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Integrated Optics|112 Article(s)
Time-space multiplexed photonic-electronic digital multiplier
Wenkai Zhang, Bo Wu, Wentao Gu, Junwei Cheng, Hailong Zhou, Liao Chen, Wenchan Dong, Jianji Dong, and Xinliang Zhang
Optical computing has shown immense application prospects in the post-Moore era. However, as a crucial component of logic computing, the digital multiplier can only be realized on a small scale in optics, restrained by the limited functionalities and inevitable loss of optical nonlinearity. In this paper, we propose a time-space multiplexed architecture to realize large-scale photonic-electronic digital multiplication. We experimentally demonstrate an 8×2-bit photonic-electronic digital multiplier, and the multiplication with a 32-bit number is further executed at 25 Mbit/s to demonstrate its extensibility and functionality. Moreover, the proposed architecture has the potential for on-chip implementation, and a feasible integration scheme is provided. We believe the time-space multiplexed photonic-electronic digital multiplier will open up a promising avenue for large-scale photonic digital computing. Optical computing has shown immense application prospects in the post-Moore era. However, as a crucial component of logic computing, the digital multiplier can only be realized on a small scale in optics, restrained by the limited functionalities and inevitable loss of optical nonlinearity. In this paper, we propose a time-space multiplexed architecture to realize large-scale photonic-electronic digital multiplication. We experimentally demonstrate an 8×2-bit photonic-electronic digital multiplier, and the multiplication with a 32-bit number is further executed at 25 Mbit/s to demonstrate its extensibility and functionality. Moreover, the proposed architecture has the potential for on-chip implementation, and a feasible integration scheme is provided. We believe the time-space multiplexed photonic-electronic digital multiplier will open up a promising avenue for large-scale photonic digital computing.
Photonics Research
- Publication Date: Mar. 01, 2024
- Vol. 12, Issue 3, 499 (2024)
Silicon photonic integrated interrogator for fiber-optic distributed acoustic sensing
Zhicheng Jin, Jiageng Chen, Yanming Chang, Qingwen Liu, and Zuyuan He
Distributed acoustic sensing (DAS) technology has been a promising tool in various applications. Currently, the large size and relatively high cost of DAS equipment composed of discrete devices restrict its further popularization to some degree, and the photonic integration technology offers a potential solution. In this paper, we demonstrate an integrated interrogator for DAS on the silicon-on-insulator (SOI) platform. The design of the chip revolves around a Mach–Zehnder modulator (MZM) transmitter and a dual-quadrature and dual-polarization coherent receiver. The integrated interrogator supports multiple DAS schemes, including the time-gated digital optical frequency domain reflectometry (TGD-OFDR), which is adopted for system performance evaluation. 59 pε/Hz strain resolution in 12.1 km sensing fiber with 1.14 m spatial resolution (SR) is realized. Besides, along 49.0 km sensing fiber, 81 pε/Hz strain resolution with 3.78 m SR is achieved. The results show that the integrated interrogator has comparable performance to the discrete DAS system. To the best of our knowledge, this is the first dedicated on-chip DAS interrogator, which validates the effectiveness of the blend of photonics integration and DAS technology. Distributed acoustic sensing (DAS) technology has been a promising tool in various applications. Currently, the large size and relatively high cost of DAS equipment composed of discrete devices restrict its further popularization to some degree, and the photonic integration technology offers a potential solution. In this paper, we demonstrate an integrated interrogator for DAS on the silicon-on-insulator (SOI) platform. The design of the chip revolves around a Mach–Zehnder modulator (MZM) transmitter and a dual-quadrature and dual-polarization coherent receiver. The integrated interrogator supports multiple DAS schemes, including the time-gated digital optical frequency domain reflectometry (TGD-OFDR), which is adopted for system performance evaluation. 59 pε/Hz strain resolution in 12.1 km sensing fiber with 1.14 m spatial resolution (SR) is realized. Besides, along 49.0 km sensing fiber, 81 pε/Hz strain resolution with 3.78 m SR is achieved. The results show that the integrated interrogator has comparable performance to the discrete DAS system. To the best of our knowledge, this is the first dedicated on-chip DAS interrogator, which validates the effectiveness of the blend of photonics integration and DAS technology.
Photonics Research
- Publication Date: Feb. 26, 2024
- Vol. 12, Issue 3, 465 (2024)
Chiral forces in longitudinally invariant dielectric photonic waveguides
Josep Martínez-Romeu, Iago Diez, Sebastian Golat, Francisco J. Rodríguez-Fortuño, and Alejandro Martínez
We calculate numerically the optical chiral forces in rectangular cross-section dielectric waveguides for potential enantiomer separation. Our study considers force strength and time needed for separating chiral nanoparticles, mainly via quasi-TE guided modes at short wavelengths (405 nm) and the 90°-phase-shifted combination of quasi-TE and quasi-TM modes at longer wavelengths (1310 nm). Particle tracking simulations show successful enantiomer separation within two seconds. These results suggest the feasibility of enantiomeric separation of nanoparticles displaying sufficient chirality using simple silicon photonic integrated circuits, with wavelength selection based on the nanoparticle size. We calculate numerically the optical chiral forces in rectangular cross-section dielectric waveguides for potential enantiomer separation. Our study considers force strength and time needed for separating chiral nanoparticles, mainly via quasi-TE guided modes at short wavelengths (405 nm) and the 90°-phase-shifted combination of quasi-TE and quasi-TM modes at longer wavelengths (1310 nm). Particle tracking simulations show successful enantiomer separation within two seconds. These results suggest the feasibility of enantiomeric separation of nanoparticles displaying sufficient chirality using simple silicon photonic integrated circuits, with wavelength selection based on the nanoparticle size.
Photonics Research
- Publication Date: Feb. 26, 2024
- Vol. 12, Issue 3, 431 (2024)
Mode-insensitive and mode-selective optical switch based on asymmetric Y-junctions and MMI couplers
Shijie Sun, Qidong Yu, Yuanhua Che, Tianhang Lian, Yuhang Xie, Daming Zhang, and Xibin Wang
Driven by the large volume demands of data in transmission systems, the number of spatial modes supported by mode-division multiplexing (MDM) systems is being increased to take full advantage of the parallelism of the signals in different spatial modes. As a key element for photonic integrated circuits, the multimode waveguide optical switch (MWOS) is playing an important role for data exchange and signal switching. However, the function of the traditional MWOS is simple, which could only implement the mode-insensitive or mode-selective switching function; it is also difficult to scale to accommodate more spatial modes because of the limitation of the device structure. Therefore, it is still challenging to realize a multifunctional and scalable MWOS that could support multiple modes with low power consumption and high flexibility. Here, we propose and experimentally demonstrate a multifunctional MWOS based on asymmetric Y-junctions and multimode interference (MMI) couplers fabricated on a polymer waveguide platform. Both mode-insensitive and mode-selective switching functions can be achieved via selectively heating different electrode heaters. The fabricated device with the total length of ∼0.8 cm shows an insertion loss of less than 12.1 dB, and an extinction ratio of larger than 8.4 dB with a power consumption of ∼32 mW for both mode-insensitive and mode-selective switching functions, at 1550 nm wavelength. The proposed MWOS can also be scaled to accommodate more spatial modes flexibly and easily, which can serve as an important building block for MDM systems. Driven by the large volume demands of data in transmission systems, the number of spatial modes supported by mode-division multiplexing (MDM) systems is being increased to take full advantage of the parallelism of the signals in different spatial modes. As a key element for photonic integrated circuits, the multimode waveguide optical switch (MWOS) is playing an important role for data exchange and signal switching. However, the function of the traditional MWOS is simple, which could only implement the mode-insensitive or mode-selective switching function; it is also difficult to scale to accommodate more spatial modes because of the limitation of the device structure. Therefore, it is still challenging to realize a multifunctional and scalable MWOS that could support multiple modes with low power consumption and high flexibility. Here, we propose and experimentally demonstrate a multifunctional MWOS based on asymmetric Y-junctions and multimode interference (MMI) couplers fabricated on a polymer waveguide platform. Both mode-insensitive and mode-selective switching functions can be achieved via selectively heating different electrode heaters. The fabricated device with the total length of ∼0.8 cm shows an insertion loss of less than 12.1 dB, and an extinction ratio of larger than 8.4 dB with a power consumption of ∼32 mW for both mode-insensitive and mode-selective switching functions, at 1550 nm wavelength. The proposed MWOS can also be scaled to accommodate more spatial modes flexibly and easily, which can serve as an important building block for MDM systems.
Photonics Research
- Publication Date: Feb. 08, 2024
- Vol. 12, Issue 3, 423 (2024)
Scalable orthogonal delay-division multiplexed OEO artificial neural network trained for TI-ADC equalization
Andrea Zazzi, Arka Dipta Das, Lukas Hüssen, Renato Negra, and Jeremy Witzens
We propose a new signaling scheme for on-chip optical-electrical-optical artificial neural networks that utilizes orthogonal delay-division multiplexing and pilot-tone-based self-homodyne detection. This scheme offers a more efficient scaling of the optical power budget with increasing network complexity. Our simulations, based on 220 nm silicon-on-insulator silicon photonics technology, suggest that the network can support 31×31 neurons, with 961 links and freely programmable weights, using a single 500 mW optical comb and a signal-to-noise ratio of 21.3 dB per neuron. Moreover, it features a low sensitivity to temperature fluctuations, ensuring that it can be operated outside of a laboratory environment. We demonstrate the network’s effectiveness in nonlinear equalization tasks by training it to equalize a time-interleaved analog-to-digital converter (ADC) architecture, achieving an effective number of bits over 4 over the entire 75 GHz ADC bandwidth. We anticipate that this network architecture will enable broadband and low latency nonlinear signal processing in practical settings such as ultra-broadband data converters and real-time control systems. We propose a new signaling scheme for on-chip optical-electrical-optical artificial neural networks that utilizes orthogonal delay-division multiplexing and pilot-tone-based self-homodyne detection. This scheme offers a more efficient scaling of the optical power budget with increasing network complexity. Our simulations, based on 220 nm silicon-on-insulator silicon photonics technology, suggest that the network can support 31×31 neurons, with 961 links and freely programmable weights, using a single 500 mW optical comb and a signal-to-noise ratio of 21.3 dB per neuron. Moreover, it features a low sensitivity to temperature fluctuations, ensuring that it can be operated outside of a laboratory environment. We demonstrate the network’s effectiveness in nonlinear equalization tasks by training it to equalize a time-interleaved analog-to-digital converter (ADC) architecture, achieving an effective number of bits over 4 over the entire 75 GHz ADC bandwidth. We anticipate that this network architecture will enable broadband and low latency nonlinear signal processing in practical settings such as ultra-broadband data converters and real-time control systems.
Photonics Research
- Publication Date: Dec. 21, 2023
- Vol. 12, Issue 1, 85 (2024)
Ultra-high extinction ratio optical pulse generation with a thin film lithium niobate modulator for distributed acoustic sensing
Yuan Shen, Xiaoqian Shu, Lingmei Ma, Shaoliang Yu, Gengxin Chen, Liu Liu, Renyou Ge, Bigeng Chen, and Yunjiang Rao
We experimentally demonstrate ultra-high extinction ratio (ER) optical pulse modulation with an electro-optical modulator (EOM) on thin film lithium niobate (TFLN) and its application for fiber optic distributed acoustic sensing (DAS). An interface carrier effect leading to a relaxation-tail response of TFLN EOM is discovered, which can be well addressed by a small compensation component following the main driving signal. An ultra-high ER > 50 dB is achieved by canceling out the tailed response during pulse modulation using the EOM based on a cascaded Mach–Zehnder interferometer (MZI) structure. The modulated optical pulses are then utilized as a probe light for a DAS system, showing a sensitivity up to -62.9 dB ⋅ rad/Hz2 (7 pε/√Hz) for 2-km single-mode sensing fiber. Spatial crosstalk suppression of 24.9 dB along the fiber is also obtained when the ER is improved from 20 dB to 50 dB, clearly revealing its importance to the sensing performance. We experimentally demonstrate ultra-high extinction ratio (ER) optical pulse modulation with an electro-optical modulator (EOM) on thin film lithium niobate (TFLN) and its application for fiber optic distributed acoustic sensing (DAS). An interface carrier effect leading to a relaxation-tail response of TFLN EOM is discovered, which can be well addressed by a small compensation component following the main driving signal. An ultra-high ER > 50 dB is achieved by canceling out the tailed response during pulse modulation using the EOM based on a cascaded Mach–Zehnder interferometer (MZI) structure. The modulated optical pulses are then utilized as a probe light for a DAS system, showing a sensitivity up to -62.9 dB ⋅ rad/Hz2 (7 pε/√Hz) for 2-km single-mode sensing fiber. Spatial crosstalk suppression of 24.9 dB along the fiber is also obtained when the ER is improved from 20 dB to 50 dB, clearly revealing its importance to the sensing performance.
Photonics Research
- Publication Date: Dec. 14, 2023
- Vol. 12, Issue 1, 40 (2024)
Dual-microcomb generation via a monochromatically pumped dual-mode microresonator
Runlin Miao, Ke Yin, Chao Zhou, Chenxi Zhang, Zhuopei Yu, Xin Zheng, and Tian Jiang
Microcombs have enabled a host of cutting-edge applications from metrology to communications that have garnered significant attention in the last decade. Nevertheless, due to the thermal instability of the microresonator, additional control devices like auxiliary lasers are indispensable for single-soliton generation in some scenarios. Specifically, the increased system complexity would be too overwhelming for dual-microcomb generation. Here, we put forward a novel approach to mitigate the thermal instability and generate the dual-microcomb using a compact system. This process is akin to mode-division multiplexing, as the dual-microcombs are generated by pumping the dual-mode of a single Si3N4 microresonator with a continuous-wave laser. Both numerical simulations and experimental measurements indicate that this innovative technique could offer a straightforward way to enlarge the soliton existence range, allowing entry into the multistability regime and triggering another microcomb alongside the main soliton pulse. This outcome not only shines new light on the interaction mechanism of microresonator modes but also provides an avenue for the development of dual-microcomb-based ranging and low phase noise microwave generation. Microcombs have enabled a host of cutting-edge applications from metrology to communications that have garnered significant attention in the last decade. Nevertheless, due to the thermal instability of the microresonator, additional control devices like auxiliary lasers are indispensable for single-soliton generation in some scenarios. Specifically, the increased system complexity would be too overwhelming for dual-microcomb generation. Here, we put forward a novel approach to mitigate the thermal instability and generate the dual-microcomb using a compact system. This process is akin to mode-division multiplexing, as the dual-microcombs are generated by pumping the dual-mode of a single Si3N4 microresonator with a continuous-wave laser. Both numerical simulations and experimental measurements indicate that this innovative technique could offer a straightforward way to enlarge the soliton existence range, allowing entry into the multistability regime and triggering another microcomb alongside the main soliton pulse. This outcome not only shines new light on the interaction mechanism of microresonator modes but also provides an avenue for the development of dual-microcomb-based ranging and low phase noise microwave generation.
Photonics Research
- Publication Date: Dec. 22, 2023
- Vol. 12, Issue 1, 163 (2024)
High-responsivity on-chip waveguide coupled germanium photodetector for 2 μm waveband
Jianing Wang, Xi Wang, Yihang Li, Yanfu Yang, Qinghai Song, and Ke Xu
Recently, the emerging 2 μm waveband has gained increasing interest due to its great potential for a wide scope of applications. Compared with the existing optical communication windows at shorter wavelengths, it also offers distinct advantages of lower nonlinear absorption, better fabrication tolerance, and larger free carrier plasma effects for silicon photonics, which has been a proven device technology. While much progress has been witnessed for silicon photonics at the 2 μm waveband, the primary challenge still exists for on-chip detectors. Despite the maturity and compatibility of the waveguide coupled photodetectors made of germanium, the 2 μm regime is far beyond its cutoff wavelength. In this work, we demonstrate an efficient and high-speed on-chip waveguide-coupled germanium photodetector operating at the 2 μm waveband. The weak sub-bandgap absorption of epitaxial germanium is greatly enhanced by a lateral separation absorption charge multiplication structure. The detector is fabricated by the standard process offered by a commercial foundry. The device has a benchmark performance with responsivity of 1.05 A/W and 3 dB bandwidth of 7.12 GHz, which is able to receive high-speed signals with up to 20 Gbit/s data rate. The availability of such an efficient and fast on-chip detector circumvents the barriers between silicon photonic integrated circuits and the potential applications at the 2 μm waveband. Recently, the emerging 2 μm waveband has gained increasing interest due to its great potential for a wide scope of applications. Compared with the existing optical communication windows at shorter wavelengths, it also offers distinct advantages of lower nonlinear absorption, better fabrication tolerance, and larger free carrier plasma effects for silicon photonics, which has been a proven device technology. While much progress has been witnessed for silicon photonics at the 2 μm waveband, the primary challenge still exists for on-chip detectors. Despite the maturity and compatibility of the waveguide coupled photodetectors made of germanium, the 2 μm regime is far beyond its cutoff wavelength. In this work, we demonstrate an efficient and high-speed on-chip waveguide-coupled germanium photodetector operating at the 2 μm waveband. The weak sub-bandgap absorption of epitaxial germanium is greatly enhanced by a lateral separation absorption charge multiplication structure. The detector is fabricated by the standard process offered by a commercial foundry. The device has a benchmark performance with responsivity of 1.05 A/W and 3 dB bandwidth of 7.12 GHz, which is able to receive high-speed signals with up to 20 Gbit/s data rate. The availability of such an efficient and fast on-chip detector circumvents the barriers between silicon photonic integrated circuits and the potential applications at the 2 μm waveband.
Photonics Research
- Publication Date: Dec. 21, 2023
- Vol. 12, Issue 1, 115 (2024)
Optical leaky fin waveguide for long-range optical antennas on high-index contrast photonic circuit platforms
Lukas Van Iseghem, and Wim Bogaerts
Long-distance light detection and ranging (LiDAR) applications require an aperture size in the order of 30 mm to project 200–300 m. To generate such collimated Gaussian beams from the surface of a chip, this work presents a novel waveguide antenna concept, which we call an “optical leaky fin antenna,” consisting of a tapered waveguide with a narrow vertical “fin” on top. The proposed structure (operating around λ=1.55 μm) overcomes fundamental fabrication challenges encountered in weak apodized gratings, the conventional method to create an off-chip wide Gaussian beam from a waveguide chip. We explore the design space of the antenna by scanning the relevant cross section parameters in a mode solver, and their sensitivity is examined. We also investigate the dispersion of the emission pattern and angle with the wavelength. The simulated design space is then used to construct and simulate an optical antenna to emit a collimated target intensity profile. Results show inherent robustness to crucial design parameters and indicate good scalability of the design. Possibilities and challenges to fabricate this device concept are also discussed. This novel antenna concept illustrates the possibility to integrate long optical antennas required for long-range solid-state LiDAR systems on a high-index contrast platform with a scalable fabrication method. Long-distance light detection and ranging (LiDAR) applications require an aperture size in the order of 30 mm to project 200–300 m. To generate such collimated Gaussian beams from the surface of a chip, this work presents a novel waveguide antenna concept, which we call an “optical leaky fin antenna,” consisting of a tapered waveguide with a narrow vertical “fin” on top. The proposed structure (operating around λ=1.55 μm) overcomes fundamental fabrication challenges encountered in weak apodized gratings, the conventional method to create an off-chip wide Gaussian beam from a waveguide chip. We explore the design space of the antenna by scanning the relevant cross section parameters in a mode solver, and their sensitivity is examined. We also investigate the dispersion of the emission pattern and angle with the wavelength. The simulated design space is then used to construct and simulate an optical antenna to emit a collimated target intensity profile. Results show inherent robustness to crucial design parameters and indicate good scalability of the design. Possibilities and challenges to fabricate this device concept are also discussed. This novel antenna concept illustrates the possibility to integrate long optical antennas required for long-range solid-state LiDAR systems on a high-index contrast platform with a scalable fabrication method.
Photonics Research
- Publication Date: Aug. 28, 2023
- Vol. 11, Issue 9, 1570 (2023)
Heterogeneous optomechanical crystal cavity coupled by a wavelength-scale mechanical waveguide
Yang Luo, Hongyi Huang, Lei Wan, Weiping Liu, and Zhaohui Li
Integrated optomechanical crystal (OMC) cavities provide a vital device prototype for highly efficient microwave to optical conversion in quantum information processing. In this work, we propose a novel heterogeneous OMC cavity consisting of a thin-film lithium niobate (TFLN) slab and chalcogenide (ChG) photonic crystal nanobeam coupled by a wavelength-scale mechanical waveguide. The optomechanical coupling rate of the heterogeneous OMC cavity is optimized up to 340 kHz at 1.1197 GHz. Combined with phononic band and power decomposition, 17.38% energy from the loaded RF power is converted into dominant fundamental horizontal shear mode (SH0) in the narrow LN mechanical waveguide. Based on this fraction, as a result, 3.51% power relative to the loaded RF energy is scattered into the fundamental longitudinal mode (L0) facing the TFLN-ChG heterogeneous waveguide. The acoustic breathing mode of the heterogeneous OMC is successfully excited under the driving of the propagating L0 mode in the heterogeneous waveguide, demonstrating the great potentials of the heterogeneous piezo-optomechanical transducer in high-performance photon–phonon interaction fields. Integrated optomechanical crystal (OMC) cavities provide a vital device prototype for highly efficient microwave to optical conversion in quantum information processing. In this work, we propose a novel heterogeneous OMC cavity consisting of a thin-film lithium niobate (TFLN) slab and chalcogenide (ChG) photonic crystal nanobeam coupled by a wavelength-scale mechanical waveguide. The optomechanical coupling rate of the heterogeneous OMC cavity is optimized up to 340 kHz at 1.1197 GHz. Combined with phononic band and power decomposition, 17.38% energy from the loaded RF power is converted into dominant fundamental horizontal shear mode (SH0) in the narrow LN mechanical waveguide. Based on this fraction, as a result, 3.51% power relative to the loaded RF energy is scattered into the fundamental longitudinal mode (L0) facing the TFLN-ChG heterogeneous waveguide. The acoustic breathing mode of the heterogeneous OMC is successfully excited under the driving of the propagating L0 mode in the heterogeneous waveguide, demonstrating the great potentials of the heterogeneous piezo-optomechanical transducer in high-performance photon–phonon interaction fields.
Photonics Research
- Publication Date: Aug. 22, 2023
- Vol. 11, Issue 9, 1509 (2023)
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