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

(19) State Intellectual Property Office (12) Invention Patent Application (10) Application Publication Number (43) Application Publication Date (21) Application Number 202511196114.2 (22) Application Date 2025.08.25 (30) Priority Data 18 / 914,303 2024.10.14 US (71) Applicant City University of Hong Kong Address Tat Chee Road, Kowloon, Hong Kong, China (72) Inventors Chen Yikun Zhang Ke Feng Hanke Wang Cheng (74) Patent Agency Shenzhen Yibao Intellectual Property Agency (General Partnership) 44588 Patent Attorney Wang Qin Cao Yucun (51) Int.Cl. H04B 10 / 516 (2013.01) H04B 15 / 00 (2006.01) H04B 10 / 70 (2013.01) (54) Invention Title: Single-Sideband Generator Based on Optical Delay Line (57) Abstract: This invention provides 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; a sideband suppression optical circuit based on a first optical delay line for generating a full-carrier single-sideband signal; and / or a sideband suppression optical circuit based on a second optical delay line for generating a carrier-suppressed single-sideband signal. This invention simplifies the structure by saving half the space occupied by redundant signal electrodes and also reduces RF power consumption by half by eliminating the RF mixer. The provided single-sideband (SSB) signal generator has the advantages of compact structure, low cost, and energy efficiency. By rationally designing the length of the optical delay line, the generator can also be easily extended to higher frequency ranges without additional cost. Claims 3 pages, Description 9 pages, Drawings 18 pages, CN 121864206 A 2026.04.14 CN 1 21 86 42 06 A 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; and a sideband suppression optical circuit, the 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 full-carrier single-sideband signal. 2. The single-sideband signal generator according to claim 1, wherein the first optical delay line path is based on the followingThin-film waveguides made from any 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 of claim 1, wherein the sideband suppression optical circuit further comprises 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 of claim 3, wherein the adjustable phase shifter is any 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. 5. The single-sideband signal generator of 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; a sideband suppression optical circuit, the 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 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 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 carrier-suppressed single-sideband signal. 8. The single-sideband signal generator of claim 7, wherein the optical combining circuit comprises an optical combiner, the optical combiner being 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 of claim 7, wherein the optical combining circuit comprises: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 full-carrier single-sideband signal; a second optical combiner, coupled to the second optical delay line path and the second optical bypass path and configured to combine the second phase-shifted optical signal and the second bypass optical signal to obtain a second full-carrier single-sideband signal; and a third optical combiner, 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 of claim 7, wherein the optical combining circuit comprises: a first optical combiner coupled to the first optical delay line path and the second optical bypass path and 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 coupled to the second optical delay line path and the first optical bypass path and configured to combine the second phase-shifted optical signal and the first bypass optical signal to obtain a second full-carrier single-sideband signal; and a third optical combiner 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 of 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 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 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. 14. The single-sideband signal generator of 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 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. (Claims 2 / 3, Page 3, CN 121864206 A) 16. The single-sideband signal generator of 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 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 of 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 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 of claim 1 and the single-sideband generator of claim 7. Claims 3 / 3 Page 4 CN 121864206 A Single-sideband generator based on optical delay line Technical Field

[0001] The present 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 Art

[0002] With the increasing demand for data transmission rates from applications such as 5G / 6G networks, the Internet of Things (IoT), massive MIMO, and RoF (RoF) systems, the infrastructure of base stations and data centers is facing unprecedented pressure. Compared to coherent detection systems, direct detection systems only require photodiodes to receive signals, thus offering advantages such as 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 be used to implement a full-carrier SSB (FC-SSB), while an IQ modulator can generate a carrier-suppressed SSB (CS-SSB). Both of these schemes require applying two radio frequency (RF) signals with a 90° phase difference to two separate signal electrodes. Achieving this phase difference typically 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 result in 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 shows a schematic diagram of a conventional FC-SSB modulation structure based on DDMZM and a CS-SSB modulation structure based on an IQ modulator. 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 overall system structure, large size, and 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.

[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 achieves the required phase delay through high-precision nanoscale integrated manufacturing processes. With this design, this invention 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, power consumption, and simplifying the overall system architecture.

[0006] According to a first aspect of the invention, a single-sideband signal generator is provided. The single-sideband signal generator includes: 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, the sideband suppression optical circuit including: 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; and a first optical bypass path coupled to a second modulation branch and configured to obtain a first photonic RF phase-shifted optical signal based on the first modulated optical signal. (Page 1 / 9 of the specification, CN 121864206 A)A first bypass optical signal is obtained by modulating two optical signals; and a first optical combiner is coupled to the first optical delay line path and the first optical bypass line 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 invention, a single-sideband signal generator is provided. The single-sideband signal generator includes: 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, the sideband suppression optical circuit including: 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 combination 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 present invention, a single-sideband (SSB) signal generator is provided, comprising a SSB signal generator according to a first aspect and a SSB signal generator according to a 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 prior art solutions, the method provided by the present invention saves approximately half the space by eliminating redundant signal electrodes, significantly simplifies the device structure, and reduces RF power consumption by half. Furthermore, this solution eliminates the need for an RF mixer and can extend to higher frequency domains through reasonable design of the optical delay line length without incurring additional costs.

[0010] The provided SSB signal generation technology can achieve compact, low-cost, and energy-efficient SSB signal output, and is suitable for various application scenarios, including direct detection systems, frequency-modulated continuous wave radar / LiDAR, frequency up / down conversion, and optical vectoring.Network analyzers and cold atom interferometer systems are also discussed. Specifically, the proposed FC-SSB signal generator can be widely used in incoherent and coherent direct detection systems (such as Kramers-Kronig receivers), and is 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.

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

[0012] FIG1 shows a schematic diagram of 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] FIG2A shows a simplified schematic diagram of an FC-SSB signal generator according to one embodiment of the invention; FIG2B shows an optoelectronic circuit diagram of the SSB signal generator of FIG2A;

[0014] FIG3A and 3B show different configurations of adjustable phase shifters according to various embodiments of the invention;

[0015] FIG4A shows a simplified schematic diagram of a CS-SSB signal generator according to another embodiment of the invention; FIG4B shows an optoelectronic circuit diagram of the SSB signal generator of FIG4A;

[0016] FIG5A to 5D show different configurations of adjustable delay lines and phase shifters according to various embodiments of the invention;

[0017] Figures 6A to 6C show three different CS-SSB generation schemes, respectively;

[0018] Figure 7A shows a simplified schematic diagram of a signal generator according to another embodiment of the present invention; and Figure 7B shows a photomicrograph of the signal generator fabricated according to the schematic diagram of Figure 7A;

[0019] Figures 8A and 8B show the measurement results of FC-SSB and CS-SSB generation; and

[0020] Figure 9 shows the resistance of the simplified SSB signal to the frequency-selective power fading problem of the double-sideband (DSB) signal. Detailed Description

[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 so as not to obscure the invention; however, this disclosure is prepared so that those skilled in the art can practice the teachings herein without performing excessive 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] FIG2A shows a simplified schematic diagram of an SSB signal generator according to an embodiment of the present invention. Instead of using an RF 90° mixer or a dual-channel RF source (FIG. 1), the proposed method utilizes a photonic RF phase shifter implemented by an optical delay line.

[0024] As shown in FIG2A, 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 photonic RF phase-shifted optical signal.

[0027] The optical delay line path 111 acts as a photonic RF phase shifter, where the delay time τm is equal to one-quarter of the time period Tm of the modulated RF signal, i.e., τm = 1 / 4Tm. 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) photonic 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 shows the optoelectronic circuit diagram of the SSB signal generator 100, 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. (Page 3 / 9, 7 CN)121864206 A. Then, the first modulated optical signal (represented by the spectrum at point b) passes through the optical delay line path 111 with a delay time (Tm) equal to one-quarter of the period of the target RF frequency, thereby introducing a 90° photonic RF phase shift to obtain a first photonic RF phase-shifted optical signal (represented by the spectrum at point c).

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

[0031] A 90° photonic RF phase shift (or delay time) is ensured by carefully designing the delay length. This benefits from the high-precision nanofabrication process in the integrated platform, which 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 multiple straight segments; and multiple circularly curved segments interposed between the multiple straight segments to form a delay line. The curved and straight segments may be arranged to form arbitrary routing structures, such as spiral shapes or similar shapes that can be used for delay. It should be understood that the routing structure may be other suitable routing configurations that can introduce additional lengths with specific delay times in one branch compared to another. 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.

[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 cumulative 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 a modulation electrode (not shown).

[0034] An adjustable phase shifter is used to ensure the correct phase for destructive interference and sideband selection. Referring to Figures 3A and 3B, the adjustable phase shifter 114 can be coupled to a first optical delay line path 111, as shown in Figure 3A. Alternatively, as shown in Figure 3B, the adjustable phase shifter 114 can be arranged along a first optical bypass path 112 and configured to fine-tune the first bypass optical signal before recombination.

[0035] In some embodiments, the adjustable phase shifter 114 can 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 can 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] FIG4A shows a simplified schematic diagram of an SSB signal generator 200 according to another embodiment of the present invention.

[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 end of which is coupled to a first output end of the beam splitter 201 to receive the first optical input signal; a second modulation branch 202b, the input end of which is coupled to a second output end 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 photonic RF phase-shifted optical signal to ensure destructive interference between the first photonic RF phase-shifted optical signal and the first bypass optical signal and / or select the sideband to be suppressed. Specification page 4 / 9 8 CN 121864206 A

[0040] The sideband suppression optical circuit 210 further includes: a second optical delay line path 211b, the second optical delay line path being 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, the second optical bypass path being 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, the optical combination circuit being 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] FIG4B shows an optoelectronic circuit diagram of the SSB signal generator 200, where the simplified spectrum of the optical signal is indicated at points A to J.

[0045] Referring to FIG4B, for carrierless SSB signal generation, the optical carrier signal (represented by the spectrum at point A) is first split into two branches and modulated by a single-drive modulator.

[0046] A phase shift of π is introduced by adjusting the bias point by applying a DC voltage to the electrodes of the modulator, which can alternatively be replaced by an additional adjustable phase shifter at the end of the recombination region. After modulation, each branch is further split into two branches, resulting in a total of four branches. Then, an optical delay line is 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, a first modulated optical signal (whose spectrum is the same as that at point B) passes through the optical delay line path 211a with a delay time (Tm) equal to one-quarter of the period of the target RF frequency, thereby introducing a 90° photon RF phase shift to obtain a first photon RF phase-shifted optical signal (represented by the spectrum at point C). Then, an 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) passes through the optical delay line path 211b with a delay time (τm) equal to one-quarter of the period of the target RF frequency, thereby introducing a 90° photonic RF phase shift to obtain a second photonic RF phase-shifted optical signal (represented by the spectrum at point E). Then, the 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] The adjustable phase shifter is used in conjunction with the optical delay line to ensure the correct phase for destructive interference and sideband selection. The first optical delay line can be arranged in the lower branch (as shown in Figures 5A and 5C) or the upper branch (as shown in Figures 5B and 5D). The second optical delay line can be arranged in the upper branch (as shown in Figures 5A and 5D) or the lower branch (as shown in Figures 5B and 5C). Adjustable phase shifterThe device can be arranged in a branch with an optical delay line, or alternatively in a branch without an optical delay line path (i.e., an optical side path). For example, as shown in FIG5A, adjustable phase shifters 214a / 214b can be coupled to optical delay line paths 211a / 211b. Alternatively, as shown in FIG5B, adjustable phase shifters 214a / 214b can be arranged along optical side path paths 212a / 212b. Alternatively, as shown in FIG5C, adjustable phase shifter 214a can be coupled to optical delay line path 211a, while adjustable phase shifter 214b can be arranged along optical side path path 212b. Alternatively, as shown in FIG5D, adjustable phase shifter 214a can be arranged along optical side path path 212a, while adjustable phase shifter 214b can be coupled to 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 plurality of straight segments to form a delay line. The curved and straight segments may be arranged to form an arbitrary routing structure, such as a spiral shape or a similar shape 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 shifter can have other suitable structures to adapt to various situations.

[0052] It should be noted that for CS-SSB generation, the sideband can be suppressed first by using waveguide cross-switching branches II and III to first combine branches I and III and then combine branches II and IV (as shown in FIG6A). 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 is 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 is 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 second phase-shifted optical signal and the second bypass optical signal to obtain a second FC-SSB signal.A first FC-SSB signal and a second FC-SSB signal are used 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 (as shown in FIG6B). 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 is 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 is 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 another embodiment shown in FIG6C, branches I to 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° photonic RF phase shift, the generation of FC-SSB and CS-SSB can be achieved by applying different phase shifts using a phase shifter.

[0056] FIG7A shows a simplified schematic diagram of a signal generator 300 according to another embodiment of the present invention. FIG7B shows a photomicrograph of the signal generator fabricated according to the schematic diagram of FIG7A. 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] Consider the optical carrier as where ω0 is the carrier frequency. The RF signal is given by sin(ωmt), where ωm represents 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 the anti-electric field causes their modulation terms to have opposite signs. After modulation, one branch passes through the optical delay line with a delay time τm equal to one-quarter of the period of the target modulation frequency. Subsequently, the phase is adjusted by a thermal phase shifter, thereby introducing a phase shift delay and the phase-shifted electric field 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:

[0066]

[0067] If only the first-order sideband is considered, the output will be:

[0068] Specification 7 / 9 pages 11 CN 121864206 A

[0069] It can be simplified to:

[0070]

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

[0072]

[0073] k is an integer. When it is equal to, the positive first-order sideband will be canceled.

[0074] 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] where, and are the optical phase shifts induced by the two thermal phase shifters and the DC voltage applied to the modulation electrode. The output can be simplified to:

[0077] F(Ea+Eb+Ec+Ed)=A0J-1(β)δ(ω +ωm-ω0) (9)

[0078] where the positive first-order sideband and the carrier are canceled in the following case:

[0079]

[0080]

[0081] k is an integer. The negative first-order sideband will be canceled when the terms in equation (10) are equal to.

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

[0083] Optical Delay Line Design

[0084] The delay time is carefully designed under the design objective of achieving the delay time required for destructive interference in the first sideband by controlling the additional routing length of one branch relative to another branch. Due to the anisotropy of the material, the waveguide in the y-z 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 are used instead of helices for routing.

[0085] The delay time of the bend is calculated by integrating the group exponent along the routing crystal angle: Specification 8 / 9 Page 12 CN 121864206 A

[0086]

[0087] where τ is the delay of the bend, r is the radius of the circular bend, and ng(θ) is the group exponent at angle θ.

[0088] Taking the delay line for FC-SSB at 25 GHz 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 25 GHz signal.

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

[0090] Figures 8A and 8B present the measurement results of FC-SSB and CS-SSB generation, showing that the sideband rejection ratios of FC-SSB and CS-SSB are 22.1 dB and 22.5 dB, respectively, and the sideband carrier rejection ratio of CS-SSB is 16.9 dB. Furthermore, Figure 9 demonstrates the good resistance of the simplified SSB signal to the frequency-selective power fading problem.

[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. Instruction manual page 9 / 9, page 13, CN 121864206 A, Figure 1; Instruction manual figure 1 / 18, page 14, CN 121864206 A, Figure 2A; Instruction manual figure 2 / 18, page 15, CN 121864206 A, Figure 2B; Instruction manual figure 3 / 18, page 16, CN 121864206 A, Figure 3A; Instruction manual figure 4 / 18, page 17, CN 121864206 A, Figure 3B; Instruction manual figure 5 / 18, page 18, CN 121864206 A, Figure 4A; Instruction manual figure 6 / 18, page 19, CN 121864206 A, Figure 4B; Instruction manual figure 7 / 18, page 20, CN 121864206 A, Figure 5A; Instruction manual figure 8 / 18, page 21, CN 121864206 A, Figure 5B; Instruction manual figure 9 / 18, page 22, CN 121864206 A Figure 5C: Appendix to the instruction manual, page 10 / 18, 23 CN 121864206 A Figure 5D: Appendix to the instruction manual, page 11 / 18, 24 CN 121864206 A Figure 6A: Appendix to the instruction manual, page 12 / 18, 25 CN 121864206 A Figure 6B: Appendix to the instruction manual, page 13 / 18, 26 CN121864206 A Figure 6C Description Drawings Page 14 / 18 27 CN 121864206 A Figure 7A Description Drawings Page 15 / 18 28 CN 121864206 A Figure 7B Description Drawings Page 16 / 18 29 CN 121864206 A Figures 8A 8B Description Drawings Page 17 / 18 30 CN 121864206 A Figure 9 Description Drawings Page 18 / 18 31 CN 121864206 A Abstract The present invention provides a single sideband signal generator including a modulator configured to generate a first and a second modulated optical signals which have equal amplitudes; a first optical delay line-based sideband suppressing optical circuit for generating a full-carrier single sideband signal and / or a second optical delay line-based sideband suppressing optical circuit for generating a carrier- suppressed single sideband signal. The present invention simplifies the structure by saving half of the space occupied by the redundant signal electrodes and also reducing the RF power consumption by half by removing the RF hybrid. The provided single sideband (SSB) signal generator has advantages of compactness, low-cost, and power-efficiency and thegenerator can be easily scaled to higher frequency domains without additional cost by appropriately designing the optical delay line length.

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.

Images