Optical Communication Applications Research Articles

Multi-format all-optical modulating of microsphere resonator operating in O-band

We propose and demonstrate an all-optical tunable silica microsphere resonator based on a dual-laser pumping scheme. The resonance tunable microsphere resonator can act as a modulator and operates in the O-band. We discussed the relationship between the extinction ratio and pump power in different coupling state, and realized an extinction ratio over 15 dB. Also, we measured the rise and fall time of the modulated signal, which is below 1 μs, and discussed its relationship with the modulation frequency. In addition, based on this scheme, a multi-format modulation is realized for the first time with signals shaping in triangular, sinusoidal and square wave under different duty cycles. Our work reveals the detail of all-optical tunning of the resonance of the silica microresonator and opens up possible applications in optical communication, microwave photonics and quantum photonics.

Low Surface Recombination in Hexagonal SiGe Alloy Nanowires: Implications for SiGe-Based Nanolasers.

Monolithic integration of silicon-based electronics and photonics could open the door toward many opportunities including on-chip optical data communication and large-scale application of light-based sensing devices in healthcare and automotive; by some, it is considered the Holy Grail of silicon photonics. The monolithic integration is, however, severely hampered by the inability of Si to efficiently emit light. Recently, important progress has been made by the demonstration of efficient light emission from direct-bandgap hexagonal SiGe (hex-SiGe) alloy nanowires. For this promising material, realized by employing a nanowire structure, many challenges and open questions remain before a large-scale application can be realized. Considering that for other direct-bandgap materials like GaAs, surface recombination can be a true bottleneck, one of the open questions is the importance of surface recombination for the photoluminescence efficiency of this new material. In this work, temperature-dependent photoluminescence measurements were performed on both hex-Ge and hex-SiGe nanowires with and without surface passivation schemes that have been well documented and proven effective on cubic silicon and germanium to elucidate whether and to what extent the internal quantum efficiency (IQE) of the wires can be improved. Additionally, time-resolved photoluminescence (TRPL) measurements were performed on unpassivated hex-SiGe nanowires as a function of their diameter. The dependence of the surface recombination on the SiGe composition could, however, not be yet addressed given the sample-to-sample variations of the state-of-the-art hex-SiGe nanowires. With the aforementioned experiments, we demonstrate that at room temperature, under high excitation conditions (a few kW cm-2), the hex-(Si)Ge surface is most likely not a bottleneck for efficient radiative emission under relatively high excitation conditions. This is an important asset for future hex(Si)Ge optoelectronic devices, specifically for nanolasers.

Ultra-broadband small-size dual-core photonic crystal fiber polarization splitter based on silver coating

We have proposed a novel silver-coated ultra-broadband small-size dual-core photonic crystal fiber (DC-PCF) polarization splitter which achieves a short length, high extinction ratio (ER) and ultra-wide bandwidth at the commonly used communication wavelength band. Finite element method-based numerical simulation is applied to carry out a thorough investigation for wavelength from 1 to 2 μm. According to the simulation results, the coupling qualities of the proposed structure can be improved by resonant coupling between the core guide mode and the surface plasmon polarization (SPP) exciton mode. By analyzing the change of ER with varying wavelength, the ER value of this work are achieved as 67.4 and 67.1 dB when the wavelength are 1.14 and 1.57 μm, respectively. The final splitting length (LS) is 17.17 μm. To the best of our knowledge, it is difficult to achieve in all previous studies. With a splitting bandwidth of 900 nm (1.0–1.9 μm) and the ER value of −50.1 dB at 1.55 μm, the E + S + C + L + U communication bands are completely covered. The proposed model has excellent beam-splitting performance, such as ultra-short LS, ultra-wide splitting bandwidth and good tolerance performance, with potential applications in optical fiber communications or fiber laser devices.

Visible-blind near-infrared organic photodetectors

The presently available commercial photodetectors have a broadband photoresponse and require different external optical filters to block the undesired light outside the detection spectrum window, e.g., near-infrared (NIR) detection. The use of an NIR bandpass has technical limitations in curved or flexible large-area photodetectors, as an NIR bandpass depends critically on the difference in the interference of the optical path in the filter. This work reports the effort to develop a high-performance filter-free organic photodetector (OPD) with a double bulk heterojunction (BHJ) structure. The visible-blind NIR photodetection is realized by eliminating the photocurrent generated in the front visible light-absorbing BHJ optical depletion layer, due to the suppression of electron transport by incorporating a copper thiocyanate-based electron-blocking layer in the OPD. Only excitons generated in the rear NIR-absorbing BHJ contribute to photocurrent in the OPD, thereby achieving visible-blind NIR photodetection. The double BHJ OPD has a high responsivity of 0.38 A/W at 1050 nm and a specific detectivity of >1013 Jones over the wavelength range from 800 to 1050 nm, making it an ideal candidate for applications in optical communication, food quality detection, wellness monitoring, and NIR image sensors.

Research Progress on Carrier-Free Phase-Retrieval Receivers

In order to deal with the chromatic dispersion-induced power fading issue for short-reach direct-detection optical fiber communication applications, such as the ever-increasing data-center interconnections (DCIs), optical filed recovery is intensively being under investigation. To date, various direct detection schemes capable of optical field recovery have been proposed, including the Kramers–Kronig (KK) receiver, asymmetric self-coherence detection (ASCD) receiver, carrier-assisted differential detection receiver (CADD), Stokes vector receiver (SVR), and carrier-free phase-retrieval (CF-PR) receiver. Among those, the CF-PR receiver attracts lots of research attention because it can circumvent the requirement of a strong continuous-wave (CW) optical carrier for the beating with the signal. Generally, the CF-PR receiver consists of only two single-ended photodiodes (PDs) and one dispersive element, for the field recovery of the quadrature amplitude modulation (QAM) signals. Based on the theoretical and experimental studies reported so far, this paper reviews the latest progress of CF-PR receivers designed for high-speed optical short-reach transmission links.

A new Ni/Bi Co-doping rare earth iron garnet crystal with high transmittance, low temperature and wavelength coefficients

Bi-doped rare earth iron garnet (Bi:RIG) crystal is an ideal magneto-optical material for optical isolators in the near-infrared band, which has been widely used in optical communication applications. In this paper, centimeter-sized and good-quality Ni2+-doped Bi:RIG crystals were successfully grown by top-seeded solution growth (TSSG). The transmittance reaches 72.6% at 1550 nm, which is higher than commercial Bi:TbIG crystal and close to the theoretical values of RIG crystals. Doping Ni can not only greatly improve the transmittance, magnetic, and magneto-optical properties, but also decrease the Faraday rotation temperature (FTC) and wavelength coefficients (FWC) of the Bi:RIG crystal. The FTC and FWC of (Bi0.37Ho1.18Eu0.83Gd0.62)(Fe4.20Ni0.25Ga0.55)O12 crystal reduced to − 6.3 × 10−4 K−1 and 8.0 × 10−4 nm−1, which are about 30% and 80% of commercial Bi:TbIG crystal, respectively. (Bi0.37Ho1.18Eu0.83Gd0.62)(Fe4.20Ni0.25Ga0.55)O12 exhibits potential for utilization in new high-performance, wideband magneto-optical isolators, and is expected to find application in the field of wavelength division multiplexing fiber communication.

Coexisting hollow chaotic attractors within a steep parameter interval

By transforming the past states of a variable to another variable, and returning the evolvement along with various functions of self-feedback, a unique gallery of chaotic maps with coexisting hollow attractors is proposed. Strikingly, these peculiar attractors stand on steep parameter intervals, some of which could only happen when the parameter accurately approaches the integer 1 instead of 1. Some maps also have direct amplitude controllers, which regulate the dynamics together with the initial condition leaving unpredicted complexity. The nested hollow attractors are arranged in phase space with great distribution diversity in the form of homogeneous and heterogeneous multistability. CH32-based digital circuit experiments show agreement with numerical simulation and theoretical prediction. Furthermore, the application in secure optical communication is explored accordingly proving higher performance in the steep parameter interval.

Photodetectors integrating waveguides and semiconductor materials.

Photodetectors integrating substrates and semiconductor materials are increasingly attractive for applications in optical communication, optical sensing, optical computing, and military owing to the unique optoelectronic properties of semiconductor materials. However, it is still a challenge to realize high-performance photodetectors by only integrating substrates and semiconductor materials because of the limitation of incident light in contact with sensitive materials. In recent years, waveguides such as silicon (Si) and silicon nitride (Si3N4) have attracted extensive attention owing to their unique optical properties. Waveguides can be easily hetero-integrated with semiconductor materials, thus providing a promising approach for realizing high-performance photodetectors. Herein, we review recent advances in photodetectors integrating waveguides in two parts. The first involves the waveguide types and semiconductor materials commonly used to fabricate photodetectors, including Si, Si3N4, gallium nitride, organic waveguides, graphene, and MoTe2. The second involves the photodetectors of different wavelengths that integrate waveguides, ranging from ultraviolet to infrared. These hybrid photodetectors integrating waveguides and semiconductor materials provide an alternative way to realize multifunctional and high-performance photonic integrated chips and circuits.

Dynamics of quadratic phase controlled Hermite-Gaussian beams in fractional systems based on different variable coefficients and potentials

The Hermite-Gaussian (HG) beam has many potential advanced applications in optical communications, electron acceleration, nonlinear optics and bio-optical disease detection, owing to its distinctive mode and intensity distribution. The research on HG beam are significant in the development of optics, medicine and quantum technology. However, the controlling of the evolutions of HG beam with quadratic phase modulation (QPM) in fractional systems under variable coefficients and potentials has been rarely studied. In this work, the propagation dynamic behaviors of the HG beam with QPM are investigated based on the fractional Schrödinger equation (FSE) under different variable coefficients and potentials by using a split-step Fourier algorithm. In the free space, the focusing spot of the beam becomes larger as the positive QPM coefficient increases or the Lévy index decreases. The QPM coefficient has little effect on the focusing amplitude when the Lévy index is 2. When the QPM coefficient is negative, the focusing of the beam disappears. Under the joint action of cosine modulations and QPM, the transmission of the beam oscillates not by the cosine law, but presents a large and a small breathing structure. The positive and the negative coefficient of QPM only alter the breathing sequence. The evolution period and width of the beam decrease as the modulation frequency increases. The trajectory of split beams turns into a parabolic shape under the linear modulation. In the joint influence of linear modulations and QPM, the HG beam exhibits either focusing or not focusing. Furthermore, the focusing position and focal plane of the beam decrease as the Lévy index increases. When the Lévy index is small, the beam keeps a straight-line transmission without distortion at a longer distance under the joint effect of the power function modulation and a positive QPM. The transmission of the beam also stabilizes and the beam width becomes larger with a negative QPM. Under a linear potential, the splitting of the HG beam disappears with the increase of the linear coefficient and shows a periodic evolution. The propagation trajectory of the beam shows a serrated pattern. By adding QPM, the beam is significantly amplified. Additionally, the evolution period of the beam is inversely proportional to the linear coefficient, and the transverse amplitude turns larger as the Lévy index increases. The interference among beams is strong, but it also exhibits an autofocus-defocusing effect under the joint action of a parabolic potential and QPM. In addition, the positive coefficient and the negative coefficient of QPM only affect the focusing time of the beam. The frequency of focusing increases as the Lévy index and parabolic coefficient rise. These features are important for applications in optical manipulations and optical focusing.

Analysis and optimization of optical frequency comb spectra of magnesium fluoride microbottle resonator

<sec>Optical frequency comb has shown great potential applications in many areas including molecular spectroscopy, RF photonics, millimeter wave generation, frequency metrology, atomic clock, and dense/ultra-dense wavelength division multiplexed high speed optical communications. Optical frequency comb in the microresonator supporting whispering-gallery mode has attracted widespread interest because of its advantages such as flexible repetition rate, wide bandwidth, and compact size. The exceptionally long photon lifetime and small modal volume enhance light-matter interaction, which enables us to realize intracavity nonlinear frequency conversions with low pump threshold. With the advantages of small size, low power consumption, wide spectral coverage and adjustable dispersion, the magnesium fluoride microresonator optical frequency comb has potential applications in optical communication and mid-infrared spectroscopy.</sec><sec>In this work, the spectral characteristics of the optical frequency comb generated by a magnesium fluoride whispering-gallery mode microbottle resonator platform are investigated. In order to optimize the spectral distribution of the optical frequency comb of the magnesium fluoride microbottle resonator, the second-order dispersion and higher-order dispersion of the bottle resonator structure under different curvatures and axial modes are solved iteratively by the finite element method, and the spectral evolutions of the optical frequency comb under different axial mode excitations are simulated by solving the nonlinear Schrödinger equation through the split-step Fourier method. The results show that near-zero anomalous dispersion tuning can be achieved in a wide bandwidth range by exciting low-order axial mode at an optimal radius of curvature, while the high-order axial mode will lead the microbottle resonator to present the weak normal dispersion. The weaker anomalous dispersion in the lower-order axial mode broadens the bandwidth of the optical comb, demonstrating that the third-order dispersion and the negative fourth-order dispersion can broaden the Kerr soliton optical comb; the weak normal dispersion in the higher-order axial mode suppresses the generation of the Kerr optical comb, and the Raman optical comb dominates. The selective excitation of Kerr soliton combs and Raman combs can be achieved by modulating the axial mode of the microbottle resonator under suitable pumping conditions. The present work provides guidance for designing the dispersion in magnesium fluoride microresonator and the experimental tuning of broadband Kerr soliton optical combs and Raman optical combs.</sec>

Thermally activated delayed fluorescence emitters for efficient sensitization of europium(III).

We demonstrate for the first time a unique approach to efficiently sensitize lanthanides(III) using photosensitizer ligands that show thermally activated delayed fluorescence (TADF). TADF ligands have very small singlet (S1) and triplet (T1) excited state energy splitting and S1/T1 energy levels are in optimum energy to the acceptor level of Eu(III) to enable high energy transfer efficiency. The synthesized Eu(III) coordination polymers with TADF ligands showed bright red luminescence with an outstanding sensitization efficiency of 90-94% and Φtot of 79-85% in poly(methyl methacrylate) encapsulated films. This rational approach of efficiently sensitizing lanthanides with TADF ligands demonstrates their great potential for imaging and optical communications applications.

Lasing in an assembled array of silver nanocubes.

We demonstrate a surface lattice resonance (SLR)-based plasmonic nanolaser that leverages bulk production of colloidal nanoparticles and assembly on templates with single particle resolution. SLRs emerge from the hybridization of the plasmonic and photonic modes when nanoparticles are arranged into periodic arrays and this can provide feedback for stimulated emission. It has been shown that perfect arrays are not a strict prerequisite for producing lasing. Here, we propose using high-quality colloids instead. Silver colloidal nanocubes feature excellent plasmonic properties due to their single-crystal nature and low facet roughness. We use capillarity-assisted nanoparticle assembly to produce substrates featuring SLR and comprising single nanocubes. Combined with the laser dye pyrromethene-597, the nanocube array lases at 574 nm with <1.2 nm linewidth, <100 μJ cm-2 lasing threshold, and produces a beam with <1 mrad divergence, despite less-than-perfect arrangement. Such plasmonic nanolasers can be produced on a large-scale and integrated in point-of-care diagnostics, photonic integrated circuits, and optical communications applications.

Generation of spatial combs digitized by orbital angular momentum

Shaping the transverse spatial domain of light has been experiencing recent growth in attention for its applications in optical tweezing, microscopy, communications, and quantum information sciences. The orbital angular momentum (OAM) of light is a transverse physical property that functions as a viable basis for many of such applications. While fields containing a single OAM mode order have extensively been used, fields containing a broad, discrete, and equally spaced OAM spectrum—an OAM comb—has largely been unexplored due to a lack of viable creation methods. Much like how frequency combs enabled myriad applications, it is conceivable that OAM combs would likewise enable further opportunities or expand upon single-OAM applications. For instance, an OAM comb may pave the way for more sophisticated particle manipulation, object detection, and pump shaping for high-dimensional spatial-mode entanglement. Here, we create four OAM combs with rectangular, sinusoidal, sinc, and Gaussian OAM spectral distributions using multiplane light conversion, which only involves phase modulations (hence is inherently lossless) and allows for improved tailoring of the spatial shape. The verification of such combs is done qualitatively by analyzing their propagation evolutions and quantitatively by employing a mode sorting technique—both exhibiting good agreement with user specifications and simulations. The scattering losses of all four combs were measured to be minimal, ranging from 0.66 to 1.04 dB.

Synthesis and optical wireless communication application of high efficiency extreme blue CsPbBr3 nanoplates

Extreme blue 435 nm emission, 97% PLQY CsPbBr3 nanoplates and up to 150 Mbps optical wireless communication data transmission rate.

Chaotic time delay feature cancellation and bandwidth enhancement in cascaded-coupled nanolasers

As an important part of optical sources, nanolasers have a prominent influence in photonic circuit integration, and their nonlinear dynamics has become one of the research hotspots in recent years. In this work, we investigate the time-delay signature and bandwidth characteristics in a cascade-coupled nanolaser system, in which the master nanolaser is connected to an external feedback cavity and injected into the intermediate nanolaser and the slave nanolaser sequentially. The 0-1 chaos test is introduced to quantify the dynamics of the nanolaser, which can accurately distinguish whether the laser is in a chaotic state, and the autocorrelation function is used to analyze the time-delay characteristics in the laser output signal. This type of calculation has the advantages of fast operation speed, high accuracy and anti-noise robustness. The lower the autocorrelation value, the more difficult it is to extract useful information from the chaotic random sequence. The bandwidth is defined as a value where the range between DC and frequency contains 80% of the spectral power, a value that is only applicable to chaotic states. In the simulation, we compare and analyze the two cases of whether the intermediate nanolaser has a peak with obvious time-delay signature. The research results show that by selecting appropriate system parameters, the slave nanolaser can always output a broadband chaotic signal without obvious time-delay signature. Under the condition of a certain injection intensity, by changing the frequency detuning parameter, the intermediate nanolaser has an obvious time-delay signature, and then the slave nano-laser can output chaotic signals which can suppress time-delay signature and enhance bandwidth in a small parameter interval. When the time-delay signal of the intermediate nanolaser is completely hidden, the slave nanolaser can achieve the suppression of the time-delay signature in a larger parameter plane, meanwhile the bandwidth is significantly enhanced. In addition, by plotting the two-dimensional spatial distribution diagram and bandwidth line diagram of the output from the nanolaser under frequency detuning and injection intensity, it is determined that the nanolaser can simultaneously suppress the delay characteristics and enhance the bandwidth under chaotic signals. This provides an important theoretical basis for realizing the practical applications in secrecy-enhanced chaotic optical communication.

Bükümlü Işıkların Yarıiletken Üzerindeki Elektriksel Etkisinin Deneysel Olarak İncelenmesi

Orbital Angular Momentum (OAM) beams are a special type of light that disrupts the circular symmetry of the optical field and carries the angular momentum of light. These beams enable new applications in optical devices and communication. In addition, as a result of their interaction with matter, OAM beams can transfer both photon energy and angular momentum, enabling the formation of higher currents. Thus, it has been shown that OAM beams can be used to obtain higher energies in increasing photovoltaic efficiency. The effect of OAM beams on photovoltaic efficiency has been a research topic in recent years. Some studies have theoretically shown that OAM beams can increase the electrical production of solar cells. The reason for this is that OAM beams impart angular momentum to electrons in addition to photon energy. The aim of this study is to experimentally investigate the electrical effect of an OAM beam spot produced using an SLM (Spatial Light Modulator) on a semiconductor solar panel. Higher currents were obtained by dropping the OAM beam onto photovoltaics. The current increase was 18.2%.

Optical wireless communications with InGaN multiple-quantum-well photodiodes grown with the prestrained superlattice interlayer for light detection

InGaN multiple-quantum-well photodiodes (InGaN MQW PDs) grown with an underlying superlattice (SL) are proposed for light detection in optical wireless communications. Experimentally, it was found that the presence of the prestrained SL interlayer with a reduced barrier width can help to relief the biaxial strain of the overlying In0.16Ga0.84N/GaN MQW. This gives rise to a stable emission spectrum and a reduced lifetime of carrier recombination or increased carrier escape from the InGaN wells in proposed InGaN PDs. The improved carrier transport in InGaN MQWs with a reduced polarization field is responsible for the improvement in PD's photoresponsivity provided their In0.16Ga0.84N/GaN MQW was fully depleted under −5 V bias. Further increasing the depletion width by reverse bias, an additional photocurrent from the prestrained SL interlayer leads to the best PD photoresponsivity despite their detectivity also degrading at such a high voltage level (V = −10 V). On the other hand, a 250 Mbit/s directed optical link with a bit error rate of 8.8 × 10−8 is proven to be feasible by using the near-ultraviolet laser diode (LD) and the proposed InGaN PDs (better 3-dB cut-off frequency of 76.1 MHz achieved even under zero bias) as the optical transmitter and the receiver, respectively. Furthermore, the practical application of LD-based optical wireless communications with the SL containing InGaN PDs through real-time transmission of digital TV signals (data rate ∼ 270 Mbit/s) is also demonstrated.

A Review of Mechanical Fine-Pointing Actuators for Free-Space Optical Communication

This paper presents a state-of-the-art overview of fine beam steering mechanisms for free-space optical communication on satellites. Precise beam pointing is a critical task for the successful operation of free-space optical communication systems. Based on past research and ongoing projects, the use of fast steering mirrors (FSMs) is still the most popular solution for free-space optical communication applications. Although a variety of commercial off-the-shelf (COTS) FSM solutions exist, there is limited publicly available data on these solutions in the space environment. Three main actuation principles are considered (electro-static force actuated, magnetic force actuated, piezo-effect actuated) and reviewed using available data from past space missions. The article describes the most important criteria in the choice of a fine beam steering solution for free-space optical communication in space.

Heterostructure nanocluster MOF-derived Ag-CuO: An emerging material for harmonic soliton pulses generation

In recent years, metal-organic framework (MOF) and their derivatives have attracted many researchers due to excellent characteristics, such as good stability, high capacity, and a modest third order nonlinear optical response. Compared with conventional optical materials, MOF-oxide are easier to benefit photonic research. However, for nonlinear optics and ultrafast photonics, research on MOFs-Transition metal oxide is still in its infancy. In this work, MOF-derived Ag-CuO was prepared by hydrothermal method and applied in passively mode-locked fiber laser. Experimental results show that MOF-derived Ag-CuO possesses excellent optical absorption, functioning as a saturable absorber (SA). The laser based on MOF-derived Ag-CuO SA realizes three different mode-locking states, including traditional soliton with the pulse width of 1.04 ps, 32nd order harmonic soliton molecule, and soliton rain pulse, with the signal-to-noise ratio (SNR) of 73 dB. This work lays the foundation of its application in ultrashort photonics and optical communication, broadening the future of MOF-derived Ag-CuO.

Adaptive methods of generating complex light arrays.

Structured light arrays of various shapes have been a cornerstone in optical science, driven by the complexities of precise and adaptable generation. This study introduces an approach using a spatial light modulator (SLM) as a generator for these arrays. By projecting a holographic mask onto the SLM, it functions simultaneously as an optical convolution device, focusing mechanism, and structured light beam mask. Our approach offers unmatched versatility, allowing for the experimental fabrication of traditional beam arrays like azimuthal Laguerre-Gaussian (LG), Bessel-Gaussian (BG), and Hermite-Gauss (HG) in the far-field. Notably, it has enabled a method of generating Ince-Gauss (IG) and LG radial mode beam arrays using a convolution solution. Our system provides exceptional control over array periodicity and intensity distribution, bypassing the Talbot self-imaging phenomenon seen in traditional setups. We provide an in-depth theoretical discussion, supported by empirical evidence, of our far-field results. This method has vast potential for applications in optical communication, data processing, and multi-particle manipulation. It paves the way for rapid generation of structured light with high spatial frequencies and complex shapes, promising transformative advances in these domains.