Showing papers in "IEEE Photonics Technology Letters in 2020"

Optical Fibre Capacity Optimisation via Continuous Bandwidth Amplification and Geometric Shaping

Abstract: The maximum data throughput in a single mode optical fibre is a function of both the signal bandwidth and the wavelength-dependent signal-to-noise ratio (SNR). In this paper, we investigate the use of hybrid discrete Raman & rare-earth doped fibre amplifiers to enable wide-band signal gain, without spectral gaps between amplification bands. We describe the widest continuous coherent transmission bandwidth experimentally demonstrated to date of 16.83 THz, achieved by simultaneously using the S-, C- and L-bands. The variation of fibre parameters over this bandwidth, together with the hybrid amplification method result in a significant SNR wavelength-dependence. To cope with this, the signal was optimised for each SNR, wavelength and transmission band. By using a system-tailored set of geometrically shaped constellations, we demonstrate the transmission of 660 $\times25$ GBd channels over 40 km, resulting in a record single mode fibre net throughput of 178.08 Tbit/s.

32 Gbps Data Transmission With 2D Beam-Steering Using a Silicon Optical Phased Array

Abstract: We demonstrate optical wireless transmission with two-dimensional (2D) beam-steering using an optical phased array (OPA). The OPA consists of 64-elements of electro-optic p-i-n phase shifters and thermo-optic tunable n-i-n grating radiators, employed for 2D beam-steering in the transversal and longitudinal directions. The design of the transmitter and receiver device parameters allowed the error-free transmission of 32 Gbps data over a distance of 3 m. The beam-steering range covered 46.0°/10.2° in the transversal/longitudinal direction with a beam divergence of 0.7°/0.9°. When compared with a transmission over fiber, it was confirmed that free-space transmission through the OPA did not degrade the quality of the tens of Gbps signals.

SPR Based Optical Fiber Refractive Index Sensor Using Silver Nanowire Assisted CSMFC

Abstract: In this article, a highly sensitive surface plasmon resonance (SPR) based concave shaped refractive index sensor (CSRIS) is designed and analyzed using silver (Ag) nanowire. The SPR effect between the surface plasmon polariton (SPP) and core guided modes of the concave shape (CS) designed sensor is used to measure the variation in refractive index (RI) of analytes (na). The sensing performance and the coupling properties of proposed sensor are numerically analyzed using finite element method (FEM) based on COMSOL Multiphysics. Results exhibit a high wavelength and amplitude sensitivity of 9314.28 nm/RIU and 1494 RIU -1 , respectively for the RI varying between 1.33 to 1.38 with the resolution of 1.073×10 -5 RIU. The designed sensor is easy to fabricate as it requires the Ag nanowire to be deposited on the concave shaped microfluidic channel (CSMFC) which is later covered with measurand. various structural parameters, i.e. distance of channel from core, diameter of Ag nanowire, and channel size, are also optimized for better sensing response.

Over 10 Gbps VLC for Long-Distance Applications Using a GaN-Based Series-Biased Micro-LED Array

Abstract: By employing a GaN-based series-biased micro-light emitting diode ( $\mu $ LED) array and orthogonal frequency division multiplexing modulation format, a high-speed free-space visible light communication system for long-distance applications has been demonstrated. The blue series-biased $\mu $ LED array, which consists of $3\times 3$ , 20 $\mu \text{m}$ -diameter $\mu $ LED elements, presents promising performance with an optical power and −6dB electrical modulation bandwidth of over 10 mW and 980 MHz, respectively. Record data transmission rates have been successfully achieved at different free-space distances. Within 5 m transmission distances, over 10 Gbps data rates at the forward error correction (FEC) floor of $3.8\times 10^{-3}$ are accomplished. Extending the transmission distances to 20 m, the data rates are maintained at the Gbps level at the FEC floor.

A Single LED Visible Light Positioning System Based on Geometric Features and CMOS Camera

Abstract: A visible light positioning system based on the optical camera communication is introduced, in which the ID data is transmitted by a circular light emitting diode (LED) and captured using common smartphone camera. We propose a planes intersection-line scheme based on the geometric features of LED projection to improve the positioning accuracy, whether the receiver is horizontal or tilted. The experimental results show that the proposed positioning scheme achieves high positioning accuracy with 3D average positioning errors of 5.58 and 5.44 cm for the heights of 1.45 and 1.75 m respectively, when the two tilted angles ranges of the receiver are ±45° and ±40°.

Highly Compact and Efficient Four-Mode Multiplexer Based on Pixelated Waveguides

Abstract: An ultra-compact mode multiplexer for TE0, TE1, TE2 and TE3 modes is proposed and demonstrated experimentally. The device is realized via pixelated waveguides with a footprint of only $5.4\times 6~\mu \,\,\text{m}^{2}$ . The measured insertion loss of the multiplexer is less than 1.5 dB. The inter-mode crosstalk is ~−20 dB at 1550 nm and below −14.6 dB from 1510 nm – 1570 nm. The fabrication and temperature tolerance of the device are investigated. The device can well tolerate the nanohole diameter variation of ±10 nm and the temperature variation of 100 K. The compactness of the proposed mode multiplexer enables potential applications in densely integrated multimode photonic circuits.

A SiPM-Based VLC Receiver for Gigabit Communication Using OOK Modulation

Abstract: The growing demand for wireless communications services means that RF systems are increasingly unable to support user’s requirement. Consequently, there is a growing interest in using visible light communication (VLC), including interest in sensitive VLC receivers. Since they have the potential to detect single photons, silicon photomultipliers (SiPMs) could potentially be used to create the most sensitive possible VLC receivers. In this paper, results of experiments to determine the optimum bias voltage and dynamic range of an off-the-shelf SiPM are reported. Results are then presented which show that in 500 lux of ambient light this receiver supports data rates of more than 2 Gbps with a bit-error-rate (BER) of 10−3.

Fibrous Al-Doped ZnO Thin Film Ultraviolet Photodetectors With Improved Responsivity and Speed

Abstract: Ultraviolet (UV) detection properties of undoped ZnO and Al-doped ZnO (AZO) based interdigitated metal-semiconductor-metal (MSM) structure are investigated in this paper. High quality of fibrous Al-doped ZnO thin films with enhanced conductivity and optical response with controlled doping of Al are synthesized using low-cost sol-gel method. The surface morphology and absorption properties of the films have been investigated. The responsivity and detectivity characteristics of both the devices are compared over 300–700 nm wavelengths. The Al-doped ZnO based Ag/AZO/Ag MSM structure show the maximum responsivity and detectivity of ~5.63 A/W and $\sim 1.8\times 10 ^{12}$ cmHz1/2W−1 while the respective values for the Ag/undoped-ZnO/Ag photodetector are ~3.65 A/W and $\sim 1.3\times 10 ^{12}$ cmHz1/2W−1 at 365 nm and $34~\mu \text{W}$ /cm2 incident UV intensity. The proposed AZO based MSM photodetector has smaller rise time (~30 s) than that (~35 s) of the undoped ZnO based MSM photodetector. However, the AZO based device shows slightly poor spectrum selectivity over the undoped ZnO based device.

Spoof Surface Plasmon Polaritons Based on Balanced Coplanar Stripline Waveguides

Abstract: Ultra-wideband spoof surface plasmon polaritons (SSPPs) based on compact balanced coplanar stripline (CPS) waveguides are proposed. Compared with the conventional CPS-based terahertz (THz) SSPP unit cell, the proposed one has achieved a size reduction of 55.2% under the condition of the same asymptotic frequency. The propagation and attenuation characteristics of the proposed SSPP waveguide can be easily manipulated by adjusting the geometry dimensions of the SSPP unit cell. It indicates that the cut-off frequency of the SSPP waveguide has its tunable flexibility thereby facilitating the filter design. To further validate the proposed idea, a similar topology in microwave regime is designed and measured, where the microwave feeding can be easily realized by embedding a balun structure from unbalanced microstrip line to balanced CPS. The measurement of the microwave filter prototype illustrates ultra-wideband bandpass filtering characteristics with return losses of over 10 dB and average insertion losses of 3.2 dB in the passband of 1.9-14 GHz. The presented work may have significant potentials to develop the miniaturization of various planar plasmonic devices and integrated circuits in microwave and THz regimes.

An Ultra-Compact 3-dB Power Splitter for Three Modes Based on Pixelated Meta-Structure

Abstract: An ultra-compact and efficient 3-dB power splitter for mode division multiplexing is proposed and demonstrated experimentally in this letter. The device is realized via pixelated meta-structure with a small footprint of only $4\times 4.5\,\,\mu \text{m}^{2}$ . The measured results show that the insertion losses and inter-mode crosstalk are lower than 1.5 dB and −15 dB for TE0, TE1 and TE2 modes across the wavelength band of 1530–1570 nm. The measured power imbalance between the two output ports are within 0.35 dB. The tolerances to the fabrication errors and temperature variations are also investigated. The demonstrated three-mode power splitter can directly split the mode multiplexed signals without the need of demultiplexing. Such an integrated functional element helps to significantly increase integration density of photonic integrated circuits.

Highly Sensitive Graphene-Based Refractive Index Biosensor Using Gold Metasurface Array

Abstract: In this letter, a highly sensitive refractive index biosensor applicable in medical devices is proposed. The biosensor design is analyzed for different concentrations of hemoglobin biomolecules. The 70 nm shift in the wavelength is observed for two hemoglobin biomolecules with 1.34 and 1.36 refractive index per unit (RIU). The highest sensitivity of 3500 nm/RIU is observed for these hemoglobin biomolecules. The results are analyzed for absorption, electric field and magnetic field. The design is also analyzed for different geometrical parameters like metasurface array thickness and silicon dioxide (SiO 2 ) layer thickness. The increase in metasurface array thickness reduces the absorption of the design. The increase in the thickness of SiO 2 layer increases the absorption till 0.6 μm thickness than the response remains the same for other thicknesses. The proposed highly sensitive graphene-based metasurface array biosensor is applicable in medical and biosensing photovoltaic devices.

A High Temperature Sensor Based on Sapphire Fiber Fabry-Perot Interferometer

Abstract: A sapphire fiber high temperature sensor based on Fabry-Perot interference was studied in the paper. A sapphire wafer served as the Fabry-Perot cavity was fixed to the end face of the sapphire fiber. The sensor was encapsulated in an alumina ceramic tube-ceramic sleeve structure to improve structural stability. Experiment results showed the sensor had a wide temperature measurement range of 25 °C–1550 °C. The temperature sensitivity reached 32.5 pm/°C at 1550 °C. Furthermore, the temperature was demodulated from the interference spectrum through fast Fourier transform algorithm. It was concluded that the sapphire fiber sensor with advantages of small size, good stability and a wide range of temperature measurement is very promising for measuring high temperature.

An Experimental Demonstration of 160-Gbit/s PAM-4 Using a Silicon Micro-Ring Modulator

Abstract: Silicon photonics has been regarded as a promising technology for future small-footprint, low-cost and low-power 400-Gbit/s datacenter interconnects (DCIs). In this work, for the first time, we report an experimental demonstration of a single-wavelength, single-polarization 160-Gbit/s four-level pulse-amplitude modulation (PAM-4) employing a single integrated silicon carrier-depletion micro-ring modulator (MRM). The measured bit-error rates (BERs) for the back-to-back (BTB) and after 1-km standard single-mode fiber (SSMF) transmission are 1.36E–3 and 2.12E–3, respectively, all below the hard-decision forward error correction (HD-FEC) coding limit with 7% overhead. A data rate of up to 170 Gbit/s with a BER lower than the HD-FEC limit is demonstrated for the BTB transmission.

Four-Channel CWDM (de)Multiplexers Using Cascaded Multimode Waveguide Gratings

Abstract: A silicon-based four-channel coarse wavelength- division multiplexing (CWDM) (de)multiplexer working in the O-band is proposed and realized. The present on-chip four-channel CWDM (de)multiplexer is composed of four cascaded optical filters with flat-top spectral responses, which are realized by combining a multimode waveguide grating (MWG) and a two-channel mode (de)multiplexer. For the realized flat-top CWDM (de)multiplexer with a ~18-nm channel-spacing, the measured 1-dB bandwidth is as large as 15 nm, which is ~75% of the channel spacing. The thermal sensitivity is also reduced from ~85 pm/°C to 46 pm/°C by introducing the compensation provided by an SU-8 upper-cladding with a negative thermo-optic coefficient.

Pixelated Blazed Gratings for High Brightness Multiview Holographic 3D Display

Abstract: Multiview 3D display can reveal wondrous information of a 3D image without any visual aids. Therefore, it has great potential in many applications, such as education, game, training, and design. Among all the multiview 3D display techniques, the one that is based on diffractive optics and metasurface can present 3D images with ultrawide field of view and low crosstalk. However, the brightness of diffractive multiview 3D display is limited by the diffraction efficiency. Moreover, the low fabrication efficiency and high cost limit the commercial development of 3D display based on metasurface. Here we propose a multiview 3D display based on multi-level pixelated blazed gratings. The period and orientation of each blazed grating in the view modulator is different to form a converged light field. A 4-view prototype was assembled by integrating the view modulator with a shadow mask for the modulation of light intensity. A 3D thoracic cage model was virtually projected within the viewing angle with minimum crosstalk. The light efficiency of the prototype is significantly improved to 60% for 4-level blazed gratings.

Simultaneous Wireless Data and Power Transfer for a 1-Gb/s GaAs VCSEL and Photovoltaic Link

Abstract: We study the trade-off between energy harvesting and data communication for a two-meter wireless gallium-arsenide vertical-cavity surface-emitting laser and photovoltaic link. The use of orthogonal frequency-division multiplexing with adaptive bit and power loading results in a peak data rate of 1041 Mb/s at a bit-error ratio (BER) of $2.2\times 10^{-3}$ under short-circuit conditions. The receiver is shown to provide power harvesting with an efficiency of 41.7% under the irradiance of 0.3 W/cm2 and simultaneous data communication with a rate of 784 Mb/s at a BER of $2.8\times 10^{-3}$ . The experimental system is envisioned to become a paradigm for next-generation wireless backhaul communications and Internet-of-Things applications.

A Compact Wideband Filter Based on Spoof Surface Plasmon Polaritons With a Wide Upper Rejection Band

Abstract: In this letter, spoof surface plasmon polaritons (SSPPs) are developed in a slotted half-mode substrate integrated waveguide (HMSIW) to realize a bandpass propagation feature instead of a traditional low-pass one. We investigate the dispersion properties to analyze the performance of an SSPP unit cell. Parametric sweepings are further performed to reveal the direct relationships between geometry and cut-off frequencies. We design a compact transition by etching gradient slots on a tapered microstrip-to-HMSIW transition. Then, we finally design an SSPP bandpass filter (BPF) with both wide passband and upper rejection band. The measured 3-dB relative bandwidth is 59.25% ranging from 4.24 to 7.81 GHz. The measured upper rejection band can reach up to 16 GHz with a rejection level better than -31.6 dB. The total size of the filter is only $2.69\lambda _{g} \times 0.42\lambda _{g}$ . This work can provide a new concept to design novel wideband and ultra-wideband (UWB) microwave filters. Significant potential applications of the strategy of developing SSPPs in HMSIW can be found in microwave versatile planar circuits and devices.

A Simple, Highly Sensitive Fiber Sensor for Simultaneous Measurement of Pressure and Temperature

Abstract: A simple, highly sensitive fiber Fabry-Perot interference sensor based on polydimethylsiloxane (PDMS) is proposed and demonstrated for simultaneous measurement of gas pressure and temperature. The sensor is fabricated by fusion splicing a short segment of hollow capillary tube to a standard single mode fiber and injecting PDMS in sections into capillary tube, then three reflecting surfaces are formed. Experimental results show that sensitivities of temperature and gas pressure are 2.62 nm/°C and 20.63 nm/MPa, respectively. The proposed sensor has advantages of compact size, low cost, robust structure, easy fabrication, and it is applicable to real sensing application.

Optoelectronic THz-Wave Beam Steering by Arrayed Photomixers With Integrated Antennas

Abstract: We developed a thermo-optic effect based silica optical phased array (OPA) chip and evaluated its tunability of phases of lightwaves. The THz waves, whose phases are controlled by the OPA chip, are generated from four arrayed uni-travelling-carrier photodiodes (UTC-PDs) based on heterodyne photomixng. Meanwhile, the UTC-PDs, which integrated with $4\times 4$ slot antennas, are fabricated on a monolithic InP substrate chip for 300-GHz wave beam combining and steering. Through the optoelectronic THz-wave phase control, the feasibility of 300-GHz beam continuous steering is successfully demonstrated in a range of 50°.

50 Gbps PAM-4 Over Up to 80-km Transmission With C-Band DML Enabled by Post-Equalizer

Abstract: In this letter, transmission of directly-modulated PAM-4 in C-band is experimentally demonstrated. Instead of introducing any optical devices for dispersion management, we employ receiver-side equalization consisting of Volterra-based FFE and Volterra-based DFE, to mitigate the signal distortions induced by the frequency chirp effect and chromatic dispersion. Results indicate that, PAM-4 transmissions of 56 Gbps over 60-km and 60 Gbps over 80-km are achieved respectively under the HD-FEC limit ( $3.8\times 10^{-3}$ ) and SD-FEC limit ( $2.2\times 10^{-2}$ ).

Mach-Zehnder silicon photonic modulator assisted by phase-shifted Bragg gratings

Abstract: We experimentally demonstrate a silicon photonic Mach-Zehnder modulator (MZM) assisted by phase-shifted Bragg gratings. Coupled resonators are inserted in the Bragg grating structure to significantly enhance the phase modulation efficiency, while maintaining a wide optical bandwidth compared to other resonator-based modulators. Fabricated using a CMOS-compatible foundry process, the device achieved a small-signal V π × L of 0.18 V.cm, which is seven times lower than a conventional silicon MZM fabricated with the same process. The device has a compact footprint, with a length of only 162 μm, and shows a modulation bandwidth of 28 GHz at a reverse bias of 1 V. Non-return-to-zero modulation is demonstrated at 30 Gb/s with a bit-error-rate (BER) below the 7%-overhead forward error correction (FEC) threshold over a bandwidth of 3.5 nm. This bandwidth should translate into an operating temperature range greater than 40 °C.

Experimental Demonstration of Complex-Valued DSB Signal Field Recovery via Direct Detection

Abstract: The recent decade has witnessed the evolution and enormous demand of the high-capacity data center interconnect (DCI), in such application scenarios spectral efficiency, optical field recovery and cost-effectiveness are highly desirable. Compared to coherent detection, direct detection does not require local oscillators, resulting in a simpler transceiver structure and thus a lower-cost solution for DCIs. To overcome chromatic dispersion induced power fading, field recovery enabled by direct detection has drawn extensive research interests. To date, various proposed direct detection schemes concentrate mainly on single sideband (SSB) modulation. Compared to double sideband (DSB) modulation, however, one sideband of SSB is unfilled and hence SSB poses higher requirement on the receiver bandwidth. Besides, the complexity and cost of implementing precisely aligned optical filtering poses burden for adopting SSB. Accordingly, we recently proposed a novel direct detection scheme called carrier assisted differential detection (CADD), which can realize the field recovery of complex-valued DSB signals with the aid of an optical carrier. In this letter, we carry out the first-time experimental demonstration of the CADD receiver. 54-Gb/s OFDM signals are transmitted over 160-km standard single-mode fiber with digital chromatic dispersion compensation at the receiver, indicating the ability to reconstruct optical field of DSB signals. For signal-signal beat interference (SSBI) which extensively exists in direct detection, experimental results show that merely two iterations of cancellation are sufficient to mitigate SSBI. More importantly, compared to various SSB based receiver schemes, the requirement of receiver bandwidth for DSB based CADD scheme is relaxed by 41%.

High-Speed PS-PAM8 Transmission in a Four-Lane IM/DD System Using SOA at O-Band for 800G DCI

Abstract: We experimentally demonstrate a high-speed intensity modulation and direct-detection (IM/DD) system with four wavelength division multiplexing (WDM) channels. With the aid of semiconductor optical amplifier (SOA) and probabilistic shaping (PS) technique, 1T (280Gbit/ $\text{s}\times 4$ ) PS-PAM8 signals can be successfully transmitted over 40-km standard single mode fiber (SSMF). As a more precise performance criteria, the normalized generalized mutual information (NGMI) should be used to report the performance of PS shaped signals. In this experiment, each WDM channel can support 280Gbit/s/channel PS-PAM8 signals transmission with a NGMI larger than the threshold of a soft-decision forward error correction (SD-FEC) code of 0.83. Considering 25% FEC overhead, the net bit rate of each WDM channel is 220Gbit/s/channel. Therefore, the net transmission rate of the WDM system is 880Gbit/s, which can support the demand of 800G data connection. To the best of our knowledge, it is the first time to realize over 1Tbit/s PAM signal transmission over 40km in a four-lane IM/DD system.

Spoof Surface Plasmon Polaritons Developed From Coplanar Waveguides in Microwave Frequencies

Abstract: In this article, a new spoof surface plasmon polariton (SSPP) waveguide developed from traditional coplanar waveguide (CPW) is proposed. The asymptotic frequency of the SSPP unit cell can be easily manipulated by changing the meander groove dimensions of the SSPPs. A simple and efficient mode-conversion structure with gradient groove lengths is designed on the CPW’s ground to match the momentum of CPW to the proposed SSPPs smoothly. The designed SSPP waveguide has a good low-pass filtering property with cut-off frequency at 10.4 GHz. On this basis, another improved SSPP waveguide based on conventional grounded CPW (GCPW) is constructed, where a defected ground structure (DGS) is employed on the bottom layer of the circuit. Compared with the above work, this design has a lower cut-off frequency (8.9 GHz) and stronger field confinement. In order to validate the propagation performance, both SSPP waveguides are fabricated and measured. The measurements show that the GCPW based SSPP waveguide can effectively reduce the cut-off frequency. Such results are of great significance to the miniaturizations of plasmonic devices in microwave regime.

W-Band Optoelectronic Oscillator

Abstract: We demonstrate the first W-band optoelectronic oscillator (OEO), that oscillates at 94.5 GHz with a measured single side band (SSB) phase noise of −101 dBc/Hz at an offset frequency of 10 kHz from the carrier. Side mode suppression of more than 65 dB has been achieved by using injection locking. This OEO has potential application as a signal source in emerging W-band applications (e.g. fiber-wireless links) and opens a path to low phase noise sources beyond 100 GHz.

An Optical Switch Based on Electro-Optic Mode Deflection in Lithium Niobate Waveguide

Abstract: We propose a 1 × 2 electro-optic miniature optical switch based on mode deflection of lithium-niobate (LN) annealed proton exchange waveguides with microstructured electrodes. Our fabricated device consists of LN waveguides covered with isosceles-triangle-shaped array electrodes, a horn-shaped input waveguide, and two tapered output waveguides. At a driving voltage of 40 V, the two-modes can switch between two output ports with an extinction ratio of 17.39 dB at the wavelength of 1530 nm. The switching speed is 22 ns. This miniature mode switch could find applications in signal processing and high-speed optical communication networks.

CMOS-Compatible Silicon Photonic Sensor for Refractive Index Sensing Using Local Back-Side Release

Abstract: Silicon photonic sensors are promising candidates for lab-on-a-chip solutions with versatile applications and scalable production prospects using complementary metal-oxide semiconductor (CMOS) fabrication methods. However, the widespread use has been hindered because the sensing area adjoins optical and electrical components making packaging and sensor handling challenging. In this work, a local back-side release of the photonic sensor is employed, enabling a separation of the sensing area from the rest of the chip. This approach allows preserving the compatibility of photonic integrated circuits in the front-end of line and metal interconnects in the back-end of line. The sensor is based on a micro-ring resonator and is fabricated on wafer-level using a CMOS technology. We revealed a ring resonator sensitivity for homogeneous sensing of 106 nm/RIU.

Phase Demodulation Based on DCM Algorithm in Φ-OTDR With Self-Interference Balance Detection

Abstract: A phase demodulation algorithm in phase-sensitive optical time domain reflectometry (φ-OTDR) with self-interference balance detection is proposed. With a simple differentiate-and-cross-multiply (DCM) operation to acquire the perturbation waveform, and a further second-order operation to compensate the amplitude fluctuation of the phase, the phase can be extracted accurately. The self-interference balance detection structure can equivalently achieve the function of dual-pulse detection, but avoid the negative impact of the common-mode noise and the difference between the dual pulses on the demodulation. In experiment, several types of vibrations are retrieved correctly under the condition of single channel and low sampling rate, which demonstrates the validity of this demodulation approach.

Dual-Band Polarization-Independent Subwavelength Grating Coupler for Wavelength Demultiplexing

Abstract: Surface grating couplers are diffractive periodic structures that enable efficient coupling of light between optical fibers and planar waveguides. Conventional grating couplers have polarization specific and limited wavelength operation, because of the intrinsic radiation angle dependency on both wavelength and polarization. In this Letter, we propose, to the best of our knowledge, the first polarization-independent surface fiber-chip grating coupler, behaving as a wavelength splitter for the O and C communication bands. Polarization insensitivity is achieved by subwavelength segmentation of the silicon gratings, together with a novel design to allow the dual wavelengths to propagate along two opposite directions in the chip. For the TE and TM polarizations, coupling efficiencies around −4.5 dB are achieved at both 1310 nm and 1550 nm, with an average 1-dB bandwidth of ~45 nm and ~60 nm, respectively. This grating coupler concept can be used as a part of transceivers to increase the data rate of wavelength-division-multiplexing (WDM) systems for fiber-to-the-home (FTTH) network services.

InP-Based Near Infrared/Extended-Short Wave Infrared Dual-Band Photodetector

Abstract: In this paper, InP based near infrared (NIR) /extended-short wave infrared (eSWIR) dual-band photodetector with In0.53 Ga0.47 As and In0.53 Ga0.47 As/GaAs0.5 Sb0.5 type-II superlattice (T2SL) back-to-back n-i-p/p-i-n structures is demonstrated. Monolithic growth of NIR/eSWIR dual-band photodetector on InP substrate enjoys the benefit of the lattice matched property of InP/InGaAs/GaAsSb material system. Low optical crosstalk (below −10 dB) between the two sub-detector is achieved for wavelength range out of 1690–1750 nm. At room temperature, the device exhibits a dark current density of $1.26\times 10 ^{\mathbf {-5}}$ A/cm2 for In0.53 Ga0.47 As sub-detector under −0.1 V bias and $3.78\times 10 ^{\mathbf {-2}}$ A/cm2 for In0.53 Ga0.47 As/GaAs0.5 Sb0.5 sub-detector under −1 V bias. The corresponding responsivity and specific detectivity are 0.57 A/W and $2.63\times 10 ^{\mathbf {11}}$ cm $\cdot $ Hz $^{\mathbf {1/2}}$ /W at 1640 nm for NIR sub-detector and 0.22 A/W and $1.96\times 10 ^{\mathbf {9}}$ cm $\cdot $ Hz1/2/W at $2~\mu \text{m}$ for eSWIR sub-detector, respectively. The characterization results show the potential for monolithically growing dual-band SWIR photodetector on InP substrate with low dark current density for SWIR applications.