Single sideband generator based on optical delay line

Abstract

The present invention provides a single sideband signal generator, comprising: a modulator configured to generate a first modulated optical signal and a second modulated optical signal having the same amplitude; and the sideband suppression light circuit based on the first light delay line is used for generating a full-carrier single-side-band signal, and / or the sideband suppression light circuit based on the second light delay line is used for generating a carrier-suppressed single-side-band signal. The present invention simplifies the structure by saving half the space occupied by redundant signal electrodes, and also reduces the RF power consumption by half by removing an RF mixer. The provided single side band (SSB) signal generator has the advantages of compact structure, low cost and energy conservation. By reasonably designing the length of the optical delay line, the generator can be easily expanded to a higher frequency range on the premise of not needing extra cost.

Description

Technical Field

[0001] This invention generally relates to the generation of single-sideband (SSB) optical signals. More specifically, this invention relates to an SSB signal generator based on an optical delay line. Background Technology

[0002] With the ever-increasing demands for data transmission rates from applications such as 5G / 6G networks, the Internet of Things (IoT), massive MIMO, and RoF (RoF) systems, base station and data center infrastructure is facing unprecedented pressure. Compared to coherent detection systems, direct detection systems only require photodiodes to receive signals, thus offering advantages in terms of simple structure and low cost. However, conventional double-sideband (DSB) signals suffer from significant limitations in transmission distance due to frequency-selective power fading caused by dispersion. Single-sideband (SSB) signaling can not only effectively alleviate this problem but also improve spectrum utilization efficiency.

[0003] Traditional SSB modulators typically rely on complex implementation architectures. For example, a dual-drive Mach-Zehnder modulator (DDMZM) can achieve a full-carrier SSB (FC-SSB), while an IQ modulator can generate a carrier-suppressed SSB (CS-SSB). Both approaches require applying two radio frequency (RF) signals, each 90° out of phase, to two separate signal electrodes. Achieving this phase difference usually relies on a 90° RF mixer (i.e., an RF Hilbert converter) or a dual-channel RF source (such as a dual-channel arbitrary waveform generator, AWG), along with a complex parallel electrode structure. These factors not only lead to at least 3dB of modulation efficiency loss and inherent RF power loss, but also significantly increase system cost, with problems being particularly severe in high-frequency applications.

[0004] Figure 1 The diagrams illustrate a conventional FC-SSB modulation structure based on DDMZM and a CS-SSB modulation structure based on IQ modulators. These architectures typically require two sets of parallel phase or amplitude modulators to apply RF signals with a 90° phase difference, resulting in a complex and large overall system structure with at least 3dB of efficiency loss. Furthermore, common implementations rely on external discrete 90° RF mixers or dual-channel RF sources to generate the π / 2 phase difference between the two RF signals, introducing additional RF losses and further increasing the overall system cost, especially at high frequencies. Summary of the Invention

[0005] This invention achieves a compact and energy-efficient generation method for SSB signals by employing an optical delay line-assisted single-drive modulator integrated on a thin-film lithium niobate platform. The optical delay line, acting as a photonic RF phase shifter, has a precisely designed length and utilizes a high-precision nanoscale integrated manufacturing process to achieve the required phase delay. This design eliminates the need for a 90° RF mixer and simplifies the traditional dual-drive electrode structure to a single-drive electrode configuration, thereby effectively reducing device size, lowering power consumption, and simplifying the overall system architecture.

[0006] According to a first aspect of the present invention, a single-sideband (SSB) signal generator is provided. The SSB signal generator comprises: a modulator configured to generate a first modulated optical signal and a second modulated optical signal with equal amplitude; and a sideband suppression optical circuit comprising: a first optical delay line path coupled to a first modulation branch and configured to obtain a first photonic RF phase-shifted optical signal based on the first modulated optical signal; a first optical bypass path coupled to a second modulation branch and configured to obtain a first bypass optical signal based on the second modulated optical signal; and a first optical combiner coupled to the first optical delay line path and the first optical bypass path and configured to combine the first photonic RF phase-shifted optical signal and the first bypass optical signal to obtain a first FC-SSB signal.

[0007] According to a second aspect of the present invention, a single-sideband (CS-SSB) signal generator is provided. The CS-SSB signal generator comprises: a modulator configured to generate a first modulated optical signal and a second modulated optical signal with equal amplitude; and a sideband suppression optical circuit comprising: a first optical delay line path coupled to a first modulation branch and configured to obtain a first photonic RF phase-shifted optical signal based on the first modulated optical signal; a first optical bypass path coupled to a second modulation branch and configured to obtain a first bypass optical signal based on the second modulated optical signal; a second optical delay line path coupled to the second modulation branch and configured to obtain a second photonic RF phase-shifted optical signal based on the second modulated optical signal; a second optical bypass path coupled to the first modulation branch and configured to obtain a second bypass optical signal based on the first modulated optical signal; and an optical combining circuit configured to combine the first photonic RF phase-shifted optical signal, the first bypass optical signal, the second photonic RF phase-shifted optical signal, and the second bypass optical signal to obtain a CS-SSB signal.

[0008] According to a third aspect of the invention, a single-sideband (SSB) signal generator is provided, comprising the SSB signal generator according to the first aspect and the SSB signal generator according to the second aspect. The provided SSB signal generator can perform full-carrier SSB (FC-SSB) and carrier-suppressed SSB (CS-SSB) signal generation, achieving sideband rejection ratios of 22.1 dB and 22.5 dB respectively, and a sideband carrier rejection ratio of 16.9 dB for CS-SSB. The generated SSB signal also exhibits good resistance to frequency-selective power fading.

[0009] Compared with existing technologies, the method provided by this invention saves approximately half the space by eliminating redundant signal electrodes, significantly simplifying the device structure and reducing RF power consumption by half. Furthermore, this solution eliminates the need for an RF mixer and, through proper design of the optical delay line length, allows for expansion to higher frequency domains without incurring additional costs.

[0010] The provided SSB signal generation technology enables compact, low-cost, and energy-efficient SSB signal output, suitable for various applications including direct detection systems, frequency-modulated continuous wave radar / LiDAR, frequency up / down conversion, optical vector network analyzers, and cold atom interferometer systems. Specifically, the proposed FC-SSB signal generator can be widely used in incoherent and coherent direct detection systems (such as Kramers-Kronig receivers), particularly suitable for short-range optical communication scenarios, such as data center communication and fiber optic radio / video transmission systems. Furthermore, its application in optical vector network analyzers has been validated. The provided CS-SSB signal generator is suitable for generating frequency-modulated continuous wave signals, a method widely used in radar / LiDAR systems. This technology can also be applied to frequency up / down conversion in microwave photonics systems and cold atom interferometer systems to achieve high-precision frequency detuning control. Attached Figure Description

[0011] Embodiments of the invention are described in more detail below with reference to the accompanying drawings, in which:

[0012] Figure 1 The diagrams show conventional full-carrier SSB (FC-SSB) modulation based on a dual-drive Mach-Zehnder modulator (DDMZM) and carrier-suppressed SSB (CS-SSB) modulation using an IQ modulator.

[0013] Figure 2A A simplified schematic diagram of an FC-SSB signal generator according to an embodiment of the present invention is shown; Figure 2B It shows Figure 2A The optoelectronic circuit diagram of the SSB signal generator;

[0014] Figure 3A and 3B Different configurations of the adjustable phase shifter according to various embodiments of the present invention are shown;

[0015] Figure 4A A simplified schematic diagram of a CS-SSB signal generator according to another embodiment of the present invention is shown; Figure 4B It shows Figure 4A The optoelectronic circuit diagram of the SSB signal generator;

[0016] Figures 5A to 5D Different configurations of adjustable delay lines and phase shifters according to various embodiments of the present invention are shown;

[0017] Figures 6A to 6C Three different CS-SSB generation schemes are shown respectively;

[0018] Figure 7A A simplified schematic diagram of a signal generator according to another embodiment of the present invention is shown; and Figure 7B It shows that according to Figure 7A A micrograph of a signal generator fabricated from a schematic diagram;

[0019] Figure 8A and 8B The measurement results generated by FC-SSB and CS-SSB are shown; and

[0020] Figure 9 The resistance of a simplified SSB signal to the frequency-selective power fading problem of a double-sideband (DSB) signal is shown. Detailed Implementation

[0021] In the following description, details of the invention are set forth as preferred embodiments. It will be apparent to those skilled in the art that modifications, including additions and / or substitutions, can be made without departing from the scope and spirit of the invention. Specific details may be omitted to avoid obscuring the invention; however, this disclosure is prepared to enable those skilled in the art to practice the teachings herein without requiring extensive experimentation.

[0022] According to various aspects of the present invention, a simplified generation scheme for compact and energy-efficient single-sideband (SSB) modulation facilitated by on-chip optical delay lines is disclosed.

[0023] Figure 2A A simplified schematic diagram of an SSB signal generator according to an embodiment of the present invention is shown. Instead of using an RF 90° mixer or a dual-channel RF source ( Figure 1 The proposed method utilizes a photonic RF phase shifter implemented using an optical delay line.

[0024] like Figure 2A As shown, the SSB signal generator 100 includes: a first beam splitter 101 configured to split an optical input carrier signal into a first optical input signal and a second optical input signal; a first modulation branch 102a, the input end of which is coupled to a first output end of the beam splitter 101 to receive the first optical input signal; a second modulation branch 102b, the input end of which is coupled to a second output end of the beam splitter 101 to receive the second optical input signal; and a modulator 103 configured to modulate the first and second input signals at a modulation frequency to generate a first modulated optical signal and a second modulated optical signal E1 and E2 with equal amplitude but opposite phase.

[0025] The SSB signal generator 100 further includes a sideband suppression optical circuit 110. The sideband suppression optical circuit 110 includes: a first optical delay line path 111, which is coupled to a first modulation branch and configured to obtain a first photonic RF phase-shifted optical signal based on a first modulated optical signal; a first optical bypass path 112, which is coupled to a second modulation branch and configured to obtain a first bypass optical signal based on a second modulated optical signal; and a first optical combiner 113, which is coupled to the first optical delay line path 111 and the first optical bypass path 112 and configured to combine the first photonic RF phase-shifted optical signal and the first bypass optical signal to obtain a first full-carrier SSB signal.

[0026] In some embodiments, the sideband suppression optical circuit 110 further includes an adjustable phase shifter 114, which is coupled to the optical delay line path 111 and configured to fine-tune the first photon RF phase-shifted optical signal.

[0027] Optical delay line path 111 acts as a photonic RF phase shifter, where the delay time τ m Equal to the time period T of the modulated RF signal m One-quarter, i.e., τ m =1 / 4T m When the first modulated optical signal and the second modulated optical signal pass through line paths 111 and 112 respectively, a 90° (or π / 2 radian) photon RF phase shift can be induced between the two optical signals due to the different path lengths between line paths 111 and 112.

[0028] Figure 2B The optoelectronic circuit diagram of the SSB signal generator 100 is shown, where the simplified spectrum of the optical signal is indicated at points a to f.

[0029] The input carrier signal (represented by the spectrum at point a) is split into two branches and modulated by a single-drive modulator. Then, the first modulated optical signal (represented by the spectrum at point b) is delayed by a time (T) equal to one-quarter of the period of the target RF frequency. m A 90° photon RF phase shift is introduced through optical delay line path 111 to obtain the first photon RF phase-shifted optical signal (represented by the spectrum at point c).

[0030] Then, the adjustable phase shifter 114 further induces an optical phase shift to obtain an optical signal (represented by the spectrum at point d) to ensure destructive interference of the sideband to be suppressed during recombination, wherein the sideband to be suppressed can be selected by adjusting the induced optical phase induced by the adjustable phase shifter.

[0031] A 90° photonic RF phase shift (or delay time) was ensured through a carefully designed delay length. This is achieved through high-precision nanofabrication processes in the integrated platform, a process that is difficult to implement in conventional bulk crystal modulators.

[0032] In some embodiments, the optical delay line path 111 is implemented using a thin-film waveguide. The thin-film waveguide may include a plurality of straight segments and a plurality of circularly curved segments interposed between the straight segments to form a delay line. The curved and straight segments may be arranged to form arbitrary routing structures, such as helical shapes or similar shapes that can be used for delay. It should be understood that the routing structure may be another suitable routing configuration that introduces an additional length with a specific delay time in one branch compared to another. The structure may be implemented on various material platforms, including but not limited to silicon, silicon nitride, lithium niobate, lithium tantalate, gallium arsenide, indium phosphide, barium titanate, aluminum gallium arsenide, etc.

[0033] After recombination of the first photonic RF phase-shifted optical signal and the first bypass optical signal (represented by the spectrum at point e), a full-carrier SSB signal (represented by the spectrum at point f) is obtained. One of the sidebands is suppressed due to destructive interference promoted by the accumulated phase difference in the upper and lower sidebands induced in the photonic RF phase shifter. The suppressed sideband can be selected by adjusting the optical phase difference between the two branches, which can be achieved by applying a DC voltage to the modulation electrode (not shown).

[0034] Adjustable phase shifters are used to ensure the correct phase for destructive interference and sideband selection. (Reference) Figure 3A and 3B The adjustable phase shifter 114 can be coupled to the first optical delay line path 111, such as Figure 3A As shown. Alternatively, as Figure 3B As shown, the adjustable phase shifter 114 can be arranged along the first optical bypass path 112 and is configured to fine-tune the first bypass optical signal before reassembly.

[0035] In some embodiments, the adjustable phase shifter 114 may be a thermo-optical phase shifter, an electro-optical phase shifter, a MEMS phase shifter, or a free carrier depletion phase shifter. For example, the adjustable phase shifter 114 may be a thermal phase shifter, which includes a waveguide; a cladding surrounding the waveguide; and a controllable heater disposed on the cladding and extending along the waveguide.

[0036] Figure 4A A simplified schematic diagram of an SSB signal generator 200 according to another embodiment of the present invention is shown.

[0037] The SSB signal generator 200 includes: a first beam splitter 201 configured to split an optical input carrier signal into a first optical input signal and a second optical input signal; a first modulation branch 202a, the input of which is coupled to a first output of the beam splitter 201 to receive the first optical input signal; a second modulation branch 202b, the input of which is coupled to a second output of the beam splitter 201 to receive the second optical input signal; and a modulator 203 configured to modulate the first and second input signals at a modulation frequency to generate a first modulated optical signal and a second modulated optical signal with equal amplitude but opposite phase.

[0038] The SSB signal generator 200 further includes a sideband suppression optical circuit 210. The sideband suppression optical circuit 210 includes: a first optical delay line path 211a, which is coupled to a first modulation branch and configured to obtain a first photonic RF phase-shifted optical signal based on a first modulated optical signal; and a first optical bypass path 212a, which is coupled to a second modulation branch and configured to obtain a first bypass optical signal based on a second modulated optical signal.

[0039] The sideband suppression optical circuit 210 further includes an adjustable phase shifter 214a, which is coupled to the first optical delay line path 211a and configured to fine-tune the first photon RF phase-shifted optical signal to ensure destructive interference between the first photon RF phase-shifted optical signal and the first bypass optical signal and / or select the sideband to be suppressed.

[0040] The sideband suppression optical circuit 210 further includes: a second optical delay line path 211b, which is coupled to a second modulation branch and configured to obtain a second photonic RF phase-shifted optical signal based on a second modulation optical signal; and a second optical bypass path 212b, which is coupled to a first modulation branch and configured to obtain a second bypass optical signal based on a first modulation optical signal.

[0041] The sideband suppression optical circuit 210 further includes an optical combination circuit 230, which is configured to combine a first photonic RF phase-shifted optical signal, a first bypass optical signal, a second photonic RF phase-shifted optical signal, and a second bypass optical signal to obtain a CS-SSB signal.

[0042] In some embodiments, the SSB signal generator 200 further includes: a first optical coupler 205 configured to couple a first modulation signal from a first modulation branch 202a to a first optical delay line path 211a and a second optical bypass path 212b, respectively; and a second optical coupler 206 configured to couple a second modulation signal from a second modulation branch 202b to the first optical bypass path 212a and the second optical delay line path 211b, respectively.

[0043] In some embodiments, the sideband suppression optical circuit 210 further includes an adjustable phase shifter 214b, which is coupled to a second optical delay line path 211b and configured to fine-tune the second photonic RF phase-shifted optical signal to ensure destructive interference between the second photonic RF phase-shifted optical signal and the second bypass optical signal and / or select the sideband to be suppressed.

[0044] Figure 4B The optoelectronic circuit diagram of the SSB signal generator 200 is shown, where the simplified spectrum of the optical signal is indicated at points A to J.

[0045] refer to Figure 4B For carrierless SSB signal generation, the optical carrier signal (represented by the spectrum at point A) is first divided into two branches and modulated by a single-drive modulator.

[0046] A π phase shift is introduced by adjusting the bias point through the modulator electrodes, which can alternatively be replaced by an additional adjustable phase shifter at the end of the recombination region. After modulation, each branch is further divided into two branches, resulting in a total of four branches. An optical delay line is then introduced between the top and bottom branches to induce a 90° (or π / 2 radian) photon RF phase shift, the length of which follows the same principle as the FC-SSB scheme.

[0047] More specifically, the first modulated optical signal (whose spectrum is the same as that at point B) is delayed by a time (T) equal to one-quarter of the period of the target RF frequency. mA 90° photonic RF phase shift is introduced through optical delay line path 211a to obtain a first photonic RF phase-shifted optical signal (represented by the spectrum at point C). Then, adjustable phase shifter 214a further induces the optical phase shift to obtain a finely tuned optical signal (represented by the spectrum at point D). After recombination of the finely tuned optical signal and the first bypass optical signal (i.e., the second modulated optical signal represented by the spectrum at point G), a first full-carrier SSB signal (represented by the spectrum at point I) is obtained.

[0048] The second modulated optical signal (whose spectrum is the same as that at point G) is delayed by a time equal to one-quarter of the period of the target RF frequency (τ). m A 90° photonic RF phase shift is introduced through optical delay line path 211b to obtain a second photonic RF phase-shifted optical signal (represented by the spectrum at point E). Then, adjustable phase shifter 214b further induces the optical phase shift to obtain a finely tuned optical signal (represented by the spectrum at point F). After recombination of the finely tuned optical signal and the second bypass optical signal (i.e., the first modulated optical signal represented by the spectrum at point B), a second full-carrier SSB signal (represented by the spectrum at point H) is obtained.

[0049] Adjustable phase shifters are used in conjunction with optical delay lines to ensure correct phase for destructive interference and sideband selection. The first optical delay line can be positioned in the lower branch (e.g., Figure 5A and 5C (as shown) or in the upper branch (such as) Figure 5B and 5D As shown). The second optical delay line can be arranged in the upper branch (e.g. Figure 5A and 5D (as shown) or in the next branch (such as Figure 5B and 5C (As shown). Adjustable phase shifters can be arranged in branches with optical delay lines, or alternatively in branches without optical delay line paths (i.e., optical bypass paths). For example, as Figure 5A As shown, the adjustable phase shifters 214a / 214b can be coupled to the optical delay line paths 211a / 211b. Alternatively, as... Figure 5B As shown, the adjustable phase shifters 214a / 214b can be arranged along the optical bypass path 212a / 212b. Alternatively, as Figure 5C As shown, adjustable phase shifter 214a can be coupled to optical delay line path 211a, while adjustable phase shifter 214b can be arranged along optical bypass path 212b. Alternatively, as Figure 5D As shown, the adjustable phase shifter 214a can be arranged along the optical side path 212a, while the adjustable phase shifter 214b can be coupled to the optical delay line path 211b.

[0050] In some embodiments, each of the optical delay line paths 211a and 211b is implemented using a thin-film waveguide. The thin-film waveguide may include a plurality of straight segments and a plurality of circularly curved segments interposed between the straight segments to form a delay line. The curved and straight segments may be arranged to form arbitrary routing structures, such as helical shapes or similar shapes that can be used for delay. The structure may be implemented on various material platforms, such as, but not limited to, silicon, silicon nitride, lithium niobate, lithium tantalate, gallium arsenide, indium phosphide, barium titanate, aluminum gallium arsenide, etc.

[0051] In some embodiments, each of the adjustable phase shifters 214a and 214b may be a thermo-optical phase shifter, an electro-optical phase shifter, a MEMS phase shifter, or a free carrier depletion phase shifter. For example, the adjustable phase shifters 214a and 214b may be thermal phase shifters, which include a waveguide; a cladding surrounding the waveguide; and a controllable heater disposed on the cladding and extending along the waveguide. It should be understood that the adjustable phase shifters may have other suitable structures to suit various situations.

[0052] It should be noted that for CS-SSB generation, sideband suppression can be achieved first by using waveguide cross-switching branches II and III to first combine branches I and III and then combine branches II and IV, followed by carrier suppression (e.g. Figure 6A (As shown). More specifically, the optical combining circuit 230 may include: a first optical combiner 230a, which is coupled to a second optical delay line path (branch III) and a first optical bypass path (branch I) and configured to combine a second phase-shifted optical signal and a first bypass optical signal to obtain a first FC-SSB signal; a second optical combiner 230b, which is coupled to a first optical delay line path (branch II) and a second optical bypass path (branch IV) and configured to combine a second phase-shifted optical signal and a second bypass optical signal to obtain a second FC-SSB signal; and a third optical combiner 230c, which is configured to combine the first FC-SSB signal and the second FC-SSB signal to obtain a CS-SSB signal.

[0053] Alternatively, this can be done in reverse, where branches I, II and III, IV are first directly combined without using waveguide crossings (such as...). Figure 6B(As shown). More specifically, the optical combining circuit 230 may include: a first optical combiner 230a, which is coupled to a first optical delay line path (branch II) and a first optical bypass path (branch I) and configured to combine a first photonic RF phase-shifted optical signal and a first bypass optical signal to obtain a first FC-SSB signal; a second optical combiner 230b, which is coupled to a second optical delay line path (branch III) and a second optical bypass path (branch IV) and configured to combine a second phase-shifted optical signal and a second bypass optical signal to obtain a second FC-SSB signal; and a third optical combiner 230c, which is configured to combine the first FC-SSB signal and the second FC-SSB signal to obtain a CS-SSB signal.

[0054] In such Figure 6C In another embodiment shown, branches I through IV can be combined simultaneously to generate a CS-SSB signal. More specifically, the optical combining circuit 230 may include an optical combiner configured to combine a first photonic RF phase-shifted optical signal, a first bypass optical signal, a second photonic RF phase-shifted optical signal, and a second bypass optical signal to obtain a CS-SSB signal.

[0055] Once the delay length meets the requirement of a 90° photon RF phase shift, FC-SSB and CS-SSB can be generated by applying different phase shifts using a phase shifter.

[0056] Figure 7A A simplified schematic diagram of a signal generator 300 according to another embodiment of the present invention is shown. Figure 7B It shows that according to Figure 7A The diagram shows a micrograph of the signal generator. As shown, the signal generator 300 is an integration of the FC-SSB signal generator 100 and the CS-SSB signal generator 200, and uses a single RF signal generator to drive the modulator.

[0057] It should also be understood that the beam splitter 201, couplers 205 and 206, and combiners 203a-203c can be any suitable type of coupler (e.g., Y-coupler, multimode interference (MMI) coupler, etc.).

[0058] Single-sideband modulation

[0059] Treat the optical carrier as Where ω0 is the carrier frequency. The RF signal is expressed by sin(ω0 / ωt). m t) is given, where ω m Indicates the modulation frequency.

[0060] For FC-SSB generation, the electric field of the light, which is split into two branches and modulated by the electric field along both sides of the signal electrode, can be expressed as:

[0061]

[0062]

[0063] Where E1 and E2 are the electric fields of the two branches after modulation, A0 is the amplitude of the input electric field, and β represents the modulation intensity. The modulation of the upper and lower branches by opposite electric fields causes their modulation terms to have opposite signs. After modulation, one branch modulates at a period equal to one-quarter of the target modulation frequency. Delay time τ m The phase shift is introduced by using an optical delay line and then adjusting the phase using a thermal phase shifter. The electric field after delay and phase shift can be expressed as:

[0064]

[0065] The Fourier transform of the combination of the two branches can be expanded using the Jacobi-Anger expansion as follows:

[0066]

[0067] If only the first-order sidebands are considered, the output will be:

[0068]

[0069] It can be simplified to:

[0070]

[0071] The negative first-order sideband is canceled out in the following case:

[0072]

[0073] k is an integer. When it equals At that time, the positive first-order sideband will be canceled out.

[0074] The CS-SSB generation can be derived in a similar manner. The Fourier transform of the combination of the four branches after the delay line and the thermal phase shifter (considering only the first sideband) can be written as:

[0075]

[0076] in, and The optical phase shift is induced by two thermal phase shifters and a DC voltage applied to the modulation electrode. The output can be simplified to:

[0077] F(E a +E b +E c +E d )=A0J -1 (β)δ(ω+ω m -ω0) (9)

[0078] The positive first-order sideband and the carrier are canceled out in the following cases:

[0079]

[0080]

[0081] k is an integer. When the term in equation (10) equals At that time, the negative first-order sideband will be canceled out.

[0082] In conventional SSB generation schemes, two RF signals with half-π phase shifts are applied to parallel phase or amplitude modulators for FC-SSB and CS-SSB generation. Therefore, in these parallel schemes, only half the power is used for modulation. If we assume the total RF power is the same as the total RF power of the delay-line assisted SSB modulator according to the present invention, then each phase modulator shares half of the total power. Since modulation strength is proportional to modulation voltage, the delay-line assisted scheme provided by the present invention can effectively save half the power to achieve the same modulation strength.

[0083] Optical delay line design

[0084] The delay time is the time required to achieve destructive interference in the first sideband by controlling the additional routing length of one branch relative to another. The design was meticulously crafted to meet specific design objectives. Due to the anisotropy of the material, the waveguide in the yz plane of the x-cut LN exhibits different group indices at different crystal routing angles, resulting in non-uniform delays at different locations along the bend. To improve the estimation and control of the delay length, straight waveguides and circular bends were used instead of helical routing.

[0085] The delay time of the bend is calculated by integrating the group exponent along the route crystal angle:

[0086]

[0087] Where τ is the delay of the bend, r is the radius of the circular bend, and n g (θ) is the group index at angle θ.

[0088] Taking the delay line for a 25GHz FC-SSB as an example, Table 1 shows the length of each segment of the two branches and the corresponding delay time. The delay time difference between the two branches is 10 picoseconds, which is one-quarter of the time period of the 25GHz signal.

[0089] Table 1. Length and delay time of the structure during FC-SSB generation at 25 GHz

[0090] Figure 8A and 8B Measurement results generated by FC-SSB and CS-SSB are presented, showing sideband suppression ratios of 22.1 dB and 22.5 dB for FC-SSB and CS-SSB, respectively, with a sideband carrier suppression ratio of 16.9 dB for CS-SSB. Furthermore, Figure 9 This demonstrates the good resistance of the simplified SSB signal to the problem of frequency-selective power fading.

[0091] The foregoing description of the invention has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Many modifications and variations will be apparent to those skilled in the art.

Claims

1. A single-sideband signal generator, comprising: A modulator configured to generate a first modulated optical signal and a second modulated optical signal with equal amplitude; as well as Sideband suppression circuit, the sideband suppression circuit comprising: A first optical delay line path, the first optical delay line path being coupled to a first modulation branch and configured to obtain a first photonic RF phase-shifted optical signal based on the first modulated optical signal; A first optical bypass path, the first optical bypass path being coupled to a second modulation branch and configured to obtain a first bypass optical signal based on the second modulation optical signal; and A first optical combiner is coupled to the first optical delay line path and the first optical bypass path and is configured to combine the first photonic RF phase-shifted optical signal and the first bypass optical signal to obtain a first full-carrier single-sideband signal.

2. The single-sideband signal generator of claim 1, wherein the first optical delay line path is based on a thin-film waveguide made of any one of the following: silicon, silicon nitride, lithium niobate, lithium tantalate, gallium arsenide, indium phosphide, barium titanate, and aluminum gallium arsenide.

3. The single-sideband signal generator according to claim 1, wherein the sideband suppression optical circuit further includes an adjustable phase shifter coupled to the first optical delay line path and configured to fine-tune the first photonic RF phase-shifted optical signal.

4. The single-sideband signal generator according to claim 3, wherein the adjustable phase shifter is any one of the following optical phase shifters: thermo-optical phase shifter, electro-optical phase shifter, MEMS phase shifter, or free carrier depletion phase shifter.

5. The single-sideband signal generator according to claim 1, wherein the sideband suppression optical circuit further comprises an adjustable phase shifter, wherein the adjustable phase shifter is coupled to: the first optical bypass path and configured to fine-tune the first bypass optical signal; or the first optical delay line path and configured to fine-tune the first photonic RF phase-shifted optical signal.

6. The single-sideband signal generator according to claim 5, wherein the adjustable phase shifter is any one of the following optical phase shifters: thermo-optical phase shifter, electro-optical phase shifter, MEMS phase shifter, or free carrier depletion phase shifter.

7. A single-sideband signal generator, comprising: A modulator configured to generate a first modulated optical signal and a second modulated optical signal with equal amplitude; Sideband suppression circuit, the sideband suppression circuit comprising: A first optical delay line path, the first optical delay line path being coupled to a first modulation branch and configured to obtain a first photonic RF phase-shifted optical signal based on the first modulated optical signal; A first optical bypass path, the first optical bypass path being coupled to a second modulation branch and configured to obtain a first bypass optical signal based on the second modulation optical signal; A second optical delay line path, which is coupled to a second modulation branch and configured to obtain a second photonic RF phase-shifted optical signal based on the second modulated optical signal; A second optical bypass path, the second optical bypass path being coupled to a first modulation branch and configured to obtain a second bypass optical signal based on the first modulation optical signal; and An optical combining circuit is configured to combine the first photonic RF phase-shifted optical signal, the first bypass optical signal, the second photonic RF phase-shifted optical signal, and the second bypass optical signal to obtain a carrier-suppressed single-sideband signal.

8. The single-sideband signal generator of claim 7, wherein the optical combining circuit includes an optical combiner configured to combine the first photonic RF phase-shifted optical signal, the first bypass optical signal, the second photonic RF phase-shifted optical signal, and the second bypass optical signal to obtain the carrier-suppressed single-sideband signal.

9. The single-sideband signal generator according to claim 7, wherein the optical combining circuit comprises: A first optical combiner is coupled to the first optical delay line path and the first optical bypass path and is configured to combine the first photonic RF phase-shifted optical signal and the first bypass optical signal to obtain a first full-carrier single-sideband signal. A second optical combiner is coupled to the second optical delay line path and the second optical bypass path and is configured to combine the second phase-shifted optical signal and the second bypass optical signal to obtain a second full-carrier single-sideband signal. as well as A third optical combiner is configured to combine the first full-carrier single-sideband signal and the second full-carrier single-sideband signal to obtain the carrier-suppressed single-sideband signal.

10. The single-sideband signal generator according to claim 7, wherein the optical combining circuit comprises: A first optical combiner is coupled to a first optical delay line path and a second optical bypass path and is configured to combine the first photonic RF phase-shifted optical signal and the second bypass optical signal to obtain a first full-carrier single-sideband signal. A second optical combiner is coupled to the second optical delay line path and the first optical bypass path and is configured to combine the second phase-shifted optical signal and the first bypass optical signal to obtain a second full-carrier single-sideband signal. as well as A third optical combiner is configured to combine the first full-carrier single-sideband signal and the second full-carrier single-sideband signal to obtain the carrier-suppressed single-sideband signal.

11. The single-sideband signal generator of claim 7, wherein each of the first optical delay line path and the second optical delay line path is based on a thin-film waveguide made of any one of the following: silicon, silicon nitride, lithium niobate, lithium tantalate, gallium arsenide, indium phosphide, barium titanate, and aluminum gallium arsenide.

12. The single-sideband signal generator according to claim 7, further comprising: A first adjustable phase shifter, coupled to the first optical delay line path and configured to fine-tune the first photonic RF phase-shifted optical signal; and A second adjustable phase shifter is coupled to the second optical delay line path and configured to fine-tune the second photonic RF phase-shifted optical signal.

13. The single-sideband signal generator of claim 12, wherein each of the first adjustable phase shifter and the second adjustable phase shifter is any of the following optical phase shifters: thermo-optical phase shifter, electro-optical phase shifter, MEMS phase shifter, or free carrier depletion phase shifter.

14. The single-sideband signal generator according to claim 7, further comprising: A first adjustable phase shifter, coupled to the first optical bypass path and configured to fine-tune the first bypass optical signal; and A second adjustable phase shifter is coupled to the second optical bypass path and configured to fine-tune the second bypass optical signal.

15. The single-sideband signal generator of claim 14, wherein each of the first adjustable phase shifter and the second adjustable phase shifter is any one of the following optical phase shifters: a thermo-optical phase shifter, an electro-optical phase shifter, a MEMS phase shifter, or a free carrier depletion phase shifter.

16. The single-sideband signal generator according to claim 7, further comprising: A first adjustable phase shifter, coupled to the first optical delay line path and configured to fine-tune the first photonic RF phase-shifted optical signal; and A second adjustable phase shifter is coupled to the second optical bypass path and configured to fine-tune the second bypass optical signal.

17. The single-sideband signal generator of claim 16, wherein each of the first adjustable phase shifter and the second adjustable phase shifter is any one of the following optical phase shifters: a thermo-optical phase shifter, an electro-optical phase shifter, a MEMS phase shifter, or a free carrier depletion phase shifter.

18. The single-sideband signal generator according to claim 7, further comprising: A first adjustable phase shifter, coupled to the first optical bypass path and configured to fine-tune the first bypass optical signal; and A second adjustable phase shifter is coupled to the second optical delay line path and configured to fine-tune the second photonic RF phase-shifted optical signal.

19. The single-sideband signal generator of claim 18, wherein each of the first adjustable phase shifter and the second adjustable phase shifter is any one of the following optical phase shifters: a thermo-optical phase shifter, an electro-optical phase shifter, a MEMS phase shifter, or a free carrier depletion phase shifter.

20. A single-sideband signal generator comprising the single-sideband generator according to claim 1 and the single-sideband generator according to claim 7.

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