A monolithically integrated wide and narrow passband reconfigurable electro-optic modulator

Abstract

This invention relates to a monolithically integrated wide and narrow passband reconfigurable electro-optic modulator, belonging to the field of electro-optic modulators. It includes a substrate, and integrated on the substrate are 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. The input terminal of the tunable optical splitter receives an input optical signal, and its output terminals are connected to the input terminals of the dual-output intensity modulator and the phase modulator, respectively. The first output terminal of the dual-output intensity modulator is connected to the input terminal of the second optical combiner, and the second output terminal is connected to the input terminal of the tunable optical attenuator. The output terminals of the phase modulator and the tunable optical attenuator are both connected to the input terminal of the first optical combiner, and the output terminal of the first optical combiner is connected to the input terminal of the second optical combiner. The output terminal of the second optical combiner outputs a modulated optical signal.

Description

Technical Field

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

[0002] Electro-optic modulators are core functional devices for converting microwave signals into optical signals. Typical electro-optic modulators (such as Mach-Zehnder modulators, MZMs) employ optical interference structures, changing the interference state by injecting microwave signals to achieve modulation conversion from microwave amplitude to optical intensity. Conventional electro-optic modulators utilize a dual-waveguide interference structure combined with the high electro-optic coefficient of lithium niobate, resulting in ultra-wide bandwidth and ultra-low loss electro-optic modulation capabilities. However, limited by the sinusoidal response curve, the linearity of current electro-optic modulators suffers from significant shortcomings.

[0003] Currently, numerous structures and methods have been proposed to improve dynamics. Although these structures—such as series-parallel interference structures and single dual-drive structures—achieve high dynamics, the use of dual-drive methods makes it difficult for current electrical devices to achieve precise and continuous power distribution over a wide frequency range, thus lacking ultra-wideband capability. Furthermore, micro-ring assisted MZI structures are also limited by the narrow-band response of the micro-ring resonator, failing to meet the requirements for ultra-wideband applications.

[0004] Because the contradiction between instantaneous bandwidth and dynamics cannot be overcome at present, current modulators can only work in a single mode. There is no modulator with tunable bandwidth and dynamics to meet the needs of microwave photonics processing systems for optimal matching of bandwidth and dynamics in different task scenarios. Summary of the Invention

[0005] In view of this, the purpose of the present invention is to provide a monolithically integrated wide and narrow passband reconfigurable electro-optic modulator that achieves wide and narrow passband tuning and simultaneously achieves optimal dynamics that match the wide and narrow passbands, so as to meet the needs of multifunctional integrated applications.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] A monolithically integrated wide and narrow passband reconfigurable electro-optic modulator is disclosed, which can achieve a large dynamic range and wideband applications by switching between wideband and narrowband operating modes. It includes a substrate, and integrated on the substrate 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.

[0008] The tunable optical splitter receives the input optical signal at its input end, and its output end is connected to the input ends of a dual-output intensity modulator and a phase modulator, respectively. 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 operates in 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, causing the dual-output intensity modulator to operate at its maximum value; the phase modulator modulates the 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 both the first and second optical combiners is set to 50:50.

[0010] In narrowband mode, the following also needs to be met:

[0011]

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

[0013] Furthermore, the electro-optic modulator operates in broadband mode as follows: the splitting ratio of the tunable optical splitter is set to 1:0; a DC signal is connected to the second RF input port of the dual-output intensity modulator, causing the dual-output intensity modulator to operate at the quadrature point; the tunable optical attenuator attenuates the input optical signal to 0; and the splitting ratios of both the first and second optical combiners are set to 50:50. In this mode, the electro-optic modulator is equivalent to a conventional MZM, suppressing second harmonics when operating at the quadrature point, thus supporting broadband applications.

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

[0015] The beneficial effects of this invention are as follows: This invention uses a dual-output intensity modulator to output a modulated signal at one end and an additional distortion at the other end, equal in amount to the inherent nonlinear distortion component. The nonlinearity is suppressed through the mutual cancellation of these distortion components. This invention eliminates the need for amplitude or phase modulation of the input RF signal, achieving linearization only in the optical domain, thus solving the problem of limited system bandwidth caused by dual-drive methods. Furthermore, this invention achieves wide and narrow tunability and dynamic matching through tunable structural units, meeting the application requirements of multi-functional integrated systems.

[0016] Other advantages, objectives, and features of the invention will be set forth in part in the description which follows, and in part will be apparent to those skilled in the art from the following examination, or may be learned from practice of the invention. The objectives and other advantages of the invention can be realized and obtained through the following description. Attached Figure Description

[0017] To make the objectives, technical solutions, and advantages of the present invention clearer, the preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings, wherein:

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

[0019] Figure 2 The graph shows the relationship between IIP3 and half-wave voltage in narrowband operating mode, obtained through MATLAB simulation software.

[0020] Figure 3 The graph shows the relationship between SFDR3 and input optical power in narrowband operating mode, obtained through MATLAB simulation software.

[0021] Figure 4 The graph shows the relationship between SFDR3 and input optical power in broadband operating mode, obtained through MATLAB simulation software.

[0022] Figure 5 A schematic diagram of the basic architecture of a wide and narrow passband reconfigurable electro-optic modulator based on thin-film lithium niobate monolithic integration. Detailed Implementation

[0023] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can be modified or changed 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 are only schematic representations of the basic concept of the present invention. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0024] like Figure 1 As shown, a monolithically integrated wide and narrow passband reconfigurable electro-optic modulator is provided in an 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 split 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 together with the output of the phase modulator into a first optical combiner. The first output port of the dual-output intensity modulator and the output of the first optical combiner are input together into a second optical combiner and then output. In addition, the first RF port of the dual-output intensity modulator is used to receive an RF modulation signal, the second RF port of the dual-output intensity modulator is used to receive a first DC power signal, and the RF port of the phase modulator is used to receive a second DC power signal.

[0026] The electro-optic modulator provided in this embodiment operates in narrowband mode as follows: the tunable optical splitter operates at 1 / a... 2 The optical splitter divides the optical signal into an upper optical path and a lower optical path; the second RF port of the dual-output intensity modulator is connected to the first DC power supply signal, causing the dual-output intensity modulator to operate at its maximum value; the phase modulator modulates the 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] Let the optical signal E be the input to the tunable optical splitter. LD The expression for (t) is:

[0028]

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

[0030] The expression for the input radio frequency signal is:

[0031] V(t)=V RF cos(ω RF t)

[0032] Where, ω RF V is the angular frequency of the radio frequency signal. RF This indicates the voltage value of the radio frequency signal.

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

[0034]

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

[0036] The light from the upper path is injected into the dual-output intensity modulator. After being modulated by the radio frequency signal, the output signals of the two paths of the dual-output intensity modulator can be expressed as:

[0037]

[0038] In the formula, L MZM Indicates the optical insertion loss of a dual-output intensity modulator; This is the bias point for the dual-output intensity modulator. Modulation depth. V DC V represents the DC bias voltage applied to the dual-output intensity modulator. π This represents the half-wave voltage of the dual-output intensity modulator. Setting 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 This indicates the optical insertion loss of the phase modulator.

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

[0044]

[0045] The expression for the detected output photocurrent is:

[0046]

[0047] Where r represents the probe 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] Based on the definition of IIP3, derive the expression for IIP3:

[0050]

[0051] Among them, R s Representing the input impedance of the modulator, it can be seen that it satisfies... When taking the value of IIP3, it can theoretically be infinitely large, thus improving linearity.

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

[0053]

[0054] Here, SFDR represents the stray-free dynamic range of a microwave photonic system, measured in dB·Hz. 2 / 3 IIP3 represents the third-order cutoff point of the input, in dBm; NF represents the noise figure, in dB. Since IIP3 can be infinite, it can improve linearity and increase the dynamic range of the link.

[0055] Furthermore, in broadband mode, the modulator operates as follows: a tunable optical splitter splits the optical output into an upper and lower beam with a 1:0 ratio; the second RF port of the dual-output intensity modulator is connected to a first DC power supply signal, causing the dual-output intensity modulator to operate at the quadrature point; a tunable optical attenuator attenuates the lower output of the dual-output intensity modulator to 0; and the splitting ratio of the first and second optical combiners is 50:50. In this configuration, the electro-optic modulator is equivalent to a conventional MZM modulator, suppressing second harmonics when operating at the quadrature point, thus supporting broadband applications.

[0056] There are many possible values ​​for the third-order intermodulation cancellation condition. The following example uses a specific link 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, the half-wave voltage is 5V; the optical insertion loss of the phase modulation is negligible at 0dB; and the detection responsivity is 0.6A / W.

[0058] In narrowband applications, to satisfy the condition of third-order intermodulation cancellation, the splitting ratio of the tunable optical splitter is set to 50:50, i.e., 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 using MATLAB simulation software, and the relationship between IIP3 and half-wave voltage was obtained as follows: Figure 2 As shown. The conventional MZM modulator has an IIP3 of 23dBm. The narrowband high linearity electro-optic modulator provided in this embodiment can achieve an IIP3 of 51.06dBm when the half-wave voltage is 5V. That is, after adopting the structure of this embodiment, the IIP3 is improved by 28dB, and the corresponding SFDR is improved by 18dB, thereby greatly improving the linearity of modulation.

[0060] The relationship between SFDR and the optical power of the input modulator is as follows: Figure 3 As shown, the modulator can achieve 128 dB·Hz when the input optical power is 20 dBm. 2 / 3 The SFDR is nearly 18dB higher than that of a conventional intensity modulator.

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

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

[0063] The wide and narrow passband reconfigurable electro-optic modulator described in this invention can be monolithically integrated onto silicon or thin-film lithium niobate material. For example... Figure 5 The image shows an electro-optic modulator based on a thin-film lithium niobate chip, which consists of five basic units:

[0064] The tunable optical splitter consists of a 1×2 MMI and a 2×2 directional coupler, achieving beam splitting tuning through a tuned phase arm. The dual-output intensity modulator, split by a 1×2 MMI, is modulated via a thin-film lithium niobate ridge waveguide and then outputs dual signals through the 2×2 directional coupler. This unit is the core of the RF loading, achieving high-frequency broadband intensity modulation. Phase modulation is achieved using a thin-film lithium niobate waveguide and electrodes, completing the carrier phase modulation. The attenuator consists of two 1×2 MMIs. A wide range of optical power adjustment is achieved through a tuned phase arm to ensure precise control of the combined beam amplitude. The combiner uses a 1×2 MMI structure.

[0065] This invention utilizes a dual-output modulator. One end generates the modulated signal, while the other end constructs an additional distortion equal to the inherent nonlinear distortion component. Nonlinearity suppression is achieved through the mutual cancellation of these distortion components. Compared to architectures such as dual-drive MZM, dual parallel / serial modulators, and dual parallel polarization modulation, this architecture only requires a single drive, eliminating the need for amplitude or phase modulation of the input RF signal. Linearization is achieved solely through optical domain modulation, solving the problem of limited system bandwidth caused by dual-drive approaches. Tunable structural units enable wide and narrow tunability and dynamic matching. In narrowband operation mode, the dynamic range is improved by an order of magnitude while maintaining comparable power consumption to conventional MZM modulators.

[0066] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A monolithically integrated wide and narrow passband reconfigurable electro-optic modulator, which achieves large dynamic range and wideband applications by switching between the wideband and narrowband operating modes of the electro-optic modulator, characterized in that, 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. The input terminal of the tunable optical splitter receives the input optical signal, and its output terminal is connected to the input terminals of the dual-output intensity modulator and the phase modulator, respectively. The first output terminal of the dual-output intensity modulator is connected to the input terminal of the second optical combiner, and the second output terminal is connected to the input terminal of the tunable optical attenuator. The output terminals of the phase modulator and the tunable optical attenuator are both connected to the input terminal of the first optical combiner, and the output terminal of the first optical combiner is connected to the input terminal of the second optical combiner. The output terminal of the second optical combiner outputs the modulated optical signal.

2. The electro-optic modulator according to claim 1, characterized in that, The electro-optic modulator operates in 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, causing the dual-output intensity modulator to operate at its maximum value; the phase modulator modulates the 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 both the first and second optical combiners is set to 50:

50.

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

4. The electro-optic modulator according to claim 1, characterized in that, The electro-optic modulator operates in broadband mode as follows: the splitting ratio of the tunable optical splitter is set to 1:0; a DC signal is connected to the second RF input port of the dual-output intensity modulator, causing the dual-output intensity modulator to operate at the quadrature point; the tunable optical attenuator attenuates the input optical signal to 0; and the splitting ratio of both the first and second optical combiners is 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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