Showing papers in "Photonics Research in 2017"
TL;DR: In this paper, an orthogonal frequency division multiplexing-based VLC system with adaptive bit and energy loading is demonstrated, and a data transmission rate of 11.95 GB/s is achieved with a violet micro-LED.
Abstract: Visible light communication (VLC) is a promising solution to the increasing demands for wireless connectivity. Gallium nitride micro-sized light emitting diodes (micro-LEDs) are strong candidates for VLC due to their high bandwidths. Segmented violet micro-LEDs are reported in this work with electrical-to-optical bandwidths up to 655 MHz. An orthogonal frequency division multiplexing-based VLC system with adaptive bit and energy loading is demonstrated, and a data transmission rate of 11.95 Gb/s is achieved with a violet micro-LED, when the nonlinear distortion of the micro-LED is the dominant noise source of the VLC system. A record 7.91 Gb/s data transmission rate is reported below the forward error correction threshold using a single pixel of the segmented array when all the noise sources of the VLC system are present.
274 citations
TL;DR: This paper comprehensively review silicon photonics for MIR applications, with regard to the state-of-the-art achievements from various device demonstrations in different material platforms by various groups, and introduces in detail of the institute’s research and development efforts on the MIR photonic platforms.
Abstract: Silicon photonic integrated circuits for telecommunication and data centers have been well studied in the past decade, and now most related efforts have been progressing toward commercialization. Scaling up the silicon-on-insulator (SOI)-based device dimensions in order to extend the operation wavelength to the short mid-infrared (MIR) range (2–4 μm) is attracting research interest, owing to the host of potential applications in lab-on-chip sensors, free space communications, and much more. Other material systems and technology platforms, including silicon-on-silicon nitride, germanium-on-silicon, germanium-on-SOI, germanium-on-silicon nitride, sapphire-on-silicon, SiGe alloy-on-silicon, and aluminum nitride-on-insulator are explored as well in order to realize low-loss waveguide devices for different MIR wavelengths. In this paper, we will comprehensively review silicon photonics for MIR applications, with regard to the state-of-the-art achievements from various device demonstrations in different material platforms by various groups. We will then introduce in detail of our institute’s research and development efforts on the MIR photonic platforms as one case study. Meanwhile, we will discuss the integration schemes along with remaining challenges in devices (e.g., light source) and integration. A few application-oriented examples will be examined to illustrate the issues needing a critical solution toward the final production path (e.g., gas sensors). Finally, we will provide our assessment of the outlook of potential future research topics and engineering challenges along with opportunities.
211 citations
TL;DR: In this article, a vector vortex beam can be decomposed into a vector beam and a vortex, whereby the generation can be realized by sequentially using a q-plate and a spiral phase plate.
Abstract: We propose theoretically and verify experimentally a method of combining a q-plate and a spiral phase plate to generate arbitrary vector vortex beams on a hybrid-order Poincare sphere. We demonstrate that a vector vortex beam can be decomposed into a vector beam and a vortex, whereby the generation can be realized by sequentially using a q-plate and a spiral phase plate. The generated vector beam, vortex, and vector vortex beam are verified and show good agreement with the prediction. Another advantage that should be pointed out is that the spiral phase plate and q-plate are both fabricated on silica substrates, suggesting the potential possibility to integrate the two structures on a single plate. Based on a compact method of transmissive-type transformation, our scheme may have potential applications in future integrated optical devices.
161 citations
TL;DR: In this article, a photoresist mold was used to reduce the optical cross-talk effect of the well-confined QDs in a window for QD jetting and a blocking wall for crosstalk reduction.
Abstract: In this study, a full-color emission red–green–blue (RGB) quantum-dot (QD)-based micro-light-emitting-diode (micro-LED) array with the reduced optical cross-talk effect by a photoresist mold has been demonstrated. The UV micro-LED array is used as an efficient excitation source for the QDs. The aerosol jet technique provides a narrow linewidth on the micrometer scale for a precise jet of QDs on the micro-LEDs. To reduce the optical cross-talk effect, a simple lithography method and photoresist are used to fabricate the mold, which consists of a window for QD jetting and a blocking wall for cross-talk reduction. The cross-talk effect of the well-confined QDs in the window is confirmed by a fluorescence microscope, which shows clear separation between QD pixels. A distributed Bragg reflector is covered on the micro-LED array and the QDs’ jetted mold to further increase the reuse of UV light. The enhanced light emission of the QDs is 5%, 32%, and 23% for blue, green, and red QDs, respectively.
158 citations
TL;DR: In this article, a composite structure where graphene is coated on one-dimensional photonic crystal (1DPC) separated by a dielectric was proposed to achieve perfect absorption at terahertz frequencies.
Abstract: In this paper, we have shown that perfect absorption at terahertz frequencies can be achieved by using a composite structure where graphene is coated on one-dimensional photonic crystal (1DPC) separated by a dielectric. Due to the excitation of optical Tamm states (OTSs) at the interface between the graphene and 1DPC, a strong absorption phenomenon occurs induced by the coupling of the incident light and OTSs. Although the perfect absorption produced by a metal–distributed Bragg reflector structure has been researched extensively, it is generally at a fixed frequency and not tunable. Here, we show that the perfect absorption at terahertz frequency not only can be tuned to different frequencies but also exhibits a high absorption over a wide angle range. In addition, the absorption of the proposed structure is insensitive to the polarization, and multichannel absorption can be realized by controlling the thickness of the top layer.
130 citations
TL;DR: In this article, a double-slot vertical split ring resonator (DVSRR) array was designed and numerically calculated in the terahertz frequency, which produces a fundament LC resonance with a quality factor of about 20 when the incidence magnetic field component normal to the DVSRR array is normal.
Abstract: An ultrasensitive metamaterial sensor based on double-slot vertical split ring resonators (DVSRRs) is designed and numerically calculated in the terahertz frequency. This DVSRR design produces a fundament LC resonance with a quality factor of about 20 when the incidence magnetic field component normal to the DVSRR array. The resonant characteristics and sensing performance of the DVSRR array design are systematically analyzed employing a contrast method among three similar vertical split ring resonator (SRRs) structures. The research results show that the elimination of bianisotropy, induced by the structural symmetry of the DVSRR design, helps to achieve LC resonance of a high quality factor. Lifting the SRRs up from the substrate sharply reduces the dielectric loss introduced by the substrate. All these factors jointly result in superior sensitivity of the DVSRR to the attributes of analytes. The maximum refractive index sensitivity is 788 GHz/RIU or 1.04×105 nm/RIU. Also, the DVSRR sensor maintains its superior sensing performance for fabrication tolerance ranging from −4% to 4% and wide range incidence angles up to 50° under both TE and TM illuminations.
120 citations
TL;DR: In this article, a variety of inorganic light-emitting diodes (μILEDs) have been designed and fabricated by transfer printing, including passive and active-matrix displays on glass and plastic substrates.
Abstract: Displays using direct light emission from microscale inorganic light-emitting diodes (μILEDs) have the potential to be very bright and also very power efficient. High-throughput technologies that accurately and cost-effectively assemble microscale devices on display substrates with high yield are key enablers for μILED displays. Elastomer stamp transfer printing is such a candidate assembly technology. A variety of μILED displays have been designed and fabricated by transfer printing, including passive-matrix and active-matrix displays on glass and plastic substrates.
109 citations
TL;DR: In this article, the authors investigate the electrically controlled light propagation in the metal-dielectric-metal plasmonic waveguide with a sandwiched graphene monolayer and show that the propagation loss exhibits an obvious peak when the permittivity of graphene approaches an epsilon-near-zero point when adjusting the gate voltage on graphene.
Abstract: We investigate the electrically controlled light propagation in the metal–dielectric–metal plasmonic waveguide with a sandwiched graphene monolayer. The theoretical and simulation results show that the propagation loss exhibits an obvious peak when the permittivity of graphene approaches an epsilon-near-zero point when adjusting the gate voltage on graphene. The analog of electromagnetically induced transparency (EIT) can be generated by introducing side-coupled stubs into the waveguide. Based on the EIT-like effect, the hybrid plasmonic waveguide with a length of only 1.5 μm can work as a modulator with an extinction ratio of ∼15.8 dB, which is 2.3 times larger than the case without the stubs. The active modulation of surface plasmon polariton propagation can be further improved by tuning the carrier mobility of graphene. The graphene-supported plasmonic waveguide system could find applications for the nanoscale manipulation of light and chip-integrated modulation.
107 citations
TL;DR: In this article, the authors studied the effect of rotation-induced Sagnac frequency shift on the transmission rate and group delay of a spinning micro-resonator, leading to a Fano-like spectrum of transparency.
Abstract: We study optomechanically induced transparency in a spinning microresonator. We find that in the presence of rotation-induced Sagnac frequency shift, both the transmission rate and the group delay of the signal are strongly affected, leading to a Fano-like spectrum of transparency. In particular, tuning the rotary speed leads to the emergence of nonreciprocal optical sidebands. This indicates a promising new way to control hybrid light–sound devices with spinning resonators.
97 citations
TL;DR: In this paper, a high sensitivity D-shaped hole double-cladding fiber temperature sensor based on surface plasmon resonance (SPR) was designed and investigated by a full-vector finite element method.
Abstract: A high sensitivity D-shaped hole double-cladding fiber temperature sensor based on surface plasmon resonance (SPR) is designed and investigated by a full-vector finite element method. Within the D-shaped hole double-cladding fiber, the hollow D-section is coated with gold film and then injected in a high thermo-optic coefficient liquid to realize the high temperature sensitivity for the fiber SPR temperature sensor. The numerical simulation results show that the peaking loss of the D-shaped hole double-cladding fiber SPR is hugely influenced by the distance between the D-shaped hole and fiber core and by the thickness of the gold film, but the temperature sensitivity is almost insensitive to the above parameters. When the thermo-optic coefficient is −2.8×10−4/°C, the thickness of the gold film is 47 nm, and the distance between the D-shaped hole and fiber core is 5 μm, the temperature sensitivity of the D-shaped hole fiber SPR sensor can reach to −3.635 nm/°C.
94 citations
TL;DR: In this paper, the authors demonstrate the first commercial production-ready white light-emitting diodes (LEDs) for the general illumination market with red colloidal quantum dots (QDs) applied in an on-chip configuration.
Abstract: We demonstrate the first commercial production–ready white light-emitting diodes (LEDs) for the general illumination market with red colloidal quantum dots (QDs) applied in an on–chip configuration. We show the red QDs with tunable peak emission and narrow full width at half-maximum in combination with a conventional phosphor material can lead to LED conversion efficiency improvements of 5% to 15% over commercial phosphor based LEDs at correlated color temperatures (CCTs) ranging from 5000 to 2700 K. Furthermore, the challenges associated with reliability under high temperature, high blue flux intensity, and high humidity operation have been overcome to meet consumer market requirements. Finally, a demonstrator lamp at 3000 K color temperature and 90 color rendering index (CRI) with QD based LEDs show a larger efficiency gain up to 17%, attributed to the reduced blue LED droop from the lower drive current and the lower heat sink temperature when compared to a standard phosphor based LED lamp output.
TL;DR: In this paper, a stable passively Q-switched all-solid-state 2-μm laser is successfully realized, where Bi2Te3 nanosheets are synthesized and deposited onto a quartz plate to form a kind of saturable absorber (SA), in which nonlinear absorption properties around 2μm are analyzed with a home-made mode-locked laser.
Abstract: By using the ultrasound-assisted liquid phase exfoliation method, Bi2Te3 nanosheets are synthesized and deposited onto a quartz plate to form a kind of saturable absorber (SA), in which nonlinear absorption properties around 2 μm are analyzed with a home-made mode-locked laser. With the as-prepared Bi2Te3 SA employed, a stable passively Q-switched all-solid-state 2 μm laser is successfully realized. Q-switched pulses with a maximum average output power of 2.03 W are generated under an output coupling of 5%, corresponding to the maximum single-pulse energy of 18.4 μJ and peak power of 23 W. The delivered shortest pulse duration and maximum repetition rate are 620 ns and 118 kHz under an output coupling of 2%, respectively. It is the first presentation of such Bi2Te3 SA employed in a solid-state Q-switched crystalline laser at 2 μm, to the best of our knowledge. In comparison with other 2D materials suitable for pulsed 2 μm lasers, the saturable absorption performance of Bi2Te3 SA is proved to be promising in generating high power and high-repetition-rate 2 μm laser pulses.
TL;DR: In this paper, a 2D nano-heterojunction between graphene and phosphorene nanosheets was constructed using a liquid phase-stripping method, and it was shown that the combined advantages of ultrafast relaxation, broadband response in graphene, and the strong light-matter interaction in phosphoreshields can be combined together by 2D heterointerfaces for applications in ultrafast photonics.
Abstract: Owing to its thickness-modulated direct energy band gap, relatively strong light–matter interaction, and unique nonlinear optical response at a long wavelength, few-layer black phosphorus, or phosphorene, becomes very attractive in ultrafast photonics applications. Herein, we synthesized a graphene/phosphorene nano-heterojunction using a liquid phase-stripping method. Tiny lattice distortions in graphene and phosphorene suggest the formation of a nano-heterojunction between graphene and phosphorene nanosheets. In addition, we systematically investigate their nonlinear optical responses at different wavelength regimes. Our experiments indicate that the combined advantages of ultrafast relaxation, broadband response in graphene, and the strong light–matter interaction in phosphorene can be combined together by nano-heterojunction. We have further fabricated two-dimensional (2D) nano-heterojunction based optical saturable absorbers and integrated them into an erbium-doped fiber laser to demonstrate the generation of a stable ultrashort pulse down to 148 fs. Our results indicate that a graphene/phosphorene nano-heterojunction can operate as a promising saturable absorber for ultrafast laser systems with ultrahigh pulse energy and ultranarrow pulse duration. We believe this work opens up a new approach to designing 2D heterointerfaces for applications in ultrafast photonics and other research. The fabrication of a 2D nano-heterojunction assembled from stacking different 2D materials, via this facile and scalable growth approach, paves the way for the formation and tuning of new 2D materials with desirable photonic properties and applications.
TL;DR: In this article, the perovskite-related CsPb2Br5 nanoplatelets (NPLs) with tunable emission wavelengths were investigated via changing the reaction temperatures to 100°C, 120°C and 140°C.
Abstract: Unlike organic–inorganic hybrid perovskites, all-inorganic cesium lead halide perovskites hold great promise for developing high-performance optoelectronic devices, owing to their improved stability. Herein, we investigate the perovskite-related CsPb2Br5 nanoplatelets (NPLs) with tunable emission wavelengths via changing the reaction temperatures to 100°C, 120°C, and 140°C. Reaction temperature plays a key role in determining the shapes and thicknesses of the resulting CsPb2Br5 NPLs. A higher temperature is in favor of the formation of smaller and thicker NPLs. To develop their potential applications in optoelectronic devices, green light emitting diodes (LEDs) and photodetectors based on CsPb2Br5 NPLs are fabricated. The green LEDs based on CsPb2Br5 NPLs synthesized at 140°C exhibit an excellent pure green emission (full width at half-maximum of <20 nm) and display a luminous efficiency of 34.49 lm/W under an operation current of 10 mA. Moreover, the photodetector based on CsPb2Br5 NPLs synthesized at 100°C has better performance with a rise time of 0.426 s, a decay time of 0.422 s, and a ratio of the current (with and without irradiation) of 364%.
TL;DR: In this article, perovskite quantum dots (QDs) were used as saturable absorbers in a passively Q-switched visible solid-state laser for the generation of soliton pulses.
Abstract: This work presents the saturable absorption (SA) properties of CsPbBr3 perovskite quantum dots (QDs). The perovskite QDs show excellent SA performance with a nonlinear absorption coefficient of −35×10−2 cm/GW and a figure of merit of 3.7×10−14 esu cm. Further, their use as saturable absorbers in a passively Q-switched visible solid-state laser for the generation of soliton pulses is demonstrated. These results demonstrate the potential for the perovskite QDs to act as saturable absorbers.
TL;DR: In this paper, a new method for designing reflectors on the prevalent thin-film-on-insulator platform by using genetic-algorithm optimization is proposed, which can achieve ∼97% reflectivity and 1-dB bandwidth as wide as 220nm.
Abstract: Reflectors are an essential component for on-chip integrated photonics. Here, we propose a new method for designing reflectors on the prevalent thin-film-on-insulator platform by using genetic-algorithm optimization. In simulation, the designed reflector with a footprint of only 2.16 μm×2.16 μm can achieve ∼97% reflectivity and 1 dB bandwidth as wide as 220 nm. The structure is composed of randomly distributed pixels and is highly robust against the inevitable corner rounding effect in device fabrication. In experiment, we fabricated on-chip Fabry–Perot (FP) cavities constructed from optimized reflectors. Those FP cavities have intrinsic quality factors of >2000 with the highest value beyond 4000 in a spectral width of 200 nm. The reflectivity fitted from the FP cavity resonances is >85% in the entire wavelength range of 1440–1640 nm and is beyond 95% at some wavelengths. The fabrication processes are CMOS compatible and require only one step of lithography and etch. The devices can be used as a standard module in integrated photonic circuitry for wide applications in on-chip semiconductor laser structures and optical signal processing.
TL;DR: In this paper, a detailed semiconductor laser rate equation model was proposed to show that unidirectional laser emission at an exceptional point (EP) is a robust regime, where small deviations from the EP condition can break preferential unIDirectional lasing near threshold via a Hopf instability.
Abstract: Recent experiments demonstrated that chiral symmetry breaking at an exceptional point (EP) is a viable route to achieve unidirectional laser emission in microring lasers. By a detailed semiconductor laser rate equation model, we show here that unidirectional laser emission at an EP is a robust regime. Slight deviations from the EP condition can break preferential unidirectional lasing near threshold via a Hopf instability. However, above a “second” laser threshold, unidirectional emission is restored.
TL;DR: In this paper, an on-chip silicon 2×2 mode and polarization-selective switch that can route four data channels on two modes and two polarizations simultaneously is proposed and experimentally demonstrated for the first time.
Abstract: Mode- and polarization-division multiplexing offer new dimensions to increase the transmission capacity of optical communications. Selective switches are key components in reconfigurable optical network nodes. An on-chip silicon 2×2 mode- and polarization-selective switch that can route four data channels on two modes and two polarizations simultaneously is proposed and experimentally demonstrated for the first time, to the best of our knowledge. The overall insertion losses are lower than 8.6 dB. To reduce the inter-modal crosstalk, polarization beam splitters are added to filter the undesired polarizations or modes. The measured inter-modal and intra-modal crosstalk values are below −23.2 and −22.8 dB for all the channels, respectively.
TL;DR: In this article, a PANDA ring-core fiber (PM-PRCF) was proposed for space-division multiplexing applications with high contrast index ring and stress-induced birefringence.
Abstract: We present a polarization-maintaining PANDA ring-core fiber (PM-PRCF) characterized by the combination of a ring-core structure with two stress-applying rods. This special fiber design separates the adjacent modes and avoids the cutoff of the higher-order modes, which is a common problem in elliptical core polarization-maintaining few-mode fibers. Using a high-contrast index ring and stress-induced birefringence, the PM-PRCF features support for 10 vector modes, with effective refractive index separations from their adjacent modes >10−4. Broadband performance is investigated subsequently over a wide wavelength range from 1500 to 1630 nm. The proposed fiber is targeted at applications in space-division multiplexing while eliminating the complex multiple-input multiple-output signal processing.
TL;DR: In this article, the authors proposed a method to enhance the photonic spin Hall effect (SHE) by covering a dielectric with high refractive index on the surface of silver film, and a giant transverse shift of horizontal polarization state was observed due to the evanescent field enhancement near the interface at the top Dielectric layer and air.
Abstract: The photonic spin Hall effect (SHE) has been intensively studied and widely applied, especially in spin photonics. However, the SHE is weak and is difficult to detect directly. In this paper, we propose a method to enhance SHE with the guided-wave surface-plasmon resonance (SPR). By covering a dielectric with high refractive index on the surface of silver film, the photonic SHE can be greatly enhanced, and a giant transverse shift of horizontal polarization state is observed due to the evanescent field enhancement near the interface at the top dielectric layer and air. The maximum transverse shift of the horizontal polarization state with 11.5 μm is obtained when the thickness of Si film is optimum. There is at least an order of magnitude enhancement in contrast with the transverse shift in the conventional SPR configuration. Our research is important for providing an effective way to improve the photonic SHE and may offer the opportunity to characterize the parameters of the dielectric layer with the help of weak measurements and development of sensors based on the photonic SHE.
TL;DR: In this paper, a 2×2 thermo-optic (TO) crossbar switch implemented by dual photonic crystal nanobeam (PCN) cavities within a silicon-on-insulator (SOI) platform is presented.
Abstract: We propose and experimentally demonstrate a 2×2 thermo-optic (TO) crossbar switch implemented by dual photonic crystal nanobeam (PCN) cavities within a silicon-on-insulator (SOI) platform. By thermally tuning the refractive index of silicon, the resonance wavelength of the PCN cavities can be red-shifted. With the help of the ultrasmall mode volumes of the PCN cavities, only ∼0.16 mW power is needed to change the switching state. With a spectral passband of 0.09 nm at the 1583.75 nm operation wavelength, the insertion loss (IL) and crosstalk (CT) performances were measured as IL(bar)=−0.2 dB, CT(bar)=−15 dB, IL(cross)=−1.5 dB, and CT(cross)=−15 dB. Furthermore, the thermal tuning efficiency of the fabricated device is as high as 1.23 nm/mW.
TL;DR: In this article, the bend radius of a single-ring hollow-core photonic crystal fiber was derived from the structural parameters of a fiber using a simple analytical formula, which can be used to derive an expression for the bending radius that yields optimal higher-order mode suppression.
Abstract: Understanding bend loss in single-ring hollow-core photonic crystal fibers (PCFs) is becoming of increasing importance as the fibers enter practical applications. While purely numerical approaches are useful, there is a need for a simpler analytical formalism that provides physical insight and can be directly used in the design of PCFs with low bend loss. We show theoretically and experimentally that a wavelength-dependent critical bend radius exists below which the bend loss reaches a maximum, and that this can be calculated from the structural parameters of a fiber using a simple analytical formula. This allows straightforward design of single-ring PCFs that are bend-insensitive for specified ranges of bend radius and wavelength. It also can be used to derive an expression for the bend radius that yields optimal higher-order mode suppression for a given fiber structure.
Abstract: Optical spin splitting has attracted significant attention owing to its potential applications in quantum information and precision metrology. However, it is typically small and cannot be controlled efficiently. Here, we enhance the spin splitting by transmitting higher-order Laguerre–Gaussian (LG) beams through graphene metamaterial slabs. The interaction between LG beams and metamaterial results in an orbital-angular-momentum- (OAM) dependent spin splitting. The upper bound of the OAM-dependent spin splitting is found, which varies with the incident OAM and beam waist. Moreover, the spin splitting can be flexibly tuned by modulating the Fermi energy of the graphene sheets. This tunable spin splitting has potential applications in the development of spin-based applications and the manipulation of mid-infrared waves.
TL;DR: In this article, the authors reported the first observation of sum-frequency generation in on-chip lithium niobate microdisk resonators with the pump of two individual 1550-nm band lasers.
Abstract: We report the first observation, to the best of our knowledge, of sum-frequency generation in on-chip lithium niobate microdisk resonators. The sum-frequency signal in the 780 nm band, distinct in wavelength from second-harmonic signals, was obtained in lithium niobate microresonators under the pump of two individual 1550 nm band lasers. The sum-frequency conversion efficiency was measured to be 1.4×10−7 mW−1. The dependence of the intensities of the nonlinear signals on the total pump power and the wavelength of one pump laser was investigated while fixing the wavelength of the other. This work paves the way for applications of on-chip lithium niobate microdisk resonators ranging from infrared single-photon detection to infrared spectroscopy.
TL;DR: In this paper, a 2.5kW counter-pumped all-fiberized laser without observation of TMI was demonstrated, and the TMI threshold was enhanced at least 50% in the counterpumped scheme, and stimulated Raman scattering and four-wave mixing were suppressed simultaneously.
Abstract: Transverse mode instability (TMI) has become the major limitation for power scaling of fiber lasers with nearly diffraction-limited beam quality. Compared with a co-pumped fiber laser, a counter-pumped fiber laser reveals TMI threshold enhancement through a semi-analytical model calculation. We demonstrated a 2 kW high-power counter-pumped all-fiberized laser without observation of TMI. Compared with the co-pumped scheme, the TMI threshold is enhanced at least 50% in counter-pumped scheme, moreover, stimulated Raman scattering and four-wave mixing are suppressed simultaneously.
TL;DR: In this paper, the operation of passively Q-switched waveguide laser at 1μm wavelength based on a graphene/WS2 heterostructure as a saturable absorber (SA) was reported.
Abstract: We report on the operation of passively Q-switched waveguide lasers at 1 μm wavelength based on a graphene/WS2 heterostructure as a saturable absorber (SA). The gain medium is a crystalline Nd:YVO4 cladding waveguide produced by femtosecond laser writing. The nanosecond waveguide laser operation at 1064 nm has been realized with the maximum average output power of 275 mW and slope efficiency of 37%. In comparison with the systems based on single WS2 or graphene SA, the lasing Q-switched by a graphene/WS2 heterostructure SA possesses advantages of a higher pulse energy and enhanced slope efficiency, indicating the promising applications of van der Waals heterostructures for ultrafast photonic devices.
TL;DR: In this paper, a normal incidence vertical p-i-n photodetectors on a germanium-on-insulator (GOI) platform were demonstrated.
Abstract: In this paper, normal incidence vertical p-i-n photodetectors on a germanium-on-insulator (GOI) platform were demonstrated. The vertical p-i-n structure was realized by ion-implanting boron and arsenic at the bottom and top of the Ge layer, respectively, during the GOI fabrication. Abrupt doping profiles were verified in the transferred high-quality Ge layer. The photodetectors exhibit a dark current density of ∼47 mA/cm2 at −1 V and an optical responsivity of 0.39 A/W at 1550 nm, which are improved compared with state-of-the-art demonstrated GOI photodetectors. An internal quantum efficiency of ∼97% indicates excellent carrier collection efficiency of the device. The photodetectors with mesa diameter of 60 μm exhibit a 3 dB bandwidth of ∼1 GHz, which agrees well with theoretical calculations. The bandwidth is expected to improve to ∼32 GHz with mesa diameter of 10 μm. This work could be similarly extended to GOI platforms with other intermediate layers and potentially enrich the functional diversity of GOI for near-infrared sensing and communication integrated with Ge CMOS and mid-infrared photonics.
TL;DR: In this article, a simple semi-empirical model for radiative and Auger recombination constants is suggested, accounting for hole localization by composition fluctuations in InGaN alloys.
Abstract: A simple semi-empirical model for radiative and Auger recombination constants is suggested, accounting for hole localization by composition fluctuations in InGaN alloys. Strengthening of fluctuation with the indium molar fraction in InGaN is found to be largely responsible for decreases in both the radiative and Auger recombination constants with emission wavelength. The model provides good fitting of the experimental spectral dependencies of the recombination constants, thus demonstrating implication of the carrier localization to light-emitting diode efficiency reduction in the “green gap.”
TL;DR: In this paper, a liquid modified photonic crystal fiber (PCF) integrated with an embedded directional coupler and multi-mode interferometer is fabricated by infiltrating three adjacent air holes of the innermost layer with standard 1.48 refractive index liquids.
Abstract: A liquid modified photonic crystal fiber (PCF) integrated with an embedded directional coupler and multi-mode interferometer is fabricated by infiltrating three adjacent air holes of the innermost layer with standard 1.48 refractive index liquids. The refractive index of the filled liquid is higher than that of background silica, which can not only support the transmitting rod modes but also the “liquid modified core” modes propagating between the PCF core and the liquid rods. Hence, the light propagating in the liquid modified core can be efficiently coupled into the satellite waveguides under the phase-matching conditions, resulting in a dramatic decrease of the resonant wavelength intensity. Furthermore, there is a multi-mode interference produced by modified core modes and rod modes. Such a compact (∼0.91 cm) device integrated with an embedded coupler and interferometer is demonstrated for high-sensitivity simultaneous temperature (∼14.72 nm/°C) and strain (∼13.01 pm/μϵ) measurement.
TL;DR: In this paper, an overview of the progress on pulse-preserving, coherent, nonlinear fiber-based supercontinuum generation is presented, starting with silica photonic crystal fibers pumped with 1.0μm femtosecond lasers up to chalcogenide step-index and microstructured fibers pumped from optical parametric amplifiers tuned to mid-infrared wavelengths.
Abstract: An overview of the progress on pulse-preserving, coherent, nonlinear fiber-based supercontinuum generation is presented. The context encompasses various wavelength ranges and pump sources, starting with silica photonic crystal fibers pumped with 1.0 μm femtosecond lasers up to chalcogenide step-index and microstructured fibers pumped from optical parametric amplifiers tuned to mid-infrared wavelengths. In particular, silica and silicate-based all-normal dispersion (ANDi) photonic crystal fibers have been demonstrated for pumping with femtosecond lasers operating at 1.56 μm with the recorded spectra covering 0.9–2.3 μm. This matches amplification bands of robust fiber amplifiers and femtosecond lasers. The review therefore focuses specifically on this wavelength range, discussing glass and nonlinear fiber designs, experimental results on supercontinuum generation up to the fundamental limit of oxide glass fiber transmission around 2.8 μm, and various limitations of supercontinuum bandwidth and coherence. Specifically, the role of nonlinear response against the role of dispersion profile shape is analyzed for two different soft glass ANDi fibers pumped at more than 2.0 μm. A spatio-temporal interaction of the fundamental fiber mode with modes propagating in the photonic lattice of the discussed ANDi fibers is shown to have positive effects on the coherence of the supercontinuum at pump pulse durations of 400 fs. Finally, the design and development of graded-index, nanostructured core optical fibers are discussed. In such structures the arbitrary shaping of the core refractive index profile could significantly improve the engineering flexibility of dispersion and effective mode area characteristics, and would be an interesting platform to further study the intermodal interaction mechanisms and their impact on supercontinuum coherence for sub-picosecond laser pumped setups.