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Integrated Optics|131 Article(s)
Integrated spatial photonic XY Ising sampler based on a high-uniformity 1 × 8 multi-mode interferometer
Xin Ye, Wenjia Zhang, and Zuyuan He
Spatial photonic Ising machines, as emerging artificial intelligence hardware solutions by leveraging unique physical phenomena, have shown promising results in solving large-scale combinatorial problems. However, spatial light modulator enabled Ising machines still remain bulky, are very power demanding, and have poor stability. In this study, we propose an integrated XY Ising sampler based on a highly uniform multimode interferometer and a phase shifter array, enabling the minimization of both discrete and continuous spin Hamiltonians. We elucidate the performance of this computing platform in achieving fully programmable spin couplings and external magnetic fields. Additionally, we successfully demonstrate the weighted full-rank Ising model with a linear dependence of 0.82 and weighted MaxCut problem solving with the proposed sampler. Our results illustrate that the developed structure has significant potential for larger-scale, reduced power consumption and increased operational speed, positioning it as a versatile platform for commercially viable high-performance samplers of combinatorial optimization problems. Spatial photonic Ising machines, as emerging artificial intelligence hardware solutions by leveraging unique physical phenomena, have shown promising results in solving large-scale combinatorial problems. However, spatial light modulator enabled Ising machines still remain bulky, are very power demanding, and have poor stability. In this study, we propose an integrated XY Ising sampler based on a highly uniform multimode interferometer and a phase shifter array, enabling the minimization of both discrete and continuous spin Hamiltonians. We elucidate the performance of this computing platform in achieving fully programmable spin couplings and external magnetic fields. Additionally, we successfully demonstrate the weighted full-rank Ising model with a linear dependence of 0.82 and weighted MaxCut problem solving with the proposed sampler. Our results illustrate that the developed structure has significant potential for larger-scale, reduced power consumption and increased operational speed, positioning it as a versatile platform for commercially viable high-performance samplers of combinatorial optimization problems.
Photonics Research
- Publication Date: May. 01, 2025
- Vol. 13, Issue 5, 1419 (2025)
Lithium tantalate microring cavities with a Q factor exceeding 10 million |Spotlight on Optics
Jianfeng He, Xinyi Zhao, Jian-Bin Xu, and Xiankai Sun
Thin-film lithium niobate has attracted great interest in high-speed communication due to its unique piezoelectric and nonlinear properties. However, its high photorefraction and slow electro-optic response relaxation introduce the possibility of transmission bit errors. Recently, lithium tantalate, another piezoelectric and nonlinear material, has emerged as a promising candidate for active photonic integrated devices because of its weaker photorefraction, faster electro-optic response relaxation, higher optical damage threshold, wider transparency window, and lower birefringence compared with lithium niobate. Here, we developed an ultralow-loss lithium tantalate integrated photonic platform, including waveguides, grating couplers, and microring cavities. The measured highest optical Q factor of the microring cavities is beyond 107, corresponding to the lowest waveguide propagation loss of ∼1.88 dB/m. The photorefractive effect in such lithium tantalate microring cavities was experimentally demonstrated to be 500 times weaker than that in lithium niobate microcavities. This work lays the foundation for a lithium tantalate integrated platform for achieving a series of on-chip optically functional devices, such as periodically poled waveguides, acousto-optic modulators, and electro-optic modulators. Thin-film lithium niobate has attracted great interest in high-speed communication due to its unique piezoelectric and nonlinear properties. However, its high photorefraction and slow electro-optic response relaxation introduce the possibility of transmission bit errors. Recently, lithium tantalate, another piezoelectric and nonlinear material, has emerged as a promising candidate for active photonic integrated devices because of its weaker photorefraction, faster electro-optic response relaxation, higher optical damage threshold, wider transparency window, and lower birefringence compared with lithium niobate. Here, we developed an ultralow-loss lithium tantalate integrated photonic platform, including waveguides, grating couplers, and microring cavities. The measured highest optical Q factor of the microring cavities is beyond 107, corresponding to the lowest waveguide propagation loss of ∼1.88 dB/m. The photorefractive effect in such lithium tantalate microring cavities was experimentally demonstrated to be 500 times weaker than that in lithium niobate microcavities. This work lays the foundation for a lithium tantalate integrated platform for achieving a series of on-chip optically functional devices, such as periodically poled waveguides, acousto-optic modulators, and electro-optic modulators.
Photonics Research
- Publication Date: May. 01, 2025
- Vol. 13, Issue 5, 1385 (2025)
Experimental evaluation of continuous and pixelated dispersive optical phased arrays for 2D beam steering
Mennatallah Kandil, Mathias Prost, Jon Kjellman, Wim Bogaerts, and Marcus Dahlem
Dispersive optical phased arrays (DOPAs) offer a method for fast 2D beam scanning for solid-state LiDAR with a pure passive operation, and therefore low control complexity and low power consumption. However, in terms of scalability, state-of-the-art DOPAs do not easily achieve a balanced performance over the specifications of long-range LiDAR, including the number of pixels (resolvable points) and beam quality. Here, we experimentally demonstrate the pixelated DOPA concept, which overcomes the scaling challenges of classical (continuous) DOPAs by introducing a new design degree of freedom: the discretization of the optical delay lines distribution network into blocks. We also present the first demonstration of the unbalanced splitter tree architecture for the DOPA distribution network, incorporated in both the continuous DOPA and the pixelated DOPA variations. The small-scale demonstration circuits can scan over a field of view of 15°×7.2°, where the continuous DOPA provides 16×25 pixels, while the pixelated DOPA provides 4×25 pixels, for a 1500 to 1600 nm wavelength sweep. The pixelated DOPA exhibits a side lobe suppression ratio with a median of 7.6 dB, which is higher than that of the continuous version, with a median of 3.6 dB. In addition, the ratio of the main beam to the background radiation pattern is 11 dB (median value) for the pixelated DOPA, while for the continuous DOPA, it is 9.5 dB. This is an indication of a higher beam quality and lower phase errors in the pixelated DOPA. The degree of discretization, combined with other design parameters, will potentially enable better control over the beam quality, while setting practical values for the number of pixels for large-scale DOPAs. Dispersive optical phased arrays (DOPAs) offer a method for fast 2D beam scanning for solid-state LiDAR with a pure passive operation, and therefore low control complexity and low power consumption. However, in terms of scalability, state-of-the-art DOPAs do not easily achieve a balanced performance over the specifications of long-range LiDAR, including the number of pixels (resolvable points) and beam quality. Here, we experimentally demonstrate the pixelated DOPA concept, which overcomes the scaling challenges of classical (continuous) DOPAs by introducing a new design degree of freedom: the discretization of the optical delay lines distribution network into blocks. We also present the first demonstration of the unbalanced splitter tree architecture for the DOPA distribution network, incorporated in both the continuous DOPA and the pixelated DOPA variations. The small-scale demonstration circuits can scan over a field of view of 15°×7.2°, where the continuous DOPA provides 16×25 pixels, while the pixelated DOPA provides 4×25 pixels, for a 1500 to 1600 nm wavelength sweep. The pixelated DOPA exhibits a side lobe suppression ratio with a median of 7.6 dB, which is higher than that of the continuous version, with a median of 3.6 dB. In addition, the ratio of the main beam to the background radiation pattern is 11 dB (median value) for the pixelated DOPA, while for the continuous DOPA, it is 9.5 dB. This is an indication of a higher beam quality and lower phase errors in the pixelated DOPA. The degree of discretization, combined with other design parameters, will potentially enable better control over the beam quality, while setting practical values for the number of pixels for large-scale DOPAs.
Photonics Research
- Publication Date: Apr. 30, 2025
- Vol. 13, Issue 5, 1330 (2025)
On-chip tunable single-mode high-power narrow-linewidth Fabry–Perot microcavity laser on Yb3+-doped thin-film lithium niobate
Qinfen Huang, Zhiwei Fang, Zhe Wang, Yiran Zhu... and Ya Cheng|Show fewer author(s)
Ytterbium ion (Yb3+)-doped lasers are widely used in precision machining and precision measurement fields because of their high efficiency and high power, which are primarily based on solid-state lasers and fiber lasers. Here, we demonstrate an on-chip Yb3+-doped thin-film lithium niobate (Yb:TFLN) Fabry–Perot microcavity laser. We achieve single-frequency laser operation at 1030 and 1060 nm with a side-mode suppression ratio above 30 dB, an emission linewidth below 40 pm, and an output power up to 1.5 mW at 1060 nm and 0.3 mW at 1030 nm. In addition, using the electro-optic effect of lithium niobate, we achieve a laser tuning efficiency of 4 pm/V. This work opens the path to on-chip high-power and mode-locked ultrafast laser output. Ytterbium ion (Yb3+)-doped lasers are widely used in precision machining and precision measurement fields because of their high efficiency and high power, which are primarily based on solid-state lasers and fiber lasers. Here, we demonstrate an on-chip Yb3+-doped thin-film lithium niobate (Yb:TFLN) Fabry–Perot microcavity laser. We achieve single-frequency laser operation at 1030 and 1060 nm with a side-mode suppression ratio above 30 dB, an emission linewidth below 40 pm, and an output power up to 1.5 mW at 1060 nm and 0.3 mW at 1030 nm. In addition, using the electro-optic effect of lithium niobate, we achieve a laser tuning efficiency of 4 pm/V. This work opens the path to on-chip high-power and mode-locked ultrafast laser output.
Photonics Research
- Publication Date: Apr. 01, 2025
- Vol. 13, Issue 4, 935 (2025)
Multi-channel Hong–Ou–Mandle interference between independent comb-based weak coherent pulses
Long Huang, Linhan Tang, Yang Wang, Minhui Cheng... and Wenfu Zhang|Show fewer author(s)
With the widespread application of quantum communication technology, there is an urgent need to enhance unconditionally secure key rates and capacity. Measurement-device-independent quantum key distribution (MDI-QKD), proven to be immune to detection-side channel attacks, is a secure and reliable quantum communication scheme. The core of this scheme is Hong–Ou–Mandle (HOM) interference, a quantum optical phenomenon with no classical analog, where identical photons meeting on a symmetric beam splitter (BS) undergo interference and bunching. Any differences in the degrees of freedom (frequency, arrival time, spectrum, polarization, and the average number of photons per pulse) between the photons will deteriorate the interference visibility. Here, we demonstrate 16-channel weak coherent pulses (WCPs) of HOM interference with all channels’ interference visibility over 46% based on two independent frequency-post-aligned soliton microcombs (SMCs). In our experiment, full locking and frequency alignment of the comb teeth between the two SMCs were achieved through pump frequency stabilization, SMC repetition rate locking, and fine tuning of the repetition rate. This demonstrates the feasibility of using independently generated SMCs as multi-wavelength sources for quantum communication. Meanwhile, SMC can achieve hundreds of frequency-stable comb teeth by locking only two parameters, which further reduces the complexity of frequency locking and the need for finding sufficient suitable frequency references compared to independent laser arrays. With the widespread application of quantum communication technology, there is an urgent need to enhance unconditionally secure key rates and capacity. Measurement-device-independent quantum key distribution (MDI-QKD), proven to be immune to detection-side channel attacks, is a secure and reliable quantum communication scheme. The core of this scheme is Hong–Ou–Mandle (HOM) interference, a quantum optical phenomenon with no classical analog, where identical photons meeting on a symmetric beam splitter (BS) undergo interference and bunching. Any differences in the degrees of freedom (frequency, arrival time, spectrum, polarization, and the average number of photons per pulse) between the photons will deteriorate the interference visibility. Here, we demonstrate 16-channel weak coherent pulses (WCPs) of HOM interference with all channels’ interference visibility over 46% based on two independent frequency-post-aligned soliton microcombs (SMCs). In our experiment, full locking and frequency alignment of the comb teeth between the two SMCs were achieved through pump frequency stabilization, SMC repetition rate locking, and fine tuning of the repetition rate. This demonstrates the feasibility of using independently generated SMCs as multi-wavelength sources for quantum communication. Meanwhile, SMC can achieve hundreds of frequency-stable comb teeth by locking only two parameters, which further reduces the complexity of frequency locking and the need for finding sufficient suitable frequency references compared to independent laser arrays.
Photonics Research
- Publication Date: Mar. 11, 2025
- Vol. 13, Issue 4, 837 (2025)
High-linearity wide-bandwidth integrated thin-film lithium niobate modulator based on a dual-optical-mode co-modulated configuration
Heyun Tan, Junwei Zhang, Jingyi Wang, Songnian Fu... and Xinlun Cai|Show fewer author(s)
High-linearity electro-optic (EO) modulators play a crucial role in microwave photonics (MWP). Although various methods have been explored to enhance linearity in MWP links, they are often constrained by the intrinsic nonlinearity of modulator materials, the complexity of external control devices, the bulkiness of structures, and bandwidth limitations. In this study, we present an integrated thin-film lithium niobate (TFLN) linear Mach–Zehnder modulator (LMZM), showing, to our knowledge, a record-high spurious-free dynamic range (SFDR) of 121.7 dB·Hz4/5 at 1 GHz with an optical power (OP) of 5.5 dBm into the photodetector (PD), based on a wide-bandwidth (>50 GHz) dual-optical-mode (TE0 and TE1) co-modulated configuration with just one RF input. Additionally, compared to conventional MZMs (CMZMs), the LMZM exhibits a >10.6-dB enhancement in SFDR with an OP of >-8 dBm at 1 GHz, and maintains a 6.07-dB SFDR improvement even at 20 GHz with an OP of 0 dBm. The novel LMZM, featuring high linearity, wide bandwidth, structural simplicity, and high integration, holds significant potential as a key component in future large-scale and high-performance MWP integrated circuits. High-linearity electro-optic (EO) modulators play a crucial role in microwave photonics (MWP). Although various methods have been explored to enhance linearity in MWP links, they are often constrained by the intrinsic nonlinearity of modulator materials, the complexity of external control devices, the bulkiness of structures, and bandwidth limitations. In this study, we present an integrated thin-film lithium niobate (TFLN) linear Mach–Zehnder modulator (LMZM), showing, to our knowledge, a record-high spurious-free dynamic range (SFDR) of 121.7 dB·Hz4/5 at 1 GHz with an optical power (OP) of 5.5 dBm into the photodetector (PD), based on a wide-bandwidth (>50 GHz) dual-optical-mode (TE0 and TE1) co-modulated configuration with just one RF input. Additionally, compared to conventional MZMs (CMZMs), the LMZM exhibits a >10.6-dB enhancement in SFDR with an OP of >-8 dBm at 1 GHz, and maintains a 6.07-dB SFDR improvement even at 20 GHz with an OP of 0 dBm. The novel LMZM, featuring high linearity, wide bandwidth, structural simplicity, and high integration, holds significant potential as a key component in future large-scale and high-performance MWP integrated circuits.
Photonics Research
- Publication Date: Mar. 11, 2025
- Vol. 13, Issue 4, 817 (2025)
Silicon-integrated scandium-doped aluminum nitride electro-optic modulator
Tianqi Xu, Yushuai Liu, Yuanmao Pu, Yongxiang Yang... and Ting Hu|Show fewer author(s)
Scandium-doped aluminum nitride (AlScN) with an asymmetric hexagonal wurtzite structure exhibits enhanced second-order nonlinear and piezoelectric properties compared to aluminum nitride (AlN), while maintaining a relatively large bandgap. It provides a promising platform for photonic circuits and facilitates the seamless integration of passive and active functional devices. Here, we present the design, fabrication, and characterization of Al0.904Sc0.096N electro-optic (EO) micro-ring modulators, introducing active functionalities to the chip-scale AlScN platform. These waveguide-integrated EO modulators utilize sputtered Al0.904Sc0.096N thin films as the light-guiding medium, with the entire fabrication process being compatible with complementary metal-oxide-semiconductor (CMOS) technology. We extract the in-device effective EO coefficient of 2.86 pm/V at 12 GHz. The devices show a minimum half-wave voltage-length product of 3.12 V·cm at a modulation frequency of 14 GHz, and achieve a 3-dB modulation bandwidth of approximately 22 GHz. Our work provides a promising modulation scheme for cost-effective silicon-integrated photonics systems. Scandium-doped aluminum nitride (AlScN) with an asymmetric hexagonal wurtzite structure exhibits enhanced second-order nonlinear and piezoelectric properties compared to aluminum nitride (AlN), while maintaining a relatively large bandgap. It provides a promising platform for photonic circuits and facilitates the seamless integration of passive and active functional devices. Here, we present the design, fabrication, and characterization of Al0.904Sc0.096N electro-optic (EO) micro-ring modulators, introducing active functionalities to the chip-scale AlScN platform. These waveguide-integrated EO modulators utilize sputtered Al0.904Sc0.096N thin films as the light-guiding medium, with the entire fabrication process being compatible with complementary metal-oxide-semiconductor (CMOS) technology. We extract the in-device effective EO coefficient of 2.86 pm/V at 12 GHz. The devices show a minimum half-wave voltage-length product of 3.12 V·cm at a modulation frequency of 14 GHz, and achieve a 3-dB modulation bandwidth of approximately 22 GHz. Our work provides a promising modulation scheme for cost-effective silicon-integrated photonics systems.
Photonics Research
- Publication Date: Jan. 31, 2025
- Vol. 13, Issue 2, 477 (2025)
Microwave-resonator-enabled broadband on-chip electro-optic frequency comb generation|On the Cover , Spotlight on Optics
Zhaoxi Chen, Yiwen Zhang, Hanke Feng, Yuansong Zeng... and Cheng Wang|Show fewer author(s)
Optical frequency combs play a crucial role in optical communications, time-frequency metrology, precise ranging, and sensing. Among various generation schemes, resonant electro-optic combs are particularly attractive for their excellent stability, flexibility, and broad bandwidths. In this approach, an optical pump undergoes multiple electro-optic modulation processes in a high-Q optical resonator, resulting in cascaded spectral sidebands. However, most resonant electro-optic combs to date make use of lumped-capacitor electrodes with relatively inefficient utilization of the input electrical power. This design also reflects most electrical power back to the driving circuits and necessitates costly radio-frequency (RF) isolators in between, presenting substantial challenges in practical applications. To address these issues, we present an RF circuit friendly electro-optic frequency comb generator incorporated with on-chip coplanar microwave resonator electrodes, based on a thin-film lithium niobate platform. Our design achieves more than three times electrical power reduction with minimal reflection at the designed comb repetition rate of ∼25 GHz. We experimentally demonstrate broadband electro-optic frequency comb generation with a comb span of >85 nm at a moderate electrical driving power of 740 mW (28.7 dBm). Our power-efficient and isolator-free electro-optic comb source could offer a compact, low-cost, and simple-to-design solution for applications in spectroscopy, high-precise metrology, and optical communications. Optical frequency combs play a crucial role in optical communications, time-frequency metrology, precise ranging, and sensing. Among various generation schemes, resonant electro-optic combs are particularly attractive for their excellent stability, flexibility, and broad bandwidths. In this approach, an optical pump undergoes multiple electro-optic modulation processes in a high-Q optical resonator, resulting in cascaded spectral sidebands. However, most resonant electro-optic combs to date make use of lumped-capacitor electrodes with relatively inefficient utilization of the input electrical power. This design also reflects most electrical power back to the driving circuits and necessitates costly radio-frequency (RF) isolators in between, presenting substantial challenges in practical applications. To address these issues, we present an RF circuit friendly electro-optic frequency comb generator incorporated with on-chip coplanar microwave resonator electrodes, based on a thin-film lithium niobate platform. Our design achieves more than three times electrical power reduction with minimal reflection at the designed comb repetition rate of ∼25 GHz. We experimentally demonstrate broadband electro-optic frequency comb generation with a comb span of >85 nm at a moderate electrical driving power of 740 mW (28.7 dBm). Our power-efficient and isolator-free electro-optic comb source could offer a compact, low-cost, and simple-to-design solution for applications in spectroscopy, high-precise metrology, and optical communications.
Photonics Research
- Publication Date: Jan. 30, 2025
- Vol. 13, Issue 2, 426 (2025)
On-chip microresonator dispersion engineering via segmented sidewall modulation
Masoud Kheyri, Shuangyou Zhang, Toby Bi, Arghadeep Pal... and Pascal Del’Haye|Show fewer author(s)
Microresonator dispersion plays a crucial role in shaping the nonlinear dynamics of microcavity solitons. Here, we introduce and validate a method for dispersion engineering through modulating a portion of the inner edge of ring waveguides. We demonstrate that such partial modulation has a broadband effect on the dispersion profile, whereas modulation on the entire resonator’s inner circumference leads to mode splitting primarily affecting one optical mode. The impact of spatial modulation amplitude, period, and number of modulations on the mode splitting profile is also investigated. Through the integration of four modulated sections with different modulation amplitudes and periods, we achieve mode splitting across more than 50 modes over a spectral range exceeding 100 nm in silicon nitride resonators. These results highlight both the simplicity and efficacy of our method in achieving flatter dispersion profiles. Microresonator dispersion plays a crucial role in shaping the nonlinear dynamics of microcavity solitons. Here, we introduce and validate a method for dispersion engineering through modulating a portion of the inner edge of ring waveguides. We demonstrate that such partial modulation has a broadband effect on the dispersion profile, whereas modulation on the entire resonator’s inner circumference leads to mode splitting primarily affecting one optical mode. The impact of spatial modulation amplitude, period, and number of modulations on the mode splitting profile is also investigated. Through the integration of four modulated sections with different modulation amplitudes and periods, we achieve mode splitting across more than 50 modes over a spectral range exceeding 100 nm in silicon nitride resonators. These results highlight both the simplicity and efficacy of our method in achieving flatter dispersion profiles.
Photonics Research
- Publication Date: Jan. 17, 2025
- Vol. 13, Issue 2, 367 (2025)
Heterogeneously integrated silicon-conductive oxide MOSCAP microring modulator array
Wei-Che Hsu, Saeed Abdolhosseini, Haisheng Rong, Ranjeet Kumar... and Alan X. Wang|Show fewer author(s)
In pursuit of energy-efficient optical interconnect, the silicon microring modulator (Si-MRM) has emerged as a pivotal device offering an ultra-compact footprint and capability of on-chip wavelength division multiplexing (WDM). This paper presents a 1×4 metal-oxide-semiconductor capacitor (MOSCAP) Si-MRM array gated by high-mobility titanium-doped indium oxide (ITiO), which was fabricated by combining Intel’s high-volume manufacturing process and the transparent conductive oxide (TCO) patterning with the university facility. The 1×4 Si-MRM array exhibits a high electro-optic (E-O) efficiency with Vπ·L of 0.12 V·cm and achieves a modulation rate of (3×25+1×15) Gb/s with a measured bandwidth of 14 GHz. Additionally, it can perform on-chip WDM modulation at four equally spaced wavelengths without using thermal heaters. The process compatibility between silicon photonics and TCO materials is verified by such an industry-university co-fabrication approach for the MOSCAP Si-MRM array and demonstrated enhanced performance from heterogeneous integration. In pursuit of energy-efficient optical interconnect, the silicon microring modulator (Si-MRM) has emerged as a pivotal device offering an ultra-compact footprint and capability of on-chip wavelength division multiplexing (WDM). This paper presents a 1×4 metal-oxide-semiconductor capacitor (MOSCAP) Si-MRM array gated by high-mobility titanium-doped indium oxide (ITiO), which was fabricated by combining Intel’s high-volume manufacturing process and the transparent conductive oxide (TCO) patterning with the university facility. The 1×4 Si-MRM array exhibits a high electro-optic (E-O) efficiency with Vπ·L of 0.12 V·cm and achieves a modulation rate of (3×25+1×15) Gb/s with a measured bandwidth of 14 GHz. Additionally, it can perform on-chip WDM modulation at four equally spaced wavelengths without using thermal heaters. The process compatibility between silicon photonics and TCO materials is verified by such an industry-university co-fabrication approach for the MOSCAP Si-MRM array and demonstrated enhanced performance from heterogeneous integration.
Photonics Research
- Publication Date: Dec. 24, 2024
- Vol. 13, Issue 1, 187 (2025)
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