High-capacity Optical Communication Research Articles

High-performance silicon PIN diode switches in the 2-µm wave band.

The 2-µm wave band has attracted significant research interest due to its potential applications for next-generation high-capacity optical communication and sensing. As the key component, fast optical switches are essential for an advanced and reconfigurable optical network. Motivated by this prospect, we propose and demonstrate two typical silicon PIN diode switches at 2 µm. One is based on a coupled microring resonator (CMRR), and the other is based on a Mach-Zehnder interferometer (MZI) with a push-pull-like configuration. The measured insertion loss of the CMRR switch is <2.5 dB, and the cross talk is <-10.8 dB. The insertion loss of the MZI switch is <2 dB, and the cross talk is <-15.6 dB. The switch times of these two structures are both lower than 12.5 ns.

Highly efficient detection of near-infrared optical vortex modes with frequency upconversion.

Vortex beams carrying orbital angular momentum (OAM) have been widely applied in optical manipulations, optical micromachining, and high-capacity optical communications. Vortex mode detection is very important in various applications. However, the detection of near-infrared vortex modes is still difficult because of the wavelength limitations of the detection device. Here, we present a study on measuring optical near-infrared vortex modes with frequency upconversion, which can convert a near-infrared beam into a visible beam. In our experiment, the optical near-infrared vortex modes can be measured by the number and orientation of the fringes of the second harmonic intensity patterns. The proposed method is a convenient and flexible way to measure the different OAM of vortex beams, which may have potential applications in all kinds of circumstances that vortex modes involve.

Active quasi-BIC optical vortex generators for ultrafast switching

The Pancharatnam–Berry phase induced by the winding topology of polarization around a vortex singularity at bound states in the continuum (BIC) provides a unique approach to optical vortex (OV) generation. The BIC-based OV generators have the potential to outperform their counterparts that rely on spatial variations in terms of design feasibility, fabrication complexity, and robustness. However, given the fact that this class of OV generators originates from the topological property of the photonic bands, their responses are generally fixed and cannot be dynamically altered, which limits their applications to photonic systems. Here, we numerically demonstrate that a silicon photonic crystal slab can be used to realize optically switchable OV generation by simultaneously exploiting the vortex topology in momentum space in conjunction with silicon’s nonlinear dynamics. Picosecond switching of OV beams at near-infrared wavelengths are observed. The demonstrated nontrivial topological nature of the active generators can significantly expand the application of BIC toward ultrafast vortex beam generation, high-capacity optical communication, and mode-division multiplexing.

Broadband Achromatic and Polarization Insensitive Focused Optical Vortex Generator Based on Metasurface Consisting of Anisotropic Nanostructures

Optical vortex (OV) beams are ideal carriers for high-capacity optical communication, and long-wave infrared (LWIR) is the ideal wavelength band for long-range optical communication. Here, we propose a method for the achromatic generation of focused optical vortex (FOV) beams with arbitrary homogenous polarization states in the LWIR using a single all-germanium metasurface. The chromatic aberration and polarization sensitivity are eliminated by superimposing a polarization-insensitive geometric phase and a dispersion-engineered dynamic phase. The method is validated using two broadband FOV generators with the same diameter and focal length but different topological charges. The results indicate that the FOV generators are broadband achromatic and polarization insensitive. The proposed method may pave the way for chip-scale optical communication devices.

High-speed photon-number-resolving detection via a GHz-gated SiPM.

Silicon photomultipliers (SiPMs) constitute a promising candidate for photon-number-resolving (PNR) detection via spatial multiplexing, which offer advantages like high integration and low cost. Up to date, there has been continuous endeavor in boosting the PNR performances, particularly on the resolved photon numbers and operation speed. Here, we demonstrate a GHz-gated SiPM in the Geiger mode, which allows to quench the photon-induced avalanche signal within 1 ns. Specifically, the capacitive response of the SiPM has been effectively suppressed by combining the low-pass filtering and self-differencing technique, which facilitates a high-fidelity extraction of the avalanche pulse with a reduced error rate. Consequently, high-speed PNR detection has been manifested in resolving up to 14 photons for laser pulses at a repetition rate of 40 MHz. The presented high-speed PNR detector may open up new possibilities to implement applications such as large-dynamic-range optical sensing, high-capacity optical communication, and multi-photon quantum optics.

Coherent generation of arbitrary first-order Poincaré sphere beams on an Si chip.

Generalized vector vortex light beams possess spatially variant polarization states, and higher-order Poincaré spheres represent a powerful analytical tool for analyzing these intriguing and complicated optical fields. For the generation of these vortex beams, a range of different methods have been explored, with an increasing emphasis placed on compact, integrated devices. Here, we demonstrate via numerical simulation, for the first time, an on-chip light emitter that allows for the controllable generation of all points on a first-order Poincaré sphere (FOPS). The FOPS beam generator consists of a waveguide-coupled, nanostructured Si microring resonator that converts two guided, coherent light waves into freely propagating output light. By matching their whispering gallery modes with the nanostructures, the fundamental TE (transverse electric) and TM (transverse magnetic) input modes produce radial and azimuthal polarizations, respectively. These two linear polarizations can form a pair of eigenstates for the FOPS. Consequently, tuning the phase contrast and the intensity ratio of these two coherent inputs allows for the generation of an arbitrary point on the FOPS. This result indicates a new way for on-chip vector vortex beam generation, which may be applied for integrated optical tweezers and high-capacity optical communications.

On-Chip Optical Vortex Generation and Topological Charge Control by Methods of Wave Vector Manipulation

Optical vortices (OVs) have received much attention in recent years and are widely explored in communication applications. The on-chip vortex emitter/modulator is preferred when it comes to photonic integration and chip-scale communication. However, the existing emitters/modulators suffer from either narrow bandwidths or extensibility problems, which actually degrade their ability to improve communication capacity. Here, we propose a metasurface OV emitter based on wave vector synthesis for vortex generation and modulation. A thorough theoretical analysis of the OV generation by two approximate methods was carried out, which suggests the superiority of Wave Vector method over Phase method. Afterwards, the wave vector manipulation implemented by Phase gradient metasurfaces was studied for controlling the topological charges of generated OVs. Finite element method simulations showed that, in the topological charge range of −6 to 6 and the wavelength range of 1.45 μm to 1.55 μm, the effective vortex emission efficiency of the proposed emitter is around 45%. The on-chip vortex generation and control by wave vector manipulation is a very promising technology for high-capacity inter-chip optical communication.

Optical frequency comb generation from a 1.65 µm single-section quantum well laser.

Optical frequency combs (OFCs) in the 1.65 µm wavelength band are promising for methane sensing and extended high-capacity optical communications. In this work, a frequency-modulated (FM) OFC is generated from a 1.65 µm single-section quantum well laser. This is characterized by a 1 kHz-wide beatnote signal at ∼19.4 GHz. Typical FM optical spectra are shown and optical linewidth of the OFC narrows through the mutual injection locking process in the comb formation. No distinct pulse train is observed on oscilloscope, which conforms with the FM operation. Furthermore, to add further evidence that four-wave mixing (FWM) is the driving mechanism of the comb formation, FWM frequency conversion characterization is conducted on a semiconductor optical amplifier (SOA) fabricated together with the tested laser. An efficiency of ∼-30 dB confirms the capability of FM mode locking.

Flat Optical Frequency Comb Generator Based on Integrated Lithium Niobate Modulators

Chip-scale electro-optic (EO) frequency combs are expected to play an essential role in future high-capacity optical communications systems and next-generation mobile communications. The application requires integrated EO frequency comb generators featuring good spectral flatness, high modulation bandwidth, low driving voltage and low insertion loss simultaneously. Here, we demonstrate a flat-top optical flat comb (OFC) generator based on high-performance lithium niobate on insulator modulators. The OFC generator shows a low on-chip loss (2.1 dB), a low driving voltage over a broad frequency range, and a large 3-dB EO bandwidth. Moreover, with consuming power of less than 2W, the presented device produces 13 lines with a power variation of less than 1.2 dB and a line spacing of 31 GHz which can further be extended to 67 GHz.

Vortex beam: generation and detection of orbital angular momentum [Invited

Recent advances in the research of vortex beams, structured beams carrying orbital angular momentum (OAM), have revolutionized the applications of light beams, such as advanced optical manipulations, high-capacity optical communications, and super-resolution imaging. Undoubtedly, the methods for generation of a vortex beam and detection of its OAM are of vital importance for the applications of vortex beams. In this review, we first introduce the fundamental concepts of vortex beams briefly and then summarize approaches to generating and detecting the vortex beams separately, from bulky diffractive elements to planar elements. Finally, we make a concise conclusion and outline that is yet to be explored.

100 Hertz frame-rate switching three-dimensional orbital angular momentum multiplexing holography via cross convolution

The orbital angular momentum (OAM) of light has been implemented as an information carrier in OAM holography. Holographic information can be multiplexed in theoretical unbounded OAM channels, promoting the applications of optically addressable dynamic display and high-security optical encryption. However, the frame-rate of the dynamic extraction of the information reconstruction process in OAM holography is physically determined by the switching speed of the incident OAM states, which is currently below 30 Hz limited by refreshing rate of the phase-modulation spatial light modulator (SLM). Here, based on a cross convolution with the spatial frequency of the OAM-multiplexing hologram, the spatial frequencies of an elaborately-designed amplitude distribution, namely amplitude decoding key, has been adopted for the extraction of three-dimensional holographic information encoded in a specific OAM information channel. We experimentally demonstrated a dynamic extraction frame rate of 100 Hz from an OAM multiplexing hologram with 10 information channels indicated by individual OAM values from –50 to 50. The new concept of cross convolution theorem can even provide the potential of parallel reproduction and distribution of information encoded in many OAM channels at various positions which boosts the capacity of information processing far beyond the traditional decoding methods. Thus, our results provide a holographic paradigm for high-speed 3D information processing, paving an unprecedented way to achieve the high-capacity short-range optical communication system.

Adaptive demodulation by deep-learning-based identification of fractional orbital angular momentum modes with structural distortion due to atmospheric turbulence

Since the great success of optical communications utilizing orbital angular momentum (OAM), increasing the number of addressable spatial modes in the given physical resources has always been an important yet challenging problem. The recent improvement in measurement resolution through deep-learning techniques has demonstrated the possibility of high-capacity free-space optical communications based on fractional OAM modes. However, due to a tiny gap between adjacent modes, such systems are highly susceptible to external perturbations such as atmospheric turbulence (AT). Here, we propose an AT adaptive neural network (ATANN) and study high-resolution recognition of fractional OAM modes in the presence of turbulence. We perform simulations of fractional OAM beams propagating through a 1-km optical turbulence channel and analyze the effects of turbulence strength, OAM mode interval, and signal noise on the recognition performance of the ATANN. The recognition of multiplexed fractional modes is also investigated to demonstrate the feasibility of high-dimensional data transmission in the proposed deep-learning-based system. Our results show that the proposed model can predict transmitted modes with high accuracy and high resolution despite the collapse of structured fields due to AT and provide stable performance over a wide SNR range.

Cylindrical vector beam multiplexer/demultiplexer using off-axis polarization control

The emergence of cylindrical vector beam (CVB) multiplexing has opened new avenues for high-capacity optical communication. Although several configurations have been developed to couple/separate CVBs, the CVB multiplexer/demultiplexer remains elusive due to lack of effective off-axis polarization control technologies. Here we report a straightforward approach to realize off-axis polarization control for CVB multiplexing/demultiplexing based on a metal–dielectric–metal metasurface. We show that the left- and right-handed circularly polarized (LHCP/RHCP) components of CVBs are independently modulated via spin-to-orbit interactions by the properly designed metasurface, and then simultaneously multiplexed and demultiplexed due to the reversibility of light path and the conservation of vector mode. We also show that the proposed multiplexers/demultiplexers are broadband (from 1310 to 1625 nm) and compatible with wavelength-division-multiplexing. As a proof of concept, we successfully demonstrate a four-channel CVB multiplexing communication, combining wavelength-division-multiplexing and polarization-division-multiplexing with a transmission rate of 1.56 Tbit/s and a bit-error-rate of 10−6 at the receive power of −21.6 dBm. This study paves the way for CVB multiplexing/demultiplexing and may benefit high-capacity CVB communication.

Experimental realization of scalar and vector perfect Laguerre–Gaussian beams

The generation of a perfect optical vortex (POV) has been an important area of research since the concept was introduced by Ostrovsky et al. [Opt. Lett. 38, 534 (2013)]. In this Letter, we provide the details of the experimental demonstration of a POV using perfect Laguerre–Gaussian beams via a phase-only spatial light modulator. The perfect beam properties, including radius, beam width, and ring thickness, are investigated in detail. We verify the vortex nature of the proposed perfect Laguerre–Gaussian beams including their topological charge value and sign. Finally, in addition to the scalar beams, we propose the vector perfect Laguerre–Gaussian beams both theoretically and experimentally and evaluate their perfect characteristics. The derived results clearly illustrate the perfect characteristics of such beams independent of the polarization state. The findings reported here can find significant applications in various fields including optical tweezers, optical imaging, and high capacity optical communications.

Enhancement of OAM and LP modes based on double guided ring fiber for high capacity optical communication

This article introduced a double guided ring-based spiral photonic crystal fiber (S-PCF) supporting both the orbital angular momentum (OAM) and linear polarization (LP) mode simultaneously with the efficient transmission. The outcomes exhibition that the designed S-PCF have good optical features such as less confinement loss (4.05342 × 10−12 dB/m for the EH9,1 mode), better mode quality and ISO (up to 98.87% and 126 dB, respectively), supported a decent amount of modes which is numerically 64 OAM and 6 LP modes, maintaining the large refractive index differences (>10-4) of all the eigenmodes, and a relatively flat dispersion variation (0.0743 ps/km-nm for the EH1,1 mode). Also, we obtained the crosstalk less than −12 dB and the power fraction is approximately 93%-99% of the S-PCF. All the optimizing properties are obtained using the full-vector finite element method (FEM) and also the perfectly matched layer (PML) as a boundary condition. Thus, the above mentioned optimizing propagation characteristic based S-PCF has effective applications like reliable long-distance communication into the space division multiplexing (SDM) process of the large-capacity fiber communication systems.

High-efficiency and high-precision identification of transmitting orbital angular momentum modes in atmospheric turbulence based on an improved convolutional neural network

In this paper, we have proposed an improved convolutional neural network model based on the ShuffleNet V2 network for recognizing the orbital angular momentum (OAM) modes for the OAM based free space optical communication systems in the environments of atmospheric turbulence (AT). The network is trained by inputting the intensity images of the Laguerre Gaussian beams, which can effectively finish the training process due to its special designs, and can recognize the OAM modes with high accuracy. Compared with previous works for the single and multiplexing OAM modes, the proposed network model has high-precision and high-efficiency characteristics. Especially for the multiplexing OAM modes, our proposed system can achieve the recognition accuracy of 99.5% under strong AT and long-distance transmission. In addition, in order to prove that our system has good generalization ability and strong robustness, we used the trained model to test several groups of data obtained under untrained AT intensities, and the results showed that our model could still maintain high accuracy under the untrained AT intensities, which is very important to the realization of high-capacity optical communication technologies based on OAM in the future

Extending the Detection Range of Optical Vortices by Dense Phase Stitching Algorithm

With the development of optical communication technology based on orbital angular momentum (OAM), more and more OAM modes are employed in communication systems, which puts forward higher requirements for the capacity of OAM state detection at the receiving end. In this work, we reported a scheme to measure and demultiplex OAM beams with topological charges from -32 to +32 by using a specially engineered two-dimensional 64-focus vortex demultiplexing array. The phase mask for generating this array was calculated by dense phase stitching algorithm which integrates four candidate phase masks that can generate four 16-focus arrays respectively. The first step of the algorithm is to extract sector phase areas from the four phase masks successively by using rotationally symmetric sector apertures whose total angular aperture is π/2. The second step of the algorithm is to form a stitched phase mask with the extracted sector phase areas. Consequently, the 64-focus vortex array can be generated by using the stitched phase mask, which is almost equivalent to generating four 16-focus arrays by four candidate phase masks simultaneously. Furthermore, by adjusting the number of sector apertures, the modal crosstalk in the OAM detection range can be greatly reduced. With the help of this scheme, both single OAM mode and multiplexing OAM modes in the range from -32 to +32 can be effectively measured. According to this scheme, simple devices can be arranged to achieve both low modal crosstalk and wide detection range of vortex beams, which can support the advanced high-capacity OAM-based optical communication systems.

Broadly tunable optical vortex beam in a diode-pumped Yb:CALGO laser

In this paper, the direct generation of vortex beams in a diode-pumped Yb:CALGO laser has been realized for the first time. The wavelength of the output vortex beam was broadly tunable from 1040 to 1086 nm by using a birefringent filter as wavelength-selecting element. The vortex beams could be maintained quite well at different wavelengths and pump powers. The maximum output power of the vortex laser in the experiment was 860mW at 1060.4 nm. The orbital angular momentums with the topological charges l = 1 and l = −1 were verified by the interferograms. Such a wavelength-tunable vortex laser can potentially be applied in high-capacity and multi-channel optical communications.

New visions of the soliton solutions to the modified nonlinear Schrodinger equation

In this article, we will study the modified nonlinear Schrödinger equation which represents the propagation of rogue waves in ocean engineering that occur in deep water, usually far out at sea, and are a threat even to capital ships and ocean liners. In related subject for all like waves which occurred at different branches of science which have the same behaviors such as fluid dynamics waveguides that have unexpected large displacements, long-wave limit of a breather (a pulsing mode), telecommunications engineering devices, etc. We will implement new multiple visions for the soliton solution to the modified nonlinear Schrödinger equation (MNLSE) that describes successfully these phenomenon. Studying this important model and its own behavior of the resulting solitons description will contribute effectively in marine safety and improvement the pulse devices which cooperate to protect human life effectively and technology for high-capacity optical communications through which the modern asocial media was built…etc. Three different techniques are invited for this purpose. The first technique is the Paul-Painlevé approach method (PPAM), while the second technique is the Ricatti-Bernolli Sub ODE method (RBSOM). In related subject, the variational iteration method VIM is implemented in the same vein and parallel to construct the numerical solutions corresponding to the achieved soliton solutions via each one of these two methods individually. A good comparison not only between these three visions of soliton solutions but also with that achieved previously by other authors has been demonstrated.

Chip-based optical frequency combs for high-capacity optical communications

Abstract Current fibre optic communication systems owe their high-capacity abilities to the wavelength-division multiplexing (WDM) technique, which combines data channels running on different wavelengths, and most often requires many individual lasers. Optical frequency combs, with equally spaced coherent comb lines derived from a single source, have recently emerged as a potential substitute for parallel lasers in WDM systems. Benefits include the stable spacing and broadband phase coherence of the comb lines, enabling improved spectral efficiency of transmission systems, as well as potential energy savings in the WDM transmitters. In this paper, we discuss the requirements to a frequency comb for use in a high-capacity optical communication system in terms of optical linewidth, per comb line power and optical carrier-to-noise ratio, and look at the scaling of a comb source for ultra-high capacity systems. Then, we review the latest advances of various chip-based optical frequency comb generation schemes and their applications in optical communications, including mode-locked laser combs, spectral broadening of frequency combs, microresonator-based Kerr frequency combs and electro-optic frequency combs.