by the auxiliary modulator are the same in magnitude and opposite in direction. By adjusting the working point of MZM3, the modulated signal output by MZM1 and the modulated signal output by MZM2 are coherently cancelled, and the third-order intermodulation amount can be offset or suppressed.

[0101] DPMZM adjusts the electro-optical modulation transmission curve by adjusting the working point and the splitting ratio of the two parallel MZMs to achieve the effect of canceling the intermodulation terms except the main signal. However, since the odd-order Bessel function has the same coefficient, when the third-order intermodulation is suppressed, the main signal is also suppressed. Similar relationships can be referred to Figure 8 It can be seen that when the third-order signal is suppressed, the main signal also suffers a large loss. At the same time, due to the thin-film lithium niobate modulator, each additional coupling will cause additional insertion loss, so the DPMZM structure has a large insertion loss.

[0102] In addition to the above linearization schemes, the linearity of the Mach-Zehnder modulator can also be improved by using microrings. Microrings are a type of optical resonator. The common structure of microring resonators is as follows: Fig. 9 As shown, 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 to the ring waveguide, and part of the light is retained in the straight waveguide. After the light coupled into the ring waveguide propagates for a circumference, it comes to the coupling region again, and part of the light is coupled into the straight waveguide, and part of the light is retained in the ring waveguide, and this is repeated. The modulation curve of the microring is also nonlinear, so the nonlinearity of the modulation curve of the microring can be used to cancel the nonlinearity of the modulation curve of the Mach-Zehnder modulator to offset part of the intermodulation distortion.

[0103] See also Fig.10 As shown, Fig.10 A push-pull two-arm micro-ring assisted Mach-Zehnder modulator is shown. 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, and the transfer function is linearized in the optical domain.

[0104] The obvious shortcoming of the push-pull dual-arm microring assisted Mach-Zehnder modulator is that both microrings need to add modulation signals, which leads to a reduction in the main signal, resulting in a relatively low overall gain, and the modulation function is obviously more sensitive to the phase. At the same time, both microrings need to add modulation signals, and consistency is difficult to ensure. Therefore, the dual microring structure also has relatively high requirements on the control accuracy of the modulator.

[0105] In order to improve the above problems, an embodiment of the present application provides a new type of modulator, which uses a push-pull double-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 area is obtained to ensure the linearization of the entire transmission function, and the two micro-rings can share the same electrode for modulation, so the consistency of the modulation signal can be guaranteed, simplifying the overall control structure.

[0106] See also Fig.11 , Fig.11 The modulator 100 provided in an embodiment of the present application is shown, 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 modulation arm 130, the second output end of the optical splitter 110 is connected to the input end of the second modulation arm 140, the output end of the first modulation arm 130 is connected to the first input end of the optical combiner 120, and the output end of the second modulation 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, entering the first modulation arm 130 and the second modulation arm 140 respectively. The light transmitted by the first modulation arm 130 and the second modulation arm 140 is 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 by 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.

[0107] 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 the present embodiment, the formed Mach-Zehnder modulator structure is called a main modulator; the main modulator is assisted by a double micro-ring, wherein the first straight waveguide 151 of the first micro-ring 150 is coupled to the upper arm of the main modulator, and the first straight waveguide 161 of the second micro-ring 160 is coupled to the lower arm of the main modulator, the first micro-ring 150 and the second micro-ring 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 micro-ring 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 slit between the signal electrode 171 and the second ground electrode 173, so that the electric fields of the same magnitude and opposite directions can be applied to the first microring 150 and the second microring 160, forming a push-pull structure. The refractive index of the straight waveguides in the upper and lower groups of microring tracks is reversely controlled by a group of modulation electrodes 170 to realize the electro-optical modulation function. The push-pull structure can ensure the elimination or suppression of the 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 the modulation structure such as the dual MZM series-parallel connection, the insertion loss of the microring structure is close to that of the single MZM, and the insertion loss is smaller than that of the modulation structure such as the dual MZM series-parallel connection, 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 group of modulation electrodes 170, and the modulation of the two micro-rings can be achieved with one RF signal, which can simplify the modulation structure and ensure the consistency of the RF signals of the two micro-rings, and the modulation efficiency is higher. Compared with the micro-ring assisted modulator in which the two-arm micro-rings are respectively controlled by electrodes, the two-arm micro-rings 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.

[0108] Exemplarily, 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.

[0109] 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. By way of 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.

[0110] In a possible implementation, the first straight waveguide 151 of the first microring 150 is coupled to the first modulation arm 130 to form the first coupler 101 and the second coupler 102. The two coupling nodes of the first coupler 101 and the second coupler 102 divide the first modulation arm 130 into three parts: a first part 130a, a second part 130b and a third part 130c, wherein the first part 130a of the first modulation arm 130 is located between the optical splitter 110 and the first coupler 101; the second part 130b of the first modulation arm 130 is located between the first coupler 101 and the second coupler 102; and the third part 130c of the first modulation arm 130 is located between the second coupler 102 and the optical combiner 120.

[0111] 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.

[0112] For example, the coupler provided in the embodiment of the present application may be a multi-mode interference coupler (multi-mode inferometer, MMI), such as Fig.12 As shown in the figure, MMI can be designed as MxN type, that is, M input ports and N output ports. Commonly used MMI structures include 1x2, 2x2, 1x4, etc. Fig.12 A 2x2 MMI is shown.

[0113] In one possible implementation, see Fig.13 The first coupler 101 includes a first end 101a, a second end 101b, a third end 101c and a fourth end 101d, and the second coupler 102 includes a first end 102a, a second end 102b, a third end 102c and a fourth end 102d.

[0114] 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.

[0115] The first coupler 101, the second coupler 102, the second part 130b of the first modulation arm 130, and the second part 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-level MZM structure. The first microring 150 is coupled to the first modulation arm 130 through the 2×2 optical beam splitter 103. By adjusting the coupling coefficient and transmission coefficient between the first microring 150 and the first modulation arm 130, the splitting ratio of the first modulation arm 130 and the first microring 150 can be adjusted. Under a suitable transmission coefficient, a better effect of suppressing the third-order intermodulation can be achieved.

[0116] 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, and satisfying the energy conservation law without considering the loss: τ 2 +k 2 =1, τ is the transmission coefficient or power transfer 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 modulation arm 130 directly passing through the 2×2 optical beam splitter 103 to the third part 130c of the first modulation arm 130; k is the coupling coefficient, which represents the proportion of the light from the first part 130a of the first modulation arm 130 coupled to the third part 151c of the first straight waveguide 151 through the 2×2 optical beam splitter 103.

[0117] In one possible implementation, see Fig.14 The first thermal tuning electrode 104 can be arranged in the part of the first straight waveguide 151 of the first microring 150 between the first coupler 101 and the second coupler 102, that is, the first thermal tuning electrode 104 can be arranged in the second part 151b of the first straight waveguide 151. The first thermal tuning electrode 104 can heat the second part 151b of the first straight waveguide 151. After heating, the refractive index of the second part 151b of the first straight waveguide 151 will change, so that the phase of the optical signal transmitted by the second part 151b of the first straight waveguide 151 can be changed, so that the splitting ratio of the 2×2 optical beam splitter 103 can be adjusted, and the transmission coefficient and coupling coefficient between the first microring 150 and the first modulation arm 130 can be adjusted.

[0118] In another possible implementation, see Fig.15The first thermal tuning electrode 104 can be arranged at the 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 arranged at the second portion 130b of the first modulation arm 130. The first thermal tuning electrode 104 can heat the second portion 130b of the first modulation arm 130. After heating, the refractive index of the second portion 130b of the first modulation arm 130 will change, so that the phase of the optical signal transmitted by the second portion 130b of the first modulation arm 130 can be changed, so that the splitting ratio of the 2×2 optical beam splitter 103 can be adjusted, and the transmission coefficient and coupling coefficient between the first microring 150 and the first modulation arm 130 can be adjusted.

[0119] 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, in combination with Fig.16 The second part 130b of the first modulation arm 130 and the second part 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.

[0120] 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, and 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, so the embodiments of the present application are only briefly introduced.

[0121] Please combine Fig.11 and Fig.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 .

[0122] The two coupling nodes, the third coupler 105 and the fourth coupler 106, divide the second modulation arm 140 into three parts: a first part 140a, a second part 140b and a third part 140c, wherein the first part 140a of the second modulation arm 140 is located between the optical beam splitter and the third coupler 105; the second part 140b of the second modulation arm 140 is located between the third coupler 105 and the fourth coupler 106; and the third part 140c of the second modulation 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, also 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, wherein 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.

[0123] 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.

[0124] The third coupler 105, the fourth coupler 106, the second part 140b of the second modulation arm 140, and the second part 161b of the first straight waveguide 161 of the second microring 160 together constitute 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 modulation arm 140 through the 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 modulation arm 140 can be adjusted. Under the condition of appropriate transmission coefficient and coupling coefficient, the effect of suppressing the third-order intermodulation can be achieved.

[0125] Accordingly, the modulator 100 provided in the embodiment of the present application further includes a second thermal adjustment electrode 108. In a possible implementation, see Fig.17The second thermal tuning electrode 108 can be arranged in the part 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 arranged in the second part 161b of the first straight waveguide 161, and the second thermal tuning electrode 108 can heat the second part 161b of the first straight waveguide 161. After heating, the refractive index of the second part 161b of the first straight waveguide 161 will change, so that the phase of the optical signal transmitted by the second part 161b of the first straight waveguide 161 can be changed, so that the splitting ratio of the 2×2 optical beam splitter 107 can be adjusted, and the transmission coefficient and coupling coefficient between the second microring 160 and the second modulation arm 140 can be adjusted.

[0126] In another possible implementation, the second thermal tuning electrode 108 can be disposed at 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 at the second portion 140b of the second modulation arm 140. The second thermal tuning electrode 108 can heat the second portion 140b of the second modulation arm 140. After heating, the refractive index of the second portion 140b of the second modulation arm 140 will change, thereby changing the phase of the optical signal transmitted by the second portion 140b of the second modulation arm 140, thereby adjusting the splitting ratio of the 2×2 optical beam splitter 107, and adjusting the transmittance coefficient and coupling coefficient between the second microring 160 and the second modulation arm 140.

[0127] In the above example, the second modulation arm 140 between the third coupler 105 and the fourth coupler 106 (that is, the second part 140b of the second modulation arm 140) and the second microring 160 between the third coupler 105 and the fourth coupler 106 (that is, the second part 161b of the first straight waveguide 161 of the second microring 160) are asymmetric, and the waveguide lengths of the two are different. However, in some other possible implementations, the second part 140b of the second modulation arm 140 and the second part 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.

[0128] Although the modulator 100 provided in the embodiment of the present application adopts a symmetrical structure, the first modulation arm 130 and the second modulation 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 modulation arm 130 and the second modulation arm 140 is exactly the same, and there may be an inherent phase difference, so it is also necessary to adjust the operating point of the main modulator.

[0129] Exemplarily, the modulator 100 further includes a third thermal tuning electrode 109, which 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.

[0130] In another possible implementation, see, for example Fig.18 The third thermal tuning electrode 109 can be set in the second modulation arm 140, for example, in the first part 140a or the third part 140c of the second modulation arm 140. The third thermal tuning electrode 109 can heat the waveguide of the second modulation arm 140 and 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 working point of the modulator 100.

[0131] The modulator 100 provided in the embodiment of the present application adopts a dual micro-ring assisted Mach-Zehnder modulator, wherein the upper arm and the lower arm of the Mach-Zehnder modulator are respectively coupled with a micro-ring, for example, wherein the first micro-ring 150 is coupled with the first modulation arm 130, and the second micro-ring 160 is coupled with the second modulation arm 140, and the first micro-ring 150 and the second micro-ring 160 are modulated by the same group of modulation electrodes 170.

[0132] Please continue to combine Fig.18 The modulation electrode 170 includes a signal electrode 171, a first ground electrode 172 and a second ground electrode 173. The first ground electrode 172, the signal electrode 171 and the second ground electrode 173 are arranged in sequence without contacting each other, and their arrangement direction is the same as the arrangement direction of the upper and lower arms of the main modulator. The microring can be modulated by the modulation electrode 170, for example, an electric field of the same magnitude and opposite direction is applied to the first microring 150 and the second microring 160, thereby changing the refractive index of the first microring 150 and the second microring 160, and modulating the radio frequency signal to the optical signal.

[0133] Exemplarily, the modulation electrode 170 is disposed between the first modulation arm 130 and the second modulation arm 140, 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 disposed between the signal electrode 171 and the first ground electrode 172, and the second straight waveguide 162 of the second microring 160 is disposed 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 disposed 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 arranged 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.

[0134] Please refer to Fig.18 and Fig.19 , the modulation electrode 170 can be divided into a signal input part 170A, a modulation part 170B and a signal output part 170C which are connected in sequence, wherein the signal input part 170A is used to input a signal, the modulation part 170B is used to modulate the first microring 150 and the second microring 160, and the signal output part 170C is used to output a signal. In order to ensure the modulation effect, the modulation part 170B can be located at the same layer as the waveguide of the modulator 100 (such as the first modulation arm 130, the second modulation arm 140, the first microring 150 and the second microring 160, etc.). The signal input part 170A and the signal output part 170C can be located at 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 a signal. 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.

[0135] In addition, in the above example, the modulator 100 provided in the embodiment of the present application adopts a traveling wave electrode, and in some other possible implementations, a lumped electrode may also be adopted.

[0136] 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 multi-mode interference coupler (eg, a 1*2 multi-mode interference coupler), a Y-type structure, and the like.

[0137] The dual micro-ring assisted modulator provided in the embodiment of the present application uses two micro-rings to assist the first modulation arm 130 and the second modulation arm 140 respectively, and has a symmetrical structure, and has a similar response to the wavelength of light as the traditional single Mach-Zehnder modulator, and similar insertion loss. It has the advantage of low insertion loss as the single Mach-Zehnder modulator, and at the same time, compared with the single micro-ring assisted modulator, due to its good symmetry, it is relatively insensitive to the response to the wavelength of light. In addition, since the micro-ring structure has no 3dB loss at the working point, the size of the micro-ring is similar to that of the Mach-Zehnder modulator, and it is not coupled with the optical fiber again. The coupling path is similar to that of the Mach-Zehnder modulator, and the coupling efficiency is high compared with the series-parallel Mach-Zehnder modulator. In addition, the dual micro-ring assisted modulator provided in the embodiment of the present application uses a group of modulation electrodes 170 to control two micro-rings at the same time, and has high modulation efficiency. Compared with the micro-ring assisted modulator in which both arms are controlled by electrodes, the phase control stability is good.

[0138] Combination Fig. 20 , Fig. 20 The relationship between the output curve and the transmission coefficient of the modulator provided in the embodiment of the present application is shown in FIG. 1 , wherein the output curve of the conventional MZM shows obvious nonlinearity. Fig. 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.

[0139] In a possible implementation, the output function of the modulator provided in the embodiment of the present application can be expressed as the following formula:

[0140]

[0141] 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 obtain:

[0142]

[0143] Let the third order be 0, and the transmission coefficient and coupling coefficient can be obtained as:

[0144]

[0145] Therefore, the transmission coefficient of the microring is adjusted to 2 When =0.25, the third-order intermodulation can be offset or suppressed, thereby improving the linearity of the modulator output signal.

[0146] Based on the modulator provided in the previous example, see Fig.21The embodiment of the present application further provides an optical module 20, which includes a light source 210 and a modulator 220. The modulator 220 here can be the modulator 100 provided in the above example, wherein the light source 210 is used to generate a light beam and transmit the light beam to the modulator 220; the modulator 220 is used to modulate the light beam to obtain a modulated light signal, for example, the light beam can be modulated according to a radio frequency signal. In a possible implementation, the light source 210 can be a semiconductor laser.

[0147] An embodiment of the present application also provides a communication device. For example, the communication device may be an RHUB or an RRU as provided in the aforementioned example, or may 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 may modulate an optical signal using a radio frequency signal and transmit the analog signal through an optical fiber.

[0148] The above is only a specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any person skilled in the art who is familiar with the present technical field can easily think of changes or substitutions within the technical scope disclosed in the present application, which should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be based on the protection scope 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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