Photonic generation of dual-band triangular chirps utilizing a monolithic integrated mutual injection laser and application in radars.

We propose and demonstrate a dual-band microwave photonic radar scheme based on a monolithic integrated mutual injection laser. Based on the photon-photon resonance (PPR) and the gain switching effect of the integrated laser, the C-/X-band triangular chirp signals with high-quality and comparable power at 4.75-5.25 GHz and 9.5-10.5 GHz are generated. In the current proof-of-concept experiment, the range resolution of the dual-band chirp signals can reach 16.9 cm, compared with the single-band chirp signal that cannot distinguish the targets. Through the application of a single integrated device and a transceiver module sharing a set of antennas, the dual-band microwave photonic radar system scheme improves the system integration.

Hybrid integrated optical chaos circuits with optoelectronic feedback.

A chip-scale chaotic laser system with optoelectronic delayed feedback is proposed and analyzed by numerical simulation. This chip eliminates the need for bulky delay components such as long optical fibers, free propagation and external cavities, relying solely on internal devices and waveguides to achieve feedback delay. This approach simplifies integration, maintaining a compact chip size. According to the results, the chip-scale system exhibits rich dynamics, including periodicity, quasi-periodicity, and chaotic states. Chaos resembling Gaussian white noise is achieved with picosecond-level delay time, highlighting the complexity of chip-scale signals. Furthermore, time delay signature (TDS) concealment is enhanced with a short delay comparable to the inverse bandwidth τ, albeit at a cost of sacrificing chaotic signal complexity. Applying the photonic integrated circuits to practical applications, 1 Gbps back-to-back communication transmission is feasible. Results demonstrate low bit error rates (BERs) for authorizers (<10-6) and high BERs for eavesdroppers (>10-2), ensuring communication confidentiality and chaotic synchronization. Lastly, preliminary experiments validate the feasibility. Our theoretical work has demonstrated the feasibility of hybrid integrated optical chaos circuits with optoelectronic feedback based on photonic wire bonding, which can provide a stable and flexible integrated chaos source.

Photonic convolution accelerator based on a hybrid integrated multi-wavelength laser array by photonic wire bonding for real-time image classification.

We propose and experimentally demonstrate a compact and efficient photonic convolution accelerator based on a hybrid integrated multi-wavelength DFB laser array by photonic wire bonding. The photonic convolution accelerator operates at 60.12 GOPS for one 3 × 3 kernel with a convolution window vertical sliding stride of 1 and generates 500 images of real-time image classification. Furthermore, real-time image classification on the MNIST database of handwritten digits with a prediction accuracy of 93.86% is achieved. This work provides a novel, to the best of our knowledge, compact hybrid integration platform to realize the optical convolutional neural networks.

Compact mode converter on SOI based on a polygonal subwavelength grating structure.

In this Letter, we design and experimentally demonstrate compact mode converters with a lightning-like and arrow-like polygonal subwavelength grating (SWG) structure on a silicon-on-insulator (SOI) platform, which can convert the TE0 mode to the TE1 and TE2 modes, respectively. The footprints of the proposed TE0-1 and TE0-2 mode converters are only 4.44 × 1.3 and 5.89 × 1.8 µm2, respectively. The experimental results show the mode converters have a low insertion loss (<1 dB) and a broad bandwidth (>50 nm). The measured cross talks of the TE0-1 and TE0-2 mode converters are -7.2 dB and -10.3 dB, respectively. In addition, the proposed mode converters with the SWG structure have the advantage in fabrication, since only a one-step full-etching process is required.

Highly-reflective facet-coated multi-wavelength DFB laser array with exact wavelength spacings.

A distributed feedback (DFB) laser array of twenty wavelengths with highly reflective and anti-reflective (HR-AR) coated facets is both theoretically analyzed and experimentally validated. While the HR facet coating enhances high wall-plug efficiency, it inadvertently introduces a random facet grating phase, thereby compromising the lasing wavelength's predictability and the stability of the single-longitudinal-mode (SLM). In this study, two key advancements are introduced: first, the precisely spaced wavelength is achieved with an error of within ±0.2 nm using the reconstruction-equivalent-chirp (REC) technique; second, the random grating phase on the HR-coated facet is compensated by a controllable distributed phase shift through a two-section laser structure. The SLM stability can be improved while the wavelength can be continuously tuned to the standard wavelength grid. The overall chip size is compact with an area of 4000 × 500 µm2. The proposed laser array has a light power intensity above 13 dBm per wavelength, a high side mode suppression ratio above 50 dB, and low relative intensity noise under -160 dB/Hz. These attributes make it apt for deployment in DWDM-based optical communication systems and as a light source for optical I/O.

Photonic convolutional neural network with robustness against wavelength deviations.

We experimentally explore the practicality of integrated multiwavelength laser arrays (MLAs) for photonic convolutional neural network (PCNN). MLAs represent excellent performance for PCNN, except for imperfect wavelength spacings due to fabrication variation. Therefore, the performance of PCNN with non-ideal wavelength spacing is investigated experimentally and numerically for the first time. The results show that there exists a certain tolerance for wavelength deviation on the degradation of the structural information of the extracted feature map, leading to the robustness of photonic recognition accuracy under non-ideal wavelength spacing. The results suggest that scalable MLAs could serve as an alternative source for the PCNN, to support low-cost optical computing scenarios. For a benchmark classification task of MNIST handwritten digits, the photonic prediction accuracy of 91.2% for stride 1 × 1 scheme using the testing dataset are experimentally obtained at speeds on the order of tera operations per second, compared to 94.14% on computer. The robust performance, flexible spectral control, low cost, large bandwidth and parallel processing capability of the PCNN driven by scalable MLAs may broaden the application possibilities of photonic neural networks in next generation data computing applications.

Microsphere-Based Microsensor for Miniature Motors' Vibration Measurement.

We present a microsphere-based microsensor that can measure the vibrations of the miniature motor shaft (MMS) in a small space. The microsensor is composed of a stretched fiber and a microsphere with a diameter of 5 µm. When a light source is incident on the microsphere surface, the microsphere induces the phenomenon of photonic nanojet (PNJ), which causes light to pass through the front. The PNJ's full width at half maximum is narrow, surpassing the diffraction limit, enables precise focusing on the MMS surface, and enhances the scattered or reflected light emitted from the MMS surface. With two of the proposed microsensors, the axial and radial vibration of the MMS are measured simultaneously. The performance of the microsensor has been calibrated with a standard vibration source, demonstrating measurement errors of less than 1.5%. The microsensor is expected to be used in a confined space for the vibration measurement of miniature motors in industry.

Research on an Enhanced Detuned-Loading Effect in Integrated Two-Section DFB Lasers with High Modulation Bandwidths.

A novel high-speed directly modulated two-section distributed-feedback (TS-DFB) semiconductor laser based on the detuned-loading effect is proposed and simulated. A grating structure is designed by the reconstruction-equivalent-chirp (REC) technique. A π phase shift is introduced into the reflection grating, which can provide a narrow-band reflection region with a sharp falling slope on both sides of the reflection spectrum, thus enhancing the detuned-loading effect. Owing to its unique dual-falling-edges structure, the bandwidth can be improved even when the lasing wavelength shifts beyond the left falling edge due to a thermal effect in the actual test, in which condition the detuned-loading effect can be used twice, which greatly improves the yield. The modulation bandwidth is increased from 17.5 GHz for a single DFB laser to around 24 GHz when the lasing wavelength is located on the left falling edge of the TS-DFB laser based on the detuned-loading effect, and it can be increased to 22 GHz for the right side. An eight-channel laser array with precise wavelength spacing is investigated, with a side-mode suppression ratio (SMSR) >36 dB. In addition, TS-DFB lasers with uniform reflection gratings are studied, and simulated results show that the modulation characteristic is far inferior to the laser with a phase-shifted grating reflector.

Spacecraft Segment Damage Identification Method Based on Fiber Optic Strain Difference Field Reconstruction and Norm Calculation.

Real-time online identification of spacecraft segment damage is of great significance for realizing spacecraft structural health monitoring and life prediction. In this paper, a damage response characteristic field inversion algorithm based on the differential reconstruction of strain response is proposed to solve the problem of not being able to recognize the small damages of spacecraft structure directly by the strain response alone. Four crack damage location identification methods based on vector norm computation are proposed, which realize online identification and precise location of structural damage events without external excitation by means of spacecraft structural working loads only. A spacecraft segment structural damage monitoring system based on fiber optic grating sensors was constructed, and the average error of damage localization based on the curvature vector 2 norm calculation was 2.58 mm, and the root-mean-square error was 1.98 mm. The results show that the method has superior engineering applicability for on-orbit service environments.

10×10 Gbs directly modulated DFB laser array based on the REC technique.

We proposed and experimentally demonstrated a directly modulated distributed feedback (DFB) laser array with a transmission rate of 100 Gbps (10c h a n n e l s×10G b p s). The grating design is based on the reconstruction equivalent chirp (REC) technique, which enables precise control of the channel wavelength spacing to 100 GHz, as specified in the ITU-DWDM standard. DFB laser arrays incorporating the REC technique demonstrate excellent consistency performance, with a side-mode suppression ratio exceeding 48 dB, threshold current of approximately 20 mA, and modulation bandwidth of greater than 13 GHz at a bias current of 100 mA. We evaluated the laser's performance by loading a 10 Gbps nonreturn-to-zero signal onto the laser using direct modulation and transmitting it over a 10 km single-mode fiber. Based on our experimental results, the proposed DFB laser array is promising to be utilized in the next generation of low-cost, 100 Gbps DWDM communication systems.

Millimeter-wave generation based on a monolithic dual-wavelength DFB laser with four phase-shifted sampled gratings and equivalent chirp technology.

A dual-wavelength DFB laser array based on four phase-shifted grating and equivalent chirp technology is first proposed, fabricated, and experimentally demonstrated. The dual-wavelength emitting is achieved by symmetrically introducing two π phase shifts into a chirped four phase-shifted sampled grating cavity. Meanwhile, the beating signal of the dual-wavelength output is stabilized by applying an electro-absorption modulator integrated at the rear of the cavity. Under different grating chirp rates, a series of RF signals from 66.8 GHz to 73.6 GHz with a linewidth of less than 210 kHz is obtained.

High-power tapered two-section distributed feedback laser based on a chirped sampled grating.

We propose and theoretically study a two-section high-power distributed feedback (DFB) laser with three equivalent phase shifts (3EPSs). A tapered waveguide with a chirped sampled grating is introduced to amplify the output power and keep a stable single-mode operation. The simulation exhibits the maximum output power and side mode suppression ratio of a 1200 µm length two-section DFB laser as high as 306.5 mW and 40 dB, respectively. Compared with traditional DFB lasers, the proposed laser has a higher output power, which may benefit wavelength division multiplexing transmission systems, gas sensors, and large-scale silicon photonics.

Four-channel all-optical wavelength conversion unit based on nonlinear effect of three-section monolithically integrated semiconductor lasers.

A simple and highly efficient four-channel all-optical wavelength conversion based on four-wave mixing effect of the directly modulated three-section monolithically integrated semiconductor laser is proposed and experimentally investigated. For this wavelength conversion unit, the spacing of the wavelength can be adjusted by tuning the bias current of the lasers and setting it to be 0.4 nm (50 GHz) as a demonstration is this work. A 50 Mbps 16-QAM signal centers at 4-8 GHz is experimentally switched to a targeted path. Up- or downconversion depends on a wavelength-selective switch, and the conversion efficiency can reach up to -2 to 0 dB. This work provides a new technology for photonic radio-frequency switching matrix and contributes to the integrated implementation of satellite transponders.

Simple multi-band linearly frequency-modulated signal generation with a multiplying bandwidth based on a gain-switching laser.

Multi-band linearly frequency-modulated (LFM) signal generation with a multiplying bandwidth is proposed and experimentally demonstrated. It is a simple photonics method based on the gain-switching state in a distributed feedback semiconductor laser without a complex external modulator and high-speed electrical amplifiers. With N comb lines, the carrier frequency and bandwidth of generated LFM signals are N times those of the reference signal. (N is the number of comb lines.) The number of bands and time-bandwidth products (TBWPs) of the generated signals could be easily adjusted by tuning the reference signal from an arbitrary waveform generator. Three-band LFM signals with carrier frequencies ranging from the X-band to K-band are given as an example, and the TBWP up to 20000. The results of auto-correlations of the generated waveforms are also given.

Preliminary study on the effect of ozone exposure on blood glucose level in rats.

BACKGROUND: In recent years, people have paid more and more attention to the health hazards caused by O3 exposure, which will become a major problem after fine particulate matter (PM). OBJECTIVE: To investigate the effects of ozone (O3) exposure on blood glucose levels in rats under different concentrations and times. METHODS: Eighty rats were divided into control group and three ozone concentration groups. Each group was continuously exposed for 1d, 3d and, 6d, and exposed for 6 hours daily. After exposure, GTT, FBG, and random blood glucose were measured. RESULTS: The FBG value increased significantly on the 6th day of 0.5 ppm and the 3rd and 6th days of 1.0 ppm exposure compared with the control group (P< 0.05). The random blood glucose value was significantly increased on the 3rd and 6th days of each exposure concentration (P< 0.05). When exposed to 1 ppm concentration, the 120 min GTT value of 1 d, 3 d and, 6 d was significantly higher than that of the control group (P< 0.05). CONCLUSION: After acute O3 exposure, the blood glucose level of rats was affected by the exposure concentration and time. The concentration of 0.1 ppm had no significant impact on FBG and random blood glucose, and O3 with a concentration of 0.1 ppm and 0.5 ppm had no significant impact on values of GTT at 90 min, and 120 min.

Study of resonant mode coupling in the transverse-mode-conversion based resonator with an anti-symmetric nanobeam Bragg reflector.

The traveling-wave like Fabry-Perot (F-P) resonators based on transverse-mode-conversion have been extensively studied as on-chip filters. However, the incomplete transverse mode conversion will lead to the coupling between two degenerated resonant modes, which brings additional loss and may further induce the resonance splitting. In this paper, we take the transverse-mode-conversion based resonator with anti-symmetric nanobeam Bragg reflector as an example and study the resonant mode coupling in both the direct-coupled and side-coupled resonators. The coupled mode equations are used to model the incomplete transverse mode conversion of Bragg reflector. The resonant mode coupling can be effectively suppressed by carefully designing the phase shifter length and adding the tapered holes. The insertion loss of less than -1 dB can be achieved in the simulation using the two methods. This work is believed to benefit the design of mode-conversion based resonators with low insertion loss and non-splitting line shape.

Detachable interface toward a low-loss reflow-compatible fiber coupling for co-packaged optics (CPO).

High-density reflow-compatible fiber I/O is one of the challenges for co-packaged optics (CPO). This paper developed a detachable coupling interface based on expanded beam edge coupling, which can be applied for optical coupling between lasers, PICs, and fibers, seamlessly supporting many channels with high efficiency. It comprises a removable fiber connector and a permanent chip/device connector, in which microlens/lens arrays are used for waveguide mode expansion and MT-like connectors are used for position registration. An effective alignment scheme based on beam detection was developed and implemented in an assembly station for building the removable fiber connectors, while the permanent chip/device connector was assembled by active alignment to a pre-made fiber connector mated with a registration connector. Promising results were obtained from the proof-of-concept demonstrations of the coupling from SiP PIC and III/V lasers to fibers using the off-the-shelf lenses and modified MT registration connectors. In both cases, less than 1 dB coupling loss was achieved with an expanded beam size of 160 µm in diameter. Even with a relatively large lens offset of ∼35 µm, the detachable fiber array connectors showed good interchangeability. Such a coupling interface is expected to be solder-reflow compatible by replacing the plastic registration connectors with ceramic ones, making it a promising candidate for the solution to CPO fiber I/O.

High-purity linearly frequency-modulated signal generation based on the integrated semiconductor laser subject to the dynamical optoelectrical feedback.

A novel photonic method of linearly frequency-modulated (LFM) signal generation with high purity based on the monolithically integrated semiconductor laser (MISL) subject to the dynamical optoelectrical feedback is proposed and demonstrated in this paper. In this approach, the MISL is firstly operated in period-one state. By introducing the dynamical optoelectrical feedback to modulate the MISL, the generated LFM signals would be constantly optimized as long as the delay of the feedback loop is matched with the repetition period of the LFM signal. In this system, no additional high-speed external modulator, high-frequency electrical LFM oscillator are required, highly simplifying the framework and reducing the power consumption. In the current proof-of-concept experiment, one LFM signal with the bandwidth as large as 5.6 GHz is generated and the corresponding frequency comb contrast can be drastically improved by 51 dB. Furthermore, the effect of the delay mismatch is also discussed in this paper.

Design of two-dimensional sampled Bragg grating for a curved waveguide.

Due to the ability of changing light propagation path direction, curved waveguide Bragg grating (CWG) plays an important role in photonic integrated circuits. In this paper, we proposed a cascaded sampled Bragg grating on tilted waveguide (CSBG-TW) structure to equivalently realize CWG. As an example, by designing two-dimensional (2D) sampled gratings, the direction of +1st sub-grating vector in CSBG-TW can be changed. Then if a curved waveguide is divided into several sections of tilted waveguide, we can keep the grating direction being always parallel to the longitudinal direction of each section of tilted waveguide, while the basic grating is uniform. Hence, the required CWG can be equivalently realized, and the light responses such as reflection Bragg wavelength shift and backward mode convert caused by the tilted grating in curved waveguide can be compensated for. The results show that the sampling structures of CSBG-TW is micro-scale and the difference between reflection intensity between the CSBG-TW with four section tilted waveguide and CWG as design target is less than 0.1 dB. Compared with CWG, the CSBG-TW allows convenient holographic exposure and the wavelength can be accurately controlled. Therefore, the CSBG-TW can be used in various photonic integrated devices that require changing propagation paths.

RMRP inhibition prevents NAFLD progression in rats via regulating miR-206/PTPN1 axis.

This study aimed to investigate the regulatory function of lncRNA RMRP in non-alcoholic fatty liver disease (NAFLD). In vitro and in vivo NAFLD models were constructed. Hematoxylin & Eosin (H&E) and Oil-Red O staining assays were conducted to observe the morphology and lipid accumulation in liver tissues. Triglycine (TG) secretion was detected by ELISA assay. The expression levels of RMRP, microRNA-206, PTPN1 (protein tyrosine phosphatase, non-receptor type 1), and their downstream genes were assessed by qRT-PCR and Western blot. The regulatory relationship among these molecules was determined by luciferase reporter and RNA pull-down assays. RMRP and PTPN1 were up-regulated, while miR-206 was down-regulated in the liver tissues of NAFLD patients and rat model. RMRP inhibition improved the pathological state and liver function-related indexes of liver lipid deposition in the liver tissues of NAFLD rats. RMRP inhibition alleviated steatosis and TG secretion in free fatty acids (FFA)-treated AML-12 cells. RMRP could bind to miR-206 and downregulate its expression. Meanwhile, RMRP inhibition attenuated lipid accumulation by downregulating the PTPN1-PP2ASP1-SREBP1C pathway. Furthermore, RMRP inhibited the miR-206/PTPN1-SREBP1C signaling pathway in NAFLD rats and FFA-treated AML-12 cells. RMRP inhibition prevented NAFLD progression in rats via targeting the miR-206/PTPN1 axis.