Showing papers in "IEEE Photonics Technology Letters in 2021"

Compact Spoof Surface Plasmon Polariton Waveguides and Notch Filters Based on Meander-Strip Units

Abstract: We demonstrate a new variety of spoof surface plasmon polariton (SSPP) waveguides and notch filters with periodic arrays of ultra-thin metallic meander-strip units for high-efficiency and strong confinement microwave SSPPs transmission and notch rejection. Firstly, the dispersion characteristics of the proposed SSPPs waveguide based on meander-strip units are investigated. The dispersion curve of the proposed waveguide presents a unique negative group velocity characteristic, and the asymptotic frequency greatly reduces to near half as that of SSPP waveguide based on traditional rectangular-grooved units with the same transverse size. To validate the proposed design, an SSPP waveguide prototype is fabricated and tested, showing good lowpass filtering performances with a high transmission coefficient ( $\text {S}21 > {-}1$ dB) and a low reflection coefficient ( $\text {S}11 dB) below the asymptotic frequency of 5.2 GHz. Based on this waveguide structure, a notch filter is designed by loading a split ring resonator (SRR). The transmission coefficient (S21) of this filter is −18 dB at the notch frequency of 2.52 GHz. Furthermore, a PIN diode is integrated into the SRR of the notch filter to make the notch frequency switchable. As the PIN diode turns from the ON state to the OFF state, the notch frequency switches from 2.5 GHz to 3.5 GHz. The proposed waveguides and notch filters with electronically adjustable functionalities may have great potential applications in microwave integrated plasmon circuits and programmable systems.

Highly Sensitive Detection of Refractive Index and Temperature Based on Liquid-Filled D-Shape PCF

Abstract: A plasmon resonance sensor (SPR) based on D-shape photonic crystal fiber (PCF) is proposed to realize the simultaneous measurement of refractive index (RI) and temperature. The upper surface of the D-shape PCF is coated with gold film as a plasmon resonance excitation material for the detection of RI. An air hole near the fiber core is coated with gold film and filled with temperature-sensitive liquid ethanol to detect temperature. Results show that the y-polarized peaks supported only shift with RI variation and is unaffected by the temperature floating. Similarly, the x-polarized peak is only influenced by the change of temperature in the external environment. The proposed sensor achieved wavelength sensitivity of 3940nm/RIU with analyte RI between 1.35 and 1.40, and 1.075nm/°C of temperature ranging from 20°C to 60°C. The proposed liquid-filled D-shape photonic crystal fiber will have potential application in solving the problem of cross-sensitivity of temperature and RI.

>5kW Record High Power Narrow Linewidth Laser From Traditional Step-Index Monolithic Fiber Amplifier

Abstract: A high-power monolithic continuous wave (CW) Yb doped fiber amplifier at 1064 nm has been demonstrated based on traditional large mode area step-index fiber, which generated 5.07 kW narrow line-width laser with near diffraction-limited beam quality. At the maximal output power, >35dB OSNR has been achieved with line-width being 370pm, and the measured beam quality is M2x = 1.252, M2y = 1.322. The influence of cooling temperature on SRS has been investigated in high power fiber lasers, which shows that the SRS at 4kW has been suppressed 24 dB by lowering the temperature from 20°C to 8°C. To the best of our knowledge, this is the highest narrow line-width laser power generated from the traditional large mode area step-index monolithic fiber amplifier.

100-GBd Waveguide Bragg Grating Modulator in Thin-Film Lithium Niobate

Abstract: An integrated electro-optic modulator based on a waveguide Bragg grating in thin-film lithium niobate is introduced. The compact device with a footprint of $10\times 400\,\,\mu \text {m}^{2}$ displays an optical extinction ratio of 53.8 dB at a wavelength of 1555.9 nm in the C-band. With a simple intensity modulation and direct detection scheme, data rates up to 100 Gbit/s are demonstrated with 2-, 4- and 8-level pulse-amplitude modulation formats. The optical filter characteristic of a waveguide Bragg grating modulator suppresses one optical sideband, resulting in inherent single sideband modulation. This enables transmission of a 100 Gbit/s on-off keying signal over 12 km of standard single-mode fiber at 1559.05 nm, without the need for chromatic dispersion compensation.

Experimental Demonstration of Over 14 AL Underwater Wireless Optical Communication

Abstract: Turbidity of water significantly affect the system performance of underwater wireless optical communication (UWOC). In this letter, we proposed and experimentally demonstrated a loss-tolerant UWOC system using a compact high-power 520-nm laser diode (LD) and a highly sensitive silicon photomultiplier (SiPM). The LD is directly modulated by the on-off keying-non-return-to-zero (OOK-NRZ) data. A precise collimation system is designed in the transmitter so that the maximum beam divergence angle is fixed at 0.75 mrad. The performance of the proposed system is investigated over a 24-m underwater channel with different attenuation lengths (ALs) mimicking the different levels of water turbidity in coastal water. Experimental results show that the data rates of 20 Mbps, 40 Mbps, 80 Mbps and 100 Mbps can be achieved under 14.3 AL, 13.2 AL, 13.2 AL and 12.3 AL with bit error rates (BERs) lower than the forward error correction (FEC) limit.

On-Chip GaAs-Based Spoof Surface Plasmon Polaritons at Millimeter-Wave Regime

Abstract: In this letter, a GaAs-based wideband spoof surface plasmon polariton (SSPP) waveguide with super compact size is presented at millimeter-wave regime. The periodic SSPP unit cell consists of a longitudinal slot and a meander slot in transversal direction, and its corresponding waveguide has good low-pass filtering feature. The momentum of microstrip line for measurement feeding to the SSPPs can be well matched without any gradient transition structures. To apply this SSPP waveguide into the design of bandpass filter (BPF), a row of vias is added with a certain distance from the SSPP unit cells. For demonstration, two on-chip examples, i.e., SSPP waveguide and SSPP-based BPF, are fabricated operating at different frequencies. Good agreement between simulations and measurements validates the propagation characteristics and implementation of the proposed SSPPs.

Distributed MIMO for Li-Fi: Channel Measurements, Ray Tracing and Throughput Analysis

Abstract: LiFi has been considered as a promising candidate for future wireless indoor networks. The IEEE P802.15.13 and P802.11bb standardization groups agreed upon channel models generated using the non-sequential ray tracing approach of OpticStudio. In this paper, in order to validate the channel modelling approach, at first $2\times2$ multiple-input multiple-output (MIMO) channel measurements are carried out over 200 MHz bandwidth using a channel sounder. The experimental scenario is also modeled in 3D by applying ray tracing. The obtained results indicate good agreement between simulations and measured channel impulse responses, from which parameters such as path loss and delay spread are derived. After validating the channel modeling approach, we investigate the singular values and the effect of user mobility onto the performance in a $4\times4$ distributed multi-user MIMO scenario.

High-Order Mode Application of Spoof Surface Plasmon Polaritons in Bandpass Filter Design

Abstract: In this letter, high-order mode dispersion of a novel spoof surface plasmon polariton (SSPP) unit cell is reported, which has excellent bandpass propagation feature. Its asymptotic frequency and intersection frequency with light line can be independently manipulated by changing the geometric parameters of the slot in proposed SSPP unit cell. In order to validate the feasibility of high-order mode of SSPPs applied in the design of bandpass filters, two SSPP waveguides based on the method with different bandwidths are fabricated and measured. No mode-conversion transition part is introduced in the procedure of waveguide design which avoids extra addition of layout area and reduces complexity of devices. The measurements show that the proposed SSPP waveguide based on high-order mode characteristics can achieve bandpass signal propagation smoothly with controllable bandwidth.

Polarization-Maintaining Fiber Long-Period Grating Based Vector Curvature Sensor

Abstract: We propose and demonstrate an optical fiber vector curvature sensor based on a long-period fiber grating (LPFG) inscribed in Panda type polarization-maintaining fiber (PMF) using CO2-laser heating and tapering system. The uniform heating approach removes the necessity of CO2-laser exposure alignment along the axis of PMFs during grating fabrication. A serial of PMF-LPFGs with grating period from 350 to 490 $\mu \text{m}$ with a step of 20 $\mu \text{m}$ have been fabricated experimentally. The curvature response of the fast and slow axis resonance dips for the LPFG with a period of 450 $\mu \text{m}$ was investigated in the curvature range from 0 to 4.137 m−1 at four bending orientations. The maximum curvature sensitivities were measured to be 9.26 and −6.89 nm/m−1 for the fast and slow axis LP15 modes, respectively. The sensor can achieve 2-dimensional bending direction recognition. The proposed grating has potential application as a vector curvature sensor.

High Power and Narrow Vertical Divergence Laser Diodes With Photonic Crystal Structure

Abstract: High power and narrow vertical divergence lasers for the 980 nm wavelength range based on the photonic crystal (PC) structure are investigated. The structure of the PC layers and the position of the quantum well (QW) are optimized through mode analysis, which to maximize the output power of the PC laser. A broad area (BA) laser with $300~\mu $ m width and 4 mm cavity length yields 41.8 W output with far-field divergence angles of 16.5° in lateral and 16.8° in vertical at full width at half maximum (FWHM) under continuous-wave (CW) 48 A operating current at 5 °C.

A 3.45 Gigabits/s SiPM-Based OOK VLC Receiver

Abstract: A relationship between irradiance and the current needed to maintain the bias voltage applied to a silicon photomultiplier (SiPM) is shown to agree with experimental data. In addition to showing the saturation of the SiPMs response this relationship can be used to determine the power consumed by an SiPM. In addition, results are presented which show that, because of its higher maximum photon count rate, a 30020 SiPM can achieve a bit error rate (BER) of 10−3 at a data rate of 3.45 Gbits/s.

Comprehensive Performance Analysis of a VCSEL-Based Photonic Reservoir Computer

Abstract: Optical neural networks offer radically new avenues for ultrafast, energy-efficient hardware for machine learning and artificial intelligence. Reservoir Computing (RC), given its high performance and cheap training has attracted considerable attention for photonic neural network implementations, principally based on semiconductor lasers (SLs). Among SLs, Vertical Cavity Surface Emitting Lasers (VCSELs) possess unique attributes, e.g. high speed, low power, rich dynamics, reduced cost, ease to integrate in array architectures, making them valuable candidates for future photonic neural networks. This work provides a comprehensive analysis of a telecom-wavelength GHz-rate VCSEL RC system, revealing the impact of key system parameters on its performance across different processing tasks.

Ultra-Broadband Interleaver for Extreme Wavelength Scaling in Silicon Photonic Links

Abstract: We demonstrate an ultra-broadband silicon photonic interleaver capable of interleaving and de-interleaving frequency comb lines over a 125 nm bandwidth in the extended C- and L-bands. We use a ring-assisted asymmetric Mach Zehnder interferometer to achieve a flat-top passband response while maintaining a compact device footprint. The device has a 400 GHz free spectral range to divide an optical frequency comb with 200 GHz channel spacing into two output groups, each with a channel spacing of 400 GHz, yielding a potential capacity of 78 total wavelength-division multiplexed channels between 1525 nm and 1650 nm. This device represents an important step towards realizing highly parallel integrated optical links with broadband frequency comb sources within the silicon photonics platform.

2.7 Gb/s Secure Key Generation and Distribution Using Bidirectional Polarization Scrambler in Fiber

Abstract: A physical-layer secure key generation and distribution (SKGD) scheme in classical fiber channel is proposed and demonstrated using a bidirectional wide-band polarization scrambler (WBPS), to alter rapidly and symmetrically the state of polarization (SOP) for the two counter-propagating optical signals in fiber. Due to the optical channel reciprocity, highly-consistent key bits can be extracted from the correlated SOP fluctuations, while the key secrecy is ensured by the fiber channel uniqueness. A final key generation rate (KGR) of 2.7 Gb/s is demonstrated over 10 km single mode fiber (SMF), where error-free and true randomness of the generated key are achieved after post-processing. The obtained KGR at Gb/s makes a further step towards the implementation of one-time-pad data encryption with perfect secrecy in fiber networks.

Net 300 Gbps/ λ Transmission Over 2 km of SMF With a Silicon Photonic Mach-Zehnder Modulator

Abstract: Employing our 47 GHz bandwidth silicon photonic (SiP) traveling wave Mach-Zehnder modulator (TW-MZM), we demonstrate the transmission of 134 Gbaud PAM-4 (net 250 Gbps) at a BER below the 6.7% overhead hard-decision forward error correction (HD-FEC) threshold of 3.8 $\times \,\,10^{-3}$ over 2 km of standard single-mode fiber (SSMF) in the O-band with only linear feed- forward equalizer (FFE). With the aid of non-linear pre-distortion and FFE, we transmit 115 Gbaud PAM-8 (net 288 Gbps) and net 305 Gbps PS-PAM-8 above the 19.02% overhead soft-decision FEC with a normalized general mutual information (NGMI) threshold of 0.8798. These results are the highest reported net rates for an all-silicon modulator in an intensity modulation direct-detection (IM/DD) system.

Optical Convolutional Neural Network With WDM-Based Optical Patching and Microring Weighting Banks

Abstract: We propose an optical convolutional neural network (OCNN) architecture for high-speed and energy-efficient deep learning accelerators. The WDM-based optical patching scheme (WDM-OPS) is adopted as the data-feeding structure for its superior energy efficiency and the microring banks are used for the large-scale weighting and summing (the computing core). We thoroughly investigate the performance (including prediction accuracy, speed, and energy efficiency) of this architecture in different system defects. The results indicate that, the prediction accuracy of OCNN can reach 97% in the MNIST dataset with a computing speed of over 100 TMAC/s on condition of achievable low insertion loss. It is also observed that the WDM-OPS notably reduces the energy consumption of the electro-optic modulation and thus the OCNN becomes an exceptionally energy-efficient architecture among several well-known optical architectures. In the evaluations, instead of merely considering the computing core, we take the holistic optical system including lasers, electro-optic modulators, data preprocessing, photodetection and transimpedance amplification into consideration. Therefore, this work provides a potential guide for the systematic implementation of the OCNN architecture.

Subcarrier and Power Allocation in OFDM-NOMA VLC Systems

Abstract: We propose a novel subcarrier and power allocation method to improve both the throughput and user fairness in orthogonal frequency division multiplexing non-orthogonal multiple access visible light communication (OFDM-NOMA VLC) systems. The proposed method considers various constraints in practical VLC systems, including bandwidth limitation, non-negative optical signal, peak power for eye safety, and quality of service. The method adopts the log utility function to improve the user fairness and is applicable to cases where the number of multiplexed users on each subcarrier is not equal to the total user number due to the decoding complexity of NOMA. The problem is generalized as a non-convex one and is solved by the genetic algorithm. Monte Carlo simulations show that at a signal to interference noise ratio of 2.5 dB, the throughput of the proposed method is 11%, 22%, and 125% higher than the conventional enhanced power allocation, the fixed power allocation, and the gain ratio power allocation algorithms, while the fairness is improved by 23%, 30%, and 49%, respectively.

Vehicular VLC: A Ray Tracing Study Based on Measured Radiation Patterns of Commercial Taillights

Abstract: In this letter, we investigate the performance of vehicular visible light communications based on the radiation patterns of different commercial taillights (TLs) using non-sequential ray tracing simulations. Our simulation results indicate a significant variation in the path loss compared with Lambertian model. Based on the ray tracing results, we propose a new path loss model as a function of the propagation distance considering the asymmetrical radiation pattern of TLs. We use this model to derive the attainable transmission distance. We further present the delay spread for various vehicular communication scenarios to demonstrate the effect of neighboring vehicles.

Thin Film Lithium Niobate Electro-Optic Modulator for 1064 nm Wavelength

Abstract: Electro-optic modulators are used in a wide variety of photonic systems, and their operation at the 1064 nm wavelength is notable for its applications such as frequency comb generation and optical interconnects. This work demonstrates the first (to the best of our knowledge) thin film lithium niobate electro-optic modulator operating at a wavelength of 1064 nm. The modulator was fabricated from crystal-ion-sliced lithium niobate wafers procured from NanoLN. Electron beam lithography was used to define the waveguides, and laser lithography was used to define the electrodes, forming a ridge waveguide in the lithium niobate, with a width of 900 nm and an etch depth of 90 nm, by inductively coupled plasma etching. The modulator was characterized using a polarization rotation technique, in which two modes of the waveguide were excited and both were shown to exhibit phase modulation. This modulator exhibits a half-wave voltage of 2.73 volts, with a 7 mm long interaction region and 1.91 V-cm modulation efficiency.

A New LED Response Model and its Application to Pre-Equalization in VLC Systems

Abstract: With the growing interest in visible light communication (VLC), it is desired to transmit data at very high rates despite the LED’s bandwidth becoming a bottleneck. The bandwidth of a white LED usually ranges between hundreds of kHz and a couple of MHz, limiting transmission rates dramatically in a VLC system. Successful design of an efficient equalizer for VLC systems heavily depends on the realistic modeling of LED’s frequency response. In this letter, we first propose a new LED response model taking the parasitic effects appearing at higher frequencies into account. The proposed model provides better match with measurements of commercially available LEDs over a wide frequency range as compared to the existing models in the literature. Then, we design a digital equalizer in line with the proposed model and implement it as an offline digital system in Matlab. The designed equalizer yields an overall flat system response over a wide frequency range. As a demonstration, we present the measured eye diagrams and bit error rate performance results of the equalized VLC system with on-off keying modulation and demonstrate improvements in data rate in comparison to the LED bandwidth.

Non-Invasive Measurement for Cardiac Variations Using a Fiber Optic Sensor

Abstract: Cardiovascular diseases (CVDs) are very common in modern society, such as atherosclerosis, hypertension, etc., which have a great impact on heart function. Therefore, hospitalization monitoring alone is far from enough. Long-term monitoring of the heart is needed in daily life. The technology of non-invasive monitoring of the cardiovascular system can meet the needs of long-term monitoring of the heart condition, helping to promote the improvement of lifestyle and daily care, reducing the overall risk of developing CVDs. The purpose of this study is to investigate the cardiac response after different exercises using a $3\times 3$ demodulation scheme-based ballistocardiography (BCG) monitoring system. A fiber optic sensor (FOS)-based smart cushion is used to replace the traditional inconvenient electrocardiogram (ECG) for heart rate variability (HRV). The correlation between BCG inter-beat interval (IBI) and ECG IBI is 0.9862, and the RMSE is 0.0139. The BCG signal can assess cardiac contractility by analyzing RJ interval with ECG, which is a practical alternative to the pre-ejection period (PEP).

Multi-Band LFM Signal With Unidentical Bandwidths Subjected to Optical Injection in a DFB Laser

Abstract: This letter demonstrates a tunable multi-band linear frequency modulation (LFM) signal with improved and unidentical bandwidths subjected to optical injection in a distributed-feedback (DFB) laser. In the proposed scheme, an optical beam is divided into two paths, one modulating with a baseband LFM signal and another with a power-varying signal. The basic principle of the proposed scheme is the optical beating of the carrier-suppressed $\pm 1^{\text {st}}$ sidebands in one path and the red-shifted emission mode of the DFB laser after optical injection in another path. In the experiment, the generated three LFM signals have the bandwidths of 11.5 GHz (from 23.0 to 34.5 GHz), 7.5 GHz (from 15.0 to 22.5 GHz), and 4 GHz (from 8.0 to 12.0 GHz) in one period of $1~\mu $ s. Moreover, we analyze the effect of the injected beam’s frequency and power on the bandwidth tunability of the generated LFM signals.

Machine Learning Methods for Discriminating Strain and Temperature Effects on FBG-Based Sensors

Abstract: The biggest challenge of using fiber Bragg grating (FBG) based sensors is the cross-sensitivity between the strain and temperature effects on FBG In this letter, we demonstrate the ability of machine learning (ML) methods to discriminate between the strain and temperature effects on FBG sensors on a single measurement of change in the Bragg wavelength Spectral data are collected using an FBG interrogation system at various strain and temperature conditions and are applied to different ML methods to determine the strain and temperature effects We further simulate FBG with the same strain and temperature conditions using VPIphotonics For comparison, the same ML methods are applied to both simulated and experimentally collected data The experimental results reveal that our proposed model can predict strain and temperature with 90% accuracy on a single measurement of Bragg wavelength We also demonstrate the stability of the model by comparing the testing and training errors of the applied ML methods Therefore, our proposed technique reduces the cost and complexity associated with the existing FBG-based sensor system

Digital Pre-Equalization for OFDM-Based VLC Systems: Centralized or Distributed?

Abstract: We propose and experimentally demonstrate a distributed digital pre-equalization (DPE) technique for orthogonal frequency division multiplexing (OFDM)-based bandlimited visible light communication (VLC) systems. In the VLC system applying distributed DPE, the subcarriers are divided into two bands, where the bandwidth and the power of each band can be flexibly adjusted to maximize the achievable data rate of the system. Hence, distributed DPE exhibits much higher tolerance against light-emitting diode (LED) nonlinearity than conventional centralized DPE. Experimental results verify the superiority of distributed DPE for OFDM-based bandlimited VLC systems. More specifically, a data rate of 976.6 Mbit/s is achieved by using distributed DPE, which corresponds to an achievable rate improvement of 25% in comparison to centralized DPE.

Curvature and Temperature Sensor Based on Anti-Resonant Effect Combined With Multimode Interference

Abstract: An inline fiber sensor for simultaneous measurement of curvature and temperature based on anti-resonant (AR) effect combined with multimode interference (MMI) is proposed and experimentally demonstrated. The sensing structure is simply formed by embedding a section of multimode fiber (MMF) and glass capillary between single-mode fibers (SMF). Thence the multimode interference (MMI) pattern with dips and the AR effect spectrum with the loss valleys at the resonance wavelengths can be observed on the optical spectrum analyzer (OSA). A curvature sensitivity of −9.25 dB/ $\text{m}^{-1}$ with almost unchanged wavelength can be achieved by intensity demodulation at an AR valley. And a temperature sensitivity of 30 pm/°C with a tiny intensity sensitivity −0.079 dB/°C is obtained by wavelength demodulation at a MMI dip. Different demodulation mechanisms enable our sensors to discriminate curvature and temperature. Moreover, the advantages such as repeatability of fabrication, robust structure and cost-effectiveness, further benefit its practical sensing applications.

Compact and Narrow-Band Bandpass Filter Using Spoof Surface Plasmon Polaritons

Abstract: This letter presents a novel narrow-band bandpass spoof surface plasmon polarition (SSPP) filter, which has a controllable passband, good rejection, and a compact structure. It is composed of two end-extending SSPP transmission lines and a pair of L-shaped coupling branches. Both the bandwidth and the central frequency can be adjusted by changing the depth of the SSPP unit and the length of SSPP transmission line behind the coupling branches. The dispersion curves of the SSPP unit are analyzed, and the influences of some structural parameters are investigated. A SSPP band-pass filter is fabricated and measured based on the proposed method, showing a wide 3-dB fractional bandwidth of 11.2% centered at 6.25 GHz and an out-of-band rejection below −15 dB within 1–10 GHz. The measured result shows good agreement with the simulated one.

Diode End-Pumped 1.37 W Er:YSGG Continuous-Wave Laser Around 2.8-μm

Abstract: We demonstrate the laser performance of a LD end-pumped Er:YSGG crystals with different doping concentrations comparatively. The experimental results show that 30 at. % Er:YSGG crystal with dimensions of 2 mm $\times2$ mm $\times8$ mm has the best laser output. In continuous-wave (CW) mode and pulse mode, the maximum output powers of 1.37 and 1.20 W are achieved, corresponding to slope efficiencies of 23.62% and 22.91%, respectively. To the best of our knowledge, compared with other Er $^{3+}$ -doped garnet laser crystals, we obtained a larger power and higher efficiency CW laser simultaneously for LD end-pumped Er:YSGG crystal. The beam quality factor M2 in x and y directions are determined to be 1.64/1.65, suggesting the Er:YSGG laser possesses a higher beam quality. All these results indicate that Er:YSGG is a promising mid-infrared gain medium for high efficiency and high power laser operation.

Low Excess Noise of Al 0.85 Ga 0.15 As 0.56 Sb 0.44 Avalanche Photodiode From Pure Electron Injection

Abstract: Avalanche photodiodes (APDs) are used in optical receivers of high-speed optical communication systems to improve signal-to-noise ratio over conventional photodiodes. Low excess noise characteristics are crucial for APDs to preserve the benefits associated with high internal gains. In this work, we presented room temperature data of avalanche gain and excess noise factors of Al0.85Ga0.15As0.56Sb0.44 APDs using pure and mixed carrier injection profiles. Using pure electron injection, the best possible excess noise performance for a given avalanche width was measured with an excess noise factor https://doi.org/10.15131/shef.data.15082455 )

Large-Scale Monolithic InP-Based Optical Phased Array

Abstract: High-speed and robust optical beam-steering device will be the key component for various applications, such as LiDAR (light detection and ranging) and free-space optical communication. Optical phased arrays (OPAs) integrated on semiconductor chips have recently received increasing attention due to the high-speed operation, compactness, and low cost. In particular, indium phosphide (InP)-based OPAs are advantageous for high-output-power applications at 1.55- $\mu \text{m}$ eye-safe wavelength, owing to their capability of monolithically integrating active components, such as high-power lasers and optical amplifiers. In this letter, we design and fabricate, to the best of our knowledge, the largest-scale InP-based OPA and experimentally demonstrate its beam-steering operations. The fabricated OPA consists of 100 waveguides with carrier-injection-based phase shifters, densely integrated on 7 mm $\times5$ mm footprint. A focused beam width of 0.11° is steered across the free spectral range of 8.88°, corresponding to more than 80 resolvable points. This is the largest number of resolvable points obtained by a monolithic InP OPA. The response time of the OPA is confirmed to be less than 16 ns, which is limited by the driver circuit. This work paves the way for realizing compact beam-steering modules for high-speed and high-output-power imaging applications.

On-Chip Selective Dual-Mode Switch for 2-μm Wavelength High-Speed Optical Interconnection

Abstract: In this work, we designed and fabricated a dual-mode switch based on triple-waveguide couplers and two thermal phase shifters, and demonstrated the first silicon-integrated mode division multiplexing (MDM) switching network for $2-\mu \text{m}$ waveband The proposed dual-mode switch shows $\mu \text{s}$ rising time and $132-\mu \text{s}$ falling time, with switching power of 192 mW High speed on-chip MDM routing of $2\times 60$ Gbps signal was experimentally demonstrated using the proposed 2- $\mu \text{m}$ MDM switching network, drawing the promising prospect for the future photonic integration and high-speed MDM networking at 2- $\mu \text{m}$ waveband