Monolithic integrated wide-narrow passband reconfigurable electro-optical modulator

Abstract

The invention relates to a monolithic integrated wide-narrow passband reconfigurable electro-optical modulator, and belongs to the field of electro-optical modulators. The optical modulator comprises a substrate, and a tunable optical splitter, a dual-output intensity modulator, a phase modulator, a tunable optical attenuator, a first optical combiner and a second optical combiner which are integrated on the substrate. Wherein the input end of the tunable optical splitter receives an input optical signal, and the output end of the tunable optical splitter is respectively connected with the input ends of the dual-output intensity modulator and the phase modulator; the first output end of the dual-output intensity modulator is connected with the input end of the second optical combiner, and the second output end of the dual-output intensity modulator is connected with the input end of the tunable optical attenuator; the output end of the phase modulator and the output end of the tunable optical attenuator are both connected with the input end of the first optical combiner, and the output end of the first optical combiner is connected with the input end of the second optical combiner. And the output end of the second optical combiner outputs a modulated optical signal.

Description

Technical Field

[0001] The invention belongs to the field of electro-optic modulators and relates to a monolithically integrated wide-narrow passband reconfigurable electro-optic modulator. Background Art

[0002] The electro-optic modulator is the core functional device for realizing the conversion of microwave signals into light wave signals. Typical electro-optic modulators (such as Mach-Zehnder modulator, MZM) use an optical interference structure to change the interference state by injecting microwave signals to realize the modulation conversion of microwave amplitude to light intensity. Conventional electro-optic modulators use a dual-waveguide interference structure combined with the high electro-optic coefficient of lithium niobate, and have ultra-large bandwidth and ultra-low loss electro-optic modulation capabilities. However, due to the limitations of the sinusoidal response curve, the linearity of current electro-optic modulators is greatly insufficient.

[0003] At present, a large number of structures and methods have been proposed to simply improve the dynamics. Although the designed structures, such as the series-parallel interference structure and the single dual-drive structure, have achieved higher dynamics, due to the use of the dual-drive method, it is difficult for current electrical devices to achieve accurate and continuous power distribution over a wide frequency range, and therefore they do not have ultra-wideband working capabilities. In addition, the micro-ring-assisted MZI structure cannot meet ultra-wideband applications due to the narrowband response limitations of the micro-ring resonant cavity.

[0004] Since the contradiction between instantaneous bandwidth and dynamics cannot be overcome at present, current modulators can only work in a single mode. There is no wide-narrow tunable modulator to meet the needs of microwave photonic processing systems for optimal matching of bandwidth and dynamics in different mission scenarios. Summary of the invention

[0005] In view of this, the purpose of the present invention is to provide a monolithic integrated wide and narrow passband reconfigurable electro-optical modulator to achieve wide and narrow passband tuning and simultaneously achieve optimal dynamics matching the wide and narrow bands to meet the needs of multifunctional integrated applications.

[0006] In order to achieve the above object, the present invention provides the following technical solutions:

[0007] A monolithic integrated wide-narrow passband reconfigurable electro-optic modulator can achieve large dynamic range and broadband applications by switching between broadband and narrowband working modes. The electro-optic modulator includes a substrate, and a tunable optical splitter, a dual-output intensity modulator, a phase modulator, a tunable optical attenuator, a first optical combiner and a second optical combiner integrated on the substrate.

[0008] Among them, the input end of the tunable optical splitter receives the input optical signal, and the output end is respectively connected to the input ends of the dual-output intensity modulator and the phase modulator; the first output end of the dual-output intensity modulator is connected to the input end of the second optical combiner, and the second output end is connected to the input end of the tunable optical attenuator; the output ends of the phase modulator and the tunable optical attenuator are both connected to the input end of the first optical combiner, and the output end of the first optical combiner is connected to the input end of the second optical combiner; the output end of the second optical combiner outputs the modulated optical signal.

[0009] Furthermore, the electro-optic modulator works in the narrowband mode as follows: the splitting ratio of the tunable optical splitter is set to 1:a 2 ; The second RF input port of the dual-output intensity modulator is connected to a DC signal, so that the dual-output intensity modulator works at the maximum point; the phase modulator modulates the optical phase of the input optical signal by 180°; the attenuation power of the tunable optical attenuator is set to A 2 ; The splitting ratio of the first optical combiner and the second optical combiner is set to 50:50.

[0010] In narrowband mode, the following conditions must also be met:

[0011]

[0012] Where, L MZM represents the optical insertion loss of the dual-output intensity modulator, L PM It represents the optical insertion loss of the phase modulator. By setting the optical insertion loss of the dual-output intensity modulator and the phase modulator to satisfy the above formula, the third-order intermodulation signal of the electro-optical modulator can be eliminated and the modulation linearity can be improved.

[0013] Furthermore, the electro-optic modulator works in broadband mode as follows: the splitting ratio of the tunable optical splitter is set to 1:0; the second RF input port of the dual-output intensity modulator is connected to a DC signal, so that the dual-output intensity modulator works at the quadrature point; the tunable optical attenuator attenuates the input optical signal to 0; the splitting ratios of the first optical combiner and the second optical combiner are both set to 50:50. At this time, the electro-optic modulator is equivalent to a conventional MZM, and when it works at the quadrature point, the second harmonic is suppressed, which can support broadband applications.

[0014] Furthermore, the substrate is made of silicon or thin film lithium niobate.

[0015] The beneficial effects of the present invention are as follows: the present invention outputs a modulated signal at one end and an additional distortion at one end equal to the inherent nonlinear distortion component through a dual-output intensity modulator, and achieves the purpose of nonlinear suppression through the mutual cancellation of the distortion components. The present invention does not need to perform amplitude modulation or phase modulation on the input RF signal, and only realizes linearization in the optical domain, which solves the problem of limited working bandwidth of the system due to the use of dual drive; the present invention realizes wide and narrow tunable and dynamic matching through tunable structural units, which can meet the application requirements of multi-functional integration.

[0016] Other advantages, objectives and features of the present invention will be described in the following description to some extent, and to some extent, will be obvious to those skilled in the art based on the following examination and study, or can be taught from the practice of the present invention. The objectives and other advantages of the present invention can be realized and obtained through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention will be described in detail below in conjunction with the accompanying drawings, wherein:

[0018] Figure 1 A schematic diagram of the basic architecture of a wide-narrow passband reconfigurable electro-optic modulator provided by an embodiment of the present invention;

[0019] Figure 2 This is the relationship between IIP3 and half-wave voltage in narrow-band working mode obtained by Matlab simulation software;

[0020] Figure 3 This is the relationship between SFDR3 and input optical power in narrowband working mode obtained by Matlab simulation software;

[0021] Figure 4 This is the relationship between SFDR3 and input optical power in broadband working mode obtained by Matlab simulation software;

[0022] Figure 5 Schematic diagram of the basic architecture of a monolithically integrated wide- and narrow-bandwidth reconfigurable electro-optic modulator based on thin-film lithium niobate. DETAILED DESCRIPTION

[0023] The following describes the embodiments of the present invention by specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the illustrations provided in the following embodiments only illustrate the basic concept of the present invention in a schematic manner, and the following embodiments and features in the embodiments can be combined with each other without conflict.

[0024] like Figure 1 As shown, a monolithically integrated wide-narrow passband reconfigurable electro-optical modulator is provided in one embodiment of the present invention, which integrates a tunable optical splitter, a dual-output intensity modulator, a phase modulator, a tunable optical attenuator, a first optical combiner and a second optical combiner on a single chip.

[0025] The input light is divided into two paths by a tunable optical splitter and injected into a dual-output intensity modulator and a phase modulator respectively; the second output port of the dual-output intensity modulator is connected to a tunable optical attenuator and then input into a first optical combiner together with the output of the phase modulator; the first output port of the dual-output intensity modulator is input into a second optical combiner together with the output of the first optical combiner and then output after being combined. In addition, the first RF port of the dual-output intensity modulator is used to access an RF modulation signal, the second RF port of the dual-output intensity modulator is used to access a first DC power supply signal, and the RF port of the phase modulator is used to access a second DC power supply signal.

[0026] The working mode of the electro-optic modulator provided in this embodiment in the narrowband mode is as follows: the tunable optical splitter is adjusted according to 1 / a 2 The optical split ratio is divided into an uplink light and a downlink light; the second RF port of the dual-output intensity modulator is connected to the first DC power supply signal, so that the dual-output intensity modulator works at the maximum point; the phase modulator modulates the optical phase of the input optical carrier by 180°; the attenuation power of the tunable optical attenuator is A 2 ; The splitting ratio of the first optical combiner and the second optical combiner is 50:50.

[0027] Assume that the optical signal E input to the tunable optical splitter is LD The expression of (t) is:

[0028]

[0029] Among them, P op represents the optical power of the input optical signal, ω c Represents the angular frequency of the input optical signal.

[0030] The expression of the input RF signal is:

[0031] V(t)=V RF cos(ω RF t)

[0032] Among them, ω RF is the angular frequency of the RF signal, V RF Indicates the voltage value of the RF signal.

[0033] After passing through the tunable optical splitter, the optical signals of the two arms can be expressed as:

[0034]

[0035] Where (1+a 2 )P=P op , a 2 Indicates the splitting ratio of the tunable splitter.

[0036] The added light is injected into the dual-output intensity modulator. After being modulated by the RF signal, the output signals of the two channels of the dual-output intensity modulator can be expressed as:

[0037]

[0038] Where, L MZM represents the optical insertion loss of the dual-output intensity modulator; is the bias point of the dual output intensity modulator, is the modulation depth. DC represents the DC bias voltage loaded on the dual output intensity modulator, V π Represents the half-wave voltage of the dual output intensity modulator. Set the dual output intensity modulator to zero The output signals of the upper and lower arms of the dual-output intensity modulator can be obtained by Taylor series expansion:

[0039]

[0040] E MZM2 (t) After attenuation, it is represented as C*. C* and the output signal of the phase modulator (represented as C) are combined by the first combiner to obtain the optical local oscillator signal E LO (t):

[0041]

[0042] in, A represents the amplitude attenuation value of the tunable attenuator, L PM Represents the optical insertion loss of the phase modulator.

[0043] The optical field after the optical local oscillator signal and the upper arm signal output by the dual-output intensity modulator pass through the second combiner is:

[0044]

[0045] The detected output photocurrent expression is:

[0046]

[0047] Where r represents the detection responsivity. The third-order intermodulation term exists in the cubic term of V(t). When the cubic term of V(t) is eliminated, the third-order intermodulation no longer exists in the signal, that is:

[0048]

[0049] According to the definition of IIP3, the expression of IIP3 is derived:

[0050]

[0051] Among them, R s represents the input impedance of the modulator, and it is known that When the value is taken, IIP3 can be infinite in theory, improving linearity.

[0052] The expression for spurious-free dynamic range is:

[0053]

[0054] Among them, SFDR represents the spurious-free dynamic range of the microwave photonic system, and the unit is dB·Hz 2 / 3 ; IIP3 represents the input third-order intercept point, in dBm; NF represents the noise factor, in dB. Since IIP3 can be infinite, it can improve linearity and increase the dynamic range of the link.

[0055] Furthermore, the modulator works in broadband mode as follows: the tunable optical splitter divides the uplink light and the downlink light into optical splitting ratios of 1:0; the second RF port of the dual-output intensity modulator is connected to the first DC power supply signal, so that the dual-output intensity modulator works at the quadrature point; the tunable optical attenuator attenuates the downlink output of the dual-output intensity modulator to 0; the splitting ratio of the first optical combiner and the second optical combiner is 50:50. At this time, the electro-optical modulator is equivalent to a conventional MZM modulator, which suppresses the second harmonic when it works at the quadrature point and can support broadband applications.

[0056] There are many values ​​that satisfy the cancellation of third-order intermodulation. The following takes a specific link as an example to illustrate this embodiment.

[0057] The system design parameters used in the embodiment are as follows: the optical insertion loss of the dual-output intensity modulator is 3dB, and the half-wave voltage is 5V; the optical insertion loss of the phase modulation is negligible and is 0dB; and the detection responsivity is 0.6A / W.

[0058] In narrowband, in order to satisfy the condition that the third-order intermodulation is cancelled, the splitting ratio of the tunable optical splitter is set to 50:50, that is, a = 1; the power attenuation of the tunable optical attenuator is set to A 2 =9dB.

[0059] The link design was numerically simulated and verified by MATLAB simulation software, and the relationship between IIP3 and half-wave voltage was obtained as follows: Figure 2 The conventional MZM modulator has an IIP3 of 23dBm, while the narrowband high linear electro-optical modulation provided by this embodiment can reach an IIP3 of 51.06dBm when the half-wave voltage is 5V, that is, after adopting the structure of this embodiment, the IIP3 is increased by 28dB, and the corresponding SFDR is increased by 18dB, thereby greatly improving the linearity of the modulation.

[0060] The relationship between SFDR and the optical power input to the modulator is as follows: Figure 3 As shown, it can be seen that the modulator can achieve 128dB.Hz when the input optical power is 20dBm. 2 / 3 The SFDR of the modulator is improved by nearly 18dB compared with the conventional intensity modulator.

[0061] In broadband mode, the splitting ratio of the tunable optical splitter is 100:0, i.e. a = 0; the power attenuation of the tunable attenuator is A 2 =60dB.

[0062] The relationship between SFDR and the optical power input to the modulator is as follows: Figure 4 As shown, the input optical power is 27dBm and the SFDR is 115dB*Hz 2 / 3 ; At this time, the modulator needs to have a high tolerance optical power.

[0063] The wide-narrow passband reconfigurable electro-optic modulator of the present invention can be monolithically integrated on silicon material or thin-film lithium niobate material. Figure 5 As shown in the figure, an electro-optic modulator based on a thin-film lithium niobate chip is composed of five basic units:

[0064] The tunable optical splitter is composed of 1×2MMI and 2×2 directional coupler, and the splitting tuning is achieved by tuning the phase arm. The dual-output intensity modulator is composed of 1×2MMI branch, modulated by thin-film lithium niobate ridge optical waveguide, and then outputs dual signals through 2×2 directional coupler. This unit is the core unit of RF loading and is required to achieve high-frequency broadband intensity modulation. The phase modulation is composed of thin-film lithium niobate optical waveguide and electrodes to complete the phase modulation of the carrier. The attenuator is composed of two 1×2MMIs. A wide range of optical power adjustment is achieved by tuning the phase arm to ensure accurate control of the beam combining amplitude. The combiner adopts a 1×2MMI structure.

[0065] The present invention utilizes both ends of a dual-output modulator, one end generates a modulation signal, and the other end is used to construct additional distortion equal to the inherent nonlinear distortion component, and the purpose of nonlinear suppression is achieved by the mutual cancellation of distortion components. Compared with architectures such as dual-drive MZM, dual parallel / serial modulators, and dual parallel polarization modulation, this architecture only needs to use a single drive method, without the need to modulate the input RF signal by amplitude or phase, and only achieves linearization in the optical domain, solving the problem of limited working bandwidth of the system due to the dual-drive method. Wide and narrow tunability and dynamic matching are achieved through tunable structural units. In narrowband working mode, the dynamic range is improved by an order of magnitude while the power consumption of a conventional MZM modulator is equivalent.

[0066] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solution, which should be included in the scope of the claims of the present invention.

Claims

1. A monolithic integrated wide-narrow passband reconfigurable electro-optic modulator, which realizes large dynamic range and broadband application by switching the broadband and narrowband working modes of the electro-optic modulator, characterized in that: The electro-optic modulator comprises a substrate, and a tunable optical splitter, a dual-output intensity modulator, a phase modulator, a tunable optical attenuator, a first optical combiner and a second optical combiner integrated on the substrate; The input end of the tunable optical splitter receives an input optical signal, and the output end is respectively connected to the input ends of the dual-output intensity modulator and the phase modulator; the first output end of the dual-output intensity modulator is connected to the input end of the second optical combiner, and the second output end is connected to the input end of the tunable optical attenuator; the output ends of the phase modulator and the tunable optical attenuator are both connected to the input end of the first optical combiner, and the output end of the first optical combiner is connected to the input end of the second optical combiner; the output end of the second optical combiner outputs a modulated optical signal.

2. The electro-optic modulator according to claim 1, characterized in that The working mode of the electro-optic modulator in the narrowband mode is as follows: the splitting ratio of the tunable optical splitter is set to 1:a 2 ; The second RF input port of the dual-output intensity modulator is connected to a DC signal, so that the dual-output intensity modulator works at the maximum point; the phase modulator modulates the optical phase of the input optical signal by 180°; the attenuation power of the tunable optical attenuator is set to A 2 ; The splitting ratio of the first optical combiner and the second optical combiner is set to 50:

50.

3. The electro-optic modulator according to claim 2, characterized in that In the narrowband mode, the following conditions need to be met: Where, L MZM represents the optical insertion loss of the dual-output intensity modulator, L PM represents the optical insertion loss of the phase modulator; by setting the optical insertion losses of the dual-output intensity modulator and the phase modulator to satisfy the above formula, the third-order intermodulation signal of the electro-optical modulator is eliminated and the modulation linearity is improved.

4. The electro-optic modulator according to claim 1, characterized in that The working mode of the electro-optic modulator in broadband mode is as follows: the splitting ratio of the tunable optical splitter is set to 1:0; the second RF input port of the dual-output intensity modulator is connected to a DC signal, so that the dual-output intensity modulator works at an orthogonal point; the tunable optical attenuator attenuates the input optical signal to 0; and the splitting ratios of the first optical combiner and the second optical combiner are both set to 50:

50.

5. The electro-optic modulator according to claim 1, characterized in that: The substrate is made of silicon or thin-film lithium niobate.

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