Broadband Achromatic Imaging of a Metalens with Optoelectronic Computing Fusion.

The remarkable ultrathin ability of metalenses gives them potential as a next-generation imaging candidate. However, the inherent chromatic aberration of metalenses restricts their widespread application. We present an achromatic metalens with optoelectronic computing fusion (OCF) to mitigate the impact of chromatic aberration and simultaneously avoid the significant challenges of nanodesign, nanofabrication, and mass production of metalenses, a method different from previous methods. Leveraging the nonlinear fitting, we demonstrate that OCF can effectively learn the chromatic aberration mapping of metalens and thus restore the chromatic aberration. In terms of the peak signal-to-noise ratio index, there is a maximum improvement of 12 dB, and ∼8 ms is needed to correct the chromatic aberration. Furthermore, the edge extraction of images and super-resolution reconstruction that effectively enhances resolution by a factor of 4 are also demonstrated with OCF. These results offer the possibility of applications of metalenses in mobile cameras, virtual reality, etc.

3D parallel pulsed chaos LiDAR system.

We propose and experimentally demonstrate a parallel pulsed chaos light detection and ranging (LiDAR) system with a high peak power, parallelism, and anti-interference. The system generates chaotic microcombs based on a chip-scale Si3N4 microresonator. After passing through an acousto-optic modulator, the continuous-wave chaotic microcomb can be transformed into a pulsed chaotic microcomb, in which each comb line provides pulsed chaos. Thus, a parallel pulsed chaos signal is generated. Using the parallel pulsed chaos as the transmission signal of LiDAR, we successfully realize a 4-m three-dimensional imaging experiment using a microelectromechanical mirror for laser scanning. The experimental results indicate that the parallel pulsed chaos LiDAR can detect twice as many pixels as direct detection continuous wave parallel chaos LiDAR under a transmission power of -6 dBm, a duty cycle of 25%, and a pulse repetition frequency of 100 kHz. By further increasing the transmission power to 10 dBm, we acquire an 11 cm × 10 cm image of a target scene with a resolution of 30 × 50 pixels. Finally, the anti-jamming ability of the system is evaluated, and the results show that the system can withstand interferences of at least 15 dB.

93-THz ultra-broadband and ultra-low loss Y-junction photonic power splitter with phased inverse design.

Optical power splitters with ultra-broadband and ultra-low insertion loss are desired in the field of photonic integration. Combining two inverse design algorithms for staged optimization, we present the design of a Y-junction photonic power splitter with 700 nm wavelength bandwidth (from 1200 nm to 1900 nm) within a 0.2 dB insertion loss, corresponding to a 93 THz frequency bandwidth. The average insertion loss is approximately -0.057 dB in the valuable C-band. Moreover, we comprehensively compared the insertion loss performance of different types and sizes of curved waveguides, and also give the cases of 1:4 and 1:6 cascaded power splitters. These scalable Y-junction splitters provide new alternatives for high-performance photonic integration.

Different-mode power splitters based on a multi-dimension direct-binary-search algorithm.

In this work, we design, fabricate, and characterize a different-mode (waveguide-connected) power splitter ((W)PS) by what we believe to be a novel multi-dimension direct-binary-search algorithm that can significantly balance the device performance, time cost, and fabrication robustness by searching the state-dimension, rotation-dimension, shape-dimension, and size-dimension parameters. The (W)PS can simultaneously generate the fundamental transverse electric (TE0) and TE1 mode with the 1:1 output balance. Compared with the PS, the WPS can greatly shorten the adiabatic taper length between the single-mode waveguide and the grating coupler. The measured results of the different-mode (W)PS indicate that the insertion loss and crosstalk are less than 0.9 (1.3) dB and lower than -17.8 (-14.9) dB from 1540 nm to 1560 nm. In addition, based on the tunable tap couplers, the different-mode (W)PS can be extended to multiple output ports with different modes and different transmittances.

Analog signal metasurface processor supporting mathematical operator reconfiguration.

Electromagnetic wave analog computing is an effective method to overcome the bottleneck of electronic computing, which has attracted the attention of scientists. However, many spatial analog signal processing systems based on electromagnetic waves can only execute one unique mathematical operator and cannot provide multiple operators for users to choose arbitrarily. In order to enhance the function of the current spatial analog computing system, we design a coding structure with amplitude-phase decoupling modulation to realize the analog signal processor that supports the switching of mathematical operators and demonstrate the precise switching from the first-order spatial differential operator to the first-order spatial integral operator. Our design idea can be used as a paradigm for designing small reconfigurable analog computing systems, paving the way for the construction of high-speed, multifunctional, and universal signal processing systems. This idea can be extended to any other range of waves.

Manipulation force analysis of nanoparticles with ultra-high numerical aperture metalens.

Metalens optical tweezers technology has several advantages for manipulating micro-nano particles and high integration. Here, we used particle swarm optimization (PSO) to design a novel metalens tweezer, which can get 3-dimensional trapping of particles. The numerical aperture (NA) of the metalens can reach 0.97 and the average focusing efficiency is 44%. Subsequently, we analyzed the optical force characteristics of SiO2 particles with a radius of 350 nm at the focal point of the achromatic metalens. We found the average maximum force of SiO2 particles in the x-direction and z-direction to be 0.88 pN and 0.72 pN, respectively. Compared with the dispersive metalens, it is beneficial in maintaining the constant of optical force, the motion state of trapped particles, and the stability of the trapping position.

Series of ultra-low loss and ultra-compact multichannel silicon waveguide crossing.

Ultra-compact waveguide crossing (UC-WC) is a basic component in optoelectronic fusion chip solutions, as its footprint is smaller in the orders of magnitude than that of traditional photonic integrated circuits (PICs). However, a large loss of UC-WC (decibel level) becomes a barrier to scaling and practicality. Here, we propose a series of ultra-low loss UC-WC silicon devices using an advanced hybrid design that combines the adjoint method with the direct binary search (DBS) algorithm. Simulation results show that our 2 × 2 UC-WC has an insertion loss as low as 0.04 dB at 1550 nm, which is about ten times lower than the previous UC-WC results. In the valuable C-band (1530-1565 nm), the insertion loss of UC-WC is lower than -0.05 dB, and the channel crosstalk is lower than -34 dB. Furthermore, for the 3 × 3 UC-WC device, the highest insertion loss in the entire C-band is approximately -0.07 dB, and the highest channel crosstalk is lower than -33 dB. Additionally, the 4 × 4 and more complex 8 × 8 UC-WC devices were also analyzed. The highest insertion loss for 4 × 4 and 8 × 8 UC-WC in the C-band is only -0.19 dB and -0.20 dB, respectively, and the highest channel crosstalk is approximately -22dB and -28 dB, respectively. These results confirm that the designed devices possess two attractive features simultaneously: ultra-compactness and ultra-low insertion loss, which may be of great value in future large-scale optoelectronic fusion chips.

High precision reconstruction of silicon photonics chaos with stacked CNN-LSTM neural networks.

Silicon-based optical chaos has many advantages, such as compatibility with complementary metal oxide semiconductor (CMOS) integration processes, ultra-small size, and high bandwidth. Generally, it is challenging to reconstruct chaos accurately because of its initial sensitivity and high complexity. Here, a stacked convolutional neural network (CNN)-long short-term memory (LSTM) neural network model is proposed to reconstruct optical chaos with high accuracy. Our network model combines the advantages of both CNN and LSTM modules. Further, a theoretical model of integrated silicon photonics micro-cavity is introduced to generate chaotic time series for use in chaotic reconstruction experiments. Accordingly, we reconstructed the one-dimensional, two-dimensional, and three-dimensional chaos. The experimental results show that our model outperforms the LSTM, gated recurrent unit (GRU), and CNN models in terms of MSE, MAE, and R-squared metrics. For example, the proposed model has the best value of this metric, with a maximum improvement of 83.29% and 49.66%. Furthermore, 1D, 2D, and 3D chaos were all significantly improved with the reconstruction tasks.

Chaotic synchronization of a distant star-type laser network with multiple optical injections.

A novel multi-injection module (MIM) is introduced into a typical distant star-type laser network, which is composed of a hub semiconductor laser node (H-SLN), star semiconductor laser nodes (S-SLNs) and tens of kilometers of fiber links. The chaotic synchronization of this distant network is investigated both experimentally and theoretically. As a result of using the MIM, a significantly low correlation (about 0.2) is successfully achieved between the H-SLN and S-SLNs in different clusters. This correlation is much lower than in previously reported results. Even when the fiber length is extended to 80 kilometers a low correlation (about 0.18) between the H-SLN and S-SLNs in different clusters is also obtained. Moreover, the dependence of chaotic synchronization on the operating conditions, such as the injection power, frequency detuning, and frequency mismatch between arbitrary nodes are examined. Lastly, using a theoretical model, we discuss the broad conditions for achieving chaotic synchronization among S-SLNs in the same cluster, and analyze the effect of the MIM branch number on chaotic synchronization.

Gbps physical random bit generation based on the mesoscopic chaos of a silicon photonics crystal microcavity.

We present an experimental and theoretical physical random bit (PRB) generator using the mesoscopic chaos from a photonic-crystal optomechanical microcavity with a size of ∼10µm and very low operating intracavity energy of ∼60 Femto-Joule that was fabricated with CMOS compatible processes. Moreover, two kinds of PRB generation were proposed with rates over gigabits per second (Gbps). The randomness of the large PRB strings was further verified using the NIST Special Publication 800-22. In addition, the Diehard statistical test was also used to confirm the quality of the obtained PRBs. The results of this study can offer a new generation of dedicated PRB solutions that can be integrated on Si substrates, which can speed up systems and eliminate reliance on external mechanisms for randomness collection.

Frequency-comb-based BOTDA sensors for high-spatial-resolution/long-distance sensing.

Frequency-comb-based Brillouin optical time-domain analysis (BOTDA) sensors were developed to achieve acquisition-time reduction and high-spatial-resolution/long-distance sensing simultaneously. We found that, for the standard frequency-comb-based BOTDA, the use of a double-sideband (DSB) pulse generates a series of pulse pairs that simultaneously propagate along the sensing fiber, leading to a nonlinear interaction between the two sidebands of each frequency comb pulse, and a significant splitting of the Brillouin gain spectrum (BGS). This problem prevents its application in high-spatial-resolution sensing due to the higher pulse power requirement. Thus, one of the sidebands of DSB pulse was proposed for greatly suppressing the BGS distortion. In combination with the phonon pre-excitation technique based on phase-shifted pulse, a sensor with a spatial-resolution approximately 60 cm along a fiber approximately 592 m in length was demonstrated. Furthermore, we explored the detailed performance of long-distance sensing by frequency- comb-based BOTDA. The use of a frequency comb for the probe wave can suppress the pulse distortion and non-local effect, which is helpful for extending the sensing distance. A spatial resolution of approximately 6 m along a sensing fiber approximately 74.2 km in length was successfully demonstrated.

Controllable optomechanical coupling and Drude self-pulsation plasma locking in chip-scale optomechanical cavities.

We demonstrate the controllable optomechanical coupling and Drude self-pulsation plasma locking in chip-scale optomechanical cavities. The optomechanical coupling between the optical and mechanical degrees-of-freedom is dependent on the intracavity energy via the coupled fiber position. With the deterministic optomechanical stiffening, the interaction between optomechanical oscillation and self-pulsation can be controlled. Intracavity locking with 1/6 subharmonics is obtained over a wide optical detuning range of 190.01-192.23 THz. These results bring new insights into implementations of nonlinear dynamics at mesoscopic scale, with potential applications from photonic signal processing to nonlinear dynamic networks.

Tbits/s physical random bit generation based on mutually coupled semiconductor laser chaotic entropy source.

Using two mutually coupled semiconductor lasers (MC-SLs) outputs as chaotic entropy sources, a scheme for generating Tbits/s ultra-fast physical random bit (PRB) is demonstrated and analyzed experimentally. Firstly, two entropy sources originating from two chaotic outputs of MC-SLs are obtained in parallel. Secondly, by adopting multiple optimized post-processing methods, two PRB streams with the generation rate of 0.56 Tbits/s are extracted from the two entropy sources and their randomness are verified by using NIST Special Publication 800-22 statistical tests. Through merging the two sets of 0.56 Tbits/s PRB streams by an interleaving operation, a third set of 1.12 Tbits/s PRB stream, which meets all the quality criteria of NIST statistical tests, can be further acquired. Finally, after additionally taking into account the restriction of the min-entropy, the generation rate of two sets of PRB stream from the two entropy sources can still attain 0.48 Tbits/s, and then a third set of merging PRB stream is 0.96 Tbits/s. Moreover, for the sequence length of the order of 10 Gbits, the statistical bias and serial correlation coefficient of three sets of PRB streams are also analyzed.

Direct generation of broadband chaos by a monolithic integrated semiconductor laser chip.

A solitary monolithic integrated semiconductor laser (MISL) chip with a size of 780 micrometer is designed and fabricated for broadband chaos generation. Such a MISL chip consists of a DFB section, a phase section and an amplification section. Test results indicate that under suitable operation conditions, this laser chip can be driven into broadband chaos. The generated chaos covers an RF frequency range, limited by our measurement device, of 26.5GHz, and possesses significant dimension and complexity. Moreover, the routes into and out of chaos are also characterized through extracting variety dynamical states of temporal waveforms, phase portraits, RF spectra and statistical indicators.

Impact of optical feedback on current-induced polarization behavior of 1550 nm vertical-cavity surface-emitting lasers.

Polarization switching (PS) between two orthogonal linearly polarized fundamental modes is experimentally observed in commercial free-running 1550 nm vertical-cavity surface-emitting lasers (VCSELs) (Raycan). The characteristics of this PS are strongly modified after introducing a polarization-preserved (PP) or polarization-orthogonal (PO) optical feedback. Under the case that the external cavity is approximately 30 cm, the PP optical feedback results in the PS point shifting toward a lower injection current, and the region within which the two polarization modes coexist is enlarged with the increase of the PP feedback strength. Under too-strong PP feedback levels, the PS disappears. The impact of PO optical feedback on VCSEL polarization behavior is quite similar to that of PP optical feedback, but larger feedback strength is needed to obtain similar results.

Non-Volatile Reconfigurable Compact Photonic Logic Gates Based on Phase-Change Materials.

Photonic logic gates have important applications in fast data processing and optical communication. This study aims to design a series of ultra-compact non-volatile and reprogrammable photonic logic gates based on the Sb2Se3 phase-change material. A direct binary search algorithm was adopted for the design, and four types of photonic logic gates (OR, NOT, AND, and XOR) are created using silicon-on-insulator technology. The proposed structures had very small sizes of 2.4 µm × 2.4 µm. Three-dimensional finite-difference time-domain simulation results show that, in the C-band near 1550 nm, the OR, NOT, AND, and XOR gates exhibit good logical contrast of 7.64, 6.1, 3.3, and 18.92 dB, respectively. This series of photonic logic gates can be applied in optoelectronic fusion chip solutions and 6G communication systems.

Ultra-Compact and Broadband Nano-Integration Optical Phased Array.

The on-chip nano-integration of large-scale optical phased arrays (OPAs) is a development trend. However, the current scale of integrated OPAs is not large because of the limitations imposed by the lateral dimensions of beam-splitting structures. Here, we propose an ultra-compact and broadband OPA beam-splitting scheme with a nano-inverse design. We employed a staged design to obtain a T-branch with a wavelength bandwidth of 500 nm (1300-1800 nm) and an insertion loss of -0.2 dB. Owing to the high scalability and width-preserving characteristics, the cascaded T-branch configuration can significantly reduce the lateral dimensions of an OPA, offering a potential solution for the on-chip integration of a large-scale OPA. Based on three-dimensional finite-difference time-domain (3D FDTD) simulations, we demonstrated a 1 × 16 OPA beam-splitter structure composed entirely of inverse-designed elements with a lateral dimension of only 27.3 µm. Additionally, based on the constructed grating couplers, we simulated the range of the diffraction angle θ for the OPA, which varied by 0.6°-41.6° within the wavelength range of 1370-1600 nm.

Massive and parallel 10 Tbit/s physical random bit generation with chaotic microcomb.

Ultrafast physical random bit (PRB) generators and integrated schemes have proven to be valuable in a broad range of scientific and technological applications. In this study, we experimentally demonstrated a PRB scheme with a chaotic microcomb using a chip-scale integrated resonator. A microcomb contained hundreds of chaotic channels, and each comb tooth functioned as an entropy source for the PRB. First, a 12 Gbits/s PRB signal was obtained for each tooth channel with proper post-processing and passed the NIST Special Publication 800-22 statistical tests. The chaotic microcomb covered a wavelength range from 1430 to 1675 nm with a free spectral range (FSR) of 100 GHz. Consequently, the combined random bit sequence could achieve an ultra-high rate of about 4 Tbits/s (12 Gbits/s × 294 = 3.528 Tbits/s), with 294 teeth in the experimental microcomb. Additionally, denser microcombs were experimentally realized using an integrated resonator with 33.6 GHz FSR. A total of 805 chaotic comb teeth were observed and covered the wavelength range from 1430 to 1670 nm. In each tooth channel, 12 Gbits/s random sequences was generated, which passed the NIST test. Consequently, the total rate of the PRB was approximately 10 Tbits/s (12 Gbits/s × 805 = 9.66 Tbits/s). These results could offer potential chip solutions of Pbits/s PRB with the features of low cost and a high degree of parallelism.

Evolution of time delay signature of chaos generated in a mutually delay-coupled semiconductor lasers system.

In this paper, evolution of time delay (TD) signature of chaos generated in a mutual delay-coupled semiconductor lasers (MDC-SLs) system is investigated experimentally and theoretically. Two statistical methods, including self-correlation function (SF) and permutation entropy (PE), are used to estimate the TD signature of chaotic time series. Through extracting the characteristic peak from the SF curve, a series of TD signature evolution maps are firstly obtained in the parameter space of coupled strength and frequency detuning. Meantime, the influences of injection current on the evolution maps of TD signature have been discussed, and the optimum scope of TD signature suppression is also specified. An overall qualitative agreement between our theoretical and experimental results is obtained.

Non-Volatile Programmable Ultra-Small Photonic Arbitrary Power Splitters.

A series of reconfigurable compact photonic arbitrary power splitters are proposed based on the hybrid structure of silicon and Ge2Sb2Se4Te1 (GSST), which is a new kind of non-volatile optical phase change material (O-PCM) with low absorption. Our pixelated meta-hybrid has an extremely small photonic integrated circuit (PIC) footprint with a size comparable to that of the most advanced electronic integrated circuits (EICs). The power-split ratio can be reconfigured in a completely digital manner through the amorphous and crystalline switching of the GSST material, which only coated less than one-fifth of the pattern allocation area. The target power-split ratio between the output channels can be arbitrarily reconfigured digitally with high precision and in the valuable C-band (1530-1560 nm) based on the analysis of three-dimensional finite-difference time-domain. The 1 × 2, 1 × 3, and 1 × 4 splitting configurations were all investigated with a variety of power-split ratios for each case, and the corresponding true value tables of GSST distribution are given. These non-volatile hybrid photonic splitters offer the advantages of an extremely small footprint and non-volatile digital programmability, which are favorable to the truly optoelectronic fusion chip.